Slow download speed via WiFi compared to upload - symmetrical connection

You're welcome.

Your questions are very relevant and I really like the logic of your thinking.

I was also puzzled about such a situation, which should theoretically affect the upload and download speeds in tandem.

But due to the different paths and conditions of uploading and downloading, it causes them to behave asymmetrically. Of course in an ideal situation, download and upload should be symmetrical, but in most practical situations, it is the download that is affected more.

I was actually testing some of the following reasons, may not be complete, just my personal testing of the conclusion:

1. Although full duplex mode is used for both upload and download, physical limitations of WiFi (e.g. signal strength, wall blocking, etc.) may cause more interference with download data. Downloading usually involves a larger amount of data and in higher frequency bands (e.g. 5 GHz) the signal attenuation is more significant, resulting in lower download speeds than upload speeds.
2. WiFi uploads and downloads may share the same frequency band or channel, so in an environment with higher interference (e.g., many devices around using WiFi at the same time), download traffic may be subject to more competition, which affects its speed. Upload traffic, on the other hand, may be more stable and maintain higher speeds with less interference.
3. Some routers or wireless adapters may have higher priority or better optimization for upload traffic when handling both upload and download traffic. For example, some routers may limit or allocate bandwidth for download traffic when upload traffic is more prioritized, resulting in lower download speeds.

Etc.

For example, nowadays there will be some techies who will provide service sharing services to share their services, when this situation will be more obvious.

In addition to that, I have an extra suggestion for you in this reply, that we try to modify the networking algorithm of Windows.

We try to switch to BBR2 (if not modified, the default should be CUBIC)

Click on “Windows Logo Key” to open the search bar -> type “Windows PowerShell” in the search bar and open it with administrator privileges.

1. Let's check the current algorithm. Get-NetTCPSetting | Select SettingName,CongestionProvider
2. Switch to BBR2 netsh int tcp set supplemental Template=Internet CongestionProvider=bbr2 netsh int tcp set supplemental Template=Datacenter CongestionProvider=bbr2 netsh int tcp set supplemental Template=Compat CongestionProvider=bbr2 netsh int tcp set supplemental Template=DatacenterCustom CongestionProvider=bbr2 netsh int tcp set supplemental Template=InternetCustom CongestionProvider=bbr2

Please note: 1. If you want to switch back, just change BBR2 in the command to the previous algorithm.

2. Some users report that they may not be able to use VPN, Proxy after switching to BBR2, this may happen, so I will inform you in advance first.

Theoretically BBR2 should make the network performance better and smoother, but it still depends on the specific situation.

I sincerely hope that the above information will help you!

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Thank you very much, Arthur for the very detailed explanation!

I will go step by step and check all options to make sure I did not miss anything.

But still, it makes me wonder - full-duplex, half-duplex... Why it is interfering only with download speed, whereas the upload remains almost as high as with a wired connection? In theory, all that you proposed should impact the same way both up and download speed, not just one. Correct?

Hi Wojciech Pluta

Welcome to Microsoft Community.

Based on your description, I understand that you are using the Asus XT8 mesh and both laptops are able to connect to WiFi.6 If you connect using Ethernet, the upload and download are both at 500; however, if you connect using WiFi, the download speed is only half of that of Ethernet, and I understand very well how you feel!

Since I used to study computer networking and computer science and technology, your situation reminds me of many situations.

One of the most likely scenarios is full-duplex and half-duplex.

To explain, let's say we have a transfer rate of 100, since full duplex is a double-ended transfer, it's actually 200. half duplex is a single channel transfer, so it's still 100. and this scenario also corresponds to the fact that after connecting to WiFi, the download speed is half of what it would be if we were connected to an Ethernet connection.

Of course this is just the most likely reason I envisioned, there are a few other reasons that could cause this problem, and I'll try to describe some of them here.

1. Other networks or electronic devices (e.g. microwaves) can interfere with Wi-Fi signals, especially in the 5 GHz band. If you notice severe interference, try switching to the 2.4 GHz band.
2. If you are using a congested channel, this can affect download speeds. Use the Wi-Fi Analyzer app to check for less congested channels and then switch to one of them.
3. Make sure your laptop is within a certain distance of the mesh node. Walls, floors, and distances can greatly affect WiFi performance, especially in the higher frequency bands.
4. Check that the mesh nodes are configured correctly and that they are not too far apart.
5. Quality of Service (QoS) settings in the router can prioritize upload traffic over download traffic. Check your router settings to see if QoS is enabled, and adjust if necessary.
6. Ensure that the firmware on your mesh system is up to date, as updates can improve performance and stability.
7. There are also a number of network configurations and software effects that can cause this issue to occur.

