Subject: [rohc] ROHC-TCP & CRC

From: "West, Mark" <[email-masked]>
Date: Sun, 7 Sep 2003 22:29:01 +0100 (GMT Daylight Time)

Hi all,

Well -- here we go again...

I'd like nothing better than to move forward!  Especially since we're
currently thinking actively about writing a sensible TCP profile.

Now, I believe that we had consensus that we wanted an IPR-free TCP
solution (ok -- a solution for which we were not obviously aware of any
IPR)?  It's becoming increasingly unclear to me exactly what this means,
mind you.

So, if anyone can help establish consensus for the CRC issue (at least), I
feel that we will have made some progress.

Some people have understandable difficulty in joining in this discussion,
but I encourage everyone else to have their say.

Options as I currently see them:

1/ Use a checksum (e.g. CRC) over just the uncompressed packet
   (as per 3095, but no context repair and no static/dynamic split)

2/ Just use the TCP checksum (as 1144/2507)

3/ Add some validation to (2) based on non-header data
   (e.g. the MSN and the compressed data)

Personally, I would go for (1), since I think there is a *ton* of prior
art on the core idea (RFCs 1950, deflate, ...).  (And I no longer see any
point in trying to fudge around this one: either use it, or do something
quite different)

(2) seems to be weak, and going that route undermines one of the reasons
for doing ROHC-TCP.  (I note in passing that (2) [RFC 2507] would also
infringe the IPR claimed on (1), except that it actually appears to be
prior art...)

(3) has some merit, but is a completely untested idea.

Ok.

I vote for (1) -- and if someone *really* wants to claim IPR on it, that's
their problem...

We need working-group consensus, though, so what say you..?!

Cheers,

Mark.

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From: Ghyslain Pelletier <[email-masked]>
Date: Tue, 09 Sep 2003 08:29:43 +0200

Hi Mark,

Thanks for activating this discussion and for listing possible
alternatives regarding decompression verification with ROHC-TCP (this is
also applicable to ROHC-CR btw).

> Personally, I would go for (1)

> I vote for (1) -- and if someone *really* wants to claim IPR on it, that's

I second that. I think your assessment of all alternatives and
especially 1/ is correct.

> So, if anyone can help establish consensus for the CRC issue
> (at least), I feel that we will have made some progress.
>

Unless we hear any objections (i.e. we have consensus), when updating
the TCP profile and the context replication draft, I will go with
alternative 1/ as you listed.

/Ghyslain

-- 
Ghyslain Pelletier, Dipl. Ing.
Wireless IP Optimizations
AWARE - Advanced Wireless Algorithm Research
Ericsson Research, Corporate Unit

Ericsson AB, Laboratoriegränd 11
Box 920, S-97128 Luleå, SWEDEN
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From: Gorry Fairhurst <[email-masked]>
Date: Thu, 11 Sep 2003 17:07:26 +0100

I'd defintely vote for (1).

It seems to be the classic way to perform a CRC.
This would give you a behaviour that is well-understood.

Gorry Fairhurst