Wireless Access

Suppose we have two neighbor access points (ap1 and ap2) working on channel 1 and channel 2, respectively. Also suppose we have an Android phone that is connected to ap1. My questions are about passive scanning of ap2:

1: when ap2 off-channel scans channel 1, can it hear from the client? I think the answer is Yes. Then would it report the client's snr value?

2: I read article from here: http://www.arubanetworks.com/techdocs/ArubaOS_60/UserGuide/ARM.php

I found when an ap performs an off-channel scan, per-channel "scan time" is 110 msec by default. Would this be one channel per scan or multiple channels per scan? If multiple, where can I find the related parameter? 

Thanks.

1.  Yes.

2.  One channel per scan.   The "scan interval" is how often it leaves the home channel to scan other channels (default 10 seconds).  The "scan time" is how long it scans the channel (default 110 miliseconds).  Very few situations require that this parameter be changed.

So suppose we use 2G band, i.e., 11 channels. Intervel time: 10 seconds; scan time: 0.11 second (per channel). And of course, it just scans 10 off channels.

Based on the above parameters, an ap is going to take (11 - 1) * (10 + 0.11) = 101.1 seconds to finish scanning all channels. Am I correct? If this is the case, would it actually miss a lot of client probes?

Thank you.

Yes, it does take that long.  The ARM scanning described is only for access points that are currently servicing clients, and go off-channel to look for other clients.  The access point that a client is connected to always has the client's current SNR.  The off-channel scanning is only supplemental to the SNR provided by the access point the client is currently connected to.

Could you please explain more about "supplemental"? What do you exactly mean? By the way, your explanation is valuable, but which official documents can I read for these information?