Wireless Issue

I have had a wireless network for about the last 3.5 years - working very well. However, in the last several months I have noticed an issue that I have been unable to diagnose. My setup is as follows:

  1. Belkin 7230-4 router ( this recently replaced a similar model because of the observed "problem". The new router also sees this issue). I assign IP's manually.
  2. Several laptops using Belkin wireless cards (win98se, and winxp pro machines)
3.A wired desktop machine.
  1. I use WEP
  2. I am running on a channel that is not crowded with other AP's - the problem seems to be independent of the channel.
  3. The SNR as reported by the Belkin utility and Netstumbler is excellent - typically the signal is at -33dbm and the noise at -82dbm
  4. I have tried both the Belkin client and WZC to manage the connection

- the issue still shows up.

  1. I have a cordless phone which operates solely in the 5.8GHZ band.
  2. The laptop (winxp pro) that primarily sees this issue is only about
10 feet away from the router. I am using the Belkin PC card in it and have also swapped the card with another identical one which I have, but the issue still persists.

The problem is that at random times (up to several weeks between incidents), my link rate will start to drop from 54mps down to 5.5mps (and lower) and then proceed to bounce around. During these periods, the SNR also bounces around but is always at a very good level. No other networks show when I do a site survey.

It would seem that this is an interference problem, but I don't see any evidence of it (i.e., SNR as indicated by Netstumbler and the Belkin utility are always good).

So, any ideas as to what may be causing this issue?

Thanks, Harvey

Reply to
Harvey Gratt
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Harvey Gratt hath wroth:

What is the model number of the new router?

Do ALL these laptops see the same problem?

Many sources of interference are also independent of channel number. For example, Frequency Hopping Spread Spectrum cordless phones will trash the entire 2.4GHz band.

That's the SNR at the client, not at the Belkin wireless router. If the interference was heard only by the router and not by the client, you would not see anything. What SNR does the Belkin router display?

Is this measurement when it operates normally or when you see the speed variations?

Do the other laptops see the problem?

Model number of the Belkin PC card?

Hint: First describe the problem you're having, then add your equipment list, and last add the detail. It's kinda odd reading the description in reverse order.

Random? Well, lets see if it has a pattern.

  1. How long does the speed reduction last? (Shortest and longest).
  2. How often does the speed reduction last? Shortest interval and longest interval).
  3. How severe? What effects do you see? All laptops or just one?
  4. Do the speed reductions coincide with meals?
  5. Do the clients disconnect or merely slow down?
  6. How are you measuring the connection speed? While traffic is moving?

That's normal for interference. However, you should see a decrease in SNR when the radios hear interference. The idea is that lower speeds require a smaller SNR to operate. By the numbers:

Speed Min Modulation Typical Noise Eb/No Sensit Floor mb/sec dB dBm dBm 11 7.0 CCK -82 -89 5.5 6.0 CCK -85 -91 2 1.6 DQPSK -86 -87.6 1 -3.0 DBPSK -89 -86

54 24.6 64QAM/OFDM -71 -95.6 48 24.1 64QAM/OFDM -71 -95 36 18.8 16QAM/OFDM -78 -96.8 24 17.0 16QAM/OFDM -79 -96 18 10.8 QPSK/OFDM -82 -92.8 12 9.0 QPSK/OFDM -84 -93 9 7.8 BPSK/OFDM -87 -94.8 6 6.0 BPSK/OFDM -88 -94

At 54Mbits/sec, you'll need at least a 24.6dB SNR. At 11Mbits/sec the system will work with 6.0dB SNR.

However, the usual criteria for causing a slow down is NOT the value of the SNR. It's the bit error rate. When the data coming through the system starts generating errors, the access point will slow things down until the error rate improves. Such increases in error rate do NOT necessarily require interference or a corresponding decrease in SNR. It can be caused by oversized or "unusual" packets. I once did some wireless router exploits testing that included some of these "unusual" packets there were crafted to hang or crash the router. It did just that on some ancient models. However, I also noticed that if the test were through a wireless connection, the connection would slow down to 1Mbit/sec before crashing the router. That's the way it's suppose to work. Slow down until the error rate improves. If it doesn't improve, go even slower until you hit bottom. After that, disconnect or crash.

