Tuesday, April 9, 2013

First Look - 802.11ac Gigabit Wi-Fi Speed

I just couldn't wait for 802.11ac enterprise WLAN gear to be released, so I went and picked up a consumer router and USB adapter to get a first look at 802.11ac.

I picked up the ASUS RT-AC66U and corresponding ASUS USB-AC53 adapter. I decided to go this route because with pre-standard equipment we've historically seen best performance when pairing the AP and client adapters from the same manufacturer.

ASUS 802.11ac Product Lineup

The router supports 3x3:3 MIMO with 80 MHz channels and 256-QAM on the 5GHz 802.11ac capable radio. This results in a raw Wi-Fi data rate capable of 1.3 Gbps. You might want to reference this 802.11ac data rate chart.

The USB adapter on the other hand is a bit handicapped, supporting only 2x2:2 MIMO, 80 MHz channels, and 256-QAM. This results in a raw Wi-Fi data rate capable of 867 Mbps. However, actual throughput performance is further limited by it's USB 2.0 interface which has a raw bus speed of 480Mbps but is limited to somewhere around 60% of that due to USB host controller overhead. So realistically, with this USB adapter I'm going to max out around 288 Mbps of actual throughput. Additionally, it's increasingly hard to pack a 3x3:3 MIMO antenna system into an external USB adapter due to physical size constraints. This is what we've seen with external 802.11n adapters for the most part, and that has continued to be the case with most first-generation external 802.11ac client adapters. We should see more spatial stream support on internal Wi-Fi adapters where the antenna can be integrated into the laptop case in order to create sufficient physical separation.

I loaded the adapter driver and utility into a Windows 7 laptop and it reported the raw speed as 866.5 Mbps, which is equivalent to the adapter's maximum raw Wi-Fi speed based on its specifications.

Windows Connection Details Reported an 866.5 Mbps Speed

Peak Performance
I decided to initially perform a simple file transfer using SMB. To accomplish this, I hooked one laptop to the wired Gigabit Ethernet LAN port on the router as the server and connected the second laptop to the 5 GHz Wi-Fi radio as the client. I pulled a 1.38GB file down from the server to the client over the wireless link. I performed this test over 10 times for reproducibility. The router was configured for 5 GHZ operation with an 80 MHz channel and a primary channel of 48.

File size: 1.38GB / 1,490,209,655 Bytes / 11,921,677,240 bits
Transfer time: 51.0 seconds (avg.)
Application throughput: 233.76 Mbps

Note - remember that this is application layer throughput, which does not include SMB, TCP, IP, or MAC layer overhead.

Next, I performed an iPerf TCP throughput transfer for 60 seconds, modifying the TCP window size to 1024KB. The test was performed ten times, with the average result clocking in at 204 Mbps.

iperf -f m -i 1 -w 1024K -c -t 60

[ ID] Interval       Transfer     Bandwidth
[156]  0.0-60.0 sec  1482 MBytes   204 Mbits/sec

Overall, I was fairly pleased with this result. Although it is nowhere near the Gigabit speeds that 802.11ac is capable of achieving, this is to be expected given the handicapped USB 2.0 adapter that I am using. Given a raw data rate of 867 Mbps peak, I would expect to see throughput around 520 Mbps without the USB 2.0 limitation (or roughly 60% of the peak data rate).

I used MetaGeek's Chanalyzer Pro and WiSpy DBx to record the 80 MHz file transfers. I configured the router to use an 80 MHz channel width, with a primary channel of 48 in the UNII-1 band. The spectrum analysis workstation was located within 5 feet of the router.

Spectrum Analysis of an 802.11ac 80 MHz Channel
You can clearly see FFT waveform across the entire UNII-1 band due to the automatic extension of the primary 20 MHz channel up to the maximum 80 MHz channel width that was configured. As a recap of how the primary and extension channels work, you might want to review my previous post on 802.11ac Channel Planning.

Performance Comparison versus 802.11n
To assess how well the 2 spatial stream 802.11ac client performed, I decided to benchmark it against similarly capable 2SS 802.11n clients. To make the test apples-to-apples, I also turned down the channel width on the ASUS router to 40 MHz, since that is the largest channel width the 802.11n clients support.

