Definition
Defined by IETF, MGCP is a protocol that specifies a call control mechanism in which call control and service bearing are separated. Call control is independent of the media gateway (MG) and is processed by the MGC. Therefore, MGCP is actually a master-slave protocol. The MG establishes various service connections under the control of the MGC.MGCP provides the following commands:
- NotificationRequest: The MGC sends this command to request the MG to detect a specified event, such as an offhook event or onhook event. After detecting such an event, the MG notifies the MGC. Through this command, the MGC can also instruct the MG to play signal tones, such as the dial tone and busy tone.
- Notify: After the MG detects the specified event as instructed by the MGC, the MG sends this command to notify the MGC of the detected event.
- CreateConnection: The MGC sends this command to instruct the MG to create a media connection. The command contains the instruction or suggestion on the bearing parameters and connection parameters.
- ModifyConnection: The MGC sends this command to instruct the MG to modify the bearing parameters and connection parameters of an established media connection.
- DeleteConnection: The MGC sends this command to instruct the MG to delete an established media connection. The MG can also voluntarily delete a connection. This means that, when the MG discovers that system resources are insufficient or the system is faulty, the MG can delete the connection and at the same time send this command to notify the MGC. Therefore, this command is bi-directionally available between the MGC and the MG.
- AuditEndpoint and AuditConnection: The MGC sends the commands to check the status of a specified endpoint and connection.
- RestartInProgress: The MG sends this command to notify the MGC that the MG or a certain endpoint managed by the MG is not available or is becoming available. This command is usually triggered by a system fault or restart.
MGCP also provides the following features:
- Encoding in the text format
- Adopting the Session Description Protocol (SDP) to describe the connection parameters of the media stream
- Introducing the concept of event package
- Adopting the wildcard to describe endpoints and events
Purpose
MGCP solves the internal problems of MG and media devices, thus realizing an open distributed system which is formed by the MG and media devices.In the MGCP mechanism, the MG and media devices are separated into two logically independent parties, the MG and the MGC, which communicate through MGCP. The MG processes the user plane, and the MGC processes the control plane and controls the actions of the MG. In other words, the MG acts under the control of the MGC.
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