Module 15 - Network structures. In a distributed (loosely coupled) system, the processors do not share memory or a clock. Instead, each processor has its own local memory. The processors communicate with one another through various communication networks, such as high-speed buses or telephone lines. In this chapter, we discuss the general structure of distributed systems and the networks that interconnect them. Detailed discussions are given in chapters 16 to 18. | Lecture Operating system concepts Fifth edition Module 15 - Avi Silberschatz Peter Galvin Module 15 Network Structures Background Motivation Topology Network Types Communication Design Strategies Silberschatz and Galvin 1999 Node Types Mainframes IBM3090 etc. example applications airline reservations banking systems many large attached disks Workstations Sun Apollo Microvax RISC6000 etc. example applications computer-aided design office-information systems private databases zero one or two medium size disks Silberschatz and Galvin 1999 Nodes Types Cont. Personal Computers example applications office information systems small private databases zero or one small disk Silberschatz and Galvin 1999 A Distributed System Silberschatz and Galvin 1999 Motivation Resource sharing sharing and printing files at remote sites processing information in a distributed database using remote specialized hardware devices Computation speedup load sharing Reliability detect and recover from site failure function transfer reintegrate failed site Communication message passing Silberschatz and Galvin 1999 Topology Sites in the system can be physically connected in a variety of ways they are compared with respect to the following criteria Basic cost. How expensive is it to link the various sites in the system Communication cost. How long does it take to send a message from site A to site B Reliability. If a link or a site in the system fails can the remaining sites still communicate with each other The various topologies are depicted as graphs whose nodes correspond to sites. An edge from node A to node B corresponds to a direct connection between the two sites. The following six items depict various network topologies. Silberschatz and Galvin 1999 Fully connected network Partially connected network Silberschatz and Galvin 1999 Tree-structured network Star network Silberschatz and Galvin 1999 Ring networks a Single links. b Double links .
