MGCP
MGCP is a voice protocol that runs in conjunction with Signaling System 7 (SS7), an
interoffice signaling protocol for circuit-switched services, and an IP protocol, such as H.323
or SIP, to bridge circuit-switched and packet networks. MGCP separates the signaling and
call control from the media gateway. A media gateway is typically a network element that
provides conversion between the audio signals carried on telephone circuits and the data
packets carried over the Internet or over other packet networks, such as trunking gateways,
residential gateways, and business gateways.
Application inspection for MGCP is disabled by default. To use MGCP, you typically need
to configure at least two ports: one on which the gateway receives commands and one for the
ort on which the call agent receives commands. Normally, a call agent will send commands
to port 2427, whereas a gateway will send commands to port 2727.
To enable MGCP application inspection for call agents and gateways using the default ports,
use the following command in global-configuration mode:
mgcp-map [map_name]
This map will then be applied to a policy-map to enable inspection using the inspect mgcp
command.
MGCP messages are transmitted over UDP. A response is sent back to the source address (IP
address and UDP port number) of the command, but the response may not be sent from the
same address to which the command was sent. Multiple MGCP call agents can be supported
by the Security Appliance.
The call-agent command specifies a group of call agents that can manage one or more
gateways. Assigning several call agents to a group for a specific gateway will allow any of the
assigned call agents to send a response. The gateway command is used to specify which group
of call agents is managing a particular gateway. These commands are applied in the mgcpmap
configuration mode:
call-agent ip-address group-id
gateway ip-address group-id