Re: Presence service

On Tue, Dec 05, 2006 at 05:37:56PM +0100, [email protected] wrote:
> Thanks for your response!
> If I am using the propagate pipe I only need to create it by using the 
> peer groups pipeservice, there is no need to publish it in the group or 
> create it on the Rdv first, right?

Correct.  What you are describing is essentially the technique of using a
"well-known PipeID", whose analogue I'm sure you've heard of with things
like SMTP, HTTP, and other important Internet standard services.  There,
they are call well-known port numbers.

Well-known in our case means all peers know the PipeID a priori to its
use.  Meaning it is available as an application constant or declaratively
configured somewhere in a config file.  There is no point publishing it
for the sake of discovery - just hard code it somewhere in your app ---
because you already know you will need it.

hth

Mark

> Vince
> 
> 
> Mark S. Petrovic wrote:
> >Vince, your propagate pipe idea is a good basis for a presence service.
> >I travelled the same path you did, first wanting to use advertisements,
> >then concluding that I wanted something more deterministic.  A propagate
> >pipe is the price you pay for knowing quickly peers are out there,
> >rather than assuming they are not on some unknown timescale if you cannot
> >discover their advertisements.
> >
> >On Tue, Dec 05, 2006 at 11:37:15AM +0100, [email protected] wrote:
> >  
> >>I implemented a presence service for my application a few weeks ago but 
> >>it is much too slow and unreliable and I want to implement it different 
> >>this time and would like to hear your comments.
> >>
> >>My current implementation is based on advertisements that are published 
> >>every 5 minutes using a timer task such as Brendon J. Wilson is doing it 
> >>in his book. Other peers are searching for these advertisments with a 
> >>timer task. So the problem with this is that it can take up to a few 
> >>minutes until a peer is found to be online and a peer could go offline 
> >>and it is not recognized. So I definitely need to change this.
> >>
> >>My new approach would be a mix of advertisments and a propagate pipe. 
> >>The advertisment is published to the peer group with an application 
> >>specific description of the peer. This advertisment for example holds a 
> >>pipeadvertisment for a JxtaSocket which is later used to transfer files. 
> >>When a peer enters my peer group it searches for the advertisments of 
> >>other peers so that they can be displayed in the GUI as offline. It also 
> >>sends a "hello" message to all other peers in the peer group with its 
> >>status such as "online" and gets a response from all other devices that 
> >>are online too.
> >>
> >>Do you have any other ideas on implementing a presence service?
> >>How did other applications solve this?
> >>
> >>thanks in advance,
> >>Vince
> >>
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-- 
Mark S. Petrovic
Pasadena, CA 
http://www.petrovic.org