OMA轻量级LWM2M技术规范

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OMA-lightweight M2M (Machine-to-Machine) 是Open Mobile Alliance（OMA）推出的一种轻量级的机器对机器通信技术规范，其目标是简化大规模设备连接和管理，适用于物联网(IoT)环境中的低功耗、资源受限的设备。LWM2M标准版本1.0在2017年2月8日获得了批准，这一版本的文档标题为"OMA-TS-Lightweight M2M-V1_0-20170208-A"，表明它是一个经过标准化的、成熟的协议。该规范的批准文档强调了版权归属，所有权利归2017年的Open Mobile Alliance所有，并且使用时必须遵循他们在文档中指定的条款。使用此文档须受《使用协议》约束，可以在OMA的官方网站上找到协议链接：http://www.openmobilealliance.org/UseAgreement.html。作为一项仍在发展中的工作，LWM2M 1.0并非正式的OMA批准标准，可能会随时进行修订或移除，因此用户只能将其用于内部或教育目的，不得修改、编辑或不恰当地引用文档内容。这个标准旨在支持设备之间的高效通信，尤其是在那些功耗低、计算能力有限的设备上，例如智能家居设备、穿戴设备、工业传感器等。 LWM2M的轻量化设计意味着它具有较低的内存和处理需求，使得设备能够更有效地连接到网络并执行远程管理任务。它通过简化协议栈，减少不必要的复杂性，提高了设备的能源效率和部署灵活性。此外，LWM2M还支持多种功能，包括设备管理、资源发现与配置、命令执行以及数据上报等，这些都是为了满足物联网环境中设备多样化和规模化的管理需求。总结来说，OMA-lightweight M2M标准是针对物联网场景下低功耗设备通信设计的一种开放标准，旨在优化设备间的连接和管理，提升物联网应用的易用性和扩展性。使用这一技术，开发者可以构建更加高效、可扩展的物联网系统，而无需过分关注底层通信细节，这对于推动IoT生态的发展具有重要意义。

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LwM2M

Server

LwM2M

Client

Read, Write, Execute, Create,

Delete, Write Attribute, Discover

Figure 5: Device Management and Service Enablement

Figure 6 shows the operation model for interface “Information Reporting”. For this interface, the operations are downlink

operations “Observe” or “Cancel Observation” and an uplink operation “Notify”. This interface is used to send the LwM2M

Server a new value related to a Resource on the LwM2M Client.

LwM2M

Server

LwM2M

Client

Observe, Cancel Observation

Notify

Figure 6: Information Reporting

The relationship between operations and interfaces is listed in the following Table 1.

Interface

Direction

Operation

Bootstrap

Uplink

Bootstrap-Request

Bootstrap

Downlink

Write, Discover, Delete, Bootstrap-

Finish

Client Registration

Uplink

Device Management and Service

Enablement

Downlink

Create, Read, Write, Delete, Execute,

Write-Attributes, Discover

Information Reporting

Downlink

Observe, Cancel Observation

Information Reporting

Uplink

Notify

Table 1: Relationship of operations and interfaces

5.1 Attributes

5.1.1 Attributes Definitions and Rules

Attributes are metadata which can be attached to an Object, an Object Instance or a Resource. The value of an Attribute is

LwM2M Server specific. These attributes can fulfil various roles: from just carrying information (e.g., Discover), up to

containing parameters for Notification for example.

Attributes attached to Object, Object Instance, Resource, are respectively named O-Attribute, OI-Attribute, R-Attribute.

These Attributes MAY be carried in the message payload of Registration and Discover operations; they also MAY be

updated - when writable - through the “Write-Attributes” operation.

Regardless to the LwM2M entity a given Attribute is attached to, the value of such an Attribute can be set at various levels:

Object, Object Instance, Resource levels. Additionally, precedence rules apply when the same Attribute receives a value at

different levels.

Several rules govern usage of LwM2M Attributes

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 The value of an O-Attribute MAY only be set at the Object level.

 The value of an OI-Attribute MAY be set at the Object Instance level, and at the Object level.

precedence rules:

 Rule 1: When set at both levels, the value of the OI-Attribute set at Object Instance level will prevail.

