• Independent failures • The programs may not be able to detect whether the network has failed or has become unusually slow. Intranets • An intranet is a portion of the Internet that is separately administered and has a boundary that can be configured to enforce local security policies • The main issues arising in the design of components for use in intranets are: file services, firewalls, cost. Chapter 1: Characterization of Distributed Systems Chapter 2: System Models. Distributed Systems Concepts and Design Chapter 10: Peer-to-Peer Systems - . Performance of communication channels • Communication performance is often a limiting characteristic. Scalability • A system is described as scalable if it remains effective when there is a significant increase in the number of resources and the number of users. Challenges • Heterogeneity • Openness • Security • Scalability • Failure handling • Concurrency • Transparency. • IIS, Apache... • Client • The requesting processes. • The Web is an open system: • Its oeration is based on communication standards and document standards tht are freely published and widely implemented. Communication Network Protocols. More Discussion of Web • Dynamic pages • CGI • Javascript • ASP, PHP... • Discussion • Hypertext model is lacking in some respects, such as ’lost in hyperspace’. Mobil and ubiquitous computing (continue) • Mobile and ubiquitous computing raise significant system issues presents an architecture for mobile compuing and outlines the issues that arise from it, including how to support the discovery of resources in a host environment; eliminating the need for users to reconfigure their mobile devices as they move around; helping users to cope with limited connectivity as they travel; and providing privacy and other security guarantees to users and the environments that the visit. Examples of Distributed Systems Distributed System Requirements Transparency • Transparency is defined as the concealment from the user and the application programmer of the separation of components in a distributed system, so that the system is perceived as a whole rather than as a collection of independent components. Download Teaching Slides for Chapter 17 Distributed Transactions. protection of electronic assets. chapter 24 in textbook. • The delay between the sending of a message by one process and its receipt by another is referred to as latency. • The implementation of the internet and the services that it suports has entailed the development of practical solutions to many distributed system issues. summary • Most DS are arranged according to one of a variety of architectural models. The nodes in the distributed systems can be arranged in the form of client/server systems or peer to peer systems. Distributed DBMSs – Concepts and Design - .