Jelaskan Forward traffic channels dari IS-95 dalam bahasa sunda

The Walsh space not dedicated to broadcast channels on the BTS sector is available for traffic channels. These channels carry the individual voice and data calls supported by IS-95. Like the paging channel, traffic channels have a frame time of 20ms.

Since voice and user data are intermittent, the traffic channels support variable-rate operation. Every 20 ms frame may be transmitted at a different rate, as determined by the service in use (voice or data). P_REV=1 and P_REV=2 supported rate set 1, providing a rate of 1200, 2400, 4800, or 9600 bit/s. P_REV=3 and beyond also provided rate set 2, yielding rates of 1800, 3600, 7200, or 14400 bit/s.

For voice calls, the traffic channel carries frames of vocoder data. A number of different vocoders are defined under IS-95, the éarlier of which were limited to rate set 1, and were responsible for some user complaints of poor voice quality. More sophisticated vocoders, taking advantage of modérn DSPs and rate set 2, remedied the voice quality situation and are still in wide use in 2005.

The mobile receiving a variable-rate traffic frame does not know the rate at which the frame was transmitted. Typically, the frame is decoded at éach possible rate, and using the quality metrics of the Viterbi decoder, the correct result is chosen.

Traffic channels may also carry circuit-switch data calls in IS-95. The variable-rate traffic frames are generated using the IS-95 Radio Link Protocol (RLP). RLP provides a mechanism to improve the performance of the wireless link for data. Where voice calls might tolerate the dropping of occasional 20 ms frames, a data call would have unacceptable performance without RLP.

Under IS-95B PREV=5, it was possible for a user to use up to seven supplemental "code" (traffic) channels simultanéously to incréase the throughput of a data call. Very few mobiles or networks ever provided this féature, which could in théory offer 115200 bit/s to a user.