Incidentally, try this exploits test on your router:

over a wireless link. It hangs my BEFW11S4v4 and some other older routers. Check what it does to the SNR during the test.

Interference usually shows up as a decrease in SNR. However, there's no guarantee that what's causing your problem is interference or that whatever interference you're seeing is causing the speed reduction. There's also no guarantee that your client computers are acting sanely in the presence of interference. For example, some Intel MiniPCI cards with Proset 9.x would slow down to 1Mbit/sec and stay there forever.

No, not really. There really isn't enough info to make an intelligent guess. I would need to know more about the effects of the interference and a much better description as to the pattern. When faced with the same problem, I usually dig out the spectrum analyzer and monitoring (SNMP based) software. There's quite a bit that can be learned from both. For example, if your interference problem coincides with meal times, look for a leaky microwave oven.

See list of probable culprits at:

Reply to
Jeff Liebermann

A very comprehensive reply!! I'll try to provide some more information.

  1. The original router was a Belkin f5d7230-4, v1111. The replacement router is a Belkin f5d7230-4, v6002.

  1. The pc cards are Belkin f5d7010, original version.

  2. Current router and pc cards are using the latest available firmware.

  1. I do believe that all the laptops see the issue - it does appear to originate at the router. Also my cordless phone was not in use and is a

5.8MHZ phone.

  1. The current router ran for about 3 weeks before I saw the problem. The incident happened last night around 9:00pm and lasted for 2 hrs. at which time I shut down and went to bed. More than one laptop was affected. Speed reduction was noted by the WZC and Belkin utilities. I also conducted the Verizon FIOS speedtest and confirmed that the degradation was real. No disconnects occurred - only a slowdown. The Client SNR was still good but was more erratic than usual (signal -35dbm, noise -82dbm). I have never been able to correlate the issue with any known time or event

  1. How do I measure the router SNR? I don't see a way for the router to display this information.
  2. Will the exploit task trash my router/system?

Thanks, Harvey

Jeff Liebermann wrote:

Reply to
Harvey Gratt

Forgot to mention that, so far today, the problem has not occurred. I've been online for several hours.


Harvey Gratt wrote:

Reply to
Harvey Gratt

Harvey Gratt hath wroth:

With all due respect, your information is lacking. I asked a number of very specific questions. You answered a few, and were fairly vague with your answers. As a rule of thumb, try supplying numbers, not generalizations.

Ok. I think (not sure) that those are actually two different routers, with different chipsets. If it happens with both, I guess it's not a defective router. I'm too lazy to dig out the FCC ID numbers and look at the internals.

I had quite a bit of entertainment value with those PCMCIA cards. The "latest" v2 drivers from the web site were trashed. Only the ones from the original CDROM worked. See:

I don't recall if this was a problem with the "original version" or not.

Incidentally, the "latest available firmware" means "I'm too lazy to find the numbers" which may or may not really be the latest, especially if there are beta versions available. It's often important to supply the hardware version (you didn't) and the firmware version because there are sometimes version specific bugs or problems. I don't think that's the case here, but it's best to supply the numbers anyway.

See my previous posting in reference to trying to assign some numbers to the interference pattern.

How did you determine that? See my previous postings and questions in reference to my question on how you located the problem, measured the SNR, and determined the extent of the problem.

That's only one incident. I'm trying to establish a pattern. See my previous posting and questions on the frequency and extent of the problem.

Did you do anything during the two hours to try and isolate the problem? Any SNR measurements? Power cycle the router? Reboot the laptops? Move antennas around?

Is that 2, 3, 4, or more laptops? Please try to be a bit less vague.

Good. That means that whatever was happening did not drop the connection or disconnect the session. It's also apparent that most of the router is still functional. That sure sounds like intereference to me.

Any chance one of the other laptops was doing a major download at the time? Self-interference is a common problem. You will see erratic signal strength when one of the other laptops is operational.

Fine. Let me try. All I need is a pattern. If you don't know the answer, just say that you don't know.

It might be in the web based configuration on some manner of status page. I'm not familiar with this Belkin model and there's no online configuration simulator. Signal strength indication is not very common in routers because it has to be displayed by the individual client connection. For example, see my home router at:

The signal level and SNR graphs are at the bottom of the page. (I'll fix the certificates problem later). You can also extract the numbers by sniffing the over the air traffic and inspecting the management packets.

