Understanding Wireless Networks — Interview with Craig Plunkett

This is the first in what will be a series of interviews with Experts of the Networks.

I recently had a chance to sit down with the very knowledgeable Craig Plunkett, a colleague and a friend, to talk about wireless networks, something he understands quite well.  How does all that data get from the Internet to our devices, wirelessly? Craig tells us.

Along with the text are illustrations I’ve created to help visualize the content.

Using Craig’s information and his diagram, I’m creating a wireless network map which I’ll link to as soon as it’s up.

Here is the interview, with some edits.


Shuli Hallak: Can I call you a Wireless Networking Expert?

Craig Plunkett

Craig Plunkett: Sure, or you can call me a magician.

It’s true, everyone seems to think that WiFi works as if by magic! 
What does WiFi stand for?

It doesn’t really stand for anything. the guys who coined it called it Wireless Fidelity – but doesn’t mean anything. Sort of like Hi-Fi.
WiFi is now a catchall for Wireless Local Area Networks (WLAN), anything that’s not cellular gets lumped into wifi mostly. A better term is wireless ethernet.

Can you define Ethernet?

Ethernet is the most successful network technology in the history of networking.  It was a standard way of physically connecting devices together in a LAN [Local Area Network].  Previously you had to do a very proprietary way of connecting things together but ethernet introduced the standard so that there was an explosion in the myriad of ways that you can connect things together.  And they were all standardized on a connector in a way of talking to each other.

Ethernet is both a hardware and a Protocol — a way of conversing with each other.

I remember the hardwired days of hooking an Ethernet cable to my computer…

That’s right, every device came with an Ethernet  jack or port, an RJ45, it looks like what we used to call a “fat phone plug”. It has 8 wires in it.  And that connects your end device to a switch and also switches to each other.  And those collections of devices and switches form a local area network.  Which is generally connected to the rest of the world by a router and a connection to the Internet.

Ethernet RJ45

Which I’ll explain in a later segment. How does wifi relate to the physical layer?

Everyone thinks that wifi is a magic technology but a very wise fellow once told me that the only thing wifi does is replace a patch cord… which is true.  At its basic level what WiFi does is replace a patch cord that we used to use to connect devices to switches so the WiFi radio inside your laptop communicates with something called an access point which is basically a WiFi switch.  It  mediates the conversation between the rest of the network and your device by taking a wired connection and allowing it to traverse the air to the radio in your device. And that’s done using unlicensed frequencies.

Wireless Access Point

Like microwave?

Yes. There’s two bands of spectrum that WiFi is allowed to use right now.  It’s in the 2.4GHz spectrum originally which is shared by microwave and lots of other devices and it has a certain characteristic of propagation and distance. And the other band that its been allowed to use is the 5GHz band which is much less crowded but it has different physical propagation. So you get more bandwidth out of 5GHz but it doesn’t go as far.  So you need to have a lot more access points when you use 5GHz than when you use 2.4GHz.

RF Wavelengths

Does 5GHz get less interference or do they both get the same relative interference?

These days they both get a lot of interference.  WiFi has become such a tremendously useful technology that the spectrum in 2.4 is very crowded with overlapping networks and lots of interference with non-WiFi devices that use that 2.4 band.  The FCC, which allocates spectrum, allows people to use 2.4 and 5 GHz within certain rules so that they are restricted in power so that they don’t blast and interfere with each other over wide distances. But WiFi is so popular that the 2.4 band has become so crowded as to almost be unusable. Plus, the speeds that we now get with WiFi require wider channels that are really only found in the 5GHz spectrum.

The concepts of channels is key.  It’s just like tuning into a radio station.  If you have multiple radio stations on the same frequency, they’re going to interfere with one another, that’s what’s happening in the 2.4 GHz band.  The radio signal is traveling very far, and networks on the same channel interfere with one another and when that happens the whole thing is useless.  So you jump to 5GHz which allows you to use more channels and each channel can be wider so that you get more bandwidth through a wider channel.  Those are things that are related to physics concepts like Shannon’s law. So when you use a wider channel, you can get more bandwidth through it but as the frequency goes up the propagation and the penetration through obstacles decreases.  Because the propagation decreases, it covers less area, so you get a smaller pool of coverage so that there’s therefore less interference.

