August 11, 2008

Visualizing predictions

After a WLAN design is created, LANPlanner uses predictive RF modeling to estimate how that network will perform. Those predictions may not be perfect; Motorola staff told us that designs created from AutoCAD files are often about 95 percent accurate when compared to post-deployment site survey data.

Nonetheless, reasonably-accurate predictions can save you a lot of time and money by letting you visualize coverage and set realistic expectations prior to deployment. For example, it’s trivial to view a high visibility area like a conference room, throwing in an extra AP to reinforce coverage and see what happens. During many installs, APs end up being mounted in slightly different locations than planned. A predictive modeler can let you “wiggle” APs on a map to anticipate the impact, stopping mistakes before they occur.

LANPlanner includes a suite of “Quick Predict” tools to simulate WLAN operation and visualize results. For example, Channel Planning predictions can plot simulated coverage for each assigned frequency. Contour predictions can display strong, moderate, or weak signal areas surrounding each device (AP or WIPS Sensor, see figure 2-5).

Forward Link predictions let you drag your cursor around the map, simulating the received signal strength (RSSI) or throughput clients would experience in that location. Client parameters, such as transmit power and handoff threshold are globally configurable; setting them by throughput area might be handy for multi-media WLANs.

Pre-deployment refinements can be made to the design at this point. For example, Switches, WIPS Sensors, and external antennas can be manually added. Quick Start recommendations can even be adjusted–for example, LANPlanner assigned channel 34, but our Motorola AP-300s did not support that channel. (Ultimately, this proved irrelevant because we configured our APs for dynamic frequency selection instead of using static channel assignments.)

When design is complete, LANPlanner can generate a Bill of Materials (a list of equipment to be ordered, complete with model numbers and pricing) and a detailed site plan report that includes AP placement maps. However, we did not see any ability to generate AP installer “work orders” nor could we generate skeleton AP config files. On the other hand, we did export our design for use by RFMS, a sibling component of Motorola’s RF Management Suite (to be discussed in Part 4).

Deploy and verify

After WLAN deployment, LANPlanner’s site survey feature can be used to verify performance. Survey results not only document actual WLAN performance; they can be used to fine-tune or expand the original design using “what-if” simulations.

LANPlanner site surveys can be conducted in two modes: RF Monitoring (where the client adapter gathers information about all APs by passively scanning the air) and AP Performance (where the client adapter associates to an individual AP to take specific measurements). Figure 2-7 illustrates measurement set-up and real-time display during an RF Monitoring run. To conduct this survey, we walked through the selected site floor, holding our LANPlanner laptop about three feet above the floor, pausing every few feet to mark our current location on the map (red dots).

As shown in this figure, a surveyor can see visible APs and their properties in real-time. More importantly, all observations are written to an ASCII log file that LANPlanner uses to optimize its predictions and validate planned vs. actual WLAN performance.

Unfortunately, LANPlanner needs help to associate APs in the design with observed MAC addresses and SSIDs. Configuring those associations is a tedious task that would be onerous in a large WLAN. Associations were also problematic for virtual APs (MAC addresses with more than one SSID). We see definite room for improvement here.

Nonetheless, we found results worthwhile. After conducting a site survey, LANPlanner could easily generate channel, coverage, data rate, SSID, SNR, and noise heat maps for any region of the plan, using intuitive “check box” drill downs to focus on any individual element. For example, Figure 2-8 depicts a heatmap for a selected SSID and AP from a specific location, with forward link signal and noise experienced at the cursor location.

By combining a site’s RF model with in-situ measurements, LANPlanner can do a better job of predicting change impact. Some of the same tasks performed during initial design can now be repeated to see the effect of increasing the number of clients or adding new application regions. Quick Start can even be repeated on an existing WLAN to suggest where APs should be added or removed to meet revised requirements. However, LANPlanner won’t use survey results to automatically find trouble spots–it’s up to you to iterate the design process.

Conclusion

One of the first questions we asked about LANPlanner was 802.11n design support. Motorola recently announced the next generation of LANPlanner–version 11–will ship by the end of 3Q08. That update will reportedly be able to simulate performance of 802.11n APs like Motorola’s AP-7131. It will also provide a new wizard to assist with 11n migration and assess coexistence impact in mixed-mode WLANs.

Overall, our experience with LANPlanner version 10 was positive. In most cases, it made common WLAN planning and design tasks easy while providing hooks to accommodate more advanced needs. Learning how to interact with this GUI does take practice, but there’s no need to study a hefty manual or become an RF expert to benefit from LANPlanner. Wizards offer enough hand-holding to generate an initial WLAN design without much coaching from “Help.”

On the other hand, there’s much more to LANPlanner than our simple designs exercised. RF terminology can be intense, and the sheer number of parameters and views that LANPlanner can generate makes for lengthy menus. While novices can use LANPlanner, experienced engineers clearly get more benefit from it.

This product’s planning and design capabilities appear to be more streamlined and mature than its site survey and reporting tools. Nonetheless, anyone responsible for designing new 802.11n networks should consider investing in a predictive modeling tool like LANPlanner v11. After all, a LANPlanner license is no more than the installed cost of half a dozen APs–that’s a small price to pay to build a large WLAN right the first time.

• For more on Motorola’s RF Management Suite, read “Review: Motorola RF Management Suite (Part 1).”
• For more by Lisa Phifer, read “RF Barrier Helps Deter Eavesdroppers,” “Cheers to Wi-Fi,” “Hotspot Safety for Business Users.”
• For more on RF management, read “Wireless Valley Maps RF Management,” “Airespace Previews Branch Office WLAN Controller,” “Chicago Public Libraries Go Wireless.”
• For more on site surveys and WLAN planning, read “RF Site Survey Steps,” “Antennas: The Key to Maximizing RF Coverage,” and “Minimizing 802.11 Interference Issues.”
• For more on Motorola, read “CTIA Preview: Motorola,” “Motorola Buys AirDefense,” “Avaya, Proxim, and Motorola Partner for Corporate VoIP.”

Lisa Phifer owns Core Competence, a consulting firm focused on business use of emerging network and security technologies. With over 25 years of experience in the NetSec industry, she has been involved in wireless product and service design, implementation, and testing since 1997.