 Rule 2: When the Attribute value is set at the Object level, the scope of the OI-Attribute value extends to all the

Instances of that Object, as long as the Rule 1 is respected.

 An R-Attribute MAY be set at 3 different levels: the Resource level, the Object Instance level and the Object level.

precedence rules:

 Rule 3: When set at the Resource level, the value of an R-Attribute prevails for that Resource whatever a value

for this R-Attribute is also specified at an upper level (Object or Object Instance level).

 Rule 4: When set at the Object Instance level, the scope of an R-Attribute value extends to all the Resources of

that Object Instance as long as the Rule 3 is respected.

 Rule 5: When set at the Object level, the scope of an R-Attribute value extends to all the resources of any

Instance of that Object, as long as the Rule 4 is respected.

An attribute is fully determined by several characteristics which are listed in the table below:

Attribute

characteristics

Description

Name

Attribute Name used to reference a specific Attribute in that Enabler (e.g., “Minimum Period”)

CoRE Link Param

the string used when this Attribute is transferred to CoAP as a CoRE link parameter (ex pmin)

Attachment

The Object, Object Instance or Resource, to which an Attribute applies

Assignation Level

The Level (Object, Object Instance, Resource) where the value of the Attribute MAY be set.

Class

Attributes are organized according to their purpose;

2 Class of Attributes are supported in LwM2M TS 1.0

<NOTIFICATION> gather Attributes regarding Notify operations parameters

<PROPERTIES> gather Attributes regarding general information

Access Mode

R, W, RW: operation allowed by the LwM2M Server.

Applicability

Condition to fulfil for allowing to attach such an Attribute

Default Value

<value> or “-” or “ ”

Value Type

Data Type (Refer Appendix C)

Value

The Value carried by this Attribute : its data type must be of “Value Type”

Table 2: Attribute Characteristics

Some Attributes MAY be exposed to the LwM2M Server in the payload response to a “Discover” command (Section 5.4.2).

The value of some Attributes MAY be changed by the LwM2M Server in using the “Write-Attributes” command (Section

5.4.4); which Attribute are concerned are marked as “W” (writable) in the table of the next Section.

Note: A payload response to a “Discover” command is a list of application/link-format CoRE Links [RFC6690] which will

include the LwM2M Attributes.

5.1.2 Attributes Classification

<PROPERTIES> Class Attributes

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The role of these Attributes is to provide metadata which may communicate helpful information to LwM2M Server for

example easing data management.

Except when specifically mentioned as required, the LwM2M Server and LwM2M Client SHOULD support

<PROPERTIES> Class Attributes listed Table 3.

Attribute

Name

CoRE

Link

param

Attachment

Assignation

Level

Support

Required

Access

Mode

Value

Type

Default

Value

Applicabili

Notes

Dimension

dim

Resource

YES

(Client)

Integer

[0:255]

Multiple

Resource

Number of

Instantiations

for a Multiple

Resource

Object

Version

ver

Object

YES

(Server)

YES

(Client)

when able

to support

Objects in

version >

1.0

String

1.0

(Initial

Version)

Provide the

version of the

associated

Object. The

rules

governing the

usage of this

parameter are

specified in

Section 6.2

and Table 19.

Table 3: <PROPERTIES> Class Attributes

<NOTIFICATION> Class Attributes

The role of these R-Attributes is to provide parameters to the “Notify” operation; any readable Resource can have such R-

attributes.

In the message sent by a LwM2M Client in response to an “Observe” operation, the current Resource value is reported; this

event can be considered as the initial notification.

Each time a Resource notification is sent, the “Minimum Period” and “Maximum Period” timers associated to this Resource

are restarted.

The notification of a Resource value will be sent when the combination of a change value condition (“Greater Than”, “Less

Than”, “Step”) and the “Minimum Period” timing conditions are both fulfilled for that Resource.

The LwM2M Server MUST support and LwM2M Client SHOULD support all the <NOTIFICATION> Class Attributes

listed Table 4.

Attribute

Name

CoRE

Link

param

Attachment

Assignation Level

Required

Access

Mode

Value

Type

Default

Value

Apply

Condition

Minimum

Period

pmin

Resource

Object Instance

Object

Integer

0 (sec)

Readable

Resource

Notes: The Minimum Period Attribute indicates the minimum time in seconds the LwM2M Client MUST wait between

two notifications. If a Resource value has to be notified during the specified quiet period, the notification MUST be sent

as soon as this period expires. In the absence of this parameter, the Minimum Period is defined by the Default Minimum

Period set in the LwM2M Server Account.

