Thursday, April 28, 2016

Commercial Grade Wi-Fi Snobbery

There is a snobbery in the Wi-Fi industry, where the large enterprise competitors paint competitors with a broad brush of being unsuitable for anything beyond consumer applications.  I encounter it frequently within the Wi-Fi community at conferences and on Twitter, as well as from current and potential customers.   It is an ugly attitude and a disparaging and discriminatory marketing practice.

Image Source:

For those of you who don't already know, I currently work as the Manager of the Field Application Engineering group at EnGenius Technologies, Inc.  One of our installer customers came to us today indicating that he is thinking of going with a more expensive competitor for a mid-market chain hotel location, because the hotel is demanding that they use "commercial grade" Wi-fi equipment.  Unfortunately, this hotel customer has bought into marketing hype and Wi-Fi snobbery, and will probably pay more money for a needlessly complex solution, rather than understanding the actual requirements and constraints and picking the right solution at the best price.

The term commercial grade is a distinction between access point designed for the consumer home markets and equipment designed for the enterprise market.  Alas, there is no standard definition of commercial grade, and thus the term has devolved into a widely abused marketing mantra.

Equipment designed for the enterprise generally has significantly more features that are tuned to the needs and requirements of enterprise deployments, such as the following:
  • VLANs
  • Multiple SSIDs
  • Band steering
  • View connected clients and collect usage statistics
  • Detection of external (i.e. rogue) access points
  • WPA2 Enterprise security
  • Use of 5 GHz DFS channels (channels 52-64 and 100-140)
  • Centralized management

Because my company manufactures and sells equipment for both the consumer market (i.e.. ESR series) and the enterprise market (i.e. Neutron and Electron series) with the same brand name, there is unfortunately confusion in the marketplace as to the positioning of our brand. Our competitors, naturally, pounce to take advantage of and further enhance this confusion in their marketing campaigns, in a brazen attempt to convince prospective customers that our equipment is not suitable for their applications.  The fact, however, is that the EnGenius Electron and Neutron equipment is designed specifically for the needs of the small-to-medium business (SMB) market, and deployed successfully in several thousands of such enterprise locations, including many hotel locations within the same chain as the one in question here. 

AP vendors tend to each gravitate to particular market niches, for which they are most suitable.  This is a natural process of market differentiation, and is true in most industries. EnGenius is focused on the SMB enterprise market, and thus has a product that is targeted to be reliable, simple, as well as comparatively inexpensive.  We are not necessarily well suited to applications in other niche markets, such as Wi-Fi in stadiums and arenas. Accordingly, there are, and will always be, certain product features that some of competitors offer that we do not. 

Thus, the selection of the AP vendor should come down to your requirements:   If your project needs particular features that a competitor offers and we do not, then by all means you should go with that competitor!  However, if you don’t need such features, then selecting our competitor means you are going to pay a premium price for unused features, additional complexity, and marketing hype.

This blog post is intended as a rant against the term commercial grade and not as a marketing piece.  However, if you've read this far and are interested to see if EnGenius is a suitable and less expensive alternative for your application, based on your requirements and constraints, feel free to browse the website and/or contact me directly. 

Saturday, April 16, 2016

Channel Bonding in Wi-Fi

Note, this blog was written for and appeared as a three-part series in Network Computing in January and February, 2016:

Channel Bonding In WiFi: Radio Frequency Physics

(Appeared in Network Computing on 1/11/2016)

