[riot-devel] mqtt-sn, multicast and riot

Michael Frey frey at informatik.hu-berlin.de
Wed Sep 7 13:46:19 CEST 2016


as probably some of you are aware, I'm working in my spare time on a
mqtt-sn client for RIOT. The mqtt-sn specification [1] doesn't make any
assumptions about the network stack, which is good and bad at the same

The "problem" is that MQTT-SN has "broadcast messages" such as the
SEARCHGW message for example and also defines for some message types a
"broadcast radius". While the latter is probably easy to "fix" using the
hop limit field in IPv6, I'm not entirely sure how to tackle the broadcast

The first thing which comes to mind is "simply" to use multicast, but the
question is which scope? Something like "ff0n::1" (all nodes) seems a bit
aggressive. Also RIOT doesn't seem to have a MLD implementation. Maybe it
would be better to create a designated multicast group for MQTT-SN?

I'm wondering if somebody was stumbling upon a similar issue? There seems
to be a proposal within the MQTT-SN community [2] which is probably
worthwhile to consider? Thanks in advance!


[1] http://mqtt.org/new/wp-content/uploads/2009/06/MQTT-SN_spec_v1.2.pdf
[2] https://github.com/mqtt/mqtt.github.io/wiki/MQTT-SN-Multicast-Addresses
Dipl.-Inf. (FH), M. Sc. Michael Frey
Humboldt-Universit├Ąt zu Berlin
Department of Computer Science
Rudower Chaussee 25
12489 Berlin, Germany

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