Wireless sensor networks are taking over.(DATA ACQUISITION)

GreenPeak's Mr. Van Dierdonck included simulation as the first step in a four-stage procedure. New ideas are simulated and then tested in wireless nodes within a well-controlled network environment. To separate the network under test from the test-logging system, a high-speed wired backbone is used to provide performance feedback. Endurance testing follows and finally field test to guarantee correct functional working.

BBN's Jason Redi described a three-step process. "We use shared-code software, where code that runs in the nodes is exactly the same code that runs in simulation. We test against traffic load, density, network size, mobility, and node failure. We also have a node emulation platform that supports real-time testing on the actual processors but with simulated radio hardware. Finally, we run our networks 24/7 throughout our building and continuously stress test new software."

In a form of self-test, Arch Rock sensor nodes send heartbeat packets periodically to check network reliability and connectivity. The packets contain key health statistics that the management server can analyze to detect any problems. Because Arch Rock WSNs use native IP, standard network management tools such as SNMP, Ping, and packet sniffers can be used to diagnose problems.

Ember's ZigBee platforms include interface ports that provide a nonintrusive trace of all packets sent or received at a device. Using an adapter that communicates with the debugging application via TCP/IP over Ethernet, PC-based tools can take advantage of the on-chip debugging I/O. This wired channel provides significant bandwidth for debugging data without swamping the wireless channel. The on-board interface port also avoids the ambiguity that can result when a sniffer receives transmissions that the node being investigated did not.

Summary

In many ways, testing a WSN is much like testing any packet-based communications network. However, network characteristics such as ultralow-power consumption, a hierarchy of node types, and a need for very high security can create challenges in addition to those usually addressed by protocol analyzers and traffic generators. Perhaps the most familiar WSN from the test point of view is the Arch Rock system. Although it actually is wireless, it behaves like a standard IPv6 network.

At this stage in WSN development, a large number of protocols are in use. As the market matures, this number should decrease. It also will be affected by standardization initiatives such as ISA-SP100.

WSNs have progressed well beyond being interesting curiosities. In many cases, they are the preferred solution. In addition to HVAC, process control, and industrial automation, WSNs are finding their way into applications as diverse as parking garage C[O.sub.2] monitoring (GreenPeak) and evaluating the temperature control of the penguin habitat at the Pittsburgh Zoo (Sensicast Systems).

by Tom Lecklider, Senior Technical Editor

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