Subject: [Sip] SigComp with EPIC compression for SIP messages

From: "Lepine, Jean-Pierre" <[email-masked]>
Date: Fri, 18 Feb 2005 13:17:43 -0500

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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.

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