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Re: [m2m-iwg] General MQTT Protocol Question

Hi Rick,

> ÂÂÂÂÂÂÂÂÂ Does the protocol indicate that a âsubscribeâ request will always
> trigger an initial notification of the last known value for a topic?

In section 2.1 it states "When a new subscription is established on a
topic, the last retained message on that topic should be sent to the
subscriber with the Retain flag set. If there is no retained message,
nothing is sent".

Although that is only a "should", there is no way to force synchronisation.

> ÂÂÂÂÂÂÂÂÂ Are there any thoughts to supporting an alternative, more
> browser-friendly client protocol layer (probably on top of web sockets) and
> using JSON as the wire format?

There has been a bit of discussion of mqtt over websockets in the
past. With a websockets -> mqtt bridge on the server and a javascript
client library (Dale Lane mentions a 20kB uncompressed javascript
implementation on http://dalelane.co.uk/blog/?p=1625 ) you should be
good to go. It's still mqtt over the wire, but then the payload can be
whatever you want of course.

> ÂÂÂÂÂÂÂÂÂ Are there any testing metrics available that give some
> guidelines/limitations for scalability and performance? (impact of # of
> topics, # of clients, # of connections, frequency of
> publications/notifications, etc.)

There are some benchmarking tests at
https://github.com/chirino/mqtt-benchmark but I can't comment any more
than that.

Cheers,

Roger