Foreword

You are holding (or perhaps reading online or in an e-book) a remarkable volume. I have been a proponent of IPv6 and an enthusiastic adopter of sensor networks for some time. I am using a commercially available 6LoWPAN system to monitor my home and especially the wine cellar. You may imagine my positive reaction to the book you are reading now. It is stunningly thorough and takes readers meticulously through the design, configuration and operation of IPv6-based, low-power, potentially mobile radio-based networking.

In reading through this book, I was struck also by the thoughtful framing of issues that reach beyond the specifics of 6LoWPAN and go to the heart of many aspects of Internet protocol design. For example, general problems, such as packet fragmentation, are explained in the context of the standard Internet protocols and then, more particularly, in the context of 6LoWPAN. This technique helps to place issues into broader contexts and takes advantage of knowledge that readers may have already of the Internet Architecture.

Sensor network utility seems to me indisputable and consequently, this book has wideranging implications for anyone thinking about the proliferation of sensor networks, the need for significant address space to support them, and their integration into the present IPv4 Internet and the future IPv6 Internet. The special requirements imposed by battery-powered operation, radio-based communication and potentially mobile operation motivate the need for books of this caliber. Whoever said “the devil is in the details” might well have had 6LoWPAN in mind!

I found the sections on mobility particularly helpful and the term “micro-mobility” especially illuminating. Mobility in the Internet’s design has long been a problem area and I had been puzzled by this since the original Internet included two mobile packet radio networks (in the San Francisco Bay area and Fort Bragg, North Carolina). It is clear that the mobility conferred by these networks was confined to mobility within a given packet radio system, in other words, micro-mobility as defined by the authors. That’s the easy kind. The hard kind is when the IP address of the mobile node has to change to reflect a new topological access point into the Internet. It is that kind of mobility that has not been well served by present-day Internet protocols. There is still much work to be done to handle this better. The need for a Home Agent is a reflection of the awkwardnessof IP mobility in general. The 6LoWPAN design does the best it can to deal with this, within the present-day IPv6 architecture.

Routing in low-power, lossy environments has been taken up by the ROLL working group in the Internet Engineering Task Force. In addition, the Mobile Ad-Hoc Network (MANET) working group has also tackled aspects of this problem. These sections of the book are extremely valuable for their pedagogical utility to say nothing of the practical consideration they give to this vexing problem area.

I found the sections on Applications (Chapter 5) especially interesting since that is where all the real action is. Figure 5.3 is a beautiful example of using simple diagrams to localize problem areas and issues. This chapter highlighted for me the importance of matching the applications to the underlying capability of the network(s) through which the application must operate. If end-to-end connectivity is not guaranteed, applications need to incorporate awareness of this if they are to operate successfully and effectively, for example. Blindly layering protocols accustomed to reliable, speedy and sequenced delivery on critical network components that cannot provide such guarantees will generally produce unsatisfactory results.

As we enter into a period where sensors networks become an integral part of energy management, building automation, and other applications, it is highly desirable to standardize application infrastructure to enable interoperability among systems from many vendors. In Chapter 5, we encounter ideas that enable the experience obtained from the proprietary ZigBee space to be adapted to operate in the UDP/IP/6LoWPAN space. It is encouraging to see such efforts at synthesizing commonality to increase interoperability and to enable competitive offerings. The so-called CAP protocol is the key element at work and strikes me as an important contribution to the Internet protocol library. The chapter finishes with a very useful compendium and summary of a variety of proprietary protocols that ultimately will have to be adapted to work in a more standard Internet environment to be broadly useful.

The convergence of ZigBee protocols with Internet-oriented ones, in the 6LoWPAN context, and the creation of the IP for Smart Objects (IPSO) alliance are healthy indications that the ad hoc solutions for low-power networking are beginning to coalesce into interoperable designs that can become the core of the Internet of Things. I cannot see all the ramifications of this emerging consensus but it is fair to say that it will deliver an information-rich environment in which to invent new applications and provide feedback that will enable wiser choices leading to an environmentally smarter society.

Vint Cerf

Vice-president and Chief Internet Evangelist, Google