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Re: Questions about Internet Packet Losses

  • From: Vern Paxson
  • Date: Tue Jan 14 00:39:52 1997

>    indicate that 9% of the packets had a 512 byte *payload*.
> 
> I already subtracted off the 40 bytes for the headers.  I meant MSS.

(By payload, I meant data, i.e., not including headers, same as you ...)

> However,
> the spikes in the packet percentages are clearly due to hosts using that
> MSS.  You would otherwise expect to see a "smooth" distribution across
> packet sizes, which is not at ALL what's happening.

Right, spikes correspond to MSS's (and other effects like acks & SYN/FIN's).

Are you saying the data shows significant spikes at other, non-standard MSS
values?  If it does, then (modulo some thinking about the particular numbers)
I agree that they're likely MSS candidates and support the notion that weird
MSS's are being used.  But if the data has a few spikes at things like 512
but no strong spikes at non-standard values, then that doesn't help distinguish
between (1) lots of weird TCP's using weird MSS's, vs (2) lots of packets
that are less than full-size because the mainstream TCP didn't have enough
bytes to fill them.

If your data is available, I'd love to take a gander at it.

		Vern
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