Do Android devices scan *actively* for WiFi networks?

Question

i am programming for google android and i wonder if the scans for wireless 802.11 networks are done passively or actively? i mean: does the device actually emit a beacon request signal on WifiManager.startScan() or does it just listen for beacons sent periodically by the access points?

Answer 1

Android does passive scans, it listens for beacons. Doing an active scan can create a lot of congestion on the network by sending out probe requests and waiting for probe responses.

Answer 2

The answer is YES

Actually, using omnipeek to capture packages from Android/iOS devices, we can get the result below:

• Most Android devices always try to send Probe Request Frame every few minutes. They keep a list of SSID you used to connect, and always try to send probe request frame with SSID to see if they are available now. I guess one of the reason is 802.11 pre-authencation , and some other reason may be: enhance the wifi list display speed.
• They are working in a active.
• iOS devices seldom do active scan

If you wanna konw more about the rules, you'd better read "802.11 Wireless Networks The Guide"

You can refer to the pciture : Packages captured by omnipeek