Will that device with a weak signal slow down the whole-home WiFi? I took the camera in the corridor and measured it for three nights, and the account is all recorded here.

This happened because of the camera at the end of my hallway. For a few days last winter, my mother was in the kitchen using her old video card. I opened the background and checked around: The broadband is not full, there are no strangers in the device list, and the channel is clean. What card is stuck? Until I clicked on the camera details page, the signal strength column said -78 , I just connected the two things. Later, I squatted for three nights and used it as a sample to figure out the calculation. I also packed away several other devices with poor signals at home. This article will explain from the beginning "How devices with weak signals slow down the FamilyMart network", and how to find out and deal with it.

Let me give a word of caution to readers who have never been exposed to this number.: There is a signal strength in the details of each device in the background of the router. The unit is dBm. It is a negative number. The closer to 0, the better. Where can I see this number and how to read it? I am How to read the signal strength I have written a complete tutorial here, and there are two entrances to Xiaomi and Mijia Apps. If you are not familiar with it, take a look first and then come back. This article will directly talk about the more ruthless account behind it.

Let’s talk about the conclusion first: Devices with weak signals are not "slow by themselves", but are pulling the entire network into a queue.

Most people’s understanding of “poor signal” is: That device's own network speed is slow. Video card swiping and slow loading are all its own problems. This understanding is only half correct. the real problem is—— WiFi is a shared medium, and devices with poor signals will take several times as long as others to work. .

To use an analogy. WiFi is like a conference room. Only one person can speak at a time. After everyone confirms that they have heard, they can change to the next one. When a device with a good signal speaks, everyone can hear it clearly. ； The one with poor signal (such as my -78 camera) has a low voice and loud noise. People often "didn't hear clearly" - OK, it says it again. If a package is sent out and does not wait for confirmation, it will be resent. If it is not confirmed, it will be resent again.

This "resending" action is called retransmission according to the rules. The mechanism of 802.11 is to wait for an acknowledgment frame after sending the data frame. If the timeout does not wait, it will send it again. The hardware layer generally allows more than ten consecutive attempts before giving up. translated into vernacular: For a device whose signal is poor enough to send one packet, it can take as long as it takes for others to send five or six packets. What it transmits hasn't changed, but the time it takes up the "microphone" has doubled.

The streaming of my hallway camera only costs a little over 2MB, and it’s not even listed in the bandwidth account. But its signal is -78, the packet loss rate is high, retransmissions are made over and over again, and the busy time is several times longer than normal. The thermometer and hygrometer, the door lock, and my mother's mobile phone, which was forced to use 2.4G at the same time, were all lined up behind it. What she was stuck on was not the bandwidth, but the queuing time.

I've really done the math: Three nights of actual measurement records

I always feel weak just talking about principles. Last December, I spent three nights squatting. For equipment, choose the corridor camera, and for reference with a good signal, choose the living room TV (5G, -49). Stupid method but it works: The device details are turned on in the background of the router, and their numbers are copied every once in a while. At the same time, another mobile phone is used to measure the speed on 2.4G.

After I finished this set of comparisons, I was stunned for a moment.: The router is the same, the broadband is the same, and the other equipment is not touched. Unplug a 2M streaming camera, and the speed of the entire 2.4G channel is directly doubled. The bandwidth account doesn't explain it at all - it only accounts for 2 MB. The only explanation is the busy time: Its signal is -78, a lot of packets are lost, and retransmissions are frequent, and a small packet of data takes up several times the opportunity for others to speak. There is also a thermometer and hygrometer and a door lock on the same 2.4G line that are sending heartbeats. My mother's mobile phone is also fast and slow at times. The experience of these devices has been dragged down by it.

The two accounts must be separated here, many people confuse them: Bandwidth is "how much goods can be moved in total", and busy time is "how long does it take to monopolize the microphone?"」 . When troubleshooting network slowness, everyone instinctively looks at the former, but eight times out of ten, the blame for slowing down the whole family is the latter. What equipment is most likely to have this problem? Features are very concentrated: Mainly smart devices (nailed to 2.4G), far away from the router, up through two walls, and the signal strength is -75 down. They themselves "look" aggrieved - the App shows online, the streaming is normal, it's not broken, it's just that the signal is bad.

How to name it: Watch the three numbers together in the background

Don't rely on your feelings when checking this matter. Look at the three numbers in the background together and you can roll your name in five minutes. How to identify the device list and how to match a bunch of unknowns with MAC addresses? This basic skill lies in The article about identifying equipment Here, first label every device in your home before we can talk about it further.

The first number is signal strength . Click on the details of the equipment throughout the house one by one and copy down the column with negative numbers. My underlining caliber: -Use as you like within 60 ； -60 to -70 accounting observation ； -70 Go down to the suspect list ； -Around 80 is the hardest hit area. The basis for this classification, which I explained in the signal strength article, was calibrated using two months of disconnection records of 62 devices of my own. It is not an official standard.

