In 1991 Mark Weiser wrote his seminal paper [167] on ubiquitous computing. It was the start of what has become an alternative vision for the use of computers in society. Wieser had realised that, as the number of computers increase within society, it would become increasingly more dicult to use them in any meaningful way. He believed that it was necessary to move away from the conventional concept of the personal computer to an approach where physical spaces would be made up of computational devices, that would be integrated into everyday objects
and embedded with technology and connectivity. In this world, people would be continually interacting with hundreds of interconnected devices that would meld into the background and eectively become invisible to those who use them. In his paper [167] Weiser wrote that:
The most profound technologies are those that disappear. They weave themselves into the fabric of everyday life until they are indistinguishable from it. [167]
The statement illustrates Weiser's belief that for technologies to truly become an integral part of our daily lives it is necessary for them to disappear from our awareness, to be so ingrained in our psyche that it is not necessary to have to think about using them. This would enable computer users to focus beyond the tools and so concentrate on their goals. Ubiquitous computing denes a technology that does not require our constant attention but at the same time is ready to be used at a glace.
In developing his vision of ubiquitous computing Weiser recognised that the millions of personal computers inhabiting society were largely isolated and disconnected from it and were, in fact, mostly getting in the way of people. He recognised that computers were not disappearing into the background but were increasingly demanding the attention of users. Weiser realised that the relationship between humans and computers had to change to one that ensured computers became vastly better at getting out of the way [168] of people. He realised for this to happen computers needed to become part of the natural human environment [167] and that it was necessary for them to vanish into the background [167] of our society. He argues that for computers to truly become an integral part of our lives it necessary for them to totally disappear from our awareness.
Such a disappearance is a fundamental consequence not of technology, but of human psychology. Whenever people learn something suciently well, they cease to be aware of it. [167]
In considering the statement above it is clear that ubiquitous computing is more than just the development and deployment of technology into physical spaces it also encompasses how people perceive and interact with such technology. Whether or not the technology is allowed
to be interwoven into the fabric of society until it becomes indistinguishable from it [167] depends on how it is perceived and used. It is only when it is accepted that such technology can be thought as ubiquitous.
Ubiquitous computing requires a fundamental change in how computers are perceived and used in our society and demands a total rethink of how such systems are designed and implemented. For researchers the main question still remains: how do technologies disappear into the background? [167]. The answer lies in the widespread proliferation of devices that are suciently small and cheap enough to be built into everyday objects. The goal is to make these devices so pervasively distributed across society that they become such an intrinsic part of peoples lives that they no longer recognise them as computers. It is also necessary to have ecient, low-powered devices that can operate for considerable periods of time without having to change the source of power or maintain them in anyway. Devices need to be forgotten about and having to constantly support them in this manner does not allow them to meld into the background of society. With the increased numbers of devices expected to occupy ubiquitous computing environments it would become problematic to maintain devices in the same manner as we do with traditional forms of computing. As can be observed in the statement below, Weiser also noted that the real power of ubiquitous computing is only achieved when all the devices in the environment can interact with each other. It is therefore essential to provide a network that facilities the interconnection of devices.
The real power of the concept comes not from any one of these devices; it emerges from the interaction of all of them. [167]
Furthermore, for devices to become interwoven into the fabric of society it is necessary for them to understand the human environment [167]. If they are unable to comprehend what is occurring in the environment it makes it extremely dicult for devices to behave in a manner that will allow them to move into the background. Knowledge of the surrounding environment is an important facet of ubiquitous computing and can be consider as a prerequisite for most scenarios. The use of context information [42, 138, 18] has allowed many systems, some of which are discussed later in the chapter, to cope with this requirement. They use context in a number of ways to adapt the system to meet the requirements of the environment. For
instance, to recongure a system to handle the changing availability of resources, or to adapt the behavior of the system to meet the requirements of the user.
Weiser observed [167] that the technology required for ubiquitous computing comes in three parts: rstly, cheap, low-powered computers; secondly, software for ubiquitous computing applications; and lastly, a network that brings them all together. The thesis concentrates on the second requirement with the aim of providing a highly decentralized method for organising components of a ubiquitous computing environment that supports spontaneous interaction between entities and provides robust system-wide behavior. The objective is to develop a framework capable of supporting Weiser's vision for ubiquitous computing. The next section investigates the challenges in building such systems, while the following section reviews the eorts made be previous projects in tackling this objective.