This is pretty interesting. And a it’s a great explanation for how you were saying that people think of this as just this thing that happens in the air… It seems like what you’re saying is that there’s an almost an actual physical layer — in the spectrum.

There is! Exactly. So the physical layer in WiFi is not a cable, it’s actually radio.  It’s multiple radios talking to each other over the air and instead of being able to see that with our eyes you need to use things like spectrum analyzers to take a look at that.

It’s almost like the predators vision in those movies or an infrared camera.

It’s still light but it’s a different frequency of light and it behaves in different ways than visible light. There are still mirrors and lenses  that can refract and reflect the light — the WiFi light  — but it  behaves in different ways.  It doesn’t directly correspond to what we see and what our eyes perceive as light.  But it follows the same rules.

Above: “Electromagnetic-Spectrum” by Victor Blacus – SVG version of File:Electromagnetic-Spectrum.png. Licensed under CC BY-SA 3.0 via Wikimedia Commons – http://commons.wikimedia.org/wiki/File:Electromagnetic-Spectrum.svg#mediaviewer/File:Electromagnetic-Spectrum.svg

The higher you up in spectrum you go, the shorter the wavelengths are, and the higher your frequency, the more data you can carry.

In a 2.4GHz wave it might be of a certain length and within a wave you can carry so much data but in a 5GHz frequency you have a lot more waves so you can carry a lot more data in the same space. It’s all light, it’s just what we call the different segments of the spectrum of light.

Down in 2.4 that’s microwaves: so you can push a lot of power, you can use that to excite molecules in food and make them hot and you can also use that for WiFi to communicate. But now you know why your WiFi goes to heck when you turn your microwave on, right?  So that’s an early anecdotal discovery. And also in the 5GHz spectrum you have radar, so if you’re in an urban area or near an airport there are certain frequencies that you can’t use because weather radar and aircraft radar and marine radar will interfere with them.

So that kind of limits us to the spectrum that we can use. But the government also sells spectrum to wireless carriers and that’s why people / companies bid millions of dollars on just reserving certain frequencies so that they don’t have to deal with interference by microwave or radar.



When you say they sell spectrum to wireless carriers, that’s for cellular networks?

That’s for cellular networks or satellite networks or anything you really want. It’s the non-visual — the radio spectrum — in that particular country is basically real estate, it’s the same thing as land because it’s defined by physical boundaries and the government chops it up into regions and it gives out licenses to companies so that they can use particular frequencies in particular regions and the companies pay a lot of money to do that.

Can you explain to me how access points connect to the rest of the Internet? Where does it go from an access point next?

You take your device. You have a bunch of laptops or mobile phones or whatever we’re talking about.  And they talk to an access point.  And modern day access points generally have two radios in them: one for 2.4GHz and another one for 5GHz.  So some devices may be talking to the 2.4GHz radio and other devices may be talking to the 5GHz radio.  But what the access point does is it combines the traffic from those two radios and puts on to an ethernet connection, a wired ethernet connection.  And that goes into a switch.  which is kind of like a power strip for multiple network devices, it can be multiple access points, it can be other switches.  So the switch aggregates connections from your Local Area Network.

and is the switch…

The switch is generally in a wiring closet where all those blue cables in the ceiling come together in an equipment rack or equipment room.  And then the device that takes all the traffic from the access points and the switches and puts it on the Internet is called a router.

On your WiFi side of the router,  you have what are called local IP addresses.  That’s you 192.168.xxx.xxx  And what that router does is take those addresses and translates them to an address that your ISP provides you. It can be one or more addresses but if it’s a cable network it might start with 24.xxx.  And then your cable provider then aggregates all of its connections into the neighborhood into something called a Node and that Node is generally connected by a fiber connection to something called a Head End in the cable company. And then that Head End is connected directly to the Internet through their own routers and then we go into cloud — Tier 2 and Tier 1 providers and carrier hotels, data centers and all that fun stuff.

Enterprise Router

So from the switch we leave the building?

From the router we leave the building. The router would be in the building.  If you have a campus or another building, you can have another switch connect to the switches and more access points and more devices in another building.

Let’s say it’s an apartment building?  Would every apartment have a switch in their closet or panel?

