[p2p-hackers] A Question about user awareness in p2p

[Anoop Mavilaveettil]

Hello,
 First of all, let me thank you for all the sharing of knowledge that
is going on in here.I must say that, I have learned a lot, ever since
I started frequenting this list.
I'm just a newbie in the p2p space and is in the process of building
up a p2p based communication and collaboration program and this
question is about one issue that I'm confronting and is kind of
confused with. If some one can point, or as much as give me a slight
hint, about techniques involved, It'd be hugely appreciated.
 The issue is with user presence/buddy awareness/ user awareness. Mind
you, I'm not talking about peer discovery, I think I have got that
part all figured out. I'm not even talking about peer presence(even
though in some way we can classify this issue as peer presence).
How would a user connected to a p2p network, through a specific peer, 
know/get a notification,whenever some other user connects to the
network through another peer?. (Some thing like the buddy system in
skype). I've kind of searched the web for answers and all most all of
them talk about discovering peers and none talks about user/peer
presence(Or may be my search isn't all that good). There are only
couple of solutions that I could some how figure out and on analysis,
both of them aren't/will not be that robust or efficient.
a) Using some kind of keep alive packets between buddies(Works as long
as the same pair of users connects through the same pair of peers all
the time).
b)Using an overlay of super peers/ meta trackers for user tracking and
then them firing all required messages to interested peers, whenever a
user connects to the p2p net.
As I said earlier, both methods aren't that great in terms of
efficiency and/or robustness. Is there some other way or any other
techniques that could be used to let a peer instantly know about the
connection status of his buddy?
 
Thanks in advance,
Sreedhar