Words Have Meanings?

Many decades ago I lived in Taiwan for a couple of years and learned Mandarin Chinese. Of all the tens of thousands of possible Chinese characters, there are only some 400 or so different sounds in the language. So many of the same characters (words) end up having the exact same sound. To counteract this obvious chance for confusion, sometimes Chinese people write out an imaginary copy of the character in question on the palm of their hand. A bit awkward, but it helps to convey which character goes with which sound.

In the English language, we too have difficulties at times with words having the same sound, but entirely different meanings. Some even represent a noun, and a verb with the exact same sound. For example, take the word Shift.

Shift – to change gears on a car
Shift – a type of woman’s apparel
Shift – a time period for work
Shift – what a Defense does in American Football
Shift – an improvised knife used as a weapon

Thus we need context around the word to help us determine which version we are referring to.

As another example – the word Braces:

“You wouldn’t want to confuse the Braces holding up Larry King’s pants, with the Braces straightening his teeth, with the guest who Braces for the next question.”

In our world of Wireless LANs we too have to be careful in the use of various terms and words that can have different possible meanings.

We banter about the term ‘Spectrum Analyzer’ but which version might we be referring to:

A $30,000 Spectrum Analyzer used in electronics labs?
A $4,000 Cognio Spectrum Analyzer with custom ASICs?
A $2,000 AirMagnet Spectrum Analyzer with software to share with WiFi NIC data?
A $400 MetaGeek Spectrum Analyzer?
An Atheros chipset with WiFi mode turned off and listening as a Spectrum Analyzer?
Or finally what Xirrus calls a Spectrum Analyzer – but is just WiFi data in tabular format?

All are referred to as a Spectrum Analyzer – but they all have far different resolutions, and capabilities. Not that the most expensive is best – you’ll need to use the one that can show you the raw (non-Modulated) RF at the resolution you need to solve your current problem.

Set SoapBox = ON

Xirrus – just calling something a Spectrum Analyzer doesn’t make it one. No more than calling me a Marathon Runner makes me one. (I have ‘run’ (managed) the electronic timers at a Marathon – that doesn’t mean I actually competed) If your device cannot ‘see’ raw non-modulated RF – don’t call it something it isn’t. It might fool your customers – but not anyone who actually knows what a Spectrum Analyzer is!

Set SoapBox = OFF

Other words we use in the pursuit of our Wireless LAN systems that can be confusing include the word Interference.

We have:

Raw RF Interference – non-802.11 modulated
Co-Channel Interference – 802.11 packets on the same frequency
Adjacent Channel Interference – 802.11 packets on nearby frequencies
Interference because AP’s and Clients are sharing the same frequency with all neighboring devices on the same channel. (Like a hub has interference from all connected devices)

Each of these effects on our data throughput differently, and each need different tools to help troubleshoot and solve the “Interference”.

Or how about the simple term Noise that gets thrown around all the time. Which version of Noise are you referring to:

Thermal Noise?
Non-802.11 Modulated RF signals?
801.11 RF on the same channel?
802.11 RF on nearby channels?
Ambient RF noise floor?
Broken Packets on the same frequency?

Which of these above is what you are thinking of for the ‘N’ in SNR? Which version of “Noise” is used in your Wi-Fi NIC?

Spectrum Analyzers can tell some of these, a Wi-Fi NIC that is in promiscuous mode can see others. Knowing when to use which tool is very important.

In conclusion – remember just like the words Shift and Braces – we need to be very precise in the use of confusing Wireless LAN terms. It will help clear up any confusion if you can be very precise when communicating terms like Spectrum Analyzer, Interference, and Noise.

Posted December 12, 2011 by Keith R Parsons · Leave a Comment To Start The Conversation

Large Scale Wi-Fi Deployments

Another post from Jared Griffith of Cinergy Wi-Fi. This is a cross-post from his new blog.

This summer I had the opportunity to do a large-scale roll out of Wireless LAN access for an entire school district. This project included: pulling cable, installing 625 Access Points, and complete post-install verification surveys across 43 schools, and 6 district buildings. This project was under a pretty intense time line, (school starting) and failure really wasn’t an option. Thus we needed to create an installation method and time line, that would give us a time advantage since the survey and cabling would take a lot more time than just the AP installs.

Installing access points is one thing, but knowing were to correctly place them is another. We were able to get the scaled floor plans from the district , and went on site to the locations with an access point and AirMagnet’s Survey Pro. We wanted to capture what the attenuation of the exterior walls, bearing walls, support walls and all other obstacles we could. We then took those data points and plugged them into AirMagnet’s Planner software for pre-deployment designs. Knowing what the customers design requests were, we could then create a proper design and know AP count and placement. We used the AirWise function in planner to verify the design requirements as well. This helped us to firm up our bid, and create a fixed cost environment for cabling within a target 10% margin.

