Media Gateway Control Protocol

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:

• The voice gateway handles media translation.
• A call agent handles call control.

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:

• Version 0.1 This is the original version of MGCP that you are probably familiar with because it has been used for years on Cisco gateways and CallManagers. 0.1 is the default version in Cisco gateways and CallManagers as of the writing of this book.
• MGCP version 1.0 This was first defined in informational RFC 2705, which was obsoleted by RFC 3435. RFC 2705 outlined some changes based on experience implementing version 0.1 of the protocol. RFC 3435 is an enhancement of MGCP that contains some new events and features, allows IPv6 addresses in endpoint names, corrects some known issues, and provides more options for existing operations.

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:

• Introduction to MGCP
• MGCP Operation
• Call Flow with MGCP
• Pros and Cons of MGCP
• Dial Plan Considerations
• Implementing MGCP Gateways
• Securing MGCP Gateways
• Troubleshooting Tools