LwM2M Gateway for the EMQX Broker.

The LwM2M Specifications is a Lightweight Machine to Machine protocol.

With emqx_lwm2m, user is able to send LwM2M commands(READ/WRITE/EXECUTE/...) and get LwM2M response in MQTT way. emqx_lwm2m transforms data between MQTT and LwM2M protocol.

emqx_lwm2m needs object definitions to parse data from lwm2m devices. Object definitions are declared by organizations in XML format, you could find those XMLs from LwM2MRegistry, download and put them into the directory specified by lwm2m.xml_dir. If no associated object definition is found, response from device will be discarded and report an error message in log.

Load emqx_lwm2m

./bin/emqx_ctl plugins load emqx_lwm2m

Test emqx-lwm2m using wakaama

wakaama is an easy-to-use lwm2m client command line tool.

Start lwm2mclient using an endpoint name ep1:

./lwm2mclient -n ep1 -h 127.0.0.1 -p 5683 -4

To send an LwM2M DISCOVER command to lwm2mclient, publish an MQTT message to topic lwm2m/<epn>/dn (where <epn> is the endpoint name of the client), with following payload:

{
    "reqID": "2",
    "msgType": "discover",
    "data": {
        "path": "/3/0"
    }
}

The MQTT message will be translated to an LwM2M DISCOVER command and sent to the lwm2mclient. Then the response of lwm2mclient will be in turn translated to an MQTT message, with topic lwm2m/<epn>/up/resp, with following payload:

{
    "reqID": "2",
    "msgType": "discover",
    "data": {
        "code":"2.05",
        "codeMsg": "content",
        "content": [
            "</3/0>;dim=8",
            "</3/0/0>",
            "</3/0/1>",
            "</3/0/4>",
            "</3/0/16>"
        ]
    }
}

LwM2M <--> MQTT Mapping

Register/Update (LwM2M Client Registration Interface)

• LwM2M Register and Update message will be converted to following MQTT message:

  • Method: PUBLISH
  • Topic: lwm2m/{?EndpointName}/up/resp (configurable)
  • Payload:
    • MsgType register and update:

      {
          "msgType": {?MsgType},
          "data": {
              "ep": {?EndpointName},
              "lt": {?LifeTime},
              "sms": {?MSISDN},
              "lwm2m": {?Lwm2mVersion},
              "b": {?Binding},
              "alternatePath": {?AlternatePath},
              "objectList": {?ObjectList}
          }
      }

      • {?EndpointName}: String, the endpoint name of the LwM2M client
      • {?MsgType}: String, could be:
        • "register": LwM2M Register
        • "update": LwM2M Update
      • "data" contains the query options and the object-list of the register message
      • The update message is only published if the object-list changed.

Downlink Command and Uplink Response (LwM2M Device Management & Service Enablement Interface)

• To send a downlink command to device, publish following MQTT message:

  • Method: PUBLISH
  • Topic: lwm2m/{?EndpointName}/dn
  • Request Payload:

    {
        "reqID": {?ReqID},
        "msgType": {?MsgType},
        "data": {?Data}
    }

    • {?ReqID}: Integer, request-id, used for matching the response to the request
    • {?MsgType}: String, can be one of the following:
      • "read": LwM2M Read
      • "discover": LwM2M Discover
      • "write": LwM2M Write
      • "write-attr": LwM2M Write Attributes
      • "execute": LwM2M Execute
      • "create": LwM2M Create
      • "delete": LwM2M Delete
    • {?Data}: Json Object, its value depends on the {?MsgType}:

      • If {?MsgType} = "read" or "discover":

        {
            "path": {?ResourcePath}
        }

        • {?ResourcePath}: String, LwM2M full resource path. e.g. "3/0", "/3/0/0", "/3/0/6/0"

      • If {?MsgType} = "write" (single write):

        {
            "path": {?ResourcePath},
            "type": {?ValueType},
            "value": {?Value}
        }

        • {?ValueType}: String, can be: "Time", "String", "Integer", "Float", "Boolean", "Opaque", "Objlnk"
        • {?Value}: Value of the resource, depends on "type".

      • If {?MsgType} = "write" (batch write):

        {
            "basePath": {?BasePath},
            "content": [
                {
                    "path": {?ResourcePath},
                    "type": {?ValueType},
                    "value": {?Value}
                }
            ]
        }

        • The full path is concatenation of "basePath" and "path".

      • If {?MsgType} = "write-attr":

        {
            "path": {?ResourcePath},
            "pmin": {?PeriodMin},
            "pmax": {?PeriodMax},
            "gt": {?GreaterThan},
            "lt": {?LessThan},
            "st": {?Step}
        }

        • {?PeriodMin}: Number, LwM2M Notification Class Attribute - Minimum Period.
        • {?PeriodMax}: Number, LwM2M Notification Class Attribute - Maximum Period.
        • {?GreaterThan}: Number, LwM2M Notification Class Attribute - Greater Than.
        • {?LessThan}: Number, LwM2M Notification Class Attribute - Less Than.
        • {?Step}: Number, LwM2M Notification Class Attribute - Step.

      • If {?MsgType} = "execute":

        {
            "path": {?ResourcePath},
            "args": {?Arguments}
        }

        • {?Arguments}: String, LwM2M Execute Arguments.

