neilmac

Wow, I stand corrected. That's a great find. I still see "b" devices in industrial settings, but I haven't seen these before, and definitely not anything like this is a school. I need to get me on of these for training classes. This is exactly the thing that will significantly affect throughput. These will definitely be a problem. Any one of these connected is going to put a major portion of the network into protected mode. I couldn't find a certificate for them from the WiFi alliance, so there's no way to know if they even operate correctly. The saving grace is that they probably transmit really low power levels, but the damage is the same as the protection triggers when it associates to an access point. If you must have these, then get as many devices as you can into 5 GHz, and reduce power in 2.4 GHZ, turn off the 2.4 radios on access points where you don't need it. Wow... If you rely on good throughput for your network, with these dotted around, you're gonna have a bad time.

I haven't seen a "b" only capable device in a long time, so I doubt anyone is really using them. It's just not relevant any more. Does anyone have anything like that ? I would be uber surprised.

Much easier, just tell me the make/model of devices you use and I can show you.

Sorry, you're right - I didn't mean to be so short but I am struggling for time, I'm in the middle of something. By asking about devices, if you cam back with an answer then I would have been able to answer by referring to your device, it would have made the explanation easier. Basically, you won't find client devices that support 40MHz in 2.4 GHz, and many access points either won't support 40 MHz or won't enable it if they detect ANY non 40 MHz transmissions. It's all to do with co-existance, and the realisation that if you put up 40MHz you will probably interfere with someone, somewhere, so 40 MHz is just not deployable in 2.4 GHz. If you want 40 MHz you MUSt go to 5 GHz. You will see the same thing with 802.11ac, people rushing to deploy it without ANY of their client devices able to make use of it. If Chazzy2501 tells me what devices he used in his test, I can point out why it would not have been 40MHz - not to embarrass him, but to show how to find these things for your own devices. Or, Psydii, tell me what you commonly deploy (Ap model and client type) and I will explain for your devices. NM

Yep. Find me any client device that's capable of 40 Mhz in 2.4 GHz. Tell me what devices you used in your test and I will reply with an explanation.

You don't get 40 MHz in 2.4 GHz. Tell me what device you were testing with ? There's a lot of misconceptions about what 802.11n offers, in 2.4GHz it's all about reliability.

timtom - You don't have any devices that are capable of ONLY 802.11b, so protection is not likely to be the issue. (There are circumstances where protection may be triggered - neighbour AP's, rogue wifi enabled printers, etc, however I would think unlikely here). What you described can have many possible causes. If it's a serious problem you need to have someone run spectrum analysis and a frame capture and look for: 1) Layer 1 problems - non wifi interference, adjacent channel overlap, transmit power 2) Layer 2 problems - co-channel interference, neighbour access points. To rule out protection, look for a beacon frame from your AP and see if the USE_PROTECTION bit is set to 1 and if the NON_ERP_PRESENT bit is also set to 1. Look specifically for the device data rates in use compared to the expected rates for the given signal to noise ratio. Get a value for retry rates and CRC errors. Capture the conversation of a specific problematic device, and if possible look for the point that triggers the device to try to roam. Only then can you begin to think about what to do to put things right. If I had to guess I would say that you probably have too much power in the system. I don't know how many access points you have, but one starting point would be to reduce the transmit power. I would also be curious to see how you have the AP's deployed. One point, on you use of frequencies, the access points should automatically steer devices on to 5 Ghz that are dual band capable. You should plan your deployment from 5GHz perspective, then only activate 2.4GHz on the access points you need to have on to support the number of 2.4 GHz devices you have. Again, if this is an important network, and you are having these kind of problems, then pay to get a certified WiFi guy with the correct tools to make an analysis. He should be able to narrow down the problem in half a day if he is any good. Before engaging someone, ask them for their wifi certifications/qualifications and what tools they use. Ask to see examples of previous jobs. I hope this helps you to get a solution. NM

