WG MMUSIC Keith Drage, Ed. Internet Draft Juergen Stoetzer-Bradler Intended status: Standards track Albrecht Schwarz Expires: February 2016 Alcatel-Lucent August 10, 2015 T.140 Text Conversation over Data Channels draft-schwarz-mmusic-t140-usage-data-channel-00.txt Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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Abstract This document specifies how the ITU-T Protocol for multimedia application text conversation (Recommendation ITU-T T.140) can be instantiated as a data channel sub-protocol, using the SDP offer/answer exchange-based external negotiation defined in [I- D.ietf-mmusic-data-channel-sdpneg]. Two network configurations are documented: a WebRTC end-to-end configuration (connecting two T.140 over data channel endpoints), and a gateway configuration (connecting an T.140 over data channel endpoint with an T.140 over RTP/UDP endpoint). Table of Contents 1. Introduction...................................................3 1.1. Motivation................................................3 1.2. Framework of WebRTC data applications.....................4 2. Conventions....................................................4 2.1. Prescriptive language.....................................4 2.2. Notation..................................................4 3. Terminology and abbreviations..................................4 3.1. Terminology used..........................................4 3.2. Abbreviations used........................................5 4. Prinicples.....................................................6 4.1. T.140 Data Channel........................................6 4.2. Session Mapping...........................................6 5. End-to-End Configuration.......................................6 5.1. Basic T.140 Support.......................................6 5.1.1. Session Negotiation..................................6 5.1.1.1. Use of dcmap Attribute..........................6 5.1.1.2. Use of dcsa Attribute...........................7 5.1.1.3. Example SDP Negotiation.........................7 5.1.2. Session Opening......................................7 5.1.3. Data Framing.........................................7 Schwarz Expires February 10, 2016 [Page 2] Internet-Draft SDP codepoints for gateway control August 2015 5.1.4. Data Sending and Reporting...........................7 5.1.5. Session Closing......................................7 5.2. Support of T.140-specific Functions.......................7 6. Gateway Configurations.........................................8 6.1. Introduction..............................................8 6.2. Gateway-embedded Interworking Functions for T.140.........8 6.2.1. WebRTC T.140 text to IP text telephony in text conversation mode...........................................8 6.2.2. WebRTC T.140 text to IP text telephony in text relay mode........................................................8 6.2.3. WebRTC T.140 text to IP text telephony in text pass- through mode................................................9 6.2.4. WebRTC T.140 text to PSTN text telephony.............9 6.3. Example gateway configuration in more detail..............9 7. Security Considerations.......................................10 8. IANA Considerations...........................................10 9. References....................................................10 9.1. Normative References.....................................10 9.2. Informative References...................................11 10. Acknowledgments..............................................11 11. CHANGE LOG...................................................13 11.1. Initial draft-schwarz-mmusic-t140-usage-data-channel-01.13 11.1.1. Status.............................................13 11.1.2. Changes against "draft-ietf-mmusic-msrp-usage-data- channel-01"................................................13 1. Introduction 1.1. Motivation Recommendation ITU-T T.140 [ITU-T T.140] defines a protocol for text conversation, also known as realtime text or text telephony. The native transport for IP networks is based on the Real-time Transport Protocol (RTP; see [RFC4103]) due to its inherent realtime characteristics, similar as conversational audio and video services. WebRTC text conversation is based on T.140, but considered as "data traffic" component (despite the fact of the native RTP-based transport in non-WebRTC environments), see [I-D.ietf-rtcweb-????]