Lesson 1.1: Introduction to system models

Here are some of the problems that the designers of distributed systems face.

Widely varying modes of use: The component parts of systems are subject to wide variations in workload – for example, some web pages are accessed several million times a day. Some parts of a system may be disconnected, or poorly connected some of the time – for example, when mobile computers are included in a system. Some applications have special requirements for high communication bandwidth and low latency – for example, multimedia applications.
Wide range of system environments: A distributed system must accommodate heterogeneous hardware, operating systems and networks. The networks may differ widely in performance – wireless networks operate at a fraction of the speed of local networks. Systems of widely differing scales, ranging from tens of computers to millions of computers, must be supported.
Internal problems: Non-synchronized clocks, conflicting data updates and many modes of hardware and software failure involving the individual system components.
External threats: Attacks on data integrity and secrecy, denial of service attacks.