Data Centers

Cheat sheet: What you need to know about 802.11ac

The newest wireless networking protocol is 802.11ac, due to be ratified sometime in 2013. Michael Kassner does the research and tells you what you need to know.

[UPDATE 06-26-2013: See below for addition of transmission testing results]

Wi-Fi junkies, people addicted to streaming content, and Ethernet-cable haters are excited. There's a new Wi-Fi protocol in town, and vendors are starting to push products based on the new standard out the door. It seems like a good time to meet 802.11ac, and see what all the excitement's about.

What is 802.11ac?

802.11ac is a brand new, soon-to-be-ratified wireless networking standard under the IEEE 802.11 protocol. 802.11ac is the latest in a long line of protocols that started in 1999:

  • 802.11b provides up to 11 Mb/s per radio in the 2.4 GHz spectrum. (1999)
  • 802.11a provides up to 54 Mb/s per radio in the 5 GHz spectrum. (1999)
  • 802.11g provides up to 54 Mb/s per radio in the 2.4 GHz spectrum (2003).
  • 802.11n provides up to 600 Mb/s per radio in the 2.4 GHz and 5.0 GHz spectrum. (2009)
  • 802.11ac provides up to 1000 Mb/s (multi-station) or 500 Mb/s (single-station) in the 5.0 GHz spectrum. (2013?)

802.11ac is a significant jump in technology and data-carrying capabilities. The following slide compares specifications of the 802.11n (current protocol) specifications with the proposed specs for 802.11ac.

(Slide courtesy of Meru Networks)

What is new and improved with 802.11ac?

For those wanting to delve deeper into the inner workings of 802.11ac, this Cisco white paper should satisfy you. For those not so inclined, here's a short description of each major improvement.

Larger bandwidth channels: Bandwidth channels are part and parcel to spread-spectrum technology. Larger channel sizes are beneficial, because they increase the rate at which data passes between two devices. 802.11n supports 20 MHz and 40 MHz channels. 802.11ac supports 20 MHz channels, 40 MHz channels, 80 MHz channels, and has optional support for 160 MHz channels.

(Slide courtesy of Cisco)

More spatial streams: Spatial streaming is the magic behind MIMO technology, allowing multiple signals to be transmitted simultaneously from one device using different antennas. 802.11n can handle up to four streams where 802.11ac bumps the number up to eight streams.

(Slide courtesy of Aruba)

MU-MIMO: Multi-user MIMO allows a single 802.11ac device to transmit independent data streams to multiple different stations at the same time.

(Slide courtesy of Aruba)

Beamforming: Beamforming is now standard. Nanotechnology allows the antennas and controlling circuitry to focus the transmitted RF signal only where it is needed, unlike the omnidirectional antennas people are used to.

(Slide courtesy of Altera.)

What's to like?

It's been four years since 802.11n was ratified; best guesses have 802.11ac being ratified by the end of 2013. Anticipated improvements are: better software, better radios, better antenna technology, and better packaging.

The improvement that has everyone charged up is the monstrous increase in data throughput. Theoretically, it puts Wi-Fi on par with gigabit wired connections. Even if it doesn't, tested throughput is leaps and bounds above what 802.11b could muster back in 1999.

Another improvement that should be of interest is Multi-User MIMO. Before MU-MIMO, 802.11 radios could only talk to one client at a time. With MU-MIMO, two or more conversations can happen concurrently, reducing latency.

What do experts say about 802.11ac?

There is a lot of guessing going on as to how 802.11ac pre-ratified devices are performing. I don't like to guess, so I contacted Steve Leytus, my Wi-Fi guy who also owns Nuts about Nets, and asked him what he thought:

Regarding 802.11ac, we are testing wireless game consoles for a large company in the Seattle area. We test performance using 20, 40, and 80 MHz channels. During the tests, we stream video data and monitor the rate of packet loss in the presence of RF interference or 802.11 congestion.

802.11ac's primary advantage is support for the 80 MHz-wide channel. And without question, the wider channel can stream more data. But, as with everything, there are trade-offs.