Using larger channels improves WLAN capacity, but the laws of RF physics can pose challenges when putting channel bonding into practice.
In the WiFi industry, we are on a never-ending quest always to push more and more data to more and more devices. A seemingly great mechanism for this ischannel bonding, where neighboring 20 MHz channels are bonded together to form a larger channel. By doubling the channel width, you get slightly more than double the data capacity of the transmission.
Alas, however, as with all throughput enhancement techniques, channel bonding comes with a price. Implementing channel bonding in ever-increasingly complex WiFi networks is a careful balance of tradeoffs that can make it difficult for even experienced WiFi professionals to properly understand. The natural inclination is to make the channels as large as possible, and most access point vendors make it very easy to do this on their equipment.
However, what generally is not provided is guidance as to where and how larger channels should, and should not, be used. As a result, many modern WiFi deployments are problematic, because their environments cannot properly handle the use of larger channels. 
In a series of blogs, I'll discuss the various tradeoffs involved in channel bonding, cover the regulatory restrictions, and provide guidance on where it should be used in WiFi deployments. In this first part, I'll discuss the immutable laws of radio frequency physics.
In radio communications, a receiver that hears multiple signals at the same time on the same (or overlapping) frequencies cannot distinguish between them. When this happens in WiFi, this is referred to as a collision. The multiple transmitters are causing co-channel interference (or adjacent-channel interference in the case of overlapping channels). The transmitted frame is corrupted, because the receiver cannot distinguish the intended frame from other signals on the same frequency.
In the WiFi protocol, a receiver sends an ACK to acknowledge proper receipt of the transmitted frame. If the transmitter does not receive the ACK, then it must assume a collision occurred and resend the same frame again (and again, and again) until the transmitter receives the acknowledgement. If a transmitter has to repeat the same frames over and over again, it diminishes the overall effective capacity of the channel.
When people complain about WiFi performance, it's a safe bet that quite a lot of collisions are occurring.
To provide contiguous coverage throughout a facility, some coverage overlap between neighboring access points is necessary. This can, however, createself-interference, where the APs within the same network cause co-channel interference and result in collisions for client devices in these overlap zones. To avoid self-interference, WiFi engineers can apply a process calledchannelization, which involves setting independent channels on neighboring access points and carefully controlling their individual transmission output powers so that their signals do not interfere with each other in these overlap areas.
 (Image: Pobytov/iStockphoto)
The ease or difficulty of channelization depends on the number of independent channels available. Since the size of the usable frequency band for WiFi per regulatory domain (i.e. country) is fixed, mathematics dictates that when the size of each independent channel is doubled, the number of available independent channels is halved, rounded down. Thus, as channel sizes get larger, channelization gets harder.
Larger channels also result in an increased noise floor, defined as the minimum threshold level below which a receiver cannot distinguish a signal from the background noise. There is naturally occurring background energy called thermal noise, as every object in the universe gives off very low levels of energy that are a function of temperature and bandwidth. For 20 MHz WiFi channels, this floor is approximately -101 dBm.
However, as channel sizes are doubled in size, the level of background energy also doubles (i.e. rises by 3 dB), increasing the noise floor to -98 dBm for 40 MHz channels, -95 dBm for 80 MHz channels, and -92 dBm for 160 MHz channels. Since the achievable data rate between two radios is a function of the signal-to-noise ratio (SNR) at the receiver, a higher noise floor results in lower effective maximum transmission speeds.
Most client devices, especially smartphones and tablets, have much weaker transmitters than the access points. Accordingly, a WiFi network really must be designed to maximize the signal strength of client devices, as received at the access point. The only practical way to increase SNR, therefore, is to minimize the distance and obstacles between the access point and the client devices. This, in conjunction with the growing need to support more and more client devices on the WiFi network, leads to deploying more access points to cover a given area.
Unfortunately, adding more access points can actually decrease the total capacity, since more access points and fewer channels makes channelization harder and self-interference more likely. Proper channelization of the access points becomes increasingly important. While counter-intuitive, larger deployments with more densely placed access points generally have higher total capacity with smaller channel sizes and proper channelization.
Below, I'll discuss how the laws of RF physics intertwine with IEEE standards and worldwide regulatory domains to make the use of bonded channels challenging.

Channel Bonding In WiFi: Rules And Regulations

(Appeared in Network Computing on 1/25/2016)