. This document defines the SDP-based negotiation and transport of the T.140 protocol over data channels, where a data channel is a bi- directional communication channel running on top of SCTP/DTLS (as per [I-D.ietf-rtcweb-data-channel]) and where T.140 is instantiated as a sub-protocol of this data channel. Schwarz Expires February 10, 2016 [Page 3] Internet-Draft SDP codepoints for gateway control August 2015 Considering an T.140 endpoint being an T.140 application that uses data channel from WebRTC specifications [I-D.ietf-rtcweb-data- channel], this document describes two configurations where the other endpoint is respectively either another T.140 over data channel endpoint (e.g., a WebRTC application) or an T.140 endpoint using native RTP transport. 1.2. Framework of WebRTC data applications There are multiple IP application protocols which using WebRTC data channels as transport, such as MSRP or BFCP besides T.140. The SDP- based indication and negotiation of such WebRTC data applications at call control signalling level follows common principles. The first WebRTC application from this suite is/was the MSRP-based instant messaging service for WebRTC, see [I-D.ietf-mmusic-msrp-usage-data- channel]. This specification for T.140 was derived from that document and uses an aligned clause structuring. It may be noted that the T.140 protocol as such is much simpler in comparison to the MSRP, which requires an extensive set of SDP elements (in comparison to T.140) for the description of specific MSRP services and their protocol parameter settings. 2. Conventions 2.1. Prescriptive language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [RFC2119]. 2.2. Notation The brief notation "T.140" is used as a synonym for the text conversation protocol according to [ITU-T T.140]. 3. Terminology and abbreviations 3.1. Terminology used This document uses the following terms: Data channel: A WebRTC data channel as specified in [I-D.ietf- rtcweb-data-channel]. T.140 data channel: A data channel specifically used to transport the text and presentation control information of one T.140 session. Schwarz Expires February 10, 2016 [Page 4] Internet-Draft SDP codepoints for gateway control August 2015 External negotiation: Data channel negotiation based on out-of-band or in-band mechanisms other than the Data Channel Establishment Protocol specified in [I-D.ietf-rtcweb-data-protocol]. In-band: Transmission through the peer-to-peer SCTP association. Out-of-band: Transmission through the call control signaling path, e.g., using JSEP [I-D.ietf-rtcweb-jsep] and the SDP Offer/Answer model [RFC3264]. Peer: From the perspective of one of the agents in a session, its peer is the other agent. Specifically, from the perspective of the SDP offerer, the peer is the SDP answerer. From the perspective of the SDP answerer, the peer is the SDP offerer 3.2. Abbreviations used DS ##### DTLS Datagram Transport Layer Security GCP Gateway Control Protocol ITU-T International Telecommunication Union Telecommunication Standardization Sector IWF Interworking Function JSEP ##### MG (H.248) Media Gateway MGC (H.248) Media Gateway Controller RTP Real-time Transport Protocol SCTP Stream Control Transmission Protocol SDP Session Description Protocol SIP Session Initiation Protocol TCP Transmission Control Protocol TDM (Synchronous) Time Division Multiplexing ToIP Text over IP Schwarz Expires February 10, 2016 [Page 5] Internet-Draft SDP codepoints for gateway control August 2015 TLS Transport Layer Security UA User Agent UDP User Datagram Protocol VBD Voiceband Data 4. Prinicples 4.1. T.140 Data Channel In this document, an T.140 data channel is a data channel for which the instantiated sub-protocol is "t140", and where the T.140-related negotiation is done as part of the SDP-based external negotiation method defined in [I-D.ietf-mmusic-data-channel-sdpneg]. 4.2. Session Mapping In this design, the T.140 session maps to the SCTP association and the "SCTP stream pair" assigned to the data channel, and each T.140 session maps to one data channel exactly. 