I asked Steve what the trade-offs were:
  • I don't think you'll find 802.11ac clients as standard equipment for computers. So, you need to buy one, connect it to the computer via Ethernet, configure the client, and finally pair the client with the router/access point.
  • Unless your application requires streaming large amounts of data, you probably will not experience a noticeable improvement in performance.
  • The 80 MHz-wide channel is more susceptible to RF interference or congestion from other Wi-Fi channels by virtue of its larger width.
  • The 80 MHz channel eats up four of the available channels in the 5.0 GHz band. Some routers implement DCS (dynamic channel selection) whereby they will jump to a better channel in the presence of RF interference. But if you are using 80 MHz channels your choices for better channels are few or non-existent.

Transmission testing results

[UPDATE] Steve Leytus finally was able to break away from his testing long enough to grab screen shots of the three channel widths. I haven't seen this anywhere else, so I thought I'd pass his explanation and slides along:

The three images are of iperf transmitting from one laptop to another at 20 Mbps; both laptops are connected to the same Buffalo 802.11ac router -- one laptop is connected via Ethernet, and the other is associated wirelessly. The transmission test was repeated three times using channel widths of 20 MHz, 40 MHz, and 80 MHz.

You can clearly see how the width of the spectrum trace increases with channel width. The other thing to notice which might not be so apparent is the power level -- as the channel width increases the power level decreases.

This is expected since the transmit power has to be spread out over a wider frequency range. The implication is that as the channel width increases then the distance the signal can reach probably decreases.

20 MHz

40MHz

80 MHz

What is my concern?

First let's gets some physics out of the way (Courtesy of Attenuation of Microwave Signal and Its Impact on Communication Systems [PDF]):

  • The higher the frequency (5.0 GHz versus 2.4 GHz), the greater the bandwidth which allows more data carrying capacity.
  • Attenuation is the reduction of signal strength during transmission.
  • RF signals are attenuated exponentially over distance.
  • Attenuation is directly proportional to the frequency.

My concern rides on 802.11ac needing to use the 5.0 GHz frequency range in order to get the monster data throughput being advertised. That means -- per the physics above -- users will have to live with a significantly smaller coverage area, something those more familiar with 2.4 GHz devices will not expect.

Final thoughts

I have been checking out the forums and early reactions seem mixed. That might be indicative of the sensitivity of each user's situation and physical surroundings when considering how well 802.11ac devices perform. Other than my coverage-area concern, my only other thought: there will always be a bottleneck. And unless you are one of the fortunate connected to Google Fiber, the Internet connection will be it.

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66 comments
techrector
techrector

I have been working on some project where I need to find out distance between device and wifi router based on its strength. I know there could be scenarios like some obstruction in the way which may hamper our signal strength but first considering the best case scenario. And I also know any such kind of method to calculate such information will vary based on device type/manufacturer.

I am new in this field. So any kind of help would be appreciated. Thanks ~ 

Gar Beals
Gar Beals

If anybody has integrated  802.11AC into their home network, do ISPs (mine is Comcast) require an upgrade to their MODEM? Are there any downstream implications from the router to  devices like DirecTV''s network devices? I know that the standard hasn't had the IEEE holy water sprinkled on it yet but 80211N and it's variations were being sold prior to the Standard gaining approval so maybe there are early adopters who could speak to their experience?

don2406
don2406

We rarely need to shift large files and our internet is limited to 10Mb, but .11ac still sounds very helpful.  When 100 users are logging on and loading up their work at around the same time, the peak load is still very high.  The greater trhoughput and multi-user MIMO could help aleviate the blocking that occurs by reducing the retries which account for a lot of the traffic during these peak periods. 

CSMA always suffers loss of effective capacity as demand increases, but with many simultaneous users even a short peak load can reduce throughput so drastically that it takes a very long time to recover. 

