I need a little help getting started in the right direction:

I'm developing an application that has a server side and a client side.
It's possible that multiple servers and multiple clients could all be
on the same network.

Whenever the server machine comes up, he needs to "look" around for
clients that aren't connected to a server. The user on the server
machine then chooses which unconnected client to connect to.

I would like the actual connection to be based on TCP-IP and I think
I've got a good handle on how to do that. My problem is finding a way:

1. For the clients to "announce" their presence on the network (I've
done this with a heartbeat type message in UDP, is it possible in TCP?)

2. For the server to recognize the unconnected clients without
establishing exclusive connections with the clients until the user
selects that client.

3. For the clients to stop "announcing" their presence on the network
after a connection has been made.

Any help coming up with a general approach is appreciated,
Stephen