When 64 kbit/s traffic channels are used on the Abis interface the speech shall be coded according to CCITT Recommendation G.711 and the data rate adaption shall be as specified in GSM 04.21 and GSM 08.20. In the case where 16 kbit/s traffic channels are used for full rate speech or Enhanced Full Rate speech or full rate data service, then this specification shall apply for frame structure and for control of remote transcoders and additional rate adaptors. The use and general aspects of the Abis interface are given in GSM 08.51. NOTE: This specification should be considered together with the GSM 06 series of specifications,GSM 04.21 (Rate Adaption on the MS-BSS Interface) and GSM 08.20 (Rate Adaption on the BS/MSC Interface).