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Managing Calls Using IP Telephony
November 2009 226
Understanding H.323 Functionality
This Brooktrout SDK supports the H.323 protocol (version 4 and
Annex D), providing end point functionality only. Our current H.323
implementation does not operate as a gateway or H.323 Gatekeeper,
but you can configure your application to communicate with a
gateway or H.323 Gatekeeper.
The H.323 implementation supports both a primary and alternate
H.323 Gatekeeper. When an application is configured to
communicate with a Gatekeeper, all the RAS messages exchanged
with the Gatekeeper are done inside of the H.323 implementation
without requiring the application to get involved. The H.323
implementation registers the end points transport address and alias
information with the Gatekeeper and resolves destination alias
addresses with the Gatekeeper. If the application turns on alternate
Gatekeeper support and the primary Gatekeeper becomes
unavailable, the H.323 implementation automatically falls back to
an alternate Gatekeeper without involving the application.
Multiple Protocols SIP and H.323 can co-exist in the same system. You can configure a
single hardware module or SR140 module to support either SIP or
H.323, selecting which protocol stack to use on a per-module basis.
The protocols can operate simultaneously on different modules.
Different modules in the same system can support different IP call
control stacks, but the SR140 Fax Software implementation only
supports one IP stack at a time.
Supporting Media The H.323 implementation supports T.38 (Fax Media) and RTP
media over UDP (H.323 Annex D).
The H.323 implementation supports the ability to negotiate a pseudo
G.711 media session with the intent of renegotiating to a T.38 media
session even when RTP prompt playback/record capability is not
desired.
This functionality is required to interoperate with certain supported
equipment. Media renegotiation to T.38 is also supported after a call
is setup.
The H.323 implementation supports basic call control functionality,
specifically outbound call setup and teardown and inbound call
detection, answering, and teardown. See the sections on Outgoing IP
Calls on page 217 and Incoming IP Calls on page 218 for information
about the functions that support these activities.