Wi-Fi “Secrets” Part 2 — Wired is Faster Than Wireless Networking

Taking turns can slow you down

As discussed in my last article, when deploying Wi-Fi networks there are a number of considerations around wireless connectivity that we need to be aware of when comparing them to the more familiar world of wired networking.

In this article we’re going to look at another of Wi-Fi’s “guilty secrets” that few people seem to be aware of. Are you ready for it..?

“Wi-Fi is a shared medium”

What does this mean? All devices connected to each wireless access point (think of laptops, iPads, smartphones etc.) have to take turns to transmit and receive data. They have to share access to the access point. This means that as more devices that join an access point and have data to send, the longer each device may have to wait before it can send its data.

Wi-Fi is a “contended” medium: everyone using it has to take their turn to “talk” to the wireless access point. When things start to get busy on your Wi-Fi network, this can be a significant challenge.

Why is this an issue compared to wired (think Ethernet) networks? Well, each device connected to an Ethernet switch has its own dedicated chunk of network access bandwidth. If an Ethernet station is connected to a 1Gbps port, then it has a full 1Gbps available and does not share it with anyone else. Each device connected to an Ethernet switch port gets its own 1Gbps of access bandwidth to use.

In a Wi-Fi network, if we have a single device connected to an AP, it has access to the full bandwidth that the AP makes available. If we add a second device, the bandwidth available is now shared between both devices (50% bandwidth each) as they take turns to send data. If we add a third device to the AP, each device now has access to 33% of the bandwidth as three devices now take turns to send data. As more devices are added to an AP, the opportunities for each one to send data will decrease, reducing the bandwidth available to each one.

Effect of Multiple Wireless Clients Contending For Wi-Fi Access (Simplified)

The contention to access the wireless network described above applies only if multiple devices need to send data at similar times. However, if wireless forms a significant part of the access layer of your network, this will very likely become an issue very quickly as the number of users (who may have several Wi-Fi devices each) increases.

How do we mitigate the limitations of Wi-Fi’s contended access method? We must optimize our wireless design to achieve the maximum throughput available. This is achieved by designing each Wi-Fi network for capacity as well as wireless coverage. Careful design & planning of the wireless RF environment, together with taking account of client & application bandwidth requirements is the only way to ensure optimized performance.

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