Arch Rock framework moves Zigbee app profiles onto IP

Oct. 27, 2008

San Francisco, Calif., - Arch Rock Corporation has proposed a new framework for running ZigBee application profiles such as Smart Energy and Home Automation over the industry-standard Internet Protocol(IP).

The Compact Application Protocol (CAP) expands the scope of the ZigBee applications to any IP-enabled device, regardless of the type of wired or wireless network to which it is connected, while preserving the resource-efficiency and compactness critical to devices networked using IEEE 802.15.4 low-power radio. Because the existing ZigBee stack runs only on 802.15.4, ZigBee devices could communicate only with other devices on the same local mesh network, unless users deployed a series of complex, costly and hard-to-maintain protocol-translation gateways.

CAP takes the application-oriented upper layers of the ZigBee stack and runs them efficiently over the same IP foundation used by millions of existing networked devices. Once built on the standard IP protocol stack, embedded devices such as utility meters, thermostats and load-control devices can become part of the larger IP infrastructure, able to communicate over any LAN or WAN links (e.g., Ethernet, HomePlug, Wi-Fi, IEEE 802.15.4 low-power radio) with other embedded devices as well as remote computers and servers. With the addition of CAP over their IP stacks, such devices benefit from the wealth of service-discovery, binding, device-description and other mechanisms provided by the ZigBee Application Protocol and the ZigBee Cluster Library. Developers' and users' investment in application software built on the ZigBee profiles is protected.

Arch Rock has submitted the CAP draft specification to the Internet Engineering Task Force (IETF) as an informational draft, available at A demonstration of CAP is available to Arch Rock customers and partners on request.

"The major utilities have been vocal about their preference for seeing a single specification to use with energy-handling devices no matter what type of link they're on--802.15.4, Wi-Fi, HomePlug or others," said Roland Acra,Arch Rock CEO. "While ZigBee proponents have done a very good job of creating high-level application profiles, such as Smart Energy, Home Automation and Hospital Care, their use of link-specific, lower-layer protocols has meant that ZigBee devices are essentially 'stranded' on 802.15.4 mesh networks. The IP community, on the other hand, has spent decades working to perfect the network and transport layers and has been so successful that IP has become a worldwide standard. Recently approved standards such as 6LoWPAN [IETF RFC4944] have further increased the reach of IP to include highly constrained and low-power devices connected by 802.15.4 radio mesh networks.

"CAP takes the application-oriented ZigBee constructs above the transport layer and ports them to run on the IP 'plumbing,' realizing the best of both worlds," Acra said. "This will ensure that orders of magnitude more energy-relevant devices can move onto the 'smart grid' using equipment already present on any router-based network. For example, a utility computer program running CAP can send secure load-shedding requests directly to a user's Wi-Fi-connected in-home display unit also running CAP over IP and Wi-Fi. Similarly, messages can be exchanged directly with a user's water-heating controller running CAP over IP and HomePlug. Both examples rely solely on the existing IP infrastructure with no translation gateways. This has tremendous implications for introducing new features selectively on end devices without causing corresponding network infrastructure changes, as would be the case with application-layer gateways.  This is exactly the way it's done on the Internet and on mission-critical private IP-based networks."

The Compact Application Protocol fully preserves the upper layers of the ZigBee protocol stack--including the application profiles, application-layer security and application protocol--while substituting the IP network (IP) and transport (UDP) layers for their lower-level ZigBee counterparts. ZigBee application protocol information is embedded in UDP packets and a UDP port is chosen, allowing devices to communicate using an IP address and port instead of a ZigBee network address. The ZigBee profile system, with its clusters, attributes, commands and datatypes, is left intact. Reliability is implemented using ZigBee APS acknowledgements and retries, and security using the ZigBee APS layer security model. ZigBee Device Profile binding commands and discovery commands are modified to include the IP address and port. The ZigBee Trust Center (a designated device entrusted with the distribution of security keys) and ZigBee Discovery Cache now run on trusted IP hosts.