Standard Chat Applications

Quick question: do most chat applications (ie开发者_开发技巧. AIM, Skype, Oovoo) use peer to peer UDP exchange for talking to other users or an echoing TCP connection with a server? Or some combination in-between?

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Traditionally, most applications used a TURN-like solution (i.e., communication via a server) to overcome NAT traversal issues. Since chat does not consume much bandwidth, servers could support thousands of communications.

But now that P2P has evolved and the NAT traversal issues are now well understood, some use direct UDP communication provided that the users' NAT allows this (i.e., STUN-like communication). They still need a central server to punch the hole though. Direct communication is also helpful when lots of data needs to be transmitted.

I believe it is fair to say that most modern frameworks use a combination of both.

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when you need small fragments of data, such as text messaging, there's no need of using P2P. data can be transmitted from client1 to server, and from server back to the client2.

When you need to transfer data quickly between clients, in cases such as VoIP (voice over IP), or file transfer, you will use P2P.

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A pretty standard IM protocol is XMPP. I know it's used by Google Talk, as well as a few other big names in chat.