Lightweight Machine to Machine Technical Specification: Core

Approved Version: 1.2.2 - 2024-06-13

Open Mobile Alliance

OMA-TS-LightweightM2M_Core-V1_2_2-20240613-A

master: 18 Jun 2024 14:22:00 rev: e58dc1c

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1. Scope

This document, the LwM2M CORE technical specification, describes the LwM2M messaging layer. The LwM2M TRANSPORT specification [LwM2M-TRANSPORT], a companion specification, details the mapping of the messaging layer to selected transports. The separation between transport and messaging layer improves readability and simplifies extending LwM2M to further transports. The LwM2M messaging layer uses a RESTful design with several interfaces and a simple data model.

1.1. Revision 1.2.2

Please refer to the ERELD LwM2M for details what has changed.

For detail changes, please refer to this link for deltas between v1.2.2 and v1.2.1.

1.2. Revision 1.2.1

This revision of the specification includes the following fixes or clarifications:

• Add an optional parameter to the Bootstrap-Pack-Request operation.
• Fix a possible ambiguity when LwM2M CBOR is used in the Create operation.
• Rewrite the text describing the usage of attributes for clarity and simplification.
• Clarify that each argument to the Execute operation is unique.
• Clarify that the LwM2M COSE Object must not be part of the "Objects and Object Instances" parameter of the Register operation.
• Clarify that the LwM2M COSE Object and the MQTT Server Object are part of the response to a Bootstrap-Discover operation.
• Indicate the LwM2M CBOR content format assigned number.
• Consolidate the list of recommended URN formats for the Endpoint Client Name.
• Move the Attributes section to the Identifiers and Resources section.
• Fix the SenML JSON syntax in the Bootstrap-Pack example.
• Fix the binary in the EF DODF-bootstrap example in Appendix G.
• Fix the examples of the "Arguments" parameter of the Execute operation to remove unauthorized spaces.
• Fix the reference of [OSCORE].

1.3. LwM2M version 1.2

This specification defines version 1.2 of the LwM2M protocol and augments [LwM2M-TS_1.1]. Version 1.2 is backwards compatible to LwM2M version v1.0 and v1.1 with respect to mandatory features.

LwM2M v1.2 adds the following new features:

• New transports for LwM2M; this allows LwM2M messaging to be conveyed over MQTT and over HTTP.
• Optimizations for the bootstrapping interface; this reduces the amount of data and the number of messages transmitted during the bootstrapping exchange.
• Optimizations for the registration interface; this reduces the amount of data transmitted during registration exchanges.
• Optimizations for the information reporting interface; observation attributes may now be included in an Observe operation.
• Support for LwM2M gateway functionality; this allows non-LwM2M IoT devices as well as LwM2M devices behind a gateway to be connected to the LwM2M ecosystem and to manage those devices remotely.
• New, highly optimized encoding format based on CBOR called LwM2M CBOR.
• Enhanced functionality for firmware updates.
• Definition of new notification attributes (edge, confirmable notification, and maximum historical queue). Edge allows notifications to be triggered on rising and falling edges. Confirmable notifications allow the control of reliable transmissions of notifications. Maximum historical queue allows the control of time-series data usage.
• Clarifications of object versioning rules.
• Updates to use the latest communication security protocols based on TLS and DTLS 1.3 (as well as the use of the Connection ID).
• Flexibility to control the use of TLS and DTLS 1.3 through configuration information.
• Untangling the relationship of security credentials and their server configuration.

There also numerous clarifications and editorial improvements as well as additional examples based on feedbacks received from the LwM2M development community.

Details about the transport bindings can be found in [LwM2M-TRANSPORT].

1.4. LwM2M version 1.1

LwM2M v1.1 added the following features to v1.0:

• Enhancement of the LwM2M bootstrapping capabilities allowing for incremental upgrades.

• Improved support for Public Key Infrastructure (PKI) deployments.

• Introduction of enhanced registration sequence mechanisms by the LwM2M Client to LwM2M Server(s).

• Support for LwM2M over TCP/TLS to better support firewall and NAT traversal.

• Support for application layer security for LwM2M based on OSCORE.

• Better support of LwM2M over Low Power WANs, including 3GPP CIoT & LoRaWAN.

• Extended LwM2M operations to enable Resource Instance level access.

• Performance improvement for retrieving and updating Resources of multiple objects.

• Support for JSON using SenML with CBOR serialization for compressed payload with highly efficient transmission.

• Addition of new data types.

1.5. LwM2M version 1.0

LwM2M v1.0 offers the following features:

• Simple resource model with the core set of objects and resources defined in this specification. The full list of registered objects can be found at OMNA.

• Operations for creation, update, deletion, and retrieval of resources.

• Asynchronous notifications of resource changes.

• Support for several serialization formats, namely TLV, JSON, Plain Text and binary data formats and the core set of LightweightM2M Objects.

• UDP and SMS transport support.

• Communication security based on the DTLS protocol supporting different types of credentials.

• Queue Mode offers functionality for a LwM2M Client to inform the LwM2M Server that it may be disconnected for an extended period and when it becomes reachable again.

• Support for use of multiple LwM2M Servers.

• Provisioning of security credentials and access control lists by a dedicated LwM2M bootstrap-server.

2. References

2.1. Normative References

2.2. Informative References

3. Terminology and Conventions

3.1. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted asdescribed in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

All sections and appendixes, except "Scope" and "Introduction", are normative, unless they are explicitly indicated to be informative.

3.2. Definitions

Kindly consult [OMADICT] for more definitions used in this document.

3.3. Abbreviations

4. Introduction

This enabler defines the application layer communication protocol between a LwM2M Server and a LwM2M Client as well as between the LwM2M Bootstrap-Server and the LwM2M Client. The LwM2M Device includes a LwM2M Client component. The OMA Lightweight M2M enabler includes device management and service enablement for LwM2M Devices. This device management protocol was designed to make use of lightweight protocols and an efficient data model.

The LwM2M messaging layer is inspired by the RESTful design model based on [CoAP]. Interactions are between clients and servers using request/response model. Uniform Resource Identifiers (URIs) are used to identify and interact with object and resources while the protocol allows stateless and layered architecture.

Four interfaces are designed between the three entities, as shown in the architecture in Figure: 4.-1 The overall architecture of the LwM2M Enabler:

• Bootstrap

• Client Registration

• Device Management and Service Enablement

• Information Reporting

4.1. Version 1.2

Version 1.2 of LwM2M introduced the following objects, which are part of core specification:

• LwM2M COSE (Object ID:23)

• MQTT Server (Object ID:24)

• LwM2M Gateway (Object ID:25)

• LwM2M Gateway Routing (Object ID:26)

• 5G-NR Connectivity Object (Object ID:27)

Version 1.2 of LwM2M modified the following objects, which are part of core specification:

• LwM2M Security Object (Object ID:0)

• LwM2M Server Object (Object ID:1)

• Firmware Update Object (Object ID:5)

• LwM2M OSCORE Object (Object ID:21)

4.2. Version 1.1

[LwM2m-TS_1.1] introduced the following objects, which are part of core specification:

• OSCORE Object (Object ID:21)

[LwM2m-TS_1.1] modified the following objects, which are part of core specification:

• LwM2M Security Object (Object ID:0)

• LwM2M Server Object (Object ID:1)

• Device Object (Object ID:3)

• Connectivity Monitoring Object (Object ID:4)

4.3. Version 1.0

[LwM2M-TS_1.0] introduced the following objects, which are part of core specification:

• LwM2M Security Object (Object ID:0)

• LwM2M Server Object (Object ID:1)

• LwM2M Access Control Object (Object ID:2)

• Device Object (Object ID:3)

• Connectivity Monitoring Object (Object ID:4)

• Firmware Update Object (Object ID:5)

• Location Object (Object ID:6)

• Connectivity Statistics Object (Object ID:7)

5. Compatibility

5.1. LwM2M Server and LwM2M Client Versions

The LwM2M Server MUST support a LwM2M Client of the same major and minor version. For example, a LwM2M Server whose version is 1.2 MUST support a LwM2M Client whose version is 1.2.

The LwM2M Server SHOULD support all LwM2M Client versions of the same major version. Backward compatibility with a common major version is strongly recommended to support deployment scenarios where LwM2M Servers are updated before the LwM2M Clients. For example, a LwM2M Server whose version is 1.2 should support LwM2M Clients that are version 1.0 or 1.1. Forward compatibility with a common major version is also recommended to support deployment scenarios where the LwM2M Clients are updated before the LwM2M Server. For example, a LwM2M Server whose version is 1.1 should support a LwM2M Client whose version is 1.2.

5.2. Optional Objects and Object Versions

Operations initiated by the LwM2M Client to the LwM2M Server may address optional objects that are not supported by the LwM2M Server. Similarly, operations initiated by the LwM2M Server to the LwM2M Client may address objects that are not supported by the LwM2M Client. This may occur because the objects are not recognized or the object versions are not compatible.

5.3. Optional Resources

Operations initiated by the LwM2M Client to the LwM2M Server may address optional resources that are not supported by the LwM2M Server. Operations initiated by the LwM2M Server to the LwM2M Client may address optional resources that are not supported by the LwM2M Client.

To enable compatibility between LwM2M Clients and LwM2M Servers for optional resources that are not supported, the LwM2M Client or LwM2M Server, when possible, MUST NOT interpret transactions targeted at those resources as errors.

6. Interfaces

According to Figure: 4.-1 The overall architecture of the LwM2M Enabler there are four interfaces: 1) Bootstrap, 2) Client Registration, 3) Device Management and Service Enablement, and 4) Information Reporting. The operations for the four interfaces can be classified into uplink operations and downlink operations. The operations for each interface are defined in this section, and then mapped to protocol mechanisms in the LwM2M Transport specification [LwM2M-TRANSPORT].

Figure: 6.-1 Bootstrap Interface with Bootstrap-Request operation and Figure: 6.-2 Bootstrap Interface with Bootstrap-Pack-Request operation show the operation model for the "Bootstrap" interface. For this interface, the operations are uplink operations named "Bootstrap-Request" and "Bootstrap-Pack-Request", downlink operations named "Bootstrap-Discover", "Bootstrap-Write", "Bootstrap-Read","Bootstrap-Delete" and "Bootstrap-Finish". These operations are used to initialize the needed Object(s) for the LwM2M Client to register with one or more LwM2M Server(s). When a "Bootstrap-Write" operation initiated on the "Bootstrap" interface by the LwM2M Bootstrap-Server, the LwM2M Client MUST write the value included in the payload regardless of an existence of the targeting Object Instance(s) or Resource(s) and access rights. In the mode where the LwM2M Bootstrap-Server is addressing the Bootstrap Information to the LwM2M Client when initiated with "Bootstrap-Request", the LwM2M Bootstrap-Server MUST inform the LwM2M Client when this transfer is over by sending a "Bootstrap-Finish" operation.

In addition to the bootstrapping interface the required information for the LwM2M Client to function with LwM2M Server(s) may also be configured during manufacturing (called Factory Bootstrap) or via a smartcard (called Smartcard Bootstrap).

Figure: 6.-3 Client Registration shows the operation model for the interface "Client Registration". For this interface, the operations are uplink operations named "Registration", "Update" and "De-register".

Figure: 6.-4 Device Management and Service Enablement shows the operational model for the "Device Management and Service Enablement" interface. For this interface, the downlink operations are "Read", "Read-Composite", "Create", "Delete", "Write", "Write-Composite", "Execute", "Write-Attributes", and "Discover". These operations are used to interact with Resources, Resource Instances, Objects, Object Instances and/or their attributes exposed by the LwM2M Client. The "Read" and "Read-Composite" operations are used to read the current values. The "Discover" operation is used to discover attributes and to discover which Resources are implemented in a certain Object. The "Write" and "Write-Composite" operations are used to update values. The "Write-Attributes" operation is used to change attribute values. The "Execute" operation is used to initiate an action. The "Create" and "Delete" operations are used to create and delete Instances, respectively.

Figure: 6.-5 Information Reporting shows the operational model for the "Information Reporting" interface. For this interface, the downlink operations are "Observe", "Observe-Composite", "Cancel Observation", and "Cancel Observation-Composite". The "Notify" is an uplink operation, which is used to send a new value of a Resource from the LwM2M Client to the LwM2M Server. The "Send" operation is another uplink operation which is used by the LwM2M Client to send data to the LwM2M Server.

The relationship between operations and interfaces is listed in Table: 6.-1 Relationship of operations and interfaces.

6.1. Bootstrap Interface

The Bootstrap Interface is used to provision essential information into the LwM2M Client to enable the LwM2M Client to perform the "Register" operation with one or more LwM2M Servers.

There are four bootstrap modes supported by the LwM2M Enabler:

• Factory Bootstrap

• Bootstrap from Smartcard

• Client Initiated Bootstrap

• Server Initiated Bootstrap

The last two Bootstrap modes require the help of an LwM2M Bootstrap-Server to achieve the ultimate goal to connect a LwM2M Client to their LwM2M Server(s). As specified in Section 6.1.3.4. Server Initiated Bootstrap, the "Server Initiated Bootstrap" mode is a method to invoke the "Client Initiated Bootstrap" mode.

The LwM2M Client MUST support at least one bootstrap mode specified in the Bootstrap Interface.

The LwM2M Bootstrap-Server MUST support the "Client Initiated Bootstrap" mode with the "Bootstrap-Request" operation specified in the Bootstrap Interface. The LwM2M Bootstrap-Server MAY support the "Client Initiated Bootstrap" mode with the "Bootstrap-Pack-Request" operation specified in the Bootstrap Interface.

This section describes what information is conveyed across the Bootstrap Interface, where the LwM2M Client puts that information and how to provision the Bootstrap Information for each of these bootstrap modes. [LwM2M-TRANSPORT] provides further security-relevant information concerning the bootstrap techniques.

6.1.1. LwM2M Bootstrap-Server

The LwM2M Bootstrap-Server is used to provision the LwM2M Client with the information required to contact the LwM2M Server(s).

In order for the LwM2M Client and the LwM2M Bootstrap-Server to establish a connection on the Bootstrap Interface, either in Client Initiated Bootstrap mode or in Server Initiated Bootstrap mode, the LwM2M Client MUST have an LwM2M Bootstrap-Server Account pre-provisioned.

Note: During the Bootstrap Phase the LwM2M Client MAY ignore requests and flush all pending responses not related to the Bootstrap sequence.

6.1.2. Bootstrap Information

This section specifies the information that needs to be configured for a LwM2M Client to connect to LwM2M Server(s) or to the LwM2M Bootstrap-Server. This Bootstrap Information can be available before performing the Bootstrap Sequence described in Section 6.1.4. Bootstrap Sequence or obtained as a result of the Bootstrap Sequence.

Bootstrap Information can be categorized into two types:

• LwM2M Server Bootstrap Information

• LwM2M Bootstrap-Server Bootstrap Information

The LwM2M Client MUST have the LwM2M Server Bootstrap Information after the bootstrap sequence specified in Section 6.1.4. Bootstrap Sequence. The LwM2M Server Bootstrap Information is used by the LwM2M Client to register and connect to the LwM2M Server.

The LwM2M Client SHOULD have the LwM2M Bootstrap-Server Bootstrap Information. The LwM2M Server Bootstrap Information MUST contain at least one LwM2M Server Account.

Note that according to the LwM2M Server Account definition, a usual LwM2M Server Account is composed of a LwM2M Security Object Instance and a LwM2M LwM2M Server Object Instance which are paired by sharing (respectively in Resource 10 and Resource 0 of that Objects) the same Short Server ID; a Short Server ID being unique in the LwM2M Client. Note also that a Security Object Instance may potentially be associated to a LwM2M OSCORE Object Instance by means of an Object Link (Resource 17 of the LwM2M Security Object Instance), a LwM2M COSE Object Instance by means of an Object Link (Resource 27 of the LwM2M Security Object Instance), and/or a MQTT Server Object Instance by means of an Object Link (Resource 26 of the LwM2M Security Object Instance), .

The LwM2M Server Bootstrap Information MAY additionally contain further Object Instances (e.g. Access Control, Connectivity Monitoring Object).

The LwM2M Client MAY be configured to use one or more LwM2M Server Account(s).

The LwM2M Client MUST have at most one LwM2M Bootstrap-Server Account.

The LwM2M Bootstrap-Server Bootstrap Information is used by the LwM2M Client to contact the LwM2M Bootstrap-Server to get the LwM2M Server Bootstrap Information.

The LwM2M Bootstrap-Server Bootstrap Information MUST be an LwM2M Bootstrap-Server Account.

(*) The LwM2M Client MUST have at least one LwM2M Server Account after completion of Bootstrap Sequence specified in Section 6.1.4. Bootstrap Sequence.

Please note that the LwM2M Client MUST accept Bootstrap Information sent via Bootstrap Interface without applying access control, as specified in Section 8.2. Authorization.

6.1.3. Bootstrap Modes

The following sub-sections provide further information for the four Bootstrap modes.

6.1.3.1. Factory Bootstrap

In this mode, the LwM2M Client has been configured with the necessary bootstrap information prior to deployment of the device. The configured information may be the LwM2M Bootstrap-Server Bootstrap Information and/or the LwM2M Server Bootstrap Information.

6.1.3.2. Bootstrap from Smartcard

When the Device supports a Smartcard, the LwM2M Client MUST retrieve and process the bootstrap data contained in the Smartcard as described in Appendix G. Storage of LwM2M Bootstrap Information on the Smartcard (Normative). When the bootstrap data retrieval is successful, the LwM2M Client MUST process the bootstrap data from the Smartcard and SHOULD apply the Bootstrap Information to its configuration to enhance security benefits.

Due to the sensitive nature of the Bootstrap Information, a secure channel SHOULD be established between the Smartcard and the LwM2M Device.

When such a secure channel is established between the Smartcard and the LwM2M Device, this secure channel MUST be based on [GLOBALPLATFORM] procedure, mainly described in Section Appendix H. Secure channel between Smartcard and LwM2M Device Storage for secure Bootstrap Data provisioning (Normative).

In this Bootstrap mode, the LwM2M Client MUST also ensure that the bootstrap data previously retrieved from the Smartcard is unchanged within the Smartcard. If bootstrap data is changed, and if the previous Bootstrap Information was applied from Smartcard, this previous Bootstrap Information MUST be disabled in the LwM2M Client and the LwM2M Client SHOULD apply the new Bootstrap Information from Smartcard to its configuration.

If the Smartcard is disabled (e.g. removing the Smartcard) then the Bootstrap Information created from the bootstrap data of the previous Smartcard MUST be deleted.

Checking for Smartcard change and disabling MUST be performed by the LwM2M Client, each time a "Register" or "Update" operation take place, with a LwM2M Server provisioned from Smartcard. As usual, the Bootstrap security rules (see Section 6.1.5. Bootstrap Security) then apply.

NOTE: Bootstrap Information in Smartcard can be updated by using Smartcard OTA protocol as specified in [ETSI 102 225] / [ETSI 102 226] and extensions such as [3GPP 31.115] / [3GPP 31.116] and [3GPP2 C.S0078-0] / [3GPP2 C.S0079-0].

6.1.3.3. Client Initiated Bootstrap

The "Client Initiated Bootstrap" mode provides a mechanism for the LwM2M Client to retrieve Bootstrap Information from an LwM2M Bootstrap-Server. The "Client Initiated Bootstrap" mode requires an LwM2M Bootstrap-Server Account preloaded in the LwM2M Client.

