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Showing posts from 2016

Spectrum Deception

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When using Wi-Fi spectrum analyzers, it's good to remember an old Russian proverb: Trust, but verify.

Recently, I was doing some work for a company that needs BYOD Wi-Fi at several office spaces in multi-tenant buildings (insert: lame excuse for not blogging more) and we ran into what seemed to be an interference problem.
Why did I think it was an interference problem? I had already completed the following checklist:
1. Cisco AP transmit power set to level 2 or 3 (that's 20 dBm to 17 dBm if you're using 3600/3700/3800 APs)? Check.
2. RRM channels 2, 3, 4, 5, 7, 8, 9 and 10 disabled? Check.
3. Excess 2.4 GHz radios disabled based on a survey done using an iPhone 4s? (What can I say? I'm a big softy for users who over-extend the life of their smartphones. They're the real MVPs of climate change.) Check.
4. OmniPeek captures, done from potential "neighbor" trouble areas, to look for channels occupied by large amounts of Retry frames? (This one has become nec…

802.11ac Wave 2 and You, Sponsored by Extreme Networks

The latest and greatest Wi-Fi standard is here (sort of).  802.11ac Wave 2 is now available in real-world Wi-Fi devices (maybe) and it's ready to supercharge your Wi-Fi performance (under some circumstances).  
Since 802.11ac Wave 2 is brand new (based on a three year-old standard), a lot of folks are looking for clear information on it.  The technology is great (or, maybe over-hyped), but how can an organization tell whether it's time to upgrade?
Luckily, Sniff Wi-Fi (in a post sponsored by Extreme Networks) has just the solution for you: an eBook!  "The 5 Essential Elements in the 802.11ac Wave 2 Business Case" covers 802.11ac Wave 2 technology, compares it to previous Wi-Fi technologies and identifies specific ways that 802.11ac Wave 2 can improve Wi-Fi performance for a number of vertical markets (no, really, it does).
When it comes to Wi-Fi deployment upgrades, I find that organizations fall into one of three groups: 
1) Organizations that keep their Wi-Fi infrastru…

Giving Voice to the (Apps That Should Be) Voice-Less

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Wi-Fi Calling is here, and that fact is causing concern for some Wi-Fi folks.  Wireless LANs that were initially installed as a value-add may be tasked with carrying mobile, high-quality, always-on voice traffic.

The 802.11 standard has had quality of service (QoS) protocols designed to accommodate voice since 2005, when the 802.11e amendment was approved.  That's good.  What's bad is that some voice applications are over-prioritizing their voice traffic, and it could lead to capacity limitations.

First, some background on Wi-Fi QoS:

The original 802.11 standard deigned that all Wi-Fi traffic would be created equally.  That is a GREAT thing for most Wi-Fi networks.  If some namby-pamby user whines to an admin, "Hey, why are you placing that AP in the OTHER room?  I want the AP closer to me," the admin can tell him (or her; women occasionally complain, too) "look, buck-o (or, buck-ess), Wi-Fi gives equal throughput to everyone who's connected.  You'll conn…

Go To Sleep, Go To Sleep, Go To Sleep Little iPhone

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In some circles, Apple Wi-Fi devices are knows to have problems with lost connections.  iPhones and iPads will unexpectedly miss incoming calls, have delays in receiving push notifications and even be forced to reauthenticate.

There is a solution to Apple devices' connection problems, and as with most "device problems", the fix resides on the infrastructure.  The DTIM setting needs to be increased.  (Apple recommends a setting of 3 or higher.)  Here's why:

Some Apple Wi-Fi connection problems stem from Apple iOS devices' use of 802.11 power management.  To understand what Apple devices are doing with power management, one must first understand how 802.11 power management works.

Let's start with unicast data.  The 802.11 standard allows devices' Wi-Fi radios to enter the Doze state in order to conserve battery life.  Wi-Fi radios in the Doze state are unable to receive data from the AP, so APs buffer all unicast data that has a destination MAC address of a…

802.11k: The Final Nail in the Coffin for RRM and ARM

Auto-channel selection protocols have been an increasingly common source of controversy for enterprise Wi-Fi administrators.  Aruba's ARM, Cisco's RRM, Ruckus's ChannelFly and Aerohive's ACSP all allow a centralize management entity -- either controller or software -- to automatically set the channels of access points (APs).  These protocols can be big time savers during the surveying and implementation stages, but also can cause big headaches once the Wi-Fi is up and running.  

The argument over whether to use auto-channel selection protocols may be coming to an end, however.  802.11k is becoming more widely supported in Wi-Fi devices, and when smartphones, tablets and other devices support 802.11k, the decision is a no-brainer: auto-channel should be avoided because it makes roaming worse.

To understand the impact that 802.11k (radio resource measurement) has on Wi-Fi devices, one first must understand a fundamental fact about Wi-Fi: devices control connections.  Smar…

Fixing President Obama's Wi-Fi

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Apparently Wi-Fi at the White House sucks!  A journalist asked me what might help it, so I figure I'll share my response:

Hi [Very Wise Journalist Who Reached Out To Me, Ben Miller, For Comment],

In some ways the White House is like any other large, multi-user space and in other ways it is very different.
Uncommon challenges at the White House are likely the result of security requirements and the need to maintain the historical integrity of the building.  The White House almost certainly has areas that are off-limits to AP installers and there may be limits on where cable drops can be made.
There is a distinct line between good and bad solutions when AP locations are restricted.  The goal of both solutions is to increase coverage to hard-to-reach areas.  The bad solution, which is likely happening at the White House, is to increase the transmit power of APs.  Increasing AP transmit power aids downlink data sent from an AP to a Wi-Fi device, but does nothing to improve the AP’s abi…

Crack the 40 (MHz Wide Channel) Open, Homie and Guzzle (the Bandwidth Available Over) It

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Everybody likes high Wi-Fi speeds.  Because high Wi-Fi speeds mean that the channel is being used more efficiently (often false).  An efficient channel means that there's more available throughput (only in sterile test environments) and more available throughput means that more users can be supported concurrently (completely wrong).

Unfortuantely, high Wi-Fi speeds sometimes (all the time) come at a cost.  To get higher Wi-Fi speeds, wider channels must be used (which makes the Wi-Fi suck).  Using wider channels means that fewer channels will be available (plus it ups minimum RSSI requirements, which just about guarantees a bad design).  It is therefore essential that wireless professionals analyze the environment and carefully choose whether to use 40 MHz or 80 MHz wide channels (or they could stop wasting everyone's time and just stick to 20 MHz channels).

But this blog post isn't about choosing the correct channel bandwidth (although it should be, because tons of Wi-Fi go…

Why You Should Stop Disabling Low Wi-Fi Rates, Illustrated

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The last Sniff Wi-Fi post; on why Wi-Fi professionals should stop disabling low data rates, was met some resistance.  Be it in the comments or on Twitter, several experienced Wi-Fi folks disagreed.

All arguments in favor of disabling low rates (the ones that were presented to me, at least) were refuted in the text of the Leave, Leave, Leave My Rates Alone blog post.  But text is a less accessible messaging method.  "A picture is worth a thousand words", as the old saying goes.

If pictures will get the message across better, then pictures are what I'll use.  What follows is an illustrated look at why disabling low data rates is a bad idea.

It's gauche to begin an illustrated work with text, but to understand the problem with disabling low Wi-Fi data rates one must first accept some facts about Wi-Fi devices (smartphones, laptops, etc.):

1. Wi-Fi devices -- not APs -- control associations and roaming.

2. Wi-Fi devices roam based on low received signal strength (RSSI) -- …