Polycom MGC Administrator, Руководство администратора

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MGC Administrator’s Guide
3-25
Defining ISDN Non-Facility Associated Signaling (NFAS)
Non-Facility Associated Signaling (NFAS) only applies to T1 lines and can
be configured in two different ways, depending on the ISDN network cards
installed in your MCU.
Each T1 span has 23 B channels for transferring audio, video, or data and one
D channel. The D channel acts as a signaling channel, and controls the call
activity.
In systems using NFAS, when you have a Net-2/4/8 card installed in your
system, only one D channel is used. The other spans share the D channel, and
this enables each additional PRI line to use the D channel as a B channel for
audio, video, or data.
The span containing the D channel is called the Master . The remaining spans,
which share this D channel are called Slaves, and the number of B channels
on each Slave line is increased to 24.
The Net-8 card has certain limitations in that you cannot aggregate PRI lines
from another Net-8 card. This means that the maximum number of
Slave
spans that can share a Master span is seven, allowing for eight spans in total.
If you are using a Net-T1 card, several PRI lines on different cards may be
aggregated to create one span. In such a case, one D channel controls the call
activity for all the aggregated PRI lines - the
Master . The remaining D
channels are used to transfer call data (video and audio data), hence
increasing the number of B channels (from 23 to 24 channels for each
Slave
PRI line) that can be used for video conferencing. You can, however,
aggregate
Slave spans from different Net-T1 cards to share with one Master .
Theoretically, you can have up to 10 Net-T1 cards having 19 Slaves sharing
with a Master (20 spans in total). However, it is not practical to have so many
Net-T1 cards connected to an MCU at any given time.