Drop in Wireless Speed

I am trying to solve this annoying puzzle. I would appreciate any help! Over the last couple of days I have noticed that while my ethernet speeds are what I expect them to be - around 6mbs - my wirless speeds have dropped by about half of that

. I have tried two different routers - a BT HomeHub 2.0 and Netgear DG834N and both with and without encryption, but the results are the same. I

have even added a Belkin wireless adaptor to my laptop, but still no joy! What could be the problem?

P.S I noticed that there are a lot of wireless networks active this weekend - even more than usual. Could that be the reason?

Interference from other users can affect your speeds. You could try using a different channel.

Have you measured your radio throughput before. If you haven't perhaps it's always been lower. If you are using Windows XP try the freeware TCPOptimizer to tweak your settings.

See http://www.speedguide.net/downloads.php

Thanks for your prompt reply John. I have solved the problem - it was the rwin setting. I carried out a tcip repair and did not realise it caused my rwin settings to revert back to default. I raised them again and speeds are back to normal again Amazing how both Netgear and Belkin technical support never suggested that.

Edited by deleted (Sun 26-Jul-09 00:47:36)

I have exactly the same problem - noticed it last night !
Wireless speed on the laptop dropped from the usually rock steady 10 Mb/s to around 4 Mb/s consistently.
No changes made during this time but double checked router settings (Linksys WAG200G) and also laptop wireless settings (Intel 54 Mb/s wireless G Dell laptop card)
Hard wired ethernet from laptop to router gives normal speed of 10 Mb/s - so it can't be my ISP (O2)
Wireless speed on another desktop PC running Windows XP SP3 is as usual (10 Mb/s) from the same router so it can't be the router that is faulty.
Laptop also runs Windows XP SP3 - 17 July was the last day I tested speed on the laptop and obtained ~ 10Mb/s.
I ran anti-virus and found one trojan - which was removed. Also restored laptop back to 17 July but still got the same low wireless speed.
Tried different sites for speed testing and still obtained ~ 4 Mb/s

I'm wondering if there was some windows update or some other virus during the last 48 hours - as only the laptop was used during this time.
Anything else to look for ?

You could try my suggestion below - use DrTCP and tweak RWIN and MTU settings. I have found the effects to be remarkable.

P.S See my post below. ("Massive Speed Gain Through Raising RWIN")

Edited by deleted (Sun 26-Jul-09 00:43:06)

Thanks. I've used Dr TCP and TCP Optimizer for many years and also checked again to see if RWIN/MTU values were somehow changed but they are still the same as before.
So my lower speeds are still a puzzle !

Sorry to hear that - I was hoping my solution would work for you.
(My experience is that persevering in investigating the source of the problem eventually pays off - at least till the next issue arises!)

Any positional change to either device. Any new obstruction. Any new source of electrical noise. Is this pairing closer to a neighbour using the same channel?

In reply to a post by john2007:

Interference from other users can affect your speeds. You could try using a different channel.

Have you measured your radio throughput before. If you haven't perhaps it's always been lower. If you are using Windows XP try the freeware TCPOptimizer to tweak your settings.

See http://www.speedguide.net/downloads.php

No, it won't be interference - wi-fi is a service designed to have may users on a given channel. If it wasn't, then wi-fi hot spots and wi-fi in hotels would not work. What can happen is a slow-down caused by lots of users using the channel at high throughput.

I suppose "other users sharing the same channel" might have been better than "interference from other users". Mind you interference has several meanings and the overall phrase is shorter.

Unless someone was using a wireless network to transfer data between PC's on the same LAN, I doubt whether it would make a vast difference. The average ADSL connection is not going to push a "wireless g" connection to anywhere near its full capacity. It should be able to support at least half-a-dozen users, even if they are all streaming video off the web.

Managed to find the solution by accident !
It appears to be the location of the laptop ! (Just also saw the question from John2007 re: this).

The laptop is always in the dining room (downstairs) while the router is upstairs in the bedroom.
On Friday night I took the laptop to the bedroom (about 6 feet away from router) because my daughter had a birthday party downstairs and when I noticed sluggish performance on the laptop I checked the speed and obtained around 4 Mbps consistently on the wireless and around 10 Mbps on the wired connection. Today, after the party, the laptop came back to the original location and lo and behold wireless speeds are back to normal (10 to 11Mbps) !