With the knowledge of the installation facts, we were able to move onto the management of the installation. I knew that having this many access points could cause for a potential disaster of not knowing were the access point was. You can see it in the controller and it is on the map but is it in the correct location? We created a spreadsheet that had a tab for each location. The sheet had columns for:

AP name
MAC Address
Serial Number
Installer Name
Installation Date
Cable Completed Date
Survey Completed Data

From all of this information we could calculate percentage of completion of the project.

To stage the equipment for each school we had the design map from Planner, that told us how many AP’s went to that school. The map listed a number next to the AP. If the school took 33 AP’s, we would use a barcode scanner and get the MAC and Serial Number from the AP and it would place it on the spreadsheet. We would then write a number on the AP box 1 -33 to coordinate with the map, and the spreadsheet. This gave us the exact location of every AP being installed, what the MAC and Serial Number of that AP was. This kept the install very clean as far as an administrative standpoint. Additionally, this was very useful when programming the controller with all of this information.

There were two different types of ceilings we would have to work with. A drop ceiling with T-bar mounting capabilities, and hard deck ceilings that would require a little bit more hardware. For the T-bar it was really simple, we had one single Panavise clip that would attach to the T-bar, and then our AP bracket, would attach to the Panavise clip and we would tighten it up with a 10mm driver. We could then mount the Access Point to the mounting bracket and secure it with zip-tie for safety measures. Using this system we could hang an access point in about 60 seconds or less. The hard deck ceiling on the other hand was quite a bit more difficult. The manufacturer suggested using a drill bit, to create a pilot hole, then insert two nylon anchors then attach the bracket using two screws. But experience has shown there is a better way.

My thought was too use single toggle bolt through the center of the mount that would securely attach the mounting bracket to the ceiling, with out having to measure two pilot holes for the nylon inserts, as suggested by the manufacturer. This process worked out great! We used a ½” inch drill bit to create the hole for the toggle bolt, and then we attached the toggle bolt through the bracket and pushed the toggles up through the hole. To tighten up the toggle bolt, we swapped the ½” drill bit for a Phillips head into our drill and could tighten it using power tools. We found that this procedure took us about 75 seconds or less to do. Using this method helped us save immense amounts of time on the physical installation of the Access Points.

Here are some simple photos of our method using the toggle bolts.

Hard Ceiling Bracket with Single Bolt

Hard Ceiling Mount with Access Point

We were able to physically install the 625 access points in just 7 days. We used three contract installers, in whom I was able to teach these steps to, and was able to turn them loose, to install all the access points.

With the installation of the Access Points out of the way we could focus on the cabling, turn up and post site survey of the project. We had sub contracted the cabling out to local company, that had approximately 6 full time cabling installers that did a phenomenal job in pulling, terminating, testing a tagging the cables. We gave them a copy of the same maps that we used, to install the access points. They were in turn able to punch down the cable on patch panel using standard EIA/TIA naming enclature but also added the AP number to it so it would be easy for us to find and trouble shoot also. They were able to do 625 cable pulls in less than 30 days. This included all the bearing wall penetrations, floor penetrations and testing of the cabling. I was very happy and impressed with their quality.

With the installation and cabling completed we then went to each of the schools and installed Gig POE injectors, since the customer did not have POE switches available for us to use. At each school, would name the access point in the controller, give the Access Point its configuration and place it on the map for the school. This also gave us an opportunity to trouble shoot any access points that issues while on site, saving us time from having to return to individual schools. This took us very little time, and we coordinated with the cable installers, so as finished a school we would arrive to complete the turn up.

The district had requested third-party verification for the site surveys, to ensure that all work was completed per the requirements of the contract. I hired Mike Young a certified AirMagnet instructor to survey all the buildings and using AirWise create the reports to show the work was completed to the specs of the customer. Mike and his team worked very diligently, to complete all the surveys, and I am sure he lost quite a few pounds with all the walking he did. We also ran the surveys by Keith Parsons for final sign off and approval. Mike completed the reports and we presented them to the customer for their approval.

This project was a lot of fun, and was a great win for me given all the timelines of the contract that had to be met. We had a signed contract from the customer on May 27^th, equipment on June 6^th and had to have the entire project completed by August 1, 2011. The calendar period was peppered with both State and Federal holidays as well as not being able to have access to the buildings on the weekends. The total project was completed in 42 working days. I was really please with my team of contractors and the School district in turn is pleased with us.

Survey Equipment used.