In MQTT-SN, gateways can take on two distinct roles. First, a transparent gateway will manage many independent MQTT-SN streams from sensor devices and convert each stream into an MQTT message. An aggregating gateway will coalesce a number of MQTT-SN streams into a reduced number of MQTT streams sent to the cloud MQTT broker. An aggregating gateway is more complex in design but will reduce the amount of communication overhead and number of simultaneous connections left open on the server. For an aggregating gateway topology to function, the clients need to publish or subscribe to the same topic:
MQTT-SN gateway configurations. A transparent gateway simply performs a protocol conversion on each incoming MQTT-SN stream and has a one-to-one relationship with MQTT-SN connections and MQTT connections to the broker. An aggregating gateway, however, will coalesce multiple MQTT-SN streams into a single MQTT connection to the server.