Sidewinder G2 6.1.2 Administration Guide - Glossary of Technical ...

Chapter 9: Configuring Proxies
Notes on selected proxy configurations
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About the H.323 proxy
H.323 is an International Telecommunications Union (ITU) standard that
provides support for audio and video conferencing across a shared medium
such as the Internet. The H.323 proxy provides for safe transfer of packets
between burbs, standard functions such as filtering on source and destination
hosts and burbs, and NAT and redirection. The H.323 proxy is a protocolaware,
application layer proxy that examines H.323 packets for correctness
and adherence to site security policy. In addition to the standard filtering
mentioned above, the H.323 proxy provides a mechanism for allowing or
disallowing certain codecs (audio or video encoding schemes) within the H.323
protocol. (See the H.323 permissions discussion in “Creating proxy rules” on
page 222.)
Microsoft NetMeeting is a popular implementation of the H.323 protocol. The
H.323 proxy enables you to use the audio and video features of data
conferencing products, such as NetMeeting.
Note: The standard data conferencing features, as well as the chat and
application sharing features of NetMeeting are not supported by the H.323 proxy.
To provide support for these features, you must also enable the T.120 proxy. You
must also add the pre-configured NetMeeting proxy rule to the active proxy rule
group. This will ensure that both proxies remain in synchronization with one
another. See “Synchronizing the T.120 and H.323 proxies for use with NetMeeting”
on page 265 for more information.
The H.323 proxy can function between two endpoints (a single client
implementation such as NetMeeting), or between one or more endpoints and a
Multi-point Control Unit (MCU). The MCU enables two or more endpoints to
simultaneously participate in a call. Each endpoint sends its audio and video
signals through the Sidewinder G2 to the MCU. The MCU then combines the
audio signals and selects one or more video signals to return to each endpoint.
Note: The H.323 proxy does not recognize any configuration difference between
an endpoint and an MCU.
At this time, the H.323 proxy will not communicate with an H.323 gatekeeper. A
gatekeeper is an entity, not unlike a Sidewinder G2, which sits between the
source and destination endpoints, and typically provides services such as
authentication, authorization, alias resolution, billing, and call routing. If there is
a gatekeeper between the Sidewinder G2 and the source or destination
endpoint, and the endpoint is configured to use the gatekeeper, the conference
will not be possible.
The H.323 proxy must examine the contents of the protocol packets for
encoded addresses and port numbers. Therefore, any sort of encryption of
H.323 sessions is not possible in conjunction with the proxy. When
implementing the H.323 protocol, you must disable NetMeeting's security
features, or the security features of any other endpoint or MCU you may be
using. Additionally, you must not route H.323 traffic through a VPN.