The second number is Online duration and disconnection records . Devices with weak signals have a common problem: It disconnected repeatedly and came back on its own. When it goes offline, it's not just the device that is disconnected - the device must first listen to the channel, send a detection request, and go through an authentication handshake process before reconnecting. Every step of the way is busy. If you lose frequently, just reconnecting will make you become a busy user. How can I check the reason for disconnection from the log? I am The article about WiFi intermittent The complete number of log flipping methods is written in it, as well as the reason code comparison table.

The third number is Negotiation rate . Note that this is auxiliary evidence and not primary evidence - poor signal will drag down this number, but a high negotiation rate does not mean that there is no illness. The negotiated speed of my camera shows 72Mbps all year round, which doesn’t look bad, but it is maintained by retransmitting over and over again. The correct way to use this number is to do it in reverse: If the negotiation rate drops ridiculously (for example, from 2882 to dozens), it means that the signal is bad enough to affect rate adaptation. The signal should be processed first. How to read the line number of velocity? What is the normal WiFi speed? That article contains three months of reconciliation records.

After the three-digit roll call, there is still one more step to verify.: Turn off the power to the station you named and do another round of testing at the same time. Symptoms disappear or are significantly relieved, real hammer ； If there is no change, continue to the next suspicion. This is what I did for the three nights of comparison. This step is cumbersome, but it can prevent you from wasting time by handling the wrong equipment.

The signal is poor and there is a hidden doubler: It drops out more than you think

This part was discovered by me paying more attention during those three nights. For devices with signal -78, the frequency of disconnection is much higher than what is seen in the App. Because both the router and the device have "lost connection determination"」: The number of packets without response is considered to be disconnected. After disconnection, the device will not shout "I lost it". It will just go through the reconnection process and continue working after it is completed. So it looks like it's always online in the app, but in the background it might be disconnected seven or eight times a night.

This "zombie-like online" device is a stealth killer that the whole family can experience, and it is particularly good at hiding.: Unless it completely loses contact, you won't know it was disconnected unless you check the logs. The reconnection process itself is busy, and coupled with the retransmission of its daily transmission, the two accounts overlap. What's worse is that the firmware of some devices will reset its own network stack and start over again after several failed reconnections, further inflating the busy time. How to read the disconnection reason code? There is a complete table in the log review article I mentioned earlier. If you have a signal-75 down device at home, it is worth a night to read it.

By the way, let’s talk about a judgment that can easily lead to injustice.: Being full but slow is not necessarily a problem of this kind. The number of grids in the status bar of a mobile phone is different from the actual signal. The number of grids is drawn by cutting the dBm into three and four levels, which is very thick. My mother's cell phone shows two bars in the kitchen, but the actual number is -72. To judge whether the signal is good or not, always use the negative number in the background as the standard. This is a pitfall for me. Full but slow piece I took the actual measurement of six points and dismantled it.

What to do after roll call: Process according to signal gear

How to deal with it after you find it? I will give you a check list according to the signal level, from zero cost to small cost.:

There are two other things worth doing on the router side. One is the signal strength level. Many firmwares default to "standard" instead of "through the wall". Manually adjust it to the strongest. I found 8 dB in the toilet, which is very cost-effective. The other thing is the placement of the router. The price of misplacement is a full house - below 70, I have two classic pitfalls, the weak current box and the TV cabinet. Where to put the router? Five positions have been tested.

Further down is the diversion. For families with many smart devices on 2.4G, if you move the cameras and sweepers to a separate WiFi, the main network will be cleared immediately. I have four specific ways. The article about separate networking of smart devices The whole process is written here. If the whole family is stuck together at night and cannot identify the device with poor signal, then the problem may be on the neighbor's channel. The number of channels to check is The one about slowing down at night , don’t waste time in the dead end of my article.

ending: My inspection habits and three reminders

The current practice has solidified into a habit: Pull up the background device list every two weeks, and only look at the signal strength column. Those from -70 down are put into the to-be-processed list, and the disconnection records are used to decide which ones should be processed first. Spending ten minutes can prevent most accidents in which "the whole family suddenly becomes stuck" in advance.

Three reminders to close. First, the premise for devices with poor signal to slow down the whole family is "same frequency band". If it is fixed on 2.4G, it will affect the equipment on 2.4G. Your mobile phone is basically insensitive to 5G. You must first confirm which frequency band the device is stuck in before making a decision. Second, the order of disposal is always to move the location first and then spend money. Most -72 equipment can be saved by moving half a meter. Don't just buy child nodes. Third, there are more than three or four devices at home with signals below -80. That is not a matter of which device, but a matter of router coverage. You can directly check the placement and repair nodes. You cannot save each device one by one.