As for 5GHz, I join the others in welcoming any reduction in signal strength with distance.  It will reduce external interference and also allow greater density of APs.  I am sceptical about the relevance of the FSPL in this context (directional antennae and multiple reflection paths), but even if the signal strength is lower, it is the signal to "noise" ratio which is important.  With less interference and lower cosmic noise, higher frequencies can work at lower signal levels.

kasb31-tr
kasb31-tr

I am trying to improve my bandwidth to help with my VoiP application which seems to be choppy lately.  It sounds like the 11ac will help but not sure.  I believe my degradation of bandwidth is due to the additional WiFi gizmos slowly entering my house (IPads, IPods, IPhones, etc). 

Question 1): Aside from upgrading my ISP, will the 11ac help my situation with allocating more (or improved) bandwidth?

Question 2): Also, most of our equipment is not 11ac ready meaning the antennae will not take advantage of the 11ac router.  Do I need to get an adapter for all laptops?

I have researched this question and have received mixed reviews.   

Vorpaladin
Vorpaladin

The only reason I am interested in having LAN data speeds this high in my home is streaming video from a NAS to my TV.  The NAS lives in the office upstairs, far from the TV; I would prefer to not run wires.  But range is a big concern; my "n" 2.4 GHz connection requires a repeater to cover the downstairs area.  Devices that are only about 50 feet from the router can't connect to it reliably due to interference from the house structure and contents.  If I would need more than 1 repeater for "ac" I would have a hard time justifying it, especially since performance is lost on every "hop".

mhammett
mhammett

FYI: The comments section doesn't work as smoothly in Chrome as it does in IE. Might want to address that. All of the speeds mentioned are the OTA (Over The Air) data rates. Real throughput is half of that. WiFi is very much a shared environment. Either one of those conditions means that 802.11ac will *NOT* be faster than gigabit Ethernet in ideal conditions In many conditions, it is likely to be barely above 100 meg Ethernet, due to poor RF conditions. Resolving the poor RF conditions will do far more towards more usable throughput than higher maximum throughput numbers. These high speeds are for enthusiasts, enterprises and service providers. Your average Joe in the home will not benefit from the increased speeds. If you were to remove the increasing modulation complexity, larger channels, etc. and just applied real, working beamforming to 802.11g, that would be sufficient for a significant number of homes. Yes, today's FIOS and Comcast connections would then require an n system to take advantage of the speeds over 25 megabit. I hope to God that the consumer routers come with a 20 MHz channel by default and not 80. Doing otherwise would just further pollute the RF environment. MU-MIMO will be great for enterprises and service providers. The latency over a Wi-Fi connection is negligible, but being able to send data to multiple clients simultaneously will be a great improvement for enterprises and service providers. It would be really nice if the APs had the intelligence to move problem clients to other, reduced chain count connections to mitigate their effect on total system performance. Frequency alone has nothing to do with bandwidth. All else equal, a 20 MHz channel at 500 MHz will pass as much data as a 20 MHz channel at 500 GHz. However, our spectrum allocation model is such that generally higher frequencies have larger amounts of spectrum allocated to them. This is due to as you go higher up in frequency, larger and larger frequency deltas are required for any noticeable change in how that frequency acts. 50 MHz and 5,050 MHz behave VERY differently. 50 MHz will go through just about any material other than Mother Earth herself (well, and bodies of water), while 5,050 MHz can't escape a concrete room or a metal shed or a tree line. 50 GHz and 55 GHz face the same penetration challenges. I believe I have commented elsewhere on here already about how the frequency to attenuation graph isn't smooth. Many things in the atmosphere affect frequencies differently. http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/rf_absor.pdf The same thing continues below 10 GHz, but it becomes less and less of a factor.

chitsamatanga
chitsamatanga

Hie, finding it difficult to print your articles!! how do you print them?

WmRobt
WmRobt

My isp connection is 65Mb [and not all that fast] and I have tested connections to specific servers which confirm that; however connecting with a google page for example takes over 3 seconds all too often. Not picking on google same goes for most other [if not all] services I connect. Of course that includes loading the page as well. But I do?t care where the time is spent. It just takes too long and I dont see a faster wifi changing that.

