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P300H P300 Series Modem Installation and Operating Handbook Page 127
the available overhead not already in use by the ESC channel. This can
provide a channel of up to 4.4% of the main data rate.
If the `Custom Features` feature is available (standard on P300-TCM), then
the overhead may be user assigned between the ESC & Aux channels,
allowing the desired Async ESC rate to be achieved for distant end M&C (but
not massively exceeded), leaving any spare overhead to maximise the Aux
channel data rate for BER testing.
IDR IDR mode is only available if the IDR Option is fitted (standard on P300-IDR
and above). The ESC channel is the 8kbps synchronous ESC channel
standard on IDR Services (which may also be used for Asynchronous ESC
data if the Async ESC feature is available).
The Aux channel may be selected to be either 32kbps (in place of one
32kbps ADPCM audio ESC channel) or 64kbps (in place of both audio
ESC's). This provides a very useful channel rate for BER testing !
Custom Framing Custom Framing mode is only available if the `Custom Features` feature is
available (standard on P300-TCM). Custom framing is based on either IBS
or IDR formats and custom framing provides the following advantages:
Based on IBS: A variable overhead may be added allowing both ESC & Aux
channels to be scaled to virtually any rate. This is achieved by setting the ESC
channel to the required Async ESC Baud rate, and changing the split of the
allocation of the overhead between ESC & Aux channels. The total overhead
then scales to provide the required ESC Baud rate in whatever part of the
overhead you have assigned to it, with the rest of the scaled overhead for the
Aux channel.
Based on IDR: As well as the features described above in standard IDR, it is
possible to reduce the normal 96kbps overhead (two audio ESC's) to 64kbps
(one audio ESC or 32kbps Aux data) or 32kbps (no audio ESC's & no Aux
data). It may also be configured to use 16kbps ADPCM instead of 32kbps,
allowing the full IDR features (two audio ESC) to be accommodated in
64kbps overhead. More interestingly using the normal IDR overhead of
96kbps together with 16kbps ADPCM for the audio ESC's, it may provide all
the normal IDR features, but with the second 32kbps audio slot free to
configure as a 32kbps Aux channel for continuous BER testing.