publish packet disconnected

[kushal bhattacharya]

hi,
Sorry i have one confusion regarding one scenario.I have thoroughly read the specs but i couldn't find anything mentioned about this scenario.Suppose publish packet from client or from server end has not reached either end by some means like internet connection failure or other disruptions.THen in that case how would the subscribed client  know of that interruption which did happen on the other end.What should be implemented in this scenario?
Thanks
Kushal

[kushal bhattacharya]

Actually i am talking about multiple topic scenario where a subscrbe client may be subscribed to multiple topic.I know that if its one subscriber subscribed to just one topic i can have a timer that can close the connection after certain time.But in this case i cannot do that because that subscriber client maybe dependent on different publishers so how do i tackle the scenario where one publisher doesn't reallly publishes to that client

[Paul Fremantle]

Kushal

The spec is actually very clear on this. 

Firstly, the TCP connection is tested by intermittent PINGs and PINGACKs.

Secondly, the QoS0 case doesn't care if messages are lost. In QoS1 and QoS2 there are clear mechanisms in the spec for how to know if messages haven't been delivered and how to redeliver them.

Paul

On 17 November 2016 at 14:56, kushal bhattacharya <bhattachar...@gmail.com> wrote:

Actually i am talking about multiple topic scenario where a subscrbe client may be subscribed to multiple topic.I know that if its one subscriber subscribed to just one topic i can have a timer that can close the connection after certain time.But in this case i cannot do that because that subscriber client maybe dependent on different publishers so how do i tackle the scenario where one publisher doesn't reallly publishes to that client

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Paul Fremantle

Doctoral Researcher, University of Portsmouth, School of Computing

Visiting Scientist, Institute of the Architecture of Application Systems, Stuttgart

Visiting Lecturer, Software Engineering Programme, Oxford University

Co-Founder, WSO2
Apache Member and Committer

email: paul.fr...@port.ac.uk, pa...@fremantle.org

twitter: pzfreo / skype: paulfremantle / blog: http://pzf.fremantle.org

[Karl Palsson]

Or, as I understood the post.

It's irrelevant. You're asking about subscribers knwoing whether
publishers are online. They don't unless you implement that in
your application. PubSub 101.

Sincerely,
Karl Palsson

> > email to mqtt+uns...@googlegroups.com.

[kushal bhattacharya]

hi,
WHat i am trying to say is supppose there's one subscriber who has subscribed to multiple topics .Suppose somehow the publisher of some topic isn't able to transmit the message to that client ,in that case should i just require some sort of handler which catches for  those situation .HOw do i communicate it between the client and the broker regarding it suppose fo srome disruptions like wifi failure or any system failure .In that case retransmitting a message to my opinion wont help me from suppose client or the broker end .The subscriber wont know if the sender(who is publishing the message .It may be  broker or client) has been offline ,so what should i do ,from that end.Actually this scenario is a must catch for my project which is what my boss demands so i have do something in order to catch for those interruptions from the subscriber end.
Thanks,
Kushal

[Paul Fremantle]

Kushal

The aim of a pub/sub system is to decouple the publishers and subscribers. Therefore, nothing in the MQTT spec will help you to do what you want to do. 

However! There are many people who want to do something at a higher level than the spec - in other words in the application that sits on top of MQTT. For example, you could simply make sure that the publisher publishes something every n seconds, and includes a timestamp in the message, and then if the subscriber doesn't see a message for a while, they know that the publisher is not behaving.

Paul

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[kushal bhattacharya]

thanks a lot sir :) i needed some help on this and am clear enough about this scenario now ;will remember the guidlines u mentioned here.