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One question:

I wonder whether ROHC should "skip compression" (if that's even
possible) on packets when compression would present a phantom MTU. I.e.,
IMO ROHC ought to be focused on reducing header overhead, which is
critical for small packets, but not on presenting a larger MTU than the
path can handle with a native (uncompressed) packet.

If that were the case, then all this MTU stuff would go away, AFAICT.

Joe


Carsten Bormann wrote:
> On May 19, 2009, at 13:25, Carl Knutsson wrote:
> 
>> As Tero pointed out, there already is a way in ROHCoIPSec to send
>> packets uncompressed.
> 
> True.  This would mean that the ROHCoIPsec path inherits the MTU of the
> tunnel minus IPsec overhead.
> But one might want to do better than that, making use of the fact that
> for many packets IPsec tunneling overhead will be mostly cancelled out
> by the inner ROHC compression.
> 
>> The tunnel already keeps track of the MTU to
>> compensate for the IP, ESP AH headers. So adding ROHC overhead should
>> not a problem. Why not let the user decide whether or not to use ROHC
>> segmentation, IP fragmentation or sending large packets through the
>> uncompressed channel.
> 
> ...where user is the person who configured the tunnel.
> Sounds good to me.
> As long as the signals that go to the end hosts allow them to do
> (PL)PMTUD predictably.
> 
>> We could list pros and cons and give some guidelines.
> 
> ...which would pretty much elaborate on my previous sentence.
> 
> Gruesse, Carsten
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