Media gateway protocol is used for interconnecting two networks, for us the IP and the PSTN networks. The Media Gateway Control Protocol (MGCP), developed by IETF, and Megaco, developed by IETF and ITU-T (recommendation H.248), are two protocols used by the media gateways.
MGCP defines a gateway that focuses on the audio signal translation function, and a call agent that handles the call signaling and call processing functions. As a consequence, the Call Agent implements the signaling layers of the H.323 standard.
In Megaco/H.248 there are two components: terminations and contexts. Terminations represent streams entering or leaving the media gateway (for example, analog telephone lines, RTP streams, or MP3 streams). Terminations have properties, such as the maximum size of a jitter buffer, which can be inspected and modified by the call agent (media gateway controller, sometimes called a softswitch). Terminations may be placed into contexts, which are defined as when two or more termination streams are mixed and connected together.
Requirements for Media Gateway Control :
- RFC 2895
- Media Gateway Control Protocol Architecture and Requirements
- The creation, modification and deletion of media streams
- Including the capability to negotiate the media formats
- The specification of the transformations applied to media streams
- Request the MG to report the occurrence of specified events within the media streams, and the corresponding actions
- Request the MG to apply tones or announcements
- The establishment of media streams according to certain QoS requirements
- Reporting QoS and billing/accounting statistics from an MG to an MGC
- The management of associations between an MG and an MGC
- In the case of failure of a primary MGC A flexible and scalable architecture in which an MGC can control different MGs
- Facilitate the independent upgrade of MGs and MGCs
- The first protocol is MGCP
- RFC 2705, informational
- To be succeeded by MEGACO/H.248
- Has be included in several product developments