现代化教室Wi-Fi的最终指南

New digital learning tools boost student success and empower the next-generation of teachers. But they are only as good as the Wi-Fi infrastructure they run on.

Aruba recently hosted a webinar with industry expert Keith Parsons who explains how to create the perfect Wi-Fi network for one-to-one learning, how many Wi-Fi access points you need in a classroom, and how to choose the right Wi-Fi technologies to meet your needs.

CWNE＃3 Wireless LAN专业人士董事总经理Keith Parsons是一位有才华的主持人，拥有丰富的经验设计和安装2,000多个K-12教室的Wi-Fi。

View the webinar slides and Q&A below. For detailed explanation, check out theon-demand webinar。

Q: As a shared resource, slow devices take proportionately more time to send/receive data than a faster device. Then should we be creating a separate SSID for very slow devices (like iPhones, etc.)??

在任何给定频率上，慢速设备的可用带宽量确实占据了比例更高。将它们移至单独的SSID绝对没有任何作用。同一频率上的所有SSID共享有限的时间资源。SSID在通话时间内没有任何区分。尽管您可以将SSID绑在VLAN上，但它们根本无法像开关上的VLAN一样工作。

Q: Any recommendations on SSID's for K-12 education. One vs. many?

通常的建议越越越好。每次SSID都从您的可用容量中脱颖而出。仅在有不同的身份验证类型时尝试使用新的SSID。您还可以根据RADIUS属性进行动态VLAN分配，以节省更多的SSID。

Q: Any recommendation on design software for Wireless LAN Access Point layouts?

• AirMagnet Survey Pro
• Ekahaus ESS
• Tamosoft Tamograph

Q: By "4 radio coverage", do you mean 2 SSID

否。我的意思是，有两个收音机覆盖2.4GHz的区域，另外两个收音机覆盖了5GHz的同一区域。基本上，涵盖-67DBM每个区域的两个访问点将满足您的大多数容量要求。即使这样，您也很可能不得不关闭2.4GHz收音机中的大部分，以减少共通道干扰。

Q: Can you recommend tools for CCI detection?

Any client device that can show you Access Points and their BSSID's (MAC Addresses) and Signal Strength will work. (inSSIDer app or the Aruba Utilities Apps as well as most client device software)

What you are looking for is two or more access points on the same channel with signal strengths (RSSI) above -85dBm.

Q: Can you set APs to block sites like YouTube for a group of users?

Yes – it depends on your vendor of choice. But this capability is built in to enterprise-class vendor products.

问:你有没有特别推荐的wi - fi映射/ testing device and/or software?

I like a Fluke AirCheck for lot of my on-site testing. For validation surveys you can try:

• Fluke AirMagnet Survey Pro
• Ekahau ESS
• Tamosoft Tamograph

Q: Do you recommend turning off the "B" channel or 2.4 altogether?

Definitely turn off the 802.11b data rates. (1, 2, 5.5 and 11Mbps). You'll probably still need to leave on 2.4GHz for legacy clients you are emotionally tied to. (see Sunk Cost Fallacy). But most likely you'll have to turn off many of the 2.4GHz radios in order to reduce CCI to a workable level.

Q: Does an Aruba 3400 controller handle frequency reuse?

It doesn't. Not part of a controller's function. The Auto-RF algorithms will try to lower Tx power, but don't have the ability currently to totally turn off radios when someone puts in too many access points.

Q: Does creating a "Guest Network" on a separate SSID alleviate the problem of older devices slowing down my Wi-Fi?

SSID's in Wi-Fi do NOT change collision domains whatsoever. (they also don't change Broadcast domains either) – on the Wireless side of an AP, all transmission share the same amount of available bandwidth – changing SSIDs does nothing to fix a slower device, or CCI.

Q: Doesn't Aruba's "mesh" and "ARM" technology mitigate CCI for AP's that are densely deployed?

两者都不。网格用无线上行链路替换AP的有线回程，并通过有线连接替换另一个AP。

ARM试图调整功率和通道以最大程度地减少CCI - 但由于工程较差的解决方案而无法克服太多AP的情况。

问：如果一所学校的设计具有5GHz的访问点，则需要重新设计访问点的访问点和位置时，需要重新设计访问点的位置？

I suggest each time you do an infrastructure upgrade you return back and do the Define, Design, Deploy and Validate process once again. You may have in your Define stage a constraint about where current AP cable drops are – and this can be used as part of the Design process.

Q: 802.11ac future specs?

Right now the 802.11ac specs are completed and you can read them on the IEEE website. As for Wave 2 – most of those are also available but as working group documentation.

Q: Cell -db overlap setting on our survey tools?