I ran the same SMB file transfer test as described previously. The SMB file transfer was run three times for each client and I averaged the results. Each client was placed in the same physical location, approximately 10 feet from the router to assess peak performance.

40 MHz throughput comparison against two different 2x2:2 802.11n clients:

Wi-Fi AdapterWi-Fi CapabilitiesMax Wi-Fi Data Rate at 40 MHzSMB File Transfer TimeSMB Throughput
MacBook Air Airport (Internal)802.11n, 2x2:2 MIMO300 Mbps1:36.7 sec123.29 Mbps
Intel 4965ABGN (Internal)802.11n, 2x2:2 MIMO300 Mbps1:15.5 sec157.90 Mbps
Asus USB-AC53802.11ac, 2x2:2 MIMO400 Mbps
(limited further due to USB 2.0 bus speed)
1:07.0 sec177.94 Mbps

Clearly, the peak performance test shows that the 802.11ac client has an edge due to the higher data rates provided at the top-end with 256-QAM modulation.

Rate over Range versus 802.11n
The aggressive 256-QAM modulation may provide higher peak throughput when a client is physically very close to the AP. But will that advantage hold up over larger distances? There has been significant discussion in the industry about the real-world usefulness of 256-QAM, especially at typical client distances of 10-20 feet or greater from an AP. Will clients realistically be able to use such aggressive modulation in practice?

However, the question about the use of higher modulation is not the only one. Newer wireless chipsets should also benefit from better manufacturing processes that improve 802.11ac client receive sensitivity, translating into the use of higher data rates at at any given distance when compared to older 802.11n clients. Put another way, does 802.11ac exhibit better rate-over-range compared to 802.11n?

For the rate-over-range testing, I ran the same iPerf TCP throughput test as described previously, using a 40 MHz channel width at varying distances from the router. The tests were performed in a residential house since that is the only space that I have available at the moment.

- Point #1: 10 feet from the router, 1 wood panel wall in-between
- Point #2: 25 feet from the router, 1 wood panel wall in-between
- Point #3: 30 feet from the router, 1 wood floor and 1 drywall in-between
- Point #4: 40 feet from the router, 2 wood floors and 1 wood panel wall in-between

Additionally, in parenthesis I provide a rough signal strength and data rate used during the tests as reported by the client supplicant/driver. I also provided the test results for the 802.11ac client using an 80 MHz channel width for reference.

LocationMacbook Air 
(40 MHz)
Intel 4965ABGN 
(40 MHz)
(40 MHz)
(80 MHz)
Point 1154 Mbps
(-50 dBm, 300 Mbps)
165 Mbps
(-50 dBm, 300 Mbps)
204 Mbps 
(-40 dBm, 400 Mbps)
204 Mbps 
(-40 dBm, 867 Mbps)
Point 2144 Mbps
(-60 dBm, 216 Mbps)
150 Mbps
(-60 dBm, 270 Mbps)
180 Mbps 
(-52 dBm, 400 and 324 Mbps)
202 Mbps 
(-54 dBm, 702 and 585 Mbps)
Point 3112 Mbps
(-65 dBm, 162 Mbps)
102 Mbps
(-70 dBm, 180 Mbps)
144 Mbps 
(-54 dBm, 243 Mbps)
201 Mbps 
(-60 dBm, 526 Mbps)
Point 435 Mbps
(-80 dBm, 54 Mbps)
61 Mbps
(-80 dBm, 120 Mbps)
119 Mbps 
(-65 dBm, 216 Mbps)
190 Mbps 
(-70 dBm, 468 Mbps)

The 802.11ac client performance beats both 802.11n clients in all tests at all locations. Additionally, the performance gap widens significantly at Point #4, the farthest distance and weakest signal from the router. Clearly, 802.11ac provides significant rate-over-range improvements over 802.11n.

