Technical Tip: Real world WIFI performance

[Adolfo_Z_H]

Description

This article describes what to expect about network throughput, using WIFI-enabled devices.

Scope

All devices using a WI-FI 802.11 a/b/g/n/ac/ax network interface.

Solution

In a very simplified way this is what happens:

In the 2.4 GHz frequency it will be difficult to obtain high bandwidth, supposing a Wi-Fi device can achieve an association rate of 72 Mbps (best scenario) the maximum that could be obtained would be a little more than 25 Mbps, this is a expected behavior, because the maximum data rate in 2.4 using a 2x2 minimum are of 76x2 = 152 Mbps.

if  2/3 of the data rate are removed for traffic control and management use, only 1/3 of that rate is destined for data. The same happens for the 5 GHz band.

Remember, these speeds are raw, that is the reason to subtract 2/3 of the data rate on best real-world scenarios, this will include overhead, management and traffic control, and some loss due a channel.

Utilization and interference from other apps on the system or from neighbors.

Related links:

https://divdyn.com/wi-fi-throughput/

https://www.centurylink.com/home/help/internet/wireless/which-frequency-should-you-use.html

Real-world speed accounts for factors like:

- Sharing bandwidth with other devices connected to the WiFi network.

- Interference from physical obstacles.

- Interference from electronics.

- Interference from nearby WiFi networks or wireless devices.

- Signal loss resulting from the distance between the device and the wireless router,

There are some raw approximate real-world speeds:

Frequency          Theoretical Speed           Real-World Speed

2.4 GHz (802.11b)           11 Mbps              2-3 Mbps

2.4 GHz (802.11g)            54 Mbps              10 -29 Mbps

2.4 GHz (802.11n)            300 Mpbs           150 Mbps <------Best case scenario with a 2*2 mimo device.

5 GHz (802.11a)                6-54 Mbps          3 - 32 Mbps

5 GHz (802.11ac)              433 Mbps-1.7 Gbps        210 Mbps - 1 G

5 GHz (802.11n)                900 Mbps           450Mbps

Important information in that link:

https://www.speedguide.net/faq/what-is-the-actual-real-life-speed-of-wireless-374

It is necessary to take in consideration the SNR needed to obtain this best cases scenario:

https://d2cpnw0u24fjm4.cloudfront.net/wp-content/uploads/802.11n-and-802.11ac-MCS-SNR-and-RSSI.pdf

On the observed test, a data rate of 65 Mbps at it was consistent for the RSSI of -64 using a 20 Mhz wide channel (1*1 Mimo - one transmitter, one receiver).

other brands also explain this expected behavior:

https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/212892-802-11ac-wirel...

Note as well that wireless is shared environment, this means that the amount of clients connected to the AP will be sharing the effective throughput between each other. On top of that, more clients mean more contention and inevitably more collision. The efficacy of the coverage cell will drastically decrease as the number of clients’ increases.

It is a rule of thumb:

Expected throughput = Data Rate x 0.65

In our case:

780 x 0.65 = 507

507 Mbps of throughput is what we may expect in good conditions in a lab with a single client."

*NOTE LAB ENVIROMENT, SINGLE CLIENT.

In conclusion, use 2.4 Ghz for low-end devices and devices that not requires high performance like IOT devices (i.e. electrical relays, lamps, thermostats)

Prefer the use of 5.2 Ghz band for high performance like multimedia collaboration and large file transfers

At this moment, readers will be wondering if 802.11 AX supporting gear will overcome those limitations on 2 GHz band, the answer is similar to the effect we observed when 802.11ac becomes popular, on a 'green field' deployment (only AX devices), only those devices can take advantage of new functionalities (MU-MIMO, BSS COLORING in this case), but legacy devices (b/g/n devices) still need to wait until channel will become available to transmit.

It is possible to review on the following documents the most important features of AX-enabled Fortinet FortiAPs.

https://docs.fortinet.com/document/fortiap/7.0.0/secure-wireless-concept-guide/506160/wi-fi-6-specif...

Here is a guide to how to properly check the WIFI network throughput using FortiGate as a wireless controller and Fortinet Access points, by using iperf client built in Fortigate OS:

https://community.fortinet.com/t5/FortiAP/Technical-Tip-How-to-check-Wireless-transfer-speed-with-Fo...

Take into consideration that WIFI throughput is not always the same as the Internet ISP speed, due to FortiGate maybe have enabled other features that control both Internet Speed and resources available for WIFI devices and/or per SSID.