Actually no, that’s interesting.  In an apartment building, generally the cable company or the ISP brings a connection to each apartment so that there’s a router per apartment.  And in most cases, in most small apartments, your access point and your router are combined into the same box.  That’s your little blue and black linksys  or something from d-link.  That combines both the routing function and the access point function into one box.

What we’ve been speaking about up until now is more of an enterprise situation where you’ve got more people gathering.  But if you want to go back to your living room example, you’ve got one box  that can perform both functions of routing and access point. And that’s how you get your Netflix.

In an apartment building, the cable company runs the wires throughout and brings them to the basement and runs them out into the street, back to the Node in the neighborhood, and then our previous example takes hold.

Wireless Network Diagram by Craig Plunkett

Wireless Network Diagram Courtesy of Craig Plunkett.


It can be cable, copper, or fiber.

Twisted pair copper, DSL, that’s the slowest

Coaxial, which is used by the cable companies, that’s the next fastest.  They have more bandwidth they can squeeze out of that copper cable.  You’re going to see improvements because they want to compete with the fiber providers that are popping up.

With Fiber, you can go to multi gigabit connections.  And anything you want can go over fiber. So in that case you have glass instead of copper that runs down to your basement and out into the street.

Fiber Cables

We know the advantages of WiFi: mobility, access. What would say are the disadvantages of WiFi, in terms of security, privacy or any other things you want to talk about.

If you want to go back to the cellular option, because WiFi is an unlicensed spectrum, you are limited to certain power limits which really imposes the constraints on the distances that WiFi can go and also a WiFi device is limited to 1 watt of power that it can output but your cellular radio is allowed to put out 3 watts of power — over 3 times the amount of power that you can use with a WiFi signal — that’s why you can get to a further cell tower than you can to a WiFi access point. And as long as WiFi is restricted to unlicensed with these power limits, you’re never going to get ubiquitous WiFi coverage like you do with a cell network. So the government has kind of set these things up – and it’s kind of good that it’s unlicensed because a lot of innovation takes place in the unlicensed spectrum.  And on the other hand it’s bad because these other companies lock up these swaths of spectrum and they’re not efficiently used and banked, just to keep out competition.

And what about security – people accessing hotspots and open networks?

Well, that’s interesting because the cellular companies deal with this by encrypting things end to end but it’s still radio, you can still listen to it. It doesn’t matter if it’s cellular or WiFi, it’s all radio, it’s all broadcast in the air. So like anything, you get the security that you care about.  With cellular networks, that stuff was designed in from the get-go. But with WiFi, it was originally an experimentally technology that people didn’t really give a lot of thought to security in the early days. But as it’s become more popular, security has become a big concern but those can be mitigated by adding secure encryption between your device and the access point or whatever WiFi network you’re using. In some cases it can actually be more secure than a cellular network — which is crackable — and any encryption is ultimately crackable. And the government probably has backdoors to most of it anyway.

But some good hygiene tips:

  • Use a VPN, a Virtual Private Network, so that all your traffic is encrypted from your end device to the VPN end point in the Internet that you use.
  • Also make sure that the websites that you do visit use the HTTPS protocol.

And hotspots, using free WiFi that’s around?

Sometimes you can put up a honeypot network where people for nefarious purposes try and capture credentials and things like that.  You definitely want to try and avoid that and it’s difficult because you can spoof a name, there’s no foolproof way of doing it. But if you can avoid the plain vanilla access points and don’t connect to an SSID [Service Set Identifier, or the name of Wireless Local Area Network] or FBI Van 11 [laughing] there’s tons of stuff out there that you need to avoid. And to be truthful that’s one of the great things about carrier WiFi, the cable companies — everybody loves to hate them — but they did do a great job of extending their product via a standardized widely available network that you can use outside of your home, that’s generally reliable for communications. But don’t rely on your provider to provide security because most WiFi networks have to be open in order for them to be easily connected to. With a cell network, your device is registered to your cellular provider and it only allows registered devices to talk to the network. But in WiFi, in order for it be useful, it’s got to be open so that people can connect to it, and then implement their security measures.

It’s got some flaws, it’s not perfect. But it’s utility far outweighs the risk of interception and decryption and if you really believe that the cellular network is more secure or takes care of your security, then you’re living under a false impression. Anybody can intercept radio and eventually decrypt the contents of it.