Slayer_
Slayer_

Cause it seems n is still a fair bit slower than normal 100mbit wired connection.

Kim SJ
Kim SJ

Having much experience of trying (and often failing) to make in-home WiFi work at 2.4GHz in the presence of devices like video repeaters, baby monitors, etc, I think there will be a big win for users with such issues. Afaiu, the "play nicely" rules are much better defined in the 5GHz band.

GrizzledGeezer
GrizzledGeezer

...that 802.11ac is a solution for problems that many users aren't likely to have. It's also possible that the great configuration flexibility possible might cause installation and deployment problems. 802.11ac appears to be more-suitable for business than consumer use. Nothing wrong with that.

thomas4442
thomas4442

I didn't get into the nuts and bolts of wifi frequency. You guys took my layman's scenario and 11ac and went in-depth. Thanks! And yes Michael, I use 2.4 and wouldn't get the area with 11ac. For the last few years I've only had to deal with home networks and home users. I graduate soon, and then will likely deviate from my simple explanations. No way I could use the terminology used here for my current clients. I look forward to advancing into the enterprise arena. Thanks again.

kfilius
kfilius

"Good, Fast, Cheap: Pick any two (you can't have all three)" (RFC 1925) I love it.

andrew232006
andrew232006

Being 5GHz only makes me wonder how 802.11ac routers will work with wireless g and n devices. Support for those devices isn't something I'm willing to give up any time soon I'm currently stuck on 20mhz because many of my devices won't work with my router set to 40mhz. So I'm guessing none of my current devices will work on 80mhz or 160mhz.

mrobbins
mrobbins

Thanks for this article. A neat summary of the key points and concerns and well worth the time spent reading it. More like this please TechRepublic.

Henry 3 Dogg
Henry 3 Dogg

"That means — per the physics above — users will have to live with a significantly smaller coverage area, something those more familiar with 2.4 GHz devices will not expect." Except that the beaming gives improved coverage range - also per the physics above. Having just replaced two 802.11n Airport Extremes with a single 802.11ac, I can tell you that the range is better.

Henry 3 Dogg
Henry 3 Dogg

"I don’t think you’ll find 802.11ac clients as standard equipment for computers." Heard of the MacBook Air?

georgeou
georgeou

The 80 MHz quad-width channels are in the 5 GHz range which has anywhere from 12 to 24 independent channels. 2.4 GHz only has 3 independent channels so you have less congestion in 5 GHz using 80 MHz wide channels than using normal 20 MHz wide channels in 2.4 GHz. As for "Attenuation is directly proportional to the frequency", that's only half the equation. The other half of the equation is that a given antenna length is effectively twice as long for 5 GHz as it is for 2.4 GHz because it covers more wavelengths. That nullifies the increased attenuation and you get more or less the same range through air or through most materials. Some materials may block one frequency more than another frequency though most materials block 5 GHz slightly more than they block 2.4 GHz. Some materials like brick or stucco can block 5 GHz substantially more than 2.4 GHz. But more effectively blocking is an asset rather than a liability In the enterprise space because it allows for denser access point deployment and higher capacity. If higher range is needed, you can always use a higher (larger) gain antenna or a directional patch antenna to optimally shape the coverage.

ok1dix
ok1dix

RF signals are attenuated with square of distance NOT exponentially. I wonder if the other informations in the article are also so reliable.

