802.11g works in 11Mbits if one client is 802.11b ?

[htsiartas]

It used to be that on a 54Mbits 802.11g network if one client is associated with 11b 11Mbits the every client on the access point works on 11Mbits. Is that correct for even the newest cisco Access points?

[thisisshanky]

Actual throughput of a 11 mbps 802.11b AP is 6 Mbps. The actual throughtput for a 54 Mbps 802.11g AP is 22 Mbps (with no 802.11b clients). In mixed mode operation, the throughput gets down to 8 mbps.

8/6* 100 = 133 percent increase in througput compared to 802.11b only AP.

[j2sw]

Most APs will throttle down to the lowest speed. We have taken the stance of locking in clients at 11Mbits. It seems if one client out of 20 connects at 5 Mbits, then they all are at that speed.

[dixho]

This is a fairly complicated answer. It all comes down to basic speed set. A basic speed set is a collection of all speeds (configured as basic or required in IOS) that are all supported by all associated wireless clients. If an AP tries to send out a management frames (e.g. RTS and CTS) or broadcast frame, it should use one of the speeds in the basic speed set.

The IEEE standard does not define how to shift up and down on the basic speed. Cisco AP always uses the slowest basic speed.

To answer your question, the AP will use 802.11g speed in the data portion if both 802.11b and 802.11g are enable. Management frames, broadcast and multicast frames will be use one of the 802.11b speeds. (you need to define one of the 802.11b speeds as basic/required speed if you want to enable both 802.11b and 802.11g) This should be the same for all vendors.

[crose]

Yes. We had this same problem with a new wireless entowrk I installed in our Surgery Area. A floor below and just outside there is aloading dock and everytime a UPS truck pulls up wiht a 802.11b AP installe don it, It would drop our entire wireless network to 11mb. I called TAC and a helpful engineer told me that if you disable the 802.11b speed on the ap, that will effectivly disable the drop in speed, but you will only be able to connect G clients. It's not a problem for us as we control who connects.