The 6LoWPAN work is opening low-power wireless networks to IP traffic, with interesting consequences.
By Ron Wilson, Editorial director -- EDN, May 12, 2011
The main reason for this trend is convenience. Third-party IP stacks and offload engines are widely available. Increasingly, IP is the lingua Franca one can expect a third-party embedded device to understand. And, as Dust Networks President and CEO Joy Weiss pointed out recently, an IP stack allows application-layer developers to write to a single network interface, independent of the physical-layer implementation and the network topology. All the world becomes just a set of IP addresses.
But an IP network has its costs. In an embedded world used to thin clients, light-weight protocols, and MCUs with little spare memory, an IPv6 stack can force replanning of the hardware resources, to say the least. The IP world-view--in which time is but a social convention and best-effort is the best you can get-is entirely foreign to the embedded world of fault-tolerant, isochronous networks and guaranteed maximum latencies. And the next logical step-actually connecting the local M-to-M network to the big, bad Internet, is fraught with uncertainties and security risks.
Dust Networks makes an interesting case study in this clash of cultures. The company has made its name selling wireless M-to-M networks in the industrial market-more than 10,000 to date, according to Weiss. Dust uses a radical, dynamically self-configuring, quasi-peer network architecture running the IEEE 802.15.4 protocol. Employing proprietary time-domain multiple-access on top of the IEEE standard and supporting wHARP (wireless Hybrid Ad-hoc Routing Protocol), Dust uses a low-frequency heart-beat with very short wake and sleep latencies to minimize the radio duty cycle, making possible single-chip nodes that can operate even on scavenged energy. In short, Dust's culture is nearly antithetical to the world of IP.
But with the introduction of SmarMesh IP on Wednesday, Dust is plunging into the IP world, supporting Internet packet traffic over its mesh network. The product rests on adding to Dust's existing node functions a speculative implementation of the specification from the IETF 6LoWPAN (IPv6 over Low-power Wireless Personal-Area Networks) working group. The specification deals specifically with carrying IPv6 traffic over 802.15.4 networks.
Support for 6LoWPAN, in turn, required Dust to increase the processing and memory headroom on their silicon, a need that ARM thoughtfully answered with the introduction of the Cortex M3 core. In the inherently low-leakage TSMC 180-nm analog process Dust combined their high-efficiency radio with a heavily power-managed Cortex M3 implementation, up to 72 kBytes of RAM, and 512 kBytes of flash. The result is an SOC that works in Dust's network, meets the company's stringent energy-consumption goals, and transports IPv6 packets.
The question of Internet security is a more complex one. Weiss said that there is an authentication protocol baked into the Dust network, preventing an unauthorized device from associating itself with the network. But Internet-connected embedded systems will also depend on a powerful firewall-outside the scope of Dust's product line-to protect the local zone from the outside world.
Another addition to the new SOC, incidentally, is a time-of-flight engine: essentially a precision timer for measuring propagation delays between nodes. Using the measured delays and a table of locations of fixed nodes in the mesh, a mobile node can locate itself within about 3 meters, Weiss said.
As the 6LoWPAN group's work moves toward a draft standard, expect the spec to become a vehicle for increasing IPv6 penetration into M-to-M networks. Other companies in the low-power wireless space, including Jennic and Energy Micro, are likely to be active early on. Jennic has already announced 6LoWPAN software, and Energy Micro, with its extreme focus on energy management, involvement in the 802.15.4 standard effort, and Cortex M3 implementation, seems likely to be involved, as well.
In addition to meeting a need that these vendors are hearing from systems developers, IPv6 support may open a wider market to companies like Dust that have been primarily focused on industrial applications. Building management, home control, and everyone's current pot of gold, the Smart Grid, are all likely to be biased toward IPv6. So 6LoWPAN might not only open a far more energy-efficient class of networks to IP traffic. It may also open a new set of markets to previously industrially focused vendors.
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