Re: [Sip] Question on RFC3840/3841

Paul Kyzivat <pkyzivat@cisco.com> Thu, 10 January 2008 15:03 UTC

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Date: Thu, 10 Jan 2008 10:03:32 -0500
From: Paul Kyzivat <pkyzivat@cisco.com>
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To: Christer Holmberg <christer.holmberg@ericsson.com>
Subject: Re: [Sip] Question on RFC3840/3841
References: <CA9998CD4A020D418654FCDEF4E707DF03F7A681@esealmw113.eemea.ericsson.se> <038901c852c3$d222b750$bd4a6c6b@sisodomain.com> <4784D96A.5010104@cisco.com> <040101c852e3$a627f730$bd4a6c6b@sisodomain.com> <004401c8533f$8d197500$bd4a6c6b@sisodomain.com> <CA9998CD4A020D418654FCDEF4E707DF03FA6BD8@esealmw113.eemea.ericsson.se> <006401c85386$59ec2370$bd4a6c6b@sisodomain.com> <478629C1.5090404@cisco.com> <CA9998CD4A020D418654FCDEF4E707DF03FD0FDC@esealmw113.eemea.ericsson.se>
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Christer,

RFC3840 by itself, without 2533, is *not* sufficient to understand how 
to do the matching.

I put an appendix in RFC 4596 that gives an algorithm without reference 
to 2533. I *think* it is right, but of course it is not normative.

Note that IMO none of this is intuitive or straightforward. Every time I 
get a detailed question on it I have to do a bunch of review before I 
can answer it. (But maybe that's just because I don't have enough 
neurons left.)

	Paul

Christer Holmberg wrote:
> Paul,
> 
> Regarding the matching, are you saying that reading RFC3840 is enough to
> understand how the matching is done in a "SIP environment"? Or, do I
> also need to read RFC2533?
> 
> I have some questions on the matching, but I will come back to them
> later. I still have some reading to do.
> 
> Regards,
> 
> Christer
> 
>  
> 
>> -----Original Message-----
>> From: Paul Kyzivat [mailto:pkyzivat@cisco.com] 
>> Sent: 10. tammikuuta 2008 16:21
>> To: Mahesh Anjanappa
>> Cc: Christer Holmberg; sip@ietf.org
>> Subject: Re: [Sip] Question on RFC3840/3841
>>
>>
>>
>> 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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