RE: [rohc] SigComp with EPIC compression for SIP messages

Hi Jean-Pierre, Pekka, Lars-Erik, all,

Apologies for the delayed response to this discussion.  Mark and I are
both at meeting this week with limited network access.

Pekka is correct in his technical explanation and labeling the algorithm
"DEFLATE with Hierarchical Huffman" rather than EPIC makes sense.  I think
it is useful to have it in the user guide, either with the other
algorithms (possibly removing the words 'well-known' in the introduction
to ch4) or in an appendix.

I hope this helps.

Best regards,

Abbie

On Thu, 24 Feb 2005, Lars-Erik Jonsson (LU/EAB) wrote:

> Date: Thu, 24 Feb 2005 11:08:19 +0100
> From: "Lars-Erik Jonsson (LU/EAB)" <lars-erik.jonsson@ericsson.com>
> To: 'Pekka Pessi' <Pekka.Pessi@nokia.com>
> Cc: "'Lepine, Jean-Pierre'" <jeanpierre.lepine@smisrd.com>, rohc@ietf.org,
>      "Abigail Surtees (E-mail)" <abigail.surtees@roke.co.uk>
> Subject: RE: [rohc] SigComp with EPIC compression for SIP messages
>
> Pekka,
>
> Thanks for the technical explanation, then it would probably be
> better to label this algorithm something like
>    "DEFLATE with Hierarchical Huffman"
> as referring to "EPIC" only confuses the reader and makes people
> look for reference material that does not exist.
>
> /L-E
>
>
> > -----Original Message-----
> > From: rohc-bounces@ietf.org [mailto:rohc-bounces@ietf.org]On Behalf Of
> > Pekka Pessi
> > Sent: den 22 februari 2005 18:49
> > To: Lars-Erik Jonsson (LU/EAB)
> > Cc: sip@ietf.org; 'Lepine, Jean-Pierre'; rohc@ietf.org;
> > sipping@ietf.org
> > Subject: Re: [rohc] SigComp with EPIC compression for SIP messages
> >
> >
> > "Lars-Erik Jonsson (LU/EAB)" <lars-erik.jonsson@ericsson.com> writes:
> > >The SigComp user guide did (I am not sure about the new version just
> > >released) refer to EPIC, which is probably a mistake as
> > algorithms are not
> > >specified in that document, and there is no reference
> > available for an EPIC
> > >algorithm.
> >
> > As you can see from the UDVM assembly code (the text also mentions
> > it) the compression algorithm referred as EPIC is just DEFLATE
> > with minor modifications. The UDVM assembly code in section 4.6
> > (and RFC 1951) is all the specification you need.
> >
> > A message compressed with DEFLATE consists of literals (bytes
> > 0..255, end-of-block) and pairs (length, distance), where length
> > is 3..258 and distance in 1..32768. "EPIC" modifies DEFLATE to use
> > INPUT-HUFFMAN-coding for literals and (length, distance) pairs
> > insted of the normal static huffman codes, as specified in RFC
> > 1951.
> >
> > So, unlike DEFLATE bytecode "EPIC" does not need tables and the
> > literal/length symbols and distance values can be directly decoded
> > with a single INPUT-HUFFMAN instruction each. Another improvement
> > (?) is with the literal/length, it has two different codings,
> > depending whether the last symbol was a literal or length+distance
> > pair.
> >
> > --Pekka
> >
> > >-----Original Message-----
> > >From: rohc-bounces@ietf.org [mailto:rohc-bounces@ietf.org]On
> > Behalf Of Lepine, Jean-Pierre
> > >Sent: den 18 februari 2005 19:18
> > >To: rohc@ietf.org; sip@ietf.org; sipping@ietf.org
> > >Subject: [rohc] SigComp with EPIC compression for SIP messages
> >
> > >Hi all,
> >
> > >I am currently looking at using SigComp with EPIC compression for
> > >SIP messages. After reading relevant RFCs and Internet drafts, a
> > >few things are not clear to me.
> >
> > >First, I understand that EPIC relies on a profile to compress and
> > >decompress data. The EPIC reference implementation from Roke
> > >Manor Research Ltd provides a profile for RTP. However, I can't
> > >find a profile for SIP.
> >
> > >Is there one out there?
> >
> > >I think I can write one but this would likely be a problem for
> > >interoperability since the decompressor MUST use the same
> > >profile. One solution would be to download the profile to the
> > >other endpoint but this does not look too good to me, partly
> > >because I have a concern about the profile size. Furthermore, I
> > >don't see how I could instruct the other endpoint to use a
> > >downloaded profile (file name and location ?).
> >
> > >Any other option?
> >
> > >Also, in the SigComp User Guide
> > >(draft-ietf-rohc-sigcomp-user-guide-00.txt), section 4.6 is
> > >talking about EPIC and SIP but never mentions the need or
> > >existence of a profile.
> >
> > >Without a profile, how can EPIC be used ?
> >
> > >The mentioned section also shows compression results for three
> > >algorithms, including EPIC. All algorithms employed a static
> > >dictionary and shared compression.
> >
> > >Exactly how the EPIC results were obtained is not clear to me, in
> > >particular how EPIC was used ?
> >
> > >Only the Hierarchical Huffman algorithm ?
> >
> > >EPIC used in conjunction with DEFLATE ?
> >
> > >Did all three algorithms used the static dictionary
> > described in RFC3485 ?
> >
> >
> >
> > >Any help would be really appreciated, Thanks.
> >
> > >_______________________________________________
> > >Rohc mailing list
> > >Rohc@ietf.org
> > >https://www1.ietf.org/mailman/listinfo/rohc
> >
> > _______________________________________________
> > Rohc mailing list
> > Rohc@ietf.org
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> >
>

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