With a couple of extra steps?

Sometimes a few sometimes a lot but even a wired network – once you’re information is on a wired network – then it’s really subject to government interception, or anybody that taps the cables.  And we all know about the NSA  and GCHQ and the whole five eyes project.

Fun stuff


Cablevision announced its new service called Freewheel — a WiFi based mobile phone — given your previous role at Cablevision let’s leave them aside, it seems like there is a move to make wifi-only based mobile phones, not using the cellular networks at all.

There’s a general concept in the industry that’s taking hold called WiFi First.  Because WiFi is widely available, it’s cheap and it’s faster than cellular networks, it’s a preferred method of connecting and getting your data because it’s a lot faster and cheaper.

I believe the WiFi First will take hold more and more and you’ll see cellular networks that are even offloading their stuff onto WiFi to relieve their capacity crunch.  That was first done by AT&T and T-Mobile, the one big resistor has been Verizon. They’re even touting that they give you a great WiFi router in your home, which is the default way to connect nowadays. So most all devices come with WiFi, some come with WiFi and cellular, but what cellular is really for is wide area mobility.  It was really to reach people at a distance when you’re not connected to anything.  It’s not for high capacity. WiFi was introduced as a Local Area Network (LAN) technology which is high capacity. It brings the Internet to a wireless device which the older cellular technology, 2G and 3G was not so great at.  But now the new LTE standard has unified the cellular world and advancements are being put forth in it but it’s really expensive to deploy that LTE technology in the density that you need to provide the service that people expect from WiFi. So WiFi is a lot cheaper to do that with.  But unfortunately because it’s limited in power, it’s not ever going to be ubiquitous because you just can’t put enough WiFi access points out there and have them all work together properly to be good enough.

There’s a complementary relationship between WiFi and cell.

Cellular is for wide area mobility and WiFi is for local area connections that are high bandwidth, where you can get a lot done in a very short period of time.

Can you tell me about your background: how long you’ve been in the industry and how you got into this?

I’ve been a network consultant for a long time – since the mid ’80’s. I was doing Internet of Things back then, but we just called it Process Control.  But in the late mid to late ’90’s, I first saw WiFi in an enterprise environment and I got very excited by the technology and I thought “oh this would be great if you had it on the trains.” And this is really before cellular was widely available – it was very slow and limited to police departments.  So here I thought this was a great idea: to bring WiFi connectivity to transportation.  So I started researching it, I built small WiFi network hotspots and in the mid 2000’s I built a wireless ISP on Fire Island and I was one of the first guys to put WiFi on buses.  We put wifi on 55 buses for the Hampton Jitney running between Manhattan and Montauk.

And that was taking cellular connection and redistributing it around the bus via WiFi.  So it was the very earliest versions of MiFi’s.

And from there I joined Cablevision and helped them build out their Optimum WiFi Network and I’ve since moved on to various roles in the WiFi hardware industry and the service provider industry.  So I’ve been working on WiFi for a very long time.

So you’ve seen it evolve quite a bit.

Yes.  It’s gone through many stages. First was the occasional hotspot use and then it was ‘get coverage in all my buildings and every corner’ and then when the iPhone and iPad hit you saw an extreme jump in the demand for WiFi. And right now a lot of WiFi networks are overwhelmed because there’s actually just too many devices on them and they’ve been built for the coverage model not a capacity or high density model of connections.  So these days if your WiFi network is more than a couple of years old, you probably have to add a whole bunch of access points and there’s a new standard coming out called 802.11 ac which allows gigabit speeds for WiFi. So in a certain theoretical maximum case, you could have a wireless network which is faster than your wired network.

That was one of my questions actually, glad you answered it.  So a wireless network can actually keep up with the wired network and it can go faster?

It can go faster but the problem is that once your data gets off the wireless network it needs to be conveyed someplace else.  It’s got to go to Google, Facebook, anyplace else. It’s got to go through the rest of the Internet to get there and so wireless is no longer the bottleneck.  Your wireless network’s connection to the Internet is the bottleneck now. The chokepoint used to be your wireless connection back in the days of 802.11b but now your wireless network can overwhelm your wired network and you may need to upgrade your infrastructure on the back end.

That’s a nice flip.

