The Media Gateway Control Protocol (MGCP) is described in a series of Internet Engineering Task Force (IETF) drafts and informational RFCs and was standardized by the ITU-T. MGCP grew out of two other protocolsthe Internet Protocol Device Control (IPDC) and the Simple Gateway Control Protocol (SGCP). MGCP separates the functions of call control and media translation into two separate devices:
This chapter describes how MGCP functions and how you implement it using Cisco CallManager as the call agent.
MGCP is a master/slave protocol that allows a call-control device (such as Cisco CallManager) to control and track the state of each voice port on the gateway. CallManager is able to exercise per-port control of connections to the public switched telephone network (PSTN), legacy private branch exchanges (PBX), voice-mail systems, and plain old telephone service (POTS) phones. This allows complete control of the dial plan from Cisco CallManager, which centralizes gateway management and provides scalable IP Telephony deployments.
Two versions of MGCP are in use:
Cisco CallManager supports only version 0.1 as of this writing, but Cisco gateways can use version 1.0 with other call agents.
Many people choose to use MGCP gateways because the configuration is much simpler than other gateway protocols. MGCP has other capabilities that can make it a good choice, such as centralized administration and QSIG facility decoding.
This chapter covers the following topics:
Part I: Voice Gateways and Gatekeepers
Gateways and Gatekeepers
Part II: Gateways
Media Gateway Control Protocol
Session Initiation Protocol
Connecting to the PSTN
Connecting to PBXs
Connecting to an IP WAN
Influencing Path Selection
Configuring Class of Restrictions
SRST and MGCP Gateway Fallback
Using Tcl Scripts and VoiceXML
Part III: Gatekeepers
Part IV: IP-to-IP Gateways
Cisco Multiservice IP-to-IP Gateway
Appendix A. Answers to Chapter-Ending Review Questions