Real time, character by character text conversation is a component that can be of value in a distant conversation. Users may have an interest to use real time text conversation alone or in any combination with voice and video. Global Text Telephony is a feature that adds the capability to use a text conversation component in a session. It is called GTT here. GTT is defined in a set of host environments, circuit switched as well as packet switched. Interworking with corresponding features in other networks is an important part of Global Text Telephony. Specifically, the different kinds of PSTN text telephone systems supported by the international text telephone modem standard ITU-T Recommendation V.18 [4] are included in the modes for interworking consideration. One important reason to offer the Global Text feature is to enable emergency service access to people who are depending on a written dialogue. A more elaborated background is found in TS 22.226, Global Text Telephony, Stage 1, Annex A.

This 3GPP Technical Specification defines the stage 2 description of the real time Text Conversation Feature called Global Text Telephony, GTT. GTT Stage 2 identifies the functional capabilities needed to support the service described in GTT Stage 1. This TS contains the core functions for a real time Text Conversation Feature GTT, to be used in combination with other media in conversational services. GTT offers real time conversation in text, to be used alone or in combination with other conversational media, and interworking with current and emerging text conversation features in the fixed networks and other mobile networks. GTT uses a number of functional entities to realise the requirements of the stage 1 description (TS 22.226). This TS describes how the service requirements are realised with these functional entities. As far as possible existing protocols shall be used for the realisation of the Global Text Telephony Feature. This may include e.g., SIP, 3G.324, or Circuit Switched Voice service as protocol environments, and CTM, AL1 and RTP/text as transmission protocols. It also means usage of existing text presentation format ITU-T Recommendation T.140 [5], common to all GTT text conversation environments.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

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