B.2 GTT-Voice specific information for CTM support via core network termination selection for networks using Iu interface

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

For networks with GERAN and UTRAN radio access using the Iu interface, a method to allocate the calls to terminations capable of handling CTM on audio channels can be provided in the core network. It can be based on the mechanisms for controlling Media Gateway functions through the control language specified on the Mc interface. The MSC Server has information on CTM indication issued by the mobile station and allocates terminations with proper CTM capabilities for the detection/conversion during the call.

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

– Setup from terminal, including CTM indication

MSC server detects CTM indication and allocates a termination with CTM capabilities in the Media Gateway.

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

– Setup from the MSC Server.

– Call Confirm from the terminal including CTM indication.

– The MSC server detects CTM indication and allocates a termination with CTM capabilities in the Media Gateway.

Figure B.3: Association of a CTM capable termination within the Media Gateway

Annex C (Informative):
GTT-Voice specific information for the CTM-SRF core network node solution

This clause describes a method how to route possible text calls via a core network node called the CTM-SRF. It should be taken as an informative example. It is based on CAMEL Phase 1 and call signalling with ISUP. Other call control environments and other IN service platforms can accomplish the same result.

This clause shows how emergency calls, terminating calls and originating calls can be routed through the CTM-SRF node without any modification to existing core network nodes. This covers also mobile-to-mobile calls.

For cases where emergency call support for text calls is wanted, all emergency calls are routed to the CTM-SRF server. The CTM-SRF server routes the call to the emergency centre. This can be done, as the CTM/textphone conversion channel itself is transparent to speech.

Originating and terminating calls, from and to possible text telephone users, are handled as CAMEL calls. A CAMEL service assures that the calls are routed through the CTM-SRF node by actions of a CAMEL application.