Wi-Fi “Secrets” Part 1 — Wired Is Faster Than Wireless Networking

No matter how many gazillions of dollars, pounds, euros or <insert your currency here> you spend on your Wi-Fi network, it is subject to the same immutable laws of physics as everyone else’s. This applies to home networks, mid-sized and even large Enterprise Wi-Fi networks.

Wi-Fi has a number of inherent limitations, compared to wired networks, that are (currently) insurmountable and limit the data throughput that can be achieved. Wi-Fi networks generally achieve a fraction of the throughout that you would expect from a modern switched, wired network. Unless you understand these limitations and design with them in mind, your wireless users are likely to have a poor experience.

The first limitation of Wi-Fi networks that we’ll look at is the fact that it uses a “half duplex” medium. This means that if your iPad, iPhone, Android tablet, laptop (in fact any client device using a Wi-Fi connection) is exchanging data with a wireless access point (AP), data flows in only one direction at any time.

Data frames can flow from the AP to the client device, or vice versa, but never in both directions at the same time. This limitation is due to the fact that the wireless AP and associated clients all use the same channel to communicate, meaning that they can only be transmitting or receiving.

Half Duplex vs Full Duplex

This contrasts sharply with wired networks, where full duplex is the general default mode of operation. This means that a device connected to an Ethernet switch port may have data frames flowing simultaneously in both directions. This effectively provides twice the available throughput for an Ethernet connected device, compared to a Wi-Fi connected device with a similar connection speed.

How does this translate in to the real world? If we consider a wired device connected to a 1Gbps Ethernet switch port, it can realize a data throughput of close to 1Gbps connection speed, if required. If we have a Wi-Fi client connected to an AP using 802.11ac at a physical connection speed of 1.3Gbps, we’re likely to achieve an actual data throughput of around half the connection speed (approx 700Mbps), due to the half duplex nature of its connection.

Unfortunately, Wi-Fi clients that can connect at 1.3Gbps are in the minority, with many 802.11ac mobile clients only able to support lower speeds. Also, there are still many legacy, lower-speed, devices that may be in use on your Wi-Fi network which provide even worse performance.

Even if you are happy with your 700Mbps throughput, there are more factors to consider which mean that even this level of performance is a pipe-dream in the real world. We’ll look at more of these in future posts.

How do we mitigate the limitations of Wi-Fi throughput? We can’t. What we must do is optimize our wireless design to achieve the maximum throughput available. Careful design and planning of the wireless RF environment is the only way to ensure optimized performance.

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