Fundementals

When is a wireless issue not a “wireless” issue?

If you're into wireless and aren't following Lee Badman's (@WiredNot) #WIFIQ (Wi-Fi Question of the Day) hashtag on Twitter, you really should. This particular question is insightful, because it emphasizes one fact about WLANs - that it's more than just the wireless. There are other very important things that need to be performing well to have a well performing WLAN. The question asks what issues do you typically run into when troubleshooting wireless networks that ARE NOT necessarily wireless issues. The answers were varied and insightful as they are for all the #WIFIQs.

There are many "wireless", or 802.11 based specifics that can affect wireless performance. A short list would be:
 

  • Client can't associate to an SSID because a particular feature (like 802.11r/k/v) is enabled and the client driver does not like that - so it refuses to connect.

  • Clients can't connect because you have WPA2 enabled, but not WPA (the older client only support TKIP).

  • You expect a certain connection speed, but the WLAN is configured for 20MHz channels, instead of 40, or 80.

  • Clients are having connectivity and throughput issues because channel reuse is poor (maybe you're using 80MHz channels) and co-channel interference is exacerbated.


These things are clearly 802.11 related and can rightly be considered "wireless" issues. But, what about the guest user that is connected to the WLAN, but can't get an IP address? Or, the client that connects to guest network and never gets the promised captive portal? These client have associated to the AP, but are unable to get network access. And of course: user complains that they enter their credentials, and they just can't connect. Are these wireless problems?

There could be several reasons why the above mentioned clients are be having these issues, and none of them are "wireless". For example, the IP address issue could simply be a depleted subnet. Many guest networks use long lease times (read: default) and don't realize a client connected several days ago could still have an address reservation that has not expired. Even with a small number of clients you could exhaust the address pool in a few days, or weeks.

Or maybe to was incorrectly configured switch ports. If that AP is placing client in specific VLANs, and those VLANs are not tagged on the port, that would also cause our "no DHCP" issue.

The captive portal could be several things: no DNS properly configured, no IP on the guest VLAN interface, the old "DHCP exhaustion" issue, etc. These are all technically not wireless issues, but can absolutely affect, and be detrimental to your wireless clients.

And the password/credential issue? The most obvious one is they forgot, or incorrectly entered the password, or login credentials. Another possibility is their account was deleted, locked, or de-actiavted, so RADIUS authentication is failing. OR, someone fat-fingered the RADIUS shared secret when setting up the server, and RADIUS is ignoring the request.

So, the moral of this story is that you need to be aware that there is more to your wireless network than wireless. You need to understand DHCP, addressing schemes, PoE, cable types, firewall rules, RADIUS servers, etc. You may not have responsibility, or access to do anything about them, but you should be able to diagnose, and troubleshoot these issues and get folks involved that can help.

Regardless, when someone says, "the Wi-Fi don't work!", and it's not a "wireless" issue - it doesn't matter. The user doesn't know, or care, they just want it fixed. Being able to quickly determine where the issue is originating will go a long way in making your users happy.

As Jake Snyder (CWNE #161) pointed out:

First Thing's First: Requirements

*Originally published on Eddie's BadFi.com.

I was at a meeting today with a large Mechanical/Electrical Engineering firm who was in need of some wireless expertise. More, and more they are getting asked to include wireless "designs" for building projects and are finding (as many do) that it's not as simple as it seems.

The discussion took many turns, but often came back to something like, "So, if we have a school with say 35 students per classroom how many APs do we need?" My answer would be, "it depends." What does it depend on? Their requirements.

How many clients (not users, but devices)? What type of clients (1 stream, 2 stream, 3 stream)? What applications will they be using (e-mail & web, video streaming vs. YouTube caching, voice, etc) What are the bandwidth requirements for their State testing? And more.

The point was - just like they could not just "make up" an electrical, or engineering design out of the blue (How many people need to be in the space? What's the total power consumption required? Do we need HVAC in all locations?) - one could not just "make up" a WLAN "design" (Well, one could, but then you get what you get). That made total sense to them which was good.

