Cisco ASA 5505 - Manual (Page 921)

44-11
Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter 44 Configuring Inspection for Voice and Video Protocols
MGCP Inspection
MGCP Inspection
This section describes MGCP application inspection. This section includes the following topics:
• MGCP Inspection Overview, page 44-11
• Configuring an MGCP Inspection Policy Map for Additional Inspection Control, page 44-13
• Configuring MGCP Timeout Values, page 44-14
• Verifying and Monitoring MGCP Inspection, page 44-14
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:
• 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.
Note To avoid policy failure when upgrading from ASA version 7.1, all layer 7 and layer 3 policies must have
distinct names. For instance, a previously configured policy map with the same name as a previously
configured MGCP map must be changed before the upgrade.
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 44-1 illustrates how NAT can be used with MGCP.