At a minimum a LwM2M Client needs to have DTLS/TLS and/or OSCORE [OSCORE] security credentials preloaded to authenticate to an LwM2M Bootstrap-Server.

Before entering the "Client Initiated Bootstrap" mode, the LwM2M Client may be registered to LwM2M Servers. Whether or not the LwM2M Client keeps these registrations active during the Client Initiated Bootstrap is implementation dependent.

Figure: 6.1.3.3.-1 Client Initiated Bootstrap with Bootstrap-Request operation and Figure: 6.1.3.3.-2 Client Initiated Bootstrap with Bootstrap-Pack-Request operation depict protocol exchange graphically for two different ways to perform Client Initiated Bootstrap.

Step #0: Bootstrap-Request or Bootstrap-Pack-Request to bootstrap URI

The LwM2M Client sends a "Bootstrap-Request" or "Bootstrap-Pack-Request" operation to LwM2M Bootstrap-Server URI, which has been pre-provisioned. When requesting the bootstrap, the LwM2M Client SHOULD send the LwM2M Client's "Endpoint Client Name" as a parameter to allow the LwM2M Bootstrap-Server to provision the proper bootstrap information for the LwM2M Client. The LwM2M Client MAY omit "Endpoint Client Name" if it is equal to the identifier utilized in the security protocol.

Step #1: Configure Bootstrap Information

The LwM2M Bootstrap-Server configures the LwM2M Client with the Bootstrap Information using the "Write" and/or "Delete" operations or using "Bootstrap-Pack", depending on the operation used in Step #0.

This Bootstrap mode MAY be used to configure some Resources of the Bootstrap Information in the LwM2M Client after initial bootstrap to update Bootstrap Information. In this case, all Bootstrap Information is OPTIONAL.

Step #2: Bootstrap-Finish

When the LwM2M Server has finished sending the Bootstrap Information to the LwM2M Client, the Server MUST send the "Bootstrap-Finish" operation to the Client to properly end this phase. "Bootstrap-Finish" operation is not required if the Bootstrap Information is sent to the client using a "Bootstrap-Pack".

If "Bootstrap-Request" operation is used in Step #0, the bootstrap procedure fails when the LwM2M Client does not receive the "Bootstrap-Finish" operation after the EXCHANGE_LIFETIME time period expired. The EXCHANGE_LIFETIME parameter is defined in [CoAP].

Step #3: Clean-up after successful Bootstrapping

Successful Bootstrapping means that the Bootstrap-Finish operation has been received by the LwM2M Client, if the "Bootstrap-Request" has been used in Step #0, and the loaded configuration is considered consistent by the LwM2M Client. In this case the Bootstrap-Finish response sent to the LwM2M Bootstrap-Server should indicate a success code. If Bootstrapping was unsuccessful, the Bootstrap-Server Account MUST retain the values it had before the unsuccessful Bootstrapping sequence started and further statements below in Step #3 do not apply. If Bootstrapping was unsuccessful using "Bootstrap-Pack-Request", the LwM2M Client MUST retry bootstrapping with "Bootstrap-Request".

In the case the LwM2M Client is registered to a LwM2M Server, if the matching LwM2M Server Account was deleted, the LwM2M Client MUST consider itself de-registered from the LwM2M Server. Note that if the matching LwM2M Server Account was modified, the LwM2M Client may need to update its registration to the LwM2M Server depending on the nature of the modifications.

If the Bootstrap-Server Account Timeout Resource is instantiated in the LwM2M Security Object Instance of the Bootstrap-Server, the LwM2M Client MUST purge the LwM2M Bootstrap-Server Account after the expiration time provided by the value of this Resource. If this Resource is not instantiated or its value is set to 0, the Bootstrap-Server Account lifetime is infinite (Section E.1 LwM2M Object: LwM2M Security).

High entropy keys that are unique per device SHOULD be used for the LwM2M Bootstrap-Server Account. In that case the LwM2M Bootstrap-Server Account SHOULD be kept after bootstrapping i.e. the Bootstrap-Server Account Timeout Resource may be set to 0, or may stay not instantiated.

In case the Bootstrap-Server Account has to be replaced, the replacement and the purge of the previous Bootstrap-Server Account MUST properly take place before the Client sends the Bootstrap-Finish response message back to the Bootstrap-Server; otherwise a "Not Acceptable" Response MUST be returned, and the previous Bootstrap-Server Account is still the only one active.

Note: If the original LwM2M Bootstrap-Server Account is purged from the device, and a new LwM2M Bootstrap-Server Account has not been created, further adding or removing of LwM2M Server Accounts will no longer be possible. Furthermore, updating security credentials e.g. X.509 certificates will also no longer be possible.

6.1.3.4. Server Initiated Bootstrap

In this mode the decision to trigger a Bootstrap Sequence is made by an authorized LwM2M Server. The LwM2M Server triggers the LwM2M Client to enter the "Client Initiated Bootstrap" mode rather than initiating a different protocol for configuring the Bootstrap Information in the LwM2M Client.

The trigger mechanism is performed through the execution of the "Bootstrap-Request Trigger" Resource available from the related Server Object Instance. A connection between a LwM2M Client and a LwM2M Server must already exist to enter this "Server Initiated Bootstrap" mode.

Note: proprietary mechanisms can be used to cause a LwM2M Client to enter the standard "Client Initiated Bootstrap" mode, but that is outside the scope of this specification.

The figure below depicts the "Server Initiated Bootstrap" flow initiated by an authorized LwM2M Server.

6.1.4. Bootstrap Sequence

The LwM2M Client MUST respect step by step the procedural sequence specified below when attempting to bootstrap an LwM2M Device:

1. If the LwM2M Device has Smartcard, the LwM2M Client tries to obtain Bootstrap Information from the Smartcard using the Bootstrap from Smartcard mode. Any Server Initiated Bootstrap attempt MUST be ignored by the LwM2M Client until it has tried to bootstrap via Smartcard or Factory Bootstrap mode.

2. If the LwM2M Client is not configured using the Bootstrap from Smartcard mode, the LwM2M Client tries to obtain the Bootstrap Information by using Factory Bootstrap mode. Any Server Initiated Bootstrap attempt MUST be ignored by the LwM2M Client until it has tried to bootstrap via Smartcard or Factory Bootstrap mode.

3. If the LwM2M Client has any LwM2M Server Object Instances from the previous steps, the LwM2M Client tries to register to the LwM2M Server(s) configured in the LwM2M Server Object Instance(s).

4. If the LwM2M Client fails to register to all the LwM2M Servers or the Client doesn't have any LwM2M Server Object Instances, the LwM2M Client performs the Client Initiated Bootstrap.

5. A Server Initiated Bootstrap attempt (e.g. for updating a LwM2M Server Account) remains possible, but only if the LwM2M Client retains the corresponding LwM2M Bootstrap-Server Account.

6.1.5. Bootstrap Security

The information conveyed through the Bootstrap Interface is sensitive and requires communication security to be used. The security requirements for the Bootstrap Interface is discussed in [LwM2M-TRANSPORT].

6.1.6. Bootstrap and Configuration Consistency

When a Bootstrap Information is loaded in the LwM2M Client, any detected inconsistency MUST be reported in sending an error response code to the Bootstrap-Finish operation. If the Bootstrap Information is delivered to the LwM2M Client with "Bootstrap-Pack", in case of any inconsistency, the LwM2M Client MUST retry bootstrapping with "Bootstrap-Request" operation.

As an example, during a Bootstrap phase, a Multi-Servers Configuration is loaded in a LwM2M Client with the associated Instances of the Access Control Object, while this particular LwM2M Client is not supporting the Access Control Object itself (Single Server context support only). In that case, the client is not able to find a satisfactory consistent configuration by itself, so that the Bootstrap sequence cannot be ended successfully.

On receipt of the error response code to the Bootstrap-Finish operation, the Bootstrap-Server MAY take corrective actions before issuing a new Bootstrap-Finish operation.

As specified in Section 6.1.3. Bootstrap Modes, the LwM2M Client MUST consider the Bootstrap procedure is failed when the LwM2M Client didn't receive a Bootstrap-Finish operation in a certain period (EXCHANGE_LIFETIME), if the bootstrap was initiated with "Bootstrap-Request" operation.

6.1.7. Bootstrap Operations

The mapping to underlying transports is detailed in [LwM2M-TRANSPORT].

The Bootstrap operations are used to help the Bootstrap-Server of setting a proper configuration in a LwM2M Client especially in the case of an incremental Bootstrap procedure for which a particular care must be observed to preserve the Client consistency (e.g. adding a new Server Account without breaking the access rights already in place in the targeted LwM2M Client).

6.1.7.1. Bootstrap-Request Operation

The Bootstrap-Request operation is only performed to initiate the Bootstrap Sequence in the "Client Initiated Bootstrap" mode.

The Bootstrap-Request operation has the following parameters:

6.1.7.2. Bootstrap-Finish Operation

The Bootstrap-Finish operation is performed to terminate the Bootstrap Sequence previously initiated in "Client Initiated Bootstrap" mode (or in "Server Initiated Bootstrap" mode by extension).

This operation informs the LwM2M Client, that all the Bootstrap Information have been provided by the LwM2M Bootstrap-Server.

6.1.7.3. Bootstrap-Discover Operation

The "Bootstrap-Discover" operation in the Bootstrap Interface is different from the "Discover" operation in the Device Management and Service Enablement interface.

The "Bootstrap-Discover" operation on the Bootstrap Interface is used to discover which LwM2M Objects and Object Instances are supported by a certain LwM2M Client. In particular, the list of LwM2M Security Object Instances (ID:0) is reported, while it is not accessible in Device Management and Service Enablement Interface. If OSCORE is supported on the client, a list of LwM2M OSCORE Objects (ID:21) is also reported, since this is not reported in Device Management and Service Enablement Interface either. If the MQTT Transport Binding is supported on the client, a list of LwM2M COSE Objects (ID:23) and MQTT Server Objects (ID:24) is also reported. This operation is useful to clean-up or to update a LwM2M Client configuration (e.g. adding (removing) a LwM2M Server Account to (from) the LwM2M Client configuration).

The returned payload is a list of application/link-format CoRE Links [RFC6690] containing the LwM2M Enabler Version and for each targeted Object - in addition to the Object Version, see Section 7.2. Object Versioning and Table: 7.3.1.-1 Class Attributes - a sub-list of the Instances of such an Object Instance. In order to fully identify the Server Accounts supported by the Client, each element of the Instances list of the LwM2M Security Object (Object ID:0) includes the associated Short Server ID and LwM2M Server URI in its parameters list while the elements of the Instances list of the LwM2M Server Object (Object ID:1) also report the associated Short Server ID in their parameters list. If the LwM2M Client supports OSCORE and/or the MQTT Transport Binding, each element of the Instances list of the LwM2M OSCORE Object (Object ID:21), LwM2M COSE Objects (ID:23), and MQTT Server Objects (ID:24) includes the associated Short Server ID in its parameters list, except the Object Instances which are associated with the LwM2M Bootstrap-Server.

The Bootstrap-Server LwM2M Security Object Instance does not include a Short Server ID in its parameter list (none is defined); therefore the LwM2M Server URI for the Bootstrap Server can also be omitted in such a parameters list.

In "Bootstrap-Discover" operation the targeted path '/' is accepted in place of the Object ID, for informing the Client to report all existing Object Instances.

The "Bootstrap-Discover" operation has the following parameters:

For example:

• when the "Bootstrap-Discover" operation targets an Object with Object ID of 0 (LwM2M Security Object), the response to the operation could be:

  </>;lwm2m=1.1,</0/0>;ssid=101;uri="coaps://server_1.example.com", </0/1/>, </0/2>;ssid=102;uri="coaps://server_2.example.com"

  with the meaning three LwM2M Servers are supported in that Client (which support the LwM2M Enabler in version 1.1), while the Instance ID:1 of the LwM2M Security Object ID:0 contains the credentials for the LwM2M Bootstrap-Server.

• when the "Bootstrap-Discover" operation targets an Object with '/' the response to the operation could be:

  </>;lwm2m=1.1,</0/0>;ssid=101;uri="coaps://server_1.example.com", </0/1>, </1/0/>;ssid=101, </3/0>,</5>,</4>

  with the meaning the Client is supporting (in LwM2M version 1.1) a LwM2M Bootstrap-Server Account (/0/1), a LwM2M Server Account (/0/0, /1/0) with a Short Server ID=101, A Device Object Instance (/3/0) and two other Objects, which are not instantiated yet (Firmware Update /5, and Connectivity Monitory Object /4).

• when the "Bootstrap-Discover" addresses a LwM2M Client supporting the LwM2M Enabler in release 1.1, and containing a configuration with Objects with Object ID of 0 (LwM2M Security Object) and Object ID of 21 (LwM2M OSCORE Object):

  </>;lwm2m=1.1,</0/0>;ssid=101;uri="coaps://server_1.example.com",</0/2>;ssid=102;uri="coap://server_1.example.com",</21/0>;ssid=101,</21/2>;ssid=102,</0/1>,</21/1/>

  with the meaning two LwM2M Servers are supported in that Client (that supports the LwM2M Enabler in version 1.1), the Instance ID:0 of the LwM2M Security Object ID:0 and the Instance ID:0 of the LwM2M OSCORE Object ID:21 contains the DTLS and OSCORE credentials, respectively, of the LwM2M Server with ssid=101. The instance ID:2 of the LwM2M OSCORE Object ID:21 contains the OSCORE credentials of the LWM2M Server with ssid=102, which supports No_Sec mode. The Instance ID:1 of the LwM2M OSCORE Object ID:21 contains the OSCORE credentials for the LwM2M Bootstrap-Server.

• when the "Bootstrap-Discover" addresses a LwM2M Client supporting the LwM2M Enabler in release 1.1, and containing a configuration with an hypothetical LwM2M Object ID:55 in Version 1.9, with one Instance (/55/0):

  </>;lwm2m=1.1,</0/0>,</0/1>;ssid=101;uri="coaps://server_1.example.com", </1/0/>;ssid=101, </3/0>,</5>,</4>,</55>;ver=1.9,</55/0>

• when the "Bootstrap-Discover" addresses a LwM2M Client supporting the LwM2M Enabler in release 1.2, and containing a configuration with Objects with Object ID of 0 (LwM2M Security Object), Object ID of 21 (LwM2M OSCORE Object), Object ID of 23 (LwM2M COSE Object), and Object ID of 24 (MQTT Server Object):

  </>;lwm2m=1.2,</0/0>;ssid=101;uri="coaps://server_1.example.com",</0/1>,</21/0>;ssid=101,</24/1>,</23/65>

  with the meaning one LwM2M Server is supported in that Client (that supports the LwM2M Enabler in version 1.2), the Instance ID:0 of the LwM2M Security Object ID:0 and the Instance ID:0 of the LwM2M OSCORE Object ID:21 contains the DTLS and OSCORE credentials, respectively, of the LwM2M Server with ssid=101. the Instance ID:1 of the LwM2M Security Object ID:0, the Instance ID:1 of the MQTT Server Object ID:24 and the Instance ID:65 of the LwM2M COSE Object ID:23 contain the TLS credentials, MQTT configuration, and COSE keying material, respectively, for the LwM2M Bootstrap-Server.

Note: In previous versions of this document, the LwM2M Enabler Version link parameter was not associated to any URI-Reference in the examples (e.g. "lwm2m=1.0,</0/0>;ssid=101,</0/1/>,</0/2>;ssid=102"). Thus, the provided examples were not in conformance with the ABNF of [RFC6690]. LwM2M Servers MAY accept this particular error in the LwM2M Client's response to the "Bootstrap-Discover" operation.

6.1.7.4. Bootstrap-Read Operation

The "Bootstrap-Read" operation in the Bootstrap Interface is a restricted form of the "Read" operation found in the Device Management and Service Enablement interface, and MUST be limited to target Objects that are strictly necessary to setup a proper configuration in a LwM2M Client.

In this specification the only acceptable targets for the "Bootstrap-Read" operation is the LwM2M Server Object (Object ID: 1) and the Access Control Object (Object ID:2). This operation will allow the Bootstrap-Server to query the existing Server Account(s) to determine validity and to add new Server Account(s) without breaking the access control rights already in place in the targeted LwM2M Client.

The "Bootstrap-Read" operation is used to access a single Instance or all Instances of the Server Object (ID:1) and the Access Control Object (ID:2).

The "Bootstrap-Read" operation has the following parameters:

As a simple illustration based on the second example of Section 7.5.5.2. Multiple Object Instance Request Examples: the "Bootstrap-Read /2" operation with JSON requested format could provide the following answer:

Any optional resources included in the "Bootstrap-Read" operation response that are not supported by, or unknown to, the LwM2M Bootstrap-Server MUST NOT be interpreted as an error by the LwM2M Bootstrap-Server.

6.1.7.5. Bootstrap-Write Operation

The "Bootstrap-Write" operation in Bootstrap Interface is different from the "Write" Operation in the Device Management and Service Enablement interface. The LwM2M Client MUST write the value included in the payload regardless of an existence of the targeted Object Instance(s) or Resource(s).

Any optional Resources included in the "Bootstrap-Write" operation targeting an Object or an Object Instance that are not supported by, or unknown to, the LwM2M Client MUST NOT be interpreted as an error by the LwM2M Client. If the LwM2M Client supports optional resources not present in the payload, it MUST NOT instantiate these optional resources.

If New Value does not contain values for all Resources (mandatory and optional) of the Object, the LwM2M Client MAY populate the missing Resources with implementation dependent default values.

The "Bootstrap-Write" operation can be sent multiple times.

Only in the Bootstrap Interface, the "Bootstrap-Write" MAY target just an Object ID, which will allow a Bootstrap-Server in using a TLV, LwM2M CBOR, SenML CBOR or SenML JSON formatted payload, to populate a LwM2M Client in a single message containing several Instances of the same Object.

The "Bootstrap-Write" operation has the following parameters:

6.1.7.6. Bootstrap-Delete Operation

The "Bootstrap-Delete" operation targets one or several Object Instances and can be sent multiple times.

Only in the Bootstrap Interface, the "Bootstrap-Delete" operation MAY target any Instance or all Instances of any Object including the LwM2M Security Object (ID:0), supported by the LwM2M Client. The two exceptions are the LwM2M Bootstrap-Server Account, potentially including an associated Instance of a LwM2M OSCORE Object ID:21, an associated Instance of a LwM2M COSE Object ID:23, an associated Instance of a MQTT Server Object ID:24; and the single Instance of the mandatory Device Object (ID:3), which are not affected by any Delete operation.

When the "Bootstrap-Delete" operation is used without any parameter (i.e. without Object ID parameter), all Instances of all Objects in the LwM2M Client MUST be removed (except for the two cases mentioned above). This functionality could be used for initialization purposes before LwM2M Bootstrap-Server sends Write operation(s) to the LwM2M Client.

The "Bootstrap-Delete" operation has the following parameters:

6.1.7.7. Bootstrap-Pack-Request Operation

The "Bootstrap-Pack-Request" operation is only performed to initiate the Bootstrap Sequence in the "Client Initiated Bootstrap" mode by the client indicating that the client wants to retrieve a "Bootstrap-Pack".

"Bootstrap-Pack" contains, at minimum, the required bootstrap information defined in Section 6.1.2. Bootstrap Information. Only by using "Bootstrap-Pack" in the Bootstrap Interface, an LwM2M client can be populated in a single message containing several Objects and several Instances of such Objects.

In "Bootstrap-Pack-Request" operation, the Bootstrap Server receives a "Bootstrap-Pack-Request" and the Bootstrap Server responds with a "Bootstrap-Pack" which the client uses to create or replace objects on the client.

