Digital cellular telecommunications system (Phase 2+); Universal Mobile Telecommunications System (UMTS); Tandem Free Operation (TFO); Service description; Stage 2 (V12.0.0; 3GPP TS 23.053 version 12.0.0 Release 12)
The present document defines the stage 2 service description for Tandem Free Operation (TFO) in and between GSM and UMTS. Tandem Free Operation applies only to speech calls. NOTE: The TFO principles are built so that they could be used as well by other systems other than GSM and UMTS. In analogy with ITU-T Recommendations I.130 [2] and with reference to ITU-T Recommendations Q.65 VI.1 (Stage 2 of the method for the characterisation of services supported by an ISDN)@ the second stage of the following three-level structure is derived from a stage 1 service description. - Stage 1 is an overall service description@ from the service subscriber's and user's standpoints@ that views the network as a single entity which provides services to the user. - Stage 2 identifies the functional capabilities and information flows needed to support the service described in stage 1. Furthermore@ it identifies various possible physical locations for the functional capabilities. The output of Stage 2@ which is signalling system independent@ is used as an input to Stage 3@ the design of signalling system and switching Recommendations. - Stage 3 defines the signalling system protocols and switching functions needed to implement the service described in stage 2.