Network Working Group G. Hellstrom Internet-Draft Omnitor Intended status: Informational A. van Wijk Expires: January 13, 2010 Real-Time Text Taskforce (R3TF) July 12, 2009 Registration of the Real-time-text Media Feature Tag draft-hellstrom-text-turntaking-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 13, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This memo defines a new Media Feature Tag "real-time-text" for use in SIP registration and session establishment. This is used to indicate Hellstrom & van Wijk Expires January 13, 2010 [Page 1] Internet-Draft Real-time-text Media Feature Tag July 2009 if a device capable of text communication has full real-time text capabilities or limitations in its capabilities requiring the users to apply some turn-taking habits. To the RFC editor Please replace y.y with the assigned ASN.1 identifier and XXXX with the RFC number of this specification. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 7. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Hellstrom & van Wijk Expires January 13, 2010 [Page 2] Internet-Draft Real-time-text Media Feature Tag July 2009 1. Introduction Media feature tags for use in SIP headers are introduced in RFC 3840 [RFC3840]. They are used with the Session Initiation Protocol (SIP). When negotiating a text communication medium in a session, a user may find it very desirable to achieve a text communication path with real-time text capabilities. In order to support routing of negotiating to support this preference, an indication in a SIP media- feature tag can be used. That media-feature tag is defined in this specification. One value is given to the parameter for indication of full simultaneous two way capabilities of the text communication. When interworking with legacy telecommunication devices through a gateway, an IP based text phone using SIP may be required to limit its capabilities to match those devices. For example, V.21 based textphones are full duplex in transport, but have varying handling of the presentation. Some types merge the two sources in one window. Some have a kind of irc-like display with labels in front of the text from different participants. And yet some do a split in two windows of real-time text from each direction. In order for a SIP-based text capable device to display an appropriate user interface when interacting with one of these legacy devices, it is necessary to convey a parameter indicating the limited capability of the legacy device. It is also of interest to route calls to the most capable device. When it is interacting with a legacy device, an IP text capable device may receive an offer that contains the 'real-time-text' tag indicating some restriction. That tag then acts as a cue to configure the user interface appropriately, although there is nothing in the generated answer to indicate that this has been done. Similiarly, if an answer is received that contains a 'real-time-text' tag with a value indicating restrictions, that indicates that the remote device has limited capabilities regarding simulaneity, and the user-interface should present some indication of this to the user. More information on handling of real-time text is found in RFC 5194. Framework for real-time text over IP using the Session Initiation Protocol [RFC5194]. This memo defines such a parameter. 2. Terminology 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]. Hellstrom & van Wijk Expires January 13, 2010 [Page 3] Internet-Draft Real-time-text Media Feature Tag July 2009 3. IANA Considerations This specification defines a Media Feature tag 'real-time-text'. Its formatting in SIP headers is described in the following: Media Feature Tag name: sip.real-time-text ASN.1 Identifier: y.y. Summary of the media feature indicated by this tag: The sip.real- time-text media feature tag indicates whether a communications device can simultaneously handle the real-time text medium and audio in its user interface or towards attached devices, or if limitations must be applied by users who communicate with the device. Values appropriate for use with this feature tag: Token with an equality relationship. Defined values are: full: The device can handle real-time text simultaneously in both directions and if it supports audio, audio and text can also be handled simultaneously. (default) restricted: The device requires some ordered turn-taking to take place. It is not specified how strict this turntaking must be, and it is left to the users to figure out what level of turntaking signaling is needed. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms: This feature tag is most useful in a communications application for describing the capabilities of a SIP multimedia communication device, SIP application servers implementing services including real-time text, or a PSTN textphone gateway, connecting SIP devices with legacy textphones, with the intention both to support routing of the call and indication to the SIP device user if turntaking must be applied. Examples of typical use: Choosing to communicate with a native, real- time text capable device rather than a legacy textphone behind a gateway, when a selection is possible. Instruct the user of the SIP device about the need to apply turntaking habits as used with legacy textphones when the call is made through a gateway with that kind of device. Related standards or documents: RFC XXXX. Security Considerations: Security considerations for this media Hellstrom & van Wijk Expires January 13, 2010 [Page 4] Internet-Draft Real-time-text Media Feature Tag July 2009 feature tag are discussed in Section 11.1 of RFC 3840. 4. Example The following example shows the use of the 'real-time-text' tag in a SIP message. REGISTER sip:example.com SIP/2.0 From: sip:user@example.com;tag=asd98 To: sip:user@example.com Call-ID: hh89as0d-asd88jkk@host.example.com CSeq: 9987 REGISTER Max-Forwards: 70 Via: SIP/2.0/UDP host.example.com;branch=z9hG4bKnashds8 Contact: ;audio;text; real-time-text=restricted Content-Length: 0 5. Security Considerations Security considerations for this media feature tag are discussed in Section 11.1 of RFC 3840. 6. Acknowledgements The need for this registration was discussed with Barry Dingle, Gonzalo Camarillo , and Colin Perkins. 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag Registration Procedure", BCP 31, RFC 2506, March 1999. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Hellstrom & van Wijk Expires January 13, 2010 [Page 5] Internet-Draft Real-time-text Media Feature Tag July 2009 Initiation Protocol (SIP)", RFC 3840, August 2004. [RFC5194] van Wijk, A. and G. Gybels, "Framework for Real-Time Text over IP Using the Session Initiation Protocol (SIP)", RFC 5194, June 2008. Authors' Addresses Gunnar Hellstrom Omnitor Box 92 054 Stockholm 12006 Sweden Email: gunnar.hellstrom@omnitor.se URI: http://www.omnitor.se Arnoud van Wijk Real-Time Text Taskforce (R3TF) NL Email: arnoud@realtimetext.org URI: www.realtimetext.org Hellstrom & van Wijk Expires January 13, 2010 [Page 6]