Chapter 22. NAT Traversal

In many real deployment scenarios, endpoints are located behind Network Address Translation (NAT) devices. The NAT functionality was designed sometime ago, when most of the Internet traffic was client to server. At that time, clients were just opening TCP connections to web or email servers in the public network, and the NAT device performed address translation and let the responses flow back to the client. Today, NAT devices are deployed everywhere—in enterprises connected to Internet, in end users who share the same public IP address among several devices, and so on. In this landscape, the new peer-to-peer multimedia services come into play, and we then find that NAT has pernicious effects on SIP and media traffic. ...

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