I will give you some options and hopefully solve your problem successfully! However, this first reply may not be able to solve your problem due to the lack of information and the fact that this issue requires different aspects to be troubleshooted, so please understand and provide more information (pictures would be great!) in your reply. Thank you very much!

As the cause of this problem from the principle and technical point of view but more, I hope you are willing to work with me together to solve this problem bro.

Option 1: We start by troubleshooting the full-duplex and half-duplex related scenarios.

However, I can only give you the way to change it from the system level, sometimes you need to change the BIOS or router settings to make sure it is completely changed.

I personally use an Intel ax210, and I suspect the steps should not be very different.

Open Device Manager with “WIN + x” -> find the “Intel AX1650s” device -> right click and select “Properties” -> select “Advanced” in the upper tab.

On the left side of the properties column, scroll down and find “Speed and Duplex”, the value on the right side should be “Auto-negotiation” by default, we need to set it to full duplex manually.

Please note: The values for Speed and Duplex may vary depending on the device model. For example, there are 1.0Gbps full duplex, 100Mbps full duplex, 100Mbps half duplex and so on. We select the highest rate + full duplex supported by your NIC.

Other than that, for other related modifications to the settings and steps I suggest you check out the relevant manufacturer's articles so that the modifications are more accurate.

Option 2: We perform some different tweaks and tests from a router and physical perspective.

1. Move your laptop closer to the mesh node and see if the download speed improves.

Please note: At this point we need to make sure that there is as little signal interference as possible.

2. We adjust different signal bands, for example, your current setup may be 2.4GHz and 5Ghz, we try to connect to these two bands and test them separately to see what the results are.

Then adjust to mixed output (2.4 + 5) for testing.

3. We try to adjust different channels to see if we can mention the download speed.

This is also very likely to happen because Ethernet and WiFi usually use different channels with transmission.

4. We check for recent firmware updates and upgrade the firmware to the latest version for testing.

Assuming the problem still exists with the latest version, we can also flash the firmware version to some known older and more compatible version.

In my personal practical use environment, I am flashing to an older stable version, and I personally feel that the stability and performance seems to be better.

5. Check the QoS settings and make different adjustments to see if there are certain settings that affect download speeds.
6. We try to completely reset the network device and reboot to see if there could be certain settings that could be affecting the download speed.

Please note: 1. Before completely resetting the network device, we need to make sure that we record the relevant settings so that we can restore the settings as soon as possible after the test.

2. After turning off the network device, try to wait for a certain period of time (more than 15 minutes) before turning it back on to avoid overloading the chip and causing the cache to still exist.

Option 3: Let's try to enter Safe Mode with Networking for testing.

Since safe mode only uses a limited set of files and drivers, it helps us to effectively troubleshoot the possibility of problems due to third-party applications, driver conflicts, etc.

For safe mode, you can refer to: Windows startup settings - Microsoft Support (select “Safe Mode with Networking”)

Option 4: Let's try to do some troubleshooting from a network configuration and NIC driver perspective.

1. We try to install the latest version of the NIC driver manually.

The driver involves the following situations:

(1) You can download the NIC driver for the corresponding laptop model from the official website of the laptop brand.

(2) You can also download the NIC driver for the corresponding model through the motherboard brand's website.

(3) You can also download the driver for the corresponding model through the official website of the NIC manufacturer (Intel).

Let's try the latest version of the driver first, assuming the problem still exists, then we will try some older and more compatible versions.

2. Modify some network-related configurations.

(1) Let's first completely reset the network via command line to avoid the possibility that there are some network states, network settings conflicts that cause problems.

Click “Windows Logo Key” to open the search bar -> Enter “cmd” in the search bar and open it with administrator privilege -> Please enter the following commands

ipconfig /release 

ipconfig /renew 

ipconfig /flushdns 

ipconfig /registerdns 

netsh int ip reset 

netsh winsock reset 

netsh winhttp reset proxy 

(2) We manually configure DNS servers, such as Google's 8.8.8.8 and so on.

(3) Since you are using an IPv6 address, make sure your network properly supports IPv6 and prioritizes it.

Other than that, I would suggest you to send this situation synchronization to ASUS after-sales or technical support, they are more familiar with their products and may be able to give you some help related to it from the network equipment. Since I haven't used similar devices and the exact modification steps are different, their manuals can help us modify the relevant settings faster and more specifically.

I sincerely hope that the above solution will solve your problem. Please feel free to contact me if you have any problems or still can't solve them. (Photos related to the question would be great!).

I look forward to hearing back from you. 

Best Regards

Arthur Sheng | Microsoft Community Support Specialist