Nope, it's fairly safe. However, it might hang your router. Be prepared to power cycle the router. If you're not sure, save or document your router settings before testing.

Reply to
Jeff Liebermann
  1. The firmware is the latest as posted on the Belkin website. I even did file compares since the dates had changed. Remember, my version1 pc card ( I believe they're up to version 4 now) is many years old - I doubt Belkin will ever update them. But FWIW, the following is for the pc cards: Board: V1799 D7010 Rev. 4.5 Chipset: BCM4306 /BCM2050 Driver Version:

  1. Problem last night happened with 2 laptops on. Problem remained when the furthest laptop was turned off. No major downloads by any laptop were in progress

  2. I did reboot the router when I decided to broadcast my SSID to see if this was an issue - it did not help.

  1. The problem is very intermittent, 3 or 4 times with the old router, and once with this new router. The problem occurred at intervals of one to several weeks and would last for at least several hours. The client SNR remains high - signal around -40dbm to -33dbm, noise level around


  1. I cannot deduce a pattern

  1. I checked my router's web pages - does not seem to indicate any SNR information.

  2. Since both laptops showed erratic behavior, I assumed the issue was at the router (interference at the router as you had indicated). This is just speculation on my part.

  1. Before I decide to try it, what will the exploit test show us?

Thanks, Harvey

Jeff Liebermann wrote:

Reply to
Harvey Gratt

Harvey Gratt hath wroth:

Belkin does not list the driver version on their web pile. However, I do note that the date is 1/24/07, which might be a new driver or the same old one. No way to tell without comparing versions numbers.

Incidentally, this is one reason I don't like Belkin products. There are usually 1 or possibly 2 firmware updates, followed by nothing. Eventually, it gets discontinued. Meanwhile, Netgear, Dlink, and especially Linksys, continue to upgrade and fix problems even on obsolete products.

Ok, so that eliminates my guess that it's your other laptop.

SSID juggling will not help with what appears to be an interference problem. However, rebooting the router was useful in case it was partially hung or insane.

If it only happens a few times every several weeks, it's going to be very difficult to identify. However, I have seen situations exactly like that. One customer was having a problem that only appeared every

3 weeks. I marked the dates and times on the calendar and found that it was the same days of the week every time. Eventually, we discovered that the neighbors had a wireless system (that was not broadcasting its SSID). The adults used their wired computer. However, their son was doing the time share routine between houses. He would arrive with his laptop full of peer to peer file sharing junk, and promptly setup a server, via wireless. The result was almost traffic continuous traffic until he disarmed the monster.

If you feel ambitious, download a Linux LiveCD with Kismet and go looking for such hidden access points.

If the interference was only being received by the Belkin router, you would not see a drop in SNR at the client end. If your Belkin wireless router is sitting in a window, where it can hear the world, you might want to move it away to a more protected location.

Deduceing the pattern is my problem. You supply the data.

Bummer. That's one reason I like using DD-WRT firmware. I can get individual stats on each client, perform scans, tweak settings, etc.

Most cheap routers lack these troubleshooting features.

It's a fair deduction. We're still not sure it's interference, but I don't have much in the way of alternatives.

I suspected that you might be sending or receiving mal-formed or mangled packets. These have a detrimental effect on router stability and might be causing a problem. I'm just guessing but it seems like an easy and fairly harmless test to try. Try it both wired and wireless. If it appears to slow down when run via wireless, then it's possible we may have a suitable culprit.

Reply to
Jeff Liebermann
  1. I believe 1/24/07 date is the one I did a file compare on with the "latest" version I had installed. The files were identical.

  1. My connection has now been on for about 10 hours with no problems.

  2. The exploit test was passed with no issues - I selected all of the exploits. My wireless speeds and connectivity were not hindered.

  1. Sorry I can't provide more data wrt a pattern. At this point, I'm still thinking it's some kind of interference. My router is about 10 feet away from a window and about 5 feet away from an outside wall, so there could be some issue there. Unfortunately I cannot move it since my FIOS connection is down the adjacent wall.

Thanks, Harvey

Jeff Liebermann wrote:

Reply to
Harvey Gratt

On Sun, 25 Mar 2007 09:14:49 -0700, Jeff Liebermann wrote in :

Some will, but not all -- I've found some that use only part of the band.

Reply to
John Navas

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