Call Agent

One or more call agents (also called media gateway controllers) are supported in MGCP to enhance reliability in the VoIP network. The following two examples are of call agent names:

Several network addresses can be associated under one domain name in the Domain Name System (DNS). By keeping track of the time to live (TTL) of DNS query/response data and implementing retransmission using other alternative network addresses, switchover and failover is achieved in MGCP.

The concept of a notified entity is essential in MGCP. The notified entity for an endpoint is the call agent currently controlling that endpoint. An endpoint should send any MGCP command to its notified entity. However, different call agents might send MGCP commands to this endpoint.

The notified entity is set to a provisioned value upon startup, but can be changed by a call agent through the use of the NotifiedEntity parameter contained in an MGCP message. If the notified entity for an endpoint is empty or has not been set explicitly, its value defaults to the source address of the last successful non-audit MGCP command received for that endpoint.

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