Data rate question

34 posts by 9 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: May 6, 2010:
  • This may be a dumb question, but I'm still fairly new to wireless theory so I still have a lot to learn.

    I have an older linksys flashed with dd-wrt. It works fairly well, but the data rate seems to jump around a lot more than it should. I have tried setting it to "G-only" mode, but I still at times see the rate at 5.5 or 11 Mbps. I'm staying in the same location all day while seeing the rate jump all over the place. Same floor as the AP, roughly 40 feet away from it. I also live in a townhouse, so there are plenty of other users in close proximity. I've set myself to use the least congested channel, which happens to be channel 1. I was under the impression that enabling the "g-only" mode would prevent any (HR)-DSSS from initiating protection mechanisms. I also tried to force the data rate to be 54 Mbps, instead of the "auto" default. That just caused me to lose connection completely. Maybe I should try a lower rate of 36 or 48? I feel like I'm missing something obvious, or perhaps the device needs a firmware upgrade?

    Any other ideas?

  • If you cant do 54mbps yes try something lower like 24 and go up or even 12. just so you have a stable connection.

    I have a Cisco 851 in my house and its tuckedin a corner, I consistemtly achieve 48mbps and thats through a floor and a cople of walls, not all stud partition but some brick.

    Im suprised that it still uses DSSS when you have said "g" only. Not familiar with linksys especially a blown one.

    Let us know how it goes.

  • Hey Pete,

    Thanks for the suggestion. When I mentioned DSSS, I was referring to the possibility of other 802.11b devices in the area causing my network to invoke protection mechanisms to accomodate the mixed environment, even though I've set it to support ERP-OFDM "g" clients only. I would think I should never see my device connect at a rate of 5.5 or 11 Mbps if it's truly operating in a "g" only environment. That's the main thing I'm wondering about.

  • Stackman,

    I am a huge dd-wrt fan also. Makes a Linksys (or other dd-wrt capable SOHO router) almost like enterprise routers. No, not exactly the same, but they have a lot more features. And lots of good support on the dd-wrt forums. (but you probably know that...)

    There is a CWSP white paper on the protection mechanism in 802.11( Even if you have your router set as "G-only", if there is another 802.11b router in the area, or another 802.11b client, your router will still enact the protection mechanism. You could disable 802.11b data rates which might help (I think you can do that in dd-wrt, but not sure). Please CWNA gurus, help me out if I am missing any details here.

    How are the other APs in your townhome interfering? Channels? Sig strength? Did some user incorrectly use another channel other than 1, 6 or 11? I found a great Xirrus free utility (both app and widget) called Wi-Fi Inspector. Here is the link and a lot of other free (I like the word free....) wifi tools: You can accurately determine sig strength, SSIDs (hidden also), auth/encryption, etc. Did I mention it was FREE?

    One last note. If you are just testing 802.11g, have fun. If however, if you want to improve your wifi signal and speed, go to 5 GHz! I just bought a reconditioned Netgear dual-band 802.11n WDNR3300 ( for only $30. Yes, dd-wrt flashable! Hardly anyone is on 5 GHz, and you can go full 802.11n speeds w/ 40 MHz channel bonding. I regulary hit 270 MBps with my N router at home.

  • Stackman

    Ah I see but I am assuming you are at home so should have a reasonable idea whats around?

    I just see lots of experiments for myself reading here. I now I have all b rates disabled and g from 24mbps upwards only and never see any issues.

    Although I know a bit about protection mechanisms I need to do the deep dives, I guess I am where you are at.

  • Hey Guys,

    Thanks for the feedback, and also thanks Glenn for the Xirrus link! I'm just downloading it now to give it a try.
    I did read that whitepaper you mentioned a little while ago, I'll have to go over it again. So even if I disable the "b" rates, other clients can cause my network to enable the protection mechanism, correct? I was under the impression that couldn't happen, but like I said, more reading required!

    Using other tools such as INSSIDer, Kismet, etc, I see a very congested 2.4 Ghz band. Easily over 20 other networks, and several on channels other than 1, 6 or 11. Not seeing anything in the 5Ghz range, might have to make the switch as suggested! Hadn't done it yet as I have 4 devices that will need an upgrade to the "n" adapters as well. Glen, how has your Netgear been so far? Consistent, no issues?

  • Stackman,

    I wanted to read the whitepaper again but just scanned it quickly before I responded to your post (I read it a bunch prepping for CWNA...) so I "think" there is not much you can do to prevent b clients from kicking in protection mechanism, other than disabling the b data rates. Look at the last page summary. But--I would like the gurus to chime in to confirm.

    Yes, I LOVE my Netgear N router! Been looking for one for a long time that did all I wanted for home, at a good price (dual band, N, dd-wrt flashable, cheap!) and found this one. If you get it, be sure to follow the dd-wrt specifics on flashing it. (don't you just hate to "brick" a perfectly good router?). If you need to upgrade cards in your laptop (as I did), the N cards are OK to buy on Ebay--pretty cheap (mini-pci cards or Cardbus slot cards) USB N adapters are OK too, I did not want anything hanging out. I upgraded my home Dell Inspiron laptop and had to go to three antennas. Again, Ebay to the rescue. Found the third antenna there and added it (I repair laptops for work, so pulling the bezel back and installing it was not a biggie for me, but might be for others). Of course, all of this "home wifi stuff" is done in the interest of enterprise wifi learning.

  • Glenn is exactly right, the protection mechanisms are still kicking in and realistically the only solution is to go to 5GHz. I've seen very few home routers that will let you turn off protection as it automatically makes them non-standard compliant. I've not seen it a lot on enterprise routers either, just a couple.
    On a last note Glenn thanks for the info on the Netgear, I've been looking for an N router I can load dd-wrt on and thought I was gonna be stuck with my Linksys and only a/b/g as for internal cards to upgrade with, I love the Gigabyte ones

  • So what we are saying is that even if we turn off 802.11b data rates, or say 802.11g only then as the standard states 802.11g is backwards compatible with 802.11b the access point will respond to 802.11b clients but will not let them associate?

  • Hello all,

    I am going to have to look into this and get a refurbished Netgear to test on, but I am wondering if there is a command line interface on can access to lock out those options? Thank you for the info and link to the white paper as well.


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