How many laptops to a wireless AP?

Alan Johnson alan at datdec.com
Sat Feb 28 21:04:50 EST 2009


On Sat, Feb 28, 2009 at 8:52 PM, Ben Scott <dragonhawk at gmail.com> wrote:

> On Sat, Feb 28, 2009 at 11:14 AM, Stephen Ryan <stephen at sryanfamily.info>
> wrote:
> > I think this is the answer right here; wireless uses the same CSMA/CD
> > algorithm that Ethernet does ....
>
>  From what I've read, not quite: It's CSMA (Carrier Sense Multiple
> Access) without the CD (Collision Detect).  Most 802.11 stuff can't
> detect collisions, because a radio which is transmitting can't tell if
> another radio is also transmitting on the same frequency at the same
> time.  Like with walkie-talkies; when you're transmitting, the
> receiver is disabled.  So collisions hurt even more because the
> equipment can't even tell there's been one.
>
>  I dunno about the stuff which uses multiple transceivers.


You just tweaked my memory, Ben.  I avoided using specific abbreviations
before because I was straining to remember, but you got me most of the way:
11b does CSMA/CA (collision avoidance), where they listen to see if any one
is transmitting and then give it a shot if all seems clear, but have no idea
if they hit anyone, leaving it to TCP (or some similar protcal up the stack)
to take care of it.  This becomes inefficient very quickly as load
increases.

11a/g does CDish stuff as I descibed before where the AP knows when a
collission occurred and lets the clients know with a little more information
who gets to go next.

-- 
Alan Johnson
alan at datdec.com
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