22.2263GPPGlobal Text Telephony (GTT)Release 17Stage 1TS
It shall be possible to use GTT to communicate with similar features in other networks as specified in ITU-T H.248 Annex F, in the Text Conversation and Text Telephone packages .
– PSTN text telephones, using voice telephony as a carrier according ITU-T V.18 .
– IP text telephones, using IP multimedia protocols and text according to ITU-T T.140 .
– IP conversational multimedia terminals using IP multimedia protocols with text according to ITU-T T.140 .
– CS multimedia with text according to ITU-T T.140 .
There is no requirement that the host environment combinations for interworking shall be extended for GTT support beyond the host environment interworking established for other media.
For interworking with text conversation in mobile networks outside the scope of the GTT specifications, interworking shall be specified as for other external networks.
For mobile services within scope of the GTT specification, interworking shall be possible between different forms of GTT, within the limits of interworking between the different host environments.
GTT shall permit use of the supplementary services defined for the host environment.
Users of both GTT and Multimedia Messaging ,, should be provided the following interoperation opportunities:
– If a call with a text component fails, it should be possible to offer the user to send a message to a MultiMedia Messaging facility such that the message may later be delivered in non-real time to the destination.
– External User Equipment interface specifications should enable both GTT and MMS text handling functions to be placed in the same device.
Note: In order to fulfil the requirement to give a consistent view of the feature from different access points, it may be of interest to give fixed network text telephone users possibilities to send and receive MMS text messages. This is however outside the scope of this specification.