| MMUSIC Working Group | R. Gellens |
| Internet-Draft | Qualcomm Technologies, Inc. |
| Intended status: Standards Track | 2013 |
| Expires: December 25, 2016 |
Negotiating Human Language Using SDP
draft-gellens-negotiating-human-language-00
Users have various human language needs, abilities, and preferences regarding spoken, written, and signed languages. When establishing interactive communication "calls" there needs to be a way to communicate and ideally match (i.e., negotiate) the caller's needs, abilities, and preferences with the capabilities of the called party. This is especially important with emergency calling, where a call can be routed to a PSAP or call taker capable of communicating with the user, or a translator or relay operator can be bridged into the call during setup, but this applies to non-emergency calls as well (as an example, when calling an airline reservation desk).
This document describes the need and expected use, and discusses the solution using either an existing or new SDP attribute.
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When setting up interactive communication sessions, human (natural) language negotiation is needed in some cases. When the caller and callee are known to each other or where context implies language, such language negotiation may not be needed. In other cases, there is a need for the caller to indicate language preferences, abilities, or needs, including specific spoken, signed, or written languages. This need exists when setting up SIP sessions (including emergency and non-emergency calling). For various reasons, including the ability to establish multiple streams each using a different media (e.g., voice, text, video), it makes sense to use a per-stream negotiation mechanism, using SDP.
This approach has a number of benefits, including that it is generic and not limited to emergency calls. In some cases such a facility isn't needed, because the language is known from the context (such as when a caller places a call to a sign language relay center). But it seems clearly useful in many other cases. For example, it seems generally useful that someone calling a company call center be able to indicate if a specific sign and/or spoken language is needed. The UE would need to set this, but could default to the language used for the interface with the user.
Including the user's natural language requirements in the session establishment negotiation is independent of the use of a relay service and is transparent to a voice service provider. For example, assume a user within the United States who speaks Spanish but not English places a voice call using an IMS device. It doesn't matter if the call is an emergency call or not (e.g., to an airline reservation desk). The language information is transparent to the carrier, but is part of the session negotiation between the UE and the terminating entity. In the case of a call to e.g., an airline, the call can be automatically routed to a Spanish-speaking agent. In the case of an emergency call, the ESInet and the PSAP may choose to take the language into account when determining how to route and process the call (e.g., language and media needs may be considered within policy-based routing).
By treating language as another session attribute that is negotiated along with media, it becomes possible to accommodate a wide range of users' needs and called party facilities. For example, some users may be able to speak several languages, but have a preference. Some called parties may support some of those languages internally but require the use of a bridged translation service for others. The standard session negotiation mechanism handles this by providing the information and mechanism for the endpoints to make appropriate decisions.
Regarding relay services, in the case of an emergency call requiring sign language such as ASL, there are two common approaches: the caller initiates the call to a relay center, or the caller places the call to emergency services (e.g., 911 or 112). In the former case, the language need is ancillary and supplemental. In the latter case, the ESInet and/or PSAP may take the need for sign language into account and bridge in a relay center. In this case, the ESInet and PSAP have all the standard information available (such as location) but are able to bridge the relay sooner in the call processing.
By making this facility part of the end-to-end negotiation, the question of which entity provides or engages the relay service becomes separate from the call processing mechanics; if the caller directs the call to a relay service then the natural language facility provides extra information to the relay service but calls will still function without it; if the caller directs the call to emergency services, then the ESInet/PSAP are able to take the user's natural language needs into account, e.g., by routing to a particular PSAP or call taker or bridging a relay service or translator.
The term "negotiation" is used here rather than "indication" because human language (spoken/written/signed) is something that can be negotiated in the same way as which forms of media (audio/text/video) or which codecs.
For example, if we think of non-emergency calls, such as a user calling an airline reservation center, the user may have a set of languages he or she speaks, with perhaps preferences for one or a few, while the airline reservation center will support a fixed set of languages. Negotiation should select whichever language supported by the call center is most preferred by the user. Both sides should be aware of which language was negotiated. This is conceptually similar to the way other aspects of the session are negotiated using SDP (e.g., media and codecs).
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].
This facility is expected to be used by NENA and 3GPP. NENA is likely to reference it in NENA 08-01 (i3 Stage 3) in describing attributes of calls presented to an ESInet, and in that or other documents describing Policy-Based Routing capabilities within a Policy-Based Routing Function (PCRF). 3GPP is expected to reference this mechanism in general call handling and emergency call handling. Recent CRs introduced in SA1 have anticipated this functionality being provided within SDP.
The desired solution is a media attribute that may be used within an offer to indicate preferred language(s) of each media stream, and within an answer to indicate the accepted language. The semantics of including multiple values for a media stream within an offer is that the languages are listed in order of preference.
An SDP attribute seems the natural choice to negotiate human (natural) language. The attribute value should be an IANA language tag from the registry www.iana.org/assignments/language-subtag-registry
RFC 4566 [RFC4566] specifies an attribute 'lang' which sounds similar to what is needed here, the difference being that it specifies that 'a=lang' is declarative with the semantics of multiple 'lang' attributes being that all of them are used, while we want a means to negotiate which one is used in each stream. This difference means that either the existing 'lang' attribute can't be used and we need to define a new attribute, or we finese/update the semantics of 'lang' (or possibly the author has misunderstood RFC 4566).
The text from RFC 4566 [RFC4566] is:
The question is: Can the 'lang' attribute be used for our purposes? Using it to negotiate the language for a media seems at first glance to violate its semantics as defined in RFC 4566 [RFC4566]. But there are existing examples of it being used in exactly the way we need. For example, draft-saintandre-sip-xmpp-chat-04 [I-D.saintandre-sip-xmpp-chat] contains an example where the initial invitation contains two 'a=lang' entries for a media stream (for English and Italian) and the OK accepts one of them (Italian), which matches what we need:
INVITE sip:juliet@example.com SIP/2.0
To: <sip:juliet@example.com>
From: <sip:romeo@example.net>;tag=576
Subject: Open chat with Romeo?
Call-ID: 742507no
Content-Type: application/sdp
c=IN IP4 s2x.example.net
m=message 7313 TCP/MSRP *
a=accept-types:text/plain
a=lang:en
a=lang:it
a=path:msrp://s2x.example.net:7313/ansp71weztas;tcp
SIP/2.0 200 OK
To: <sip:juliet@example.com>;tag=534
From: <sip:romeo@example.net>;tag=576
Call-ID: 742507no
Content-Type: application/sdp
c=IN IP4 x2s.example.com
m=message 8763 TCP/MSRP *
a=accept-types:text/plain
a=lang:it
a=path:msrp://x2s.example.com:8763/lkjh37s2s20w2a;tcp
Instead of re-using 'lang' we may define a new media-level attribute 'humlang' to negotiate which human language is used in each media stream:
TBD.
TBD
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3066] | Alvestrand, H., "Tags for the Identification of Languages", RFC 3066, DOI 10.17487/RFC3066, January 2001. |
| [RFC4566] | Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, DOI 10.17487/RFC4566, July 2006. |
| [I-D.iab-privacy-considerations] | Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M. and R. Smith, "Privacy Considerations for Internet Protocols", Internet-Draft draft-iab-privacy-considerations-09, May 2013. |
| [I-D.saintandre-sip-xmpp-chat] | Saint-Andre, P., Loreto, S., Gavita, E. and N. Hossain, "Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): One-to-One Text Chat", Internet-Draft draft-saintandre-sip-xmpp-chat-06, June 2013. |