Contests Contests ä Introduction to DS Introduction to DS Distribuerade system - VT2001 Distribuerade system - VT2001 ä Schedule Schedule ä Litterature Litterature ä Laboration Laboration Jerry Eriksson Jerry Eriksson Defining DS Defining DS Examples of DS; Internet Examples of DS; Internet ä Network computers that communicate and Network computers that communicate and intranet coordinate their actions only by passing coordinate their actions only by passing � � ISP � messages messages � ä Consequences Consequences backbone ä Concurrency Concurrency ä No global clock No global clock satellite link ä Independent failure Independent failure desktop computer: server: network link: Mobile computing Mobile computing Intranet Intranet Desktop email server computers print and other servers Internet Local area Web server network WAP Host intranet email server Home intranet Wireless LAN gateway print File server other servers Mobile phone the rest of Printer the Internet Laptop Host site Camera router/firewall 1
Litterature Litterature Schedule Schedule ä Distributed systems;concepts and design Distributed systems;concepts and design ä Foundations Foundations ä Focus on Focus on ä security security ä Middleware Middleware ä Secrets and lies Secrets and lies ä programming programming ä Distributed algorithms Distributed algorithms ä Some (just a few) articles Some (just a few) articles ä algorithms algorithms ä Shared data Shared data ä Start to work at once; Start to work at once; ä Multimedia system Multimedia system This is a D-cource !!! This is a D-cource !!! Laboration Laboration People People ä Only one lab. Rather big. Only one lab. Rather big. ä Jerry Eriksson Jerry Eriksson ä Groups of three. Groups of three. ä Jonny Pettersson Jonny Pettersson ä Requirement specification (High level) Requirement specification (High level) ä Amanuens Amanuens ä Up to you to design, implement and test. Up to you to design, implement and test. ä Erik Lindström, guest lecturer Erik Lindström, guest lecturer ä Weekly report of progess. Weekly report of progess. ä A lot of hard work, I guess. Hopefully, most A lot of hard work, I guess. Hopefully, most valueable when applying for job. valueable when applying for job. My lectures My lectures Resource sharing; the web Resource sharing; the web ä Follow the book structure Follow the book structure http://www.google.comlsearch?q=kindberg ä self-study fully possible self-study fully possible www.google.com Browsers ä (Not true for multimedia) (Not true for multimedia) Web servers ä Today chapter 1-3 Today chapter 1-3 Internet www.cdk3.net http://www.cdk3.net/ www.w3c.org http://www.w3c.org/Protocols/Activity.html File system of Protocols www.w3c.org Activity.html 2
Challenges Challenges Heterogeneity Heterogeneity ä Heterogeneity Heterogeneity ä applies to applies to ä Middleware - software Middleware - software layer that provides layer that provides ä networks networks ä Opennes Opennes programming programming ä computer hardware computer hardware ä Security Security abstraction abstraction ä operating systems operating systems ä Scalability Scalability ä programming programming ä Mobile code - code Mobile code - code languages languages that be sent from one that be sent from one ä Faliure handling Faliure handling ä implementations by implementations by computer to another. computer to another. ä Concurrency Concurrency different developers different developers Java applets Java applets ä Transparency Transparency Openness Openness Scalability Scalability ä Extended and re- Extended and re- ä Open systems; Open systems; ä Controlling the cost of physical resourses Controlling the cost of physical resourses implemented implemented ä Key interafces are Key interafces are ä Controlling the performance loss Controlling the performance loss published published ä Very important in the Very important in the ä Preventing software resourse running out Preventing software resourse running out ä Open distributed Open distributed industry industry ä Avoiding performance bottlenecks Avoiding performance bottlenecks systems can be systems can be ä RFC (requests for RFC (requests for ä constructed from constructed from comments) comments) hetergenous hardware hetergenous hardware ä You’ll use it in your You’ll use it in your Date Web servers Computers and software. and software. work. In this course. work. In this course. 188 0 1979, Dec. And probably in the And probably in the rest of your life rest of your life 1989, July 130,000 0 1999, July 56,218,000 5,560,866 Scalability Scalability Failure handling Failure handling ä Techniques for dealing with failures Techniques for dealing with failures ä Detecting failures Detecting failures Date Computers Web servers Percentage ä Masking failures Masking failures 1,776,000 130 0.008 1993, July ä Tolerating failures Tolerating failures 1995, July 6,642,000 23,500 0.4 ä Recovery from failures Recovery from failures 1997, July 19,540,000 1,203,096 6 ä Redundancy Redundancy 1999, July 56,218,000 6,598,697 12 3
Transparency Transparency 2. System Models 2. System Models ä Architectural models Architectural models ä Fundamental models Fundamental models Access transparency : enables local and remote resources to be accessed using identical operations. ä Concerned with the Concerned with the ä Concerned with mode Concerned with mode Location transparency : enables resources to be accessed without knowledge of their placements of its parts placements of its parts formal description of formal description of location. Concurrency transparency : enables several processes to operate concurrently using shared and the relationships and the relationships the properties that are the properties that are resources without interference between them. between them. between them. common in architetural common in architetural Replication transparency : enables multiple instances of resources to be used to increase models models reliability and performance without knowledge of the replicas by users or application ä Examples Examples programmers. ä Models Models ä Client-server Client-server Failure transparency : enables the concealment of faults, allowing users and application ä peer-peer peer-peer ä Interaction model Interaction model 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 ä Failure model Failure model without affecting the operation of users or programs. ä Security model Security model 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. Software and hardware layers Software and hardware layers Platform and middleware Platform and middleware ä Platform Platform Applications, services ä Middleware Middleware Middleware Operating system Platform Computer and network hardware Client-server Client-server Multiple - servers Multiple - servers Service Server Client Client invocation Server invocation result result Server Server Client Client Key: Process: Computer: Server 4
Web proxy server Web proxy server Peer processes Peer processes Application Application Web Coordination Coordination Client code code server Proxy server Web Client server Application Coordination code Mobile code - web applets Mobile code - web applets Thin clients Thin clients a) client request results in the downloading of applet code Compute server Network computer or PC Web Client server Application Applet code Thin network Process Client b) client interacts with the applet Web Client Applet server Mobile devices and spontaneous Mobile devices and spontaneous Key features and other issues Key features and other issues networking networking ä Easy connection to a local network Easy connection to a local network Music ä Easy integration with local services Easy integration with local services service Alarm gateway service ä Other issues Other issues Internet ä Limited connectivity Limited connectivity ä Security and privacy Security and privacy Hotel wireless network Discovery ä Discovery services Discovery services service Camera ä Registration. Lookup services Registration. Lookup services TV/PC Guests Laptop PDA devices 5
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