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Gigabit Wi-Fi: 802.11ac is here: Five things you need to know

Gigabit Wi-Fi, 802.11ac is not really going to give you gigabit speeds - and there are other factors you need to consider before adding it to your wireless network.
Written by Steven Vaughan-Nichols, Senior Contributing Editor

Gigabit Wi-Fi, 802.11ac, is officially here, but what does that really mean? Here's my list of the five things you need to know before you invest in this new wireless technology.

1) 802.11ac is not going to give you a Gigabit of throughput

True, 802.11ac access points working with 802.11ac devices will give you faster data transmission feeds than 802.11n. The Wi-Fi Alliance claims that Wi-Fi Certified 802.11ac can deliver data rates up to more than double those of a typical 802.11n network. Practically speaking the Alliance claims that "this means a network can support simultaneously streaming multiple HD-quality videos to multiple devices."


Fair enough, but in practice you're not likely to see an 802.11ac reach its theoretical maximum of 1.3 Gigabit per second (Gbps). That's because the conditions you need to reach that speed requires a laboratory not your office.

To reach the highest speeds you need three data-streams, each of which can run up to 433 Megabits per second (Mbps). A typical 802.11ac access point can support up to eight data streams. Client devices must only support one.

For example, the Samsung Galaxy S4 supports 802.11ac with the Broadcom BCM4335 Wi-Fi chipset. This chipset only supports a single stream so, even in the best of all possible worlds, you'll only see 433Mbps.

The "unofficial" 802.11ac devices that have been shipping for the last few months, and the first generation of the standard 802.11ac devices aren't likely to hit these speeds even on a testbed. The fastest speeds here in CNeET/ZDNet land we've seen to date came from the NetGear R6300 WiFi Router, which hit a high of 331Mbps.

That's great, but it's not gigabit great. It is, however, a lot faster than you'll see then with any combination of 802.11n gear.

2) Working out the range

802.11ac only supports the 5GHz frequency. The good news about that is that there's far more room in that frequency spread than there is in the over-used 2.4GHz . The bad news is that a 5GHz signal has less range.

At the same time, 802.11ac has another feature, beam-forming, that gets around the general 5Ghz range problem. For the Wi-Fi access point in your office today, the signal is omni-directional--it forms a communications sphere around the device. With 802.11ac the signal is broadcast directly from the access point (AP) to a specific device and back again.

While no one seems to have published much on what this means, I expect it means that if you're in an environment with few 802.11ac devices, say eight, you'll actually see excellent range. But, if you're in at a convention center with hundreds of 802.11ac devices I suspect you'll need to be much closer to an AP to get a signal. That said, life is always miserable for Wi-Fi users in hotels and large meetings rooms.

3) Backwards Compatibility

All 802.11ac devices will support older Wi-Fi technologies such as your 802.11n-equipped laptop or even your old 802.11g network bridge. 802.11ac can't do magic though. For example, if you buy an 802.11ac AP you'll still be limited to your older devices' maximum speeds.

Soon, there will be a lot of new gear that supports 802.11ac as clients. If you buy an 802.11ac AP now you're really buying for future use. It's not going to do you much good today.

As always you should remember that any network is only as fast as its slowest link. For instance, if you're buying 802.11ac to improve your Netflix viewing experience and your Internet connect is 10Mbps, it won't do you a darn bit of good. 802.11n, or even 802.11g, is all you'll need.

4) AP Channel Conflict Ahoy

Anyone who does any Wi-Fi network management knows that the 2.4GHz range is as crowded as a Best Buy store on Black Friday morning. In theory, you can use up to 14 channels. In practice, to avoid interference, you can only use three or four channels. If you have conflicting channels, you'll see your network performance go down the toilet. The advantage of 802.11a and 802.11n's 5Ghz range is that was so much room that you didn't need to worry about interference. Get worried again.

One of the big ways that 802.11ac gains its speed is by using 80MHz wide channels. In 802.11ac wave two devices--the next generation of 802.11ac, which will start showing up in 2014--the channels will take up 160MHz of frequency. What that means exactly depends on your country, since there are a wide variety of rules on how the 5GHz range can be used. But, in the United States that means 802.11ac will have at most five available channel selections. When 802.11ac second-wave appears it will go down to one or two.

The 5GHz frequency range is messy, and using it is only going to get a lot messier as 802.11ac continues to evolve. (Credit: Cisco)

In other words, network administrators should start working out now where they'll be placing 802.11ac APs, because once more you'll need to be wary of fouling up performance because of AP interference. And, let's not talk about that business on the floor below you that's always munging up your network.

5) 802.11ac requires additional infrastructure

I know, you thought 802.11ac would let you get rid of some of your Gigabit wiring. Nope. Not going to happen. First, as I already explained you're not really going to get Gigabit speeds out of 802.11ac.

Second, and what many people don't know, is that second-wave 802.11ac APs will require two, not one, Gigabit Ethernet ports. That just doubled your need for switch ports and cable runs. Oh boy!

Sure, you can get by with one port for now, but remember you're not really going to have that many 802.11ac clients in 2013. Next year is when they'll start showing up in large numbers and that's when the second wave 802.11ac APs will be appearing.

So, you can forget about doing a drop and replace for your existing 802.11g/n network APs. You won't be able to do it. Look on the bright side: Even with the next generation of 802.11ac you probably won't need to back them up with 10Gbps up-links.

What all this means is that Gigabit Wi-Fi isn't really here. Faster Wi-Fi is but it's not really going to take off until 2014 and when it does come deploying it is going to be expensive. I foresee all of us using 802.11n Wi-Fi for years still to come. 802.11ac is not going to roll out quickly.

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