6.2.3 and 6.2.1.1 proposals about scope of RTT functionality and interoperability
There is a desire to have wording of 6.2.1.1 RTT communication and 6.2.3 RTT Interoperability in the January 2024 draft version of EN 301 549 that is closer to final than the ones in version 3.2.1. Here is a proposal that can be used as an intermediate solution. Both clauses are proposed here because they are closely interlinked and need to be studied together.
The scope of interoperability must be stated in 6.2.1.1. Discussions have shown that the wording in version 3.2.1 is not sufficient. The wording proposed by Mike on Nov 8 at the end of #78 (closed) can be used as a better solution but with the exception about hardware added
6.2.1.1 RTT Communication
Where ICT provides functionality that allows continuous real-time conversation with one or more individuals,
the ICT shall provide functionality that allows RTT communication with those same individuals, except where this would require design changes to add input or output hardware to the ICT.
For 6.2.3 RTT Interoperability, it has been said that "Loic's proposal" would be a possible compromise:
"6.2.3 RTT Interoperability
Where ICT is an electronic communication service providing two-way voice conversational real-time communication with another electronic communication service, the ICT shall provide a means for two-way RTT communications between the end-user devices in the two services";
But this requirement only involves services, and not the devices and not interoperability within the same services. Our discussions with ETNO also reveals that the current standards for RTT are not generally known among service providers. Information about current standards should therefore be included at least as an informational note. There is still a discussion if the M/2022/587 requires us to be specific about which technical solution standards to use for achieving interoperability or not. This discussion should be included as an editors note until it is resolved.
Thus the proposal for 6.2.3 is:
6.2.3 RTT Interoperability
Where ICT is an electronic communication service providing two-way voice conversational real-time communication with end-user devices in the same or another electronic communication service, the ICT shall provide a means for two-way RTT communications between these end-user devices.
[EDITORS NOTE: There is discussion in STF614 if M/2022/587 requires the information in the note below to be provided as normative clauses in EN 301 549 or in a separate standard.]
NOTE 1: The following information on existing state of the art standards for RTT is provided for the purpose to ease the fulfillment of the interoperability requirement.
Presentation
ITU-T has published a standard for coding and presentation of RTT, in Recommendation ITU-T T.140 [i.36] .It is used by all technologies below.
General VoIP and Multimedia calling
IETF, providing standards for Voice Over IP (VOIP) and Multimedia calls over IP based on the Session Initiation Protocol (SIP), has published IETF RFC 4103 [i.13] for session establishment and transport of RTT and its update RFC 9071 for multiparty use [i.rfc9071] .
Mobile Multimedia Telephony
Mobile standards: 3GPP, providing standards for mobile communication systems, including IP Multimedia Sub-System (IMS) has standardised the Multimedia Telephony concept, for calls with voice, video and RTT using the set of protocols specified in 3GPP TS 26.114 (= ETSI TS 126 114) [i.10] to create the services including RTT and Total Conversation services specified in TS 22.173 (=ETSI TS 122 173) [i.11]. Multimedia Telephony is specified to use IETF RFC 4103 [i.13] updated by RFC 9071 for session establishment and transport of RTT or the IMS Data Channel for RTT in Web Technologies. It should be noted that 3GPP uses the following varying terms for RTT: GTT, GTT-IP, RTT, real time text, text.
Mobile product profiles: GSMA, providing selected profiles of standards for implementing globally interoperating mobile communications services has in NG.114 [i.ng114] specified how to apply TS 126 114 to implement Voice over LTE (VoLTE) and Video over LTE (ViLTE). RTT is specified in NG.114 Annex B.2 to use IETF RFC 4103 [i.13] for session establishment and transport of RTT.
Web technologies
For communication in Web Technologies, W3C and IETF have created the WebRTC concept [i.rfc8825]. IETF has published RFC 8865 [i.rfc8865] for implementation of RTT in web technologies using the WebRTC Data channel concept.