Chapter 6. SIP Protocol Operation

In this chapter, we present the way SIP operates. We will look at the basic types of SIP messages and scenarios where they are used. The SIP message format is also outlined, and we will describe the most important SIP headers. Then we will show how SIP routing works, and highlight the relevance of DNS in routing SIP messages. Last, we will describe a complete end-to-end call flow, including all the signaling messages involved in it.

SIP Mode of Operation

SIP operation is based on the exchange of SIP messages. Any exchange of messages in SIP is organized in requests and responses. A request, together with all the responses associated with it, is called a transaction. This transaction-oriented approach is taken from ...

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