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Throughput 802.11g radio with cisco a/b/g client

Level 1
Level 1

I had no other devices associated besides my laptop.

I did a 100+ meg download and noticed I was getting about 750-850KB per sec = approx 6mbs. In my a/b/g client card I unchecked the 2.4 - 11M seeting. So I was hoping to see the stated 22 Mbs throughput. So I then set up the AP to require 54M data rate and I got about 16mbs throughput. Once I enabled the 11M data rata - my throughput dropped even though no other clients were associated. I did notice that my client would associate to a 802.11b radio even though I had the 2.4 - 11M unchecked.

Any ideas ?

4 Replies 4

Level 6
Level 6

Throughput is depended on various other factors like your site and errors in your networks, Did you do a initial site survey??

Level 1
Level 1

I have noticed similar results in my testing. When testing a g client to g ap the best throughput I have seen is ~9Mb. When I introduce a b client to this my throughput doesn't seem to be affected and still gives ~9Mb. Testing 802.11a client to 802.11a radio the best I saw was ~16Mb.

So far, g doesn't seem to be much better than b as far as throughput is concerned.

After doing extensive testing and opening a tac case we have proven that the reason for the decrease in speed is because we have the AP with the B rates enabled and the AP can here a B radion on its channel. To clearify if you have a G AP on channel 1 and there is another B AP in the vacinity on Channel 1 and the G AP can hear it then you will get max ~9Mb. If there is a laptop running in Adhoc mode in the vacinity on channel 1 and the G AP can here it you'll get max ~9Mb. if you get some B AP signal bleed over from neighboring houses on channel 1 you will get ~9Mb. During the hype for G i read many articles that said that the only time you will drop rate is when a B client is associated to the G AP well that is not true all there needs to be is B traffic on the same channel.

If you turn of the B rates on the G AP then you will get the higher throughput for G only clients.

This isn't entirely accurate. The rule for Cisco APs to turn on Protection Mode (use of RTS/CTS or CTS-to-Self) is:

If the AP is required to respond to a probe request with a probe response, then protection mode is automatically enabled. To prevent this from happening, simply disable broadcasting the SSID in beacons - which, btw, also disables probe responses when probe requests contain the "broadcast" SSID (which is blank (or null)). The 802.11 standard says that APs are required to respond to probe requests from any station that sends one with the broadcast SSID or the SSID of the AP. Since you would have implemented it such that the AP won't respond to null SSID fields in the probe request, the AP won't have to turn on Protection Mode (which will cost you half of your throughput in an 802.11g environment). Also, any 802.11b associated clients on an 802.11g AP will enable protection mode. Cisco has Association ACLs to prevent accidental associations.

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