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INTRODUCTION

Currently, most users think of computers as associated with their desktop appliances or with a server located in a dungeon in some mysterious basement. However, many of those same users may be considered to be nomads, in that they own computers and communication devices that they carry about with them in their travels as they move between office, home, airplane, hotel, automobile, branch office, and so on. Moreover, even without portable computers or communications, there are many who travel to numerous locations in their business and personal lives and who require access to computers and communications when they arrive at their destinations.

Indeed, even a move from a desk to a conference table in the same office constitutes a nomadic move since the computing platforms and communications capability may be considerably different at the two locations. The variety of portable computers is impressive, ranging from laptop computers, notebook computers, and personal digital assistants (or personal information managers) to "smart" credit card devices and wristwatch computers. In addition, the communication capability of these portable computers is advancing at a dramatic pace from high-speed modems to PCMCIA modems, e-mail receivers on a card, spread-spectrum hand-held radios, CDPD transceivers, portable GPS receivers, and gigabit satellite access, and so on.

The combination of portable computing with portable communications is changing the way we think about information processing. We now recognize that access to computing and communications is necessary not only from "home base" but also while in transit and after reaching a destination.

These ideas form the essence of a major shift to nomadicity (nomadic computing and communications), which we address in this paper. The focus is on the system support needed to provide a rich set of capabilities and services, in a transparent and convenient form, to the nomad moving from place to place.

In this paper we propose location independent naming as a mechanism to support nomadic computing on the Internet. Nomadic computing is a limited, but common form of mobile computing.Nomadic users compute from different locations, but do not require network connectivity while they are moving. For example, a salesman will travel from customer to customer, using his laptop at each location but storing it while driving to the next location.

While Mobile IP was designed for continuously moving computers, it can also support nomadic users. Mobile IP allows users to maintain existing connections while traveling between networks by allowing machines to carry their IP address with them when they move to a new network. Unfortunately, preserving IP addresses across networks introduces several drawbacks, including the performance penalties of triangle routing; the security problems of IP tunneling through fire-walls, and the loss of connectivity due to packet loss from source address filters. The drawbacks are inherent to Mobile IP since it breaks the one-to-one mapping between IP address and network location that is used by the Internet to route packets to the correct destination.

Our approach, Location Independent Naming (LIN), allows a machine to keep the same name as it moves around the Internet by rebinding its name to its local address when it moves. Once this binding has been made, the machine can communicate with any other host on the Internet using standard IP routing, since the source address on its packets identifies the machine's actual location. Further, other machines on the Internet can communicate with this machine, since its host-name maps to its current address. While this machine remains at its current location, it behaves just like any other machine at that location - no special support is needed except to setup and teardown the name-to-address binding. Because LIN preserves the association between IP address and location, it avoids the performance and security drawbacks of Mobile IP for nomadic computers, as well as the complexities of optimizing Mobile IP.

LIN represents an advance of the state of the art as it allows correspondent hosts to communicate with a nomadic host using its well-known name without the performance penalties, security issues, or need for infrastructure support of Mobile IP. It leverages and extends existing and pro-posed functionality of DNS (Domain Name System) and DHCP (Dynamic Host Configuration Protocol) to allow a mobile host to keep its name while moving across security domains using existing trust relationships.

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