Jeremy Visser wrote:
On 01/11/2011, at 13:06, Jake Anderson wrote:
On 11/01/2011 11:26 AM, Adrian Chadd wrote:
The problem, unfortunately is:
* Supporting 30+ connections on a single AP is doable;
* .. and the commercial APs do it;
* .. but that source isn't open source.
I think what jeremy is saying is whilst you could have 30 devices associated
with an AP your not going to be able to push much data through the rather
congested airspace.
And I think what Adrian is saying is not that 30+ devices on open source is
impossible, but the commercial APs have some hacks to improve performance. I'm
not sure precisely what Adrian is referring to though, to be honest.
Seems WiFi might be experiencing the similar growing pains, to those
Ethernet overcame.
Another variable to consider is the frequency bands that are available (at
AP, at User Equipment, in Spectrum)/selected.
<http://en.wikipedia.org/wiki/IEEE_802.11#Channels_and_international_compatibility>
<http://en.wikipedia.org/wiki/Comparison_of_Open_Source_Wireless_Drivers>
<http://en.wikipedia.org/wiki/IEEE_802.11>
I digress here, as the following does not help Sridhar find a better AP, but
interesting background nonetheless:
One similar example that I know of is Ubiquiti AirMax (who uses Atheros
chipsets in their hardware). AirMax is a proprietary version of Wi-Fi (read:
incompatible with vanilla clients) that *vastly* improves performance with (a)
many clients, and (b) hidden nodes. [0]
Vanilla Wi-Fi relies on CSMA/CA [1] -- in other words, a client will listen for
a gap in the radio signal, and if it detects one, it will fire away. The more
clients, the fewer gaps, and the more chance of a collision.
AirMax (or standardised protocols such as WiMAX) adds TDMA -- time division
multiple access. [2] With TDMA, the access point itself is in charge of when
clients are allowed to transmit, so collisions are reduced to zero, and in
practice vastly improves congestion.
Obviously the above is not relevant to Sridhar, as he can only use solutions
that are compatible with vanilla clients, but no doubt there are some
performance hacks (which would break or bend the standards) that remain
compatible.
--
[0] http://en.wikipedia.org/wiki/Hidden_node_problem
[1]
http://en.wikipedia.org/wiki/Carrier_sense_multiple_access_with_collision_avoidance
[2] http://en.wikipedia.org/wiki/Time_division_multiple_access
--
Marghanita da Cruz
http://ramin.com.au
Tel: 0414-869202
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