      • If {?MsgType} = "create":

        {
            "basePath": "/{?ObjectID}",
            "content": [
                {
                    "path": {?ResourcePath},
                    "type": {?ValueType},
                    "value": {?Value}
                }
            ]
        }

        • {?ObjectID}: Integer, LwM2M Object ID

      • If {?MsgType} = "delete":

        {
            "path": "{?ObjectID}/{?ObjectInstanceID}"
        }

        • {?ObjectInstanceID}: Integer, LwM2M Object Instance ID

• The response of LwM2M will be converted to following MQTT message:

  • Method: PUBLISH
  • Topic: "lwm2m/{?EndpointName}/up/resp"
  • Response Payload:

  {
      "reqID": {?ReqID},
      "imei": {?IMEI},
      "imsi": {?IMSI},
      "msgType": {?MsgType},
      "data": {?Data}
  }

  • {?MsgType}: String, can be:
    • "read": LwM2M Read
    • "discover": LwM2M Discover
    • "write": LwM2M Write
    • "write-attr": LwM2M Write Attributes
    • "execute": LwM2M Execute
    • "create": LwM2M Create
    • "delete": LwM2M Delete
    • "ack": CoAP Empty ACK
  • {?Data}: Json Object, its value depends on {?MsgType}:

    • If {?MsgType} = "write", "write-attr", "execute", "create", "delete", or "read"(when response without content):

      {
            "code": {?StatusCode},
            "codeMsg": {?CodeMsg},
            "reqPath": {?RequestPath}
      }

      • {?StatusCode}: String, LwM2M status code, e.g. "2.01", "4.00", etc.
      • {?CodeMsg}: String, LwM2M response message, e.g. "content", "bad_request"
      • {?RequestPath}: String, the requested "path" or "basePath"

    • If {?MsgType} = "discover":

      {
          "code": {?StatusCode},
          "codeMsg": {?CodeMsg},
          "reqPath": {?RequestPath},
          "content": [
              {?Link},
              ...
          ]
      }

      • {?Link}: String(LwM2M link format) e.g. "</3>", "<3/0/1>;dim=8"

    • If {?MsgType} = "read"(when response with content):

      {
          "code": {?StatusCode},
          "codeMsg": {?CodeMsg},
          "content": {?Content}
      }

      • {?Content}

        [
            {
                "path": {?ResourcePath},
                "value": {?Value}
            }
        ]

    • If {?MsgType} = "ack", "data" does not exists

Observe (Information Reporting Interface - Observe/Cancel-Observe)

• To observe/cancel-observe LwM2M client, send following MQTT PUBLISH:

  • Method: PUBLISH
  • Topic: lwm2m/{?EndpointName}/dn
  • Request Payload:

    {
        "reqID": {?ReqID},
        "msgType": {?MsgType},
        "data": {
            "path": {?ResourcePath}
        }
    }

    • {?ResourcePath}: String, the LwM2M resource to be observed/cancel-observed.
    • {?MsgType}: String, can be:
      • "observe": LwM2M Observe
      • "cancel-observe": LwM2M Cancel Observe
    • {?ReqID}: Integer, request-id, is the {?ReqID} in the request

• Responses will be converted to following MQTT message:

  • Method: PUBLISH
  • Topic: lwm2m/{?EndpointName}/up/resp
  • Response Payload:

    {
        "reqID": {?ReqID},
        "msgType": {?MsgType},
        "data": {
            "code": {?StatusCode},
            "codeMsg": {?CodeMsg},
            "reqPath": {?RequestPath},
            "content": [
                {
                    "path": {?ResourcePath},
                    "value": {?Value}
                }
            ]
        }
    }

    • {?MsgType}: String, can be:
      • "observe": LwM2M Observe
      • "cancel-observe": LwM2M Cancel Observe
      • "ack": CoAP Empty ACK

Notification (Information Reporting Interface - Notify)

• The notifications from LwM2M clients will be converted to MQTT PUBLISH:
  • Method: PUBLISH
  • Topic: lwm2m/{?EndpiontName}/up/notify
  • Notification Payload:

    {
        "reqID": {?ReqID},
        "msgType": {?MsgType},
        "seqNum": {?ObserveSeqNum},
        "data": {
            "code": {?StatusCode},
            "codeMsg": {?CodeMsg},
            "reqPath": {?RequestPath},
            "content": [
                {
                    "path": {?ResourcePath},
                    "value": {?Value}
                }
            ]
        }
    }

    • {?MsgType}: String, must be "notify"
    • {?ObserveSeqNum}: Number, value of "Observe" option in CoAP message
    • "content": same to the "content" field contains in the response of "read" command

Feature limitations

• emqx_lwm2m implements LwM2M gateway to EMQX, not a full-featured and independent LwM2M server.
• emqx_lwm2m does not include LwM2M bootstrap server.
• emqx_lwm2m supports UDP binding, no SMS binding yet.
• Firmware object is not fully supported now since mqtt to coap block-wise transfer is not available.
• Object Versioning is not supported now.

DTLS

emqx-lwm2m support DTLS to secure UDP data.

Please config lwm2m.certfile and lwm2m.keyfile in emqx_lwm2m.conf. If certfile or keyfile are invalid, DTLS will be turned off and you could read a error message in the log.

License

Apache License Version 2.0

Author

EMQX Team.