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P300H P300 Series Modem Installation and Operating Handbook Page 80
O/h use: 1=TS16=XXX 2=TS32b5&6=XXX (YES)
3=TS32b7&8=XXX 4=TS48=XXX
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Change, Tx/Rx, ESC/Aux/BA Define (IBS) ESC/Aux Custom 1
O/h use: 1=TS0b1=XXX 2=TS32b1=XXX
3=TS32b3=XXX 4=TS32b4=XXX
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Change, Tx/Rx, ESC/Aux/BA Define (IBS) ESC/Aux Custom 2
6.6.28 Custom IBS Overhead Allocation
Several of the above paths lead to the following screen where the available overhead can be allocated
between the Aux port (if set to Sync Channel) and the ESC port (if set to Custom). This option is only
available of the `Custom Features` feature is available (standard P300-TCM).
This sophisticated facility allows the operator for example to:
On high rate links specify a low proportion of the overhead to be assigned to the ESC channel (still
enough to provide the require async Baud rate) but then allocate the remaining overhead to the
Aux port configured for a Sync Channel, allowing external access to the rest of the overhead for
example other data or BER testing (internal or external).
When using Custom, IBS, Min overhead, allocate the overhead between ESC & Aux ports. The
overhead will scale to provide the set ESC Baud rate however much of the overhead is assigned
to it, and increase / reduce the total overhead as appropriate. The remainder of the overhead can
be allocated to the Aux channel, again for extra data of BER testing (internal or external). This
effectively allows the sync channel rate to be varied (by changing the ESC rate & overhead ESC
assignment, which the overhead then adjusts to provide).
The screens are as follows:
Each of the `XXX` fields can display the following uses for that part of the overhead, and be toggled
between the different uses by pressing the appropriate numbered key:
--- The overhead locations are unused
ESC Defined for use by the ESC port
Aux Defined for use by Aux port
CAS In use for Channel Associated Signalling
B/A In use for the Backward Alarm
MFW In use for the TS32 Multi Frame Word.
TS16 and TS48 are both bytes of the overhead structure which are free when CAS is not in use, they are
each equivalent to 8/32nd of the total overhead and can be allocated to ESC or Aux.
TS32 bits 5 and 6 (allocated together) and bits 7 and 8 (allocated together) both correspond to 2/32nds
of the overhead. These are normally spare, see note 1, and can be allocated to ESC or Aux.
TS0 bit 1 is 1/32nd of the overhead, and are normally spare again see note 1. This bit can only be
allocated to the ESC.
TS32 bit 1 is 1/32nd of the overhead, and is the bit allocated by INTELSAT for the low rate oversampled
ESC (available on the Aux port if so configured). Spare if the Aux port is not set to INTELSAT mode or
Note 1, can be allocated to ESC or Aux.
TS32 bit 3 is 1/32nd of the overhead and is normally used for the backward alarm, but is spare if Custom
IBS mode is selected, and the backward alarm facility has been disabled. This bit can only be
allocated to the ESC.
TS32 bit 4 is 1/32nd of the overhead and is normally used for the Satellite TS32 Multiframe but is spare
if Custom IBS mode without a TS32 multiframe is selected. This bit can only be allocated to the ESC.