Subject: RE: [rohc] Re: multiplexing SigComp and non-SigComp messages on t he same TCP connection

From: "Price, Richard" <[email-masked]>
Date: Tue, 24 Feb 2004 17:23:06 -0000

> Hi Richard,
> 
> It looks now you have more time working/talking on SigComp. :-)

Not as much as I'd like ;-)

I can probably make some time to help out with any updates for
SigComp, if the WG concludes that there's a pressing need to
improve the support for lower-layer security. Anyone else got
an opinion on this?

Regards,

Richard

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From: Simran Suri <[email-masked]>
Date: Tue, 24 Feb 2004 20:59:39 -0600

Hi All,

I am working on providing an implementation (compression/decompression) 
for the SigComp specification, but am not making much headway. I would 
really welcome it if any of you can provide help/pointers with the 
following:

1. Does anyone have experience providing an end-to-end SigComp 
implementation? If so, are there any documents which provide information 
regarding the same?

2. Has there been any addition to the UDVM assembler/interpreter since 
March 2002? Specifically, has the implementation expanded to work with 
all the instructions in the UDVM instruction set? Also does anyone have 
any programming experience with the UDVM instruction set that can be shared?

3. I tried out the examples posted by Carsten and these worked 
perfectly. However, can anyone tell me how we got the compressed message 
in the first place? It doesn't seem that DEFLATE was used to generate 
the message, since I used the zlib shared library (which uses DEFLATE) 
on the uncompressed message and got a different message. There is some 
mnemonic code posted by Richard, but I'm guessing it's for compression 
not decompression- please correct me if I'm wrong.

4. Has anyone provided an implementation of the 
compression/decompression algorithms which use predefined dictionaries, 
for example the SIP/SDP dictionary?

Looking forward to hear from someone.

Thanks and regards,
Simran

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From: Carsten Bormann <[email-masked]>
Date: Wed, 25 Feb 2004 11:05:43 +0100

Hi Simran,

> all the instructions in the UDVM instruction set? Also does anyone 
> have any programming experience with the UDVM instruction set that can 
> be shared?

Does "the UDVM assembler/interpreter" refer to my half-baked 
implementation of the -05 draft?
I haven't got around to work on this implementation to upgrade it with 
respect to the changes we made on the way to RFC3320 and the revised 
assembler syntax we agreed on for the implementers guide.

> perfectly. However, can anyone tell me how we got the compressed 
> message in the first place?

A UDVM implementation is not a complete SigComp implementation.  In 
addition you need:
-- an interface to the higher layer protocol (e.g., SIP)
-- a state manager
-- a portfolio (>= 1) of compression algorithm implementations, and
-- UDVM code to send to the decompressor for each of these.

Clearly, these are significant pieces of work, some of which also have 
interesting IPR complications.

Gruesse, Carsten