thomas4442
thomas4442

I currently have a home network with AT&T as my ISP. I have 6mb speed. I tested the speed by bouncing a 30mb file off of a server in North Carolina, I'm in S.Ga. I consistently was >upload/download>5.9/5.2. The new modem/router is a 300mb. (WiFi). I have a TPlink wireless usb adapter (150mb) on my office PC in my room. Once I have established my ISP speed, I test the wireless streaming speed like this> Go to YouTube and watch a video (Netflix too), at the bottom of the screen is the video (data) progress bar. It's RED for what's been and being watched. It moves as the video is watched. Just in front of the DOT at the beginning of the RED line is the "Grey area". This tells you how much data is stored in the cache or buffer. If the "Grey area" is staying ahead of and increasing in distance from the DOT, then the wireless>stream>buffer is fine. It was ok at 150mb but not 54mb. 802.11n is better. As for distance, I live in an apartment on the second floor. When I switched to "N" my signal strength doubled outside of my apartment. I needed this as I do PC repair and networking by contract occasionally. Now I can pull up in my parking lot at 30/35 meters or 100ft., and log onto my network in my apartment to retrieve files I may need via laptop without getting out of my car. Switching to "N" made my download speeds on wifi go from good to better, and made access from a distance go from not possible or not worth it to possible. I could remote in also, but my daughter is in college and I can leave files in a personal shared folder for her to access when I'm not home. Just goes to the parking lot! P.S. I have 7 to 10 active wifi networks I can pick up various strengths. Occasionally the wifi signal slows. This is a recent issue since my switch to AT&T Uverse. I resolve the issue by changing channels in the router. It has a "best channel" feature that doesn't work well, haven't figured out why yet!

said.fox
said.fox

The article could be regarded very good introduction about the new protocol. However, what about the covering range area that new protocol may offer to me as a home end user. Nowadays, in our houses we swim over a lake of wifi signals of our neighbours, interference and shortage of coverage inside the house may be an important concern. What I need to know, what's the max. distance, horizontally and vertically (up stares, down stares) that my ac wifi network reach?

stasys.lukaitis
stasys.lukaitis

Mimo has another unforeseen effect - that is called a microcellular effect. The transmission radii from a pre-"n" technology was even and predictable. The transmission radii for mimo devices is unpredictable and very jagged because of signal bouncing/absorption/magnification. Transmission density patterns resemble a mosaic and beamforming doesn't address it. Sticky client phenomenon still exists causing trauma when moving from one AP to another. "N" and post-"n" technologies really work well when there is a high density of APs with each using low(er) power output and configured in greenfield mode.

dennis.cb
dennis.cb

The comment regarding the Internet being the bottleneck is somewhat misplaced.. That's like giving the impression there isn't much use for Gigabit Ethernet, because the internet is still a bottleneck. Many people, including myself, transfer/stream large files and storage around to PCs/consoles/external HDDs on our private home networks. Right now, even with 802.11n, it is still painfully slow when compared directly to wired Gigabit Ethernet. Assuming you have a fairly clean/quiet radio spectrum environment where you are, this could provide pretty significant gains for short-range wireless connectivity.

Smart_Neuron
Smart_Neuron

Hi there. If you are running your own internal network and your components are matched, 802.11ac is a very nice choice for those who *need* to upgrade. Otherwise, 802.11 is quite sufficient. The external internet is the real problem, which causes a terrible bottleneck in throughput. The technology is there to overcome it - but will your ISP provide it yet at a reasonable cost? I say no! Read this link... http://news.cnet.com/8301-1023_3-57589353-93/is-cable-holding-back-superfast-broadband-adoption-on-purpose/?tag=nl.e703&s_cid=e703&ttag=e703&ftag= The industry as a whole needs to step up it's efforts to produce more bandwidth.

JCitizen
JCitizen

so yeah - I'm very interested in this article; which was exceptionally clear and well written! Thanks again for another blockbuster Michael! :) Dang! Just as I had thought I found another good UTM appliance! I might as well wait now! I want that fast client side speed! :O

stephenmj
stephenmj

My ISP provides me with a 30 Mbps download speed (more or less consistent). The most heavy light I do though WiFi is stream movies. I currently have a 802.11 n router. Even if I get a 802.11 ac router, will it help me in any way? I mean, does it help that the router has a data rate of 450 Mbps (single stream) if I "get" data at only 30 Mbps? It seems to me that even my current 802.11n is very much under-utilized. P.S.: I am a Mechanical Engineer. Very much interested in technology, but know just enough to be dangerous. So, I would surely appreciate any explanation.

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