New vibe in sensor networks

* Alliance advocates use of IP standards in WSNs

What will reign as the wireless sensor network platform of the future? To date, the ZigBee Alliance has taken it upon itself to build networking and development standards for low-power, low-memory sensor devices communicating across 802.15.4 wireless personal-area networks. However, work toward promoting the use of the more pervasive and medium-agnostic IP protocol stack heated up last week with the formation of the IP for Smart Objects (IPSO) Alliance.

The new IPSO marketing alliance, which counts Cisco, SAP, Sun and several sensor-specialist companies among its 25 charter members, could challenge ZigBee’s dominance in the sensor space. IPSO is the latest in a series of efforts to push the use of an “IP light” protocol stack in wireless sensor networks (WSN), rather than relying on custom-made ZigBee protocols.

In May, an IETF working group began work on a routing protocol, called Routing Over Low-Power and Lossy Networks (ROLL), for use with IPv6 and optimized for wireless networks with limited power, memory and processing resources. Another emerging standard, 6LoWPAN, aims to adapt underlying link formats of 802.15.4 sensor networks to IPv6’s frame-size requirements. IPv6’s 128-bit addressing space will be required to scale to a world full of small communicators embedded in everyday objects.

The IPSO Alliance will conduct plugfests that determine ROLL interoperability among WSN components, says Geoff Mulligan, industry consultant and IPSO chairman. He explains that the alliance is “not writing new standards,” but is working to show how existing standards can work in a WSN and to create WSN architectures and design guides. One aim with advocating the use of IP in WSNs is to eliminate today’s requirement for separate gateways for each WSN application that must communicate upstream to an IP network, Mulligan says.

Memory-efficient implementations of the IP stack consume as little as a few kilobytes of RAM, and require less than 10 kilobytes of ROM, according to a white paper on the IPSO Alliance Web site. Such implementations were not available when the ZigBee Alliance was formed and took on the task of building communications protocols and application development environments specifically for WSNs.

Said Bob Heile, chair of the ZigBee Alliance in an e-mail statement: “ZigBee is already architected as an integral part of the IP-enabled world....What the casual observer does not appreciate is that even though IP on the individual devices seems like a simple and practical idea, it does not enable such fundamental services like device discovery/service discovery, which are essential in truly useful home-area networks (or in commercial/industrial settings for that matter)….As they say, the devil is in the details.”

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