[MLB-WIRELESS] Multiple APs

[Donovan Baarda]

On Thu, Aug 15, 2002 at 12:50:16PM +0930, Jamie Lovick wrote:
> On Thu, 15 Aug 2002, Matt Chipman wrote:
> >
> > > Logically, yes. If they are all on the same wired network backbone, they
> > > should all bridge DHCP requests from a single server, so it wouldn't
> > > matter which "cell" it is connected to.
[...]
> Also, changing the topic a little, it is best, though it is occasionally
> done with all AP's on the same wireless channel, to have adjoining AP
> cells on different channels.

Yeah, that's what I thought. With all the AP's on the same channel, they
would be colliding with each other all the time. Wouldn't you ideally want
any two APs on the same channel not only out of each others range, but
sufficiently out of range that no client in the middle could see both?

This has probably been beaten to death on this list, but I can't find exactly
what the benefit of AP's is. There is a lot of waffly stuff about how
"infrustructure mode" relays all traffic through the AP to clients and how
they can do bridging, but I still don't get it.

With all the clients in peer-to-peer mode, the whole system would be just
like ethernet, with colliding clients backing off and retrying. This gives
you effective bandwidth of 1/2 the total available bandwidth. This I
understand.

With an AP in the mix, all traffic must be relayed through the AP. This
means packets between clients must be transmitted twice, once to the AP, and
again to the destination client. Now unless AP's negotiate some sort of
collision avoidance, you still have 1/2 total available bandwidth from
collisions, and then you halve it again because of the double transmits,
giving you only 1/4 total available bandwidth. The only use I can see for an
AP is relaying between two clients that are in range of the AP but not each
other.

Is there some other voodoo that AP's do that buys you something that I've
missed? Is it something to do with the incomplete direct conectivity between
all clients? Surely this could be better handled by smart dynamic routing
between clients in peer-to-peer mode?


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