Wirebook › Bonus lesson
Why does the video call freeze when you walk to the kitchen?
You're on a video call in the living room and you wander off to the kitchen. Halfway down the hall, the picture freezes, even though there's a Wi-Fi box right next to you. Why? Because a phone can only hold one Wi-Fi box's hand at a time, like a runner holding one baton, and the phone decides when to pass it on.
What's really going on
- Signal fades fast. Wi-Fi is radio. Every time you double the distance from a box, the signal gets much weaker, and every wall soaks up a bit more. Grown-ups measure it in dBm: about -50 is brilliant, -67 is fine for a video call, and below -80 the box can barely hear you.
- Weaker signal means slower speed. The box and phone switch to slower, more careful ways of talking when the signal is weak, a bit like speaking slowly across a noisy playground. A video call needs a steady amount of bandwidth, so once the speed drops below that, the picture stutters.
- The phone holds one box at a time and it chooses when to swap. The boxes can't grab your phone. Switching to a new box is called roaming, and each phone has its own rules for when to try. A sticky phone hangs on to a weak box for ages, because swapping costs a tiny pause and it's being cautious.
- Calls keep almost nothing in hand. A film app downloads a few seconds ahead, so a short wobble goes unnoticed. A video call is live, so it keeps only a moment of picture ready, and a hand-over that takes too long shows up as a freeze.
- Good boxes give hints. Mesh systems can tell the phone which neighbours exist (so it doesn't have to search every channel), suggest "you'd be better off over there", and hand over a quick pass so the phone doesn't sign in from scratch. Grown-ups call these 802.11k, 802.11v and 802.11r.
So how do you stop the freeze?
Put the boxes where their circles overlap a little, not at opposite ends of the house, so there's always a spot where both are loud enough to pass the baton. Give every box the same network name and password, so the phone can switch without asking you. Mesh systems do the clever hint-giving for you; a plain Wi-Fi extender with a different name makes you do the switching. And if one phone is always sticky, a quick Wi-Fi off and on in the kitchen does the hand-over by hand.
Grown-up twin: Tooltern's help pages on Wi-Fi that keeps dropping when you move rooms, where to put mesh units and Mbps vs MB/s show the same ideas on a real network.
Related: how a text message finds its way to someone's phone, the frog that only hops twice.