4 The RA0 Function

3GPP44.021Rate adaption on the Mobile Station - Base Station System (MS - BSS) interfaceTS

4.1 Asynchronous-to-Synchronous Conversion (RA0)

The RA0 Function is only used with asynchronous interfaces. Incoming asynchronous data is padded by the addition of stop elements to fit the same or nearest higher synchronous rate defined by 2 to the power n (where n 6) times 600 bit/s, 14,4 kbit/s or 28,8 kbit/s. Thus the 300 bit/s user data signalling rate shall be adapted to a synchronous 600 bit/s stream. The resultant synchronous stream is fed to RA1′ or Split/Combine Function. The RA0 used in PLMN is not identical to that described in ITU-T Recommendation V.110 which converts 14,4 and 28,8 kbit/s user rates to 19,2 and 38,4 kbit/s, respectively.

Asynchronous user rate

Synchronous user rate

 0.6 kbit/s

0.6 kbit/s

1,2 kbit/s

1,2 kbit/s

2,4 kbit/s

2,4 kbit/s

4,8 kbit/s

4,8 kbit/s

9,6 kbit/s

9,6 kbit/s

14,4 kbit/s

14,4 kbit/s

19,2 kbit/s

19,2 kbit/s

28,8 kbit/s

28,8 kbit/s

38,4 kbit/s

38,4 kbit/s

4.2 Break signal

The RA0 shall detect and transmit the break signal in the following fashion:

If the converter detects 2M to 2M+3 bits, all of start polarity, where M is the number of bits per character in the selected format including start and stops bits, the converter shall transmit 2M+3 bits of start polarity.

If the converter detects more than 2M+3 bits all of start polarity, the converter shall transmit all these bits as start polarity.

The 2M+3 or more bits of start polarity received from the transmitting sides shall be output to the receiving terminal.

The terminal shall transmit on circuit 103 at least 2M bits stop polarity after the start polarity break signal before sending further data character. The converter shall then regain character synchronism from the following stop to start transition.

4.3 Overspeed/Underspeed

A RA0 shall insert additional stop elements when its associated terminal is transmitting with a lower than nominal character rate. If the terminal is transmitting characters with an overspeed of up to 1 %, the asynchronous-to-synchronous converter may delete stop elements as often as is necessary to a maximum of one for every eight characters at 1 % overspeed. The converter on the receiving side shall detect the deleted stop elements and reinsert them in the received data stream (circuit 104).

The realization of overspeed handling, as described above, at the interface to the associated terminal is implementation dependent. Possible implementations are e.g. the reduction of the length of the stop elements according to V.110 [9] or increased data rates between the TA and terminal.

4.4 Parity Bits

Possible parity bits included in the user data are considered as data bits by the RA0 function.

4.5 Flow Control

Where applicable, this function is as specified in the relevant terminal adaptation function Specification (see 3GPP TS 07 series).