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Re: [paho-dev] MQTT-SN talk at EclipseCon


I think this is an interesting question. MQTT-SN, like MQTT is publish-subscribe, which means messages are sent to topics rather than a particular receiver. In MQTT, you have to connect to a server, so to some extent that server becomes part of the destination of the message along with the topic. The same thing happens in MQTT-SN when you connect to a server.

But when you use QoS -1 in MQTT-SN, without a connection to a server, then what does that mean? For a UDP implementation, you can send messages to a particular multicast group, so you could say that that group becomes part of the destination. Receivers of those messages can forward them on, so that the message can reach a destination to which the originator was not visible.

So, I think that MQTT-SN applications could take advantage of the underlying transport's mesh networking capabilities. An application could interpret a topic as containing a destination for instance, and use the transport's capabilities to get it there.


On 16/03/15 16:08, Stefano Costa wrote:
Il 16/03/2015 16:46, Ian Craggs ha scritto:

I think that means MQTT-SN allows mesh networking (depending on the
capabilties of the underlying transport like ZigBee, UDP).  Do you?

well actually in the context of mesh networking as implemented in Zigbee and others (DASH7, ZWave, BATMAN to name a few) it's common understanding that "mesh" relates to the possibility that a message going from A to B, where A and B are not mutually directly connected because of topology, can pass through C (and so forth up to a configured maximum number of intermediate nodes) and the protocol integrates a transparent logic so that the best (or possible) route from A to B is determined once / continuously / when needed.

This is not exactly what's given by MQTT-SN I think: retransmission is there but not a proper routing protocol like AODV or any other.

Thanks S
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