The LwM2M client MUST delete the existing Objects and their Instances in the client with the Objects and their Instances given in the "Bootstrap-Pack" if the Object IDs are the same. Object IDs available in the LwM2M Client which are not provided in the "Bootstrap-Pack" MUST NOT be deleted. The two exceptions are the LwM2M Bootstrap-Server Account, potentially including an associated Instance of an OSCORE Object ID:21, and the single Instance of the mandatory Device Object (ID:3), which are not affected by any Delete operation. Thus, when checking the configuration consistency, the LwM2M Client MUST ensure that the LwM2M Bootstrap-Server Account is still present.

The LwM2M Client MUST write the value included in the "Bootstrap-Pack" payload regardless of a previous existence of the targeted Object Instance(s) or Resource(s). Any optional Resources included in the "Bootstrap-Pack" targeting an Object or an Object Instance that are not supported by, or unknown to, the LwM2M Client MUST NOT be interpreted as an error by the LwM2M Client. If the LwM2M Client supports optional resources not present in the payload, it MUST NOT instantiate these optional resources.

If the LwM2M Bootstrap-Server does not support "Bootstrap-Pack-Request", it MUST return an error code indicating not implemented to the LwM2M Client when "Bootstrap-Pack-Request" is received. If the LwM2M Server supports the "Bootstrap-Pack-Request" but wishes the LwM2M Client not to use "Bootstrap-Pack" for bootstrapping, it MUST return an error code indicating that the method is not allowed to the LwM2M Client. After receiving an error in response to a "Bootstrap-Pack-Request", the LwM2M Client MUST use "Bootstrap-Request" operation to continue Client Initiated Bootstrap.

If the LwM2M Client does not receive any response from the LwM2M Bootstrap-Server during the EXCHANGE_LIFETIME time period, the LwM2M Client MAY retry bootstrapping with "Bootstrap-Pack-Request".

The "Bootstrap-Pack-Request" operation has the following parameters:

LwM2M Bootstrap-Server Account Object Instances, if present, MUST be expressed in the CoRE Link Format defined in [RFC6690], so that each Object Instance is described as a Link according to that format. The Target component of the link is required, and consists of the Object Instance path. The link MUST NOT include any parameter.

For the LwM2M Client example defined in Section Appendix F. Example LwM2M Client (Informative), the LwM2M Bootstrap-Server Account Object Instances would be: </0/0>.

For another LwM2M Client where the LwM2M Bootstrap-Server Account is defined by the Instance 2 of the LwM2M Security Object and Instance 0 of the LwM2M OSCORE Object, the LwM2M Bootstrap-Server Account Object Instances would be: </0/2>,</21/0>.

As a simple illustration based on the LwM2M Client example defined in Section Appendix F. Example LwM2M Client (Informative), a Bootstrap-Pack could look like the following in SenML JSON encoded format below. For editorial purposes line breaks have been added to the example.

6.2. Client Registration Interface

The LwM2M Server MUST support all operations in this interface. The LwM2M Client MUST support the "Register" and the "Update" operations. The LwM2M Client SHOULD support the "De-register" operation.

The Client Registration Interface is used by a LwM2M Client to register with one or more LwM2M Servers, maintain each registration, and de-register from a LwM2M Server. The registration is based on the Resource Model and Identifiers defined in Section 7. Identifiers and Resources. When registering, the LwM2M Client performs the "Register" operation and provides the information required by the LwM2M Server (e.g. the supported Objects and existing Object Instances) as well as optional parameters (e.g. Endpoint Client Name). The LwM2M Client and the LwM2M Server maintain the LwM2M Registration Session based upon the configured parameters (e.g. Lifetime, security context). The ability to maintain an LwM2M Registration Session may be impacted by a change in the Transport Session, e.g. a binding change.

The LwM2M Client periodically performs an update of its registration information to the registered LwM2M Server(s) by performing the "Update" operation.

If the lifetime of a registration expires without receiving an update from the LwM2M Client, the LwM2M Server will consider it a de-registration:

• The LwM2M Server MUST remove the registration of that LwM2M Client and existing observations. If the LwM2M Client is unaware of the expiration, when the LwM2M Client performs a registration update the LwM2M Server will respond with an error.

• Upon receipt of the error message, the LwM2M Client SHOULD reset its state and register again. The LwM2M Client MUST re-register ("Update" is not sufficient) to the LwM2M Server in order to be connected again, before initiating any further communication.

If the LwM2M Server or the LwM2M Client sets a value to the Lifetime Resource of the Server Object Instance, this value becomes the new lifetime of the Registration.

During "Register" or "Update" operations, the parameter Lifetime – if present – MUST match the current value of the Mandatory Lifetime Resource of the LwM2M Server Object Instance.

Finally, when shutting down or discontinuing use of a LwM2M Server, the LwM2M Client SHOULD perform a "De-register" operation.

The Binding Resource of the LwM2M Server Object informs the LwM2M Client about the transport protocol preferences of the LwM2M Server for the Transport Session between the LwM2M Client and LwM2M Server. The LwM2M Client SHOULD perform the operations with the modes indicated by the Binding Resource of the LwM2M Server Object Instance.

The mapping to underlying transports is detailed in [LwM2M-TRANSPORT].

6.2.1. Register Operation

Registration is performed when a LwM2M Client sends a "Register" operation to the LwM2M Server. After the LwM2M Device is turned on and the bootstrap procedure has been completed, the LwM2M Client MUST perform a "Register" operation to each LwM2M Server that the LwM2M Client has a Server Object Instance. Table: 6.2.1.-1 Registration Parameters describes the parameters used for the "Register" operation.

The "Register" operation SHOULD include the Endpoint Client Name parameter along with other parameters listed in Table: 6.2.1.-1 Registration Parameters. When the Endpoint Client Name parameter is provided in the "Register" operation then it MUST contain a value for the Endpoint Client Name parameter that is unique on that LwM2M Server.

Upon receiving a "Register" operation from the LwM2M Client, the LwM2M Server records the connection information of the registration message (e.g. source IP address and port or MSISDN) and uses this information for all future interactions with that LwM2M Client.

If the LwM2M Client sends a "Register" operation to the LwM2M Server, even though the LwM2M Server has registration information of the LwM2M Client, the LwM2M Server removes the existing registration information and performs the new "Register" operation. This situation happens when the LwM2M Client forgets the state of the LwM2M Server (e.g. factory reset).

The LwM2M Server MUST support all the parameters and payloads listed at Table: 6.2.1.-1 Registration Parameters, except for the Profile ID. The LwM2M Client MUST implement LwM2M Version, Lifetime, Object and Object Instances and MAY implement all other parameters.

The syntax of the "Profile ID" argument value is as follows:

value = profileID / ( """ profileID *( "," profileID ) """ )
profileID = dynamicID / preConfigID
dynamicID = suite-identifier ":" 1*(ahlc)
suite-identifier = 1*( DIGIT )
ahlc = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
preConfigID = ("oma" / "v") ":" 1*(ALPHA / DIGIT / "-")

The Profile ID can be used in two different deployment modes, namely

• In the pre-configured mode, the identifier used in the Profile ID refers to a list of Objects supported and Object Instances available on the LwM2M Client (LwM2M Security Object ID:0, LwM2M OSCORE Object ID:21, and LwM2M COSE Object ID:23, if present, MUST NOT be part of this list). The value is either registered with the Open Mobile Naming Authority (OMNA) or a vendor-specific value. The value needs to be pre-configured on the LwM2M Client and on the LwM2M Server so that both communication peers understand how to map the Profile ID value to the list of Objects and Object Instances it represents.

• In the dynamically generated mode the LwM2M Client itself creates a fingerprint (in form of a cryptographic hash) of a list of Objects supported, the object versions and Object Instances available on the LwM2M Client (LwM2M Security Object ID:0, LwM2M OSCORE Object ID:21, and LwM2M COSE Object ID:23, if present, MUST NOT be part of this list) it wants to convey with the register operation to the LwM2M Server. Object versions MUST always be included in the finger print calculation even for version 1.0 of objects as well as those that can be inferred from the LwM2M protocol version. The LwM2M Client then puts this fingerprint value into the Profile ID parameter. To avoid collisions, the selected hash algorithm needs to be sufficiently long, i.e. 32 bits and longer.

If the LwM2M Server cannot retrieve the list of Objects and Object Instances based on the received Profile ID value, it MUST reply to the registration message with an error code. The LwM2M Client MUST then perform the register operation with a registration message that MUST include the list of Objects supported and Object Instances available on the LwM2M Client.

Using the dynamically generated mode the LwM2M Server may be able to determine the mappings between the Profile ID value and its corresponding list of Objects and Object Instances.

An LwM2M Client MAY include multiple Profile ID parameters in a single message and MAY mix the Profile ID parameter with a list of Objects and Object Instances in the payload of the message. The latter allows the LwM2M Client to use the Profile ID for a commonly used combination of Objects and Object Instances while offering the possibility to include rarely used configurations in the payload.

The LwM2M Server uses all provided Profile ID values and the provided Objects and Object Instances to determine the list of supported Objects and Object Instances of the LwM2M Client. If no information is provided in the registration request the LwM2M Server MAY determine the list of supported Objects and Object Instances of the LwM2M Client through pre-configuration, which is outside the scope of this specification. If the LwM2M Server cannot determine the list of Objects and Object Instances it MUST reply to the registration message with an error code.

The value used in the Profile ID follows a naming convention:

• For hashes this specification uses the numerical ID value of IANA registered Named Information Hash Algorithms defined by [RFC6920] to indicate the hash algorithms used. For example, the use of SHA256 truncated to 32 bits is indicated by the profile ID value "6:1234abcd".

• For values used in application domains registered via the OMNA, the prefix is "oma:" followed by the registered value. The list of standardized values can be found at [OMNA].

• For values used in vendor-specific deployments, the prefix "v:" followed by the value is used.

An LwM2M Server MUST refuse a Client's Registration request, if it does not support the LwM2M Enabler version indicated by the Client.

An LwM2M Server MAY refuse to use the Profile ID by returning an error requiring the LwM2M to indicate the list of Objects and Object Instances in a subsequent registration message.

When an Object defined outside of an LwM2M Enabler has to be registered by the Client, but is not supported by the Server (unknown Object or unsupported Object version) it MUST NOT be interpreted as an error by the Server and will not prevent the Client's Registration request to be accepted.

The Media-Type of the registration message, if used, MUST be the CoRE Link Format (application/link-format) defined in [RFC6690], so that each Object is described as a Link according to that format. The Target component of the link is required, and consists of the Object path and Object Version CoRE link parameter "ver" if required as it is defined in Section 7.2. Object Versioning of this document. Any other parameters included in the link MUST NOT be interpreted as an error, unless specified for use by the LwM2M Enabler.

As an example, the payload for a LwM2M Client supporting LwM2M Server, Access Control, Device, Connectivity Monitoring and Firmware Update Objects from Section Appendix E. LwM2M Objects defined by OMA (Normative) would be (for the example client of Section Appendix F. Example LwM2M Client (Informative)):

</1/0>,</1/1>,</2/0>,</2/1>,</2/2>,</2/3>,</2/4>,</3/0>,</4/0>,</5>

If the LwM2M Client supports optional data formats, it MAY inform the LwM2M Server by including the content types in the root path link using the ct= link attribute defined in [CoAP]. An example is as follows (note that the content type value 110 is the value assigned in the CoAP Content-Format Registry for the SenML JSON format used by LwM2M).

</>;ct=110, </1/0>,</1/1>,</2/0>,</2/1>,</2/2>,</2/3>,</2/4>,</3/0>,</4/0>,</5>

Another example if the LwM2M Client supports the SenML JSON format, the CBOR format, and the SenML CBOR format:

</>;ct="110 112 60", </1/0>,</1/1>,</2/0>,</2/1>,</2/2>,</2/3>,</2/4>,</3/0>,</4/0>,</5>

6.2.1.1. Bootstrap and LwM2M Server Registration Mechanisms

In order to provide robust mechanisms for LwM2M Server registrations, resources have been defined in the LwM2M Server Object to configure the order of LwM2M Server registrations, registration retry behavior and the ability for the LwM2M Client to react during registration failure conditions. These resources are optional, so the behavior is only enabled when these resources are defined. If these resources are not defined, default values in Table: 6.2.1.1.-1 Registration Procedures Default Values or a manufacturer defined implementation may be used.

The first step is for the LwM2M Client to determine the registration order when multiple LwM2M Servers are defined (i.e. multiple instances of LwM2M Server Objects). The LwM2M Client orders the LwM2M Server registrations in ascending order of the "Registration Priority Order" value. It is recommended that each ordered LwM2M Server has a unique priority, so it is implementation dependent how to order those LwM2M Servers with the same priority. If this value is not defined for a LwM2M Server, registration attempts to that LwM2M Server are managed independently and do not impact other LwM2M Server registrations.

For each LwM2M Server that is defined in the registration order, the "Registration Failure Block" resource indicates the behavior of the LwM2M Client upon registration failure to that LwM2M Server. When the "Registration Failure Block" value is set to true and registration to the LwM2M server fails, the LwM2M Client performs additional registration retry sequences and blocks registration to other LwM2M Servers in the priority order. When the "Registration Failure Block" value is set to false, the LwM2M Client proceeds with registration to the next LwM2M Server in the priority order whether the current LwM2M Server is successfully registered or not.

The procedure to manage the registration to LwM2M Servers that have a "Registration Priority Order" resource included is defined here:

When registration fails to non-blocking LwM2M Servers in the "Ordered Servers Procedure", it is outside the scope of this specification how the LwM2M Client retries registration with those LwM2M Servers. One solution could be to execute the "Single Unordered Servers Procedure" for all failed non-blocking LwM2M Servers.

The "Communication Retry Count", "Communication Retry Timer", "Communication Sequence Delay Timer" and "Communication Sequence Retry Count" resources indicate to the LwM2M Client the retry mechanism to be used for registration attempts to a single LwM2M Server. The registration mechanism to a LwM2M Server consists of a sequence of "Communication Retry Count" attempts within a retry sequence. The "Communication Retry Timer" value is multiplied by two to the power of the current attempt minus one (2^(Current Attempt-1)) to create an exponential back-off between attempts within a single retry sequence to a LwM2M Server. If one retry sequence of attempts to a LwM2M Server fails, then a new sequence of attempts may be retried after "Communication Sequence Delay Timer." The maximum number of retry sequences to a LwM2M Server is set by the "Communication Sequence Retry Count."

How these values are applied to those LwM2M Servers that are part of the ordered registration is defined in the "Single Ordered Server Procedure" here:

How these values are applied to those LwM2M Servers that are NOT part of the ordered registration is defined in the "Single Unordered Server Procedure" here:

Note: Current Attempt and Current Sequence start at 1 to represent the first attempt or sequence in the "Single Ordered Server Procedure" and "Single Unordered Server Procedure". These values should be reset to 1 at the start of each sequence and between sequences.

The "Initial Registration Delay Timer" defines the delay before the single registration procedure (ordered or unordered) is attempted for a LwM2M Server.

The "Bootstrap on Registration Failure" resource indicates to the LwM2M Client whether to re-bootstrap in case of a registration failure to the LwM2M Server. The exact behavior in case of bootstrap registration success, triggered by a server registration failure, is implementation dependent. For example, already successful LwM2M Server registrations may be maintained.

Note: It is recommended to set the "Bootstrap on Registration Failure" resource to true only when "Registration Failure Block" is set to true for any ordered LwM2M Server (i.e. that LwM2M Server is critical) to avoid a situation where the device has no recovery method. On the other hand, if the “ Bootstrap on Registration Failure” resource is set to false, it is recommended to set the “Registration Failure Block” resource to false for an ordered LwM2M Server.”

Note: It is recommended to set the "Communication Sequence Retry Timer" resource sufficiently large to accommodate for an entire registration attempt sequence to avoid an immediate retry sequence.

The registration retry mechanisms for the Bootstrap Server are implementation dependent.

The following table represents the recommended default values to use when the resources are not defined in the LwM2M Server Object:

6.2.1.2. Behaviour with Current Transport Binding and Modes

Behaviour of the LwM2M Server and the LwM2M Client is differentiated by Current Transport Binding and Modes. Current Transport Bindings are decided by "Binding" Resource set by the LwM2M Server. The "Binding" resource contains a combination of supported transports, for example UDP and TCP.

Table: 6.2.1.2.-1 Behaviour with Current Transport Bindings describes the behaviour of the LwM2M Server and the LwM2M Client for each Current Transport Bindings.

• While multiple transports are supported, only one transport binding can be used during the entire Transport Session. As an example, when UDP and SMS are both supported, the LwM2M Client and the LwM2M Server can choose to communicate either over UDP or SMS during the entire Transport Session.
  

• "Preferred Transport" is an optional resource in the LwM2M Server Object (/1/x/22). If this resource is defined, the LwM2M Client SHALL use this to initiate a connection over the specified transport, unless unable to do so. If this resource is not defined, the LwM2M Client SHALL use a client-preferred binding supported by both the LwM2M Server (from the list in the "binding" resource of the LwM2M Server Object - /1/x/7) and LwM2M Client (from the list in "Supported Binding and Modes" resource in the Device object - /3/x/16). The "Preferred Transport" resource can also be used to select a required transport. For example, when Non-IP is normally indicated as preferred, this resource can be set to UDP temporarily to perform a firmware update.

• "Registration Update Trigger" is a mandatory resource in the LwM2M Server Object (/1/x/8). The client SHALL use the argument when the "Registration Update Trigger" resource is executed unless not supported by the client or not indicated as supported by the server in the "binding" resource of the LwM2M Server Object (/1/x/7). When that argument indicates an overriding binding that is supported by the client, the client SHALL immediately release the existing transport connection and establish a new transport connection using the overriding binding if that overriding binding is different than the current transport connection.

• UDP SHALL be supported by the Server for binding and support for TCP is Optional. Clients SHALL assume UDP binding is supported by the Server even if the Server does not include UDP (“U”) in the "binding" resource of the LwM2M server object (/1/x/7).

• When the APN Connection Profile object is defined with a "PDN Type" resource (/11/x/24), that "PDN Type" SHALL be preferred when present in the "binding" resource of the LwM2M server object (/1/x/7).

• When configurations related to the bindings change, those new values SHALL NOT affect the current Transport Session, and the new values SHALL be applied to the future Transport Sessions. The existing LwM2M client registration SHALL NOT be affected by the use of updated bindings configuration.

• Queue Mode and device triggering can be enabled independently, and can be used in conjunction with one or more transports. Using the device triggering, the LwM2M Server MAY request the LwM2M Client to perform operations, such as the "Update" operation by sending an "Execute" to the "Registration Update Trigger" Resource via SMS. An LwM2M Client is not expected to send an SMS response for a device trigger message.

6.2.2. Update Operation

Periodically or based on certain events within the LwM2M Client or initiated by the LwM2M Server, the LwM2M Client updates its registration information with a LwM2M Server by sending an "Update" operation to the LwM2M Server.

The "Update" operation can be initiated by the LwM2M Server via an "Execute" operation on the "Registration Update Trigger" Resource of the LwM2M Server Object. The LwM2M Client can perform an "Update" operation to refresh the lifetime of its registration to a LwM2M Server.

When any of the parameters listed in Table: 6.2.2.-1 Update Parameters changes, the LwM2M Client MUST send an "Update" operation to the LwM2M Server. This "Update" operation MUST contain only the parameters listed in Table: 6.2.2.-1 Update Parameters which have changed compared to the last registration parameters sent to the LwM2M Server.

