Voice Conference - how to have more people in conversation?

Question

Hi, first of all, I'm just a hobbyist, so I'm sorry if this is dumb question or if I'm being too naive. (It also means that I can't buy expensive libraries)

This is the situation: I'm building a simple voice chat application in C#.NET (something like Ventrilo or TeamSpeak but only for about 15 or 20 people, and running on 100Mbps LAN). I have working server (spawning thread for each client) and client application using UDP for connection and DirectSound for capturing and playing the sound. I can make "1 on 1" calls but I can't figure out one of the most important things:

How do i have more than two people in the conversation?

Answer 1

You need some centralized place to send the packets back out via a multicast, or else you need a decentralized approach where every client is connected to every other client, and each client is hosting a multicast. What you want to avoid is making the machines forward out their data to every other machine, which would result in O(n) time to send a message to each machine (and I/O is slow!).

In either scenario, you end up with the same problem: how to combine the audio streams. One simple mechanism to accomplish this is to bitwise-or the signals together before you send them back out (either out the network port, or out to your speakers), but this assumes you have access to non-compressed and reasonably-synchronized streams.