trƯỜng ĐẠi hỌc cÔng nghỆ bộ môn mạng và truyền thông máy tính

TRƯỜNG ĐẠI HỌC CÔNG NGHỆBộ môn Mạng và Truyền Thông Máy Tính

TRƯỜNG ĐẠI HỌC CÔNG NGHỆBộ môn mạng và truyền thông máy tính


Các hệ thống phân tán

Chapter 1: Characterization of Distributed Systems

Người trình bày: TS. Hoàng Xuân Tù[email protected]



Examples of DS

Internet

BrowsersWeb servers

www.google.com

www.cdk3.net

www.w3c.org

Protocols

Activity.html

http://www.w3c.org/Protocols/Activity.html

http://www.google.comlsearch?q=kindberg

http://www.cdk3.net/

File system ofwww.w3c.org



Examples of DS

the rest of

email server

Web server

Desktopcomputers

File server

router/firewall

print and other servers

other servers

print

Local areanetwork

email server

the Internet



Examples of DS

Laptop

Mobile

PrinterCamera

Internet

Host intranet Home intranetWAP

Wireless LAN

phone

gateway

Host site



Concepts

• Distributed System– A collection of autonomous computers– Linked by a computer network– Run distributed system softwareForm 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.

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