When present, the Objects and Object Instance list and/or the Profile ID MUST follow the same rules as in the Register operation.

The payload Media-Type of that "Update" operation is the same as the one of the "Registration" operation.

When an Object defined outside of an LwM2M Enabler is part of the LwM2M Client update registration list, but is not supported by the LwM2M Server (unknown Object or unsupported Object version), it MUST NOT be interpreted as an error by this LwM2M Server and will not prevent the LwM2M Client's "Update" operation to be accepted.

Two common operations are:

1. Extending the lifetime of a registration

In this case the LwM2M Client sends an "Update" operation with no parameters.

Figure: 6.2.2.-1 Update Example Flow #1 shows an example exchange where the LwM2M Client sends an "Update" operation that only refreshes the registration, i.e. the message does not contain any parameters. With the second "Update" the Client changes the lifetime field to 6000 (seconds) and hence the lt parameter is included in the message.

2. Adding and removing Objects and Object Instances

In this case the LwM2M Client sends an "Update" with a body listing the complete list of objects and object instances.

Figure: 6.2.2.-2 Update Example Flow #2 shows an example exchange whereby the LwM2M Client starts with an initial registration of two instances for an LwM2M Object with ID 12. Later, the LwM2M Server adds a third instance and subsequently deletes the second. With the "Update" operation the LwM2M Client includes the new list of Objects and Object Instances.

6.2.3. De-register Operation

When a LwM2M Client determines that it no longer requires to be available to a LwM2M Server (e.g. LwM2M Device factory reset), the LwM2M Client SHOULD send a "De-register" operation to the LwM2M Server. Upon receiving this message, the LwM2M Server removes the registration information from the LwM2M Server.

6.3. Device Management and Service Enablement Interface

The LwM2M Server and the LwM2M Client MUST support all the operations on this interface unless clearly stated otherwise. Support for some of the non-mandatory operations may also be dependent on the choice of transport layer and the services it provides.

The Device Management and Service Enablement Interface is used by the LwM2M Server to access Object Instances and Resources available from a registered LwM2M Client. The interface provides this access through the use of "Create", "Read", "Read-Composite", "Write", "Write-Composite", "Delete", "Execute", "Write-Attributes", or "Discover" operations. The operations that a Resource supports are defined in the Object definition using the Object Template. The Object Template is described in Section Appendix D. LwM2M Object Template and Guidelines (Normative). The Normative Objects defined by the LwM2M Enabler are described in Section Appendix E. LwM2M Objects defined by OMA (Normative).

The LwM2M Client MUST ignore LwM2M Server operations on this interface until the registration procedure with the respective LwM2M Server is completed.

The LwM2M Client MUST reject any LwM2M Server operation on the LwM2M Security Object (ID: 0) with a response code indicating that the operation is not authorized.

The LwM2M Client MUST reject any LwM2M Server operation on the LwM2M OSCORE Object (ID: 21) with a response code indicating that the operation is not authorized.

The LwM2M Client MUST reject any LwM2M Server operation on the LwM2M COSE Object (ID: 23) with a response code indicating that the operation is not authorized.

The LwM2M Server SHOULD NOT perform any operation on this interface before replying to the registration request of this LwM2M Client.

The mapping to underlying transports is detailed in [LwM2M-TRANSPORT].

6.3.1. Read Operation

The "Read" operation is used to access the value of a Resource, a Resource Instance, an array of Resource Instances, an Object Instance or all the Object Instances of an Object. The "Read" operation has the following parameters:

If the Resource ID is specified and if the requested Resource does not support the "Read" operation, the LwM2M Client MUST return an error code indicating that the method is not allowed to the LwM2M Server.

If the Resource ID is not specified, the LwM2M Client MUST retrieve all the requested Resources except the Resource(s) which does not support the "Read" operation and send the retrieved Resource(s) information to the LwM2M Server.

Any optional Resources included in the "Read" operation response that are not supported by, or unknown to, the LwM2M Server MUST NOT be interpreted as an error by the LwM2M Server.

6.3.2. Discover Operation

The "Discover" operation is used to discover LwM2M Attributes attached to or inherited by an Object, Object Instances, and Resources. This operation can be used to discover which Resources are instantiated in a given Object Instance. The returned payload is a list of application/link-format CoRE Links [RFC6690] for each targeted Object, Object Instance, or Resource, along with their attached or inherited Attributes including the Object Version attribute if required (see Section 7.2. Object Versioning and Table: 7.3.1.-1 Class Attributes).

The "Discover" operation has the following parameters:

The LwM2M Client SHOULD support the "Depth" parameter. If the LwM2M Client does not support the "Depth" parameter, it MUST ignore it and use the default value from Table: 6.3.2.-2 Depth Modifier.

The LwM2M Client MUST respond to the "Discover" operation with the list of Object, Object Instances, Resources, and Resource Instances instantiated under the targeted Object according to Table: 6.3.2.-2 Depth Modifier, with their respective attached Attributes.

If a Resource, an Object Instance, or an Object have attributes for multiple LwM2M Servers, then the Attributes returned in the link, MUST only be related to the LwM2M Server which performed the "Discover" operation.

In addition, the list of Attributes attached to or inherited by the targeted Object, Object Instance, or Resource MUST be returned (see Section Attributes Classification). If a Resource Instance, a Resource, an Object Instance, or an Object have attributes for multiple LwM2M Servers, then the Attributes returned in the link, MUST only be related to the LwM2M Server which performed the "Discover" operation.

For example:

• when the "Discover" operation targets an Object with Object ID of 3, the response to the operation could be:

</3>;pmin=10, </3/0>;pmax=60, </3/0/1>, </3/0/2>, </3/0/3>, </3/0/4>, </3/0/6>;dim=2, </3/0/7>;dim=2;gt=50;lt=42.2, </3/0/8>;dim=2, </3/0/11>, </3/0/16>

which means that the LwM2M Client supports the Device Object (Instance 0) Resources with IDs 1, 2, 3, 4, 6, 7, 8, 11, and 16 among the Resources of Device Info Object. A Maximum Period Attribute has been attached to the Object and a Minimum Period Attribute has been attached to the Object Instance. The Resources 7 and 8 both have two Resource Instances. A Greater Than and a Less Than Attributes has been attached to Resource 7.

• when the "Discover" operation targets an Object with Object ID of 1 and a Depth of 1, the response to the operation could be:

</1>, </1/0>, </1/4>;pmax=300

which means that the LwM2M Client has two Object Instances of the Server Object with IDs 0 and 4. A Maximum Period Attribute has been attached to the Instance 4.

• when the "Discover" operation targets an Object with Object ID of 3 and Object Instance ID of 0, the response to the operation could be:

</3/0>;pmin=10;pmax=60, </3/0/1>, </3/0/2>, </3/0/3>, </3/0/4>, </3/0/6>;dim=2, </3/0/6/0>, </3/0/6/3>, </3/0/7>;dim=2;gt=50;lt=42.2, </3/0/7/0>, </3/0/7/1>;lt=45, </3/0/8>;dim=2, </3/0/8/1>, </3/0/8/2>, </3/0/11>, </3/0/16>

which means that regarding the Device Object Instance, a Maximum Period Attribute has been attached to this Instance level and a Minimum Period Attribute inherited from the Object level; the LwM2M Client supports the Multiple-Instance Resources 6, 7, and 8 with a dimension of 2 and has 2 additional Notification parameters attached to Resource 7.

• when the "Discover" operation targets an Object with Object ID of 3, Object Instance ID of 0, and a Depth of 0, the response to the operation could be:

  </3/0>;pmin=10;pmax=60

  which means that regarding the Device Object Instance, a Maximum Period Attribute has been attached to this Instance level and a Minimum Period Attribute inherited from the Object level.

• when the "Discover" operation targets an Object with Object ID of 3, Object Instance ID of 0, and Resource ID of 7 the response to the operation could be:

</3/0/7>;dim=2;pmin=10;pmax=60;gt=50;lt=42.2, </3/0/7/0>, </3/0/7/1>;lt=45

which means that regarding the Power Source Voltage of the Device Object, two Resource Instances with IDs 0 and 1 are present; a Less Than Attribute has been attached to this Resource, a Maximum Period Attribute and a Minimum Period Attribute are inherited from the Object and Object Instance levels; a different Less Than Attribute has been attached to the Resource Instance 1.

• If the Device Object (ID:3) having the Resource ID:7 with attached Attributes from two LwM2M Servers 1 and 2, then the answers to the "Discover" operation on both LwM2M Servers will be differentiated e.g.

from LwM2M Server 1: Discover /3/0/7 could provide the answer: </3/0/7>;dim=2;gt=50;lt=42.2, </3/0/7/0>, </3/0/7/1>

from LwM2M Server 2: Discover /3/0/7 could provide the answer: </3/0/7>;dim=2;pmax=300;gt=80;lt=65.5, </3/0/7/0>, </3/0/7/1>

6.3.3. Write Operation

The "Write" operation is used to change the value of a Resource, the value of a Resource Instance, the values of an array of Resources Instances or the values of multiple Resources from an Object Instance. The "Write" operation can also be used to request the deletion or the allocation of specific Instances of a Multiple-Instance Resource.

The LwM2M Client MUST perform the operation only if all the Resources conveyed in the operation are allowed to support the "Write" operation. If any Resource does not support the "Write" operation, the LwM2M Client MUST inform the LwM2M Server that the Object Instance cannot perform the requested operation by returning an error code indicating that the method is not allowed.

The request includes the value to be written encoded in one of the data format defined in Section 7.5. Data Formats for Transferring Resource Information.

The TLV, LwM2M CBOR, SenML CBOR or SenML JSON data format MUST be used in a "Write" request:

• when more than a single value of a Resource has to be changed
• when one or several Instances of a Multiple-Instance Resource have to be deleted or allocated.

The Write request MUST be rejected:

• if the specified data format is not supported by the LwM2M Client
• or if, checking the value of the incoming Resource against its data type, at least one of the following conditions is not met:
  • the value matches the expected format
  • the value is in the range specified in the Object definition
  • if the value is an Objlnk value, it must either point to an Object actually present in the LwM2M Client (the value will then be ObjectID:MAX_ID), or point to an Object Instance actually present in the LwM2M Client, or contain the null pointer (the value will then be MAX_ID:MAX_ID)
• or if the deletion or allocation of an Instance of a Multiple-Instance Resource is not allowed by the LwM2M Client.

The LwM2M Client and LwM2M Server MUST support the following mechanisms to change multiple Resources or an array of Resource Instances:

• Replace: replaces the Object Instance or the Resource(s) with the new value provided in the "Write" operation. When the Resource is a Multiple-Instance Resource, the existing array of Resource Instances is replaced to the condition the LwM2M Client authorizes that operation.
• Partial Update: updates Resources provided in the new value and leaves other existing Resources unchanged. When the Resource is a Multiple-Instance Resource, the existing array of Resource Instances is updated meaning some Instances may be created or overwritten to the condition the LwM2M Client authorizes such operations. Deleting via Partial Update is not possible.

Note: Partial Update can also be done by the "Write-Composite" operation.

The "Write" operation has the following parameters:

6.3.3.1. Examples

Let's consider a hypothetical Object 34 having a Multiple-Instance Resource 1 of type String with the following values:

/34/0/1/0: "Red"
/34/0/1/1: "Green"

The LwM2M Server performs a Write on /34/0/1 with the New Value containing:

[ { "n": "/34/0/1/1", "vs":"Yellow" },
  { "n": "/34/0/1/3", "vs":"Blue" }]

For a Write Replace, the Object new values will be:

/34/0/1/1: "Yellow"
/34/0/1/3: "Blue"

For a Write Partial Update, the Object new values will be:

/34/0/1/0: "Red"
/34/0/1/1: "Yellow"
/34/0/1/3: "Blue"

6.3.4. Write-Attributes Operation

Only Attributes from the <NOTIFICATION> class MAY be changed in using the "Write-Attributes" operation.

The general rules for Attributes which are specified in Section Attributes Definitions and Rules fully apply here. Table: 7.3.1.-1 Class Attributes in Section Attributes Classification provides explanation on the Attributes supported by the "Write-Attributes" operation.

The value of a writable Attribute MUST be LwM2M Server specific.

The operation permits multiple Attributes to be modified within the same operation.

Including <NOTIFICATION> class Attributes specified in Table: 7.3.1.-1 Class Attributes Section 6.2.1. Register Operation, the "Write-Attributes" operation has the following parameters:

6.3.5. Execute Operation

The "Execute" operation is used by the LwM2M Server to initiate some action, and can only be performed on individual Resources. An LwM2M Client MUST return an error when the "Execute" operation is received for Object Instance(s) or Resource Instance(s).

If the Resource does not support the "Execute" operation, the LwM2M Client MUST return an error code indicating that the method is not allowed to the LwM2M Server.

The "Execute" operation MAY have arguments.

The syntax of the arguments is as follows:

arglist = arg *( "," arg )
arg = DIGIT / DIGIT "=" "'" *CHAR "'"
DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
CHAR = "!" / %x23-26 / %x28-5B / %x5D-7E

Examples of valid lists of arguments:

• 5

• 2='10.3'

• 7,0=' <https://www.omaspecworks.org>'

• 0,1,2,3,4

6.3.6. Create Operation

The "Create" operation is used by the LwM2M Server to create Object Instance(s) within the LwM2M Client. The "Create" operation MUST target an Object, and MUST follow the rules specified in Section 8. Access Control and its sub-sections. If any error occurs, it MUST NOT create anything.

The Object Instance created in the LwM2M Client by the LwM2M Server MUST be an Object type supported by the LwM2M Client and announced to the LwM2M Server using the "Register" and "Update" operations of the LwM2M Client Registration Interface.

Object Instance whose Object supports at most one Object Instance MUST be assigned an Object Instance ID of 0 when the Object Instance is Created.

The "Create" operation has the following parameters:

The New Value parameter included in the payload MUST follow the TLV, LwM2M CBOR, SenML CBOR or SenML JSON data format according to Section 7.5. Data Formats for Transferring Resource Information.

When there is no reference to an Object Instance in the TLV/LwM2M CBOR payload of the "Create" operation, the LwM2M Client MUST assign the ID of the created Object Instance.

If a new Object Instance is created through that operation and the "Access Control-Enabled" configuration is used, then the LwM2M Client creates an Access Control Object Instance for the created Object Instance (see Section 8. Access Control) with the following requirements:

• The Access Control Owner MUST be the LwM2M Server.
• The LwM2M Server MUST have full access rights to the created Object Instance.

Any optional Resources included in the "Create" operation that are not supported by, or unknown to, the LwM2M Client MUST NOT be interpreted as an error by the LwM2M Client.

If a New Value parameter is not present or if it does not contain values for all Resources (mandatory and optional) of the Object, the LwM2M Client MAY populate the missing Resources with implementation dependent default values. If all the mandatory Resources of the created Object Instance are not instantiated, the LwM2M Client MUST return an error.

The values of the Read-only Resources MUST be setup by the LwM2M Client. If a value of a Read-only Resource is present in the "New Value" parameter then this value MUST NOT be processed nor should it result in an error. If the payload (New Value) conveys an Object Instance ID in conflict with one already present in the LwM2M Client then the entire request MUST be rejected and an error code indicating that the request is incorrect MUST be returned.

The LwM2M Client MAY reject the "Create" operation by returning an error code to the LwM2M Server.

6.3.7. Delete Operation

The "Delete" operation is used for LwM2M Server to delete an Object Instance or a Resource Instance within the LwM2M Client.

The Object Instance that is deleted in the LwM2M Client by the LwM2M Server MUST be an Object Instance that is announced by the LwM2M Client to the LwM2M Server using the "Register" and "Update" operations of the Client Registration Interface.

The only exception concerns the single Instance of the mandatory Device Object (ID:3) which SHALL NOT be affected by any Delete operation.

The LwM2M Client MAY reject the "Delete" operation by returning an error code to the LwM2M Server.

The Delete operation has the following parameters:

6.3.8. Read-Composite Operation

The LwM2M Client MAY support the "Read-Composite" operation.

The "Read-Composite" operation can be used by the LwM2M Server to selectively read any combination of Objects, Object Instance(s), Resources, and/or Resource Instances of different or same Objects in a single request. The list of elements to be read are provided as SenML Pack where the records contain Base Name and/or Name Fields, but no Value fields as specified in [RFC8790]. The Read-Composite operation is treated as non-atomic and handled as best effort by the LwM2M Client. That is, if any of the requested resources do not have a valid value to return, they will not be included in the response. Section 7.5.6. SenML JSON shows examples of Read-Composite use.

The LwM2M Client MUST retrieve all the requested Resources except the Resource(s) which does not support the "Read" operation and sends the retrieved Resource(s) information to the LwM2M Server.

6.3.9. Write-Composite Operation

The LwM2M Client MAY support the "Write-Composite" operation.

In contrast to "Write" operation, the scope of which is limited to a Resource(s) of a single Instance of a single Object, the "Write-Composite" operation can be used by the LwM2M Server to update values of a number of different Resources across different Instances of one or more Objects. Similar to Read-Composite the Write-Composite operation provides a list of all resources to be updated, and their new values, using one of LwM2M CBOR, SenML JSON/CBOR, or SenML-ETCH JSON/CBOR formats. Unlike for Write operation, the Resources that are not provided are not impacted by the operation. Examples are shown in Section 7.5.6. SenML JSON.

The LwM2M Client MUST perform the operation only if all the Resources conveyed in the operation are allowed to support the "Write" operation. If any Resource does not support the "Write" operation, the LwM2M Client MUST inform the LwM2M Server that the Object Instance cannot perform the requested operation by returning an error code indicating that the method is not allowed.

The "Write-Composite" operation is atomic and cannot have partial success. That is, if the Lwm2M Client supports this operation, it MUST reject a LwM2M Server request where it cannot successfully write all the requested values to the requested list of Resources. Therefore, before processing Write-Composite, the client MUST ensure that all addressed objects exist and that the Server has write access to those Objects and Resources.

6.4. Information Reporting Interface

The Information Reporting Interface is used by a LwM2M Server to observe any changes in a Resource on a registered LwM2M Client, receiving notifications when new values are available. This observation relationship is initiated by sending an "Observe" or "Observe-Composite" operation to the L2M2M Client for an Object, an Object Instance or a Resource. An observation ends when a "Cancel Observation" or "Cancel Observation-Composite" operation is performed.

The LwM2M Server and the LwM2M Client MUST support all the operations on this interface unless clearly stated otherwise.

The LwM2M Client MUST ignore LwM2M Server operations on this interface until it received its Registration acknowledgement.

The LwM2M Server SHOULD NOT perform any operation on this interface before replying to the registration request of this LwM2M Client.

The LwM2M Client MUST reject any LwM2M Server operation on the LwM2M Security Object (ID: 0) with a response code indicating that the operation is not authorized.

The LwM2M Client MUST reject any LwM2M Server operation on the LwM2M OSCORE Object (ID: 21) with a response code indicating that the operation is not authorized.

The LwM2M Client MUST reject any LwM2M Server operation on the LwM2M COSE Object (ID: 23) with a response code indicating that the operation is not authorized.

The mapping to underlying transports is detailed in [LwM2M-TRANSPORT].

6.4.1. Observe Operation

The LwM2M Server initiates an observation request for changes of a specific Resource, Resources within an Object Instance or for all the Object Instances of an Object within the LwM2M Client.