The second part of this blog series examines the IEEE standards and government regulations that impact channel bonding.
Channel bonding has become a very useful mechanism for accommodating growing WiFi data capacity requirements. But as I explained in my last blog, the laws of radio frequency physics can make channel bonding challenging to use in practice. In this post, I discuss the impact of IEEE standards and regulatory restrictions on channel bonding, and how this makes the use of channel bonding even more complicated.
In the IEEE 802.11a and 802.11g WiFi standards, channel widths were strictly defined as being 20 MHz in size.  The number of independent channels varied by country, but most regulatory domains allowed for at least three channels on the 2.4 GHz band (802.11g) and at least five channels on the 5 GHz band (802.11a). Channel bonding was first introduced with 802.11n to allow 40 MHz channels, and then ultimately extended further with 802.11ac to allow 80 MHz and 160 MHz channels.
As mentioned in my last blog, the size of the usable frequency band for WiFi per regulatory domain (i.e. country) is fixed. Accordingly, mathematics dictate that when the size of each independent channel is doubled, the number of available independent channels is halved, rounded down.  
While simple enough to understand, the laws of mathematics wreak havoc on the 2.4 GHz band when channel bonding is applied. The usable frequency band for most of the world on the 2.4 GHz band is only 72 MHz wide (2.401 GHz to 2.473 GHz). Accordingly, there are only three independent 20 MHz channels, and it is mathematically impossible to have more than one independent 40 MHz channel.

In contrast, the 5 GHz band has up to 500 MHz in the US, providing up to 25 independent 20 MHz channels, as opposed to only three independent channels on the 2.4 GHz band. I say “up to,” however, because this band is only semi-contiguous; many regulatory domains and the historical evolution of FCC regulations of this band make it much more complicated to use, especially when bonding the channels together.
Nearly half of the frequency range of the 5 GHz band requires dynamic frequency selection (DFS), a process by which the access point must detect the signature of existing government weather radar and other radio systems and vacate the channel for an hour. If a particular WiFi network is located in range of such an existing radar system on a DFS channel, the particular DFS channel is unusable at that location, and channelization must be redone to avoid that specific channel.
In March 2014, the Federal Communications Commission (FCC) extended DFS detection requirements to apply to client devices as well. Unfortunately, many WiFi consumer device and appliance manufacturers, driven by cost and time-to-market constraints, took the easy way out: simply do not operate on any channels in the DFS channel range. This significantly limits the practical number of channels available if those client devices are on the network, especially when channel bonding for larger channels. But don’t worry: All of your Apple and virtually all of your Android smartphones and tablets currently support operation on DFS channels. The problem is with low-end laptops and wireless USB adapters, which will revert back to 2.4 GHz operation if they cannot see a 5 GHz signal because the AP is using a DFS channel.  
The following table shows the full range of 5 GHz channels for different channel sizes.

  • UNII-1 (Channels 36 – 48, 5.170 – 5.250 GHz):  This 80 MHz wide band historically was regulated by the FCC for low-power indoor use by WiFi, but is currently allowed for both indoor and outdoor WiFi at the same power levels as all other 5 GHz channels. Most regulatory domains worldwide allow WiFi operation in this band. All 802.11n and 802.11ac client devices can use this band.
  • UNII-2 (Channels 52 – 64, 5.250 – 5.330 GHz):  This 80 MHz wide band historically was reserved by the FCC for government weather radar systems, so DFS sensing is required by access points and client devices. Most regulatory domains worldwide allow WiFi operation in this band. Only higher end 802.11ac client devices and older 802.11n client devices support use on this band.
  • UNII-2e (Channels 100 – 144, 5.49 – 5.730 GHz):  This 240 MHz wide band also was reserved by the FCC for government weather radar systems, so DFS sensing is required by access points and client devices. To complicate matters further, Channel 144 was only added for WiFi use in 2013, with the emergence of 802.11ac, in order to support an additional 80 MHz channel. Hence, older 802.11n client devices and some access points do not recognize and therefore cannot operate on Channel 144. Furthermore, several worldwide regulatory domains don’t allow the use of this band. Only higher end client devices and older 802.11n client devices support use on this band.
  • UNII-3 (Channels 149 – 161, 5.735 – 5.815 GHz):  This 80 MHz wide band was historically designated by the FCC for both indoor and outdoor WiFi use, though several worldwide regulatory domains do not allow WiFi in this band. All 802.11n and 802.11ac client devices support use on this band.
  • ISM (Channel 165, 5.825 – 5.845 GHz):  This 20 MHz wide band is also allowed by the FCC for WiFi, though. several worldwide regulatory domains do not allow WiFi in this band. All 802.11a, 802.11n, and 802.11ac client devices can use this band, though this band is not used when larger channel sizes are deployed.
The FCC is considering the addition of additional 5 GHz spectrum, including the 5 MHz between the UNII-2e and UNII3 bands as well as adding additional channels (i.e. 68 – 96 and above 165). Given that there are more government systems currently using those frequencies and the general speed of decision making, do not expect to see any further expansion of the channel space in the next three to five years. Even if additional spectrum is made available, DFS or similar restricted use of these expanded frequency bands will likely apply.
So where can you actually use these larger bonded channels?

