RE: [rohc] RE: [Sipping] SIGCOMP and large binary content SIP messages

[zhigang.c.liu@nokia.com]

Lars-Erik,

IMO, binary content in application message is a general issue for
SigComp multiplexing. It's not specific to SIP. I already explained 
this in rohc and sipping mailing list. But here is a simple example. 

Let's say endpoint A already knows endpoint B supports SigComp on TCP 
port number 5000. A sends, on port 5000, uncompressed message 1 followed 
by message 2 compressed using SigComp. From RFC 3320, message 2 starts
with bit pattern 11111. So, if message 1 has no binary content, endpoint
B can easily detect the beginning of message 2 (i.e. end of message 1)
by detecting 11111. However, if message 1 contains binary content,
that means the (uncompressed) binary part may contain byte 11111xxx.
This "mimicking" will make endpoint B mistakenly think a new SigComp
message starts at that byte. Obviously, things will be messed up
from that point.

This is what I referred to as the multiplexing issue. I hope I explained
it better this time for you. 

Anyway, I'll submit a personal draft to help the discussion, although the 
above example should make it obvious already.

Zhigang


> -----Original Message-----
> From: ext Lars-Erik Jonsson (EAB)
> [mailto:Lars-Erik.Jonsson@epl.ericsson.se]
> Sent: March 27, 2003 2:18 AM
> To: Liu Zhigang.C (NRC/Dallas)
> Cc: rohc@ietf.org
> Subject: RE: [rohc] RE: [Sipping] SIGCOMP and large binary content SIP
> messages
> 
> 
> Zhigang,
> 
> > My question is the handling of binary content in application 
> > messages. In my view, this is a generic issue although it started
> > with SIP. My thought was to have a *separate* document that
> > addresses this issue (and perhaps other generic SigComp "bugs" if
> > we find out).
> 
> First of all, it is not yet clear to me that this is a general issue,
> at least I have not been able to see consensus on that. Secondly, if
> we have general unclear issues with SigComp, those would go into the
> Implementer's guide at this point.
> 
> Currently, I therefore think we can and should avoid having even more
> documents.  However, you can always provide input by writing a draft,
> that is up to you.
> 
> Regarding the SigComp&SIP document, it does not matter much
> in which WG it is "hosted", as long as it is written and well 
> reviewed 
> by people from both sides.
> 
> 
> Rgds,
> /L-E 
> _______________________________________________
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> Rohc@ietf.org
> https://www1.ietf.org/mailman/listinfo/rohc
> 
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