802.11ac: The Bicycle Fix For The Mobile-First Era


With the Wi-Fi Alliance certification program for 802.11ac earlier this year, and the subsequent release of the first .ac devices, the world is talking seriously about this new wireless networking standard. One of the most common questions people ask is why it makes sense to upgrade to 802.11ac when the client population is still largely 802.11n.

I have four devices on my desk – laptop, tablet, phone, and music player. Each is connected to the wireless network, and I’ll access different apps from different devices, sometimes simultaneously, depending on what I’m doing. Many of my colleagues have an identical addiction to electronics, and I’m guessing it’s a similar picture in your organisation.

This is the mobile-first era – users expect to use wireless by default, and if they are young enough, might not even know what wired Ethernet looks like. As a result, congestion is unfortunately now a fact of life in networking, and it’s something that network technology designers have to deal with. The solution lies in the basis of packet-switched networking, and how networks behave in response to congestion.

Packet-switched networks cope with congestion well, up to a point, and then they suffer from a sudden collapse.

One of my favourite analogies for describing this scenario is to compare your computer network to the transportation network. Let’s say that you set out to drive somewhere early in the morning, say around 2 am. The road will be empty and you can drive at the speed limit. There’s no congestion. An unloaded network behaves the same. Packets line up for transmission, and head out to their destination immediately.

Add a few cars to the road, and not much happens. The throughput of the road (the number of cars) is high, but traffic is not yet high enough to degrade latency (otherwise known as the time spent in traffic).

Eventually, though, too many cars get on the road, and traffic suddenly starts to crawl. Adding more cars increases throughput, but the cost of adding a car is slowing everybody else on the road to a near stop. Welcome to the M25.

So, if the network is so congested that latency is high, what can be done? Remove the congestion. Put more formally, the average latency of a packet on the network is inversely related to available airtime, so freeing airtime is good for everybody using the network.

One of the reasons that major cities have focused on increasing trips taken by bicycle is that bicycles take up much less road capacity. For the price of a car’s worth of roadway, you can have half a dozen bicycles.

What’s The ‘Bicycle Fix’ For Wi-Fi?

We have a fixed and costly resource – the radio medium – and need to wring more out of it. By reducing the transmission time for frames, 802.11ac enables network administrators to push back against congestion collapse.

In the 802.11 radio link, the load is measured in demand for airtime, not in terms of demand for the transfer of bits. By increasing the data rate, it’s possible to transfer more data while decreasing the load on the radio network.

As you add 802.11ac clients, they will reduce the amount of airtime required to transmit data. Increasing free airtime will improve the quality of user experience regardless of device.

The lesson in here is that if you have a network running close to the traffic volume at which congestion takes hold, you should move to 802.11ac. Decreased loads are like traffic-free roads – they are good for everybody.

Matthew Gast

Matthew Gast is the Director of Product Management at Aerohive Networks. He currently serves as chair of both the Wi-Fi Alliance's security task groups, was the first chair of the Wireless Network Management Marketing task group, and is the past chair of the IEEE 802.11 revision task group.