Wi-Fi at 802.11ac: Fast and Maddening
Test and Monitor | Posted April 15, 2014

Good news: Wi-Fi networking technology is improving. Bad news: The top speed may surpass your backhaul, and carriers will become the most frequent bottleneck.

There will be joy, and there will be disappointment. The latest IEEE 802.11ac spec will allow wireless speeds in excess of a gigabit per second in actual payload. The sad news is that most wired or backhaul speeds are slower than this. Practically, this means the bottleneck will become the slower circuit from a carrier's point-of-presence in a building to its routers, and then, the increasing congestion of the Internet. For a short period of time, it will be a case of the last mile likely being faster then the routes through telco or carrier Internet routes.

To get the fastest speeds from 802.11ac, there are very specific requirements on matching top-spec equipment with top-spec equipment on your devices. You don't have those capabilities now, so upgrades will be the only way to satisfy the need for speed.

The 802.11ac standard requires fairly sophisticated router technology, and sometimes the number of external antennas start to make the 802.11ac router look like a tarantula on its back. The reason is that extra antennas provide a method to render still faster connectivity between a client and an 802.11ac router, using differential information between and among the antennas. Some antennas may be located inside the housing or bezel of the router to hide them, which is often okay in close quarters. The advantage of mounting antennas externally is that they can be manipulated to fine-tune signals and increase distances while retaining speed.

How It's Faster

802.11ac has advances in three areas, although they're not revolutionary, just evolutionary. When you combine these three, however, wahoo! A lot of bandwidth is available. And if your backhaul/carriers are up to date, connection speeds will be excellent under uncongested circumstances.

Note that phrase: under uncongested circumstances. Uncongested circumstances may become increasingly difficult because of the rapid adoption of the Internet for dense, not-to-be-interrupted media types (such as videos from Hulu, NetFlix, and others) and the scariest prospect: 4K video, which multiplies 1080p video streams by four — if uncompressed. Although very little 4K media is currently available, let alone being streamed, you know it’s inevitable. The problem won't arrive soon, but eventually, 4K media will be like dragging an elephant through a garden hose.

Clearly, we need more bandwidth. The way the products in this group obtain it is by increasing the size of channels, using MU-MIMO methods to obtain up to four multipliers via the eight antennas described, and using 256 Quadrature Amplitude Modulation (256QAM) to stuff more data into each time interval. (That’s not new on its own; 256QAM was used originally in both fiber optic systems and cable TV systems.) All of these are known technologies, and they're being combined to provide additive communication in the 802.11ac spec.

You're not guaranteed the highest rate all the time, however, and you won't find smartphones negotiating the terrific speeds possible. Indeed, any particular device won't get the maximum stream possible unless it has four antennas, which probably are hidden inside the device.


There are two Wi-Fi data frequencies in unlicensed bands set by the FCC and channelized by the NTIA: one at 2.4 gigahertz, the other at 5 gigahertz. Most 802.11ac devices will work in both areas, but the 2.4GHz area is crowded, and only three channels (of eleven) don't overlap. That makes interference a problem in dense Wi-Fi areas such as apartments, retail blocks, and urban areas. The 5GHz area has more non-overlapping channels, as well as more “room” and less crowding, as it's a more recently added area.

The 802.11ac spec allows vendors to bond together adjacent or non-adjacent channels. Early channels were only 20MHz wide, then 40, now 80 — and two 80s can be bonded together. The 80MHz channels only live in the 5GHz area, but the rules say: You can bond channels that are adjacent or not. More/wider channels means more data can be stuffed into them — and the bigger channels, all in the 5GHz area, are more plentiful.

We’re not done quite yet: Then we add Multiuser-Multiple Input Multiple Output (MU-MIMO) into the additive bandwidth. This is done by using multiple antennas, up to eight (1, 2, 4, or 8) and by using a differential algorithm (hidden to users) to serve like having multiple radios/transceivers—that jump the throughput dramatically. It’s at maximum, adding three more radios to each Wi-Fi node/client/supplicant for a total of four radios. Each radio is riffing off several antennas, using two of the widest channels, bonded together.

In essence: They act as though they were four former Wi-Fi clients as one. Only when you add antennas, bonded wide-channels, and do this on both the access point and the client-side hardware, do you get the most screaming data possible in this spec.

The final way that more data can be crammed is by reducing the interval between packets. Less quiet time means more data can be crammed per period. This is automatic when possible.

