Subject: [rohc] Sigcomp presence-specific dictionary

From: Miguel Garcia <[email-masked]>
Date: Tue, 06 Mar 2007 09:23:50 +0200

Hi.

I have been working on a presence-specific static Sigcomp dictionary for 
SIP presence. The draft is addressed to the SIMPLE WG, which is working 
on SIP presence. But I want to make the ROHC WG aware of the draft and 
solicit comments.

Until the draft is officially available, you can download a copy from:

http://people.nokia.net/~miguel/drafts/pre/draft-garcia-simple-presence-dictionary-02.txt
http://people.nokia.net/~miguel/drafts/pre/draft-garcia-simple-presence-dictionary-02.html

I don't expect that ROHC comments on the input strings (Appendix A), but 
on the result dictionary.

BR,

         Miguel
-- 
Miguel A. Garcia           tel:+358-50-4804586
Nokia Research Center      Helsinki, Finland

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From: cco <[email-masked]>
Date: Mon, 26 Mar 2007 12:03:09 +0200

> http://people.nokia.net/~miguel/drafts/pre/draft-garcia-simple-presence-dictionary-02.html

cristian: hi! the section "1.  Introduction" says at some point:

"Sigcomp endpoints will announce the availability of
   one or both dictionaries during the Sigcomp initialization phase."

what exactly do you mean by "Sigcomp initialization phase"? sigcomp is
piggy-backed on SIP in this case and there is no explicit sigcomp
"signalling".

on the other hand rfc3485, "The Session Initiation Protocol (SIP) and 
Session Description Protocol (SDP) Static Dictionary for Signaling 
Compression (SigComp)", defining a similar dictionary (sigcomp "local" state)
puts a requirement on the implementation of sigcomp stacks for sip:

"The static dictionary is unique and MUST be available in all SigComp
   implementations for SIP/SDP."

(and the need for such a requirement is also explained in the rfc.)
why not having the same kind of req. in your draft?

bye now!
cristian

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From: Miguel Garcia <[email-masked]>
Date: Mon, 26 Mar 2007 14:46:07 +0300

Hi Cristian:

Thanks for your comments. Inline answers.

> piggy-backed on SIP in this case and there is no explicit sigcomp

"SigComp initialization phase" refers to when the
endpoint has not received an acknowledgment from the other end
that the other end has received the message containing the
announcement about presence dictionary. Perhaps the text would be better
phrased as:

    Sigcomp endpoints will initially announce the availability of one
    or both dictionaries until the other end acknowledges that it has
    received the announcement.

> why not having the same kind of req. in your draft?

We were able to mandate the SIP dictionary for SigComp because they were 
created at the same time. However, nowadays, there are millions of 
deployed SIP endpoints that implement SigComp (and the SIP static 
dictionary), presence, and other services, that do not obviously 
implement the presence-specific dictionary that we are discussing here. 
So, obviously, we cannot assume that an implementation will have a 
built-in presence-specific dictionary, unless it is advertised.

BR,

      Miguel

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From: cco <[email-masked]>
Date: Mon, 26 Mar 2007 14:18:34 +0200

On Mon, Mar 26, 2007 at 02:46:07PM +0300, Miguel Garcia wrote:
> >>I have been working on a presence-specific static Sigcomp dictionary 
> >>for SIP presence. The draft is addressed to the SIMPLE WG, which is 
> >>working on SIP presence. But I want to make the ROHC WG aware of the 
> >>draft and solicit comments.
> >>

cristian: o.k. I understand; however this will reduce the "initial" 
compression efficiency (compared to a scenario where the dictionary will 
be used right on from the start). 

bye now!
cristian