Deploying, Testing, and Tuning 802.11ac
By now you’ve probably heard quite a bit about the newest generation of Wi-Fi, 802.11ac. I’ll save you the gory details, just know it’s about 3x faster than 802.11n and will help to improve the capacity of your network. Jameson Blandford and I were recently guests on the No Strings Attached Show podcast with Blake Krone and Samuel Clements (Click to listen to the podcast).
I wanted to follow up the podcast with a blog to go over considerations for deploying, testing, and tuning 802.11ac.
Considerations for deploying 802.11ac
The first question you’ll want to ask yourself, is, if your switching infrastructure can handle 11ac? The answer probably is, yes. The things to consider are the port speed and power-over-Ethernet (PoE) capabilities. You’ll want the access point to have a gigabit uplink to the switch. Each 11ac access point could potentially dump several hundred megabits per second of traffic onto your wired network. It’s also not a bad idea to have 10 Gig uplinks on your access switches to distribution or your core. If you have even just a couple access points on a single access switch, you may quickly find yourself wishing you had 10 Gig uplinks.
Next you’ll need to consider how you will power the access points. If you are like the majority of our customers, you will use PoE from your switches. While 11ac access points require 802.3at (PoE+) for full functionality, the Aironet 3700 will run happily on standard 802.3af PoE. In fact, it remains 3 spatial-streams on both radios, so performance does not suffer because you have a PoE infrastructure.
Will you deploy 80 MHz channels?
If you deployed an 11n network, you probably wrestled with if you should stick to the 20 MHz channels you knew, or move to 40. Now with 11ac, you have the option of 80 MHz channels. Well, which should you deploy? The answer is, it depends. That’s not helpful, I know. 80 MHz channels means you have fewer non-overlapping channels; four to be exact. Whereas with 20 MHz channels, there are 21 non overlapping channels. So if you have a super dense deployment where one AP can hear several other AP’s, you may want to stick to 20 or 40 MHz channels. However, if you have a medium density network, where one AP doesn’t hear too many other AP’s, by all means, take the leap, and harness the full potential of 11ac by deploying 80 MHz channels.
Another consideration for the channel bandwidth you select, is the viability of using UNII-2 and UNII-2 extended channels on your network, the so-called DFS channels. Using DFS channels is almost a necessity for 80 MHz channels. Without DFS channels, there are only two 80 MHz channels.
Don’t feel bad if you decide not to deploy 80 MHz wide channels. You’ll still see a benefit over 802.11n. Besides increased channel bandwidth in 11ac, there’s also increased modulation. That is, more bits are able to get on the air at once. So if you deploy 20 MHz 11ac, you’ll still see a 30% advantage over 20 MHz 11n.
How does 11ac impact your RF Design?
Cisco’s 11ac offerings have a very similar coverage area to the previous generation of 11n AP’s, such as the 1142, 3502 or 2602. So if you designed your network for 5 GHz last time around, don’t fret, you can do a 1:1 swap. In the same token, while you are replacing access points, it never hurts to revisit your capacity requirements. If you’re coming from a legacy network surveyed for 2.4GHz only, it’s probably a good idea recalculate the capacity requirements of your network and to do a proper site survey for 5GHz.
Say you’ve upgraded your network to 802.11ac, or are considering upgrading; how do you go about evaluating it? Well, you’ll obviously want to look at the performance of the AP. In this case, performance refers to raw throughput as well as enterprise grade features. It’s like when you buy a new car, yea you want to see what it can do, but you also want some safety features and maybe other things too, like power locks and Bluetooth. With an access point, yea you want to see how fast it can go, but other features on the access point are important too.
For throughput testing, single client will show you the biggest number, that’s the wow factor of 11ac, but how many times do you have just one client on your network? You really want to take a look at multi-client throughput. While multi-client is more effort, it’s a more realistic test case than single client.
For throughput testing, I’m a fan of using Iperf (Free) and IXIA IxChariot (Paid) for generating traffic. You could also use file transfers or video streaming to put load on the network.
As I mentioned before, there’s more to consider when evaluating an 11ac access point than just throughput. What about the rest of the features you came to know and love on your 11n AP? Features such as Interference detection/mitigation, spectrum intelligence and rogue detection/mitigation. These are just as important to test.
At the end of the day, evaluate 11ac in a way that most closely mimics your use case.
Your 11ac network is deployed, how can you go about tuning it?
There’s a myriad of tools out there for tuning/troubleshooting a Wi-Fi network, not all of them have been updated for 802.11ac, but many have.
If I suspect a layer 1 issue, the first place I’ll check is CleanAir. I want to verify there’s no interference on channel. The controller and Cisco Prime Infrastructure are great at identifying interferers and giving a channel quality metric. Sometimes I want to drill down further, so I’ll launch Spectrum Expert or Metageek’s Chanalyzer Pro with CleanAir to take a look at the raw spectrum data directly from the AP.
I would be remiss if I did not talk about sniffing 802.11ac. Existing 11n sniffers will be able to sniff 802.11 management frames on an 11ac network, but that’s about it. As you would expect, you’ll need a new 11ac capable sniffer to sniff 11ac. The good new is, two of the most popular packet capture tools have been updated to support 802.11ac; Wireshark and WildPackets’ OmniPeek. The bad news is finding something that will actually sniff 11ac. These are the options currently.
- Linksys AE6000 with OmniPeek. Wildpackets has a special driver for this little adapter. The adapter is only 1ss and is USB 2.0. So it will not sniff everything.
- Apple MacBook. The Recent MacBook Air (with 2 spatial streams) and MacBook Pro (with 3 spatial streams) can both be used to sniff 11ac with Wireshark.
- 11ac AP in sniffer mode. The 3700 can be placed into sniffer mode and forward the OTA frames to Wireshark or Omnipeek.
From a network wide tuning perspective, Cisco Prime Infrastructure (PI) is able to provide a tremendous amount of insight. I’m a big fan of the RRM Page in PI, it will tell you which AP’s are changing channel and why. This is a great place to look for instability in your network. I’m also a fan of going to the maps in PI. There’s a tremendous amount of information to be gleaned from the maps. For example, from both a coverage and capacity perspective, it can be useful to see how many neighbors a particular AP can hear.