IP telephony networks use call control protocols to make call routing decisions. This chapter detailed three call control protocols: H.323, SIP, and MGCP. H.323 represents the most mature of the call control standards. However, in a Cisco Unified CallManager environment, designers might prefer to use MGCP, which leverages Cisco Unified CallManager's centralized call control capability. SIP is an emerging standard suitable for environments where development and deployment of new services and applications in a distributed call control environment is required.