Introduction

One of the defining trends of the 1990s has been the explosive growth of the Internet. A growing number of people have Internet access at work, at home, and on the road. Meanwhile, other types of networks, such as cell phones and pager networks, are proliferating rapidly. In the next decade, more and more people will expect ubiquitous network access--the ability to communicate with anyone, anywhere. These trends present us with a number of challenges:

Enabling ubiquitous reachability. Most people will continue to use a variety of network-enabled devices and applications to communicate with others. The notion of a one-size-fits-all communication device is just as misguided as a universal network link or operating system. Basic tradeoffs like weight, speed, and ease of use will not vanish anytime soon; in the meantime, people will use different devices and applications at different times. Our ideal of ubiquitous network access cannot be achieved unless people can be reached regardless of the communication devices or applications they choose to use.

Maintaining location privacy. Enabling ubiquitous network access unfortunately makes privacy issues even more urgent than they are now. A system that keeps track of how a person is reachable and distributes that information without limits could be used to deduce the person's location and compromise his privacy. Ideally, people should be able to receive messages anywhere, without revealing their whereabouts to the entire world.

Thwarting ``spam.'' Receiving unwanted messages is another type of invasion of privacy. Many messaging applications have no way to deliver messages unintrusively. For example, most telephones can either ring or not ring when a call arrives, instead of ringing for some callers and taking a message for others, or ringing during the day and taking a message at night. Users should be able to have all their incoming communications prioritized and filtered on their behalf.

Converting among protocols. Not all application-layer communication protocols can be used by all devices. For example, most phones are not capable of receiving email. Optimally, communications would be converted automatically from the sender's preferred type to the recipient's preferred type.

We have designed the Mobile People Architecture (MPA) to address each of these challenges. In Section II, we describe how MPA fits into the big picture of networking. In Section III, we give an overview of MPA. In Section IV, we describe the design of MPA by giving detailed descriptions of four different usage scenarios. In Section V, we describe the functions of the Personal Proxy, the key component of the MPA system, which tracks the mobile person and handles communications on his behalf. In Section VI, we describe related work, and in Section VII we state our conclusions.

Figure 1: The Layering Model. We show the traditional networking layers, extended with the People layer. Name Types shows examples of the kinds of names used at each layer. Name Lookup shows some methods of mapping names from each layer to names in the next lower layer. Packet Headers shows examples of actual names at each layer, and their relative locations in a typical email packet.