At 17:55 17/11/2003, Geek wrote:
or rephrasing, when two nearby APs A and B use the same channel,and a client C receives signals from both,by how much should the signal strength of one be over another for C to correctly receive a packet?
If A and B are within reach of each other, A and B should not transmit when the other one does (like Ethernet, 802.11 includes a "carrier sense" mechanism which will postpone tranmission if the media is already in use). If A and B are not within reach of each other, then it can be pretty bad (that's the usual "hidden node" problem). The threshold here is the SNR, where the "other" AP will count as noise and yours as signal. The minimum SNR varies from card to card and even from bit rate to bit rate, and is usually between 3 and 20 dB. 20 dB is quite a lot, that means the "other" AP needs to be 10 times further than your AP (or there must be enough walls to cause a 20 dB loss).
If i have an AP and someone who lives next door also has an AP on the same channel, whats the best way to quantify my loss in performance(in terms of throughput or maybe delay)?
Depends on how much traffic is sent/received by that other AP. You can consider that you "share" the nominal bandwidth. If the two APs can "hear" each other, the total throughput of the two networks should be close to the available throughput. If they can't, then you have additional loss because of retransmits.
How far should i be looking in my neighbourhood to see if anyone has an AP on the same channel as mine? Will the client software on my wireless lan card tell me about nearby APs?
Unless they have SSID broadcast disabled, yes, you should see them. Some APs or cards also have a feature that scans the different channels for noise, and sometimes even select the least noisy automatically (cisco APs do that).
What strategy is used in general to be followed by someone installing wireless LANs in a residential complex by themselves (witohut any knowledge of surrounding installations)?
Find the channel with the least noise. Avoid defaults.
Jacques.
-- Jacques Caron, IP Sector Technologies Join the discussion on public WLAN open global roaming: http://lists.ipsector.com/listinfo/openroaming
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