Skip to main content

Chasing a Wifi Ghost

For quite a while, I have not been so confused (and excited) by a technical issue.

The problem is: I got very slow download speed (~10Mbps) on my Windows laptop, when connected to Wifi.

To make it a bit more puzzling:

- The upload speed is much better (~60Mbps).

- Sometimes the download speed may reach ~100Mbps for a few seconds, before quickly fall back to ~10Mbps.

Having been suffering from it for a few months, I finally decide to take on this issue today.


Beginning of the Journey

As usual, there are some troubleshooting routine I should do. Also as usual, they don't help much.

- Try other devices with the same Wifi
- Try to connect to other Wifi
- Try to connect to Ethernet
- Reset the Wifi router
- Run Windows troubleshooter

Well, eventually I did get some information. The download & upload speed is actually normal for all my other devices, which includes Android/iOS phones, MacBook Pro etc. 

This pieced of info narrowd the root cause down to the laptop itself: The router must be working well, and I'm not throttle by my ISP.


The Chase1: Killer

My machine has a Killer wifi card, which had some issues before. At the beginning, I try to examine all Killer componenets thoroughly:

- Try the latest Wifi driver
- Try some older Wifi drivers
- Install / Uninstall Killer software & services

Not surprisingly, nothing worked.

The Chase2: Windows

Next, I tried to exhaust my knowledge about Windows networking,  in order to examine all relevant aspects:
- run sfc /scannow
- Reset TCP settings
- Reset network stack (run ipconfig, netsh etc.)
- Disable SmartByte service (which is actually not available on my machine)
- Disable WMM/QoS (which is actually not available for my router)
- Disable power saving move for the adapter
- Altering Wireless mode (802.11) of the adapter
- Disable network discover
- Disable firewall
- Remove custom DNS servers
- Disable features (e.g. ipv6) of the adapter
- Disable other network adapters
- Disable bluetooth
- Disable Windows TCP autotuning
- Dissable WAN miniport

Again. Nothing worked.

The Ghost

After reading the Killer troubleshooting pages for a few times (one, two), I finally noticed an instruction, to set the "channel width" to 20MHz. This is relevant since I'm using a 5GHz Wifi.

Having absolutely no expection, I changed the settings in the router, and that's how I captured the ghost.
Now I have ~100Mbps download speed, finally. Still not as fast as the Ehternet, but good enough.

Summary

Previously the router had been configured to use choose from 20/40/80MHz automatically. The router has been using 80MHz according to my Wifi scanner. If I understand correctly, changing to 20MHz helps because there are many other Wifi signals "nearby": both "physically close" and "similar channel frequencies). This probably can also explain why the download speed was unstable.

It is yet unsolved why my Killer wifi card is not able to handle the broader width, while others can.

Anyway, I'm happy to meet this new cute ghost, and keep it with its friends together.
Labels:

Comments

Post a Comment

Popular posts from this blog

Exploring Immutable Distros and Declarative Management

My current server setup, based on Debian Stable and Docker, has served me reliably for years. It's stable, familiar, and gets the job done. However, an intriguing article I revisited recently about Fedora CoreOS, rpm-ostree, and OSTree native containers sparked my curiosity and sent me down a rabbit hole exploring alternative approaches to system management. Could there be a better way? Core Goals & Requirements Before diving into new technologies, I wanted to define what "better" means for my use case: The base operating system must update automatically and reliably. Hosted services (applications) should be updatable either automatically or manually, depending on the service. Configuration and data files need to be easy to modify, and crucially, automatically tracked and backed up. Current Setup: Debian Stable + Docker My current infrastructure consists of several servers, all running Debian Stable. System Updates are andled automatically via unattended-upgrades. Se...
Post a Comment
Read More »

A Rocky Migration: Moving from docker-compose to Podman and gVisor

I've been running a few containers for several years. They were all running under rootless Docker with a single user. Initially, I planned to  migrate the containers to VMs , but I couldn't get a stable workflow after about two months of effort. Later,  gVisor caught my attention , and I decided to migrate to Podman with gVisor instead. The new plan is to run each container with  --userns=auto  and use Quadlet for systemd integration. This approach provides better isolation and makes writing firewall rules easier. I'm now close to migrating all my containers. Here are a couple of rough edges I'd like to share. Network Layout I compared  various networking options  and spent a few hours trying the one-interface-per-group approach before giving up. I settled on a single macvlan network and decided to use static IP addresses for my containers. To prevent a randomly assigned IP address from conflicting with a predefined one, I allocated a large IP range for my ...
Post a Comment
Read More »

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...
3 comments
Read More »