Gentlemen, good day.
I'll tell you about one of my projects, from the beginning of design to implementation. The article does not claim to be the ultimate truth, I will be glad to hear constructive criticism addressed to me.
The events described in this article took place about two years ago. The case began when a company approached us with a request to modernize one of its partially open storage warehouses, mostly unheated hangars about 7-8 meters in height, if my memory serves me, and with a total area of ββββabout 50 square meters. The customer already has a controller with a dozen access points. The service for which the wireless network is being designed is data collection terminals that exchange information with the WMS server. About 000 terminals for the entire wireless network. Low client density and minimal bandwidth and latency requirements. The material stored in the warehouse is, to put it mildly, unfriendly to the signal: when passing through one row of products, it attenuates as if it were passing through several load-bearing walls. The height of the product is at least 150 meters, if not more.
Antenna selection
It was decided to use directional antennas in order to reduce the number of access points, their mutual influence, and cover more area. The use of horned access points would not help due to the fact that the ceiling height was much greater than the distance between the rows, TPC with all the consequences. And it was necessary to organize the coverage exactly in a row, because through a four-meter wall of products on both sides of the row, the signal is very strongly attenuated, and the only chance to raise at least some kind of network is to install access points in the client's line of sight.
Range selection
We decided to use 2.4 GHz as the operating band. Perhaps this decision caused genuine bewilderment among pundits, and they stopped reading the post from here, but this range was more suitable for our goal: to cover a large area with the required throughput at a minimum and low client density. In addition, our facility was located outside the city, it was something like a free economic zone, where there were other large factories and warehouses at a decent distance from each other (fencing, checkpoint, everything ...). So the problem of channel utilization in 2.4 GHz was not as acute as if we were in the city center.
Model Selection
Next, it was necessary to decide on the model and form factor of the access point. We chose between points 27/28 + 2566 or street point 1562D with a built-in directional antenna. The 1562 won in terms of price, antenna gain, and ease of installation, and we chose it. So, 80% of access points were 1562D, but somewhere we still used omni points to βpatchβ various pockets and connections between corridors. We took in the calculation one point per corridor, two points per corridor in case of long corridors. Of course, this approach simply did not give a damn about the recommendations about the symmetry of the powers of the access point and clients in order to avoid consequences in the form of one-way audibility, but in my defense I can say that the audibility was two-way and the data we needed went unhindered. Both during the tests and during the pilot, this scheme proved to be quite good in the light of our specific task.
Drawing up a specification
The specification was collected, the coverage map was drawn and sent to the customer for approval. They had questions, we answered them, and they kind of gave the go-ahead.
Here comes a request to reduce the cost of the solution. In general, this often happens, especially with relatively large projects. This happens for two reasons: either the customer says that he has enough money, as he would like and injects, or many vendors and integrators participate in the competition for the implementation of the project, and the price gives your company a competitive advantage. Then there is a scene like a Martian in a movie: the ship must fly, but it is too heavy and then they throw out equipment, provisions, a life support system, skin, and as a result, a person flies almost on one stool with a jet engine. As a result, at the third or fourth iteration, you catch yourself thinking that you look like a boy from a Soviet cartoon who mixes the dough with firewood and throws it into the oven with the words: βAnd so it will do.β
This time, thank God, there was only one iteration. We borrowed an access point with an antenna from distributors and went to the examination. In fact, the search for the equipment for examination is a separate conversation. You need a specific model for the fairness of the test results, but sometimes there is none, especially in a short time and you choose the lesser of two evils: either nothing or at least some equipment with dancing with a tambourine, turning on the imagination and calculating the trajectory of the ship's flight from Earth to Jupiter . We came to the customer, deployed the equipment and took measurements. As a result, we decided that it is possible to painlessly reduce the number of points by 30%.
Next, the final specification and technical specifications are agreed upon, and an order is made for a batch of equipment from the vendor. In fact, these approvals of various specifications and various details can take more than a month or two, sometimes even up to a year. But in this case, this stage passed relatively quickly.
Next, we learn that the delivery time is being delayed due to a lack of spare parts in the factory. This eats up the amount of time we have set aside for leisurely tuning with a cookie break and thinking about how the universe works, so as not to set everything up in a hurry and not make a lot of mistakes as a result of this. As a result, it turns out that there is exactly a week between the date of delivery of the project and the arrival of the equipment. That is, in a week you need to do the network setup and installation.
Installation
Then the equipment arrives and the installers take over. But since they are primarily installers and are not required to know about the nuances of the propagation of an electromagnetic signal, you write a short guide for them on how points can be hung, and how not, etc.
Since the access points we chose are outdoor, sometimes they come in bridge mode depending on the nuances in the specification, and in this state they do not connect to the controller. To do this, go to the console of each point and manually change the mode. Which is what we planned to do before giving all the points to the installers. But as usual, the deadlines are burning, a fully working network was needed yesterday, and we just started to beep boxes with a barcode scanner. In general, we decided to hang like this. Then we recorded the poppies of all access points and added them to the MAC filter on the controller. The points were connected, the mode was changed to local via the WEB GUI of the controller.
Debugging the network and access points
We hung up all the access points, about 80 in total. Of these, there are no 16 points on the controller, and only two points knock on the controller. We figured out the points that did not send join requests. There were two access points left, which, due to a bug, could not connect to the controller, because they could not download the firmware, because they could not decrypt the discovery response from the controller. We have replaced them with spare access points. The radio of one access point was down due to lack of power, we did not have access points of this model in stock, because we were cut down on the specification, so we had to decide something.
We replaced the Chinese switch, in which only the first four ports were distributed to the cisco switch and everything worked. Similar actions were required to be carried out with another Chinese, since one of the ports simply did not work on it. After we put all the access points in order, we immediately found holes in the coverage. It turned out that some access points were mixed up during installation. They put it in place. Further problems with roaming of clients were found out. We tweaked the coverage hole detection and optimized roaming settings and the problem went away.
Controller setup
A deferral advisory notice has been issued to the current version of the customer's controller. When upgrading the controller firmware, the old controller firmware remains on the controller and becomes emergency firmware. For this reason, the controller was flashed twice with the most stable firmware in order to βoverwriteβ the old firmware with bugs. Next, we connected the old and new controllers in an ON SSO pair. It turned out, of course, not immediately.
So, the project is ready. Handed over on time, the customer accepted it. At that time, the project was a landmark for me, added experience, knowledge to my piggy bank and left a bunch of positive emotions and memories.
Source: habr.com