RADVision SCOPIA 400, User Manual

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96 SCOPIA 400/1000 Gateway User Guide
Configuring Gateway Settings
Endpoints on the ISDN network usually support the G.711 and G.728 codecs.
Endpoints on IP networks support G.711 and G.723.1 codecs. By performing
transcoding between these audio protocols, the Gateway can support
communication between endpoints with codecs that are incompatible with each
other.
Audio transcoding can also optimize the audio bandwidth usage either on the IP
network (G.723.1
< >
G.711) or on the ISDN network (G.728
< >
G.711).
Transcoding is particularly useful for ISDN codecs, where bandwidth can be
limited to 128 Kbps for a video call. For example, when transcoding between
G.728 and
G.711 takes place, the audio bandwidth usage is compressed to 16
Kbps. This provides an additional 40 Kbps of bandwidth to the existing video bit
rate on the ISDN network, contributing to improved video quality.
Note The Gateway automatically performs A-Law G.711-to-µ-Law G.711
translation between the IP and ISDN sides if needed.
You can configure the Gateway to prioritize the transcoding, giving preference to
a particular codec that is applied to calls, thus optimizing the resource allocation
utilized by each call.
A
BOUT
T.120 D
ATA
C
OLLABORATION
S
UPPORT
The Gateway provides full end-to-end support for T.120 data collaboration
sessions, provided all terminals support the T.120 standard in their conferencing
applications. In video calls with data transfer, the Gateway accepts whatever
bandwidth the ISDN connection defines for the data and dynamically adjusts the
outgoing bandwidth used for data by using the MLP, HMLP and VarMLP
formats.
If transcoding or T.120 capabilities are required, the Gateway has to reserve
resources for these. The Gateway can differentiate between those calls that
support T.120 and those that do not. When receiving calls, the Gateway can
check whether you are reserving resources for transcoding or for T.120
capabilities.
The Gateway enables the user to determine the trade-off between the number of
non-T.120 calls that the Gateway can support and the number of calls sent with
T.120 capabilities. The total number of calls that the Gateway can support is
accordingly reduced by this reallocation of resources.
The H.320 standard defines space allocation within a call. The H.320 standard
defines the logic for bit rate allocation among audio, video and data channels in
the context of the overall bit rate of a call. If you work with T.120, reallocation of
bandwidth is always at the expense of available video resources. The