Dick Davies wrote:

> What's the overhead then? I'd guess 11Mbps / 8 =~ 1.5MBps - the rest is 
> lost in collisions, is it?

There is no 'collision detection' on wireless LANs. You
have to use 'collision avoidance' because you would need
to be able to receive and transmit at the same time (full
duplex) *and* you can not be sure that if another stations
can hear you that you can hear it's answers.

So, if a station wants to send a packet it waits for
silence then sends a RTS packet (request to send) waits
for the CTS packet (clear to send) of the receiver and
then has a specific time frame to send the real packet
which contains the data. (During that time all the other
stations will power down their radios to save energy)

Well, this is why you lose about the half of the marketed
bandwidth on the physical layer. The rest is the normal
MAC & IP level overhead.

> And yes, this is 802.11b - I have an old iBook on the LAN. AFAIK 
> internal airport cards only do 'b'. And I guess it would be pointless to
> have 802.11g cards on that WLAN if the Mac is going to drag them down to
> its level?

Well, this depends on your normal usage. If you Mac is not
always online, 11g will of course bring a speed increment
of about factor 4.

But I am in a somewhat stupid situation: I own a 11g
access point, a 11g desktop workstation and a 11b
notebook. When the notebook is 'on air' both the desktop
and the notebook have bad connection instabilities. (Don't
know if it's the really old firmware of the notebook's
Prism or the Netgear AP)

So, the best for *me* is to force 11b on the AP until I
get a 11g card for the notebook or updated the 11b's firm-
ware which I'll try at work today, since I cannot find
any software to do that on NetBSD ;(

> Thanks for the clarification.

I'm sorry if I faced you with the truth about
"54MBit/s!!!" ;)

Cheers, Rob.
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