Channel Bonding In WiFi: Use Cases

(Appeared in Network Computing on 2/15/2016)
Bonded channels make sense in certain types of WLAN deployments, but not others.
In this series on channel bonding in WiFi, I've discussed bonded channels from a technical perspective, both in terms of the radio frequency physics as well as the regulatory domains and standards. In this final post, I'll provide guidance as to where -- and how -- you should use bonded channels.
As with all engineering efforts, the choice of using bonded channels depends on the requirements (i.e. what level of service do you need) and constraints (i.e. what factors must you live with) of your WiFi network. Bonded channels are more appropriate when used in WiFi networks driven by WiFi coverage, such as those in private homes and s small or medium businesses, as opposed to WLANs driven by WiFi capacity like those  in large venue environments.
I discussed how two APs on the same or overlapping channels create co-channel interference, which prevents frames from being received, resulting in retransmissions and a lower total channel capacity. Co-channel interference can occur from either your own APs (i.e. self-interference) or from external neighboring WiFi systems. While the effects of co-channel interference are independent of the original sources of that interference, there are two distinct practical differences when designing and deploying WiFi networks:
  • In networks consisting of multiple APs, most interference is self-interference (i.e. from your own APs). This should be readily apparent, as most of the immediate neighboring APs will be internal to the same network.
  • While you cannot control neighboring WiFi systems, the access points within your own network are under your own control. Thus, self-interference from your own APs is largely avoidable with proper design and deployment.
One can get away with a single 40 MHz channel on 2.4 GHz and a single 80 MHz channel on 5 GHz in a small to medium size private home with neighbors that are not close enough to cause interference. Hence, consumer wireless routers are suitable for this environment. Unfortunately, this starts to break down in larger private homes, where multiple access points need to be deployed. In such environments, 20 MHz channels must be used at 2.4 GHz, though here the driving requirement is coverage and not capacity, so 80 MHz channels on 5 GHz can usually be used.

Most WiFi vendors advertise “auto channel” or “radio resource management” (RRM) features to perform channelization automatically. This is clearly convenient, especially as the number of access points grows into the tens, hundreds, or even thousands. However, such adaptive algorithms, no matter how elaborate, have inherent limitations, especially with a small number of independent channels. A channel change on a single AP can ripple throughout the entire network, causing service disruptions and creating new sources of co-channel interference, which will lead to further AP channel changes, and so forth. It's generally best not to rely on such automation, but instead establish a static channel plan to avoid self-interference.
WiFi networks consisting of more than two access points require a minimum of three independent channels to control self-interference. That said, some level of self-interference is generally unavoidable with only three channels, especially as the density of access points increases to add additional network capacity. The more independent channels there are to work with, the easier it is to minimize or even simply avoid self-interference.
As mentioned above, the 2.4 GHz band has only three independent channels at 20 MHz, and thus only one independent 40 MHz channel can be created. Accordingly, for the 2.4 GHz band, it is never appropriate to use 40 MHz channels in any multi-AP environment. On the 5 GHz band, 40 MHz is typical for a wide variety of deployments. Given the current channel allocations, using 160 MHz is impractical in any multi-AP deployment, and 80 MHz channels tend to be practical only in relatively small deployments (on the order of up to 20 – 25 APs) where DFS channels are usable.
The “consumer side” of WiFi can generally be broken down into small private homes, large private homes, and multi-dwelling units such as  apartment buildings and student dormitories. WiFi tends to be supplied by consumer-grade wireless routers designed to cover a 2,000 to 2,500 square-foot area, either purchased from a consumer electronics store or supplied by bandwidth providers such as telco or cable companies.
These wireless routers often default to using 40 MHz channels on 2.4 GHz and 80 MHz channels on 5 GHz, and often don’t even provide the “nerd knobs” in the configuration GUI to change them. On the 5 GHz band, generally only the UNII-1 (channels 36 – 48) and UNII-3 / ISM bands (149 – 165) are available, meaning that there are only two 80 MHz channels available on the 5 GHz band.
Where bonded channels become really problematic is in multi-dwelling units, such as apartment buildings, assisted living, and student housing. Consumer wireless routers are generally designed to cover a 2,500 square-foot private house. When they are placed in an apartment larger than 1,000 square feet, the signal bleeds over into several surrounding apartment units (both horizontally and vertically), each of which generally has its own consumer wireless router. It is a testament to the robustness (or perhaps stubbornness) of the 802.11 protocol that WiFi in such environments can even work at all.
In these environments, therefore, it is more appropriate to install a centralized WiFi network using enterprise-grade access points that are not necessarily deployed in every single unit. Deploying the APs in hallways is convenient, and sometimes unavoidable, from a cabling perspective. However, the hallway itself will acts as a focusing lens for the RF signals, which can result in self-interference with APs that may be quite a distance apart from each other.
Additionally, the strongest signal coverage winds up being in the hallways, when you really want the strongest coverage to be in the units. Most apartment units put bathroom mirrors, metal appliances, and other structure on the hallway wall, which all serve to attenuate RF signals and thus decrease the quality of the coverage inside the unit itself.

