Interoperability between 802.11g and 802.11b

[teresa]

Hello,

I've already seen in this forum this question: when I have a 802.11g AP if there exists a 802.11b wireless client card then the AP will work at the rate of 802.11b for everybody. I would like to know what is the reason for this to happen, and if anyone has any document explaining this.

Thank you

[girig]

Hi teresa,

the problem is with the different modulation techniques used in 802.11b and 802.11g phys.

visit
http://www.wi-fiplanet.com/news/article.php/1577701
for a news update on this.

to my knowledge, in the CSMA mechanism, the AP behaves just like any other station. so when the 802.11g client starts transmitting the data, the 802.11b AP may sense the channel as idle, which may cause problems if AP starts operation.

Thanks
Giri.

[teresa]

Thanks Giri.

I found a white paper that explains this issue in a simple but clarifying way. You can find it in http://itpapers.zdnet.com/abstract.aspx?docid=16337 an the document is "A detailed examination of the environmental and protocol parameters that affect 802.11g network performance". To be able to download the document you must first register but it's free.

The reason for the 802.11g AP work at the 802.11b rate in a mixed environment, has to do with what you say but not only. The main reason is that the client cards are limited by the slowest client in the network. The time to transmit a packet is viewed not only by the time it takes to transmit it (length of the packet/bit rate) but with the time between 2 consecutive packets. This is all very well explained in the document.