Practical VoIP Using VOCAL

Chapter 15. MGCP Translator

Media Gateway Control Protocol (MGCP, RFC 2705) is a master/slave protocol in which the endpoints, known as gateways, are slaves of the gateway controllers , the call agents (CAs). The CAs maintain statefulness with all registered gateways at all times, telling them to give dial tone to analog phone sets, interpreting the dual-tone multifrequency (DTMF) tones sent through the gateways by the phones, and enabling all features and functionality.

One of our original designs of VOCAL was based on MGCP, and during its implementation, we had to write our own stack because there was no open source MGCP stack available anywhere else. When we realized that SIP served our needs better than MGCP did, for reasons spelled out in Chapter 1, we took our MGCP Call Agent design and converted it into an MGCP/SIP translator. Our work on the MGCP stack has continued, and the mailing list is highly active, with most of the questions (and answers!) coming from members of the community outside of our core development group.

Media Gateway Control Protocol

The MGCP standard, derived from a combination of the two draft protocols, Simple Gateway Control Protocol (SGCP) and IP Device Control (IPDC) , stipulates a call control architecture that puts network devices, called call agents, in control of the endpoints, called gateways. Like SIP and H.323, there are dedicated MGCP phones. There are also MGCP gateways that are dedicated hardware units that support large numbers of ...