802.11g Throughput

Unanswered Question
Jun 4th, 2009

Hi,

I've a quick question regarding throughput, i think i've got this right in my head but would like confirmation.

Scenario... I've a single AP with a G radio and a WLAN configured. For simplicities sake we'll say there is no other AP's around, no interference etc.

If i connect 1 client to it, i should in an ideal world get around 22Mbps of throughput to the client?

If i then connect a further 9 cleints to to the AP the typical throughput for each client would fall to around 2Mbps? - i.e. 22/10?

Thanks,

Neil

I have this problem too.
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mark.cronin Thu, 06/04/2009 - 05:59

Your logic is correct.

But in reality due to the random nature of the DCF virtual CCA clear channel assessment of the wireless station this can vary.

And remember not all control and management wireless traffic from the AP will be at (data rate 54mbps / throughput approx 22mbps) it does transmit as 1mbps thus lowering the overall throughput

George Stefanick Thu, 06/04/2009 - 06:04

Hi Neil,

You are close in your thinking. Access points are "hubs" in the true sense of the word. Only one client can talk at a time and they use CSMA-CA to play traffic cop. A client will do 2 types of carrier sense physical and virtual. With all that being said…. For every client you add to an access point (in your example) they have to share the same “pipe”. Keeping in mind, the nature of the application / bandwidth use is VERY important. If you have all 10 clients pulling down ISOs all day long, you will see a large hit in bandwidth use and it could be as low as you mentioned depending on conditions, but I would expect your throughput in my example to be bit higher than 2 meg. In normal everyday typical use your client isn't exposed to that type of load, so clients will benefit from much higher throughput. Again, the amount of traffic is key …

nbailiecisco Thu, 06/04/2009 - 06:21

Hi,

Thanks for the info, i understand what you mean about the type of traffic being important.

For the scenarios I'm involved in managing wireless for I see a lot of users needing throughput at the same time for short periods of time. So i'm always thinking worse case.

I don't know too much about 802.11n but have read that typical throughput when using a 20MHz channel width is about 120Mbps. Again roughly speaking if i've 10 users does that work out to be around 12Mbps per user?

Thanks,

Neil

George Stefanick Thu, 06/04/2009 - 13:14

802.11n is a much different beast. No you should expect more becuase the use of MIMO. How much more, dont know never tested it ... lots of reading ... :)

nbailiecisco Fri, 06/05/2009 - 00:44

If we forget about the benefits MIMO gives would it be fair to say with typical throughput for a single 802.11n user being 122Mbps that worse case 10 users connected to the same AP could expect at least 12Mbps throughput?

Thanks,

Neil

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