[6939] in North American Network Operators' Group
Re: Questions about Internet Packet Losses
daemon@ATHENA.MIT.EDU (Vern Paxson)
Tue Jan 14 00:29:19 1997
To: Tony Li <tli@jnx.com>
Cc: nanog@merit.edu
In-reply-to: Your message of Mon, 13 Jan 1997 20:24:46 PST.
Date: Mon, 13 Jan 1997 21:17:57 PST
From: Vern Paxson <vern@ee.lbl.gov>
> 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
