MQTT-SN stands for "MQTT for Sensor Networks" which aims at embedded devices on non-TCP/IP networks, such as ZIGBEE. Its offical site says:
MQTT-SN is a publish/subscribe messaging protocol for wireless sensor networks (WSN), with the aim of extending the MQTT protocol beyond the reach of TCP/IP infrastructure for Sensor and Actuator solutions.
MQTT-SN specification can be downloaded from http://mqtt.org/new/wp-content/uploads/2009/06/MQTT-SN_spec_v1.2.pdf.
MQTT-SN vs MQTT
MQTT-SN looks similar to MQTT in most parts, such as Will message, such as Connect/Subscribe/Publish command.
The very difference between MQTT-SN and MQTT is the TopicId which replaces topic name in MQTT. TopicId is a 16 bits integer which stands for a topic name. Device and broker use REGISTER command to negotiate the mapping bewteen TopicId and topic name.
MQTT-SN is able to update Will message, even delete it. But MQTT is not allowed to change Will which is set in CONNECT command only.
MQTT-SN introduces gateways in its network. Gateway translates between MQTT-SN and MQTT, exchanges messages between device and MQTT broker. And there is a mechanism that called gateway discovery, which enables device to find gateways automatically.
MQTT-SN supports sleeping client feature which allows device to shutdown itself to save power for a while. Gateway needs to buffer downlink publish messages for sleeping devices, and pushes these messages to devices once they are awake.
EMQX-SN is an EMQ X plugin which implements most features of MQTT-SN. It serves as an MQTT-SN gateway on cloud, who is the neighbor of EMQ X Broker.
mqtt.sn.port = 1884 mqtt.sn.advertise_duration = 900 mqtt.sn.gateway_id = 1 mqtt.sn.username = mqtt_sn_user mqtt.sn.password = abc
|mqtt.sn.port||The UDP port which emqx-sn is listening on.|
|mqtt.sn.advertise_duration||The duration(seconds) that emqx-sn broadcasts ADVERTISE message through.|
|mqtt.sn.gateway_id||Gateway id in ADVERTISE message.|
|mqtt.sn.username||This parameter is optional. If specified, emqx-sn will connect EMQ X Broker with this username. It is useful if any auth plug-in is enabled.|
|mqtt.sn.password||This parameter is optional. Pair with username above.|
./bin/emqx_ctl plugins load emqx_sn