channel bonding uses 1.jpg

Predicted signal level (left) and self-interference (right) for a hotel with APs installed in hallways.
Consequently, it's better to place individual access points inside every few units in a staggered pattern both horizontally and vertically. While capacity is an ever-increasing concern, the WiFi requirements for multi-dwelling units are still oriented towards providing coverage vs. capacity. Hence, 40 MHz channels on the 5 GHz band are typical, and in some environments even 80 MHz channels on the 5 GHz band are usable.

channel bonding uses 2.jpg

Predicted signal level (left) and self-interference (right) for a hotel with APs installed in rooms.
For high user density environments, such as conference centers, stadiums, arenas, shopping malls, and lecture halls, the requirements are driven by capacity, as there are a large number of devices that are connecting in a relatively small area. In these environments, multiple APs are installed, usually with highly directional antennas, to segment the area into as many parallel sectors as possible to handle hundreds or even thousands of simultaneous users. There can be a large number of overlapping access points, so typically 40 MHz or even simply 20 MHz channels on the 5 GHz band are used.
Overall, channel bonding is a very useful feature of WiFi to increase capacity, but applicable to particular environments. Without carefully controlling channelization and channel sizes, simply adding more access points isn’t always better, and in fact can make the network worse.

Friday, April 15, 2016

Deploying Wi-Fi in the Real World

Note, this blog post was written for and originally appeared in Network Computing on 4/14/2016:

Over the last decade, the proliferation of WiFi has been tremendous. However, this proliferation is fueled by one major misconception: Deploying Wi-Fi is EASY! How difficult can it be to go to your local big-box or consumer-electronics store, buy the shiniest WAP router you can find, and plug it in? When WiFi was new and consumers and business were wary about deploying a seemingly complex and unknown technology, this messaging made a lot of sense. Plus, back in the day, deploying WiFi was actually fairly easy. When data rates were low and the modulation and coding schemes (MCS) were simple, WiFi networks were quite tolerant to errors in deployment and issues in the environment.
Moreover, WiFi is a very robust protocol designed to work in the presence of interference -- even self-interference from other access points on your own network. The success of WiFi is at least partially due to its durability; WiFi as a protocol will continue to try and pass data, long after logic and sound engineering principles indicate that it should have already crashed and burned.
However, as WiFi became more popular, there's been ever-increasing demand for higher speeds and capacity. While we cannot break the laws of physics, engineering as a discipline is all about using mathematics to “bend” the laws of physics. Hence, we add more mathematical complexity to squeeze more performance: more complex MCS rates like quadrature amplitude modulation (QAM), MIMO, and transmit beamforming MU-MIMO. We also increase the channel size, which allows us to push more data on the channel. There is always a price, however: As we add more complexity, we add more fragility or sensitivity. Modern WiFi now requires much better signal-to-noise ratios (SNR), accurate antenna alignment, and position feedback from the client devices so we know where they are relative to the access point.