I love explaining how wireless works and seeing their eyes light up. I love how it makes sense to them when I explain why they're not going to see 1.3GBs throughput, or adding more APs is not a default answer to a problem, how coverage & capacity are different things, how having a bunch of low-end single stream devices is not as efficient as have a bunch of 2, or 3 stream devices, etc.

The FIRST step to wireless network design, and the best way to avoid the BAD-FI, is to determine the REQUIREMENTS and EXPECTATIONS of the customer. Here just a few of things you should consider:

  • How many clients will be using the WLAN?

  • What are the types/capabilities of the devices? (# of streams, 5GHz support, DFS support, 802.11r/k/v support, etc.)

  • What applications will be using the WLAN and what are the requirements of those applications?

  • Is there a budget for the project?

  • Are there accurate, scale floor plans available?

  • What security and authentication types are you looking to support?

  • What the total bandwidth coming into your facility?

  • What is the time-frame for the project?

  • Aesthetics: Are external antennas ok? Do LEDs need to be off Should APs be inconspicuous?

  • Cable lengths: where are/is the MDF/IDFs located? More than 300ft from the APs?

These are a few off the top of my head, but you get the gist. DEFINE your requirements and expectations BEFORE you design a solution.

Anything else and you're just guessing.

802.11ac "Waves" 1 & 2: A Reality Check

801.11ac (the so-called "Wave 1") arrived with much fanfare early last year, and despite the hype, it did not saturate our wired networks. Now "Wave 2" has arrived and the pundits are out again saying your wired network needs to be upgraded to 2.5, or 5 Gig Ethernet depending on whose technology they're pushing.

The reality is whether you're deploying "Wave 1", or "Wave 2" (don't get me started on the "Wave" marketing) it's unlikely that you will max-out your 1 Gig ports. Unless you have only one, or two APs, and are bittorrenting Avatar, the chances that you need to run out and upgrade all your switching infrastructure (or run two cables to every AP) are small for the foreseeable future. 

Here are some of the reasons why:

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1. WIRELESS IS A HALF-DUPLEX, SHARED MEDIUM

So, even if you were the only client on that brand-new 802.11ac access point the best you could possibly achieve is around 60+% of the max connection speed - maybe. It's important to understand is that 802.11 is a shared medium - only one device can transmit at a timeThat means that if multiple clients are connected to an AP, on the same channel, individual throughput will be further reduced as more users try to access the medium. The key thing to remember here is that the bandwidth is shared.

 

2. THEORETICAL MAXIMUM SPEEDS REQUIRE LARGE CHANNELS, CLOSE PROXIMITY TO THE AP, AND LINE-OF-SIGHT

There are only three non-overlapping 80MHz channels in 5GHz (five if you can use DFS channels). Three/Five channels is great in a small environment with few APs, but in an enterprise environment with tens, hundreds, or thousands of APs - 80MHz is not an option because of co-channel interference, due to so many APs, and so few channels being re-used. "Wave 2" brings us two 160MHz channels which, if you do the math, is less...

* Screen cap from the greatest show ever, "Firefly".

* Screen cap from the greatest show ever, "Firefly".

So, at best you're using 40MHz channels which has effectively brought your max throughput down half again. If you're in a high-density (HD) environment like a Higher-Ed campus, or large event space, where you may have hundreds to thousands of APs, you're more than likely going to be using 20MHz channels, thus halving you throughput yet again. So, when you are designing for capacity you will be using smaller channels to increase that capacity at the expense of the maximum possible throughput of your shiny 802.11ac APs.

Lastly, those fancy-pants, "hyper-speeds" that are all the rage? Well, what they don't tell you in the marketing brochure is those speeds are only attainable when you are very close (less than 25-30ft) and have line-of-sight, with no obstructions, or interference, or other clients, on the AP. You need extremely high SNR (Signal-To-Noise-Ratio) to reach the unicorn-like 256-QAM that is required to get there. Reality is in most environments there are walls, desks, bookshelves, people, kitchens, and more, all between the client and the APs.

