Terminal Adaptation Functions (TAF) for services using asynchronous bearer capabilities
The present document defines the interfaces and Terminal Adaptation Functions (TAF) integral to a Mobile Termination (MT) which enable the use of asynchronous bearer services in the PLMN and the attachment of asynchronous terminals to a MT (see 3GPP TS 24.002 [3] and 3GPP TS 23.101 [6]).
The general aspects of Terminal Adaptation Functions are contained in 3GPP TS 27.001 [10].
The present document covers support of these services for the following interfaces and procedures:
(i) ITU-T V.14 [16] procedures.
(ii) ITU-T  V.21 [17] DTE/DCE interface.
(iii) ITU-T  V.22bis [18] DTE/DCE interface.
(iv) ITU-T  V.32 [24] DTE/DCE procedures.
(v) ITU-T  I.420 [14] S interface.
(vi) ITU-T  V.250 [22] signalling procedures.
The asynchronous data rates between the MT and the IWF are defined in 3GPP TS 22.002 [5].
NOTE: From GSM R99 onwards the following services are no longer required in a PLMN:
- the dual Bearer Services "alternate speech/data" and "speech followed by data";
- the dedicated services for PAD and Packet access;
- the BS 21 ... 26 and BS 31 ... 34.
The support of these services is still optional. The specification of these services is not within the scope of the present document. For that, the reader is referred to GSM Release 98.
NOTE: Please note that the Gb interface does not play any role in the scope of the present document although the term "A/Gb mode" is used. GERAN Iu mode is for further study.