Related attributes for "Observe" operation are described in Table <NOTIFICATION> Class Attributes in Section 7.3. Attributes. The rules <NOTIFICATION> Attributes which are specified in this section fully apply here.

The "Observe" operation includes the following parameters:

If the Resource ID is specified and if the requested Resource does not support the "Read" operation, the LwM2M Client MUST return an error code indicating that the method is not allowed to the LwM2M Server.

If the Resource ID is not specified, the LwM2M Client MUST retrieve all the requested Resources except the Resource(s) which does not support the "Read" operation and sends the retrieved Resource(s) information to the LwM2M Server.

Until the LwM2M Client sends a new registration, the LwM2M Server expects the LwM2M Client to remember the observation requests. If a LwM2M Client forgets the observation requests (e.g. device factory reset) it MUST perform a new "Register" operation. The LwM2M Server MUST re-initiate the desired observation requests whenever the LwM2M Client registers.

In order to avoid network traffic increase, the LwM2M Client SHOULD maintain previous observation states in case of reboot, power cycle.

It has to be noted that an "Observe" operation containing only Object ID, will produce the report of all Object Instances information.

The LwM2M Client SHOULD support the "Observation Attributes" parameter. If the LwM2M Client does not support the "Observation Attributes" parameter, it MUST reject an observation that includes Observation Attributes.

Note: The <NOTIFICATION> Class Attributes can also be configured by the "Write-Attributes" operation described in section 6.3.4. Write-Attributes Operation. In that case, the Attributes will be permanent and apply to all "Observe" operations not specifying their own.

Note: The <NOTIFICATION> Class Attributes contained in the "Observation Attributes" parameter are not part of the LwM2M Client response to a Discover operation since they are not attached.

Note: When a LwM2M Client deregisters, the LwM2M Server should assume past states are nullified including the previous observations.

6.4.2. Notify Operation

Note: For readability in this section, the term "Resource value" is used to designate either the value of a Single-Instance Resource, or the value of an Instance of a Multiple-Instance Resource, according to the nature of the considered Resource (i.e. Single- or Multiple-Instance Resource).

The "Notify" operation is sent from the LwM2M Client to the LwM2M Server during a valid observation on an Object, Object Instance, Resource, or Resource Instance. The "Notify" operation MUST be sent when the state of the observed item changes and all conditions (i.e. Minimum Period, Maximum Period, Greater Than, Less Than, Step) are met, or when the "Maximum Period" timing condition is fulfilled. These conditions are either "Observation Attributes" sent as parameters or attributes attached at the level of the "Observe" operation.

Any attributes attached at lower levels (e.g., at the Resource level if the observation is created at the Object Instance level) MUST be ignored.

The LwM2M Client MUST retrieve all the observed Resources values except for the Resource(s) which does not support the "Read" operation and send the retrieved Resource value(s) to the LwM2M Server.

The response sent by a LwM2M Client to an "Observe" or "Observe-Composite" operation MUST be considered as the initial notification.

Each time a "Notify" operation is sent, the "Minimum Period" and "Maximum Period" timers associated to this "Observe" or "Observe-Composite" operation are restarted.

Additionally, a "Maximum Period" (pmax) applied to an observation smaller than the "Minimum Period" applied to the same observation MUST be ignored for that observation.

Note: The conditions may be modified by the "Write-Attributes" operation after the observation request. The LwM2M Client behavior is implementation dependent for the evaluation of the Change Value Conditions started prior to the "Write-Attributes" operation. For deterministic behavior when changing observation attributes, the current observation SHOULD be cancelled and a new observation SHOULD be created with the desired observation attributes. However, some information may be lost in the transition between the two observations.

The following example shows how the Minimum and Maximum period parameters work as shown in Section 6.3.4. Write-Attributes Operation. An LwM2M Server makes an observation for a Temperature Resource that is updated inside the LwM2M Client at irregular periods (based on change). The LwM2M Server makes an observation when the Minimum Period = 10 Seconds and Maximum Period = 60 Seconds attributes have been set for that Resource. The LwM2M Client will wait at least 10 Seconds before sending a "Notify" operation to the LwM2M Server (even if the Resource has changed before that), and no longer than 60 Seconds before sending a "Notify" operation (even if the Resource has not changed yet). The "Notify" operation is sent anywhere between 10-60 seconds upon change.

Note: In case an "Observe" operation is initiated on a Resource, an Object Instance or an Object without any conditions previously configured, and with the "Default Minimum Period" in the LwM2M Server Object set to 0 (possibly by default), the "Notify" operation will be sent upon any change of, respectively, the observed Resource value, any Resource value of the observed Object Instance or any Resource value of any Instance of the observed Object. As specified in Section 6.4.1. Observe Operation and in Table: 6.4.1.-1 Observe Parameters, in case of an "Observe" operation on a certain Object the "Notify" operation includes all Resources of all Instances of the observed Object.

In this example the Minimum Period has been set to 10 and the Maximum Period set to 60 for the Resource /4/0/2 before making the observation.

6.4.3. Cancel Observation Operation

The "Cancel Observation" operation is sent from the LwM2M Server to the LwM2M Client to end an observation relationship that was previously created with an "Observe" operation.

6.4.4. Observe-Composite Operation

The LwM2M Client MAY support the "Observe-Composite" operation.

The LwM2M Server can use the "Observe-Composite" operation to initiate observations for a group of resources and/or resource instances across multiple object instances within the client. As with the "Read-Composite" operation, the list of elements to be observed is provided as a separate parameter to the operation in SenML JSON/CBOR format.

The <NOTIFICATION> Class Attributes for each resource that is observed through the "Observe-Composite" operation may be individually configured by the LwM2M Server using the "Write-Attribute". Each resource can have multiple observe conditions attached. If any of the conditions attached to one or more resources under observation meets the notification criteria a notify will be generated by the LwM2M Client, which will include the value for each of the resources listed in the "Observe-Composite" operation. Hence, the resources that have not met the notify condition will still be included in the notification message.

Note: It is the responsibility of the LwM2M Server to ensure that the Minimum and Maximum Period Attributes attached to observed resources follow the rules defined in Section Attributes Classification. For example, the Minimum Period Attributes attached to targeted resources must be less than the Maximum Period Attributes attached to all targeted resources.

As with the "Observe" operation, <NOTIFICATION> Class Attributes can be provided as a separate parameter to the operation. However, these attributes MUST have the Object Attachement Level, i.e. Minimum Period, Maximum Period, Minimum Evaluation Period, Maximum Evaluation Period, and Confirmable Notification. When these attributes are present, all the attached or inherited Attributes with the Object Assignation Level of the targeted URI MUST be ignored for this Observation-Composite.

For example, the following attributes are attached to the Device Object and the Connectivity Monitoring Object:

</3>;pmin=60
</4>;pmax=300

if the LwM2M Server performs an Observe-Composite operation on the Resources /3/0/8 and /4/0/2 with a parameter Minimum Evaluation Period set to 30, when evaluating the Notification conditions for this Observation-Composite, the LwM2M Client will ignore the Minimum Period and Maximum Period attributes inherited by the Resources and will consider only the Minimum Evaluation Period on both Resources.

6.4.5. Cancel Observation-Composite Operation

If the "Observe-Composite" operation is supported by the LwM2M Client, the "Cancel Observation-Composite" operation MUST be supported by the LwM2M Client.

The "Cancel Observation-Composite" operation is sent from the LwM2M Server to the LwM2M Client to end the previously set up composite observation relationship.

6.4.6. Send Operation

The LwM2M Client and the LwM2M Server MAY support the "Send" operation.

The "Send" operation is used by the LwM2M Client to send data to the LwM2M Server without explicit request by that LwM2M Server.

The "Send" operation can be used by the LwM2M Client to report values for Resources and Resource Instances of LwM2M Object Instance(s) to the LwM2M Server. The Resources and Resource Instances to send is implementation specific. The LwM2M Server MAY use the "Mute Send" Resource in the LwM2M Server Object (Resource ID 23) to enable or disable the use of the "Send" operation. When information reporting should be controlled by the LwM2M Server, the "Observe" or "Observe-Composite" operations can be used.

The reported LwM2M Object Instances (potentially different Object types) MUST have been registered by the LwM2M Client to the LwM2M Server. That LwM2M Server MUST have Read access right granted on the Object Instances of the reportable Resources which MUST support the Read operation (see Section 8.2. Authorization). If these criteria are not met for some Resources, the LwM2M Client MUST NOT include those Resources in the "Send" operation.

Any optional Resources included in the "Send" operation that are not supported by, or unknown to, the LwM2M Server MUST NOT be interpreted as an error by the LwM2M Server.

In addition, if any of the rules mentioned below is violated, the LwM2M Server MUST respond with an error in reply to the "Send" operation.

The value included in the payload MUST be either LwM2M CBOR, SenML JSON, or SenML CBOR format described in Section 7.5. Data Formats for Transferring Resource Information. As example:

Reporting the location of the LwM2M Client and the radio signal strength in a JSON payload:

Send
New Value:
[
  {"n":"/6/0/0", "v":43.61092},
  {"n":"/6/0/1", "v":3.87723},
  {"n":"/4/0/2", "v":-49}
]

7. Identifiers and Resources

This section defines the identifiers and resource model for the LwM2M Enabler.

7.1. Resource Model

The LwM2M Enabler defines a simple resource model where each piece of information made available by the LwM2M Client is a Resource. Resources are logically organized into Objects. Each Resource is given a unique identifier within that Object and a data type among those defined in Section Appendix C. Data Types (Normative).

Figure: 7.1.-1 Relationship between LwM2M Client, Object, and Resources illustrates this structure, and the relationship between Resources, Objects, and the LwM2M Client. The LwM2M Client may have any number of Resources, each of which belongs to an Object; for example the Firmware Update Object contains all the Resources used for firmware update purposes.

Each Object, defined for the LwM2M Enabler, is assigned a unique OMA LwM2M Object identifier allocated and maintained by [OMNA]. The LwM2M Enabler defines standard Objects and Resources, see Section Appendix E. LwM2M Objects defined by OMA (Normative). Further Objects may be added by OMA or other organizations to enable additional M2M Services.

As an Object only specifies a grouping of Resources, an Object MUST first be instantiated so that the LwM2M Client can use the Resources of such an Object and the associated functionalities.

When an Object is instantiated – either by the LwM2M Server or the LwM2M Client – an Object Instance is created with a subset of the Resources defined in the Object specification; a LwM2M Server can then access that Object Instance and its set of instantiated Resources.

A Resource which is instantiated within an Object Instance is a Resource which can either:

• contain a value (if the Resource is Readable and/or Writeable)

• or can be addressed by a LwM2M Server to trigger an action in the LwM2M Client (if the Resource is Executable)

Data Type checking on a Resource value MUST be performed:

• by the LwM2M Client when the LwM2M Server tries to set such a Resource,
• by the LwM2M Server when the LwM2M Server retrieves such a Resource

The LwM2M Client MUST reject a request, if an error is detected when checking an incoming Resource value against its data type.

The Object specification defines the operations (Read, Write, Execute) which are individually supported by the Resources belonging to that Object; this specification also defines the Mandatory or Optional characteristics of such Resources.

A Resource specified as Mandatory within an Object MUST be instantiated in any Instance of that Object.

A Resource specified as Optional within an Object MAY be omitted from some or even all Instances of that Object.

As illustration, the following example using the discover operation on the Server Object, exposes a configuration in which the Server Object (ID:1) has 2 Instances (ID:0, ID:1): the Optional Resources ID:2, ID:4 are only instantiated in the Instance 1 of the Object, while the Optional Resources ID:3 and ID:5 are not instantiated in either of the Server Object Instances. In Server Object ID:1, the Resources 0,1, and 6,7,8 are Mandatory Resources.

According to the DISCOVER /1 request, the following payload is returned:

</1/0/0>,</1/0/1>,</1/0/6>,</1/0/7>, </1/0/8>, </1/1/0>,</1/1/1>,</1/1/2>,</1/1/4>,</1/1/6>,</1/1/7>, </1/1/8>

Objects and Resources have the capability to have multiple instances. Multiple-Instance Resources can be instantiated by LwM2M Server operations in using SenML JSON, SenML CBOR, LwM2M CBOR, or TLV formats (see Section 7.5. Data Formats for Transferring Resource Information). The LwM2M Client also has the capability to instantiate Single or Multiple-Instance Resources.

The LwM2M Server performs operations on an Object, Object Instance and Resources as described in Section 6. Interfaces. These operations are conveyed as described in [LwM2M-TRANSPORT] and how to convey the Operation data is defined in Section 7.5. Data Formats for Transferring Resource Information.

The LwM2M Enabler defines an access control mechanism per Object Instance. Object Instances SHOULD have an associated Access Control Object Instance. An Access Control Object Instance contains Access Control Lists (ACLs) that define which operations on a given Object Instance are allowed for which LwM2M Server(s).

Figure: 7.1.-2 Example of Supported operations and Associated Access Control Object Instance shows an example of the operations the Resources support and how Object Instances and Resources are associated with Access Control Object Instance. In the example, Object Instance 0 for Object 1 has 2 Resources. Resource 1 supports the "Read", "Write" operations, while Resource 0 supports only the "Read" operation. The associated Access Control Object Instance has ACL of Object Instance 0 for Object 1. LwM2M Server 1 is authorized to perform "Read" and "Write" operations to the Object Instance 0 for Object 1 and Resources of the Object Instance. However, due to the supported operations of each Resource, LwM2M Server 1 can perform the "Read" operation on Resource 1 and 0, and also can perform the "Write" operations on Resource 1, but LwM2M Server 1 cannot perform the "Write" operation on Resource 0. The detailed access control mechanism is defined in Section 8. Access Control.

7.2. Object Versioning

7.2.1. General Policy

The official specification of the Objects is available at [OMNA].

An LwM2M Server MUST be able to determine without ambiguity the specification of the Objects intended to be registered by the LwM2M Client.

An LwM2M Object can evolve. Object versioning aims at identifying these LwM2M Object modifications, which can be categorized in two types:

• Evolution of type I: representing non-backwards-compatible ("breaking") evolutions are:

  • changing the "Instances" characteristic of the Object.
  • changing the normative text in the Object description.
  • adding or removing a mandatory Resource.
  • modifying the list of allowed operations of a Resource.
  • changing the "Instances" characteristic of a Resource.
  • changing the Data Type of a Resource.
  • modifying the Range of a Resource value (not associated with new enumeration values described in type II).
  • removing a Resource enumeration value.
  • changing the unit of a Resource.
  • changing the normative text in a Resource description.

• Evolution of type II: representing backwards-compatible ("non-breaking") evolutions are:

  • changing the non-normative text in the Object description.
  • adding or removing an optional Resource.
  • adding a Resource enumeration value.
  • reusing a Resource enumeration value, which was marked as "reserved".
  • changing the non-normative text in a Resource description.

Any other changes are forbidden (e.g. changing the name of an Object, changing the name of a Resource, or reusing a previously removed Resource ID).

With Object versioning, the Object Identifier is not changed but a new URN identifying that particular version of the Object specification MUST be registered according to the following format

"urn:oma:lwm2m:{oma, ext, x}:ObjectID[:{version}]" where 'version' is the Object Version as defined in the following section

7.2.2. Object Version format

The Object Version of an Object is composed of 2 digits separated by a dot '.':

• the first digit represents the Major Version of the Object: this digit marks the non-backward compatible evolution of such an Object (Object evolution of type I: Section 7.2.1. General Policy)

• the second digit represents the Minor Version of the Object: this digit marks the backward compatible evolution of such an Object (Object evolution of type II: Section 7.2.1. General Policy)

By convention when an Object is in version 1.0, the Object Version MAY be omitted in the URN.

To be more precise, two separate URNs are accepted as valid for the corresponding version of the object specification:

• the URN where the Object Version is mentioned explicitly: "urn:oma:lwm2m:{oma, ext, x}:ObjectID:1.0"

• the URN where the Object Version is absent: "urn:oma:lwm2m:{oma, ext, x}:ObjectID" (and supposed to be 1.0).

Example: "urn:oma:lwm2m:oma:44:2.2"

This URN uniquely identifies Object ID:44 in its version "2.2". Registered Objects are available at [OMNA], see Section 7.4. Identifiers and Section Appendix J. LwM2M Schema and Object Definition File (Informative) for further information.

7.2.3. Object Definition and Object Version Usage

Objects can be either:

• Core Objects, which are LwM2M Objects specified within the LwM2M Enabler specification (e.g. the Device Object).
• Non-core Objects, which are LwM2M Objects specified outside of an LwM2M Enabler specification (e.g. the Cellular Connectivity Object, which is defined in its own OMA specification, or any Object from a third party).

An LwM2M Client can always attach Object Version information to an Object. In certain circumstances Object Version information can, however, be omitted.

If a Core Object version does not correspond to version contained in the LwM2M Enabler release supported by the LwM2M Client, the Object Version MUST be provided by the LwM2M Client to the LwM2M Server.

If a Non-core Object is not version 1.0, the Object Version MUST be provided by the LwM2M Client to the LwM2M Server.

In "Register", "Register Update", and "Discover" operations, when the Object Version of a given Object is communicated, the LwM2M Client MUST use the Object Version <PROPERTIES> Class attribute ("ver"). If the Object has no Object Instance or several Object Instances, the Object Version attribute MUST be attached to the Object link. If the Object has exactly one instance, the Object link MAY be omitted. In that case, the Object Version attribute MUST be associated to the Object Instance link.

A few examples:

1. An LwM2M Client supporting LwM2M Enabler version 1.1 registers the Server Object version 1.1 ("urn:oma:lwm2m:oma:1:1.1"), and the Device Object version 1.1 ("urn:oma:lwm2m:oma:3:1.1"). The registration payload is:

   </1/0>,</1/1>,</3/0>

2. An LwM2M Client supporting LwM2M Enabler version 1.1 registers the Server Object version 1.0 ("urn:oma:lwm2m:oma:1"), and the Device Object version 1.1 ("urn:oma:lwm2m:oma:3:1.1"). The registration payload is:

   </1>;ver=1.0,</1/0>,</1/1>,</3/0>

3. At [OMNA], the Object ID:44 will be registered at least twice:

   • with the URN "urn:oma:lwm2m:oma:44" (version 1.0)
   • with the URN "urn:oma:lwm2m:oma:44:2.2"

   An LwM2M Client supporting LwM2M Enabler version 1.0 registers this Object in version 2.2 along with the Server Object version 1.0 ("urn:oma:lwm2m:oma:1"), and the Device Object version 1.0 ("urn:oma:lwm2m:oma:3"). The registration payload is:

   </1/0>,</1/1>,</3/0>,</44/0>;ver=2.2

4. An LwM2M Client supporting LwM2M Enabler version 1.1 registers the Server Object version 1.1 ("urn:oma:lwm2m:oma:1.1"), the Device Object version 1.1 ("urn:oma:lwm2m:oma:3:1.1"), and the Connectivity Monitoring Object version 1.2 ("urn:oma:lwm2m:oma:4:1.2"). Because each of these Object versions correspond to the Object versions released as part of the LwM2M Enabler version 1.1, the Object version information can be omitted. The registration payload is:

   </1>,</1/0>,</1/1>,</3/0>,</4/0>

7.3. Attributes

Attributes are metadata which can be attached to an Object, an Object Instance, a Resource, or a Resource Instance. These attributes can fulfil various roles, from carrying information only (e.g. Discover) to carrying parameters for setting up certain actions on the LwM2M Client (e.g. Notifications). These Attributes may be carried in the message payload of Registration and Discover operations. They can be updated - when writable - through the "Write-Attributes" operation.

