Dropped connections.

Discussion in 'Cisco/Linksys Wireless Routers' started by patfla, Apr 6, 2006.

  1. patfla

    patfla Network Guru Member


    Unless I do a lot of expensive cabling (no) I have to put my wireless AP at one end of a long 1700 sq ft rectangular hour. And I want my laptop (Thinkpad T43) to connect wirelessly from the other end.

    Which I had been doing, reasonably well, for some time with a WRT54G running 3rd party DD-WRT on one end and the using the Intel 2915 a,b,g built into the T43.

    But sometimes once in 2 or 3 days, but other times twice a day I’d have to go to the other end of the house and reboot the router (it was always rebooting the router, and not doing anything on the client side, that fixed things). Measuring signal levels I was usually running at about -70 to -80 dBm. Pretty low.

    Looked at various solutions. Ended up buying a combination WRT54GX4 (router) and WPC54GX4 (Cardbus card for the laptop). With the two you should get full 3rd gen MIMO.

    Not problems with the set up like others in reviews I’d read (but I’m a programmer and, over time, have set up several wireless networks).

    But performance has been a disappointment/problem.

    The new configuration has been up, what, only 2 or 3 days. Was measuring speed at first with iperf (http://dast.nlanr.net/Projects/Iperf/). This was consistently giving me between 10 Mbps and 55 Mbps. Not quite 240 Mbps.

    Then discovered (duh) the Statistics windows in Wireless Network Monitor. This was giving me reasonable receive speeds of 194 or 216 Mbps (am at work, don’t have my router here – what are the two speed steps below 240? Anyway, those two). And preposterous transmit speeds of, say, 384 Mbps (huh!).

    So obviously I need to better understand how iperf really works.

    Connectivity (as opposed to speed) is the big problem. Drops connections at least every 20-30 minutes (if not more frequently). My router firmware is 1.00.15 and the driver on my GX4 card is 2.01.19 (the latest to judge by linksys’ support web site).

    Signal strength. With the laptop at one end of the house and the AP at the other, even with the new MIMO gear, I’m getting between -65 and -75 dBm. Pretty weak.

    But I thought that was precisely one of the things that MIMO was supposed to improve? Making multi-path a plus and not a minus. And I would have thought that this would show up in signal strength (?).

    One thing is significant, my fix is no longer to reboot the router but rather to do a Repair on the Connection in Windows Network Connections (i.e. client-side). I believe this has worked every time. So is that telling me it’s a client-side problem?

    I’ve tried all kinds of config changes (mostly on the router by definition). Using differing combinations (adaptive) channels. A linksys tech support person (1 call so far) had me go into Advanced wireless settings and do: Speed: auto -> some figure <= 56; Beacon interval 100 -> 50. Fragmentation threshold 2346 -> 2304. RTS threshold: 2347 -> 2304 (so both the same value). Reboot etc. Didn’t help.

    Her suggestions (above) came after I speculated to her that it looked to me like channel expansion wasn’t kicking in. And this is what she gave me. Interesting, but as best I can tell ineffective.

    A question: is there anyway to see what’s going on with channel-expansion directly? (not that I’ve found).

    And if channel expansion were working correctly I’d expect to get better dBm numbers for signal strength. Say, instead of -70 maybe it moves up (stronger) to -30 or -40. And if so, I wouldn't expect to get these dropped connections.

    When the connection drops, in Windows eventvwr, I see, as best I can tell, only:

    Suggestions? Diagnostics I’m unaware of? Take the card and/or router back to Comp-USA and swap and try again? Or return and wait a while longer for a solution that will really work (and return to my old configuration that at least worked better than what I have currently)?

    Sorry for the length. This is my second, shorter version of writing it up.


  2. vincentfox

    vincentfox Network Guru Member

    Obvious things:

    1) How is your signal levels now? You talk about a long house but never mention how the signal is. If it's good your problem is not signal-related. Although, still check for and disable any competing 2.4 GHz appliances like phones, microwaves, etc. Could also be a neighbor if you are in urban area.

    2) Consider it might be the client side that is dropping out. Try a simple old B or G card with bultin XP drivers and see if it experiences the same problems. Example I had an Intel card that was constantly dropping connections on me, switched to another client card no problems at all.

    IMHO, the MIMO stuff is a bunch of marketing mumbo-jumbo made to sound like a fantastic solution. It may well be, but so far the implementations often suck, and you can't use 3rd-party firmware nor change out antenna to address it's issues. Plain 802.11G units with alternate firmware like HyperWRT or DD-WRT and a good antenna, has been very stable for me.
  3. patfla

    patfla Network Guru Member

    Hi Vincent.

