Subject: [Sip] signaling message compression - speed up

From: "Liu Zhigang.C (NRC/Dallas)" <[email-masked]>
Date: Wed, 29 Aug 2001 16:03:31 -0500

Hi,

Three weeks has past since the last IETF meeting. Is there
any news on the official change of ROHC charter to include 
the work of signaling compression?

The schedule of this work item (from what I heard) is
quite aggressive. To achieve that, should we start to
piece good ideas from different proposals together and 
create a new draft? From there, we can proceed with a 
few cycles to refine it.

Specifically, besides the current discussion on Huffman 
encoding and tree structured dictionary, we should also
consider the following:

1) User specific dictionary (seems every agreed during
the discussion)

2) Maintain dynamic dictionary across session. It is 
reasonable not to throw away the synchronized dictionary.

3) Shared mode. Should help, especially for SIP messages.

4) Make sure the dictionary synchronization is robust
against packet loss/misordering. Complexity may be
affected by dictionary structure.

5) Concurrency issue (re dictionary updates) in shared
mode.

6) Make sure a misordered message can still be decompressed
correctly (related to 4 and 5 but a different issue)

7) Protocol is generic. E.g. if tree structured dictionary
is used, should make sure Lempel-Ziv is still possible and
not penalized. Also, should not depend on SIP-specific
knowledge (although is should work well compressing SIP).

8) Template encoding. Very useful for simple low-end terminals, 
which are probably the majority during the introduction
of SIP to cellular.

9) Anything else?

Above are just some tools we already have and can be used
to tackle the problem. Most of them are simple. It would be 
good if we put them together and then tune the protocol to 
reach a good tradeoff between compression efficiency, 
complexity and flexibility.

Comments?

BR,
Zhigang

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