Sniff Wi-Fi

It's been over two-and-a-half years since yours truly last wrote about Oscium WiPry , but there is reason to today: they fixed it!  Now the only 2.4 GHz spectrum analyzer for Apple iOS reads signal level correctly.  And using the new, corrected version reminded the author why WiPry is a nice product at a reasonable price. The concept of a spectrum analyzer hasn't changed in decades, and for good reason.  It's simple.  A device listens for activity at a given frequency and displays a readout of said activity, usually in a fancy, colorful way. In the last two years, however, many things have changed about spectrum analysis for WiFi.  PC card slots have become increasingly rare, thus leaving the Cisco Spectrum Expert in the margins.  Sensor-based spectrum analysis has increased in popularity.  Metageek, makers of my favored spectrum analyzer , stopped offering free software with their signature WiSpy series of spectrum analyzers. What hadn't chang...

It's time to switch things up a bit.  WiFi sniffing is a fascinating topic and all, but good ol' Yours Truly wants to try something new.   This will be the first in the "Not Sniffing, but..." series on the Sniff WiFi blog.  I come across interesting topics outside of sniffing all the time, so I want to add short blog posts on some of these topics. Several months ago WLAN bon vivant Keith Parsons  posted a blurb on his WLANPros.com blog about the Fluke Networks LinkSprinter .  I contacted someone from Fluke Networks to ask about the LinkSprinter, and they were gracious enough to send me one to test. LinkSprinter is a wired testing tool.  It's more for people who install APs than for people who, like me, primarily do frame captures.  Still, we both do troubleshooting.  The LinkSprinter is definitely for troubleshooting. The tool is pretty simple.  You plug in an Ethernet cable, and you pre...

Two years ago tomorrow Apple introduced the iPhone 5.  It was a big deal.  It was a big deal for gadget folks who wanted a bigger iPhone.  It was a big deal for wireless LAN folks who wanted users to use smartphones with speedier WiFi.   Now the iPhone 6 has been announced and it appears to be more of the same.  Gadgeteers get their bigger iPhone.  Wireless folks get their faster speeds.  Problem is, the faster wireless speeds likely won't mean anything for high capacity wireless deployments. The big news about the iPhone 6 is 802.11ac.  Yippee!  Apple has finally adopted the latest and greatest WiFi standard in a mobile device. 802.11ac has data rates as high as 6.9 Gbps in the standard, but wireless LAN folks know that's not what happens in real life.  Real 802.11ac devices top out at a 1.3 Gbps data rate when multiple input-multiple output (MIMO) antenna systems are supported, while non-...

In the beginning, there was Coverage.  And so it was that 802.11 and his only begotten Son, WiFi were blessed upon PCMCIA cards who doth receiveth adequateth Coverage. And then as Coverage grew and the lands of Tablets wereth discovered, so came Capacity.  And thus did Capacity grow to represent all that was good and great about deploymenteths upon this fruitful land. And now, my Sons and Daughters, things have changeth again.   For Coverage and Capacity will both leave the Higheth of Densiteth WiFi wanting.  And so we shun them both.  For it is Neither -- Coverage nor Capacity -- that will taketh thy to the WiFi promised land. In case it was unclear, designing wireless LANs for Capacity has become an article of faith in some circles.  Keep it to 40 devices per AP.  Or 50.  Or 150.  Whatever the number is, the whole concept is misguided. WiFi uses radio frequency as its physical layer, and ther...

I've seen a lot of inexplicable stuff in my day.  Landlords advertising Free WiFi and then telling you to use the neighbor's.  Twitter praise from people whose employer I had just criticized in a blog post.  USC journeyman quarterback Mark Sanchez picked fifth in the entire NFL Draft.  But when I saw that my sturdy Apple Airport Extreme (single radio, dual band, two-stream 802.11n) wireless router was tagging all of my apps as Background traffic, I just couldn't explain it. For those who are unfamiliar with WiFi quality of service (QoS), a quick primer: WiFi Multimedia (WMM) certified devices use QoS protocols from the 802.11e amendment.  Primarily, that means classifying APPLICATIONS (not networks, not devices) as either Voice, Video, Best Effort or Background.  What happens when a device classifies an application as Voice (highest priority)?  Whenever that device is ready to send a frame (sometimes called a packet) from that ...

I recently got into a little tiff on Twitter.  In part it was an argument about blogging and reaching a broad audience, but mostly it was about site surveys.  Site surveys are hot right now, but I find that surveyors often overlook an important aspect of WiFi: different devices act differently. Conventional wisdom for WiFi site surveys is to get some site survey software , upload a floorplan and start a-surveyin'.  First predictive (letting the software estimate where coverage will go), then active (temporarily mounting access points in the locations chosen in the predictive survey and testing connectivity) and finally verification (walking the site after APs have been installed). The problem with all three types of surveys (predictive, active and verification) is that they are done with site survey software.  Site survey software is great for selling APs or pacifying execs, but it usually requires using a specific adapter.  So every time you verify conn...

I defend Apple a lot.  When Network World wrongly accused  the original iPhone of flooding Duke University's network, I defended Apple .  (It was later found to be a Cisco problem.)  When a health care provider I was doing some work for blamed SIP-enabled iPhones for a VoIP problem, I eventually found out that the APs were to blame .  (The APs were failing to respond to WiFi frames tagged as "Background" QoS.)  Time and time again networking folks blame device makers like Apple, and time and time again the problem ends up being the network. There are times, however, when it really is Apple's fault.  When the network is operating just fine.  This is one of those times.  The problem is that I just don't know why. 802.11n (HT) and 802.11ac (VHT) networks operate in co-existence with first generation (802.11a/b/g, that is) WiFi a lot.  When that happens, the HT or VHT access point o...