Well, it's irrelevant because OP does not have any "B" only devices, so protection is not the issue. I am happy to get into the technical side any time you want, but you are wrong on so many levels I wouldn't be able to easily answer you. I would need to run a couple of days of classes to even scratch the surface. FWIW, disabling "B" rates is a critical mistake. If you want to stop "B" devices from associating, then make 6Mbps a mandatory rate. Honestly, it's nothing personal, you just don't understand wifi well enough, though you are clearly making an effort to learn. You shouldn't take offence, but the harsh reality is that you are giving out BAD advice from an untrained viewpoint. Your advice is manifestly wrong, I am afraid to say, and I call you out not to embarrass you, but to prevent the OP from making a bad situation worse. Until you know better, please don't give out this kind of advice. Keep going, by my estimation it will take you about 2 years of full time WiFi design and analysis to truly understand how these things play out in real networks. That's not a reflection on you - it took me 6 years to get my CWNE, this is working as a full time WiFi engineer and trainer. I also write courseware for AirMagnet and teach advanced analysis classes. What you're referring to is probably the most difficult things to troubleshoot and diagnose, many many senior engineers have problems understanding the big picture. NM

It depends on how serious you are about the reason for the survey and the information you need to collect. If you start with asking those questions first then decide on the survey software to meet your needs. If you need a proper survey done then you should call someone in who is trained and knows how to use survey software. What's your situation ? NM

Good spot ! Naturally, I meant a professional WiFi person / company :>)

Sigh.... 1) Start with your requirements, work out what the ipads are capable of and what you want to do with them. Browsing ? Streaming ? How many simultaneously? Will your requirements today change in 1 yr, 3yrs, 5 yrs ? How will you handle security ? 2) Match those requirements to the capabilities of an access point. 3) Rule out vendors that do not match your requirements. Remember, budget is a constraint so get a decision on how much money you will have available to have a finished set up. Don't forget to calculate day 1 costs, then 3 year cost then 5 year cost (in case you get a licensed model). Do you have capex or opex choices ? (Buying or leasing). 4) Select the vendor from those that do match your requirements, and buy the best that your budget will allow. Metrics to judge "best" are not only performance. Vendor choice should NEVER be the first question. PS - this sounds like a small project but as it's for a school, it could have the potential to get bigger. Any project in education deserves to be treated as important and approached with the same attention to detail as bigger projects. Ask yourself if you really know enough about wifi to make an educated decision. If not seek professional help, but make sure the person advising you does know what they are doing.

What is the retry rate and the crc error rate ? What data rate are the frames being transmitted at ? How many other devices are visible and how many more are visible and active as you do your test ?

MIMO was introduced with 802.11n. A spatial stream is a transmission from a single antenna, 2 spatial streams = 2 transmissions. So true MIMO means you have to have 2 antennas/radios at the transmitter and receiver. Many client devices only support 1 spatial stream, and in 2.4 GHZ there are no 40MHz channels, so the BEST data rate available is 72 Mbps, which is a long way from the 300 mbps advertised. Nm

OK, quick answer - OFDM (Orthogonal Frequency Division Multiplexing) is the modulation method used in 802.11a, 802.11g, 802.11n and 802.11ac. OFDM uses distinct sub carriers within a channel, each subcarrier will transmit a wave that has an amplitude and phase difference when compared to a pilot wave. The difference denotes a bit value, the meaning of which is derived from the specific coding and error rate. It's an advanced topic,covered in depth in the advanced CWNP classes (CWAP/CWDP). You don't need to know how OFDM is technically performed, more important is to understand why a specific modulation rate is in use when you would expect a different modulation. The antenna is the means by which a radio creates an energy wave in the air. Antennas can be internal or external. Antennas are used to shape the energy of the wave. The CWNA class has a whole section dedicated to antenna theory, and it's important to understand the characteristics of the antenna pattern when planning a network. When it comes to spatial streams, the first number usually denotes transmit radios or antennas, and the second, receive radios or antennas. So, a 2 x 3 would be transmit on 2 simultaneously and receive on 3, for example. I thought about making videos but decided against it. For a living I teach WiFi classes and help end users understand wifi planning and deployment. If I were to produce videos, it would really be to help promote my work. With all due respect to everyone here, I don't think there is any interest in training videos. Most people are happy just to get by without professional level consultancy, which is fine. Education has pretty tight budgets and the decision makers usually wear many hats and have lots of conflicting responsibilities, usually being knowledgeable on WiFi is not a high priority. If you personally really want to learn the best place to start is by studying, and possible taking a class. I recommend the CWNP Certified Wireless Technology Specialist (CWTS) track, it's a great course for beginners. I am happy instead to step back and just help out when people would like to understand a technical point a bit better. NM

What was the question again ?