Introduction
| AirMagnet Surveyor | |
|---|---|
| Summary | Intuitive, easy to use site survey tool with impressive graphic display back-end. |
| Update | None |
| Pros | • Easy to use • Flexible and powerful graphic presentation of data • Simulation mode provides limited ‘what if’ capabilities |
| Cons | • Documentation lacks applications tips • No tools or help for site map creation |
One of the most tedious, but necessary, tasks required for a good wireless LAN installation is a site survey. Sure, you can guess where to locate your access points, or just adopt a put-one-every-n-feet/meters approach, but most environments have physical, RF and budgetary obstacles that necessitate a more analytical approach.
AirMagnet’s new Surveyor tool is aimed at taking the pain out of wireless site surveys and, more importantly, converting all the gathered data into graphical representations that are nicely suited for human consumption.
Functional Overview
In a nutshell, Surveyor takes AirMagnet’s WLAN scanning engine and marries it to an interactive display tool. The display tool is actually the back-end for a data-cruncher that takes the RF and location information gathered during a survey walk-around and transmogrifies them into visual maps of the WLAN signal profile in the survey area.
The signal profiles can be overlaid on a map of the physical layout of the survey area, or just displayed scaled to a length and width that you must enter. There’s probably more than one way to do what Surveyor does, but AirMagnet has done it with their signature easy-to-use approach that will have you surveying and analyzing your first results within minutes of installing it. Figure 1 shows an example of Surveyor’s handiwork, so that you can get an idea of what all this looks like.
Figure 1: Surveyor Passive Survey result
(click on the image for a larger view)
Although this screen looks pretty daunting, it’s easy to navigate once you get the lay of the land. I’ll walk through the process of building this display step-by-step later.
Running Surveyor requires a computer running WinXP or 2000 and a supported wireless adapter. AirMagnet figured that most folks won’t want to haul a desktop around to perform a survey, but will probably want a larger screen to look at all the pretty pictures that Surveyor can produce. So Surveyor’s license lets you install one copy in a computer equipped with a MAC-address-locked WLAN card and one “display-only” copy in another machine.
AirMagnet continues to expand its list of supported cards which now includes adapters from 3Com, Cisco, Enterasys, IBM, NETGEAR, Nortel, Proxim and its own three CardBus adapters. AirMagnet shipped me its dual-band, tri-mode NL-5354CB, which is sourced from Senao and also available re-branded from EnGenius and other vendors. Note that none of Intel’s Centrino, nor any other internal WLAN adapters are supported.
AirMagnet uses a licensing scheme that requires entering a serial number and serial “key” from the install CD and MAC address of the wireless adapter used. This info is sent via Internet to AirMagnet, which then issues a license file that’s downloaded to your computer to activate the product. (There are also “alternate ways” to get a license file if you don’t have an Internet connection handy.) The process worked without a problem for both my notebook and desktop installs.
Tip: The best way to experience Surveyor is to download a demo copy.
Setting Up
The preparation required to use Surveyor involves configuring the WLAN capture parameters and entering a physical layout of the survey area. Figure 2 shows general Survey settings which include the ability to set a threshold for captured AP signal strength and control the data sampling rate.
Figure 2: Survey settings
Figure 3 is where most of the action is and lets you control various parameters for the wireless card driver. Note that you can enter a WEP key (useful for active scans), but newer WPA security isn’t supported.
Figure 3: 802.11 settings
Figure 4 is what appears when you click on the Advanced button on the 802.11 tab. It lets you enter information for Cisco LEAP authentication and control additional “advanced” parameters for the wireless adapter.
Figure 4: Advanced settings
I didn’t mess with any of these settings for my testing, but did click on the Scan tab to limit channel capture to just the 11 802.11b/g channels being used by the two APs in my test WLAN.
Selections include all fourteen 11b/g and twelve 11a channels and you can set the speed of scan from a minimum of 150ms to maximum of 10 seconds per channel.
Figure 5: Scan settings
Once you get the radio side of things squared away, you need to give Surveyor a little info that it uses to figure out how to physically map its signal samples. In the setup process, this is done via a “Project Wizard” that guides you through the data input. But after the “Project”,i.e. survey is established, you can access the data in Figure 6 via the View > Project Properties menu.
Figure 6: Project properties
You can see that you enter the maximum Length and Width and information about the signal propagation characteristics of the survey area. You can choose from three “Environment” presets – Restricted Closed Office, Open Space Office and Commercial – with default propagations of 20, 40 and 60 feet respectively, or enter your own value. You can also enter the default transmit power used for signal propagation calculations for all APs.
