B.1 GTT-Voice specific information for CTM support in GSM networks with A-interface, via access network circuit pooling

23.2263GPPGlobal Text Telephony (GTT)Release 17Stage 2TS

A-interface pooling, and routing to a selected pool, is an intrinsic capability within current GSM Networks and is used to select transcoding for EFR, FR and in future AMR. It is an option to create circuit pools on the A-interface, which support the CTM detection/conversion. The circuit pools are defined in TS 48.008 [15]. These pools may be incorporated in the transcoder, in a separate entity associated with a transcoder or in a separate entity located in particular A-interface circuits but remote from the transcoder.

The main steps of the process for a mobile originated call are:

– Setup from terminal, including CTM indication.

MSC detects CTM indication and allocates a circuit with CTM capabilities.

The main steps of the process for a mobile terminated call are:

– Setup from MSC.

– Call Confirm from terminal including CTM indication.

MSC detects CTM indication and allocates a circuit with CTM capabilities.

Figure B.1: CTM adaptor contained within a transcoder pool

Figure B.2: CTM adapter present on specific A-interface circuits