Subject: [Sipping] Offer Answer / SDP a=sdplang was [Sip-implementors] Accept-Language Header

From: "Manroa, Arun [CTO]" <[email-masked]>
Date: Thu, 25 Jan 2007 09:45:08 -0600

Hi,

I am trying to understand how to negotiate human language (audio output) preferences using SDP or SIP headers;
RFC 2327 defines a=sdplang at the media level and so does the HTTP /SIP specs at the signaling level (Accept-Language Header). RFC 3264 offer answer does not delve into this.

Consider the following use case, where User A is an "English" language speaker using say G711 codec and want to conference in only certain members of a group call that not only support the G711 codec, but also understand the "English" language.
 
Assume following are the users characteristics:
User A (English), Codec G711
User B (English), Codec G711
User C (Spanish), Codec G711
User D (English), Codec AMR
User E (English, Spanish), Codec G711
 
So in this use case User A wants to connect to User B & E only, since the language and codec both match.(English, G711)
 
RFC 3261 20.3 Accept-Language says..

		The Accept-Language header field is used in requests to indicate the
		   preferred languages for reason phrases, session descriptions, or
		   status responses carried as message bodies in the response.

The text says session descriptions but I not clear how that is handled in offer answer. Does the "Conferencing Server" send out INVITES with Accept-Language: en (with SDP Offer) to all participants and user C is going to send a 415 indicating Spanish only, and B & E are going to respond with a 200 OK (SDP Ans). Of course User D is going to reject the SDP Offer with a 415 since it does not support G711.
 
Also the Accept-Language in REGISTER is used by the Registrar for generating a response, which I think is a different semantic meaning, maybe using RFC 3840 the users could register the appropriate language in the contact header, that way there is no need to send the INVITES to them etc.

Could someone please clarify?
 
Thanks,

Arun

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---

From: "Tom-PT Taylor" <[email-masked]>
Date: Thu, 25 Jan 2007 11:57:58 -0500

These attributes concern themselves only with signalling content, not 
the language of the media stream. For that I think you need to use 
Caller Preferences.

---

From: Colin Perkins <[email-masked]>
Date: Fri, 26 Jan 2007 11:13:23 +0000

RFC 4566 defines "a=sdplang:" for the language of the signalling  
content, and "a=lang:" to indicate the language of the media stream.

Colin

On 25 Jan 2007, at 16:57, Tom-PT Taylor wrote:
> These attributes concern themselves only with signalling content,  
> not the language of the media stream. For that I think you need to  
> use Caller Preferences.
>
>> I am trying to understand how to negotiate human language (audio  
>> output) preferences using SDP or SIP headers;
>> RFC 2327 defines a=sdplang at the media level and so does the  
>> HTTP /SIP specs at the signaling level (Accept-Language Header).  
>> RFC 3264 offer answer does not delve into this.
>> Consider the following use case, where User A is an "English"  
>> language speaker using say G711 codec and want to conference in  
>> only certain members of a group call that not only support the  
>> G711 codec, but also understand the "English" language.
>>  So in this use case User A wants to connect to User B & E only,  
>> since the language and codec both match.(English, G711)
>> The text says session descriptions but I not clear how that is  
>> handled in offer answer. Does the "Conferencing Server" send out  
>> INVITES with Accept-Language: en (with SDP Offer) to all  
>> participants and user C is going to send a 415 indicating Spanish  
>> only, and B & E are going to respond with a 200 OK (SDP Ans). Of  
>> course User D is going to reject the SDP Offer with a 415 since it  
>> does not support G711.
>>  Also the Accept-Language in REGISTER is used by the Registrar for  
>> generating a response, which I think is a different semantic  
>> meaning, maybe using RFC 3840 the users could register the  
>> appropriate language in the contact header, that way there is no  
>> need to send the INVITES to them etc.

-- 
Colin Perkins
http://csperkins.org/