An attribute is fully determined by several characteristics, which are listed in Table: 7.3.-1 Attribute Characteristics.

The value of Attributes marked as "R" (readable) are exposed to the LwM2M Server in the payload response to a "Discover" operation (Section 6.3.2. Discover Operation).

The value of Attributes marked as "W" (writable) can be changed by the LwM2M Server in using the "Write-Attributes" operation (Section 6.3.4. Write-Attributes Operation).

Note: A payload response to a "Discover" operation is a list of application/link-format CoRE Links [RFC6690], which will include the LwM2M Attributes.

7.3.1. <PROPERTIES> Class Attributes

The role of these Attributes is to provide metadata which may communicate helpful information to the LwM2M Server for example easing data management.

The LwM2M Server, the LwM2M Bootstrap-Server, and the LwM2M Client SHOULD support Table: 7.3.1.-1 Class Attributes, except when specifically mentioned as not required.

7.3.2. <NOTIFICATION> Class Attributes

The role of these Attributes is to provide parameters to the "Notify" operation.

These Attributes can be attached at various levels: Object, Object Instance, Resource levels, or Resource Instance. The rules below govern the usage of these Attributes:

• Inheritance: <NOTIFICATION> attributes apply to the level they are attached to, and to the lower.

  For instance, a <NOTIFICATION> attribute attached to an Object Instance applies also to "Notify" operation on the Resources and Resource Instances of this Object Instance.

• Precedence: <NOTIFICATION> attributes attached to a level prevail over the same attribute attached to an upper level.

  For instance, if the same <NOTIFICATION> attribute is attached to both an an Object Instance and a Resource of this Object Instance, "Notify" operation on this Resource (and its Resource Instances in the case of a Multiple-Instance Resource) will consider only the value of the attribute attached to the Resource.

The "Greater Than", "Less Than", and "Step" values MUST respect the two following conditions:

• "lt" value < "gt" value
• ("lt" value + 2*"st" values) <"gt" value

When the "Greater Than", "Less Than", and "Step" Attributes are set in a Write-Attributes operation, or passed as parameter to an "Observe"or "Observe-Composite" operation, the operation MUST be rejected if the conditions above are violated.

The "Minimum Evaluation Period" (epmin) and "Maximum Evaluation Period" (epmax) values can be used to configure the device to perform reporting evaluations. After the expiry of epmin, the device MAY immediately perform an evaluation per the "Notification Conditions" above. After the expiry of epmax, the device MUST perform an evaluation per the "Notification Conditions". If both the epmin and epmax attributes are defined, the epmin value must be less than the epmax value.

The behaviour of Notification class attributes MUST follow [Cond_Attr] unless stated otherwise in this specification.

Note: The attribute Maximum Historical Queue is specified in this specification but currently not referenced in [Cond_Attr]. [Cond_Attr], however, introduced the Notification Band (c.band) attribute, which is not used in this version of LwM2M specification.

The LwM2M Server MUST support and LwM2M Client SHOULD support all the <NOTIFICATION> Class Attributes listed in Table: 7.3.2.-1 class Attributes.

7.4. Identifiers

The LwM2M Enabler defines specific identifiers for entities used within the LwM2M Protocol. These identifiers are defined in Table: 7.4.-1 LwM2M Identifiers.

7.4.1. Endpoint Client Name

The Endpoint Client Name is a string. URIs and URNs are RECOMMENDED formats for this identifier. The Endpoint Client Name identifier MUST be unique at the LwM2M server or servers it is being used with. Note that the Endpoint Client Name is unauthenticated and can be set to arbitrary value by a misconfigured or malicious client and hence MUST NOT be used alone for any decision making without prior matching the Endpoint Client Name against the identifier used with the security protocol protecting LwM2M communication. This parameter MAY be omitted when the security protocol provides the server an authenticated identifier that is identical to this parameter. For more discussion consult the security consideration section in the [LwM2M-TRANSPORT] specification. This security consideration section also provides a description of the privacy implications of re-using the same identifiers across multiple servers.

This specification RECOMMENDS the Endpoint Client Name to be in a URI or a URN format for uniqueness reasons. The following table lists URN formats. Other URI and URN formats MAY also be used. In particular, URN formats defined in [RFC9039].

Note: Implementations need to be careful when using the Endpoint Client Name to perform database lookups due to the risk of SQL injection attacks.

Note: The URN syntax is specified in [RFC8141] as: "urn:<NID>:<NSS>", <NID> being the namespace identifier, <NSS> being a namespace-specific string. NIDs are registered in an IANA registry: at https://www.iana.org/assignments/urn-namespaces/urn-namespaces.xhtml.

The previous versions of this specification were recommending other URN formats for historical reasons. Some are defined in [DMREPPRO] Section 5.5 Identifiers. However these URN formats are not respecting [RFC8141]. The table below lists these formats.

7.4.2. Reusable Resources

When Objects are designed for a similar purpose, for example Objects for use in network management, or Objects for use in embedded device automation, similar Resources are useful in more than one Object. For example in embedded device automation, Objects for different purposes may contain common Resource types such as digital input, digital output, analogue input, analogue output, dimmer value, unit, min measurement, max measurement, value range etc.

If a Resource can feasibly be re-used with the same meaning in multiple Object definitions, it can be defined as a Reusable Resource ID and registered with [OMNA]. Other Objects may then make use of this Reusable Resource ID in another Object definition.

The definition of a Reusable Resource and its usage when hosted in an Object specification MUST follow several rules:

• the Name, ID, Operation, Type, Range and Units are frozen characteristics when the Reusable Resource is registered at [OMNA] and cannot not be changed when such a Resource is specified in the definition of a hosting Object.

• the registered Description field of a Reusable Resource is also a frozen characteristic; when extension is required to fit the real need of the Object hosting such a Resource, that extension must be mentioned in the Object specification but outside of the Description field itself; furthermore any extension MUST be compatible with the content of the registered Description field.

• a Reusable Resource is registered without defining "Multiple-Resource", or "Mandatory" characteristics; both characteristics will be determined when such a Resource is specified in the definition of a hosting Object.

Note: The strict guidelines about Reusable Resources, as indicated in the above bullets, are specified to ensure that the definition remains consistent across different implementations. [OMNA] is the only official reference for Reusable Resources to which all implementations should adhere. There is no versioning for a resource definition. Name, ID, Operation, Type, Range, and Units of the Reusable Resource cannot change. In addition, any semantics captured in the Description cannot change. If the existing Reusable Resources need to evolve or are not sufficient, it is recommended to propose a new Reusable Resource.

7.5. Data Formats for Transferring Resource Information

The following data formats are defined by the LwM2M Enabler in this section: plain text, opaque, TLV, LwM2M TS 1.0 JSON, CBOR, LwM2M CBOR, SenML JSON, and SenML CBOR. Additionally, the LwM2M Enabler uses the CoRE Link data format defined in [RFC6690].

The LwM2M Server MUST support all data formats, including TLV that was mandatory to support for LwM2M TS 1.0 Clients.

The LwM2M Client MUST support plain text, opaque, and CoRE Link data formats and it SHOULD support at least one of SenML CBOR, SenML JSON, or LwM2M CBOR data formats. In addition, a LwM2M Client MAY choose to support other data formats. LwM2M Clients supporting [LwM2M-TS_1.1] or newer SHOULD NOT use the legacy TLV or JSON formats.

Messages containing data MUST specify the payload encoding by using one of the supported data formats.

An LwM2M Server data request MAY contain an option specifying the data formats the Server would prefer to receive for the payload; if this data format is not accepted by the LwM2M Client, the request is rejected; if the LwM2M Client doesn't support that option or if the LwM2M Server expresses no data format preference, the LwM2M Client will use its own preferred data format.

The IANA registered Media Types supported in [LwM2M-TS_1.0] are listed in the table below.

In addition, [LwM2M-TS_1.1] adds support for the following standardized media types.

In addition, this specification adds support for the following IANA registered Media Type.

7.5.1. Plain Text

The plain text format is used for "Read" and "Write" operations on singular Resources or Resource Instances where the value of the Resource is represented as described in Section Appendix C. Data Types (Normative).

For example, a request to the example client's Device Object Instance, Manufacturer Resource would return the following plain text payload:

This data format has a Media Type of text/plain.

7.5.2. Opaque

The opaque format is used for "Read" and "Write" operations on singular Resources or Resource Instances where the value of the Resource is an opaque sequence of binary octets. This data format is used for binary Resources such as firmware images or application specific binary formats.

This data format has a Media Type of application/octet-stream.

7.5.3. CBOR

The Concise Binary Object Representation format is used for "Read" and "Write" operations on singular Resources or Resource Instances.

This data format has a Media Type of application/cbor which covers all the LwM2M data types via the use of its major types with or without optional tags.

7.5.4. LwM2M CBOR

When a LwM2M Client is supporting the LwM2M CBOR data format and the format is used to transport resource values for LwM2M operations, LwM2M CBOR payload MUST use the format defined in this section.

This data format has a Media Type of application/vnd.oma.lwm2m+cbor.

The syntax of this data format is as follows:

payload = CBOR_map_with_length 1*(ID, VALUE) / CBOR_infinite_map_start 1*(ID, VALUE) CBOR_break
ID = CBOR_unsigned_integer / CBOR_array_with_length 1*(CBOR_unsigned_integer) / CBOR_infinite_array_start 1*(CBOR_unsigned_integer) CBOR_break
VALUE = CBOR_value / payload

According to the ABNF syntax above, the values are encoded in a CBOR map (Major type 5). The key of the data items is the ID of the underlying Object, Object Instance, Resource, or Resource Instance. The IDs inside the top-level payload MUST start with the Object ID.

In the LwM2M CBOR payload of the "Create" operation, MAX_ID 65535 MAY be used to indicate there is no reference to an Object Instance.

7.5.4.1. Single Resource Example

A request to the Device Object on Resource 0 of the LwM2M example client from Appendix F (Read /3/0/0) would return the following LwM2M CBOR payload. This example has a size of 26 bytes.

A1                                             # map(1)
   83                                          # array(3)
      03                                       # unsigned(3)
      00                                       # unsigned(0)
      00                                       # unsigned(0)
   74                                          # text(20)
      4F70656E204D6F62696C6520416C6C69616E6365 # "Open Mobile Alliance"

The same example using the CBOR diagnostic notation is shown below.

{[3, 0, 0]: "Open Mobile Alliance"}

Note that the following payload is also valid:

A1                                      # map(1)
   03                                   # unsigned(3)
   A1                                   # map(1)
      00                                # unsigned(0)
      A1                                # map(1)
         00                             # unsigned(0)
         74                             # text(20)
            4F70656E204D6F62696C6520416C6C69616E6365 # "Open Mobile Alliance"

{3: {0: {0: "Open Mobile Alliance"}}}

7.5.4.2. Multiple Resource Example

A request to the Device Object on Resource 6 of the LwM2M example client from Appendix F (Read /3/0/6) would return the following LwM2M CBOR payload. This example has a size of 10 bytes.

A1       # map(1)
   83    # array(3)
      03 # unsigned(3)
      00 # unsigned(0)
      06 # unsigned(6)
   A2    # map(2)
      00 # unsigned(0)
      01 # unsigned(1)
      01 # unsigned(1)
      05 # unsigned(5)

The same example using the CBOR diagnostic notation is shown below.

{[3, 0, 6]: {0: 1,
             1: 5}}

7.5.4.3. Single Object Instance Example

A request to the Device Object (Read /3/0) of the LwM2M example client would return the following LwM2M CBOR payload. This example has a size of 118 bytes.

A1                                      # map(1)
   82                                   # array(2)
      03                                # unsigned(3)
      00                                # unsigned(0)
   AD                                   # map(13)
      00                                # unsigned(0)
      74                                # text(20)
         4F70656E204D6F62696C6520416C6C69616E6365 # "Open Mobile Alliance"
      01                                # unsigned(1)
      76                                # text(22)
         4C69676874776569676874204D324D20436C69656E74 # "Lightweight M2M Client"
      02                                # unsigned(2)
      69                                # text(9)
         333435303030313233             # "345000123"
      03                                # unsigned(3)
      63                                # text(3)
         312E30                         # "1.0"
      06                                # unsigned(6)
      A2                                # map(2)
         00                             # unsigned(0)
         01                             # unsigned(1)
         01                             # unsigned(1)
         05                             # unsigned(5)
      07                                # unsigned(7)
      A2                                # map(2)
         00                             # unsigned(0)
         19 0ED8                        # unsigned(3800)
         01                             # unsigned(1)
         19 1388                        # unsigned(5000)
      08                                # unsigned(8)
      A2                                # map(2)
         00                             # unsigned(0)
         18 7D                          # unsigned(125)
         01                             # unsigned(1)
         19 0384                        # unsigned(900)
      09                                # unsigned(9)
      18 64                             # unsigned(100)
      0A                                # unsigned(10)
      0F                                # unsigned(15)
      0B                                # unsigned(11)
      A1                                # map(1)
         00                             # unsigned(0)
         00                             # unsigned(0)
      0D                                # unsigned(13)
      1A 5182428F                       # unsigned(1367491215)
      0E                                # unsigned(14)
      66                                # text(6)
         2B30323A3030                   # "+02:00"
      10                                # unsigned(16)
      61                                # text(1)
         55                             # "U"

The same example using the LwM2M CBOR diagnostic notation is shown below.

{[3, 0]: {0: "Open Mobile Alliance",
          1: "Lightweight M2M Client",
          2: "345000123",
          3: "1.0",
          6: {0: 1,
              1: 5},
          7: {0: 3800,
              1: 5000},
          8: {0: 125,
              1: 900},
          9: 100,
          10: 15,
          11: {0: 0},
          13: 1367491215,
          14: "+02:00",
          16: "U"}}

7.5.4.4. Multiple Object Instances Example

A request to the LwM2M Server Object (Read /1) of the LwM2M example client would return the following LwM2M CBOR payload. This example has a size of 63 bytes.

A1                   # map(1)
   01                # unsigned(1)
   A2                # map(2)
      00             # unsigned(0)
      A7             # map(7)
         00          # unsigned(0)
         18 65       # unsigned(101)
         01          # unsigned(1)
         1A 00015180 # unsigned(86400)
         02          # unsigned(2)
         19 012C     # unsigned(300)
         03          # unsigned(3)
         19 1770     # unsigned(6000)
         05          # unsigned(5)
         1A 00015180 # unsigned(86400)
         06          # unsigned(6)
         F5          # primitive(21)
         07          # unsigned(7)
         61          # text(1)
            55       # "U"
      01             # unsigned(1)
      A7             # map(7)
         00          # unsigned(0)
         18 66       # unsigned(102)
         01          # unsigned(1)
         1A 00015180 # unsigned(86400)
         02          # unsigned(2)
         19 0258     # unsigned(600)
         03          # unsigned(3)
         19 1770     # unsigned(6000)
         05          # unsigned(5)
         1A 00015180 # unsigned(86400)
         06          # unsigned(6)
         F4          # primitive(20)
         07          # unsigned(7)
         61          # text(1)
            55       # "U"

The same example using the CBOR diagnostic notation is shown below.

{1: {0: {0: 101,
         1: 86400,
         2: 300,
         3: 6000,
         5: 86400,
         6: true,
         7: "U"},
     1: {0: 102,
         1: 86400,
         2: 600,
         3: 6000,
         5: 86400,
         6: false,
         7: "U"}}}

7.5.4.5. Composite Operation Example

A composite request to the manufacturer name (/3/0/0), battery level(/3/0/9), and registration lifetime (/1/0/1) of the LwM2M example client would return the following LwM2M CBOR payload. This example has a size of 39 bytes.

A2                                      # map(2)
   82                                   # array(2)
      03                                # unsigned(3)
      00                                # unsigned(0)
   A2                                   # map(2)
      00                                # unsigned(0)
      74                                # text(20)
         4F70656E204D6F62696C6520416C6C69616E6365 # "Open Mobile Alliance"
      09                                # unsigned(9)
      18 64                             # unsigned(100)
   83                                   # array(3)
      01                                # unsigned(1)
      00                                # unsigned(0)
      01                                # unsigned(1)
   1A 00015180                          # unsigned(86400)

The same example using the CBOR diagnostic notation is shown below.

{[3, 0]: {0: "Open Mobile Alliance",
          9: 100},
 [1, 0, 1]: 86400}

7.5.4.6. Create Operation Example

A Create operation to the LwM2M ACL Object (Create /2) of the LwM2M example client could contain the following LwM2M CBOR payload. This example has a size of 17 bytes.

A1             # map(1)
   82          # array(2)
      02       # unsigned(2)
      05       # unsigned(5)
   A4          # map(4)
      00       # unsigned(0)
      05       # unsigned(5)
      01       # unsigned(1)
      00       # unsigned(0)
      82       # array(2)
         02    # unsigned(2)
         18 66 # unsigned(102)
      00       # unsigned(0)
      03       # unsigned(3)
      18 65    # unsigned(101)

The same example using the CBOR diagnostic notation is shown below.

{[2, 5]: {0: 5,
          1: 0,
          [2, 102]: 0,
          3: 101}}

In the example above, the LwM2M Server requests the creation of a new Object Instance with ID: 5. To let the LwM2M Client assign the ID of the created Object Instance, the LwM2M CBOR payload could be the following:

A1             # map(1)
   82          # array(2)
      02       # unsigned(2)
      19 FFFF  # unsigned(65535)
   A4          # map(4)
      00       # unsigned(0)
      05       # unsigned(5)
      01       # unsigned(1)
      00       # unsigned(0)
      82       # array(2)
         02    # unsigned(2)
         18 66 # unsigned(102)
      00       # unsigned(0)
      03       # unsigned(3)
      18 65    # unsigned(101)

The same example using the CBOR diagnostic notation is shown below.

{[2, 65535]: {0: 5,
              1: 0,
              [2, 102]: 0,
              3: 101}}

7.5.5. TLV

For "Read" and "Write" operations, the binary TLV (Type-Length-Value) format can be used to represent an array of values or a singular value using a compact binary representation, which is easy to process on simple embedded devices. The format has a minimum overhead per value of just 2 bytes and a maximum overhead of 5 bytes depending on the type of Identifier and length of the value. The maximum size of an Object Instance or Resource in this format is 16.7 MB. The format is self-describing, thus a parser can skip TLVs for which the Resource is not known.

This data format has a Media Type of application/vnd.oma.lwm2m+tlv.

Each TLV entry starts with a Type byte that indicates if the TLV contains an Object Instance, a Resource, multiple Resources, or a Resource Instance. Object Instance and Resource with Resource Instance TLVs contains other TLVs in their value. The hierarchy is as follows and may be up to 3 levels deep.

• Object Instance TLV, which contains

  • Resource TLVs or

  • multiple Resource TLVs, which contains

    • Resource Instance TLVs

For simplicity and to prevent any ambiguity on Object Instance Identity, when the Object Instance ID is not specified in the request, the Object Instance TLV MUST be used, whatever the number of Object Instances (1 or more) to return to the LwM2M Server. When the Object Instance ID is specified in the request, the Object Instance TLV is optional.

When a Multiple Resource has to be returned to the LwM2M Server, the Multiple Resource TLV MUST be used whatever the number of Instances (0, 1 or more) of that resource.

Figure: 7.5.5.-1 TLV nesting illustrates the possible nesting of Object Instance, Resource, multiple Resources, and Resource Instance TLVs. One or several Resource TLVs, and/or one or several multiple Resource TLVs MAY be nested in an Object Instance TLV. A multiple Resource TLV contains one or several Resource Instance TLVs.