Performance improvement at each location:
- Point #1: 32.5% (vs MBA), 23.6% (vs Intel)
- Point #2: 25.0% (vs MBA), 20.0% (vs Intel)
- Point #3: 28.6% (vs MBA), 41.2% (vs Intel)
- Point #4: 240% (vs MBA), 95.1% (vs Intel)

The peak performance improvement at Point #1 (32.5%, 23.6%) is squarely in-line with 802.11ac's 33% theoretical improvement over 802.11n due to the higher modulation rate of 256-QAM (400 Mbps) versus 64-QAM (300 Mbps).

The receive sensitivity of the 802.11ac client is also better than the 802.11n clients. At most test locations the 11ac adapter exhibited an 8-15 dB signal advantage over the older 11n adapters. This highlights the fact that newer wireless chipsets offer improved hardware quality over older chipsets. Receive sensitivity also appears to be better for the same 802.11ac adapter when smaller channel widths are used. This highlights the fact that as channel width increases, clients will need to maintain a slightly better signal strength to maintain the same modulation rate. In practice, this will mean there is a slight trade-off with decreased modulation rate when increasing channel width, while maintaining all other variables constant (such as transmit power, antenna gain, etc).

To answer the questions surrounding the use of 256-QAM at distances greater than 10-20 feet, I've found that the usable distance and signal strength required to use 256-QAM data rates is around 25-30 feet (in my case with one light wall in-between) and around -52 dBm signal strength. I note multiple data rates being used for the 802.11ac client at Point #2 because the client appeared to be data rate shifting during the test, likely unable to sustain 256-QAM modulation at times and shifting to a lower rate. These values are almost certain to vary between client adapters based on receive sensitivity, but this should provide a rough estimate for WLAN administrators.

Results Recap

Let's add up the 802.11ac test results:
  1. Decent peak performance at 80 MHz channel width, although it we should see double this performance with integrated adapters or USB 3.0 external adapters.
  2. Better peak performance than 802.11n at comparable 40 MHz channel width due to the use of more aggressive 256-QAM at relatively close distances to the AP.
  3. Better rate-over-range performance than 802.11n, especially as distance from the AP increases and signal level deteriorates.

Final Thoughts
It was great to get a first-look at 802.11ac equipment, even though the currently available client adapters are a bit disappointing from a peak performance standpoint due to their reliance on USB 2.0 bus speed. You might consider waiting for integrated 802.11ac client adapters or external USB 3.0 adapters to hit the market, which should be capable of supporting the full throughput that 802.11ac offers. A few are already out there; I found this 802.11ac hardware wiki that seems to be keeping track of consumer equipment.

Even though you might not see awe-inspiring peak performance for any single client with this early release equipment, 802.11ac still stands to improve the aggregate performance and capacity of the network through more efficient use of airtime. WLAN administrators should expect to see this aggregate increase in network capacity even with 802.11ac capable mobile devices such as tablets and smartphones. Since they will be using higher Wi-Fi data rates, they will be getting on and off the air quicker for a given application throughput level than they would by using 802.11a/g/n. This will translate into the ability to support more clients or higher throughput per-client, and will be a big boost for enterprise WLAN capacity!


Read the Entire 802.11ac Gigabit Wi-Fi Series:

Tuesday, April 2, 2013

High-Density Wi-Fi Design Part 3 - WLAN Configuration Best Practices

In this video, I explain the best practices for configuring a Wi-Fi network for high-density environments. These include:
  • Proper encryption required to use 802.11n high throughput data rates
  • Proper use of Quality of Service (QoS) through Wi-Fi Multimedia (WMM)
  • Disabling lower data rates to maintain high performance
  • Prioritizing key business applications over recreational applications
  • Client rate-limiting to prevent "greedy" clients from hogging bandwidth
  • The important role that bi-directional band steering plays in optimizing spectral use
  • Load balancing clients based on airtime utilization on different channels to serve users where the most capacity exists
  • Using airtime fairness to adequately handle a mixed-client environment
  • Proper consideration of wired network resources, including switch port bandwidth, power over Ethernet, and Internet/WAN bandwidth
  • Appropriately sizing IP subnets to account for device density and user mobility

These principles are covered in more depth in the Aerohive High-Density Wi-Fi Design and Configuration Guide.

