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P300H P300 Series Modem Installation and Operating Handbook Page 58
Select bearer: [?]
1=G.732 2=T1-D4 3=T1-ESF
Change, Tx/Rx, Baseband, Drop/Insert, Bearer Menu
Drop TS: 1, 3-5, 17-15, 23
Toggle: ??-?? (YES)
Help
Change, Tx/Rx, Baseband, Drop/Insert, Timeslot Menu
Finally for data rate of 48kbps or 56 kbps, in IBS modes the Modem automatically activates the X.50 `bit
stuffing` to convert to/from 64kbps (as defined for IBS operation). However in Custom IBS modes the
operator is offered the option of not using this facility. In Normal IBS modes then with 48 or 56kbps data the
satellite rate is 64kbps x 16/15, but in custom modes this can be reduced to just 48 or 56 kbps x 16/15 (or
less if Minimum overhead mode is selected).
6.6.5 Change, Tx/Rx, Baseband, DROP/INSERT Menu
These screens are only shown if the Drop/Insert feature is available, standard on the P300-IBS and above.
Drop/Insert selects the baseband mode where the Tx data is removed (dropped) from a T1 or E1 PCM
bearer, and the Rx data is placed (inserted) into a similar bearer. The modem is capable of operating in
Drop/Insert with any terrestrial interface, although in practise it is rarely used without a G.703 (DS1)
interface.
The first step is to specify to the modem which format of PCM bearer it is working with:
Following the bearer type selection, the timeslots from which the Tx data is to be Dropped (or in the Rx case
where the Rx data is to be inserted) must be specified:
The screen above shows groups of eight timeslots selected: 1, 3, 4, 5, 17, 16, 15, 23, although any
combination is possible. The selection system works by toggling timeslots or groups of timeslots into or out
of the selection:
In G.732 mode timeslots are labelled 0 - 31. In T1-D4 and T1-ESF modes timeslots are labelled 1 -
24.
Timeslots already in the selection are toggled out from any position of the selection when the
timeslot number is entered.
Timeslots not already in the selection are toggled on, and placed on the end of the selection.
Enter any single timeslot as a single or dual digit, eg 0, 5, 05, 23, 31
Enter groups of timeslots as two pairs eg 02-5 (two through five), 11-17, 12-2
For those familiar with other manufacturers equipment which use the term `mapping` (to relate the
terrestrial timeslot selection to the order in the satellite frame). The terrestrial timeslots are
`mapped` into the satellite frame in the order listed on this timeslot selection screen. If you want
to revise the mapping, simply re-order the timeslots on this screen. For the example shown above
the mapping would be as follows:
Terrestrial:134517161523
to Satellite:12345678
st nd rd th th th th th
NOTE: If the Extended D/I feature is available (standard on P300-TCM) timeslots can be arbitrarily re-
ordered, and so group selections may be down as well as up eg 11-17 means send in order 11,12,13...17,
whereas 17-11 means send in order 17, 16, 15, ...11
NOTE: In G.732 mode whilst TS0 can be dropped, it must always be replaced in TS0 at the distant end
(otherwise there is the possibility of frame alignment ambiguity).