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:
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Distance between the client device to the AP
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Signal-to-Noise Ratio (SNR)
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Interference (radio, physical, electrical)
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Physical obstructions
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Other nearby wireless networks and devices
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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):
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Proper AP placement
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Proper antenna selection
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Number of SSIDs (limiting wireless overhead)
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Ensuring at least a 25 dB SNR (signal-to-noise ratio) across the desired coverage area
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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 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.
- A wireless packet capture on the AP via Meraki Dashboard would show the bitrate of the data frames and the number of retries, while client device is connecting to the SSID. Click on a data packet from/to your wireless client and scroll down to the “802.11 radio information” section of the packet.
- To check high latency or loss, pinging the AP interface (10.128.128.128) from a connected client would be useful
- Troubleshooting client speed using Jperf documentation
- An outside tool to test general client-to-Internet speeds such as speedtest.net