5. End-to-End Configuration This section describes the network configuration where each T.140 endpoint is running T.140 over a data channel. 5.1. Basic T.140 Support 5.1.1. Session Negotiation 5.1.1.1. Use of dcmap Attribute The SDP offer shall include a dcmap attribute line (defined in [I- D.ietf-mmusic-data-channel-sdpneg], within the media description for the SCTP association for each T.140 data channel session to be negotiated. The attribute includes the following data channel parameters: o "label=" labelstring o "subprotocol=" "t140" Schwarz Expires February 10, 2016 [Page 6] Internet-Draft SDP codepoints for gateway control August 2015 The labelstring is set by the T.140 application according to [I- D.ietf-mmusic-data-channel-sdpneg]. The max-retr, max-time and ordered parameters shall not be used. Rest of the SDP offer/answer procedures are per [I-D.ietf-mmusic- data-channel-sdpneg]. The following is an example of the dcmap attribute for an T.140 session to be negotiated (on default SCTP port 5000) with stream=3 and without any label: a=dcmap:3 subprotocol="t140" 5.1.1.2. Use of dcsa Attribute FIXTHIS 5.1.1.3. Example SDP Negotiation FIXTHIS 5.1.2. Session Opening FIXTHIS 5.1.3. Data Framing FIXTHIS 5.1.4. Data Sending and Reporting FIXTHIS 5.1.5. Session Closing FIXTHIS 5.2. Support of T.140-specific Functions FIXTHIS (e.g., T.140 specific reliable transport requirements) Schwarz Expires February 10, 2016 [Page 7] Internet-Draft SDP codepoints for gateway control August 2015 6. Gateway Configurations 6.1. Introduction This section describes the network configuration where one T.140 endpoint uses data channels as T.140 transport, the other T.140 endpoint uses a different protocol stack. There is consequently an interworking function (IWF) in the media plane required, associated with correspondent interworking in the signalling plane. Such type of IWFs are provided by gateway devices, given here by WebRTC gateways as defined by [I-D.ietf-rtcweb-gateways], [ITU-T H.248.94], [3GPP 29.334], etc. 6.2. Gateway-embedded Interworking Functions for T.140 There are a plethora of interworking functions knowns for T.140 [ITU-T T.140] due to the long history and usage of this service in legacy packet-switched and circuit-switched networks. Some examples are indicated below. 6.2.1. WebRTC T.140 text to IP text telephony in text conversation mode Service "IP text telephony in text conversation mode": Transport service according to [RFC4103]. Media plane IWF: "T.140-over-SCTP stream-over-SCTP association-over-DTLS-over-L4" to "T.140-over-RTP/UDP" 6.2.2. WebRTC T.140 text to IP text telephony in text relay mode Service "IP text telephony in text relay mode": Transport of T.140 over IP networks, according to [ITU-T V.151]. Also known as Text-over-IP (ToIP). Media plane IWF: "T.140-over-SCTP stream-over-SCTP association-over-DTLS-over-L4" to "T.140-over-IP TLP-UDP". NOTE: [ITU-T V.151] uses the concept of an "IP Transport Layer Protocol" (IP-TLP) above the native IP transport layer, which Schwarz Expires February 10, 2016 [Page 8] Internet-Draft SDP codepoints for gateway control August 2015 again allows different framing protocol options (such as RTP-based or SPRT-based framing (Simple Packet Relay Transport, see Annex B of [ITU-T V.150.1])). 6.2.3. WebRTC T.140 text to IP text telephony in text pass-through mode Service "IP text telephony in text pass-through mode": Transport of analogue PSTN text telephones signals over PCM encoded voice over IP networks, according to [ITU-T V.152]. Also known as Voiceband-over-IP (VBDoIP). Media plane IWF: "T.140-over-SCTP stream-over-SCTP association-over-DTLS-over-L4" to "text/modem-over-G.711-over-RTP/UDP". NOTE: This is the VBD mode according to [ITU-T V.152], using ITU-T G.711 as VBD codec (i.e., a different codec configuration as in comparison to G.711 as audio codec). 6.2.4. WebRTC T.140 text to PSTN text telephony Service "PSTN text telephony": Transport of analogue PSTN text telephones signals over a) analogue lines or b) circuit-switched 64-kbit/s channels. Media plane IWF: "T.140-over-SCTP stream-over-SCTP association-over-DTLS-over-L4" to "text/modem-over-DS0/TDM" (in case of circuit-switched networks). 