This chapter discussed the need for gateway control protocols. For example, when an IP phone on an IP telephony network needs a connection with a phone on the PSTN, the phone call traverses a gateway. The gateway and the CCM server need a common language (that is, protocol) for communication.
Three gateway control protocols include H.323, MGCP, and SIP. H.323 represents the most mature of the gateway control protocols and is appropriate for a distributed deployment environment.
MGCP uses a call agent (for example, a CCM server) to store call-forwarding intelligence, while H.323 stores call-forwarding intelligence in gateways throughout the network.
SIP represents a newer gateway control protocol targeted at vendor interoperability. Cisco continues to enhance SIP features available in the CCM.