Comment by daneel_w
4 years ago
A bit of a clickbait-y tweet. Exact same thing happens with any OS and Wi-Fi device when briefly scanning for surrounding access points. In the case of my setup (2017 MacBook Air running 10.15/Catalina) the penalty seems forgettable - avg. ping jumps from 2 ms to 25 ms during 1.5 seconds, on 802.11n/5GHz with about 20 other 2.4GHz/5GHz access points in my vicinity. My Asus ZenBook running Linux Mint and equipped with Intel Centrino Wi-Fi suffers a lot more from the same procedure.
Why would someone program an OS to do this when it's already connected to an access point? This is like me eating a sandwich and stopping mid-chew every minute to check the fridge.
Reason one is that one doesn’t generally connect to an access point (BSSID), but rather to a an SSID. That SSID may have many access points, as the device may roam. Periodic scans check to see if another access point for the same SSID is now a better choice, and switch accordingly. On Linux, configuring the connection to a specific BSSID generally disables periodic scans.
Reason two is to determine location from WiFi network data. Location may not be static even if connected to a single network, since that network may cover a large area and be roam-able, or be moving (hotspot, train, etc.).
> Reason one is that one doesn’t generally connect to an access point (BSSID), but rather to a an SSID. That SSID may have many access points, as the device may roam. Periodic scans check to see if another access point for the same SSID is now a better choice, and switch accordingly.
Maybe I don’t fully understand the Wi-Fi “space” but I gotta wonder why the standard hasn’t embraced a CDMA-like system where your device can just roam around without really caring which AP is the strongest… the access points would all communicate with each other to figure out which one should be responsible for a device.
It would also fix all the nonsense with picking channels for each access point. They’d all use the same spectrum.
But I’m only an armchair observer so who knows…
A moving wifi AP wouldn't really help with establishing a location, since it's, well, non-stationary :)
In theory, it could establish that you are on a bus/train/airplane... and then look up any public transport information for whereabouts of that vehicle, but I don't think anyone does that.
Because on devices with only WIFI the only way to give you 'GPS' like data is to scan for nearby wifi access points. There are several big databases in the sky that know about a great many Access Points and when your laptop says 'i see these 10 APs with this amount of signal' it can figure out where you are.
It's not really forgettable if any app can request a scan at any time – collect wireless logs, then start the Maps app, you will see repeated scans. Locationd doing this ever so often might be acceptable, but not when any app can do this, repeatedly.
Also, 25 milliseconds is about a round trip across half the continental US. Not really sure that's a good tradeoff for devices that are mostly stationary.
A 750-1000 ms increase would be disturbing, but a 20 ms round trip increase for a brief two seconds is entirely forgettable. It's nothing. It (and more) happens all the time between you and practically any destination out on the Internet as part of normal traffic/congestion patterns.