Teaching Points
In this article, you will learn:
- reason why you can never achieve manufactured advertised throughput (not even close)
- physical link throughput (PHY)
- wireless (in)efficiency
- theoretical max speed of Wi-Fi connection
Chief Compaints
- “I can never reach my internet service provider’s speed wirelessly.”
- “My router/access point seems not much different from the original.”
- “I can never reach full potential of my router’s rated speed (not even close).”
Signs/Symptoms
I have Asus Ax11000 router, supporting the latest WiFi 6 standard. I got 1 Gbps download speed from my internet service provider. I have finally got my first WiFi 6 capable client device, iPhone 11 Pro. The best internet speed test result I can get it is only 600 Mbps. What’s going on? Why is my WiFi test result slower than what I am paying/paid for?
Assessment/Diagnosis
Theoretical speed maximum. Mis-understanding/mis-advertisement.
There are many reasons and causes why WiFi could be slow but one of the reason is “misunderstanding” or “mis-advertisement”. Today, let’s take a look at theoretical max speed.
Treatment
In order to achieve router manufacture’s claimed number, all parameters and environment must be optimized. There are five components to this:
- Physical Distance
- Single band vs. Aggregated speed
- MIMO
- Channel Bandwidth
- Wi-Fi (in)efficiency
Theoretical Max speed & bottleneck
Here I’d like to introduce a concept I call “theoretical max speed.” Based on the different setting, max speed that is achievable is different. This achievable max speed is what I call “theoretical max speed.” At each step of internet or Wi-Fi connection, theoretical max speed may change, but in the end the weakest link/bottleneck determines the overall system theoretical max speed.
With a subscription of 1 Gigabit per second download service from my internet service provider (ISP), the ISP states maximum speed is 940 Mbps.
Note that the maximum speed for Xfinity Gigabit Internet service over WiFi is limited to 1000 Mbps and the maximum speed over a hardwired Ethernet connection is limited to 940 Mbps. Make sure your device meets the minimum system requirements for Gigabit service.
https://www.xfinity.com/support/articles/xfinity-wifi-gigabit-download-speeds
I have indeed confirmed 940 Mbps on internet speed test when speed at the router was measured by directly connecting Macbook Pro to router ethernet port by physical ethernet cable. At this level, you must ensure modem and router units support the speed you are paying for.
So theoretical max speed set at this level is 940 Mbps. In another word, I would no be able to get any number above this when connected to internet.
Distance
I like to think Wi-Fi signal with a sound analogy. This should be no-one’s surprise but like a sound, further a way you are from the Wi-Fi source (router), slower your device internet connection becomes on the client device. So for the highest speed, you need to be next to the router.
*Technically, too close to the router could be slower just like putting your ears on loud speaker is not the best music experience.
Single band vs Aggregated Speed
The router I had was Asus AX11000 router, which is WiFi 6 capable. Asus just like other manufactures put on their website 11000 Mbps number and also actual name of the router. However, 11000 Mbps is a number adding all three bands together: 2 x 4804 Mbps for each of 5GHz band and 1148 Mbps for 2.4 GHz band.
Analogy here is your household may have 3 cars with each having their own speed capability, but if you are the only driver in the home, you can only drive one car at a time.
Similarly, there is no single client device uses multiple band simultaneously so aggregate throughput would never be seen on a single client device. Therefore, at this stage rather than 11000 Mbps, the theoretical max speed for single client goes down to 4804 Mbps.
no single client device uses multiple band simultaneously so aggregate throughput would never be seen on a single client device.