6.3. Example gateway configuration in more detail The signalling plane and media plane interworking functions are elaborated in more detail at the example of a WebRTC gateway with support of interworking to IP text telephony in text conversation mode. Schwarz Expires February 10, 2016 [Page 9] Internet-Draft SDP codepoints for gateway control August 2015 This example describes the network configuration where one T.140 endpoint uses data channels as T.140 transport, the other T.140 endpoint uses RTP/UDP connections as T.140 transport, and the two T.140 endpoints interwork via an appropriate interworking function. FIXTHIS - details 7. Security Considerations FIXTHIS 8. IANA Considerations FIXTHIS 9. References 9.1. Normative References [RFC2119] RFC 2119 (03/1997), "Key words for use in RFCs to Indicate Requirement Levels", BCP 14. [RFC3264] RFC 3264 (06/2002), "An Offer/Answer Model with the Session Description Protocol (SDP)". [RFC4103] RFC 4103 (06/2005), "RTP Payload for Text Conversation". [RFC4566] RFC 4566 (07/2006), "SDP: Session Description Protocol". [I-D.ietf-rtcweb-data-protocol] draft-ietf-rtcweb-data-channel (##/2015), "WebRTC Data Channel Establishment Protocol". [I-D.ietf-rtcweb-data-channel] http://tools.ietf.org/wg/rtcweb/draft-ietf-rtcweb-data- channel/draft-ietf-rtcweb-data-channel (##/2015), "WebRTC Data Channels". [I-D.ietf-mmusic-data-channel-sdpneg] draft-ietf-mmusic-data- channel-sdpneg (##/2015), "SDP-based Data Channel Negotiation". [I-D.ietf-mmusic-msrp-usage-data-channel] draft-ietf-mmusic-msrp- usage-data-channel (##/2015), "MSRP over Data Channels". Schwarz Expires February 10, 2016 [Page 10] Internet-Draft SDP codepoints for gateway control August 2015 [ITU-T T.140] Recommendation ITU-T T.140 (02/1998), "Protocol for multimedia application text conversation". Free copy via: https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC- T.140-199802-I!!PDF-E&type=items 9.2. Informative References [I-D.ietf-rtcweb-gateways] draft-ietf-rtcweb-gateways (##/2015), "WebRTC Gateways". [ITU-T H.248.94] Recommendation ITU-T H.248.94 (10/2015), "Web- based real-time communication services - H.248 protocol support and profile guidelines". Status: still work in progress in ITU-T SG16 Question 3 Free copy via: FIXTHIS [ITU-T V.151] Recommendation ITU-T V.151 (05/2006), "Procedures for the end-to-end connection of analogue PSTN text telephones over an IP network utilizing text relay". Free copy via: https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC- V.151-200605-I!!PDF-E&type=items [ITU-T V.152] Recommendation ITU-T V.152 (09/2010), "Procedures for supporting voice-band data over IP networks". Free copy via: https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC- V.152-201009-I!!PDF-E&type=items [3GPP 29.334] 3GPP TS 29.334 Release 13 (2015), "Digital cellular telecommunications system (Phase 2+); Universal Mobile Telecommunications System (UMTS); LTE; IMS Application Level Gateway (IMS-ALG) - IMS Access Gateway (IMS-AGW); Iq Interface; Stage 3". Free copy via: ftp://ftp.3gpp.org/specs/archive/29_series/29.334/ 10. Acknowledgments FIXTHIS Schwarz Expires February 10, 2016 [Page 11] Internet-Draft SDP codepoints for gateway control August 2015 Authors' Addresses Keith Drage (editor) Alcatel-Lucent Quadrant, Stonehill Green, Westlea Swindon UK Email: keith.drage@alcatel-lucent.com Dr. Juergen Stoetzer-Bradler Alcatel-Lucent Lorenzstrasse 10 D-70435 Stuttgart GERMANY Email: Juergen.Stoetzer-Bradler@alcatel-lucent.com Dr. Albrecht Schwarz Alcatel-Lucent Lorenzstrasse 10 D-70435 Stuttgart GERMANY Email: Albrecht.Schwarz@alcatel-lucent.com Schwarz Expires February 10, 2016 [Page 12] Internet-Draft SDP codepoints for gateway control August 2015 11. CHANGE LOG 11.1. Initial draft-schwarz-mmusic-t140-usage-data-channel-01 11.1.1. Status o The initial document represents a skeleton where still a number of clauses are still empty. o The intention is to propose a document structure aligned with the MSRP draft, and to emphasize WebRTC gateway flavours. 11.1.2. Changes against "draft-ietf-mmusic-msrp-usage-data-channel-01" o Replace protocol "MSRP" by "T.140" plus protocol specific adaptations o Initial scope of gateway section Schwarz Expires February 10, 2016 [Page 13]