Communications - February 2009

ing universities access to online training materials).

Declining interest in computing is disheartening and must be addressed for the future health of both the Canadian and the U.S. technology industries. For industry, money and effort spent today on education should be seen as an investment in its own future.

Bill Bushey, New Paltz, NY

trickle algorithm Corrections

The article “The Emergence of a Networking Primitive in Wireless Sensor Networks” on the Trickle algorithm I coauthored in July 2008 had two errors:

Sun SPOT sleeps. The article’s description of the Sun SPOT platform said SPOT sleeps by writing its RAM contents to flash while requiring significant time and energy to do so. The SPOT has an external RAM bank to which it saves its internal processor state when it sleeps and, by itself, does not incur a significant cost. However, SPOT wakeup requires tens of milliseconds to stabilize timing circuits and restore processor state. The alternative, used in most simple sensor-node designs, is to require just a few kilobytes of RAM and microcontroller wakeup times of tens of microseconds. This fast wakeup time allows nodes to quickly check for network traffic while spending less energy warming up to perform the checks; and

Srcr mesh routing protocol. The citation for the Srcr mesh routing protocol designed by John Bicket incorrectly cited Douglas S.J. De Couto’s MobiCom 2003 paper “A High-Throughput Path Metric for Multi-Hop Wireless Routing” when it should have cited John Bicket’s MobiCom 2005 paper “ Architecture and Evaluation of an Unplanned 802.11b Mesh Network.” The citation for De Couto’s paper also incorrectly listed the author’s name as Couto, D.D. rather than as De Couto, D.

Please accept my apology for these errors. I thank Randy Smith, as well as Douglas De Couto, for pointing them out.

Philip Levis, Stanford, Ca

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