WLAN Design – A Compromise between Quality and Cost

As with many things in live, WLAN design is a compromise. Somehow not getting everything you want, but in order to make both sides agree. In our case, this negotiation is usually between designing the Wireless LAN to meet specific and defined goals, contrasted with staying inside of some arbitrary budget.

The sad part to this story is what happens when there are no negotiations, and price ends up driving the design. So you might want to treat this as a morality tale – and learn from the mistakes of others.

One of the great things about 802.11 Wi-Fi is its inherent resiliency. This is built into the protocol at the very lowest levels. Since we’re using CSMA/CA – we must find mechanisms to give some level of reliability to the wireless packet transfer – these techniques actually work. Some times to the detriment of the overall network throughput.

This extra resiliency can also be an issue when counteracting the “build it cheap” mentality. You can design a ‘workable’ wireless LAN that can send packets from end to end, and thus the bean counters love the cheap price and say that “it works” because some packets can flow. Yet this inexpensive design does not meet even the lowliest of performance criteria.

I personally come from the school of thought that great Wireless LAN design happens during the preliminary meetings, far before any actual design work happens. Way back when discussing the features and capabilities desired by those who will actually be using the Wi-Fi network. This is the time that can make or break a great WLAN design.

It must be at this early stage where expectations are being set… this is where a good WLAN designer takes his/her stand. Each level of expectations has an appropriate cost tied to it. Mistakes at this stage usually happen when people talk about expectations in one meeting, and the money people come up with a budget in an entirely different meeting.

Anxious for the work/contract, many WLAN designers accept both – yet mutually exclusive – expectations. Then later when the system isn’t performing end up blaming everyone and everything involved with the project except the people who are truly at fault. The designers themselves, for allowing the project to move forward with disparate goals.

I’m positive I’m not alone in this next experience. Directly after finishing a large WLAN installation, and doing post verification surveys to “prove” the design meets the written design goals and expectations, you’re feeling quite good about a job well done and about ready to pack it up and head to the next job. You feel confident the wireless network will meet the RF Coverage, Data Throughput, and User Experience outlined in the scope of work… then out of the blue the local contact says something along the lines of…

“Now that the Wi-Fi is working, we can use this for Voice, right?”

Aaaarrgghh – it’s happened to me so many times in the past, I now have a document that I have the customer sign before the start of the design works that explicitly states “This WLAN design does not, and will not support Voice over IP over Wi-Fi” – and have the customer sign and date it in front of me.

Even then, I’ve still had customers come back and expect Voice to work on their data designed wireless LAN.

The downside of this dilemma between a quality wireless LAN design that meets stated criteria, and one that barely works usually comes down to costs. The almighty buck drives the project and if we as WLAN Professionals don’t stop it early enough in the process we’ll be part of those being blamed for the network’s failure.

Below are just a small sample of networks I’ve been involved in fixing, after the fact, to try and salvage some of the sunk cost of the current Wi-Fi system that is not meeting the needs of the customer.

I’m sure you also have many of these types of examples. Feel free to share yours in the comments below.

Treat this like a warning – please do not repeat these mistakes in your own practice!

Using Mesh instead of Wireless Bridges
Thinking you can push Wi-Fi from the outside in, without CPE
Not doing a Link Budget to see if the connection will work
Not doing an onsite RF analysis to measure wall RF loss
Doing point to point links without knowing if any obstacles are in the Fresnel Zone
Installing Mesh instead of bringing cable to all the Access Points
Stringing a series of standard Omni Mesh AP’s to ‘pretend’ to be a bridge link
Not running simple calculations to see how much ‘Pipe’ will be shared between customers
Putting indoor AP’s under the eaves to save money out outdoor Access Points
Using Omni antennas directly against some wall or post
Using High-Gain Omni antennas 15m high above a warehouse floor
Using High-Gain Omni antennas 25m above an outdoor parking lot
Using Point to Multipoint setup in 2.4GHz and wondering where your bandwidth went to
Putting an AP to cover the ground on the 22^nd floor because that’s where the Ethernet drop was
Putting too many AP’s close together to ‘get’ high density client deployment
Doing a pre-installation site survey then never returning for verification
Using SoHo equipment in an enterprise deployment and hoping for the best
Not ever testing the copper plant – wondering why not getting gig speeds
Having network bottlenecks between AP’s and Controller
Thinking if a handheld device can see the AP, why can’t the AP see the handheld device
Designing for merely coverage, then wondering why throughput doesn’t work
Cutting out half the AP’s of a great design, because you don’t have budget for it
Aiming a Point to Point link directly at a wall, since the customer didn’t have rights to be above the wall

Each of the above sentences has at least one full-page story to emphasize the point, but I’m not going to waste the time to go into all the depressing details. Each of the above problems was caused by someone NOT designing for the needs of the customer, but just wanted to stay within some arbitrary budget.

The process should be to make the budget and the Wi-Fi expectations to match.

As my friend Jared mentioned to me this morning,

“You can fail in your design by designing for the budget—then the system won’t meet the needs of the clients. Or you can fail by designing for the needs of the clients—and fail to get the deal because it now costs too much.”

We can mitigate that situation by better communication—much earlier in the cycle to make sure both goals are met at the same time. Or at least the expectations are set to match the budget and what the customer will receive for that amount of money.

This is NOT an easy problem for WLAN professionals – but it is one that will define our collective reputations.

Posted December 21, 2011 by Keith R Parsons · 5 Comments - Join 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.