Subject: [rohc] TCP packet formats

From: "West, Mark" <[email-masked]>
Date: Wed, 24 Mar 2004 10:41:25 -0000

Hi all,

Thought I'd try something a bit radical and forward looking...  So, amongst
the questions on RFC 3095 & SigComp, here's something a bit different!

I'm currently revising and refining the packet formats for TCP header
compression, and we'd quite like this set to be very close to, if not
actually, the 'right' answer.

In terms of general structure, I don't see any real problems, but in terms
of targetting the *compressed* packet formats, it's worth polling for
opinions.  So, come on, don't be shy...

The issue is really this: what environment are we aiming for?

TCP is a complex protocol and there are a number of variables that affect
compression including end-system configuration; end-to-end latency; link
bandwidth; and error rates.  I'm trying to run a few simple experiments to
assess how sensitive the compression might be to changes.  

At the end of the day, though, we are going to have to pick a 'sweet-spot'
expectation.  Let me stress that this decision will *not* cause the header
compression to 'break', under any circumstances.  However, using it on a
link with wildly different characterstics from those chosen will almost
certainly reduce the compression efficiency.

My gut feel is that we are looking at systems that are configured
appropriately for links of up to a small number of Mbit/s; with up to (say)
200-300ms latency; and a modest error rate (2-3%)?

I will say again: this is *not* about constraining TCP compression to work
only on links with these characteristics: it *is* about trying to dimension
the expected changes that the compressed packet formats should deal with
most efficiently.

Any thoughts..?

Cheers,

Mark.

-- 
Mark A. West, Senior Consultant Engineer
Roke Manor Research Ltd., Romsey, Hants.  SO51 0ZN
Phone +44 (0)1794 833311   Fax  +44 (0)1794 833433

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