Wireless Networks Thread, Hi, I am a WiFi trainer and engineer, happy to answer questions. in Technical; Hello Everyone.
I am a WiFi trainer and field engineer. I know there is a lot of confusion about WiFi ...
6th September 2013, 01:00 PM #1
Hi, I am a WiFi trainer and engineer, happy to answer questions.
I am a WiFi trainer and field engineer. I know there is a lot of confusion about WiFi training and the use of professional tools in the field, so I thought it might be useful for me to offer to answer any questions anyone may have. This isn't a sales opportunity so please no questions on costs or where to go to get these things.
Feel free to ask about CWNP certifications, AirMagnet, or why professional surveys cost so much.....
6th September 2013, 01:44 PM #2
Thank you, @neilmac
It will be very useful to be able to pick your brains about all things related to wireless
6th September 2013, 11:16 PM #3
- Rep Power
Thanks for your generous offer of help. I have recently inherited an ageing network and am having particular problems with AP's in my school. We have around 40 yet in some parts, rogue ap's have started popping up as networks around areas which have started completely dropping connect to the point of being unusable. Could you spare a moment to share some of your tips on how you would start to troubleshoot these area of the school? I have teachers needing to take registers with the school's MIS on laptops!
6th September 2013, 11:17 PM #4
- Rep Power
dropping 'connections' rather! :-/
7th September 2013, 01:33 AM #5
Yep, for sure.
As with a visit to the doctor, first we need to diagnose before we can cure, so we start with getting an understanding of the environment.
The first thing you have to do is take a site survey, where you plot coverage against a floor plan. Do you have any tools available for that ?
Secondly, what access points do you use ?
7th September 2013, 02:16 PM #6
- Rep Power
Hi there, thx for reply. At my last school i used a free tool called erkhau heat mapper i think. AP's are something very similar, if not
Are there any better tools you would use?
As an aside, I have been given the go ahead to upgrade the whole school ready for BYOD in 6 months to one years time, so will be picking your brains about his in the coming months if that is okay?
In the meantime, I could still do with troubleshooting what we have.
7th September 2013, 03:00 PM #7
PM sent - I'd like to keep the thread specific to training and tools, and generic questions rather than address a specific issue.
Your case is a classic example of where you need to have a professional survey done that can test signal strength, signal-to-noise ratio, data rate, retry rate and loss rate as a minimum and plot the figures against a plan. Additionally you would do well to check out any interference. For surveys the tools are Ekahau Site Survey, with Metageek WiSpy for Spectrum Analysis, or AirMagnet and Spectrum XT. There are expensive tools, so you would usually not have these to hand. If you are considering paying a consultant, you need to make sure they know what they are doing. Ask what certifications and tools they have. Tools are expensive and take a long time to master.
Are the access points managed or standalone ?
Most networks fail because the correct process wasn't followed form design to installation to post install verification. The reason for this is that WiFi is usually added on by people who aren't trained in wifi, so the procedures aren't known.
Many problems can be traced to too many access points, too much power, and problematic set up (bad channel planning).
If you work with WiFi you should consider training, check out CWNP | Certifications - the CWTS is a great place to start. You will learn a lot about how wifi works, the application of that knowledge will help you set up the network correctly and may show you where your current network is failing.
7th September 2013, 03:34 PM #8
- Rep Power
This is very helpful and I'll certainly check out qualifications. I am exceedingly interested in this subject.
7th September 2013, 03:39 PM #9
Download InSSIDer from Metageek.net. Go and stand in one of the positions where you know you have the most problems. Run a scan on 2.4 GHz for a few minutes and post a screenshot of the output. Obscure the SSID's if you are concerned about security. If you don't want to post it publicly, email it to me.
One of your main problems is all your networking is being done on 2.4 Ghz so let's have a look at the channels.
7th September 2013, 05:01 PM #10
- Rep Power
I'll get on that on Monday....
Have a good weekend!
7th September 2013, 06:56 PM #11
What information would you expect to be provided to the customer in a "wireless survey" and why? It would perhaps be helpful to rank it in order of importance.
Originally Posted by neilmac
8th September 2013, 01:05 PM #12
There are many flavours of Wireless Site survey, each with a specific purpose, I'll describe each here:
1) A predictive survey - this is done from a desk using survey software. A plan of the site is imported in to the software, then we add virtual walls overlaid on the map. Once the walls are in we add virtual access points, and set power, antennas and other configurables. The software will predict things like signal strength, data rate, throughput, interference and so on to a very accurate degree. From this you can work out how many access points you will need and where to place them. You use this information to work out your budget for equipment and cable drops. The predictive survey will take into account coverage vs capacity, so you need to have a very clearly defined requirements. You can't say "we just need wifi" you need to say "We need to support, in the designated areas, 200 users for Voip (Signal -67dbm), 100 for data (-80 dbm), 200 for video streaming ( 24Mbps min)..." Details like this are used to score the design and the designer will attempt to reach all the requirements. If they can't be met, the project need to be redefined.
2) A passive survey is made on site and is an investigative survey. You use a passive survey to identify and locate all access points that transmit into the area (including from neighbouring areas, ie offices above, building next door etc). You scan all channels and also look for interferers, such as microwaves, video cameras, radar, anything non wifi that could interfere with your network. As it's a passive survey, you aren't connected to the network, you are just listening to what we call "management" traffic, and these are transmitted at the lowest data rate the access points support.
