By Art Reisman
CTO, APconnections
Over the last year or so, when the work day is done, I often find myself talking shop with several peers of mine who run wireless networking companies. These are the guys in he trenches. They spend their days installing wireless infrastructure in apartment buildings , hotels, professional sports arenas to name just a few. Below I share a few tidbits intended to provide a high level picture for anybody thinking about building their own wireless network.
There are no experts.
Why? Competition between wireless manufacturers is intense. Yes the competition is great for innovation, and certainly wireless technology has come a long way in the last 10 years; however these fast paced improvements come with a cost. New learning curves for IT partners, numerous patches, combined with differing approaches, make it hard for any one person to become an expert. Anybody that works in this industry usually settles in with one manufacturer perhaps 2, it is moving too fast .
The higher (faster) the frequency the higher the cost of the network.
Why ? As the industry moves to standards that transmit data at higher data rates, they must use higher frequencies to achieve the faster speeds. It just so happens that these higher frequencies tend to be less effective at penetrating through buildings , walls, and windows. The increase in cost comes with the need to place more and more access points in a building to achieve coverage.
Putting more access points in your building does not always mean better service.
Why? Computers have a bad habit of connecting to one access point and then not letting go, even when the signal gets weak. For example when you connect up to a wireless network with your lap top in the lobby of a hotel, and then move across the room, you can end up in a bad spot with respect to original access point connection. In theory, the right thing to do would be to release your current connection and connect to a different access point. Problem is most of the installed base of wireless networks , do not have any intelligence built in to get you routed to the best access point,hence even a building with plenty of coverage can have maddening service.
Electro Magnetic Radiation Cannot Be Seen
So What? The issue here is that there are all kinds of scenarios where the wireless signals bouncing around the environment can destroy service. Think of a highway full of invisible cars traveling in any direction they wanted. When a wireless network is installed the contractor in charge does what is called a site survey. This is involves special equipment that can measure the electro magnetic waves in an area, and helps them plan how many and where to install wireless access points ; but once installed, anything can happen. Private personal hotspots , devices with electric motors, a change in metal furniture configuration are all things that can destabilize an area, and thus service can degrade for reasons that nobody can detect.
The more people Connected the Slower their Speed
Why? Wireless access points use a technique called TDM ( Time Division Multiplexing) Basically available bandwidth is carved up into little time slots. When there is only one user connected to access point, that user gets all the bandwidth, when there are two users connected they each get half the time slots. So that access point that advertised 100 megabit speeds , can only deliver at best 10 megabits when 10 people are connected to it.
Related Article
NetEqualizer News Blog 
February 6, 2017 at 10:39 AM
Yours is an interesting approach to the wireless realm. I’ve been in wireless engineering for the last 5 years and I by no means consider myself and expert. Infact I agree that their are none. But, as an industry their are solutions to the issues you mention. Primarily the issue with walls,windows, etc. and radiation.
Providing you are building a enterpise level wireless infrastructure, a wireless survey of the area is a best practice to avoid those pitfalls. Produces like AirMagnet and Ekahau will map out the number of AP’s required and db loss per wall and window.
Most Cisco AP’s can provide air monitoring that may help identify magnetic fields like x-ray machine in the area.
Any Access Point from the last few years from the major players (Cisco, Aruba, Ruckus) have MIMO technology and multiple antennas due to wireless being unidirectional. Like any radio system, wireless radios can only broadcast 1 at a time.
February 28, 2017 at 8:53 AM
“Wireless access points use a technique called TDM ( Time Division Multiplexing)”, It is not TDM but CSMA, the time frame is given by CSMA, Carrier sense multiple access, The client asks for a period of time to “talk” with the access point, The access point give a time period to send/receive data based in the requests that were asked from all the connected clients. Thats why WiFi cant garantee QoS
February 28, 2017 at 9:45 AM
I feel I must disagree on the detail of a few of your points.
1. There are wireless experts (but not as many as the world needs) who can provide in depth capability across multiple vendor solutions. CWNP offers a number of vendor-agnostic certifications that are the gold standard for evaluating an individual’s Wi-Fi expertise in different areas (design, troubleshooting, security etc.).
2. The need for more access points is less to do with frequency than to do with throughput. Networks are becoming capacity driven rather than coverage driven and many of the techniques that deliver increased capacity (such as higher order modulations and wider channels) also reduce the effective range of an access point.
3. The problem of ‘sticky’ clients is not entirely due to a lack of intelligence within the infrastructure. The WiFi standards make it the client device’s responsibility to initiate a change of access point. Unfortunately many clients do not make good decisions. Having said that there are measures one can take in terms of design and configuration to encourage clients to make better roaming decisions.
4. As mentioned by another respondent. WiFi is NOT a TDM system. It uses CSMA/CA. What this means is devices do not have allocated timeslots. They wait listening to the channel and then once they believe it is clear they attempt access. In a busy system they may attempt at the same moment as another device which causes a collision. In this case each device will back off for a random period before trying again. The amount of airtime wasted through collisions and backoffs increases as the channel loads up. So all other things being equal if for example a single device can obtain a continuous 100Mbps, 10 devices would in practice obtain considerably less than a continuous 10Mbps each.
Andrew
March 12, 2017 at 8:36 PM
[…] Five Things to Know About Wireless Networks […]