Mgcp Inspection Overview - Cisco FirePOWER ASA 5500 series Configuration Manual

Chapter 25 Configuring Application Layer Protocol Inspection
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MGCP Inspection Overview

MGCP is a master/slave protocol used to control media gateways from external call control elements
called media gateway controllers or call agents. A media gateway is typically a network element that
provides conversion between the audio signals carried on telephone circuits and data packets carried
over the Internet or over other packet networks. Using NAT and PAT with MGCP lets you support a
large number of devices on an internal network with a limited set of external (global) addresses.
Examples of media gateways are:
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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 arrive from the same address as the
command was sent to. This can happen when multiple call agents are being used in a failover
configuration and the call agent that received the command has passed control to a backup call agent,
which then sends the response.
Figure 25-4
to
OL-10088-01
Verifying and Monitoring MGCP Inspection, page 25-56
Trunking gateways, that interface between the telephone network and a Voice over IP network. Such
gateways typically manage a large number of digital circuits.
Residential gateways, that provide a traditional analog (RJ11) interface to a Voice over IP network.
Examples of residential gateways include cable modem/cable set-top boxes, xDSL devices,
broad-band wireless devices.
Business gateways, that provide a traditional digital PBX interface or an integrated soft PBX
interface to a Voice over IP network.
Using NAT with MGCP
To PSTN
Cisco
PGW 2200
209.165.201.11
Gateway is told
to send its media
MGCP
209.165.200.231
(public address
of the IP Phone)
209.165.200.231
Figure 25-4 illustrates how NAT can be used with MGCP.
H.323
209.165.201.1
GW GW
RTP to 209.165.201.1
from 209.165.200.231
Cisco Security Appliance Command Line Configuration Guide
M
Cisco
M
CallManager
M
209.165.201.10
209.165.200.231
SCCP
RTP to 10.0.0.76
from 209.165.200.231
IP IP IP
10.0.0.76
Branch offices
MGCP Inspection
25-53