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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Which Channels Can I Use On The 2.4GHz Band for Wi-Fi Networks?

2-4ghzThere is often confusion around which channels may be used when deploying a Wi-Fi network using the 2.4GHz band.

Depending on where you are in the world, the band generally has either 11 channels (numbered 1 to 11) or 13 channels (numbered 1–13) available to use.

Unfortunately, it’s not as easy as just using any channel that you might feel inclined to use. In short, the convention is generally to use channels 1, 6 and 11.

Why not the intervening channels (you may ask)?

The 11 (or 13) channels available on the 2.4GHz band are each 5Mhz apart. Wi-Fi communications requires a channel width of 22MHz to operate (the equivalent of 5 channels). We cannot use channels that are adjacent to each other, as we would get an effect called “adjacent channel interference”. This is a very bad thing in Wi-Fi networking, leading to very poor network performance.

You may have heard that is best for your network to use its own dedicated channel, which is true (when feasible). But if you find that neighboring Wi-Fi networks are already using channels 1,6 & 11, do not be tempted to try to use intervening channels for your network (e.g. 2, 7, 12). Co-existence on the same channels as nearby networks is better than trying to use other channels.

The generally accepted convention is to use channels 1, 6 and 11. I strongly advise that you stick to the same convention.

(Side note: You really should be leveraging the 5GHz band as far as possible for Wi-Fi networks — 2.4GHz is generally not a good choice in many instances in terms of Wi-Fi network performance)

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What Makes a Wi-Fi Device “Wi-Fi”?

selection_of_wifi_devices

Your fave smartphone or tablet will often support a number of different wireless technologies. Most people have heard of “Bluetooth”, “Wi-Fi” and “cellular”, but what is the difference between them? Wireless is wireless, right?

In addition to those mentioned above, there are also other lesser-known wireless technologies such as “Zigbee” and “Z-Wave” that you may also find in consumer-grade and commercial devices.

Each wireless technology has its applications, dependent upon its capabilities. Cellular technology is used primarily to provide cellular phone services around towns, cities and highways. Bluetooth, Zigbee and Z-Wave are used to provide close proximity services for devices such as wireless headsets, keyboards, door entry systems etc. Wi-Fi is primarily used to provide in-building data, voice and video services for laptops, tablets and smartphone type devices.

My area of interest is Wi-Fi wireless networking, so we’ll take a quick look at what makes a Wi-Fi device “Wi-Fi” capable.

All of the wireless technologies we’ve mentioned previously have earned their wireless technology classification as they have been manufactured to adhere to a particular industry standard. Many of these are defined by an organization called the “Institute of Electrical and Electronics Engineers” (or IEEE, for short).

The IEEE define standards that ensure that devices operate to a particular specification to earn their stripes as a “WiFi”, “Bluetooth” or “Zigbee” capable device. Based on these standards, manufacturers of smartphones, tablets, laptops etc. will included chip-sets and software that implements its wireless connectivity using one or more of these standards.

ieee_wireless_committees
IEEE Wireless Committees

The standards are created by a number of standards committees within the IEEE and are given a number of rather cryptic numerical designations:

  • Wi-Fi : 802.11
  • Bluetooth: 802.15.1
  • Zigbee: 802.15.3

Going back to our original question, a “Wi-Fi” device is a device that supports the IEEE 802.11 standard. This is implemented within a device using a combination of 802.11-capable wireless chipsets and software.

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