Access Points

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Contributor II

802.11n, 40MHz benefits on different radios?

Hi all, I'm setting up some new AP-105s for High Throughput use (802.11n) and noticed that by default a 40MHz channel width is only enabled for the "a-only" radio, but not the "g-only" radio.

Is there any specific reason for this? Is there any harm in allowing the 40MHz width to be used on both the "a" and "g" radios?

For now I've left both both radios enabled, along with 40MHz for each, to allow for maximum throughput. I'm just hoping this doesn't mess up anything else.

PS - On a side note, what types of actual throughput are you guys getting on your 802.11n deployment? I've done some basic tests (iPerf, large file transfers), and have only been getting a max of around 60-80Mbps, even when connected on the 5GHz range at 300Mbps.

Thanks.
Occasional Contributor I

Re: 802.11n, 40MHz benefits on different radios?

Hey,

The 40 Mhz channel width is really only available with 5 Ghz band. On 2.4 Ghz band you have only 3 non-overlapping channels (eg. 1-6-11) and usage of the 40 Mhz channel width bonds 2 non-overlapping channels 1-6 or 6-11. You can see that in both cases the channel 6 is used then in a multi-APs environment you will have interference between AP using 1-6 and 6-11. In the contrary with 5 Ghz band you have plenty of non-overlapping channels.

The advice is:
Use 40 Mhz with 5 Ghz frequency
Use 20 Mhz with 2.4 Ghz except if you have only one Access-Point

About the speed I have done a workshop last october with AP125 and AP105. Both APs performs the same in relation to the bandwidth to the users. I have reached a max ~150 Mbps user traffic with Iperf between one Wireless PC and one wired PC.

A few thing to take care to maximize the output:
-Use Gigabit ports for the APs and Wireless Controller
-Use 40 Mhz in 5 Ghz band
-Check that the client Wireless card is supporting 2 spatial streams (otherwise you will have
only half the throughput

Kind regards
Occasional Contributor II

Re: 802.11n, 40MHz benefits on different radios?

As far as the throughput, we have done some testing with 40Mhz channels in the 5Ghz range. 3x3 MIMO antenna on both ends (PC-wire-AP|air|PC) gave us 112Mb max throughput. Tested by sending a 3GB file on FTP. Once you start adding hops the performance drops significantly. Make sure to run the tests on your LAN first through optimum conditions. If the throughput is 90Mb then you have a 100Mb link somewhere down the pipe.

Have Fun!
Contributor I

FTP inefficiencies

Throughput in an 802.11n world cannot be effectively tested with FTP; due to the inefficiencies of the FTP protocol itself. You should send multiple streams with something like Iperf, or Chariot to really test the bandwidth. If you use FTP you will NEVER get above the levels you are testing at.
Contributor I

Client NIC setup

As mentioned not all client firmware supports frame aggregation by default, depending on drivers, go into NIC setup and make sure this feature is on as well.
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