7.5.5.1. Single Object Instance Request Example

In this example, a request for the Device Object Instance (ID:3) of an LwM2M Client is made (Read /3/0). The LwM2M Client responds with a TLV payload including all of the readable Resources. This TLV payload would have the following format. The total payload size with the TLV encoding is 121 bytes:

C8 00 14 4F 70 65 6E 20 4D 6F 62 69 6C 65 20 41 6C 6C 69 61 6E 63 65
C8 01 16 4C 69 67 68 74 77 65 69 67 74 20 4D 32 4D 20 43 6C 69 65 6E 74
C8 02 09 33 34 35 30 30 30 31 32 33
C3 03 31 2E 30
86 06
   41 00 01
   41 01 05
88 07 08
   42 00 0E D8
   42 01 13 88
87 08
   41 00 7D
   42 01 03 84
C1 09 64
C1 0A 0F
83 0B
   41 00 00
C4 0D 51 82 42 8F
C6 0E 2B 30 32 3A 30 30
C1 10 55

7.5.5.2. Multiple Object Instance Request Examples

A) Request on Single-Instance Object

In this example, a request for the Device Object Instance (ID:3) of an LwM2M Client is made (Read /3). The Device Object is a Single-Instance Object, but the Object Instance TLV is used (to be compared with the example of the previous section).

The LwM2M Client responds with a TLV payload including the Object Instance ID and all its readable Resources. This TLV payload would have the following value (indented for readability) and format. The total payload size with the TLV encoding is 124 bytes:

08 00 79
   C8 00 14 4F 70 65 6E 20 4D 6F 62 69 6C 65 20 41 6C 6C 69 61 6E 63 65
   C8 01 16 4C 69 67 68 74 77 65 69 67 74 20 4D 32 4D 20 43 6C 69 65 6E 74
   C8 02 09 33 34 35 30 30 30 31 32 33
   C3 03 31 2E 30
   86 06
      41 00 01
      41 01 05
88 07 08
   42 00 0E D8
   42 01 13 88
87 08
   41 00 7D
   42 01 03 84
C1 09 64
C1 0A 0F
83 0B
   41 00 00
C4 0D 51 82 42 8F
C6 0E 2B 30 32 3A 30 30
C1 10 55

B) Request on Multiple-Instance Object having 2 instances

In this example, a request on the Access Control Object (ID:2) of an LwM2M Client is made (Read /2). The Access Control Object is a Multiple-Instance Object. In this simplified example, it has only 2 instances describing the access rights of two LwM2M Servers with Short IDs 127 and 310 on Objects Instances /1/0 and /3/0.

The LwM2M Client responds with a TLV payload including the 2 Object Instances (ID:0 and ID:2) and their Resources. This TLV payload would have the following value (indented for readability) and format. The total payload size with the TLV encoding is 38 bytes:

08 00 0E
   C1 00 01
   C1 01 00
   83 02
      41 7F 07
   C1 03 7F
08 02 12
   C1 00 03
   C1 01 00
   87 02
      41 7F 07
      61 01 36 01
   C1 03 7F

C) Request on Multiple-Instance Object having 1 instance only

In this example, a request to the Server Object Instances of an LwM2M Client is performed (Read /1). The Server Object is a Multiple-Instances Object. The LwM2M Client has only one Server Object instance and will respond with a TLV payload including the single Object Instance (0) and their Resources. This TLV payload would have the following value (indented for readability) and format. The total payload size with the TLV encoding is 18 bytes:

08 00 0D
   C1 00 01
   C4 01 00 01 51 80
   C1 06 01
   C1 07 55

7.5.5.3. Example of Request on an Object Instance containing an Object Link Resource

Examples are based on the LwM2M Object Tree illustration presented in Figure: C.-1 Object link Resource simple illustration. The TLV format doesn't report the object hierarchy.

Example 1) request to Object 65 Instance 0: Read /65/0

88 00 0C
   44 00 00 42 00 00
   44 01 00 42 00 01
C8 01 0D 38 36 31 33 38 30 30 37 35 35 35 30 30
C4 02 12 34 56 78

Example 2) request to Object 66: Read /66: TLV payload will contain 2 Object Instances

08 00 23
   C8 00 0B 6D 79 53 65 72 76 69 63 65 20 31
   C8 01 0F 49 6E 74 65 72 6E 65 74 2E 31 35 2E 32 33 34
   C4 02 00 43 00 00
08 01 23
   C8 00 0B 6D 79 53 65 72 76 69 63 65 20 32
   C8 01 0F 49 6E 74 65 72 6E 65 74 2E 31 35 2E 32 33 35
   C4 02 FF FF FF FF

7.5.6. SenML JSON

When a LwM2M Client is supporting the SenML JSON data format and the format is used to transport Object Instance(s), multiple resource and single resource values for both "Read" and "Write" operations, SenML JSON payload MUST use the format defined in this section. This format MAY be used also for transporting a single value of a Resource.

The format MUST comply to [SENML] JSON representation extended for supporting LwM2M Object Link data type and MUST support all attributes defined in Table: 7.5.6.-1 SenML JSON format and description.

According to [SENML] semantics, the SenML JSON data format is composed of an array of entries (SenML Records) with optional and mandatory fields.

Each entry of the SenML JSON format is a Resource Instance, where the Name attribute need to be prepended by the Base Name attribute to form the unique identifier of this Resource instance.

The Name attribute in an entry is a URI path relative to the Base Name; namely the Name attribute could simply be the full URI path of a requested Resource Instance when Base Name is absent.

The SenML JSON format is useful for transporting multiple Resource Instances for example when transporting all Instances of an Object with all Resources, and Resource Instances within a single LwM2M Client response.

In particular, when Base Name is set to the LwM2M Object root (e.g. "/"), the SenML JSON format may support to return a hierarchy of Object Instances when Object Link datatype resources are reported (example given below). The resource instances tree report is performed in using a Breadth-First traversal strategy (see SenML JSON second example below); a given Object Instance MUST appear at most once in that report. The SenML JSON format also includes optional time fields, which allows for multiple versions of representations to be sent in the same payload or indicating the time when the representation was created (e.g., measurement made).

Note: SenML time values (Base Time and Time) are represented in floating point as seconds and a missing time attribute is considered to have a value of zero. Base time and time are added together. In general, positive time values represent an absolute time relative to the Unix epoch, while negative values represent a relative time in the past from the current time. For details see [SENML].

Historical version of notifications are typically generated when "Notification Storing When Disabled or Offline" resource of the LwM2M Server Object is set to true (see Appendix E. LwM2M Objects defined by OMA (Normative)) and when the Device comes on line after having been disabled for a period of time.

The SenML JSON data format has a Media Type application/senml+json.

[LwM2M-TS_1.0] defined the format for application/vnd.oma.lwm2m+json based on an early draft version of SenML. [LwM2M-TS_1.1] aligned the SenML JSON format with the final version of the SenML specification. However, SenML specification does not define the necessary semantics for its use with LwM2M Read-Composite or Write-Composite operations. This issue was partially resolved by [LwM2M-TS_1.1] and since its publication, [RFC8790] has formally defined application/senml-etch+json and application/senml-etch+cbor media types and their semantics in line with what was specified in [LwM2M-TS_1.1].

For backward compatibility, LwM2M Server implementations of [LwM2M-TS_1.1] MUST support both application/senml+json and application/vnd.oma.lwm2m+json. LwM2M Client implementations of [LwM2M-TS_1.1] and later MUST NOT use the application/vnd.oma.lwm2m+json format. Furthermore, LwM2M Clients implementing LwM2M TS 1.2 or later that support READ-Composite and/or Write-Composite operations MUST also support either application/senml-etch+json, or application/senml-etch+cbor.

For example, a request to a Device Object (Read /3/0) of the LwM2M example client would return the following SenML JSON payload. This example has a size of 399 bytes.

For example, a notification about a Resource containing multiple historical representations of a Temperature Resource (ID:2) (e.g. Instance ID:1 of hypothetical Object ID 72) could result in the following SenML JSON payload:

For example, a request to Object 65 of the LwM2M example seen in Figure: C.-1 Object link Resource simple illustration (Read /65/0) would return the following SenML JSON payload.

Because the Base Name is specified, the full hierarchy linked to the Instance 0 of Object 65 can be reported in a single response (Object 66 Instance 0 & 1, and Instance 0 of Object 67 are part of the payload). This example has a size of 412 bytes.

For example, a request to Device Object on Resource 0 of the LwM2M example client (Read /3/0/0) could return the following SenML JSON payload.

For example, a Read-Composite operation from a LwM2M Server to the LwM2M Client to read manufacturer name and battery level from the LwM2M Device Object together with the registration lifetime Resource from the LwM2M Server Object will look as follows:

In response to the Read-Composite operation above the LwM2M Client will return a SenML JSON payload similar to the one shown below.

For example, a Read-Composite operation from a LwM2M Server to an LwM2M Client to read its Location Object together with Network Bearer, Available Network Bearer and Radio Signal Strength resources in Connectivity Monitoring Object will look as follows:

Note: As shown above, SenML records used with a Read-Composite operation do not contain any value field while the responses will. Prior to [RFC8790], this implied the need for SenML parsers to be context aware, i.e. to distinguish between SenML records received in Read-Composite operations and responses to such requests. However, media types, application/senml-etch+json and application/senml-etch+cbor, defined in [RFC8790] have removed the requirement for context aware parsing.

For example, a Write-Composite operation by a LwM2M Server to switch off 2 light sources, to dim a 3rd to 20% and to set the thermostat to 18 degrees will have a SenML JSON payload as shown in table below. All lights are controlled by instances of the IPSO Light Control Object (Object ID 3311), while the thermostat is controlled by an instance of the IPSO Set Point Object (Object ID 3308).

Note: The Write-Composite operation with SenML format in [LwM2M-TS_1.1] could only be used to add or replace a Resource in a Multiple-Instance Resource as there was no support for use of a "null" value in a SenML record to indicate the deletion of a specific Resource Instance. The media types, application/senml-etch+json and application/senml-etch+cbor, defined in [RFC8790] post LwM2M v1.1 have removed this constraint.

The following example shows a Read-Composite operation from a LwM2M Server to the LwM2M Client to read all objects. This example offers the same functionality as a Read operation for all objects. Note that a response may not return all objects on the LwM2M Client since access control settings have to be taken into account as well.

Next we show an example of a Read-Composite operation issued by a LwM2M Server to the LwM2M Client to read all object instances of the LwM2M Server Object.

The final example illustrates how to request all Resources in the first and the third instance of the LwM2M Server Object using a Read-Composite operation issued by a LwM2M Server to the LwM2M Client.

7.5.6.1. LwM2M TS 1.0 JSON format

The JSON format used by [LwM2M-TS_1.0] with media type application/vnd.oma.lwm2m+json is formally defined in [LwM2M-TS_1.0]. The JSON payload shown below is an example reply to a request to the Device Object of the LwM2M example Client ("Read /3/0").

7.5.7. SenML CBOR

When a LwM2M Client is supporting the SenML CBOR data format and that format is used to transport Object Instance(s), multiple resource and single resource values for both "Read" and "Write" operations, the SenML CBOR payload MUST use the format defined in Section 6 of [SENML]. The same format MAY be used for transporting a single value of a Resource. The object links use a string map key "vlo" also in SenML CBOR representation.

The example from Table: 7.5.6.-2 SenML JSON payload returned from example request to Device Object (Read /3/0) is shown below in the SenML CBOR format.

90 a3 21 65 2f 33 2f 30 2f 00 61 30 03 74 4f 70
65 6e 20 4d 6f 62 69 6c 65 20 41 6c 6c 69 61 6e
63 65 a2 00 61 31 03 76 4c 69 67 68 74 77 65 69
67 68 74 20 4d 32 4d 20 43 6c 69 65 6e 74 a2 00
61 32 03 69 33 34 35 30 30 30 31 32 33 a2 00 61
33 03 63 31 2e 30 a2 00 63 36 2f 30 02 01 a2 00
63 36 2f 31 02 05 a2 00 63 37 2f 30 02 19 0e d8
a2 00 63 37 2f 31 02 19 13 88 a2 00 63 38 2f 30
02 18 7d a2 00 63 38 2f 31 02 19 03 84 a2 00 61
39 02 18 64 a2 00 62 31 30 02 0f a2 00 64 31 31
2f 30 02 00 a2 00 62 31 33 02 1a 51 82 42 8f a2
00 62 31 34 03 66 2b 30 32 3a 30 30 a2 00 62 31
36 03 61 55 

For details see Table: 7.5.6.-2 SenML JSON payload returned from example request to Device Object (Read /3/0).

The same example using the SenML CBOR diagnostic notation is shown below.

[{-2: "/3/0/", 0: "0", 3: "Open Mobile Alliance"}, 
{0: "1", 3: "Lightweight M2M Client"}, 
{0: "2", 3: "345000123"}, 
{0: "3", 3: "1.0"}, 
{0: "6/0", 2: 1}, 
{0: "6/1", 2: 5}, 
{0: "7/0", 2: 3800}, 
{0: "7/1", 2: 5000}, 
{0: "8/0", 2: 125}, 
{0: "8/1", 2: 900}, 
{0: "9", 2: 100}, 
{0: "10", 2: 15}, 
{0: "11/0", 2: 0}, 
{0: "13", 2: 1367491215}, 
{0: "14", 3: "+02:00"}, 
{0: "16", 3: "U"}]

8. Access Control

When a LwM2M Client interacts with multiple LwM2M Servers there is a need to determine which operation on a certain Object or Object Instance is authorized for which LwM2M Server. The Access Control Object has been designed to offer this access management capability.

An LwM2M Client can be implemented and configured in two ways:

• In the "Access Control-Enabled" configuration the LwM2M Client is capable of granting access rights to one or several LwM2M Servers. When a LwM2M Client is connected to multiple LwM2M Servers in this configuration then the Access Control Object MUST be instantiated unless all LwM2M Servers are granted full access rights on all Objects and Object Instances in the LwM2M Client.

• In the "Access Control-Disabled" configuration the LwM2M Client is only able to interact with a single LwM2M Server. Hence, the capability to manage access rights for multiple LwM2M Servers is not supported, i.e., the Access Control Object is not instantiated. In this configuration the LwM2M Server implicitly has full access rights on all Objects and Object Instances in the LwM2M Client. The Access Control Object need not be instantiated when a LwM2M Client is connected to a single LwM2M Server (i.e., a single LwM2M Server Account exists in the LwM2M Client).

Subsequent sections use the terms "Access Control-Enabled" and "Access Control-Disabled" to refer to these two types of configurations.

8.1. Access Control Object

8.1.1. Access Control Object Overview

In the presence of several LwM2M Servers, there is a need to determine if a certain LwM2M Server is authorized to instantiate a supported Object in the LwM2M Client. Provisioning the necessary authorization policies can only be done by the LwM2M Bootstrap-Server.

Furthermore, the LwM2M Client needs to determine - per supported Object Instance - who the "Access Control Owner" of that Object Instance is and which access rights have been granted to other LwM2M Servers for that Object Instance.

The Access Control Object is specified in Section LwM2M Object: Access Control and examples are presented in Appendix F. Example LwM2M Client (Informative).

8.1.2. Access Control Object Management

8.1.2.1. Access Control on Object

To authorize a LwM2M Server to instantiate a certain Object supported by the LwM2M Client, not only an Access Control Object Instance - as defined in Section Table: 8.1.2.1.-1 Access Control on Object - MUST be associated to such an Object, but this AC Object Instance MUST also contained an ACL Resource Instance targeting the authorized LwM2M Server.

This kind of Access Control Object Instance associated with a certain Object, MUST only be created or updated during a Bootstrap Phase. The absence of such an association for a certain Object, prevents this Object to be instantiated by any LwM2M Server.

When such an Access Control Object Instance already exists for a certain Object, this Access Control Object Instance MAY be updated for supporting additional LwM2M Servers; in that case a new ACL Instance per Server is created in that Access Control Object Instance with the Short Server ID of the LwM2M Server as index of this new ACL Instance, and with the "Create" ("C") access right as ACL Resource value.

8.1.2.2. Access Control on Object Instance

For being able to register which operations MAY be performed on an Object Instance by a certain LwM2M Server, this Object Instance MUST be associated to an Access Control Object Instance as defined in Section Table: 8.1.2.2.-1 Access Control on Object Instance.

This kind of Access Control Object Instance associated with a certain Object Instance, MAY be created or updated either during a Bootstrap Phase or through the Device Management and Service Enablement Interface.

In particular:

• when a LwM2M Server creates under authorization an Object Instance (see Section 8.2. Authorization) in the LwM2M Client, an Access Control Object Instance MUST be created in the LwM2M Client with the Resources values which MUST be set as given in the table just below. The Access Control Owner Resource is configured with the Short Server ID of the LwM2M Server.

• when this Access Control Object Instance is created during the Bootstrap Phase, ACL(s) and Access Control Owner MUST be set with values respecting the consistency of the LwM2M Client configuration.

• through the Device Management and Service Enablement Interface, an Access Control Object Instance MUST only be managed by the LwM2M Server declared as the "Access Control Owner" in it.

• when the LwM2M Server - which is the "Access Control Owner" - adds or modifies (using "Write" operation) access right on the Object Instance for a certain LwM2M Server,

  1. an ACL Resource having the targeted Short Server ID as ACL Resource Instance ID, has to be instantiated by the LwM2M Client if ACL Resource Instance for the LwM2M Server doesn't exist yet

  2. the appropriate access right (R,W,D,E) for that targeted Server on the Object Instance has to be set as ACL Resource Instance value

• A specific ACL Resource Instance MAY be used to grant access rights to LwM2M Servers (except the one defined as the Access Control Owner) which don't have their own ACL Resource Instance. The ID of this ACL Resource Instance containing the default access rights MUST be 0.

• when an Object Instance is removed via "Delete" operation performed by the LwM2M Server which is the "Access Control Owner", the associated Access Control Object Instance MUST be removed by the LwM2M Client.

Figure: 8.1.2.2.-1 Illustration of the relations between the LwM2M Access Control Object and the other LwM2M Objects illustrates the Access Control Management of an Object Instance (/X/2) supported by a LwM2M Client. An Access Control Object Instance (/2/Y) is declared in ② which defines the Access Rights applicable to the Instance 2 of the Object X pointed in ①.

In this Access Control Object Instance ②, 4 Instances of the ACL Resource are defined:

• ACL Instance 101 contains the operations granted to the Server having 101 as Short ID (Instance ID:2 of the Server Object ID:1 as pointed in ③)

• ACL Instance 22 contains the operations granted to the Server having 22 as Short ID

• ACL Instance 31 contains the operations granted to the Server having 31 as Short ID

• ACL Instance 0 contains the operations granted by default to any Server for which a specific ACL Instance is not defined in this Instance of the Access Control Object (default Access Rights).

This Access Control Object Instance ② also contains a reference to a Server (Access Control Owner) which is the only one Server authorized to manage that Instance of the Access Control Object.

8.1.3. LwM2M Access Control Context Switch

In an "Access Control-Disabled" context, the Access Control Object is not instantiated. In that case, adding a new LwM2M Server Account, requires the LwM2M Client to switch from the current "Access Control-Disabled" context to an "Access Control-Enabled" context which means the Access Control Object MUST be instantiated. This context switch must be managed in a Bootstrap Phase.

Note: The "Bootstrap-Discover" operation allows to retrieve data regarding the configuration of the initial "Access Control-Disabled" context (list of Objects, Object Instances and Short Server IDs). The Bootstrap-Server has then all information to setup a proper "Access Control-Enabled" context from the initial context one.

