Setting RWIN

[Rik]

I normally have two machines, a desktop (XP Pro SP2) and a laptop (XP Home SP2), networked through a DG834G. Unless I'm going walkabouts, I use a wired connection for the notebook. The notebook actually only just predates moving to IDNet, and I'd noticed it gave a lower throughput on speedtests than the desktop, but I hadn't had time to delve. However, as my desktop, with on-site warranty, has been taken back to the factory by Evesham, I thought the time had come.

What I discovered was that neither DrTCP nor TCP Optimizer were setting RWIN to my chosen value (I find 32120 works best on my line), but were leaving it at 8760. (I had chosen the correct adaptors and the issue affected wireless as well as wired.) The only way I could change the values was to search the registry for the TCPWindowSize key and modify each of them manually.

Has anyone else met this kind of problem or know any cure? Google didn't show up much, at least for the search phrases I used.

Thanks.

[Nerval]

I've never come across that rik.
All Dr TCP does is mod the registry anyway, isn't it? And presumably you rebooted to make the change effective?

That said, I've tried every combination of MTU and RWIN under the sun, and it's made not a blind bit of difference to anything.  Perhaps Dr TCP wasn't actually doing anything for me either.
The router shows the MTU, but how do you check the RWIN other than by looking at the registry?

[Rik]

Go here:

http://www.speedguide.net/index.php

and select the TCP/IP analyzer. It will report your actual MTU/RWIN values.

[Rik]

Replying to self...

Peculiarly, my MTU/RWIN from two sites are being reported as 1460/32660, which bear no relationship to the settings I have in Windows or the router.

MTU could be controlled by IDNet's network, I think, but RWIN...

[Nerval]

Right
In the interests of science, I've just used Dr TCP (version 21) to change the RWIN

It says settings in your router could limit your MTU anyway - mine is 1458 and always has been as far as I know.

The RWIN was 65535 - presumably some sort of default, so I changed it to 521824 ( or something like that that it recommended) and rebooted.  Anyway, your check confirmed that it had worked, and a speedtest showed it had knackered my speed, so I changed it back, your check confirmed that it had changed back, and the speedtest returned to normal.

Not much help to you I'm afraid, but it showed at least that Dr TCP did change the RWIN for me.

[BassoProfundo]

I've used Dr TCP many times in the past and have generally been dissatisfied with it. As far as I can tell, it doesn't go into the adapter settings in the Registry and change RWIN as it should.

Instead, I've used TCPOptimizer (from speedguide.net) which does altogether a better job.

All in all though, I've found that any improvements due to changes in RWIN tend to be totally swamped by the natural variations in download speed caused by countless other factors. I've given up messing with it.

[Rik]

Not much help to you I'm afraid, but it showed at least that Dr TCP did change the RWIN for me.

Thanks for trying. The one thing I can't eliminate is the computer, as my desktop is in for repair. This is one of those frustrating issues that proves comms is still a black art! 

[Rik]

All in all though, I've found that any improvements due to changes in RWIN tend to be totally swamped by the natural variations in download speed caused by countless other factors. I've given up messing with it.

I know what you mean, though I find that increasing RWIN by much, eg x2, tends to slow my system, the line being poor.

However, I wish I could explain the change in the figures being reported from those I've set, especially as they were reporting correctly yesterday.

Typically, my desktop is in for repair, so I don't have a spare machine to test with, thus eliminating something weird in the notebook setup.

Computers!

[BassoProfundo]

Well I'm a bit lost as to which router you're on now.

What is the MTU set in your router?

Is PathDiscovery turned on?
Is Window Scaling turned on?

Have you tried:

1) setting the MTU in the router to 1500, then
2) set the MTU on the laptop to 1500, then
3) reboot, then
4) perform a ping -f -n xxxx www.bbc.co.uk
with varying values of xxxx ? Start at 1400 and carry on upwards until it tells you the packet is fragmented. Your MTU should be set (on the PC) to your last successful ping size + 40.

