Will older devices slow down WiFi 6? The old iPad kept getting stuck in FamilyMart, and I've figured out the AirTime account

during the New Year, my mother-in-law brought her old iPad mini 2 to my house—a 2013 machine, even connected to WiFi for video play. As soon as the device connected, something strange happened: the 2.4G camera at home started spinning, the door lock responded half a beat slower, and my mom's phone was lagging while watching videos in the kitchen. My first reaction was that the router was dead, so I tried restarting it, but it didn't help. After spending the whole night looking at the device list, I realized the problem was with that old iPad—as soon as it sent data, the entire 2.4GB cable was queued.

there's a saying circulating online: 'If there's a slow device on the network, the entire WiFi will drop to its speed.' This statement was half true, half false; the false side caused many people. Today, I'll lay out the account I've figured out. The key word is just one: airtime, which translates to 'empty time.'

to get to the conclusion: downgrading the entire internet is an old calendar; the real culprit is the time fragment being occupied

the phrase "downgraded to the slowest device across the network" originated around 2010 during the era of WiFi4/WiFi3 hybrid models. Back then, the router had B/G mixed mode enabled, and to accommodate old devices that couldn't hear clearly, it had to send a 'Everyone, don't speak yet' protected frame, which really slowed down the whole network. Even now, thinking about this set of inheritances still gives me a headache. Back then, I had to replace all the SIM cards at home just for it.

But nowadays, WiFi 5 and WiFi 6 routers are no longer playing this way. When mixing new and old devices, each should negotiate for higher speeds. My phone still runs at 2402Mbps, so it won't drop just because an old iPad runs 72Mbps. I tested this when I wrote about mixing two routers before. so-called full-network downgrade, only the weak signal device's empty port half is truly .

this "half truth" is exactly how old devices slow down the network: it's not slowing down your speed, it's taking up your speaking time.

WiFi is a walkie-talkie, not a telephone line

first need to understand how WiFi works. The phone line is handled separately; you and the operator each have one line, so you don't interfere with each other. WiFi is not; WiFi is more like a group of people sharing a single channel through a walkie-talkie: only one person can speak at a time, and when two people speak simultaneously, it's a total noise that no one can hear clearly.

So before every piece of equipment is contracted, you have to listen carefully and make sure no one speaks before speaking—I explained this queuing rule in detail when I wrote OFDMA before. The router acted as the host here, holding the right to speak.

The

pitfall lies in the queue rules: traditional WiFi queues by "round," not by "duration." Each piece of equipment has roughly equal chances of being on your turn; how much you can move in one round depends on your own ability. New equipment moves brick by cart, old equipment moves brick by cart—but they occupy the same rights to the "round."

result: transferring the same 100MB file takes 20 to 30 times more rotation time for the old device than for the new device, and the microphone takes 20 to 30 times longer in its hand. This "microphone holding time" is called airtime. It is a truly scarce resource in WiFi networks, more valuable than bandwidth.

I did the math: the same file was more than twenty times worse

just talking about the principle is pointless; I actually did the math with my home equipment. Take a 100MB file as an example, which converts to 800 megabits.

that old iPad mini 2, WiFi 4 card, negotiated speed of 72Mbps, actual throughput is halved again and again, and 30Mbps is the best. After transferring this 100MB, it takes nearly 23 seconds of channel. On my phone, with WiFi 6 connected to 5G band, copying files to the NAS runs at 90MB/s, and the same 100MB speeds just over a second.

What does 23 seconds mean? The door lock, sensors, and old laptops forced into 2.4G on the same channel are all lined up in the background, waiting for it to finish speaking. You can't wait for camera streaming—wait two seconds and lose frames, and after a few frames, you see a spinning circle. This is the whole truth behind the saying, "When an old iPad is installed one after another, the whole family becomes lagging."

there are even worse variants: old devices with poor signal. My mother-in-law's iPad sits in the bedroom farthest from the router for years, with signal strength below -75dBm. Even sending and receiving is a struggle, and having to retransmit packets and retransmit again doubles the time. Low signal acceleration rate and dual congestion, making it an airtime black hole. previous post about blind spot self-checking I taught you how to read dBm—old devices below -70 are prime suspects.

