In this chapter, you learn about the theory and configuration of the following gateway control protocols: H.323, Session Initiation Protocol (SIP), and Media Gateway Control Protocol (MGCP). The discussion begins with the most mature of these protocols, H.323.
H.323 is not a single protocol. Instead, it is a suite of protocols. This suite specifies such things as audio/video codecs and call signaling.
You should be aware of the following two protocols used to establish an H.323 call:
H.225: Performs call setup and registration, admission, and status (RAS) functions
H.245: Performs call control, including a capabilities exchange (for example, codec negotiation)
In addition ...