TCP Optimizer will do step 4 for you to determine the maximum MTU for your connection.

Let us know how you get on.

[Rik]

You're lost, how do you think I feel! 

I'm on a DG834G now. MTU in the router is set to 1500. MTU on the computer, all adaptors, is set to 1500 while RWIN is set to 32120. I've searched right through the registry and verified that these values are set. They also show when DrTCP or TCP Optimizer are run.

Maximum defragmented ping to the BBC is 1472, which I think is the correct figure for an MTU of 1500? (ISTR the overhead is 28 bytes)

I did the testing both manually and with TCP Optimizer, to double check.

Scaling wasn't on (I could have sworn it was, path discovery was. Changed!

[Rik]

Talking to myself... nothing new there. 

Just been playing with RWIN values. If I set the computer to 256960, it is reported back correctly by all three sites. A value of 32120 is reported as 32660, a value of 62240 is reported as 62480.

I'm sure there's a logical answer, I just can't work it out. 

[maxping]

I use 200480 / 1500 and it works fine.

Remember to reboot when you change and save any settings in DrTcp.

[Rik]

Thanks, I'll try plugging them, well RWIN,  in and see if it makes any difference.

Why do laptops take such an age to boot (or any machine if you're waiting, tbh )?

[Nerval]

Well rik
In the interests of avoiding carp on the telly, I've done some further tinkering with Dr TCp.
I used it to put the MTU and RWIN to Max's recommendations - 1500 and 200480 (and changed MTU on router)

When I rebooted and checked what they were, the MTU was 1460 and the RWIN 201640.
And just out of interest, the speedtesters trickled stuff through so slowly I thought I'd gone back to Plusnet.

So I reset them to 1458 and 65535, which it did correctly, and everything is flying through again.

Odd that it changes some values right, but amends others for you.

But anyway, that is my final foray into changing those parameters, and I'll stick with the settings that it defaulted to for me in the first place.

None of this helps you, but I thought you'd be interested.

[MoHux]

As a matter of interest rik, Window Scaling should NOT be 'ON' if the RWin is under 65535.

It sounds to me you are a good canditate for Vista!  These settings are made dynamically by the system I read yesterday!!

BTW especially if you're on Max, and want to know the RWin to set.
Use DrTCP and set a VERY high RWin (500000'ish), then go to dslreports and do the tweak test.  At the bottom as you probably know it will tell you the range that the RWin should be between for your given MTU/MSS.  Use either of their numbers as a starting point

HTH   

[Nerval]

Rik

A further thought occurs as I let the cats out, you could ask about your RWIN problem on tweak guides where they claim to be all-knowing.  Whether they are, or not......................?

[Rik]

As a matter of interest rik, Window Scaling should NOT be 'ON' if the RWin is under 65535.

Thanks, I didn't know that. I'll change it back.

It sounds to me you are a good canditate for Vista!  These settings are made dynamically by the system I read yesterday!!

I'm only a candidate for Vista when it reaches SP1 and all the bugs are sorted! I don't trust MS enough to risk a first-release of any product, especially if they are making it difficult to use external security products.

BTW especially if you're on Max, and want to know the RWin to set.
Use DrTCP and set a VERY high RWin (500000'ish), then go to dslreports and do the tweak test.  At the bottom as you probably know it will tell you the range that the RWin should be between for your given MTU/MSS.  Use either of their numbers as a starting point

HTH   

Thanks, I've been there and it likes my current value. Given I've got a long, aluminium line, I have an IP profile of 2500. Much larger valuess for RWIN tend to slow the system down significantly. If only I could persuade BT to give me some nice thick copper.

[Rik]

Rik

A further thought occurs as I let the cats out, you could ask about your RWIN problem on tweak guides where they claim to be all-knowing.  Whether they are, or not......................?

Thanks, I'll try that.

