Multiple Calls On One Call Signalling Connection; Viewing Connection Status; Technical Background - Cisco Catalyst 6500 Series Configuration Manual

Detailed Information About Inspection Engines

Multiple Calls on One Call Signalling Connection

Allowing multiple calls on the same call signaling channel reduces call setup time and reduces the use
of ports on the FWSM.
To configure how long the H.225 call signaling channel stays open, enter the following command:
FWSM/contexta(config)# timeout h225 hh [: mm [: ss ]]
The default is 1 hour.
For example, to keep the channel open without any timeout, set the timer to 0 by entering the following
command:
timeout h225 00:00:00
To disable the timer and close the TCP connection immediately after all calls are cleared, set the timeout
value to 1 second, as follows:
timeout h225 00:00:01

Viewing Connection Status

To display the status of H.225 connections, enter the following command:
FWSM/contexta(config)# show conn state h225

Technical Background

The H.323 collection of protocols collectively can use up to two TCP connections and four to six UDP
connections. FastConnect uses only one TCP connection, and RAS uses a single UDP connection for
registration, admissions, and status.
An H.323 client might initially establish a TCP connection to an H.323 server using TCP port 1720 to
request Q.931 call setup. As part of the call setup process, the H.323 terminal supplies a port number to
the client to use for an H.245 TCP connection.
In environments where an H.323 gatekeeper is in use, the initial packet is transmitted using UDP.
Note
The H.323 inspection engine monitors the Q.931 TCP connection to determine the H.245 port number.
If the H.323 terminals are not using FastConnect, the FWSM dynamically allocates the H.245
connection based on the inspection of the H.225 messages.
Within each H.245 message, the H.323 endpoints exchange port numbers that are used for subsequent
UDP data streams. The H.323 inspection engine inspects the H.245 messages to identify these ports and
dynamically creates connections for the media exchange. Real-Time Transport Protocol (RTP) uses the
negotiated port number, while RTP Control Protocol (RTCP) uses the next higher port number.
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide
13-8
Chapter 13 Configuring Application Protocol Inspection
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