Re: [Sip] Question on RFC3840/3841

Paul Kyzivat <pkyzivat@cisco.com> Thu, 10 January 2008 14:21 UTC

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Date: Thu, 10 Jan 2008 09:20:49 -0500
From: Paul Kyzivat <pkyzivat@cisco.com>
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To: Mahesh Anjanappa <mahesha@samsung.com>
Subject: Re: [Sip] Question on RFC3840/3841
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Mahesh Anjanappa wrote:
> Yes the ';' is a mistake. But i'm not sure if  each Contact should 
> contain "alice@atlanta.com"

Well, it has to have a URI to be syntactically correct.

Your problem is that you are trying to express something that cannot be 
expressed with the callee caps syntax. It only maps to a subset of the 
syntax supported by RFC 2533.

> because the predicate that i'm trying to represent is as follows meanig 
> to say
> alice supports a communication which whose capability is Duplex Audio + 
> One Way Video.

You just can't say that. Sorry.

A little history may help you to understand, though it won't solve your 
problem:

The initial draft for callerprefs came out a very long time ago. (The 
earliest draft I have is -03 which came out in november of 2000.) It set 
the basic syntax and the initial set of capabilities.

It was however very weak on the semantics of matching. I eventually got 
involved because I was interested in it and identified many of the 
semantic issues. Jonathan and I worked on it for a long time. 
Eventually, because of some review comments I think, Jonathan tried to 
define the semantics using RFC 2533 because it was a standard that 
seemed to be at least partially suitable to the task. (In retrospect 
this may not have been such a good idea, since it adds an additional 
layer of complexity.)

RFC 2533 syntax is much richer. But it was not a goal to provide that 
richness. (Mapping that all onto SIP header syntax would be awful.) It 
was only used as an intermediate form to define the semantics of the SIP 
headers.

Its understood that there are lots of things one might want to express 
that you can't express.

If you aren't already aware of it, you might want to look at RFC 4596 
(Guidelines for Usage of the Session Initiation Protocol (SIP) Caller 
Preferences Extension).

	Paul

> If each of the COntact contains alice@atlanta.com wouldnt it be 
> interpreted as " alice
> supports duplex audio and oneway video separatley and not both at the 
> same time".
> Actually i'm not quite sure how to represesnt the predicate in the 
> Contact header correctly, hence
> my Queries. It all stems from the statement which you too noted " There 
> MUST only be one instance of any
> feature tag in feature-param." in RFC 3840
> 
> 
> Predicate:
> ------------
> & ( & (sip.audio) (sip.duplex=full) )
>    (  & (sip.video) (sip.duplex=receive-only) )
> 
> regards
> Mahesh
> ----- Original Message ----- From: "Christer Holmberg" 
> <christer.holmberg@ericsson.com>
> To: "Mahesh Anjanappa" <mahesha@samsung.com>om>; "Paul Kyzivat" 
> <pkyzivat@cisco.com>
> Cc: <sip@ietf.org>
> Sent: Thursday, January 10, 2008 11:30 AM
> Subject: RE: [Sip] Question on RFC3840/3841
> 
> 
> 
> Shouldn't each Contact also contain "alice@atlanta.com"?
> 
> Also, why do you have ";" at the end of each Contact?
> 
> Regards,
> 
> Christer
> 
> 
> 
>> -----Original Message-----
>> From: Mahesh Anjanappa [mailto:mahesha@samsung.com]
>> Sent: 10. tammikuuta 2008 6:16
>> To: Paul Kyzivat
>> Cc: sip@ietf.org; Christer Holmberg
>> Subject: Re: [Sip] Question on RFC3840/3841
>>
>> hi Paul,
>> Sorry there is a mistake in Contact header i
>> described.Following is what i wanted to:
>> Contact:sip:alice@atlanta.com;
>> Contact:audio;duplex=full;
>> Contact:video;duplex=recieve-only;
>>
>> Thanks
>> Mahesh
>> ----- Original Message -----
>> From: "Mahesh Anjanappa" <mahesha@samsung.com>
>> To: "Paul Kyzivat" <pkyzivat@cisco.com>
>> Cc: <sip@ietf.org>rg>; "Christer Holmberg"
>> <christer.holmberg@ericsson.com>
>> Sent: Wednesday, January 09, 2008 10:48 PM
>> Subject: Re: [Sip] Question on RFC3840/3841
>>
>>
>> > Thanks Paul.
>> > So would it be right if i have a Contact Headers describing
>> Duplex Audio &
>> > one-way Video Capabilities as follows?
>> >
>> >    Contact:sip:alice@atlanta.com;
>> >    Contact:sip:audio;duplex=full;
>> >    Contact:sip:video;duplex=recieve-only;
>> >
>> > NOTE: The Predicate(for above) for which i'm attempting is
>> > & ( & (sip.audio) (sip.duplex=full) )
>> >    (  & (sip.video) (sip.duplex=receive-only) )
>> >
>> > regards
>> > Mahesh
>> >
>> > ----- Original Message ----- > From: "Paul Kyzivat" 
>> <pkyzivat@cisco.com>
>> > To: "Mahesh Anjanappa" <mahesha@samsung.com>
>> > Cc: "Christer Holmberg" <christer.holmberg@ericsson.com>om>;
>> <sip@ietf.org>
>> > Sent: Wednesday, January 09, 2008 7:55 PM
>> > Subject: Re: [Sip] Question on RFC3840/3841
>> >
>> >
>> >>
>> >>
>> >> Mahesh Anjanappa wrote:
>> >>> hi
>> >>> That is my understanding as well. But if that is the case
>> then it should
>> >>> apply to Contact header as well
>> >>> when describing Capabilities using Feature parameters in
>> Contact Header.
>> >>> But i'm not sure if it applies the same way. I had posted
>> this question
>> >>> long ago but didnt get any comments on it.
>> >>
>> >> The rule forbidding multiple instances of a parameter
>> applies to all
>> >> headers, so it applies to Contact.  E.g. the following is illegal:
>> >>
>> >> Contact:sip:alice@atlanta.com;methods="INVITE";methods="CANCEL"
>> >>
>> >> Paul
>> >
>> >
>> >
>> > _______________________________________________
>> > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
>> > This list is for NEW development of the core SIP Protocol
>> > Use sip-implementors@cs.columbia.edu for questions on current sip
>> > Use sipping@ietf.org for new developments on the application of sip
>>
>>
> 
> 


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