Review: Motorola RF Management Software v2.0 (RF Management Suite Part 4) - Page 3

By Lisa Phifer

January 15, 2009

Real-time Status: Are you there now?

 

After Sites have been associated with floor plans and populated with devices, the RFMS Presence tab can be used to visualize their current status, coverage, and location. All of this information is displayed by RFMS in near-real-time, reflecting the latest SNMP poll results.

 

For example, the Devices page lets you easily see which switches, APs, and/or clients are currently up or down. Clients—called Mobile Units (MUs)—are displayed in the Site list only when actively associated to an AP. "Access Points" (thick APs) and "Access Ports" (thin APs adopted by switches) are persistently displayed both in the Site list and on your floor plan, along with a green or red marker indicating current status (up or down).

 

RFMS also summarizes Site status by presenting total MU, AP up, and AP down counts. These counts are handy and intuitive for thick APs, but we found them confusing for thin APs. "AP up" grows whenever a thin AP is adopted by a switch. But if that AP is disconnected, "AP down" count does not change. If someone steals an Access Port or yanks its Ethernet cable loose, that thin AP simply disappears from RFMS. That reflects current status and simplifies map maintenance when thin APs are relocated (e.g., for load balancing across switches), but we think it impedes troubleshooting.

 

Fig43-RFCover.jpg

Figure 4.3 – RF coverage heat map

 

Coverage and Spectrum pages can be used to eyeball your Site's 11a or 11b/g RF footprints in real-time. The Coverage page generates a heat map—red hot areas surrounding each AP, gradually diminishing to orange and yellow as signal strength falls due to distance and attenuation. Hover your mouse over this map to display the RSSI that a client might currently experience at that location, based on RFMS's understanding of that Site's RF environment, active devices, and recently-polled performance attributes. Spectrum takes a somewhat broader perspective, helping you visualize per-channel coverage, plotted across your entire floor plan in a similar fashion.

 

Near-real-time up/down status and heat maps like these are aimed at WLAN help desks responsible for trouble-shooting user connectivity issues from a central location. By the time you can send someone to a user's location, RF coverage may have changed—help desks need to see these kinds of measurements in real-time, and RFMS lets you do so without requiring the user to run client-side diagnostic tools.

 

Device locationing: Where are you?

 

These status tools become more powerful when combined with near-real-time locationing. RFMSv2.0 can take a snapshot of currently-active MU or rogue AP locations, plotting them on your floor plan.

 

Specifically, the Presence / Locate MUs page can be used to request the location of one, some, or all currently active client devices. Two locationing methods are available for MUs: RSSI triangulation or fingerprinting.

 

  • MU fingerprinting requires at least three APs near the target MU, which must itself be configured to respond to AP probes. Fingerprinting compares real-time RSSI reports to earlier readings, taken at specified coordinates. To fingerprint a site, an administrator performs a site walk-through, using a laptop or PDA to record RSSI values using the RFMS Fingerprint page. Later, when you want to plot an MU's current location, the Locate MUs page tells APs to probe a specified MU so that RFMS can compare stored RSSI values to AP-reported RSSI values.

 

  • MU triangulation also uses real-time RSSI readings, but estimates a "rogue" client's current location by computing probable distance from at least three nearby APs to identify their intersection. According to RFMS documentation, both methods are accurate to within ten meters—but RF fingerprinting based on good reference samples can be more precise than triangulation. Due to our test bed set-up, we could not test fingerprinting. However, triangulation for MUs between our three APs was fairly accurate.

 

RFMSv2.0 also provides two mutually exclusive methods of rogue AP detection: standard and enhanced.

 

  • Standard rogue AP detection relies upon observations made by Motorola switches, configured to overhear nearby APs and report them via SNMP. In this case, RFMSv2.0 simply aggregates all reported rogues into one Security / Rogue AP table, using charts to help you visualize rogue RSSI and channel distribution. Although Motorola APs can be configured to recognize (and ignore) selected APs, RFMS does not let you tag or remove neighbors from its rogue AP list.

 

  • Enhanced rogue AP detection lets RFMS locate rogue APs using RSSI-based triangulation (similar to MU triangulation). Standard detection must be disabled and Enhanced detection enabled for each switch, specifying rogue scan interval, scan duration, and scanned channel list. Thereafter, the RFMS Security / Rogue AP table will be empty. However, the RFMS Presence / Locate Rogues page can now be used to generate a current snapshot of active rogue APs, mapped in relationship to your own APs on your Site floor plan.

 

 Fig44-StdRogue_sm.jpg

Click to enlarge.

 

 

Fig45-AdvRogue_sm.jpg

Figure 4.4 (above) and 4.5 – Standard vs. Enhanced rogue AP detection. Click to enlarge.

 

In our experience, Standard detection worked well, but Enhanced detection results for each rogue AP varied quite a bit. Our APs may not have been separated enough: three AP-300s were placed as far apart as we could in a 200 x 100-foot area. In larger WLANs, locationing can also be strengthened by RFID readers, which we did not test.

 

Alternatively, rogue AP detection and locationing can be performed by the Motorola (AirDefense) Wireless IPS—a fourth member of the RF Management Suite. Customers that deploy the entire suite can dynamically convert any AP-300 into a full-time WIPS sensor, then use the WIPS console to view rogue AP alerts and locations. Given Motorola's recent acquisition of AirDefense, we expect to see this part of RFMS evolve as the WIPS, MSP, and RFMS become more tightly integrated.

 

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