Presence service

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