3) An active survey is used when you connect to a specific SSID or a specific access point. You associate to the access point and send small data frames. These frames are sent at the best data rate available, so an active survey will give you an idea of the data rates used in specific locations. An active survey is performed for two reasons. First is when a site has no wifi. By placing an access point and performing an active survey you can work out where the signal boundaries are and therefore where to place the next access point. In these circumstances, you would usually be following the predictive design plan, confirming the predictive findings and tweaking the positioning and power settings according to the on site results. The second reason for performing an active survey is to analyse your existing network. An active survey will connect you to the network the same way as a client device. You can see data rates, signal to noise ratio, co-channel interference and many other useful pieces of data. You can use this information to help you decide if you need to play with power settings, antenna placement, and so on.
4) An active iPerf survey uses the iPerf utility to conduct a configurable throughput test. You would use this kind of survey to test a number of things, mainly, data rate, retry rate, loss rate and roaming performance. If you aren't getting the results you expect, you will see this clearly marked on a the plan, then you need to find out why. Alternatively, if all is well then this survey is used a close out report as the project is closed and signed off.
Mainly, wifi projects run into trouble as they aren't properly understood from the outset. The longer a project goes on for, the harder it is to affect the outcome. If you, and the people installing the network, don't know enough about wifi you will design faults in to the network. Beware of equipment vendors who have done a one-day course in order to sell the equipment - they will encourage you to overspend on their solution, rather than use an analytical approach to plan properly, reduce expense and select other vendors that may have a better hardware offering. It's only by truly understanding your requirements and following a proper design and install approach that you will have a good network that will provide your needs for the next 3 - 5 years.
CompTIA project+ Project management certification, CompTIA Project+ certification
CWNP: Certified Wireless Design Professional http://www.cwnp.com/certifications/
AirMagnet: WLAN Design and Analysis - Wireless Network Design and Analysis | Fluke Networks
Last edited by neilmac; 8th September 2013 at 05:43 PM.
3 Thanks to neilmac:
buzzard (17th October 2013), pcstru (8th September 2013), plexer (8th September 2013)
9th September 2013, 07:06 AM #13
Thank you. The CWNP does not churn out marketing drones who blather on about how their access point can defy the laws of physics and cover more area or service more clients because of their magic RF algorithm. RF is RF and you have to plan for it, and this means paying for a proper survey both pre-install and post-install. Quit being so cheap You know who you are.
Originally Posted by neilmac
9th September 2013, 10:37 AM #14
That's a good point.
I am going to recount a quick true story that illustrates where I think the disconnects are.
I learnt of a school installation last week that was having problems.
The school was one of many that had were serviced by a company with an ongoing contract for cabling. When they decided they wanted wifi, they fell back to the cabling company (preferred supplier, and hey, it's a cable and we put access points on cables...). The cable company had no-one who knew anything about WiFi so they sent a junior staff member on a one-day vendor course. Now, this junior staff member can now pass himself off as an installation engineer for the vendor.
The installation is made and now doesn't work. The cable company called for help to a friend of mine, who works for a small IT company as a Windows Server IT support engineer, to help with the WiFi, He doesn't know anything about wifi so he called me for a quick chat about how to fix it.
So, how did we end up in this mess ?
1) The person running the project didn't know HOW to run a project.
2) The requirements were not defined or understood by anybody.
3) The responsibility for delivering a critical WiFi installation was given, not to a WiFi company, but a cabling company. (They are not the same thing...)
4) The cabling company had a one day vendor course to turn them into an expert. Vendor training is not WiFi training. All as you learn on a vendor course is how to sell your product. Advanced vendor training is about configuring the equipment. It's not about designing a network. If you run a project and you go straight to a reseller you are going to get that reseller's solution, and you may be getting the sum total of knowledge of a junior cabling technician who drew the short straw and had to sit in on a one day lecture so the company could qualify to resell the kit. Vendor training is not WiFi training. It's not in the interestes of these companies to sell a solution, they sell product.
5) No checks were made on the process, certification or qualification of the designer / installer. A certified person has studied and passed a test. A qualified person has lots of experience. The best is someone who has both. Time and time again, I come across installations made by companies who should not be getting the contract as they don't know what they are doing. In this case, the cable company had someone walk around, point at the ceilings and say "there" every so often. Apparently, that looked professional enough so it was accepted. A good company will spend time doing a design for you. You may be charged for that - why ? Because if you get it for free you use it to go to different suppliers and beat down prices. Also, if the designer is like me, I don't sell hardware, so I can't absorb the cost into the kit resale. But, that's a good thing, because my design is the best for you, not for my reseller target.
So, back to the school - the network does not work, yet no-one wants to know about the right solution. The shout for help went out, the cable company couldn't fix it as they were at the limit of their knowledge. (They made it tidy profit, though). My friend got asked to help, also not a WiFi guy. He doesn't know why he was asked for help, he is a Windows guy, so he tried to involve me. Good call, I have the CWNE certification, teach professional courses in design and analysis all over the world, help small to medium sized enterprises develop strategy for WiFi, of course I can help. I also have software worth 5 figures to fall back on. I know I can fix this network.
However, this IS my day job, so I would expect to charge a fee for this. But now there is no budget/method/process that will allow for funds to be available, so my offer of help was declined (if you are asking, my fee would have been 300 pounds, favour to my friend. 300 pounds is "way too much", apparently). So the network stays broken.
Moral of the story: If you want a professionally installed network, start with yourself and learn how to define and run a project. Use companies with trained, certified engineers and the tools to do the job. If you miss either of these, and your network is still problematic, call a professional to help sort it out. We don't bite, and we don't charge unreasonably (contrary to popular myth).
Last edited by neilmac; 9th September 2013 at 10:42 AM.
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