The European Wireless LAN Professionals conference was recently held in Lisbon, Portugal.
The conference featured a host of knowledgeable speakers sharing a wide variety of information on a range of Wi-Fi related topics. Fortunately for those of us who were unable to attend, Keith Parsons, the conference organizer, ensures that all sessions are recorded and are made available for free to anyone who would like to view them!
I’d strongly recommend you get along to the YouTube playlist and check them out. You will learn an extraordinary amount of information about Wi-Fi by reviewing these videos from this amazing resource. I’d recommend you also visit @KeithRParsons on Twitter and personally thank him for this service.
In this next installment of the “guilty secrets” of Wi-Fi networking, we take a look at another facet of wireless connectivity that you may need to think about. Did you know that if you’re using a Wi-Fi network in your home or business, your neighbours may be eating up some of your potential wireless bandwidth? An interesting consideration, especially if Wi-Fi is a mission critical service for you or your organization…
In part two of this stroll through Wi-Fi secrets, we discussed how Wi-Fi networking is a contended medium, where every device that needs to send data needs to wait its turn. As more devices start to use the same channel on your network, the throughput enjoyed by each device starts to degrade as the time-slots available to send data become more scarce.
Part of the solution to this contended medium “problem” is to carefully plan how you configure your wireless network so that you can install more wireless access points on unique channels and add more capacity to your network. Note the word “carefully”, as it’s incredibly easy to cause unintended contention within your own wireless network and have zero overall increase in capacity when adding more access points.
Anyhow, back to your neighbours…
Although you may go to great lengths to ensure your own network is well planned and causing minimal self-interference, you have no control over nearby Wi-Fi networks. Maybe you have other organisations in the same building as your own organization? Maybe you even have co-located organizations or a service provider network inside your own work spaces? There are also a multitude of ‘mini’ Wi-Fi networks created by visitors and employees using their own devices (think smartphones, Mi-Fi devices) to tether other devices to give themselves unfettered Internet access at work. All of these networks have the potential to use the same channels as your carefully built, carefully planned Wi-Fi network.
All of these networks, large and small, use the same contention (sharing) mechanism as your Wi-Fi network. They will have to wait for your networks’ Wi-Fi devices to send data, and you network will have to wait for their clients to send data. There is no escape from this basic medium sharing requirement of Wi-Fi, which is built in to the 802.11 “Wif-Fi” standard. Due to this fundamental mechanism of Wi-Fi networking, you must share available airtime (and hence available bandwidth) with neighbours using the same channels as your network.
Fig 1 – Access Points on the same channel (even if they are a neighbor) must share available bandwidth (air-time)
The caveat to this issue is that the signal levels from neighbouring networks have to be strong enough to be detected in the areas occupied by your organization. However, if your neighbors have their access point powers cranked up to the max, or you have Mi-Fi devices in-use in your organization, this isn’t an uncommon scenario.
How can you mitigate this effect to maximize the throughput of your Wi-Fi network? Ultimately, you cannot stop nearby organizations using the same channels as your organization for their Wi-Fi, but you can lessen the impact by:
Careful design of your wireless network. Ensure your RF design takes account of neighbouring networks (in terms of your network channel planning)
Encourage employees to switch off their Mi-Fi devices and Wi-Fi phone tethering while at work
Monitor your RF environment over time to look at changes in usage by neighbouring networks and modify your network channel planning to suit
Perhaps look at using the built-in automatic channel planning capabilities of your Wi-Fi solution to automatically avoid neighbouring networks. Caveat: keep a close eye on your channel planning if using this option: you do not want to avoid neighbouring networks at the expense of causing self-interference on your own network
Fig 2 – Switch your access point to a new channel to avoid sharing available Wi-Fi bandwidth
In my past couple of articles looking at the differences between wired and wireless networking, we’ve looked at the fact that Wi-Fi is a half duplex medium and that it is also a contended medium. Although Wi-Fi is a fabulously convenient network access method, understanding some of its technical limitations will help you get the best out of your Wi-Fi network.
There is another nuance of Wi-Fi networking, which is related to the contended nature of access to the RF medium. As devices using Wi-Fi have to take turns to send their data, there is an additional effect caused by the varying capabilities of the devices using network.
Different Wi-Fi devices have varying capabilities depending on when they were manufactured and the components used to construct them. Some may have the “latest and greatest” super-fast wireless cards, whereas others may be a few years older and may not have speed capabilities of newer equipment. Even the “latest and greatest” Wi-Fi equipment may have different performance characteristics dues to differences in numbers of antennas, antenna size, power availability and chip-set capabilities.
The best analogy to understand this subtlety of Wi-Fi networking is to think back to our example of a single lane highway from part one of this series. We discussed how only one vehicle can travel in each direction at any time, in the same way that half-duplex Wi-Fi connections operate.
We can extend this analogy a little further and consider the impact if we have a mix of vehicle types. Instead of having only fast vehicles using our road, we may have a mix of sports cars, family saloons, trucks, farm tractors and bicycles.
When sports cars are using the highway, they use the road at high speed and quickly complete their journey to make it available for other vehicles to use. But, when a bicycle decides to use the highway, it takes a lot longer to travel along its length. This means that all of the other vehicles (even the fast ones) are waiting longer to use the highway again.
We have exactly the same issue with Wi-Fi networks. Devices which are “less capable” and connect at lower speeds will have an impact on faster devices that need to use the network. When a slower device sends its data, as it uses a slower connection speed, it will take longer to send its data than a faster device. As we add more slower devices that need to send data, then the more impact they will have on the faster devices that have to wait longer for their turn to use the RF medium and send their data.
What can we do about this?
The best solution is to ensure that our Wi-Fi is correctly designed to be as efficient as possible. If we ensure that all devices can operate at their highest possible speeds, we will at least ensure that we gain the maximum possible throughput available from all devices. This will maximize the air-time (i.e. throughout) available to all clients. A good RF design for your Wi-Fi network is critical — get an expert to design your Wi-Fi RF environment.
Another approach is to consider upgrading the devices that use the Wi-Fi network. This is a particularly important consideration if your wireless network is mission critical and provides the primary access method to your wired network. If you have any 802.11b, 802.11g or 802.11a devices on your network, seriously consider replacing them with 802.11n or 802.11ac devices.
Another useful approach is to relegate slower, legacy devices to the less-desirable 2.4Ghz band. By creating an SSID that is specific to only 2.4GHz and getting slower devices to use only that SSID, you can keep the higher performance 5GHz band for your higher-spec, mission critical devices. This approach obviously depends on the requirements of your particular network, but can be useful in some scenarios.