Paradise P300 specifications Appendix F Framing and DROP/INSERT Overview IBS/SMS Framing

APPENDIX F: FRAMING AND DROP/INSERT OVERVIEW

IBS/SMS FRAMING

IBS/SMS Service Features

The INTELSAT definition of IBS framing (IESS 309) is intentionally very similar to Eutelsats SMS framing (EESS 501 "SMS QPSK/FDMA System Specification"), as they are both designed to allow common equipment to provide for both services. From here on we will refer to IBS framing, but the text applies equally to SMS framing

Standard Features (specified in IBS/SMS definitions)

The addition of standard IBS framing increases the data rate by exactly 1/15th (approx 6.7%). IBS framing is added to provide the following extra features compared to `closed network` links:

A Synchronous Scrambler, which replaces the self synchronising (V.35) scrambler used in most closed network links. The closed network V.35 scrambler outputs 3 errors for every error received, and so increases the error rate by a factor of 3. The IBS/SMS synchronous scrambler does not multiply errors, and so give a factor of three BER performance increase over the V.35 scrambler. A Backward Alarm facility, which raises a local deferred alarm if the distant end modem cannot receive data transmitted from this station (ie a possible Tx problem this end).

A Low Rate Oversampled async ESC Channel (1/2000th the data rate), this is available on the Aux port of the modem. This results in async rates of <50 Baud at 64kbps and 110 Baud at >256kbps.

A TS32 Multiframe Sequence to allow the transmission of satellite encryption control vectors, and three 8 bit carrier ID’s (referred to as Station, Channel, and Spare ID).

Overhead channels to convey Channel Associated Signalling (CAS) corresponding to an extra

'2kbps per 64kbps transmitted by use of a separate CAS Multiframe sequence (in TS16/48). Timeslot ID Maintenance: which is the facility to maintain the identity of individual data streams when multiplexed together into one aggregate rate carrier (eg two independent 64kbps circuits in one 128kbps carrier).

Additional Features (Paradise products)

In addition to the basic INTELSAT definition above, the P300 Modems provide the following additional features in IBS/SMS mode:

A high rate ESC channel carried in spare parts of the overhead. This allows up to 68% (22/32nd) of the overhead to be used for ESC providing a 2400 Baud ESC with a 64kbps carrier, and

'proportionally higher ESC rates with higher data rate carriers.

In addition to the INTELSAT low rate oversampled async ESC Channel (on the shared ESC/Aux port), The P300 when fitted with the IDR option (standard on P300-IDR and above) also provides a clock so the port may be used as a synchronous Aux channel. In addition the overhead usage can be varied from the one bit per frame (TS32 bit 1) defined by INTELSAT, up to 21 bits per frame, providing a synchronous Aux channel at up to 4.3% of the main data rate. This may be used for example with external or internal BER testers to provide a continuous measurement of the live BER.

IBS/SMS Definition

Frame Format

IBS framing is a derivative of the framing used on 2048kbps PCM bearers within Europe specified in ITU- G.732. G.732 specifies a frame of 32 timeslots (each timeslot is 8 bits of data) and the timeslots are labelled TS0 - TS31. TS0 and TS16 are reserved for special functions, leaving the remaining 30 timeslots available for data, ie 30 data timeslots with 2 overhead timeslots, a ratio of 32/30 or an increase of 1/15th. G.732 uses an awkward definition of having even & odd numbered frames with TS0 having different functions in even & odd frames. Thankfully the IBS specification parted from the G.732 definition at this point and instead of having even & odd frames of 32 timeslots, it defined one longer frame equivalent to an even then an odd G.732 frame. An IBS frame therefore has 64 timeslots, with special functions for TS0,

P300H P300 Series Modem Installation and Operating Handbook Page 207