What is a Distributed System? Computing (CPU) Mass Storage User Interface Just insert a network?

Distributed System Network Servers (Storage, Compute) Services User Interfaces Users

D.S. Design Issues Transparency Flexibility Reliability Performance Scalability

More Design Issues Global Clocks? Causality Information Consistency

Distributed Control Master/Slave (Issue: Response Time) –Polled –Command -> <-Response –Schedule under control of server Client/Server (Issue: Server Size) –Interrupt, or Event, Driven –Aperiodic Scheduling Peer-to-Peer (Issue: Coordination) –No single critical node –Hard to describe or predict

Distributed System: Why or Why not? Performance Economics Reliability Security

D. S. Architectures Cooperating Peers Client-Server Tiered Client-Server –Data Repository –Compute Servers –Client Stations

“Intranets” Definition –Using Internet protocols, especially Web tools, for internal MIS Motivation –Information “push” vs “pull” Problems –User Capabilities –Corporate Policy or Personal Opinion

Key Protocol Areas Directory Services RPCs Security/Authentication (Performance) Management Programming Models

References ISO RM-ODP –ITU-T X.901/ISO /2/3/4 Amjad Umar Distributed Computing: A Practical Synthesis –PTR Prentice-Hall, Englewood Cliffs, NJ, 1993 Sape Mullender Distributed Systems, 2d ed. –Addison Wesley, 1993