This specification defines Terminal Adaptation Functions (TAF) which are integrated in a Mobile Termination (MT) and which enable the attachment of Synchronous Terminals to an MT (see GSM 04.02). The general aspects of Terminal Adaptation Functions are contained in specification GSM 07.01. This specification covers support of synchronous data services (see GSM 02.02) for the following interfaces and procedures: - V.22 DTE/DCE Interface - V.22bis DTE/DCE Interface - V.26ter DTE/DCE Interface - V.32 DTE/DCE Interface - X.21 DTE/DCE Interface - X.21bis DTE/DCE Interface - X.25 Procedure - X.32 Procedure - V.25bis Procedure - I.420 Interface (S) LAPB is the only synchronous non-transparent protocol which is considered here.