ITU-T Recommendation V.110¶

V.110 is an ITU standard for bit-rate adaptation of low-speed async serial signals to 64 kbit/s ISDN B-channels. It was primarily used in the context of interworking between GSM Circuit Switched Data (CSD) and ISDN.

Synchronous¶

Rate adaptation of synchronous serial signals of 600, 1200, 2400, 4800, 7200, 9600, 12000, 14400, 19200, 24000, 28800 or 38400 bit/s

Frame structure¶

The protocol uses an 80bit (10 byte) frame. The Frame contains a frame sync pattern (similar to e.g. E1 TS0 or TRAU frames) consisting of the first byte and the first bit of every following byte.

Each frame consists of

• 17 bits of above-mentioned frame sync pattern plus:
• 48 D-bits (D1..D48)
• 7 E-bits (E1..E7)
• 8 S/X-bits (S1,S3,S4,S6,S8,S9)

Rate Adaptation Functions¶

RA1¶

The rate-adaptation function RA1 converts from the V-series rates (e.g. 2400bps) to an intermediate rate of 8/16/32/64 kbit/s.

RA2¶

RA2 converts from the RA1 output rate of 8/16/32/64 kbit/s to 64 kbit/s and is actually specified in I.460

Asynchronous¶

Rate adaptation of asynchronous serial signals of 50, 75, 110, 150, 200, 300, 600, 1200, 2400, 3600, 4800, 7200, 9600, 12000, 14400, 19200, 24000, 28800 or 38400 bit/s

Rate Adaptation Functions¶

RA0¶

The RA0 function is only used with asynchronous V-series interfaces. Incoming asynchronous data is padded by the addition of stop elements to fit the nearest channel rate defined by 2 × 600 bit/s. Ther esulting synchronous bit stream is then processed with RA1 and RA2 like in the synchronous serial case.