Big Temporary Networks

Niels Bakker niels=nanog at bakker.net
Tue Sep 18 00:52:46 UTC 2012


* joelja at bogus.com (joel jaeggli) [Sun 16 Sep 2012, 18:42 CEST]:
>We tend to engineer for a maximum of around 50 associations per radio
>(not AP). beyond that performance really starts to suck which can be
>measured along a multitude of dimensions. The most visible one to the
>client(s) being latency due to loss and subsequent retransmission.
>
>Reduction in coverage is done on a couple of dimensions. that ap with
>the 3-5dBi gain dipoles probably shouldn't  be 100mW. but the noise
>floor is in a different place when the room is full of clients so it
>can't be to low either. Dropping the low speed rates backward
>compatibility with 802.11b and setting the multicast rate to something
>higher will force clients in marginal coverage situations to roam more
>quickly, hog the air less and allow for higher throughput.

This is all good advice that you should implement.

The difficulty with high user density deployments is getting stations 
to associate to the nearest access point on the optimal band.  When 
presented with the same SSID for 2.4 and 5 GHz, clients usually 
prefer te 2.4 GHz one because its S:N ratio usually seems better 
(inherent to the lower frequency).  However, in practice this isn't 
always the case as there usually are many more clients on 2.4.  
Various vendors of lighweight access points use tricks to get clients 
to associate on the 5 GHz band: e.g. Cisco, I think, will reject an 
initial association request at 2.4 GHz in the hope that the client 
will retry at 5 GHz before retrying at 2.4, which will both be 
accepted.


	-- Niels.



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