That’s always the way.  Each evolution uncovers a new bottleneck.  It’s a constant cycle of care and maintenance.

Is that where you think WiFi is headed?

I think that the advances in the standards and the devices and the thirst for bandwidth is only going to push WiFi to new limits and people are going to start screaming because their bottleneck is going to be their Internet provider’s connection.  So I think you’ll see new Internet providers evolve to support that bandwidth demand and you’ll see new applications and new innovations over the WiFi networks that are in your homes and the enterprise and in the public space.

I think certainly cable WiFi is going to be more and more popular.  You see it popping up in stadiums and concert halls because the cellular networks simply get overwhelmed by the amount of people and density in those venues.

That’s what we’re hoping for — better connections to the Internet to allow us to do more on it.  What do you think about the state of the Internet as a whole?

It’s good but it’s threatened by the people that currently control it who want to maintain their grip on things. I can empathize with the large investments that they’ve made and the care and feeding it takes to maintain those networks but you have to pick your poison.  You can either have competition or you can have regulation. And you have to pick one.  The incumbents want to have their cake and eat it too. But as people get more and more educated and sunshine falls on how this all works, I think people will understand the issues and eventually get to the right decision.

Where do you think we’re headed in terms of that?

I think we’re headed to a showdown!  We’re headed to a showdown in many levels of government because the incumbents have deep roots in all levels of government and they have a vested interest in maintaining the status quo. But I think consumers of Internet connections really are demanding more and should have better quality connections for a reasonable price.  You can’t keep new entrants out of the market forever. And I think those need to be enabled.  Like the State of the Union address.

Do you think end users are starting to understand what’s at stake?

I think end users are beginning to understand what’s at stake because it affects their wallet so much.  I don’t think they understand the technical aspects nor do they want to. But I think an educated populace is essential for economic growth and stability.  Everyone needs to know how all this stuff works.  You need to know how it works just like water and sewer and electricity.  It’s the same thing.  It’s the same thing as electricity, no matter what the lobbying organization tells you, it’s still delivering something to your home and taking something away – it’s bits instead of gallons of water or kilowatts of electricity.

It’s a utility.

It is a utility.  It’s a dumb pipe, it really is.  It’s a commodity.  People want to have a high quality commodity and they want it do be delivered to them at a reasonable price.  But it’s a difficult job and a large network is a difficult thing to maintain and upgrade.  It’s like changing a tire on a bus while you’re going down a highway.  So people want it to be as reliable as the electric system but you don’t get there without a lot of investment so everybody’s got a point of view and a lot of them are equally valid. We want to find the right way forward that keeps that high level of service or if it’s not such a high level, improves on that high level of service and gives it to people for a reasonable price.

In your years of doing this, what kind of problems have you routinely experienced?

I think everyone wants the “living room” experience which is your basic single access point in your home which supports anywhere between five and ten devices.  A single access point WiFi network is a pretty easy thing to maintain.  But once you start adding access points to it to cover more areas or provide higher capacity, it becomes a different animal.  And I don’t think people really understand that. They want WiFi to be super cheap and have it work all the time.  It’ll get there, it’s not there yet. So you need to spend some money on a WiFi network if it’s of any kind of size.  I don’t think people understand that but I think they’re getting there.

It reminds me of the Louis C.K. routine where some guy on an airplane is complaining about the speed of his Internet connection.  It’s amazing – the number of moving parts that go into a network. and sometimes they don’t work right, but we strive to get there.

It’s a testament to how we take things for granted.

We really do.  But we should get to the point where it’s taken for granted.  And then it becomes like electricity.

That’s a sign of good infrastructure,  when you don’t see it or notice it.

The WiFi industry isn’t there yet, but it’ll get there.

Certainly the future is bright for the broadband industry as a whole and I think that you’re going to see lots of new innovative providers pop up because the cable companies and telephone companies have raised prices to such a level that it now becomes cost effective for new companies to enter the market.  I think what really needs to happen is the regulatory regime needs to be changed so that it becomes cost effective for these new companies to operate on a level playing field with these larger companies.  So we’ll see how that all shakes out over the next couple of years  but it’s good times for consumers and people that need their Internet connections.


Illustrations copyright Shuli Hallak, 2015.

Diagram courtesy of Craig Plunkett.