Date Downstream Upstream
26/07/09 21:11 9786.50 Kbps 935.01 Kbps
26/07/09 21:10 10920.33 Kbps 934.98 Kbps
26/07/09 21:10 11037.20 Kbps 934.43 Kbps
25/07/09 17:51 3541.19 Kbps 893.99 Kbps
25/07/09 17:50 3834.60 Kbps 885.29 Kbps

The puzzle for me is why is the wireless speed so low when the laptop is so close to the router ?
And why does the speed double when the laptop is located downstairs - where the signal has to go through many thick walls ? (The Windows wireless connection icon shows it is connected at 54 Mbps at both locations)

I vaguely remember seeing a post a year or so ago saying that placing the PC very close to the router had negative effects because of signal interference etc ?
I'm sure there is a scientific explanation for what I observed and someone will come forward with it.
Thanks for your help anyway.

Yes, the cause was apparently the location - see my reply to HAS below.
I would normally always look for the CHANGE as you suggested - however this time the change was apparently so insignificant that I did not think of taking it seriously !
I never ever thought that moving the laptop closer to the router would reduce speed by half !

Glad you sorted it out

I've got a new issue now lol! Intermittent momentary loss of Wlan connection. I have played around with different channels and different forms of encryption and it still occurs. I used Inssider and discovered that there are around 16 or so wireless networks in the immediate vicinity all using different channels - particularly 1,6 and 11. So I have deduced it must be interference causing the wlan dropouts (wan connection seems stable). Not sure if much can be done about this ?

Are you sure that the signal is dropping ? Or is the laptop busy doing something else ? Check that the wi-fi on the laptop isn't set for power saving. Wi-fi isn't a physical "connection" as such - you're only tapping in to an RF bitstream.

Does the problem happen with both your routers ?

Cordless phones on your land line, sited close to the router or laptop may also ineterfere with the WLAN signal as they are at similar frequencies.
The only other thing I can think of is to check the strength of each of your neighbourhood signals on Inssider (using the latest update) and then change your own WLAN channel to one which lies in the region of least overlap with the others.

Did you get the WLAN loss of connections previously i.e. before you increased RWIN ?

I am sure it is not to do with power saving, as that is off, and I am not sure if it happens with the HomeHub, as unlike the DG834N it does not seem to keep a record of WLAN uptime.

P.S have mobiles but not cordless phones.

P.P.S I do check my neighbours' signals and change channels. The problem is that I have a lot of wireless signals around, using every channel under the sun!

Edited by deleted (Mon 27-Jul-09 12:35:29)

In reply to a post by JoeKidd:

I'm sure there is a scientific explanation for what I observed and someone will come forward with it.

The receivers in WLAN systems use automatic gain control to ensure that the signal fed to the ADCs is within the required amplitude limits for successful demodulation.

If the two are very close together, even with the receiver gains at their lowest values, it is possible for the AGC to be unable to ensure that the modem receives a clean enough signal to keep the packet error rate low enough. As this changes on a packet to packet basis you will find that some packets will need retries while others don't.

Result, slow down in throughput. Some APs are able to reduce their output power when transmitting to a station at short range but not all do this.

Another possibility is that moving the laptop upstairs allows its receiver to hear signals from other users on the same frequency and thus to miss those from the AP, but I suspect this is less likely than the other explanation.

Edited by rippedcotton (Mon 27-Jul-09 18:16:58)

Thanks !
I presume this means that this is a specfic problem of my router (Linksys WAG200G) ?
i.e. my O2 router (Thomson TG585) may behave differently ?
I noticed that the signal strength upstairs was -28 (dBm) and downstairs it was -54 (dBm)
There are only one or two other wireless users in the neighbourhood on channel 1 and 6 and I am on 11 - so your first explanation is probably the relevant one.

If packet errors/loss is the problem, would this not show up on the standard tweak test ?

http://www.dslreports.com/tweaks

I will try it sometime at both locations.

You can get a lot of signal reflections in rooms caused by metal objects. If the reflected signal arrives in phase with the original signal, it adds to the signal strength, but if it arrives out of phase, it subtracts. Since the wavelength at 2.4GHz is only about 4 inches, just moving the aerial a couple of inches can have a profound difference on performance. In any room you will have areas where wi-fi will work extremely well, and others where it will hardly work at all - all caused by addition and cancellation effects.