How WiFi Works - Computerphile

Why do WiFI speeds vary so much? Dr Steve Bagley demonstrates how even a poor signal for one person can affect those with a seemingly perfect signal!


This video was filmed and edited by Sean Riley.

[yuriiradiev]

Wow, I've never thought about the fact that Wi-Fi routers can only transmit one packet at a time to a single receiver. And the final example with two people using the same network and the person with a slow connection results in a slow connection for everyone -- it was just mindblowing!

[UpLateGeek]

Yeah, been a network engineer for a decade, studied and worked with multiple wireless data transmission technologies, and whenever anyone asks how wifi works, my stock response is "surprisingly well, when it's not working poorly". What they really want to know is "how can I fix my wifi speed", and most of the time my suggestion is to switch off the 2.4GHz radio in your router and just use the 5GHz one, because there's a lot more free channels so a better chance it will pick one that's not congested. And then if the reception is poor in the furthest reaches of the house, it's really time to invest in a better wifi solution.

But at least now if they really want to know how wifi works, I can just point them to this video and save myself the 20 minute explanation!

[scienteer]

I find it best to think about Energy required to receive a single bit. You can increase the transmitted Energy per Bit by either slowing it down, or increasing the Power.

[Norsilca]

This was fascinating. I had no idea about this aspect of wifi. I feel like this could use a better title than the generic "how wifi works". I almost didn't click on it because I thought it'd be another basics I already knew. This is more like "how your bad signal can slow everyone's wifi".

[orlovsskibet]

Me: Yeah I know how wi-fi works
Steve: Explains how wi-fi really works
Me: Ok then, I'm glad I watched it
😄

[kristoffseisler]

guys stop posting interesting topics when i am currently watching something else which i am also interested in

[thelegalsystem]

This is a great explainer! Do OFDM and MIMO next :)

[BooBaddyBig]

One thing I didn't think of for a long while. There's usually only one radio receiver in a laptop/phone etc which can only listen to one channel at a time. Yet when you click the WiFi button it has to show you all the different base stations, many of which are on different channels. So your device retunes the radio for about a tenth of a second, per second through each of the different channels to find all the base stations. But while it's doing that, it misses packets on the channel it's actually connected to, so they have to be resent! That's why the announcement is every tenth of a second. So there's a bit of jitteriness on WiFi that you don't get with Ethernet.

[mareau]

My favourite way of explaining these concepts is using food dye in water. The more dye, the more power. The further out from the origin point of the dye in the water, the further from the wifi router. Add lots of different food dye colors in represents interference from other devices, which you can overcome by using more power (putting more dye in), but eventually you're so saturated that it would take unreasonable amounts of dye to get something representing color, instead of a gross brown/black.

[charlielidbury]

Thanks for uploading this now, my networks exam is tomorrow! Good luck Imperial Computing second year, hope this video finds you

[rodvik]

Atari ST in the background? Thats some legit cred right there :)

[servv]

this should have 10 million subs by now - love computerphile.

[JeremyMcMahan]

~30 years in IT. Still learned a lot! Thanks for this video!

[Muthwill]

Very interesting video

I'm now playing with the idea that all of my slow IoT objects in my house (Google Home Minis, Ikea outlets, etc.) should say use the 2.4Ghz network while my laptops and phone should be "isolated" on the 5Ghz network as the far away IoT objects might be slowing down the network?

[sanchopanza]

Great video as always. Please talk about DHT some time!

[DrRChandra]

Thank you for explaining this. I had a few different experimental SSIDs being broadcast by my AP, each tied to a different VLAN. Now that I know that it's more-or-less radio pollution (because I'm not actively using those SSIDs), I've turned them off until I'm ready to resume experimentation.

[olivier]

Thank you for that video.

I see a trend to use WiFi for everything. Don't use cable, it is something of the past, use WiFi, it is so convenient, event for the desktop of the secretary, that is sitting on their desk and will never move anywhere, even for that huge printer that obviously needs a cable for main power.

You demonstrate clearly that using WiFi when it is not needed is a bad idea (i.e. slow)

[Pilsnerpc]

10:27 - A small correction if you'll allow me to be a pedant for just a moment. I think the presenter meant to use the term Beacon frame rather than Beacon packet when talking about network discovery. The distinction is minor, but frames and packets are different, have different header/trailer information, refer to a different layer of the OSI model, and have other implications.

[DanielLiNeutrinos]

Love to see a video on wifi channels if it's not already done

[TheGodpharma]

So if the access point is sending its SSID beacon 10 times a second at its slowest speed, does this noticeably impact the overall connection speeds? Does disabling SSID broadcasting (which I think is possible on most routers) potentially improve performance for devices that are already connected?