Read the Entire High-Density Wi-Fi Design Series:
Design Your WLAN for High Capacity
Video Blog: High-Density Wi-Fi Design Part 1 - Forecasting AP Capacity
Video Blog: High-Density Wi-Fi Design Part 2 - RF Planning
Video Blog: High-Density Wi-Fi Design Part 3 - WLAN Configuration Best Practices


Monday, April 1, 2013

¡Viva la Revolución! Three Years of Revolution Wi-Fi

Three years ago today I started the Revolution Wi-Fi blog as a way to aid my Cisco CCIE Wireless studies. What started out as a location to store and share my notes as I strived to achieve those prestigious "digits" quickly turned into a platform that allowed me to voice my opinions on the state of the industry and to help educate others seeking to know the mysterious ways of WiFi. Now here I am, 212 posts later!

Finding My Style
My writing over time has changed quite a bit. Early on my posts were strictly technical, in a "just-the-facts" type of way. I wasn't accustomed to putting my own analysis and opinions down on paper. Being an engineer meant sticking to the technology allowed me to stay in my comfort zone while trying out this whole blogging thing. This was also quite easy to do since my wireless studies back in 2010 has progressed beyond learning the basic RF foundations (thank you CWNP) and I became entrenched in Cisco-world. Therefore, the early posts focused on the ever-present "Cisco Way" of implementing wireless networks: learning their features, how to configure Cisco networks, and how controllers and APs operated in tandem.

However, as I became more comfortable with blogging, I definitely learned to dive a bit deeper beyond the 0's and 1's to provide a well-reasoned opinion and analysis. I also became more comfortable in my knowledge by interacting with other professionals on social media (especially Twitter) and realizing that the world was woefully short of great Wi-Fi engineers (relative to demand) and needed those with experience and expertise to share their knowledge with others and help grow our ranks. Some of my posts have been controversial, some have touched a nerve (especially with vendors), but mainly I've received overwhelmingly positive feedback on my analysis. Many of my posts have also spurred great conversations that allow me to see alternate perspectives on topics and re-examine my own analysis. That is perhaps the biggest personal benefit I have found through blogging, the ability to deepen my own understanding by interacting with others.

Finally, I've found that I like writing about many complex topics through a series of posts. In the article archives section you'll find series on wireless QoS, fast roaming, high-density networks, 802.11ac Gigabit Wi-Fi, industry analysis, and vendor-specific products. Let's face it, Wi-Fi is a complex subject and requires integration with other equally complex technologies (*ahem* EAP). Designing and deploying wireless networks aren't for the timid; it requires good organization, a focus on planning, thoroughness of execution, and significant attention to detail. I find such complex topics to be best examined with a matching level of detail, broken down into digestible chunks, which lends nicely to writing multi-part articles.

What I've Learned
First, I found early on it was extremely important to establish guiding principles with which I would blog. Those include: 1) to be as objective as possible, 2) to provide relevant and timely content to readers researching often sparsely documented topics, and 3) to help educate others engineers that aspire to be Wi-Fi experts. Without these principles as a blogger, I might as well get paid for my writing as an analyst or vendor-shill. This does not mean that I am unbiased, I'm not. No one is in my estimation. But I strive to take an objective eye, ensure that I'm well-informed, consider alternate perspectives, and provide an honest opinion that I believe is accurate. It's important to understand that the blog post does not end when I hit the publish button. Rather, it only begins. I've placed my knowledge and opinion out there for the world to read and react to. The dialogue after a post has been published is where the topic grows legs, spurs conversations, and allows those participating to grow better at our craft through dialogue with others.

Second, despite working in a digital world, not everything is black and white, 0 or 1. Analysis matters! Where vendor materials pronounce great capabilities but gloss over the important details, independent bloggers pick up the slack and dive-in to separate the oil from the water, the marketing FUD from the real-world benefits.

