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Environment

The environment in this project consists of a single (trusted) stationary file server that services multiple (untrusted) mobile clients. The types of mobile clients supported are discussed in Section 2.1. The service provided is access to shared data (files). The server can be considered as the true home of the shared data and the mobile clients as caching sites as in the traditional client/server model.^1.3

In my environment, a mobile computer can be either connected to (the same network as) the server or disconnected. The connections can be by use of a variety of different technologies, such as Ethernet, dial-up telephone line, dial-up wireless communication, see Figure 1.1. Hence, the communication bandwidth may vary substantially as does the cost of using this bandwidth, see Section 2.2.

Figure 1.1: System overview

The server should have no explicit support for stationary workstations, but of course, they can be considered as odd cases of mobile clients that never move and are always (fully) connected, see Section 2.2.1.

The mobile clients are in contact with the server on a regular basis, i.e., they do not stay disconnected forever^1.4 and can be said to be permanent members of the distributed system in which the server resides. The server does not support "visitors", i.e., mobile clients that do not fall into the category above, and for the sake of simplicity assumes that they do not exist (so that security concerns can be ignored).

Footnotes

... model.^1.3

The similarities with the traditional client/server model end when the mobile clients are no longer (fully) connected, and varying degrees of self-reliance are needed.

... forever^1.4

Except in the case where a client for some reason is no longer used (because it is replaced by a newer and better one or simply refuses to work any longer)--but that is a special case that requires special attention anyway!

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