(Image: iSergey/iStockphoto)
Consumer marketing continues to promote WiFi ease of use, but so have many enterprise WiFi vendors, telling customers to put APs wherever they wanted, and that the APs would figure it all out in the firmware. However, we no longer live in a “best effort” era, where if the WiFi works for you great, and if not, too bad. WiFi is a requirement, and bad WiFi is bad for business. Just look at the hotel industry, where the importance of fast WiFi is consistently rated more important than clean sheets and towels!
As with any complex engineering system, the ultimate success of a WiFi network comes down to the following, all which have their own set of challenges:
Proper understanding of WiFi requirements and constraints. Formulating requirements are often overlooked or disregarded, because on the surface, requirements seem deceptively easy: WiFi is a commodity, and it should be readily obvious what's needed! Unfortunately, this is generally not true. Most customers and end users are not WiFi experts, nor do they usually even have more than a passing knowledge of networking or information technology. Hence, they don’t appreciate what is impossible vs. impossible, or what is easy and cheap vs. what is difficult and expensive.
Accordingly, expectations can be skewed because many requirements and constraints end up in direct conflict, such as providing both the best performance and the cheapest price, or providing WiFi coverage everywhere while hiding the access points from view to preserve aesthetics. If deploying in an existing building, there are often hidden constraints that may not emerge until the deployment, such as the ease or difficulty of running backhaul cabling, or walls that are made out of materials that are more RF shielded or RF transparent than previously thought.
Requirements and expectations also change unpredictably over time, both during the life of the project as well as the life of the WiFi network as a whole. If a WiFi network installed today has an expected lifetime of three to five years or more, then it needs to handle devices and user expectations that don’t exist today. The networks we design today must be designed for the iPhone 10. How do we design a network to handle client devices, and client expectations, that don’t yet exist or haven’t even been conceived of yet?
Proper product selection. Again, picking the right solution is deceptively easy in a world where WiFi is thought of as a commodity, and thus WiFi vendors and WiFi solutions are treated as interchangeable, not only by the customers, but by the vendors and solution providers themselves. The reality is that most network vendors have optimized their products and services to meet the typical requirements of specific vertical markets like hospitals, schools, stadiums, and SMB; a solution tuned for one environment may be a very poor choice for another, because the requirements are very different.
However, WiFi systems are sufficiently complicated that no reseller, system integrator, or even WLAN engineer, can possibly be an expert in all of the diverse offerings from multiple access point vendors, so most tend to deploy equipment from either a single or a small set of sources. The vendors actively encourage this with pricing promotions and training and certification programs because, like all businesses, they like having a loyal customer-base and the repeat business it generates.
Proper implementation. We have endless debates in the WLAN industry about site surveys, and the validity of performing predictive modeling vs. going on-site to perform pre-deployment and post-deployment surveys. A predictive model is, by definition, a model, which is a simplified mathematical representation of reality. The modeling tools we have today, such as Ekahau, AirMagnet, and TamoGraph, are quite mathematically sophisticated at computing RF propagation, but they can only ever be as accurate as the inputs you put in. Garbage in produces garbage out.
Since every environment is at least somewhat unique in its construction, on-site surveys are obviously better, but these require specialists with custom, hard-to-learn tools and take a lot of time. This makes site surveys quite expensive in terms of both cost and time, and most customers who perceive the WiFi as “easy” don’t want to pay for it, so they tend not to get done or, at best, rushed.
So what do we do as WiFi engineers? The best we can. We try to standardize on a set of solutions and best practices, but not make this standardization so rigid that we cannot be flexible and adapt to unique requirements or unusual constraints. We also build robust designs that are built conservatively with a lot of margin for capacity and growth. We may not know what the iPhone 10 is, but we can safely assume it will consume more data and that there will be more of them compared to what we are used to today.
We also hopefully build service contracts to periodically tune and refine the WLAN while it is in operation. Undoubtedly, channels will need to be tweaked, coverage may need to be extended, or capacity may need to be increased over the life of a network. Finally, we as WiFi engineers must continue to hone our craft. WiFi is still a rapidly changing technology, and our understanding of what works in practice and what doesn’t will keep evolving as we deploy more networks and encounter real-world issues.