Chapter 15. Extending SIP

So far, we have seen what the core capabilities of SIP are. These capabilities need to be present in any SIP-compliant implementation. Therefore, any SIP UA can always assume that the UA it is communicating with (or trying to communicate with) will always support the core SIP.

In some cases, new applications appear for which it makes a lot of sense to use SIP, but that requires some kind of extension to the protocol. Foreseeing these situations, the core SIP specification defined built-in mechanisms to allow protocol extension while not disrupting the core SIP behavior.

In this chapter, we will first describe what these mechanisms are. Then we will present some of the general-purpose SIP extensions. In subsequent chapters, ...

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