The overall effect is that the lowly original 2.4GHz Wi-Fi, 802.11b, is approximately 500 times slower than the fastest possible in 802.11ac. Some 802.11ac routers may snort, trying to go that slow. Indeed, the access points are programmable to ignore slower speeds, but are very likely to support the popular 802.11g and almost certain to be backwards compatible with 802.11n-type client stations. Wise installers will disable all but 802.11N and 802.11ac—if all of the client hardware agrees. Then you can start complaining about the backhaul speed in terms of heels on garden hoses.

Making Them Work

More cross-platform/cross-vendor concerns have been built-into the 802.11ac spec than ever before. But only time will tell how much actual interoperability there will be among differing brands and models of equipment. History suggests that users get frustrated when things don't work at optimal speeds, and this frustration is addressed in the spec—it's clearer than ever before.

However, security, never a fond topic of the IEEE, hasn't progressed. No new and important security methods are used or mandated, just the ones we have now. Those are vendor-specific but include at minimum, WPA-2, which uses AES256 encryption. Early firmware hopefully employs WPA-2 effectively. Firmware updates are likely, and sadly, not frequently implemented, leaving some access points (APs) with gaps large enough to fly a hacker through.

This is then coupled to expectations that all IEEE 802.11ac equipment will be able to instantly negotiate and maintain the top speed all the time. Today, there are virtually no devices that can obtain the maximum speed for the spec. All new 802.11ac gear for clients, access points, and routers will need to be obtained, and then, the maximum speed will require the top specs present in both sides of the wireless links. Currently, but a handful of companies make APs and client devices suitable for the new spec. The Wi-Fi guts needed to link to any 802.11ac are incredibly scarce today, but they are on most mobility vendors’ product announcements for 2014 or at least 2015 as demand increases and chipset costs drop from the ozone layers.

Carefully choose the equipment to obtain the fastest Wi-Fi speeds. Smartphones are unlikely to be able to obtain the highest specs, but as smartphones and phablets become the first or primary go-to-device for some users, that may change. Currently, it takes less than a minute to fill up the entire memory of an average smartphone at the highest proposed net data rates possible with IEEE 802.11ac. So, for now, it’s not so useful in smaller hand-held devices.

You want an eight-antenna AP/router. The client-side needs a minimum of a four antenna device built-in, or added onto a phablet, tablet, notebook, or other device. Expect many devices logically attached to an 802.11ac AP/router to stress the backhaul circuit. If you plan many users per AP/router, you need 10GBE backhaul, depending on the average duty cycle of transactions that constitute user demand for the available bandwidth.

Little testing has been done on the actual throughput of 802.11ac AP and routers’ ability to contend with mode-switching – which clearly is required. Support for prior Wi-Fi types is expected; support for older Wi-Fi types is mandated in the IEEE 802.11ac-2014 spec. Both 802.11g and 802.11a must be honored. Can the AP or router switch contexts and support multiple streams quickly, handing off transactions among mixed types of access methodologies? The jury is out. The jury hasn’t even been called, yet. There is no evidence, no judges, and most importantly, hardly any equipment.

The sophistication of the equipment used, on both the AP/router and client-side, will be incredibly sophisticated, as there are several 802.11ac modes to support, not counting a healthy variety of older Wi-Fi modes to support. That’s all while encrypting according to WPA-type, and in connected office infrastructure, and keeping out of the way of other AP/router networks that might interfere with each other. Debugging problems also require you to acquire new test equipment and heuristic software that can track the modes, the relationships, and the new possible combinations, and render useful results. Today, everyone's working on adaptations, and only a handful are delivering early units.

The Results

High volume data delivery needs, especially for comparative extreme demands like 4K video, extreme gaming, multiple concurrent media streams, and large event support can be supported by products meeting the new 802.11ac spec. But you need to look carefully. The AP/router, backhaul, and configurations — not to mention client device support — need to be set before you can obtain delicious fast and optimized throughput.

Don’t worry too much: You'll likely receive excellent speeds. If the AP/router doesn't have a carrier's foot on the data hose, the fastest available speeds will be attained by paying attention to configuration and good client-side 802.11ac hardware. The good news is: the new Wi-Fi spec can be plentifully fast, perhaps 6GB+ speed, with actual payloads approaching a third of that speed. You may not need to wait.

See also:

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