[Rik]

Well rik
In the interests of avoiding carp on the telly, I've done some further tinkering with Dr TCp.
I used it to put the MTU and RWIN to Max's recommendations - 1500 and 200480 (and changed MTU on router)

When I rebooted and checked what they were, the MTU was 1460 and the RWIN 201640.
And just out of interest, the speedtesters trickled stuff through so slowly I thought I'd gone back to Plusnet.

I appreciate your suffering in my cause. The fact that we're both seeing 1460 as the reported MTU suggests to me that it's a limitation within IDNet. Curiously, if I ping the Beeb using the -l and -f flags, or use TC Optimizer to do it for me, it tells me the maximum unfragmented packet is 1472, so an MTU of 1500 is OK. What puzzles me is the RWIN change. I thought that was purely a Windows setting, and should be fixed, regardless of the network.

So I reset them to 1458 and 65535, which it did correctly, and everything is flying through again.

I'm still using 1500 for MTU, though I know Miriam prefers 1458, perhaps I'll try that next (more re-booting <sigh>). We use a similar RWIN, so I wonder if your line characteristics are as bad as mine? Anything much larger and the re-transmits shoot up.

Odd that it changes some values right, but amends others for you.

But anyway, that is my final foray into changing those parameters, and I'll stick with the settings that it defaulted to for me in the first place.

None of this helps you, but I thought you'd be interested.

Indeed I am. I know that DrTCP or TCP Optimizer are changing the values on the machine, as I've looked at the registry. As I say, I can see how MTU can get squeezed anywhere along the way, but the RWIN change does confuse me. I'll let you know if I find the answer.

[Nerval]

I wonder if your line characteristics are as bad as mine? Anything much larger and the re-transmits shoot up.

Not a good line at all apparently. 
Atten 50, and SNR margin varies from 6 to FA during the day.
When I first went broadband, they said I'd need an engineer visit to get 1Mb, but I'm stable at 4.5 on Max, somehow or other. Though the Netgear router definitely helps here - I couldn't get above 3 with Solwise or Safecom.

[Rik]

Line sounds a bit better than mine, I've got 56db attenuation. My target noise margin is 9db, but that will fluctuate from 2 - 9db, during the day it's usually in the 6-9db range, evenings it goes lower. When I had the 6db 'normal' margin, I was going to -1db and losing sync, so I requested the extra 3db on the target and that solved the problem. At 6db, I could get a 3000kbps profile, but an unstable line which meant it often dropped. At 9db, I only get a 2500 profile, but it stays that way (did briefly lift when I migrated in last week), but my sync speed was only 32k inside the 3M profile - BT should use smaller increments imo.

OTOH, my neighbour, who has an unsecured wireless router with an SSID of NETGEAR and an unchanged admin password, has attenuation of 62db, with a fixed 512k service. What a difference a few yards make.

Opinions on routers seems to have changed drastically since Max. Netgear were often derided before, but they seem to have come into their own now. Certainly, I find it gets a better sync and holds it compared to other brands that we considered 'cream' before Max, eg Draytek. (This may only apply to long lines, of course.)

Turning back to tweaking, I have found that I get optimum performance, and accurate reports of my settings with an MTU of 1458 and RWIN of 63810. This suggests to me that, IDNet do have some sort of throttle (I use to use 1430 on Wanadoo), and I'm speculating that if the machine's MTU is larger than the system's, it somehow throws the RWIN 'perception' out. I'll dig some more, but I think these settings are where I'll leave it now.

Thanks for your help. (BTW, DSLreports didn't lke 65535 as an RWIN for me, hence the 63810.)

[bat400]

Hi there,

Just joined idnet from virgin.  Already impressed.  I too have a
Netgear DG834G router.

After virgin my MTU was 1430 and RWIN was 13900.  Using info
from this page I eventually settled on MTU 1458 and RWIN 65228
with no scaling.  I set the router MTU to 1458 as well.

This took my speedtest.net speed from 2478kbps to 2929kbps,
and my ping from 74ms to 54ms!

Thanks guys,
Al Reynolds

[Lance]

Welcome to the forum, Al. Have a welcome karma!

Glad the forum has helped!

[Simon]

  Al!