Wireless Throughput Calculations and Limitations

Overview

This article is intended to provide details on MR Access Points’ (APs) advertised maximum data transfer rates, how they are calculated, and expectations for real world data transfer speeds. This includes:

• Limitations and factors affecting throughput
• Maximizing throughput
• Testing client-to-AP throughput

Limitations and Factors Affecting Throughput

802.11 is a shared medium which comes a multitude of factors that can limit speeds when using wireless technology. The nature of wireless communication as a whole can make predicting throughput a difficult task, and network administrators should maintain reasonable expectations for speeds when using 802.11.

Factors that can limit throughput include:

• Distance between the client device to the AP

• Signal-to-Noise Ratio (SNR)

• Interference (radio, physical, electrical)

• Physical obstructions

• Other nearby wireless networks and devices

• Device capabilities

While it is theoretically possible for 802.11ax-capable clients to achieve maximum throughput up to or over 1Gbps (depending on the beamforming capabilities of the AP and wireless client), limiting factors within the environment will hinder the overall aggregate throughput. The half-duplex nature of wireless, combined with overhead and the above factors, means that the aggregate throughput in a wireless network is typically 50% or less of the advertised data rate.

Maximizing Throughput

Achieving optimal throughput rates and wireless performance, especially in a high density deployment, can be achieved by performing a site survey and verifying the design. A proper design will do its best to make sure that the above factors are mitigated or accounted for as much as they can be. While no two wireless designs will be the same, general design principles can be implemented such as (but not limited to):

• Proper AP placement

• Proper antenna selection

• Number of SSIDs (limiting wireless overhead)

• Ensuring at least a 25 dB SNR (signal-to-noise ratio) across the desired coverage area

• Ensuring a proper Channel Plan

In a mesh environment, throughput rates will be significantly better with fewer hops to the Gateway AP. Each hop will reduce bandwidth by 50%, so ensuring there are as few hops as possible across the mesh link(s) will provide better throughput.

Testing Client-to-AP Throughput

When testing the throughput of a Cisco Meraki MR Access Point, it is important to understand that any advertised maximum data transfer rate is a theoretical total maximum data transfer rate (both transmit and receive) for the AP’s radio(s). If you are interested in what the theoretical total maximum data transfer rates are for an AP model, look at the datasheet for the specific model of AP, but know that these will be different per AP model due to which wireless standard is used (802.11ac, 802.11ax, etc) as well as antenna and radio capabilities.

When testing a Client-to-AP connection speed, it is important to differentiate the speeds between the client device to the AP itself, and the speeds for the client device to the Internet when distinguishing bandwidth concerns in a network. To accurately assess the speed between the client device and the AP itself, the Speed Test option on the APs local status page should be used (and not an outside test such as speedtest.net). Before using an outside tool to test general client-to-Internet speeds, confirm first what is seen between the client device and AP and use the results of these tests to determine if the client-to-AP connection should be investigated, or if a further upstream problem should be scoped.