[Network] Theory-crafting: CPU ≈ access point performance

One of the fact I’ve learned recently during WiFi 6 access point comparison testing is that not all access point are created equal even if with the same PHY. So how do we tell which AP is worth buying when looking for the best performance? Perhaps, CPU specification maybe the answer.

Background

Manufactures list the maximum theoretical throughput on their access point specifications. While these numbers are useful to estimate the minimum performance, they do not offer, which AP can perform better than the other beyond the minimum.

If we compare Ubiquiti UniFi’s U6 Pro and U7 Pro AP’s 5GHz radio specifications, U6 Pro lists significantly higher number than U7 Pro on the throughput rate. However, for majority of users, U7 Pro will give better throughput on 5 GHz than U6 Pro even on the same WiFi 6 client device. Why?

Client bottleneck

The key principle of networking is “bottleneck determines the throughput”. Since most WiFi clients are 2×2 MIMO, 4×4 would not give practical throughput advantage in most situations*. Additionally, 160 MHz channel width in 5 GHz radio is often impractical or unusable for many**.

Therefore, the actual 5 GHz WiFi link (PHY) for WiFi 6 client and U6 Pro is 1200 Mbps (1/4 of advertised).

The bottleneck principle also applies to WiFi generation as well. So if we have WiFi 6 client connected to WiFi 7 capable AP, U7 Pro, the PHY is at the rate of WiFi 6. So with WiFi 6 client, U7 Pro’s PHY is also 1200 Mbps.

*There are situations where 4×4 can be useful such as in mesh setup, those who owns 3×3 or 4×4 capable client devices, or have ability to utilized MU-MIMO etc.
**Apple has not supported 160 MHz channel width until the most recent iPhone 15 series. 160 MHz in 5 GHz radio requires to use DFS channels i.e. DFS strikes make the channel unstable.

WiFi Efficiency

The graph above is from my recent U7 Pro review article. The comparison graph shows the average throughput of U7 Pro is significantly higher than that of U6 Pro. Neither is anywhere close to 1200 Mbps. This is related to what I call “WiFi efficiency”. Typically, the maximum Wi-Fi efficiency ranges between 50-70% of PHY. This 20% range is what we are seeing the difference between U6 Pro and other APs on the graph.

As a network hobbyist who like to keep trying new access points, and looking for the best I can afford, I like to have a rough idea of Wi-Fi efficiency of the new AP before purchasing one. After staring at the specifications for a while, I came to a brilliant (not really) hypothesis. The relative WiFi efficiency can be predicted by the chipset used by each access point. With each generation, chipset/platform category changing, I need a step further. So within the chipset, I hypothesize more specifically the “CPU” specification as the best predictor.

Let’s me show how this hypothesis holds true for various testing I have done so far.

Theory-crafting

Although each venders had their proprietary, perhaps marketing, technology, I hypothesize the real difference in maximum throughput performance comes from the chipset used by each AP.

This should be a fairly easy guess if we think about other electronics e.g. computer, smart phone, and tablet. However, just looking at the chipset did not quite explain a difference between certain AP performance comparison. It also won’t help when new chipset is released as I have no reference to compare from previous generations. So I looked one step further than the chipset.

So my current hypothesis is “the best (specification parameter) predictor for wireless access point performance (max throughput) is CPU”.

The best test to prove this point would be to have two matched setup that is identical for everything, but CPU and measure the max throughput as output. However, this is not practical because there are many other variable such as vender specific software and other hardware difference.

So rather than scientifically proving my hypothesis, I will show my hypothesis holds true in multiple real world tests of my own.

Qualcomm Home Immersion vs. Networking Pro | Specification

Before going into the actual test result comparison, we need to know the basic fact that not all chipsets are made equal. There are several companies that make access point WiFi chipsets. Two big names are Broadcomm and Qualcomm. Qualcomm chipset was used by all APs that I have tested recently. So this is the focus of current article.

In the last 3 WiFi generations (WiFi 6, 6E and 7), there have been two platforms in Qualcomm WiFi Chipset: immersive home and networking pro series. The latter is top of the line platform while the former is more budget friendly platform.

