different SSIDs on the same APs, different standards (b/g, g only), what speed

[msporleder]

hi cisco support community,

following scenario:

LAPs configured on a 5508, 2 different SSIDs on the same LAP

ssid1: 802.11g only

ssid2: 802.11b/g

clientA connects to the LAP with ssid1 an communicates with 54MBit/s

clientB comes up and connects to the same LAP with ssid2 using 802.11b standard and communicates with 11MBit/s

what is the result?

is it that clientA is "downgraded" to 11MBit/s ?

or

is it that clientA is communicating with 54MBit/s and clientB is communcating with 11MBit/s?

thanks you very much for answering my question.

[Stephen Rodriguez · Accepted solution]

Client A will still be connecting to the AP at 54Mbps.

What will happen, is when cleintb connects at 'b' rates, cleintA will need to wait for it to finsih sending

So it doesn't affect the connection between the cleint and the AP, but it will cause the faster clients to need to wait for the slower client to finish sending.

Steve

[msporleder]

thank you very much for your fast reply, Steve

if I understand you correctly, it does not affect the speed when the clientA is sending something, but if there is a clientB connected, clientB may cause the whole network to be slower in that way, that the radio can not handle communication at the same time for different speeds ?

[Stephen Rodriguez · Accepted solution]

Correct.  Wireless is half-duplex.  Only one device can speak at a time.  Everytime the slower client send, all the others have to wait.

Steve

[msporleder]

okay, this was the answer I needed... half-duplex... stupid me!

but than, to bring this to an end, if a client, for some reason, connects with just 1Mbps, it is the same procedure.

correct?

[Stephen Rodriguez · Accepted solution]

yes, it would be the same.

[George Stefanick]

To be more specific WiFi uses CSMA-CA which uses 2 senses, Phyiscal and Virtual. Phyiscal where by a device listens to the medium before transmitting. Virtual whereby a device will use NAV timers.