However, there is an important scope limitation here: don't wrong good devices: most older devices only recognize 2.4G, and 2.4G and 5G are two channels that do not interfere with each other. If your new phone is connected to 5G, no matter how much your old iPad uses 2.4G, you basically won't feel it. The real victims are the devices crammed on 2.4G: cameras, door locks, speakers, and unlucky phones that were "guessed" to be 2.4G by dual-band integration.

three tricks to pull out outdated equipment that holds you back

understood the mechanism, the next step was to name the "microphone occupants" at home. I use three tricks to go from easy to troublesome:

first trick: log in to the router backend to check the negotiated speed. Each device in the device list has a connection rate. Directly compare with the table below, with key surveillance points starting with 72 and 144:

the origin of this set of numbers, I broke it down when I wrote about spatial flow : multiplying antenna count by bandwidth multiplied by modulation order, stacked step by step. By the way, I once bought a 39-yuan 1x1 USB network card for an old desktop. After negotiation at 144Mbps, I tested 72-80MB. It's really cheap, but the cable usage is also very busy.

second trick: check your computer's real-time speed. On Windows, open the command line, type netsh wlan show interfaces, and the output columns for "Receive Rate" and "Transfer Rate" are the current negotiated values. When your phone is flawed, first check which generation standard you are being satisfied with.

third trick: elimination. If you're suspicious about which device is being choked: turn off its WiFi and test again during the same period to see if the lag on the 2.4G system disappears. It's a simple method, but it works. I usually run the speed test page on my phone and try it one by one, two minutes per round.

Four Tips for Handling Them: Separate Rooms, Run a Nursing Home, Extend Lives, Be Cautious with Plugins

What to do after

is caught? Four moves are arranged from small to major based on cost.

first trick: disconnect dual-band and live in separate rooms. turn off the dual-band integration , 2.4G and 5G are called two different names. Old devices and camera speakers are stuck at 2.4G, while phones and computers manually connect to 5G. New devices completely leave the old device's channel and don't disturb each other. This trick solves most of the problems without spending a penny.

second trick: set up nursing homes for old equipment. If you have an old unused router at home, switch to AP mode dedicated to serving IoT and old devices, and set up an independent SSID, physically separate from the main network. The camera lock is fully loaded with an old iPad, and the main router's 5G is spotless. smart devices only recognize 2.4G's temperament, which is a perfect match for this solution.

third move: extending life. Old desktops and laptops that can still be used shouldn't be left to drag on WiFi4 network cards. For about 30 yuan, buy a USB wireless network card and swap it in, negotiate for a speed straight to 867—leap two generations in one step. It's much more cost-effective than replacing the whole machine.

fourth trick: the router's built-in "plugin"—Airtime Fairness, called "Transmission Time Fairness" in Chinese. The idea is quite literal: queue is not by turn or by time, and when the time quota for old equipment is used up, make room for the new equipment, and free up the saved time for the new equipment. In the "Professional Settings for Wireless Network →" on ASUS routers, each frequency band has a switch and advanced options, which are turned off by default.

default closing has its reasons. It downgrades slow devices, and smart hardware with small data volumes is easily "cut in line," causing the patient to mistakenly think the device has disconnected and reconnect frequently. I once saw a case where all smart home devices were disconnected, they checked the area thoroughly, and only after turning off the function did it settle down. So my advice is: almost all the equipment at home is new, only one or two old ones that can be driven; If the whole room is full of cameras and door lock sensors, don't touch them.

take the line personally: Is your situation the fault of old equipment

a checklist at the end to avoid wrongly accusing old equipment and missing the real culprit:

finish with a processing sequence to avoid detours: first check the backend and name the devices on 2.4G to identify the WiFi 4 ones; then remove dual-band and move the new devices to 5G; replace the old machines that still work, and put the unusable ones into the IoT nursing home; leave the ATF switch at the end to confirm the home devices and reactivate them. After one set, my mother-in-law's iPad plays its videos, my camera pushes its stream, and neither of us delays the other.