 

3. THE MAJORITY OF CLIENTS ARE NOT FULLY UTILIZING THEIR CONNECTIONS, OR THE CAPABILITIES OF THE AP.

Most wireless clients in enterprise, educational, or event environments are not streaming HD video, bittorrenting, or otherwise using as much bandwidth as they can. The majority are doing average things like web surfing, watching YouTube, e-mailing, accessing databases, Tweeting, Facebooking, Instagraming, listening to music, etc. - things that don't require extremely high, or even consistent bandwidth.

So, if you have 60-100 clients on an AP, many are likely just idley connected, and maybe a few are pushing serious bandwidth. If you look at statistics on your WLAN you will probably see that most users are not serious bandwidth hogs. Most likely your bandwidth bottleneck will happen on 1Gb uplinks between switches. This would be a good place to look to upgrade.

Also, there is wide disparity between clients. You may have a 3-Stream, 3-Radio, 802.11ac access point, but most smartphones are single-stream, or at best dual-stream. Even with laptops the MacBook Pro appears to be the only 3-Stream device on the market (for now). The fact is most devices (typically mobile devices) aren't even CAPABLE of matching the APs capabilities. So, those gigabit speeds you've been reading about? Ain't gonna happen.

¯\_(ツ)_/¯

Here's a good video that discusses client capabilities:

4. MU-MIMO IS NOT THE BANDWIDTH HOG YOU MAY HAVE READ IT IS. 

Multi-User MIMO (Multiple-Input-Multiple-Output), is the latest feature added to 802.11ac "Wave 2" along with160MHz channels. Unlike what many have stated - it is NOT wireless switching. Also, as discussed previously, Wi-Fi is a half-duplex medium. MU-MIMO does not change that. The idea for MU-MIMO is to create efficiency by using as many spatial streams as possible - whether that's one 3-Stream device, or three Single-Stream devices - and it's only supported for downstream transmissions from the AP to the client. Also, the clients need to support MU-MIMO as well as the AP.

The benefits of MU-MIMO are that an AP can transmit to multiple clients at once (so far, three is the max on the market), but the APs cannot receive from multiple clients. What this actually does is increase the EFFICIENCY on the downlink, but not necessarily THROUGHPUT.

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The takeaway here is that all the marketing on 802.11ac (Waves 1 and 2) boast of the amazing speeds that can be achieved (It's right there on the box!). But, what they don't tell you is that in reality those speeds are only attainable when you use 80/160MHz channels, are very close (less than 25-30ft) to the AP, line-of-sight, with no obstructions, interference, or other clients, on the AP. The reality is, in most environments, these are not options for the majority of clients, or the infrastructure itself.

So, remember, just because you CAN have a throughout of say, 800+ Mbps, it doesn't mean you will. More likely, you won't. So, don't succumb to the hype. The Tsunami of "Wave 2" in all in the marketing, not so much the reality.

802.11AC Wave 2 Technology Deep Dive from Aruba Atmosphere

No joke, when they say this is a "deep dive, they mean it. The video from this year's Aruba Networks Atmosphere Conference goes into the technical aspects of beam-forming in 802.11ac (Wave 2), MU-MIMO, and real world  throughput. Enjoy.

“Wave 2 data rates are insanely high, and they’re also farther from reality than ever before.” - Peter Lane

802.11ac Wave 2 technology deep dive and deployment recommendations - 802.11ac Wave 2 is right around the corner. Now's the time to prepare yourself and impress your colleagues with knowledge about multi-user MIMO, Wave 2's most sought-after capability. Our experts will share their planning recommendations so you'll know the perfect time to migrate to this new technology. We'll also give you an updated about the latest on mobile device support for the protocol.