Chapter 2: System models 2.1 introduction 2.2 Physical models 2.3 Architectural models 2.4 Fundamental models

Fundamental Models Interaction model – performance and time. Failure model – processes and communication. Security model - processes and communication.

Introduction : Problems & threats The three different models Difficulties of D.S. widely varying models, wide range of system environments, internal problems external threats

Physical models Three generation of Distributed System: Early distributed systems Internet-scale distributed systems Contemporary distributed systems Distributed systems of systems

Architectural models Approaches like: client-server,peer-to- peer,distributed objects, distributed components, and distributed event based systems.

Architectural elements Communication entities Communication paradigms (figure 2.2)

Architectural elements

Classifying processes Server processes Client processes Peer processes - Symmetrical manner Goal – identifies the roles and responsibility Specify the placement of the processes.

Architectural style based on there role Client-server peer-to-peer

Client-server

peer-to-peer

Dynamic systems Built as: moving code from one process of another. discover available services of others.

placement Mapping of services to multiple servers Caching Mobile code Mobile agents

Architectural pattern Software architecture – structure of software, services, requests. Layering Services layers

Architectural pattern Tiered Architecture

Architectural pattern Thin Clients

Architectural pattern Other commonly occurring patterns The proxy pattern The use of brokerage

Middleware Solution.

Fundamental models Interaction model Failure model Security model

Interaction model Factors Affecting the interaction processes in D.S. Performance of communication channels Computer clock & time events -synchronous D.S. -asynchronous D.S.

Interaction model Event ordering

Failure model Omission failures Process Omission failures Communication Omission failures Arbitrary failure Timing failure

Timing failures

Security model Protection object Securing process