User`s guide

Dialogic
®
System Release 6.0 PCI for Windows
®
Release Update, Rev 62 — January 30, 2008 213
Dialogic Corporation
1.52 Early Media
With the Service Update, early media when using H.323 on Dialogic
®
DM/IP Boards is
now supported.
1.52.1 Enabling Early Media
To enable early media on a board level, add the following PrmEarlyMedia parameter
content in the CONFIG file that corresponds to the PCD file in use on your board:
[0x40]
SetParm=0x400a,1 ! PrmEarlyMedia (0=Disabled, 1=Enabled)
After the parameter is added, generate an updated FCD file and start system services on
the board. See the Dialogic
®
DM3 Architecture PCI Products on Windows
®
Configuration
Guide for more information on CONFIG files, PCD files, and FCD files.
Note: Early media support can only be enabled/disabled at the board level via the CONFIG file.
Early media support cannot be set at runtime and cannot be set at the channel level.
1.52.2 Early Media Call Setup Scenarios in Global Call
When using IP technology, the establishment of RTP media streaming is normally one of
the final steps in establishing and connecting a call. This is in contrast to the public
switched telephone network (PSTN), where call progress signaling is commonly provided
to the calling party via audible, in-band call progress tones, such as ringback, busy signal,
and SIT tones. When implementing a VoIP gateway, it is often imperative to initiate media
(RTP) streaming from the local endpoint to the calling party before the call is connected.
This capability is commonly referred to as early media.
The Dialogic
®
Global Call IP call control library automatically enables media streaming at
the earliest possible point in the pre-connect process. This is generally the earliest point at
which the remote endpoint provides the remote RTP/RTCP transport addresses and
media capabilities. The precise point at which media can be enabled is dependant on a
large number of factors, and the following figures illustrate some common best-case
scenarios. Each figure illustrates the Global Call library’s behavior from the application’s
perspective, either in the calling party role or in the called party role.
Note that in some cases it is possible to enable streaming in one direction significantly
earlier than in the other direction. To take full advantage of this fact, the Global Call IP call
control library initially enables a temporary unidirectional connection, then modifies the
connection to be full duplex as soon as that is possible. Note that this capability is only
supported on Dialogic
®
IPT Boards, however.
1.52.2.1 H.323 FastStart Mode
The library’s default for H.323 operation enables the Global Call FastStart mode, in which
the channel capability information is embedded in a fastStart element (indicated in the