25 associations per AP or per Band?

[Koevi Vong]

Hi,

Cisco best practices states that no more then 25 associations per AP, otherwise wireless bandwidth issues would occur.

Is it 25 associations "PER AP" or is it "PER BAND e.g 2.4Ghz and 5.0Ghz" which equals to 50 associations (25 on 2.4Ghz and 25 on 5.0Ghz) if you have a Dual band AP.

Thanks

[Leo Laohoo]

Per AP.

[George Stefanick]

Actually this is a loaded question and a time to share some education

You have 2 potential issues that can cause bandwidth degrade.

1. If you had 25 on 2.4 and 25 on 5ghz, each channel would support its own Csma/ca. So really you could get 50 clients on the 2 channels with little wireless degrade.

2. The issue becomes when the traffic is merged onto the wired side of the ap. if you had 50 clients pumping heavy traffic you will see degrade.

Just my two penny's

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[Koevi Vong]

Thanks George,

So basically wireless collisions would be segmented to their own band 2.4Ghz and 5.0Ghz, in the sense that the 50 clients (25 on 2.4Ghz and 25 on 5Ghz) would be just web browsing and the AP has a gigabit connection back to the switch, I should see no bandwidth issues correct?

Also is the wireless bandwidth cut up in relation to the band? e.g 25 clients on 2.4Ghz = 54mb/25 = ~2mb per user

and if you have only 1 client on 5.0Ghz do they get the full bandwidth? On the same AP.

Thanks

[George Stefanick · Accepted solution]

CSMA-CA which 802.11 uses, is based around a physical and Virtual

, which is used on channel. So clearly, 5 and 2.4 will each have their separate CSMA-CA events.

If either channel is saturated, say 5 clients are all doing a FTP on 2.4 GHz, in theory yes it would be shared among the 5 clients and should 1 of the clients have a higher QoS they would be more favorable to get their traffic on the wireless before the others due to shorter back off timers for the higher QoS client.

yes if you had 1 client on 5 ghz he would have a higher throughput and not beimpacted by 2.4. The impacted could be when the wireless traffic is bridged over to the wired side.

But in best practice 25 should be max.

But now you know a little more what is going on under the hood.

Also, note -- a Phy rate of 54 ONLY means the client is trigger data that includes 54 million bits. This has nothing to do with actual throughput. It simple means when your client is able to trigger a frame it will send a frame with 54 million bits in it ?

Make sense?





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[Koevi Vong]

Awesome, thanks for all the help =)

[George Stefanick]

No worries. Thanks for supporting the rating system !

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