TRƯỜNG ĐẠI HỌC CÔNG NGHỆ Bộ môn Mạng và Truyền Thông Máy Tính

Các hệ thống phân tán Chapter 1: Characterization of Distributed Systems Người trình bày: TS. Hoàng Xuân Tùng

Examples of DS Internet Browsers Web servers Protocols Activity.html File system of

Examples of DS

Concepts Distributed System –A collection of autonomous computers –Linked by a computer network –Run distributed system software  Form an integrated computing facility Autonomous computer: –Fully control its own resources Memory/harddisk/networking bandwidth Integrated computing facility: –Same purpose

Characteristics Resource sharing Openness Concurrency Scalability Fault tolerance And Transparency

Resource Sharing “Resource” = things that can be used –Can be hardware: disk, printer, network, … –Or software: files, windows, databases, sockets, software objects, … –Resource are usually limited Resource sharing in DS –By sending message Remote procedure call Remote method invocation

Why resource sharing ? Make different computers doing something for the same purpose Example: –Separation between computation and presentation –Network file system –Shared database servers –…

Openness Ability in extending features or capabilities –Hardware: Peripheral devices Network printers Computational units –Software: Software features (kernel modules, software modules, communication protocols, resource sharing services …) Openness is achieved by standardized interfaces –Standardization !!!

Openness Standards and specifications –Programming languages: ANSI (C) JSR (Java Specification Request) –System API BSD System calls IEEE’s POSIX –Communication protocols IETF RFC/Internet Draft

Concurrency Multiple and relatively independent systems working at the same time –Processes –Threads They possibly don’t know all information about each other. –Lack of information sharing –Unreliability of computer networks Resource access can be in arbitrary patterns.

Scalability DS can be in different scale –Very big system require scalability Scalability: –The ability to operate efficiently when system is at large scale Scalability is NOT matter of hardware Scalability is a matter software and system design

Fault tolerance Faults: –Computer crashes –Disconnection of networks Detect fault and the reason of fault are not easy But people want high availability system Fault tolerance = ability of a system that can work event when faults happen.

Fault tolerance Hardware redundancy –Using redundant hardware component Software redundancy –Designs of software that can recover from faults. –Example ???

Transparency Access transparency: enables local and remote resources to be accessed using identical operations. Location transparency: enables resources to be accessed without knowledge of their physical or network location (for example, which building or IP address). Concurrency transparency: enables several processes to operate concurrently using shared resources without interference between them. Replication transparency: enables multiple instances of resources to be used to increase reliability and performance without knowledge of the replicas by users or application programmers.

Transparency Failure transparency: enables the concealment of faults, allowing users and application programs to complete their tasks despite the failure of hardware or software components. Mobility transparency: allows the movement of resources and clients within a system without affecting the operation of users or programs. Performance transparency: allows the system to be reconfigured to improve performance as loads vary. Scaling transparency: allows the system and applications to expand in scale without change to the system structure or the application algorithms.