Third, your employer will have hesitation about you blogging! This can take a variety of shapes, but in general I've found that your employer will be cautious about one of their employees taking such an active role in social media. This can include fear about divulgence of sensitive information, potential impact to brand image (if a public company) or to vendor and partner relationships, and HR related concerns about the opinions you express reflecting the company. Be sure to set clear expectations and guidelines with your employer when you begin blogging, and be prepared to re-visit these topics periodically with management.

Blog Statistics
Over the course of the past 3 years, I've received a total of 904,000+ page views! Wow! Just wow! I'm astonished at how many people visit my little corner of the web. I'm even more amazed at this considering two things: the Wi-Fi engineering world is incredibly small (but is growing daily), and my writing is extremely niche - focusing typically on deep technical subject-matter that not many engineers would even need to read.

My readership has grown over time and my blog receives approximately 2,500 views/day (weekdays) 1,500 views/day (weekends), and 55,000 views/month.

Monthly Readership

It also helps when influential industry websites and experts pick up your content and link to it. That big noticeable spike in August 2012 directly correlates to my post on the Defcon cracking of MS-CHAPv2 being picked up in the comments on one of Bruce Schneier's posts (yes, just mentioned in the comments)!

Most Popular Posts:

Article Title Date Published Total Page Views Avg. Page Views / Month
Wake on Wireless LAN Nov. 8, 2010 65,446 2,256/mo
Apple iPad 3 Wi-Fi Specifications Mar. 8, 2012 34,690 2,668/mo
Is WPA2 Security Broken Due to Defcon MS-CHAPv2 Cracking? July 31, 2012 32,973 4,121/mo
Mac OS X Lion Creating Wi-Fi 802.1X Profiles Feb. 7, 2012 26,257 1,875/mo
Wi-Fi Roaming Analysis Part 2 - Roaming Variations Feb. 2, 2012 7,233 517/mo

Several of my most popular posts are from the past year. Hopefully this means that my content is increasingly touching on the most relevant subjects in the industry and resonating with readers!

Opening Doors
The great thing about blogging is the opportunity it has afforded me in my professional career. I've found that people value independent analysis and that translates into establishing a solid reputation in the industry. I can't count how many times I've been fortunate enough to run into one of my readers who has thanked me for the information that I share through this blog.

Before starting this blog, I thought like many others, that Wi-Fi professionals are too few and far between and that I was alone in my quest for knowledge. Although the group is still comparatively small to route/switch/data center professionals, I've found that other great Wi-Fi engineers do exist. And I've been able to meet many of them through the opportunities presented by blogging and interacting on social media. I've been invited to participate in multiple industry events such as Wireless Field Day and Interop, which are always a pleasure.

Blogging has also opened doors to new jobs, mainly by establishing a reputation as a solid networking professional. A great blog is a digital portfolio you can use to highlight your work, often replacing your resume/CV completely. The best opportunities come through those individuals you meet on the path of enlightenment, which is really what a great blog does - informs your readers and yourself!

What's Next
I've recently started experimenting with vlogging through the high-density Wi-Fi design series. It's my first real attempt at using video to explain concepts and share information. But I'm still not sure if it's right for me; it feels awkward being in front of a camera.

I'll continue to write, for sure, and hope to post articles more frequently. However, that is a struggle with my the amount of travel I'm currently engaged in, and my approach to learning is still very much focused on knowing the subject-matter in-depth. That tends to lead to a very similar approach to writing in depth, which takes significant time and effort to research, lab, and organize my thoughts on a subject.

Final Thoughts
What a ride it's been these last 3 years writing this blog. What started out as a personal journey to acquire my CCIE digits (which I did by the way) turned into a place that I could share my experience and knowledge with world and interact with others equally passionate about Wi-Fi as I am. I've learned a great deal and become a better engineer through the conversations my articles have prompted. I've met many of my readers and received great feedback, giving me the motivation to continue writing. I've met other Wi-Fi professionals and been able to network in the community in ways I never imagined when I started.

I'd like to thank all of my readers, new and old, for having the desire to learn, being passionate about wireless and networking technologies, questioning and challenging my opinions at times, and helping me become a better engineer through the process.

¡Viva la Revolución!