Presentation is loading. Please wait.

Presentation is loading. Please wait.

1 Distribuerede systemer og sikkerhed – 7. februar 2002 From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley.

Similar presentations


Presentation on theme: "1 Distribuerede systemer og sikkerhed – 7. februar 2002 From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley."— Presentation transcript:

1 1 Distribuerede systemer og sikkerhed – 7. februar 2002 From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley 2001 Presentation based on slides for the book: Slides modified by Jens B Jorgensen, University of Aarhus

2 2 Instruktorer  Hold 1: Onsdag 8-11, lokale 1-532-316, y Lisa Wells.  Hold 2: Mandag 12-15, H2.28,  Thomas Ljungberg (Thomas Mailund vikar 11/2).  Hold 3: Torsdag 11-14, lokale 1-532-316,  Thomas Mailund.  Hold 4: Torsdag 11-14, lokale 1-521-228,  Thomas Ljungberg (Thomas Pedersen vikar 14/2).  Hold 5: Onsdag 9-12, Kollokvium G4, y Thomas Pedersen.

3 3 Chapter 2: System Models From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley 2001

4 4 System models – what and why? zSystem model: yAbstract, consistent description of a relevant aspect of a distributed system. yDescription of the main entities of a system and their interaction, and individual and collective behaviour zAid for design, analysis, discussion, etc. yMake assumptions explicit. yInvestigate what is possible or impossible.

5 5 Architectural and fundamental models zArchitectural model: Description of the components of a system and the relationship between them. zFundamental models: Description of properties that are common in architectural models: y Interaction model. y Failure model. y Security model.

6 6 Architectural models zDescribe the components of systems and their interaction; describe mapping of components to computers. zDefine useful patterns for the distribution of data and workload. zDefine the functional roles of components and the patterns of communication between them.

7 7 Architectural models – layered architecture

8 8 Basic architectural models – client-server

9 9 Basic architectural models – multiple servers Partition set of objects or replicate set of objects

10 10 Basic architectural models – proxy server and caching Cache: Store of recently used data objects closer than the objects themselves Proxy servers increase performance and availability

11 11 Basic architectural models – peer processes

12 12 Other architectural models – mobile code, web applets a) client requests results in the downloading of applet code Web server Client Web server Applet Applet code Client b) client interacts with the applet

13 13 Other architectural models – spontaneous networking Internet gateway PDA service Music service Discovery Alarm Camera Guests devices Laptop TV/PC Hotel wireless network Easy connection and integration; limited connectivity; problems with security and privacy; discovery service with registration and lookup.

14 14 Architectural models – design requirements zPerformance issues: yResponsiveness. yThroughput. yBalancing computational loads. zQuality of service: yReliability. ySecurity. yPerformance. yAdaptability. zUse of caching and replication. zDependability issues: yCorrectness. ySecurity. yFault tolerance.

15 15 Architectural models in practice zOften specified in UML, the Unified Modeling Language, e.g., as: yClass diagrams. yObject diagrams. yComponent diagrams. yDeployment diagrams. zFor more info, see www.uml.orgwww.uml.org

16 16 Fundamental models zDescription of properties that are common in architectural models: yInteraction model (performance/timing model?): Performance of processes and communication channels, absence of a global clock, timing problems, … yFailure model: Failures of processes and communication channels, reliable communication, … ySecurity model: Possible threats to processes and communication channels, secure channels, …

17 17 Interaction model – basic issues zPerformance of processes. zPerformance of communication channels: yLatency. yBandwidth. yJitter. zComputer clocks and timing events. yLack of global notion of time.

18 18 Interaction model – synchronous vs. asynchronous zSynchronous distributed systems – bounds on: yProcess execution speed. yMessage transmission delays. yLocal clock drift rates. zAsynchronous distributed systems – no bounds.

19 19 Interaction model – event ordering

20 20 Failure model – basic issues zThe ways in which failures in a distributed system may occur. zTypes of failures: yArbitrary (Byzantine) failures. yOmission failures. yTiming failures.

21 21 Failure model – process omission failures zA process fails to perform actions that it is supposed to do. zProcess omission failures: yCrash. yFail-stop. zUse timeouts.

22 22 Failure model – communication omission failures Network transmission error Send-omission failure Receive-omission failure

23 23 Failure model – timing failures zApplicable in synchronous distributed systems. zBounds exceeded for: yProcess execution time. yMessage transmission delay. yClock drift rate.

24 24 Failure model – remedies zMasking failures: yHiding failures. yConverting failures into less severe ones. zEnsuring reliability of one-to-one communication: yValidity: Any message sent is eventually delivered. yIntegrity: All messages received have been sent; no messages are delivered twice.

25 25 Security model – basic issues zProtecting objects against unauthorized access. ySpecify who is allowed to perform which operations. yUse access rights. zSecuring processes and their interactions. zSecuring communication channels. zIdentifying threats.

26 26 Security model – objects and principals

27 27 Security model - enemies Communication channel Copy of m Process p q m The enemy m’ An enemy is capable of sending any message to any process, and read or copy any message in transfer between a pair of processes

28 28 Security model – threats zIssues: yServers. yClients. yCommunication channels. yDenial of service. yMobile code. zRemedies: yCryptography. yAuthentication. ySecure channels.

29 29 Security model – secure channels Principal A Secure channel Process p q Principal B

30 30 Summary zArchitectural models: yBasic client-server. yMultiple servers. yProxies and caching. yPeer processes. y… zFundamental models: yInteraction. yFailure. ySecurity.


Download ppt "1 Distribuerede systemer og sikkerhed – 7. februar 2002 From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley."

Similar presentations


Ads by Google