Tip: You can later tweak transmit power and a number of other AP parameters in Display mode by right-clicking on an AP and selecting Properties.
Making your Map
Though the above sounds like a lot of info to enter, most of it is set to default values by the Project Wizard and therefore takes only a few seconds. Your more daunting task is likely to be obtaining a map of the survey area in digital format. For the most part, AirMagnet leaves this important step as an exercise for the user, but tries to be accommodating in accepting files in BMP, DIB, DXF, EMF, JIF, JPG and WMF formats.
Large corporations might maintain up-to-date floor maps in digital format, but I suspect that most small to medium businesses don’t. And even if they have a hardcopy drawing that can be scanned into digital form, it most likely represents only the floor / building outline and permanent / structural walls. Cubicle walls usually come and go as needed, with accurate maps drawn up only during major floor remodels.
I found this part of the Surveyor experience to be the most time consuming, taking about a half-day to complete. I was fortunate that I had the plans for my recently-built home available. But getting the D-sized prints scanned into digital form was not an option, since the round-trip to the nearest shop capable of doing the scan would have entailed another half-day and an expenditure that I was too cheap to make.
Since I’m also too cheap to have a copy of Visio lying around for occasional use, I instead hit Google and Download.com in search of a drawing tool that would display size and distance information of objects as they are created and placed. You’d think that some easy-to-use and inexpensive program would have this ability that Apple’s MacDraw provided years ago! But the best I was able to come up with quickly (and for free!) and learn to use without devoting hours was VectorEngineer’s QuickTools.
After going up a short learning curve with QuickTools, I used my house drawings as a guide and created a floor map that I then imported into Surveyor (Figure 7).
Figure 7: The naked Site Map
(click on the image for a larger view)
Doing the Survey
Allrighty then! With all the preliminaries out of the way, we can now start the survey. Surveyor uses a simple, but effective way for the user to communicate the path taken during the survey. You simply estimate where you are on the Site Map, move your mouse pointer and click to mark the spot. Figure 8 shows what this ends up looking like after a survey walk.
Figure 8: Site Map plus Survey Path
(click on the image for a larger view)
Each of the slightly larger red square dots indicates a clicked (entered) location point while each smaller blue square dot represents a location where Surveyor calculated that a signal data sample was taken.
Though this seemed simple enough to start, it wasn’t long before I starting wondering how often I was supposed to indicate my position. The printed User Guide was no help, saying only “Click on the map accurately where you are as you walk”. It turns out that the key to knowing how often and where to click lies in understanding how Surveyor marries the Site Map location clicks and signal data samples.
Because Surveyor has no innate way of knowing where each data sample was made, it relies on the user to accurately click his / her location on the Site Map as the survey progresses. Surveyor then uses that information, along with a time stamp for each data sample, to estimate where each sample was actually taken and attach calculated X and Y coordinates to each sample.
Since the calculation is done using a straight line interpolation, it’s important that you click just before each change in direction and estimate your location as accurately as possible. An example will show how important it is to watch where you click!
Let’s say I start a survey by clicking my start location on the Site Map and I’m using the default data logging rate of 3 seconds between samples. Right after I click, I drop my favorite pen and spend about 10 seconds finding and picking it up. Pen retrieved, I now move 20 feet down the hallway and click to indicate my location. If I stopped the survey at this point, Surveyor would show a survey path something like Figure 9.
Figure 9: Misleading Survey Path
Note that Surveyor has taken the three data points that were actually taken at the same location while I was hunting for my pen and distributed them evenly along a 20 foot path. This is obviously incorrect – the correct diagram would show three data samples clustered near the starting point – but accurate according to the location information I gave Surveyor.
What I should have done is either click again on the survey start point before I began to move, paused the survey (using Surveyor’s Pause feature) right after I dropped my pen, or just restarted the survey after clearing out the incorrect data. If you end up in a blind alley, or just decide that you don’t want data you gathered along a particular survey leg, you can also use Surveyor’s Retract function to erase the most recent path.
Surveyor lets you perform two survey types. A “passive” survey gathers signal, noise channel and SSID data from all in-range APs – much like AirMagnet’s Laptop and Handheld products. You can also perform “active” surveys that log signal info from a specific AP that you choose to associate with or multiple APs in a specified SSID. The setup for both survey types is pretty much the same with the “active” survey only requiring you to choose an SSID or AP to associate with.
