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CWNE Essay #3

Off Duty Wi-Fi

While employed at my first wireless VAR, I was part of a project to provide Military and Federal Law Enforcement members with Wi-Fi at multiple locations throughout the US. The project required me to design and implement Wi-Fi in all barracks and adjacent common areas on a number of military bases and federal law enforcement training facilities. The Wi-Fi was to be for off duty use. The system would be paid for by subscription (this project was in 2010).

The overall design plan would be similar at each location. We performed a proof of concept in one section of a large Marine Corps base in southern CA. This area had 13 barracks buildings with approximately 120 individual rooms each. Each building would be connected to the network via point-to-point links. Users would self-onboard with a credit card choosing from multiple levels of service.

The project had many layers we needed to design including, access point installation locations throughout the barracks buildings, backhaul point to point network, self-onboarding, payment, and SLA management. I was primarily responsible for developing the point-to-point system but worked on all aspects of the project.

There were many different building configurations, from all indoor MDU's, hotel-style with rooms on either side of an interior hallway, motel style with rooms back-to-back with doors opening to an outdoor walkway, and duplex/multiplex bungalows. There were indoor and outdoor common areas as well.

I performed extensive site surveys and point to point link assessments. I needed to determine and document the RF characteristics and AP placement for each building type. One of the significant limitations imposed on the project was that AP's could not be placed inside barracks rooms. I had to find creative ways to mount and shield AP's from each other while installing them mostly in hallways. While this part of the project was challenging, my favorite part was the point-to-point links.

Each link had to be visually confirmed and documented. I had to find the nearest data closets, identify cable runs, determine mounting locations, find access to power and ground, even specify the equipment's color. All of this had to be documented, coordinated, submitted, and approved by base public works. A job that should have taken a few weeks ended up taking months. Since our company wasn't local to these sites, we rented apartments for the project's duration.

Once the design was created and all aspects approved, the installation phase began. A low voltage electrical subcontractor was engaged. I was responsible for training the installation crew on indoor and outdoor radio installation methods, documenting each type of radio and each location type graphically so that there would be no confusion about what needed to be done. I performed inspections of the indoor mounting locations and did final link alignment on each point-to-point link. I even painted all of the outdoor radios.

The point-to-point radios were selected primarily for their throughput speed (1 GB+ duplex). We had plenty of spectrum available, ten high throughput radios used 60 GHz., 26 x 600 MBps radios used 5 GHz. Since they were outdoor, they were well isolated from the indoor AP’s, so we had plenty of free channels. We decided to use integrated antennas to simplify installation. The links were relatively short, so they didn't require high gain directional antennas, although the 60 GHz radios had a very narrow beamwidth. The alignment was challenging with these. It required using a voltmeter and three hands. I created detailed documentation on link budgets, radio configurations, radio positions, channel use, antenna polarity, management interface access, and throughput speeds.

One of the lessons that we learned the hard way on this project was PoE power budget. This project was during the early days of AP manufacturers OEM'ing their own PoE switches. This particular manufacturer listed their switch as full 802.1af PoE but did not list the total available power or max number of powered ports. We spent far too much time troubleshooting why random AP's would drop off the network. We had the cabling contractor go back and inspect all terminations. We opened a ticket with the manufacturer; they weren't able to diagnose the issue.

We finally figured out that AP's would drop when they were powered from a 24-port switch with more than 12 AP's connected. While any of the 24 ports would supply power, the switch could only fully power 12 ports. As AP's would boot, they would draw full power. After some time, they would only draw as much energy as they needed to idle. Some amount significantly less than full power. This allowed more than 12 AP's to come online on a single switch. As soon as the switch's power budget was exceeded, random switch ports would reset. There was no PoE information available within the switch management interface. This just took a lot of trial-and-error troubleshooting. We eventually returned all of the switches and went with a more established manufacturer so that we could effectively manage the PoE power budget.

After the successful completion of the POC I was promoted to project lead. We were able to go live at three other locations throughout the US with a total of 1,828 access points.

I have since started my own wireless network engineering company and value all of the experience that I was able to gain from this and many other projects earlier in my career.


Mike Wade



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