Saturday, March 27, 2010

Have you ever wondered what was inside that AP?

Sometimes we never get around to opening up the case to see what's inside.. luckily it occurred to me on a couple of occasions to break out the screwdriver and find out.

Cisco 351 AP on left, Cisco 352 AP on right

From ccie(w)
Cisco 1200 with no cover

From ccie(w)
Cisco 1140 - has internal cable management!

From ccie(w)
From ccie(w)

From ccie(w)

Friday, March 26, 2010

Link-a-palooza delicious style

Here's a compendium of all the links I keep to different blogs/sites/etc related to wireless technologies or the CCIE wireless lab itself.  In no particular order mind you.. 

Seems to make the most sense to just link to my delicious account & go update that one with tags & links & whatnot.

Tuesday, March 23, 2010

What's in *my* backpack?

Inspired by Keith's post "What's In Your Backpack" I thought it would be fun to done one of my own!

Obviously I'm not nearly as organized as Keith, but there is a method to the madness, I swear!
I've had this backpack for five years, and considering all the wear and tear it has been through, it has held up pretty well. I've had it so long, I can't find a photo of it online..   It's an older model of a Wenger Swiss Army backpack.
Clockwise starting with the Edwin pencil case
Just about one of every color of pen/sharpie
yes I know I have a problem with the number of pens I carry..
1 White Out tape
1 Glue Stick
2 Composition Books
    one for CCIE Wireless notes

    one for work/project info
1 Business Card Case
 - many, many stickers! (for postcards)
2 leftover Hampton room keys (these are from Kansas)
 - several Index cards (blank & with notes)
 - several Hand Sanitizer packs
 - several alcohol swab packs
1 Southwest Drink Coupon
3 Nail Files
1 Hand Lotion
 - various Tums/Pepto/Tylenol
1 small can Static Guard
1 box of matches
2 Day-Quil tablets
1 brightly colored envelope for reimbursement receipts
1 airline regulation corkscrew (courtesy of the Chateau Frontenac, Quebec City)
1 Seagate FreeAgent 320GB external HD
1 Lenovo X60 tablet latpop
2 legal pads for miscellaneous notes
 - various print outs of current project details (I like paper)
1 Employee badge
3 ziploc bags

      separated into:
         - phone related cabling
         - audio/visual cabling
         - survey cards/spectrum analyzer cards1 power supply for laptop
1 USB mouse (tried a wireless one, hated it)
1 Lomo LC-A camera
1 Cisco console cable
1 VPN RSA Key fob/office door key
-  more business cards

These items are kept in the burgundy zippered bag

2 band-aids
6 various USB key fobs
2 binder clips
misc SD media
1 patch cable connector
1 cross-over cable connector
1 fuse for the Terra-Wave site survey battery pack
1 Mardi Gras coin from my pal Brooke :)

Other things that come and go from my pack pack:
ziploc bag with Garmin Nuvi/Garmin Cabling/Blackberry car charger
extended battery for the X60 tablet
Cisco WLC console cable
ziploc bag with travel sized toiletries
eyeglass case (if staying overnight)

If I'm traveling for a business meeting, I'll carry my black Furla purse.  If I'm traveling to *work* I'll carry my Dickie's bag.
I keep all these other things in my bag:
FujiFilm FinePix z5 (in brown)
Cisco Flip (wish it *wasn't* pink, but it was a gift, so I can't complain!)
my wallet and a bunch of other junk.. (I'm a pack-rat)
..stamps!  I always carry stamps!

Monday, March 1, 2010

Omnidirectional antennas, sectorized antennas, location tracking and RRM

Recently there has been some debate between two wireless vendors regarding which type of antenna is better than another.  Words were exchanged, and the one side made the statement that omnidirectional antennas suck.

I started to think on this a little more and tried to see where they were going with this train of thought.  There are instances where you need a patch, yagi or otherwise sectorized antenna - usually when getting the longest range is the goal of your wifi deployment.  This being said, I'd hardly agree with the statement that omnidirectional antennas suck.

If you're deploying a wireless infrastructure to support location tracking - omnidirectional antennas are your best friend.  Since the horizontal lobe of an omnidirectional antenna spreads out in a 360 degree fashion - this RF spread pattern aides the access point in reporting client location data back to a Cisco Mobility Services Engine (MSE) or an AeroScout Engine (for non Cisco shops).

The Cisco Wi-FI Location Based Services 4.1 Design Guide has a good graphic that explains mathematically how the location of a client device is calculated based on tri-lateration (using the combined client RSSI data from at least three or more APs).
  • ...the concept of ToA tri-lateration. The amount of time required for a message transmitted from station X to arrive at receiving sensors A, B, and C is precisely measured as tA, tB, and tC. Given a known propagation velocity (stated as c), the mobile device distance from each of these three receiving sensors can then be calculated as DA, DB, and DC, respectively. Each calculated distance value is used to construct a circular plot around the respective receiving sensor. From the individual perspective of each receiver, station X is believed to reside somewhere along this plot. The intersection of the three circular plots resolves the location of station X as illustrated in Figure 2-3. In some cases, there may be more than one possible solution for the location of mobile device station X, even when using three remote sensors to perform tri-lateration. In these cases, four or more receiving sensors are employed to perform ToA multi-lateration

From ccie(w)

OK - now that we know how a group of APs send the client RSSI information to an MSE or AeroScout Engine to calculate the approximate location of a client device - how would an access point that uses sectorized antennas calculate a client location using this same type of RF location calculation?  I would think that the access point using sectorized antennas would have to have a central "brain" in the array to combine all the client RSSI information that could be "heard" by the separate arrays.  Every sectorized antenna has some sidelobe to its RF beam, and surely antenna arrays arranged close next to one another would have some overlap, and therefore neighboring array antennas could potentially "hear" the RSSI of a given client device.

colorized array RF footprint to show channelization of the arrays' antenna orientation

From ccie(w)

My point is - from the information at hand regarding how client locations are triangulated, I believe that using patch, yagi or sectorized antennas would adversely affect the accuracy of location tracking.  The RF footprint has been changed to such a degree by the use of a sectorized antenna that the mathematical calculations used to determine client locations are no longer valid.

The same could be said of using sectorized antennas in a deployment utilizing Radio Resource Management (RRM).  RRM calculations are based upon each AP "hearing" a given number of neighboring APs at a given RSSI signal strength (usually -75dBm).  If antennas that have non omnidirectional lobes (patch/directional) the access points nearer the smaller back lobe of a patch/directional antenna would most likely sense this neighbor with a patch antenna at a lower RSSI and attempt to adjust RRM to power up in order to compensate for their "less heard" neighbor.

Point being - if you're using RRM and patch antennas - you should be very aware of how your access points are deployed and perhaps statically assign power levels to APs that are RF neighbors of the AP using sectorized antennas.

-- I invite additional information about how an array type access deployment handles calculating clients' RSSI and turning that into an X,Y location.. I'd like to understand how that works.