Data Display and Manipulation
Once the survey is complete, you switch to Surveyor’s Display mode to view the fruits of your labors. As you make the switch, you’ll probably encounter a pop-up window asking you whether you want to specify the locations for the access points in your survey.
AirMagnet recommends you do this and I agree with their recommendation, since nailing down the APs’ locations removes a variable from Surveyor’s signal map generation algorithms and centers calculated peak signal areas on the APs instead of where Surveyor estimates the APs to be.
You can see the difference that adding the AP location information makes by examining Figures 10 and 11. The screenshots show two views of the same passive survey data from a test WLAN that included a Gigabype GN-A17GU 11g access point (red) and OvisLink WMU-9000VPN 11g VPN router (blue).
Figure 10: Passive Survey display – without APs specified
(click on the image for a larger view)
Figure 10 doesn’t have the AP locations input and although it still accurately shows that the Channel 1 (red) AP is more powerful than the Channel 4 (blue) AP, you can’t really see a defined signal center.
Figure 11: Passive Survey display – with APs located
(click on the image for a larger view)
Figure 11 shows that adding the AP locations produces definite signal centers and moves them to where the APs are actually located. Since the display algorithm always places the strongest AP’s signal on top, you can see that the Gigabyte AP seems to overpower the OvisLink router. This is validated by the FCC test reports which list an average 802.11g mode peak power output of 62mW for the Gigabyte’s Atheros-based radio vs. 34mW for the OvisLink’s Conexant PRISM based radio.
It also looks like two APs are probably overkill to cover the 1500+ sq feet of my home’s main level. But let’s use one of Surveyor’s nifty features to see if that’s really true.
Figure 12 shows the display after removing Channel 4 (blue) data and adjusting the lower “range setter” (the vertical bar graph in the right-hand toolbar) to filter out Signal data below -65dBm.
Figure 12: Passive Survey, Ch 1 only, -65dBm cutoff
(click on the image for a larger view)
The display now shows gray where the signal data falls below the -65dBm cutoff. I really like this feature because it gives color-challenged people like me who have trouble discerning shades of particular colors an easier way to understand the data. Note that the “range setter” feature also lets you adjust the high displayed data limit in case you want to filter out strong signal areas too.
With these display tweaks, you can see that the even the stronger Gigabyte AP won’t cover my entire floor with a signal level that I’ve deemed acceptable. Since few client cards can provide a reliable (and fast enough) connection at very low signal levels, I found myself generally moving the lower “range setter” to the -70dBm or so level to look at usable signal levels.
Getting Active
The second, “active”, flavor of scan can show speed, retry rate and % packet loss in addition to the signal, noise and S/N data logged by passive scans. Figure 13 shows the connection Speed results from a scan of the Channel 4 (OvisLink) 11g router.
Figure 13: Active Survey – Chan 1 speed
(click on the image for a larger view)
Since connection speed tends to be the bottom line for many applications, this can be a very informative map. But before you go telling the boss that everything is peachy, you need to remember that this map, and all of Surveyor’s pretty pictures, are just one card’s “opinion” of your WLAN’s signal environment.
WLAN performance is just as dependent on client card performance as it is on that of your array of access points. More to the point, roaming and speed selection algorithms are strictly a function of a client’s driver and firmware. So for most accurate results, AirMagnet recommends that surveys be done with either the same brand and make of client card used most often by WLAN users, or at least one of AirMagnet’s supported cards using the same chipset as your favorite card.
An approach to achive more realistic surveys might be to perform multiple surveys using a different Surveyor client each time. Unfortunately, AirMagnet’s current licensing scheme doesn’t allow you to swap client cards easily, so this could get costly with a Surveyor license required for each card. But AirMagnet says they are working on improved scheme that will provide a “dual licensing” mechanism.
I think that AirMagnet also needs to add at least one mini-PCI design using each of the major wireless chipsets to its list of supported devices, since built-in WiFi has become the way to go for many enterprises. AirMagnet’s list already includes Cisco’s MPI350 and IBM’s ThinkPad Mini PCI a/b/g (based on Atheros’ AR5212 chipset), but Centrino is obviously the most significant omission that needs to be corrected.
Minding the Overlap and Simulation
As with AirMagnet’s other offerings, Surveyor has too many modes and features for me to cover in one review. But here are a few other features that you’ll probably like to play with.
Surveyor can show you the overlap between APs (Figure 14), which is especially handy for adjusting AP spacing and/or power levels.
