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P300H P300 Series Modem Installation and Operating Handbook Page 137
2048K IBS mode: [?]
1=Normal (6.7% overhead) 2=G.732 (0% overhead)
Change, Tx/Rx, Baseband, Continuous, 2048k G.732 Menu
Channel Assoc Sig (CAS) in TS16: [?]
1=Normal (No CAS) 2=CAS
Change, Tx/Rx, Baseband, Cont', 2048k IBS, G.732 CAS Menu
7.2 IBS/SMS OPERATION WITH 2048KBPS CONTINUOUS DATA
7.2.1 Change, Tx/Rx, Baseband, Continuous, 2048k G.732 Menu (IBS)
2048kbps IBS/SMS operation is a special case, in which there are two modes of operation. These modes
are confusingly referred to as 1920/1984kbps and 2048kbps mode in the IBS/SMS service definitions, but
both operate with a 2048kbps terrestrial data rate !
NORMAL The content of the 2048kbps data is ignored (ie it can be unframed), and the
normal 6.7% overhead is added bringing the rate to 2184.53kbps. This is referred
to as 2048kbps operation in the service definitions. If NORMAL is selected then
the dialogue returns to that covered in the main section of the handbook.
G.732 The data is G.732 formatted data, ie it already contains a terrestrial G.732 frame
comprising of 32 Timeslots, TS0 to TS31. Although the aggregate data is
2048kbps, as only 30 or 31 timeslots are available for data (TS0 is framing and
TS16 may be signalling) the user data rate is 1920 or 1984kbps (30 or 31 x
64kbps). This is referred to as 1920kbps or 1984kbps operation in the service
definitions, but the data rate at the terrestrial port is actually 2048kbps !
When selected instead of the unit inserting extra IBS/SMS framing on to the data
(ie +6.7%), it uses the similar G.732 framing already present (+0%). Some
locations in the G.732 framing are changed over satellite (such as TS0 Odd bit
4 which is used by the IBS/SMS TS32 multiframe word) and so it is not entirely
transparent to all the overhead. Parts of the overhead unused for frame
alignment, and also not `borrowed` by IBS/SMS features may be set to be either
Transparent or Fixed High. This is controlled under Change, User-Opt,
Operation, Terr/Sat, G.732 Spares.
If G.732 mode is selected the operator is then prompted with:
Channel Associated Signalling (CAS) is described in para 10.2 "Signalling Systems Introduction: CCS, CAS
& RBS" on page 210 if required.
NORMAL
(NO CAS) TS16 does not contain CAS (ie a terrestrial CAS multiframe and `abcd` signalling
nibbles for each timeslot). It is treated as a normal data timeslot, and this
corresponds to modes defined as 1984kbps in the service definitions.
CAS This feature is only available if the Extended D/I feature is available (standard on
P300-TCM). TS16 contains CAS and by implication a terrestrial multiframe in
order to carry the CAS (this corresponds to modes defined as 1920kbps in the
service definitions). If selected, the terrestrial multiframe will be acquired, and
CAS removed from/replaced into the Drop/Insert bearer. The CAS will be
conveyed transparently from end to end of the link within IBS (or Custom IBS)
overheads.