Ascend Archive
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Re: (ASCEND) Optimal MTU & RWIN Settings ?
On Fri, May 22, 1998 at 02:04:21PM -0400, Wes Parker wrote:
> One of our customers who is heavily into gaming, is interested in having the
> most optimal dialup K56flex connection possible to our Max4004. He had
> questions about what MTU and RWIN settings we use on our Max. I believe the
> default MTU is set for 1500, not sure about RWIN.
Max default MTU is 1524. RWIN probably stands for the TCP Receive Window
Size the client is announcing to bypass TCP slow start and convince the
peer to send segments faster and with less acking expected to optimize
TCP download efficiency. This is likely of absolutely no use to gaming.
Gaming will probably use UDP anyway. RWIN tweaking can gain better down-
load rates when FTPing or surfing, but is a two-bladed sword. If you have
a modem and spurious "comm overruns" (the PCish euphemism for trash hard-
ware can't keep up with something as simple as 115.2 kbps) then a single
comm overrun will cause a retransmit of the whole RWIN of data downstream.
Besides all that, RWIN is only of interest to the two TCP peers, your
Max is not remotely involved here.
> He claims that an MTU of 576 is the most efficient. Is this something we
For his purposes this may be true. Small, interactive, almost connection-
less packet transmit & receive.
> need to tweak on the Max, or does a PPP connection auto-negotiate the MTU
> when connecting?
It does. But remember, there are two independent values, the MTU and
the MRU. This is because you have independent negotiations for the up-
and downlink. The MTU is what you want to transmit, the MRU what you can
receive. The values obviously cross over between peers.
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