Sniff Wi-Fi

Voice over WiFi is scary.  Retries, packet errors (due to lots of Retries) and high latency (usually due to packet errors that happen because of lots of Retries) will murder a WiFi network's ability to handle Voice and leave your users screaming (not actually screaming) like they were cast in a horror movie (or, at the very least annoyed like a character from Office Space).  But there's one thing that sometimes scares people, but really shouldn't: Voice Arbitration.  It's not going to kill your WiFi voice calls.  In fact, it will almost certainly help. Arbitration is a process defined in the 802.11 standard .  Every device (client/station and AP) goes through it. The simplest way I can describe 802.11 Arbitration is like so: If your AP or station has heard a quiet channel for 37 microseconds (0.000037 seconds), then your AP or station transmits a frame (what most people call a packet, but I call a frame). If your AP or station has been hearing a busy channel fo

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 Voice application the device has to wait l

QoS the packets of iPad ,  and all through the air  not a station was Probing, not even a hair When suddenly on to my Wireshark screen Appeared Video, Voice and Background, it seemed "But alas", I exclaimed, as I looked at the MACs This is only one tablet, not a bushel or stack To the standard I looked, to decipher the meaning And to you, dear reader, I offer this gleaning The standard in question is dot11e and the goal of its authors was to keep the air free from clutter like YouTube and Facebook or Twitter that might cause your voice conference to lag and/or jitter But remember, dear sniffers, we're still talking WiFi A world where each access point, smartphone and MiFi makes its own way to the channel or not deciding on rates, QoS and the lot So take heed if your WiFI must work for those apps that users just love but treat admins like saps a smartphone may say, "this packet is Voice" but the AP may reply, "Best Effort; no choice"

In my last (real) post, I detailed how I used WildPackets OmniPeek to solve an iPhone 5 QoS problem.  But what about AirMagnet WiFi Analyzer?  I am a fan of both of those fine WiFi sniffers, so I figure it's a good idea to show you how QoS can be analyzed with Fluke Networks' signature WiFi protocol analyzer. WildPackets OmniPeek is more of a hardcore protocol analyzer than AirMagnet WiFi Analyzer is.  If you're going to be doing the type of sniffing I detailed in the last blog post , you will have an easier go of it with WildPackets' product.  But AirMagnet is popular and both tools are expensive.  So if you happen to be a gal (or guy) who needs to troubleshoot WiFi voice or video and you have AirMagnet, this brief tutorial should help. To begin analyzing QoS, one must first capture on the VoFi devices channel.  In my case I associated my iPhone 5 to a network with the SSID of "R&T".  Then I looked at the Start screen in AirMagnet: The "R&a