Maximum

Period

pmax

Resource

Object Instance

Object

Integer

Readable

Resource

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Note: the following rules MUST be respected (“lt” value + 2*“st” values <“gt” value)

Table 4: <NOTIFICATION> class Attributes

Examples illustrating Attributes setting are provided in Section 8.2.5 (Device Management & Service Enablement Interface).

5.2 Bootstrap Interface

The Bootstrap Interface is used to provision essential information into the LwM2M Client to enable the LwM2M Client to

perform the operation “Register” with one or more LwM2M Servers.

During the Bootstrap Phase, the Client MAY ignore requests and flush all pending responses not related to the Bootstrap

sequence. 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 a LwM2M Bootstrap-Server to achieve the ultimate goal to connect a

LwM2M Client to their LwM2M Server(s).

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

The LwM2M Bootstrap-Server MUST support Client Initiated Bootstrap and Server Initiated Bootstrap modes 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.

Notes: The Maximum Period Attribute indicates the maximum time in seconds the LwM2M Client MAY wait between

two notifications. When this “Maximum Period” expires after the last notification, a new notification MUST be sent. In

the absence of this parameter, the “Maximum Period” is defined by the Default Maximum Period set in the LwM2M

Server Account. The maximum period parameter MUST be not smaller than the minimum period parameter.

Greater

Than

Resource

Float

Numerical

&Readable

Resource

Notes: This “Greater Than” Attribute defines a threshold high value. When this Attributes is present, the LwM2M Client

MUST notify the Server each time the Observed Resource value crosses the “Greater Than” Attribute value with respect

to pmin parameter.

Less Than

Resource

Float

Numerical

&Readable

Resource

Notes: This “Less Than” Attribute defines a threshold low value. When this Attributes is present, the LwM2M Client

MUST notify the Server each time the Observed Resource value crosses the “Less Than” Attribute value with respect to

pmin parameter.

Step

Resource

Float

Numerical

&Readable

Resource

Notes: This “Step” Attribute defines a minimum change value between two notifications. When this Attribute is present,

the change value condition will occur when the value variation since the last notification of the Observed Resource, is

greater or equal to the “Step” Attribute value.

When the “Step” change value condition occurs, the LwM2M Client MUST notify the Server with respect to “Period

Minimum” rule.

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5.2.1 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 a LwM2M

Bootstrap-Server Account pre-provisioned in it.

5.2.2 Bootstrap Information

This section specifies the information that needs to be configured in LwM2M Client for connecting to the LwM2M Server(s)

or the LwM2M Bootstrap-Server. This Bootstrap Information can be available before performing the Bootstrap Sequence

described in Section 5.2.4 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 5.2.4.

The LwM2M Client SHOULD have the LwM2M Bootstrap-Server Bootstrap Information.

The LwM2M Server Bootstrap Information is used by the LwM2M Client to register and connect to the LwM2M Server.

The LwM2M Server Bootstrap Information MUST contain at least a LwM2M Server Account.

Note that according to the LwM2M Server Account definition, a usual LwM2M Server Account is composed of a Security

Object Instance and a 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.

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 a LwM2M Bootstrap-Server Account.

Bootstrap Information Type

Entity

Required

The LwM2M Server Bootstrap

Information

LwM2M Server Account

Yes*

Additional Object Instances (e.g.,

Access Control, Connectivity

Monitoring Object)

The LwM2M Bootstrap-Server

Bootstrap Information

LwM2M Bootstrap-Server Account

(Security Object instance)

Table 5: Bootstrap Information List

*the LwM2M Client MUST have at least one LwM2M Server Account after completion of Bootstrap Sequence specified in

5.2.4.

Please note that the LwM2M Client MUST accept Bootstrap Information sent via Bootstrap Interface without applying

access control as specified in Section 7.3.2 Authorization.

5.2.3 Bootstrap Modes

This section of the specification provides description and further information for each of the following Bootstrap Modes:

 Factory Bootstrap

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OMA轻量级LWM2M技术规范

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