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Cisco Security Appliance Command Line Configuration Guide

OL-6721-01

Chapter 21 Applying Application Layer Protocol Inspection

Managing H.323 Inspection

seq_tpdu_up: 0 seq_tpdu_down: 0

signal_sequence: 0

upstream_signal_flow: 0 upstream_data_flow: 0

downstream_signal_flow: 0 downstream_data_flow: 0

RAupdate_flow: 0

The PDP context is identified by the tunnel ID, which is a combination of the values for IMSI and

NSAPI. A GTP tunnel is defined by two associated PDP contexts in different GSN nodes and is

identified with a Tunnel ID. A GTP tunnel is necessary to forward packets between an external packet

data network and a MS user.

You can use the vertical bar (|) to filter the display, as in the following example:

hostname# show service-policy gtp statistics | grep gsn

Managing H.323 Inspection

This section describes how to enable H.323 application inspection and change the default port

configuration. This section includes the following topics:

• H.323 Inspection Overview, page 21-24

• How H.323 Works, page 21-24

• Limitations and Restrictions, page 21-25

• Enabling and Configuring H.323 Inspection, page 21-26

• Configuring H.225 Timeout Values, page 21-28

• Verifying and Monitoring H.323 Inspection, page 21-28

H.323 Inspection Overview

The inspect h323 command provides support for H.323 compliant applications such as Cisco

CallManager and VocalTec Gatekeeper. H.323 is a suite of protocols defined by the International

Telecommunication Union for multimedia conferences over LANs. The security appliance supports

H.323 through Version 4, including H.323 v3 feature Multiple Calls on One Call Signaling Channel.

With H323 inspection enabled, the security appliance supports multiple calls on the same call signaling

channel, a feature introduced with H.323 Version 3. This feature reduces call setup time and reduces the

use of ports on the security appliance.

The two major functions of H.323 inspection are as follows:

• NAT the necessary embedded IPv4 addresses in the H.225 and H.245 messages. Because H.323

messages are encoded in PER encoding format, the security appliance uses an ASN.1 decoder to

decode the H.323 messages.

• Dynamically allocate the negotiated H.245 and RTP/RTCP connections.

How H.323 Works

The H.323 collection of protocols collectively may use up to two TCP connection and four to six UDP

connections. FastConnect uses only one TCP connection, and RAS uses a single UDP connection for

registration, admissions, and status.

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