5 Functions to support data services

07.013GPPGeneral on Terminal Adaptation Functions (TAF) for Mobile Stations (MS)TS

The main functions of the MT to support data services are:

– functions to ensure conformity of terminal service requests to network capability;

– physical connection of the reference points R and S;

– flow control of signalling and mapping of user signalling to/from GSM PLMN access signalling;

– rate adaptation of user data (see GSM 04.21);

– flow control of non-transparent user data and mapping of flow control for asynchronous data services;

– support of data integrity between the MS and the interworking function in the GSM PLMN;

– end-to-end synchronization between terminals;

– filtering of status information;

– functions to support non-transparent bearer services e.g. termination of the Radio Link Protocol (RLP) and the Layer 2 Relay function (L2R) including optional data compression function (where applicable);

– terminal compatibility checking;

– optional support of local test loops.

In addition, functions to support autocalling and autoanswering are optionally specified in accordance with CCITT Rec. V.25 bis or with ITU‑T Rec. V.25 ter (although the use of other autocalling/auto-answering procedures are not prohibited provided that mapping in a functionally equivalent way to GSM 04.08 call control is also provided).

Other functional entities can be envisaged apart from the TAF. One of the physical interface to all these functions is the DTE/DCE interface to the MT. Normally, this DTE/DCE interface is associated with the TAF, if available. Therefore the access to any of these other functional entities, if implemented, via the DCE/DTE interface must be triggered by appropriate command sequences which are described in the applicable specifications (although the use of other procedures is not prohibited provided that mapping in a functionally equivalent way is also provided). These command sequences can be issued by the DTE only when the MT is in the appropriate command status and there is no data connection pending. They are interpreted by an MT internal control function and result in an association of the DTE/DCE interface with the addressed function, if available.