MGCP
Media Gateway Control Protocol (MGCP) was published by the Internet Engineering Task Force (IETF). From our earlier discussion of H.323 and SIP; it is noticeable that media gateways have signaling intelligence. For example, MG sends signals to MGC like “Admission Request” in H.323 or “180 ringing” in SIP.
When an MGC and MG communicate with MGCP protocol, then MG acts like a slave, means it does not send any signals to control MGC; it only controlled by signals from MGC. So, in MGCP the power of call control resides in soft switch or MGC.
MGCP is a master-slave protocol where media gateway controller or softswitch is the master and MG is the slave. MG only executes commands sent by the softswitch. In MGCP protocol, the media gateway controller or softswitch is referred as call agent. A call agent uses nine commands to direct gateways and their operational behavior.
The MGCP protocol defines nine commands for controlling endpoints and connections.
A call agent uses control commands or messages to direct its gateways and their operational behavior. Gateways use the following control commands in responding to requests from a call agent and notifying the call agent of events and abnormal behavior:
- EPCF Endpoint Configuration ----- Call agent issues this command to inform gateway the coding type of the voice expected on the end point of the gateway.
- RQNT NotificationRequest ------- -Call agent instructs the gateway to watch for the situation of the endpoint or called party.
- NTFY Notify ---------- Gateway issues this command to notify call agents in response to notification request.
- CRCX CreateConnection --------- Call agent instructs the gateway to create connection with the endpoint or called party.
- MDCX ModifyConnection ------- Instructs the gateway to update its connection parameters for a previously established connection. The call agent issues the command.
- AUEPR AuditEndpoint ------------ Call agent requests the gateway to audit the status of an endpoint.
- AUCX Audit Connection ----------- Call agent issues this command to inform gateway to collect the parameters of the connection.
- DLCX DeleteConnection --------- The call agent or the gateway can issue the command while caller or called party ends the call to advise each other that the connection can no longer be sustained.
- RSIP RestartInProgress ----------- Gateway notifies the call agent that the gateway and its endpoints are removed from service or placed back in service.
A media gateway is capable of corresponding MGCP commands from numerous call agents simultaneously. All three protocols discuss here features similar performance which is to enable communication between media gateways and media gateway controller or softswitch .Whether to use H.323, SIP or MGCP is a personal decision who be in possession of the gateways or gateway controller.