This Global System for Mobile communications Technical Specification ( GTS) defines rate adaptation functions to be used in GSM PLMN Base Sta tion Systems (BSS) and transcoders for adapting radio interface data r ates to the 64 kbit/s needed at the MSC in accordance with GSM 03.10. The number of Base Station System - Mobile-services Switching Centre ( BSS - MSC) traffic channels supporting data rate adaptation may be lim ited. In this case some channels may not support data rate adaptation. Those that do, must conform to this specification. NOTE: This specification should be considered together with GSM 04.21 to give a complete description of PLMN rate adaptation.