Figure 14: Cell overlap (Interference) view
(click on the image for a larger view)
To generate Figure 14, I used a merged file – another of Surveyor’s features that allows combining the results of multiple surveys so that they can be viewed together – of active surveys taken while associated with each of the two APs in my test WLAN. I then adjusted the “range setter” to show only signals down to -55dBm, and clicked on the Interfere button at the bottom of the right-hand toolbar to highlight the APs’ overlap in bright red.
So what would I have to do, you might ask, to eliminate the signal overlap between the two APs? That’s where Surveyor’s Simulation function can be helpful. Clicking on the Simulation button at the bottom of the Surveyor display brings up the Figure 15 window where you can tweak Channel, SSID and Simulation and original transmit power levels.
Figure 15: Simulation mode controls
I tried various values and finally found that I had to reduce the Gigabyte AP’s transmit power to one tenth of its original value in order to eliminate overlap with the weaker AP (Figure 16).
Figure 16: Simulated effect of reducing Ch 1 AP power 10x
(click on the image for a larger view)
I suspect that there is more work to be done with this feature, since this seemed like too much of a change to achieve the desired effect. I also noticed that the close-in signal level for the Gigabyte AP read -20dBm both before and after the simulated power reduction was applied!
Playing with the Noise Simulation slider didn’t seem to have much effect, and changing channels on one of the APs only changed its display color, leaving the overlap area unaffected. I also noticed that when I set both APs to the same channel, the Interference / overlap area disappeared. This isn’t correct in my opinion, since signals from two APs are still overlapping, same channel or not.
As is the norm with AirMagnet’s documentation, the User Guide is no help in figuring how best to use the Simulator, or any of Surveyor’s features for that matter. All you get are helpful tips such as “Highlight the Sim Power and enter a value you want to use” as the sum total of all information for that control.
Other Features
One of the features that I showed way back in Figure 1, but didn’t explain is Measure Mode. Clicking this button turns your cursor into a push-pin which you click to “stick” into the Site Map. You then get constant readout of the distance from the stuck pin to the pin at the end of your cursor.
This is mainly handy for double checking distances between objects on the Site Map, but AirMagnet has enhanced this function in their latest build. The new version throws up a pop-up asking if you want to recalibrate site measurements after measuring. This new feature lets you use the Measure tool to see what Surveyor thinks the distance is between two Site Map points, allows you to tweak that measurement, then re-calculates the appropriate distances in the Site Map using the input distance information.
Surveyor also includes a number of handy calculators that can be handy to have around when you’re laying out a large wireless LAN. Figure 17 shows the Free Space Loss calculator and the tabs in the shot show the other calculators available.
Figure 17: Free Space Loss calculator
Given that Surveyor lets you define the Site Map distances in Feet or Meters, I think it would be nice if the Calculators offered this option, too. Note that the Calculators are available even if you’re running your copy of Surveyor that doesn’t have a wireless card attached.
Finally, when you do have a card installed, you also get access to the Signal Distribution, DHCP and Ping tools from AirMagnet’s Laptop and Handheld tools.
Room for Improvement
As wonderful as Surveyor is, there is still plenty to be done to improve this first-generation product. Here’s my short list:
- Did I mention the lack of applications information in the documentation?
- Need to add the ability to control the colors used in the displays, but more importantly the text font colors.
- The ability to add callouts and/or “sticky notes” to the displays would be a welcome addition.
- I found the size of the logged and entered points in the Survey path to be too small.
There are also various display refresh issues that should be tracked down and fixed, which might just entail making them operate consistently, or documenting how they work!
Closing Thoughts
Score another hit for AirMagnet. I don’t do site surveys for a living, but Surveyor looks like it can take what must be a dreaded and tedious task and makes it quick and relatively painless to perform. So easy, I’d say, that even your boss could learn to run it in no time!
I guess AirMagnet has had some sensitivity to pleas to reduce the price of their excellent products, because at $1995, Surveyor is priced about 33% lower than their flagship AirMagnet Laptop product. AirMagnet said this pricing is an attempt to broaden the available market for Surveyor and you have to give them credit for trying.
But I think this pricing could still keep it beyond the reach of small businesses and installers. On the other hand, a good site survey probably costs much more than $2000, and that expense needs to be incurred for repeat surveys. So maybe $2K isn’t a deal-breaker after all.
At any rate, if wireless LAN site surveys are a part of your regular routine, Surveyor deserves a place in your toolkit.