MTU & RWIN recommendations

[Rik Bean]

I'm running XP Pro SP1 with a 10/100/1000 NIC and a Netgear DG834
router. My ISP provides a 1mbps service, ADSL, PPoA. I'm trying to
decide the best values for MTU and RWIN, but everywhere I look I seem
to get different advice. Currently I am using 1430/65535 as these
figures seem to give me the best results using a UK speed test and a
17.8MB d/l from a consistent site (times will vary by about 1 second on
repeated attempts, different times and days).

However, DSL reports recommends a much smaller RWIN, between 11120 and
29190. This slows both speed test and download speeds noticeably.

(full details:
http://tinyurl.com/augpf )

I don't know enough to work out why the figures I use seem to work
better than the figures advised, so any help would be appreciated.

 

[Jack]

Hi
May be this can Help.
Optimizing the TCP/IP Stack - http://www.ezlan.net/Internet_Speed.html
Jack (MVP-Networking).

 

[Hans-Georg Michna]

I'm running XP Pro SP1 with a 10/100/1000 NIC and a Netgear DG834
router. My ISP provides a 1mbps service, ADSL, PPoA. I'm trying to
decide the best values for MTU and RWIN, but everywhere I look I seem
to get different advice. Currently I am using 1430/65535 as these
figures seem to give me the best results using a UK speed test and a
17.8MB d/l from a consistent site (times will vary by about 1 second on
repeated attempts, different times and days).

However, DSL reports recommends a much smaller RWIN, between 11120 and
29190. This slows both speed test and download speeds noticeably.

(full details:
http://tinyurl.com/augpf )

I don't know enough to work out why the figures I use seem to work
better than the figures advised, so any help would be appreciated.

Rik,

I see no reason whatsoever to reduce the RWIN much below 65,535,
escept that you should lower it to the nearest multiple of your
MSS value (usually MTU - 40, a typical RWIN value for a PPPoE
router connection is 63888 if the MTU is 1492 bytes).

Reducing RWIN will only reduce your throughput on long distance
connections with longer lag.

Hans-Georg

Hans-Georg