Although two platforms differ in the features, the specifics change between generations. So let’s just focus on the CPU. We should see some difference amongst CPUs; otherwise, my hypothesis immediately fails.

I’ve listed below Networking Pro platform’s the highest and the lowest end models, and Immersive Home platform’s chipsets for each generations.

	1620	620	3210	326
WiFi Version	7	7	7	7
Platform	Networking Pro	Networking Pro	Immersive Home	Immersive Home
CPU	Quad Cortex-A73	Quad Cortex-A73	Quad Cortex-A53	Quad Cortex-A53
Clock	2.2 GHz	2.2 GHz	1.5 GHz	1.5 GHz

	1610	610	318	316
WiFi Version	6E	6E	6E	6E
Platform	Networking Pro	Networking Pro	Immersive Home	Immersive Home
CPU	Quad Cortex-A53	Quad Cortex-A53	Dual Cortex-A53	Dual Cortex-A53
Clock	2.2 GHz	1.8 GHz	1.0 GHz	1.0 GHz

	1200	400	216	214
WiFi Version	6	6	6	6
Platform	Networking Pro	Networking Pro	Immersive Home	Immersive Home
CPU	Quad Cortex-A53	Quad Cortex-A53	Dual Cortex-A53	Dual Cortex-A53
Clock	2.2 GHz	1.0 GHz	1.0 GHz	1.0 GHz

In WiFi 6 and 6E generation, immersive home platform used dual core CPU at 1.0 GHz. In contrast, networking pro series used quad core CPU with variable clock speed depending on the specific chipset model.

In the latest, WiFi 7 generation, Immersive Home now uses Quad core CPU, but Networking Pro has moved to from A53 to A73. If we assume manufacture’s claim for CPU performance improvement on each Cortex ARM generation, A73 should be more than twice that of A53.

So in every generation, we can expected twice the CPU performance difference between networking pro and immersive home on the paper. Conceptually, this is like comparing Intel’s Celeron/Pentium chips against Core series. This drastic difference in CPU specification looks to be a good target to use for performance prediction.

Case Analysis

Now let’s look at several different scenarios to see if CPU difference indeed can be an explanation for throughput test result observed.

Throughput Test Setup

• Client device: iPhone 14 Pro Max (WiFi 6, 2×2, 80 MHz)
• AP to client position: 5 ft with full line of sight
• Test Methods: iPerf3 to local NAS server with 10 Gbps connection. The tests were run at least twice on each, and if there is significant discrepancy, I had ran more to ensure stability is achieved. Took the best.
• [math]WiFi Efficiency = \frac{Practical Throughput}{PHY}[/math] is calculated for better of the two (download vs. upload). PHY in all test cases are 1200 Mbps as that is the max limit of WiFi 6 for given client specification.

Result:

R350 showed nearly 20% improvement in WiFi Efficiency over the U6 Pro. This performance gain is equivalent to estimated throughput gain from WiFi 6 to WiFi 7 by new 4K-QAM technology i.e. it’s quite a significant gain.

Summary

		Ubiquiti UniFI	Ubiquiti UniFi	Ruckus	HPE Aruba	Ruckus
		U7 Pro	U6 Pro	R750	535	R350
Hardware
	Chipset	Q Home 3210	Q Home 216	Q Pro 1200	Q Pro 1200	Q Pro 400
	CPU	Quad A53 1.5GHz	Dual A53 1.0 GHz	Quad A53 2.2 GHz	Quad A53 2.2 GHz	Quad A53 1.0 GHz
5 GHz
	WiFi Version/MIMO/Max Channelization (MHz)	7/2×2/160	6/4×4/160	6/4×4/160	6/4×4/160	6/2×2/80
	Max PHY rate (Mbps)	2882	4800	2400	2400	1200
Practical Throughput
	Download (Mbps)	871	659	861	813	874
	Upload (Mbps)	764	622	760	791	799
	WiFi Efficiency	73%	55%	72%	68%	73%

Although throughput of wireless access points depends on many factors, CPU specification can be useful predictable factor.

Reference

• Qualcomm Immersive Home Platform
• Qualcomm Networking Pro Platform