1. Introduction
Light weight machine to machine (LWM2M) is an application communication protocol based on client-server architecture. This protocol was first introduced by OMA. The OMA lightweight M2M facilitate device management and service enablement for LWM2M Devices. Four interfaces are designed for these purposes as shown below:
- Bootstrap: is used to prepare vital information on client side to perform registration. Main operations in Bootstrap are: loading client profile from smartcard, obtain bootstrap from LWM2M Bootstrap Server…..
- Client Registration: is used by a LWM2M client to register with one or more LWM2M Servers, maintain each registration by updating.
- Device management and service enablement: is used by the LWM2M Server to access Object Instance or resources on client side. Main operation are: read, write, delete, execute, write attribute, discover.
- Information report: is used by a LWM2M Server to observe any changes in a resource on a LW2M2 client, receive notification when new value are available.
LWM2M uses the Constrained Application Protocol (CoAP) with UDP and SMS bindings. Datagram Transport Layer Security (DTLS) provides security for UDP transport layer.
2. Resource Model:
OMA defines a simple resource mode for LWM2M where each piece of information made available by the LWM2M client is a Resource. Resources are logically organized into Object. Client may have many objects which contains many resources. Resources and object have the capability to have multiple instances. OMA also provides a Resource Model Template for LWM2M client.
3. Bootstrap interface:
To perform bootstrap process, LWM2M client sends a COAP POST request to the Bootstrap Server at the /bs path using Endpoint Client Name as main parameter. When the Bootstrap server receive request, server will perform Write or Delete operation to create bootstrap on client side.
4. Registration Interface:
Registration is performed by sending a CoAP POST to the LWM2M server. This request contains registration parameter in URI and list of Object included in the payload. Server response includes Location-Path which indicate the path for updating or deleting.
5. Device management:
OMA LWM2M supports device management interface for accessing an Object or resource on client devices. An Object is identified by the path “/{Object ID}/{Object instance ID}”. Repose message from client is encapsulated under Plaitext, Opaque, TLV or JSON format depending on setting. Main operations are shown below:
6. Information report:
LWM2M support periodic reporting about resource value from client to server through CoAP Observation. This simple mechanism allows the LWM2M Server to send an Observe GET request for and Object, Object Instance, or Resource which results in asynchronous notification whenever that Object Instance changes.
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