8.2. Authorization

For authorizing an operation to proceed on Object Instance(s) or Resource(s), the LwM2M Client MUST:

1. obtain the access rights for the involved Object Instances:
   • in "Access Control-Disabled" context, full access rights are granted to the LwM2M Server
   • in "Access Control-Enabled" context, access rights MUST be granted to the LwM2M Server according to Section 8.2.1. Obtaining Access Right
2. check if that access rights granted to the Server are sufficient for the requested operation according to Table: 8.2.-1 Authorization
3. verify –when the check in 2. on access rights is successful– if the requested operation is supported by the targeted Resource(s) (details are provided in Section 8.2.2. Operation on Resource(s) and Object Instance(s) and Section 8.2.3. Operation on Object).

The LwM2M Object specification defines which operations are allowed to be performed on Resource within an Object Instance, see supported operations in Section Appendix D. LwM2M Object Template and Guidelines (Normative). The operations allowed on a given Resource MUST apply to all the Resource Instances of that Resource.

8.2.1. Obtaining Access Right

In "Access Control-Disabled" context, the LwM2M Server get full access rights.

In "Access Control-Enabled" context:

• for "Create" operation sent by the LwM2M Server, the LwM2M Client MUST get the access right from the ACL Resource Instance corresponding to this LwM2M Server and located in the Access Control Object Instance associated to the targeted Object. Such an Access Control Object Instance – if it exists – has been provisioned during a Bootstrap Phase (Access Control Owner is MAX_ID=65535). If this access right does not have the "Create" value, or cannot be obtained, the LwM2M Server has no access right.

• For operations, except the "Create" operation, the LwM2M Client MUST retrieve the Access Control Object Instance associated with the Object Instance the LwM2M Server has requested access to, and MUST proceed according to the sequence below:

  1. If the LwM2M Server is declared as the Access Control Owner of this Object Instance and there is no ACL Resource Instance for that LwM2M Server, then the LwM2M Client gets full access right.

  2. If the LwM2M Client has an ACL Resource Instance for the LwM2M Server, the LwM2M Client gets the access right from that ACL Resource Instance.

  3. If the LwM2M Server is not declared as the Access Control Owner of this Object Instance and the LwM2M Client does not have the ACL Resource Instance for that Server, the LwM2M Client gets the access right from the ACL Resource Instance (ID:0) containing the default access rights if it exists (Section 8.1.2.2. Access Control on Object Instance).

  4. If the LwM2M Client does not have the ACL Resource Instance ID:0 containing the default access rights, then the LwM2M Server has no access rights.

  5. In case of a Composite operation (Read-Composite, Write-Composite, Observe-Composite), the previous four conditions apply to determine the access right for any Object Instance targeted by the Composite Operation. Composite operations have additional characteristics to determine the final access right granted to the LwM2M Server:

  • due to the atomic nature of the Write-Composite operation, all Object Instances involved in that operation MUST have the "Write" access right granted to the requesting LwM2M Server to establish that the "Write" access right is globally granted to such a LwM2M Server for that operation; otherwise, the LwM2M Server has no access right granted.
  • due to the non-atomic nature of the Read-Composite and Observe-Composite operations, any Object Instance involved in the requested operation which has no "Read" access right granted to the requesting LwM2M Server MUST be ignored. If at least one of the Object Instances involved in the requested operation has a "Read" access right granted to the LwM2M Server, the "Read" access right is globally granted to such a LwM2M Server for that operation; otherwise the LwM2M Server has no access right granted.

8.2.2. Operation on Resource(s) and Object Instance(s)

When the LwM2M Server targets Resource(s) or Object Instance(s) in a operation, the LwM2M Client MUST obtain an access right for that Server on the Object Instance(s) involved in that operation according to Section 8.2.1. Obtaining Access Right. The LwM2M Client MUST then check if the access right is granted prior to performing the requested operation. If the operation is not permitted, the LwM2M Client MUST send an "Unauthorized" error code to the LwM2M Server.

If the operation is permitted, for the "Read-Composite" and "Observe-Composite" operations, and for all Object Instances which have not been ignored during the access right determination (see Section 8.2.1. Obtaining Access Right), the LwM2M Client MUST retrieve all the requested Resources supporting the "Read" operation and sends such retrieved Resource(s) information to the LwM2M Server.

8.2.3. Operation on Object

When the LwM2M Server targets an Object for the "Create" operation, the LwM2M Client MUST obtain an access right for the LwM2M Server of the Object according to Section 8.2.1. Obtaining Access Right and MUST check if the access right is granted prior to perform the requested operation.

No access rights are needed for the "Discover" operation on an Object, i.e. the LwM2M Client MUST perform the operation.

For the "Read" and "Observe" operations, the LwM2M Client MUST obtain the access right for the LwM2M Server on each Object Instance according to Section 8.2.1. Obtaining Access Right and the LwM2M Client MUST retrieve all the Object Instances for which the LwM2M Server has the "Read" access right. For each of these qualified Object Instances, the LwM2M Client MUST retrieve all Resources except the Resources which do not support the "Read" operation. The LwM2M Client MUST then aggregate the information produced by the operation on each of these Object Instances individually and then send it to the LwM2M Server.

For the "Write-Attributes" operation, the LwM2M Client MUST perform the operation.

8.2.4. Notify Operation Consideration

If the LwM2M Client needs to send a "Notify" operation containing an Object Instance or a Resource to the LwM2M Server, the LwM2M Client MUST check if the LwM2M Server is authorized for the "Read" operation. If the LwM2M Server is not authorized, the Client MUST NOT send the "Notify" operation.

Appendix A. Change History (Informative)

A.1 Approved Version History

Appendix B. Static Conformance Requirements

This appendix is voided.

Appendix C. Data Types (Normative)

This appendix defines the data types that a Resource can be defined to be.

An Object Link referencing no Object Instance will contain 2 MAX-ID values (null link).

Appendix D. LwM2M Object Template and Guidelines (Normative)

This appendix provides the template to be used for the specification of LwM2M Objects. Furthermore, guidelines for the creation of LwM2M Objects are provided.

The XML versions of LwM2M Objects MUST comply with one of the approved XML schema files: http://openmobilealliance.org/tech/profiles/LWM2M.xsd or http://openmobilealliance.org/tech/profiles/LWM2M-v1_1.xsd.

D.1 Object Template

Appendix LwM2M Object: <LwM2M object name>

Description

Object definition:

• Name: specifies the Object name.

• Object ID: specifies the Object ID.

• Object Version: specifies the version of the Object. The first version of an Object must be version "1.0".

• LWM2M Version: specifies the version of the LwM2M protocol, e.g. version "1.1".

• Instances: indicates whether this Object supports multiple Object Instances or not. If this field is "Multiple" then the number of Object Instance can be from 0 to many. If this field is "Single" then the number of Object Instance can be from 0 to 1. If the Object field "Mandatory" is "Mandatory" and the Object field "Instances" is "Single" then, the number of Object Instances MUST be 1.

• Mandatory: if this field is "Mandatory", then the LwM2M Client MUST support this Object. If this field is "Optional", then the LwM2M Client SHOULD support this Object.

• Object URN: specifies the Object URN. The format of the Object URN is "urn:oma:lwm2m:{oma,ext,x}:{Object ID}[:{version}]" and {} part means that those values are variable and filled with real value. For example, the Object URN of the LwM2M Server Object is "urn:oma:lwm2m:oma:1". The "version" field, follows the rules specified in Section 6.2 related to Object Versioning Policy.

Resource definition:

• ID: specifies the Resource ID, which is unique within an Object or globally unique in case of Reusable Resources.

• Name: specifies the Resource name.

• Operations: indicates which operations the Resource supports in the given interface. This field can be set to a combination of Read (R), Write (W), and Execute (E). The Execute Operation cannot be used together with the Read and Write operations. This field may also have an empty value, which means that this field can only be accesses by the "Bootstrap" interface. More information about the interfaces and their operations can be found in Section 6. Interfaces.

• Instances: indicates whether this Resource supports multiple Resource Instances or not. If this field is "Multiple" then the number of Resource Instance can be from 0 to many. If this field is "Single" then the number of Resource Instance can be from 0 to 1. If the Resource field "Mandatory" is "Mandatory" and the field "Instances" of the Resource is "Single" then, the number of Resource Instance MUST be 1. A Resource, which supports the "Execute" operation, MUST have "Single" as value of the "Instances" field.

• Mandatory: if this field is "Mandatory", then any Instance of the Object that Resource belongs to, MUST instantiate such a Resource (refer Section 6.1, Resource Model). If this field is "Optional", then this Resource MAY be omitted from some - or even all - Instances of the Object that Resource belongs to.

• Type: Data Type indicates the type of Resource value. Data Types used in this enabler are described in Appendix C Data Types. A Resource, which supports the "Execute" operation, MUST have no associated Data Type (none) encoded as an empty value in Object DDF file.

• Range or Enumeration: this field limits the possible values of a Resource. A range is defined using two numeric values separated by two dots ("..") to indicate the lower and upper limits (inclusive). Enumeration is defined using one or more comma separated values. For the opaque data type, the value in this field represents constraints on the length of the Resource expressed in octets. For example, 1..42 indicates that the Resource can be 1 to 42 octets long. A value of 5,10,15 in this field indicates that the Resource can be 5, 10, or 15 octets long. A value of 8 in this field indicates that the Resource is always 8 octets long. For the string data type, a numeric range or enumeration has the same meaning as the opaque data type. Additionally, a comma separated list of quoted strings indicates the enumerated string values. For example, "foo","bar" indicates that the string Resource can only have the value foo or bar.

• Units: specifies the unit of the Resource value.

• Description: specifies the Resource description.

In addition to the object and resource templates described in the previous two tables of this section it is also important to document the syntax and semantic of the arguments of Executable Resources. The table below illustrates the method for documenting the arguments based on the plain text format following the ABNF format described in Section Execute.

An example can be found with the Portfolio Object.

D.2 Open Mobile Naming Authority (OMNA) Guidelines

This appendix defines guidelines for OMNA regarding registries and protocol ID ranges to be maintained.

D.2.1 Object Registry

LwM2M Objects must be registered with the OMNA Lightweight Object registry. The rules for Object registry are documented at: http://www.openmobilealliance.org/wp/OMNA/LwM2M/LwM2MRegistry.html

Several LwM2M Object classes are defined with the matching Object ID ranges:

The URN format for an Object is automatically built from the class of Object, the Object ID and potentially the Object Version (see Section 6.2 Object Versioning) as follows:

urn:oma:lwm2m:{oma,ext,x}:{Object ID}[:{version}].

D.2.2 Resource Registry

LwM2M Objects are specified as being composed of Resources, each identified by a Resource ID. Resources can either be specific to each Object with meaning only when used in that Object, or Reusable Resources can be registered, assigned an ID from the OMNA range and re-used in any Object.

The rules for registering Resource are documented at: http://www.openmobilealliance.org/wp/OMNA/LwM2M/LwM2MRegistry.html

Appendix E. LwM2M Objects defined by OMA (Normative)

This appendix provides LwM2M Objects defined by OMA SpecWorks that are a core part of the LwM2M specification. Other organizations and companies may define additional LwM2M Objects according to the guidelines provided in Appendix D. LwM2M Object Template and Guidelines (Normative).

The following LwM2M Object descriptions are contained in this appendix of the LwM2M v1.1 specification. Other objects can also be used with this version of LwM2M v1.1 and can be found in the OMNA registry.

Note: The objects found in this appendix are the versions that existed at the time of the enabler release. Please be aware that these objects evolve independently of the enabler release and the latest object versions are found in the LwM2M Registry.

The LwM2M Server MUST support the Security, Server, and Device Objects. The LwM2M Server SHOULD support the Access Control, Connectivity, Firmware Update, Location, and Connectivity Statistics Objects.

E.1 LwM2M Object: LwM2M Security

The LwM2M Client SHALL support the mandatory features in Object 0 as follows:

When the Security Mode resource 2 = 3 (NoSec) resource 3 SHALL be set to null.
When the Security Mode resource 2 = 3 (NoSec) or 0 (Pre-Shared Key) resource 4 SHALL be set to null.
When the Security Mode resource 2 = 3 (NoSec) resource 5 SHALL be set to null.
When the Security Mode resource 2 = 4 (Certificate mode with EST) resources 3 and 5 SHALL be set to null.

Description

This LwM2M Object provides the keying material of a LwM2M Client appropriate to access a specified LwM2M Server. One Object Instance SHOULD address a LwM2M Bootstrap-Server. These LwM2M Object Resources MUST only be changed by a LwM2M Bootstrap-Server or Bootstrap from Smartcard and MUST NOT be accessible by any other LwM2M Server.

Object definition

Resource definitions

E.2 LwM2M Object: LwM2M Server

Description

This LwM2M Objects provides the data related to a LwM2M Server. A Bootstrap-Server has no such an Object Instance associated to it.

Object definition

Resource definitions

E.3 LwM2M Object: LwM2M Access Control

Description

Access Control Object is used to check whether the LwM2M Server has access right for performing an operation.

Object definition

Resource definitions

E.4 LwM2M Object: Device

Description

This LwM2M Object provides a range of device related information which can be queried by the LwM2M Server, and a device reboot and factory reset function.

Object definition

Resource definitions

E.5 LwM2M Object: Connectivity Monitoring

Description

This LwM2M Object enables monitoring of parameters related to network connectivity. In this general connectivity Object, the Resources are limited to the most general cases common to most network bearers. It is recommended to read the description, which refers to relevant standard development organizations (e.g. 3GPP, IEEE). The goal of the Connectivity Monitoring Object is to carry information reflecting the more up to date values of the current connection for monitoring purposes. Resources such as Link Quality, Radio Signal Strength, Cell ID are retrieved during connected mode at least for cellular networks.

Object definition

Resource definitions

E.6 LwM2M Object: Firmware Update

Description

This LwM2M Object enables management of firmware which is to be updated. This Object includes installing a firmware package, updating firmware, and performing actions after updating firmware. The firmware update MAY require to reboot the device; it will depend on a number of factors, such as the operating system architecture and the extent of the updated software. The envisioned functionality is to allow a LwM2M Client to connect to any LwM2M Server to obtain a firmware image using the object and resource structure defined in this section experiencing communication security protection using TLS/DTLS. There are, however, other design decisions that need to be taken into account to allow a manufacturer of a device to securely install firmware on a device. Examples for such design decisions are how to manage the firmware update repository at the server side (which may include user interface considerations), the techniques to provide additional application layer security protection of the firmware image, how many versions of firmware images to store on the device, and how to execute the firmware update process considering the hardware specific details of a given IoT hardware product. These aspects are considered to be outside the scope of this version of the specification. A LwM2M Server may also instruct a LwM2M Client to fetch a firmware image from a dedicated server (instead of pushing firmware images to the LwM2M Client). The Package URI resource is contained in the Firmware object and can be used for this purpose. A LwM2M Client MUST support block-wise transfer [CoAP_Blockwise] if it implements the Firmware Update object. A LwM2M Server MUST support block-wise transfer. Other protocols, such as HTTP/HTTPs, MAY also be used for downloading firmware updates (via the Package URI resource). For constrained devices it is, however, RECOMMENDED to use CoAP for firmware downloads to avoid the need for additional protocol implementations.

Object definition

Resource definitions

E.6.1 Firmware Update State Machine

Figure: E.6.1-1 Firmware Update Mechanisms shows a possible implementation of the firmware update mechanism, described as a UML 2.0 state diagram. The state diagram consists of states, drawn as rounded rectangles, and transitions, drawn as arrows connecting the states. The syntax of the transition is trigger [guard] / behaviour. A trigger is an event that may cause a transition, guard is a condition and behaviour is an activity that executes while the transition takes place. The states additionally contain a compartment that includes assertions and variable assignments. For example, the assertion in the IDLE state indicates the value of the “Update Result” resource (abbreviated as “Res”) must be between 0 and 11. The State resource is set to zero (0) when the program is in this IDLE state.

Any operation to the Firmware Update Object that would result in undefined behavior because that specific operation is not identified as a trigger in the state machine (e.g. Write to Package URI while in DOWNLOADING state) SHOULD be rejected.

Errors during the Firmware Update process MUST be reported only by the “Update Result” resource. For instance, when the LwM2M Server performs a Write operation on resource “Package URI”, the LwM2M Client returns a Success or Failure for the Write operation. Then if the URI is invalid, it changes its “Update Result” resource value to 7.

E.6.2 Examples

The example depicted in Figure: E.6.2-1 Example of a LwM2M Server pushing a firmware image to a LwM2M client illustrates a successful message exchange where a LwM2M Server pushes a firmware image to a LwM2M Client using the block-wise transfer. In this example the LwM2M Server indicates a block size of 128 bytes and the firmware image of 80 KiB (=81920 bytes) will be sent to the LwM2M Client in 640 messages with each 128 bytes payload. Since the LwM2M Server-provided block size matches the preferences of the LwM2M Client the exchange proceeds until the full firmware image is downloaded. In this example, no messages are lost during transmission.

The second example shown in Figure: E.6.2-2 Example of a client fetching a firmware image illustrates the case where the client was provided with a URI by the LwM2M Server (using the Package URI resource) and therefore fetches the firmware image from the indicated server. Note that only the retrieval of the firmware image from the LwM2M Server is shown in Figure: E.6.2-2 Example of a client fetching a firmware image and not the initial configuration of the Package URI.

E.6.3 Firmware Update Consideration

If some Objects are not supported after firmware update, the LwM2M Client MUST delete all Object Instances of the Objects that are not supported.

E.7 LwM2M Object: Location

Description

This LwM2M Object provides a range of location telemetry related information which can be queried by the LwM2M Server.

Object definition

Resource definitions

E.8 LwM2M Object: Connectivity Statistics

Description

This LwM2M Objects enables client to collect statistical information and enables the LwM2M Server to retrieve these information, set the collection duration and reset the statistical parameters.

Object definition

Resource definitions

Note: When reporting the Tx Data or Rx Data, the LwM2M Client reports the total KB transmitted/received over IP bearer(s), including all protocol header bytes up to and including the IP header. This does not include lower level retransmissions/optimizations (e.g. RAN, header compression) or SMS messages.

E.9 LwM2M Object: LWM2M OSCORE

Description

This LwM2M Object provides the keying material and related information of a LwM2M Client appropriate to access a specified LwM2M Server using OSCORE. One Object Instance MAY address a LwM2M Bootstrap-Server. These LwM2M Object Resources MUST only be changed by a LwM2M Bootstrap-Server or Bootstrap from Smartcard and MUST NOT be accessible by any other LwM2M Server. Instances of this Object are linked from Instances of Object 0 using the OSCORE Security Mode Resource of Object 0. Instances of this Object MUST NOT be linked from more than one Instance of Object 0.

Object definition

Resource definitions

E.10 LwM2M Object: LwM2M COSE

Description

This Object provides the keying material and related information for use with COSE.

Object definition

Resource definitions

E.11 LwM2M Object: MQTT Server

Description

This object defines configuration parameters for an MQTT client to interact with a MQTT server.

Object definition

Resource definitions

E.12 LwM2M Object: LwM2M Gateway

Description

This object is used by a LwM2M Gateway to maintain the devices connected to the gateway.

Object definition

Resource definitions

E.13 LwM2M Object: LwM2M Gateway Routing

Description

This object is used by a LwM2M Gateway to maintain the routing table.

Object definition

Resource definitions