Try reading the 'Fallacy of Channel Overlap' white paper on my website:http://www.wlanpros.com/wp-content/uploads/2010/06/The-fallacy-of-channel-overlap1.pdf

Q: Should schools be running 2 x Cat6a drops to classrooms now if they have the funds? (refresh cycle giving us this hint)

A lot of the costs of running cable is in the labor. Adding an extra strand of cable to each AP drop won't cost very much additional… but might pay off handsomely in the future. It is a prudent thing to do if you are refreshing your cable plant.

问：我们通常会过滤-76DB的单元重叠的调查，作为“漫游”点。这是一个好计划吗？

If I understand your statement – I would strongly disagree. Setting your cell overlap during a survey at -67Bm means you never walk and collect data in the areas outside -67dBm… this is where most, if not all, of your CCI problems will exist. So if you don't collect data there, you'll have an overly optimistic view of your WLAN. Then end up with CCI issues and capacity reductions because you never measured it.

Q: How do I figure out if I should use a 20 MHz channel or 40 MHz channel?

始终在2.4GHz中使用20MHz。我也喜欢在5GHz中使用20MHz。它允许两倍的频道，从而更容易重复使用。在您的大多数客户支持40MHz频道并支持DFS频道之前，也要在5GHz中坚持20MHz。

Q: How do we know we've found a vendor that will help us engineer the best solution?

By asking lots of questions, ask for references, and be comfortable with their ENGINEERING skills, not just their marketing techniques. Ask about their engineering design processes – and confirm they are doing a good job of working with you to define your detailed requirements, and using appropriate engineering design techniques and tools, and then always ask for a post-installation validation survey.

Q: How do you match the capability of your Wi-Fi to the broadband capability the telco is trying to sell? In other words, does moving from 20 Mbps symmetrical to 100 Mbps.

Two different, yet related items. You might have a fantastic Wi-Fi network, with a terrible WAN connection. That would look like a wireless problem to your staff and students. Having a fast Internet pipe, and terrible Wi-Fi would exhibit the same complaints. But the solutions are different.

Q: How long will it be when 802.11ac Wi-Fi standard going to be found in over 50% of the devices?

Already all Smartphones available today and in the future have 802.11 chips on board. You can help this buy purchasing exclusively only gear with 802.11ac on board. BYOD will probably also all be 802.11ac capable from now on.

问：与控制器自动完成多少无线电计划需要手动完成多少？

RF计划在控制器中根本没有完成。只有TX功率和频道选择。实际放置访问点和使用墙来减轻信号以帮助频率重复使用的方法是物理世界问题。

Q: I work in a school district that is doing a 1:1 distribution of iPads. We have run into issues with excessive amounts of bonjour traffic. What are your suggestions on how to manage that?

首先，请确保您的所有Apple TV均已接线，并且不会使用Wi-Fi进行网络访问。这将对您的无线网络吞吐量负载有很大帮助。接下来 - 使用您的供应商解决方案进行Bonjour“网关”服务，以保持Bonjour的广播流量。

Q: Is a spectrum analyzer worth the investment?

Yes – today you can get SpecAns for $500 to $4000 in the Professional ranges designed specifically for Wireless LAN usage. They are very helpful in seeing the raw ambient RF interfering devices.

问：附近AP的前端重载是否是关注渠道的？超越相邻的通道干扰？这个问题可能归结为“过滤器有多好？”

You should never place adjacent Access Points within a meter of each other. Their front end RF processers are not designed to handle the extremely high power levels within the 1 meter range. Also – you should design your channel plans to NOT have adjacent channel interference in the first place.

Q: With BYOD and 1-1 this means 18 to 30 devices per room and so if there is a limit to the number of devices using an AP - coverage and Density are two different things... right?

覆盖范围容易的密度更加困难。非常困难的是摆脱频率重复使用中的共通道干扰和设计。这是真正获得我们所谈论客户级别所需的额外能力的唯一方法。

Q: It's easy to say don't get 2.4 Ghz devices on your network. Unfortunately, many laptop and computer manufacturers still are making 2.4 GHz only devices. This basically means that the computer and hardware manufacturers need to also get on board.

But you don't have to buy them! They produce only what people ask for and purchase. You can ask your purchasing department to "Never buy 2.4GHz-only devices again."

问：由于这仍然是一个问题，您仍然可以使其与5和2.4一起使用吗？

Usually you'll end up with a 5GHz plan that works well – and then you'll be turning off ½ or more of the 2.4GHz radios.

Q: Max throughput for 802.11ac in the future? Any guesses? We are running two cables to each AP. Waste of resources?

