Chapter 13. SIP Proxies

In Chapter 4, we presented the different SIP entities. SIP proxies were briefly described there. In the present chapter, we will explain a bit more in detail how SIP proxies work. The chapter starts by defining what a SIP proxy is, and by explaining its crucial role in the routing of SIP messages in the SIP architecture.

Then we classify the mode of behavior of SIP proxies into stateless and stateful. A detailed explanation of the proxy behavior is then presented. This is particularly useful for the last part of this chapter, in which we will show some practical examples of how a very much simplified SIP proxy might be implemented using JAIN SIP.

What Is a SIP Proxy?

SIP proxies are defined in the base SIP spec [RFC 3261

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