    #1. It probably got lost in the lenght of my first post (but is there). The signal levels currently (and this is part of what's disappointing) are pretty much the same with the new configuration as with the old.

    Above-and-below -70 dBm. Pretty weak.

    And this is a good part of the reason why, when I made the one call to a Linksys tech support person, a major guess of mine was that the channel adaptivity (increasing from a 20 GHz range to 40 GHz) was not working.

    I thought that if the multi-path (contributing and not cancelling) were working correctly I would have seen markedly better signal strenghts with the WRT54GX4 and WPC54GX4 as opposed to my old config (WRT54G talking to built-in Intel 2915 a/b/g in the T43).

    #2 it is the client-side that I'm looking at currently. In my old config, to restore a connection, the surest method I found was to reboot the router. Now it's the opposite, I stay on the laptop; go into Network Connections and do a 'Repair' operation on the relevant Connection. And that's restored the connection every time (but it usually drops again not long afterwards).

    I'm still within Comp-USA's 21 day return period and I may have to throw in the towel on the new technology and just go back to what I had. I had and have thought about getting better antennas for the WRT54g.

    Long-term though I'm not at all sure that MIMO is a flash-in the-pan. I did a fair amount of research on the technology before I bought the two GX4 products.


    MIMO originated in Bell Labs in 1984. It was a popular reasearch topic for 10 yrs. Until 1996 when two guys (also at Bell Labs) increased its efficiency and made it viable for commercialization. And the idea, all along, was founded on a basic (and presumably important) result in information theory (think Claude Shannon). One of the two latter Bell Labs guys, Greg Raleigh, became the founder of Airgo whose chips are in the two GX4 products.

  4. vincentfox

    vincentfox Network Guru Member

    Check your settings carefully. 802.1x authentication enabled on client end is a frequent cause of disconnects.

    My issue with MIMO is not the theory, it's the practice. Maybe one day I'll find a product that knocks my socks off with it. Not so far. Some of the more outrageous marketing claims they put on boxes doesn't help my impression.

    Much like "diversity" which is rather poorly implemented in Linksys products.

    I've not yet seen a MIMO box with antenna connectors, or alternate firmware.

    A simple WRT54GL and a high-gain antenna of my choice, seems a much more flexible solution.

  5. patfla

    patfla Network Guru Member

    Tried two more things last night.

    I'd read various places here that some people had found 1.00.15 'flakier' than 1.00.13. So moved my GX4 router firmware back from 15 to 13.

    And then I read elsewhere (here) that there are possibly problems with the Firewall (thinking that wireless packets are DoS attacks and then dropping the connections). So turned off the Firewall as well.

    I had a long period of stability last night after I'd done both of these and the necessary rebooting etc.

    Woke up this morning; turned on the machine; and it dropped connections 3 or 4 times in a row, with maybe 5 minutes between each.


    Maybe one last thing. The official 1.00.15 has hit linksys' download site of course. And I'd guess that this is at least slightly different from the beta 1.00.15 that I've had up until now (and got off of a link here in the linksysinfo forums).

    So try applying the new official and see what I get.

    If that doesn't work, I'll go back to Comp-USA for a swap.

    And then if the new pair of GX4s (card and router) still continue to work as poorly as this, return them both.

    And wait.

    Besides. My first post was way too long and even then I didn't include the following. My original configuration was a WRT54gv3 running DD-WRT. The connectivity problem was almost invariably when I'd wake up the T43 from standby and try to connect (that is, when I was connected I was generally OK [it didn't drop connections in mid-stream]). Waking up from standby would be either when I got up in the morning, or when I'd brought the laptop home from work and after I'd had my dinner.

    I'd found an improvement (maybe a solution of a kind) maybe 2 wks before I went out and bought the GX4 card and router.

    Always close Firefox before letting the machine go on standby. OK I confess: I'd have between 50 and 100 tabs open in Firefox. And before I learned to close Firefox before letting the machine go into standby, when it came back from standby the return was excruciatingly long.

    Firefox is a memory hog (another problem I've been researching for a long time). So anyway, Firefox (with 50-100 tabs) can take 300-400 MB of DRAM. But's that was 'OK' because all my machines have a gig of memory or more.

    So I'm guessing that when I let the machine go to standy with Firefox still open, it must have been swapping the whole damn thing out to disk. And obviously when the machine needed to come back from standby the whole thing had to be swapped back into memory (very long).

    And this latter at the same crucial time, when the machine is starting back up, when the wireless client is trying to connect. And couldn't because Firefox was hogging the show.

    So the point is, if and when I need to go back to my original config, it's actually not too bad because I'd figured out this one last piece. And under those conditions, things were working pretty well.

    Then I got greedy (and profligate at the same time).

    Warren Buffett on greed and fear:

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