Nope – I think running two cables to each AP location is a great use of resources. Max throughput… hmmm… perhaps very close to the gig Ethernet of today – but also could be higher. Thus bringing along a spare Ethernet drop might be needed.

Q: On average, how often should APs be replaced?

I tell my customers to think 2-3 years less than your wired infrastructure. Perhaps instead of a wired infrastructure update every 5-7 years – think and plan for Wi-Fi in the 3-5 year range.

问：计划阶段？可以设计客户灵活性吗？今天是iPads明天的Chromebook或Win8.1平板电脑或产品X。我们如何解释未知的未来。

这就是为什么您在定义阶段花费大量时间的原因。不仅收集了今天的要求，而且还对未来进行有根据的猜测。

Q: Refresh cycle? Is there a need to redesign for all hardware refreshes? Or only if bigger changes? Example, redesign from 802.11a to 902.11ac?

我建议您进行一个完整的过程，包括每次更改基础基础架构时定义，设计，部署和验证。（从.11n到.11ac）您可以通过建议仅在必要时移动AP电缆下降来添加设计阶段的约束。

Q: So let's say you're one of those schools with Aruba 225's in every classroom, and the performance isn't sub par. What do you do now? Is a spectrum analyzer the answer?

You might not know if your performance is sub-par. The downside of too much co-channel interference doesn't raise its ugly head until under heavy loads. You perhaps haven't stressed your Wireless LAN to that point yet. Nothing at all wrong with having One AP per Classroom… IF that is the result of properly engineering your solution to meet your requirements. I have just found many don't do post-install validation surveys, never measure CCI, and don't load test. Spectrum Analyzers won't do anything if you have too many AP's all sharing the same frequencies. The answer is to turn off many of your 2.4GHz radios, and perhaps even some of the 5GHz radios if you are measuring co-channel interference there as well.

问：应多久审查一次安装解决方案？

At least every time there is a significant change in the infrastructure. Changing from 802.11a to 802.11ac for example. Or when you have very large changes in client devices. Like adding 1:1 iPads for all students.

Q: How do you feel about using the UNII (2) channels in regards to channels getting shifted due to radar.

我喜欢使用DFS频道。它使得频率重复使用变得容易得多。但是您必须小心，并确认目标客户端设备可以看到和使用这些渠道。如果没有，您将为这些设备设计覆盖孔。在这种情况下，仅回到5GHz设备可以使用的通道。

Q: Understanding that it not a good design strategy is 1 AP to 1 Classroom ever the right solution?

Of course it is! If after defining your requirements, the design calls for that density of access points, and you do a post-install validation that confirms you don't have co-channel interference – then of course you have a design that has been engineered to meet all your requirements. If, on the other hand, you don't do a validation survey, don't measure where you have CCI. Then you might have extra AP's that aren't adding any additional capacity. That would mean you spent more than you needed to.

Q: What frequency scanning tools would you suggest to best do the "first glance" to get an idea of how to design/improve a wireless installation?

The fastest, quickest way is to use a validation survey tool to confirm where and what your RF is doing in your facility. You can also use this to prove and verify if you are meeting your design goals and see where you may or may not have CCI issues.

Q: What the most practical way to eliminate CCI? Or the proper term CCC.

Use properly engineered designs that allow for frequency reuse rather than cause CCC. Usually it involves doing an on-site post-validation survey, reviewing the results, and then turning off radios – moving AP's and perhaps even adding directional antennas where appropriate.

Q: Where can I learn more about CCI?

我总是建议从一开始，例如Coleman和Westcott的CWNA学习指南。http://www.amazon.com/CWNA-Certified-Wireless-Administrator-Official/dp/1118893700/ref=sr_1_1?ie=UTF8&qsrc=1416359756&sr=8-1&keywords=cwna+study+guide&pebp=1416359757905

问：借助如此复杂的WLAN工程设计，您如何为客户提供可预测的价格报价？

通过正确进行工程，它不仅仅是一个“预测”，而且您可以非常接近实际定价。RFP应首先包括工程，以便知道RFP的其余部分应包括什么。

问:你会建议使用汽车频道希利ction feature of access points and letting them decide their own wireless channels vs manually picking the channels?

这是一个规模问题。在较小的设施我莱克阀门e to do the channel plans manually so I can control exactly what is going on. But as you scale to bigger facilities, this gets a bit cumbersome and time intensive. So the vendors have produced algorithm-based wizards that help your access points move to channels and stay out of each other's coverage zones as much as possible. I still like reviewing manually what the controller does. Any post-validation survey can be used to see whether or not it met the RF requirements. But remember, algorithms can only work with in the installed AP's and can't turn off individual radios to reduce CCI.