System Types Distributed Systems
System types1 Personal systems that are designed torun on a personal computer orworkstation Distributed systems where thesystem software runs on a looselyintegrated group of cooperatingprocessors linked by a networkDistributed systemcharacteristics Resource sharingConcurrencyScalabilityFault toleranceTransparencyDistributed systems2 Virtually all large computer-basedsystems are now distributed systems Information processing is distributedover several computers rather thanconfined to a single machine Distributed software engineering isnow very important3Distributed system disadvantages 4ComplexitySecurityManageabilityUnpredictability1
Distributed SystemsArchitectures5Issues in distributed systemdesign Architectural design for softwarethat executes on more than oneprocessorTopics covered Multiprocessor architecturesClient-server architecturesDistributed object architecturesCORBA7Distributed systems architectures8 Multiprocessor architectures– System composed of multiple processes thatmay execute on different processors Client-server architectures– Distributed services which are called on byclients. Servers that provide services aretreated differently from clients that useservices Distributed object architectures– No distinction between clients and servers. Anyobject on the system may provide and useservices from other objects2
Multiprocessor architectures910A multiprocessor traffic control system Simplest distributed system model System composed of multiple processeswhich may execute on different processors Architectural model of many large realtime systems Distribution of process to processor maybe pre-ordered or may be under thecontrol of a dispatcherSensorcontrolprocess The application is modelled as a set ofservices that are provided by servers and aset of clients that use these services Clients know of servers but servers neednot know of clients Clients and servers are logical processes The mapping of processors to processes isnot necessarily 1 : 1LightcontrolprocessDisplayprocessTraffic lightsTraffic flow sensorsand camerasClient-server architecturesTraffic light controlprocessorTraffic flowprocessorSensorprocessor11Operator consoles12A client-server systemc3c2c4c12c11c1Server processs4s1c10c5s2c6c7Client processs3c9c83
13Computers in a C/S networkThin and fat clients14 Thin-client modelc1c2CC1CC2CC3Networks1, s2Servercomputers3, s4c5, c6, c7c8, c9CC4CC5CC6Presentation15ServerData pplication processingClient– In this model, the server is only responsible fordata management. The software on the clientimplements the application logic and theinteractions with the system user.Clientcomputerc10, c11, c12Thin and fat clientsFat-clientmodel Fat-client modelSC1SC2Thin-clientmodel– In a thin-client model, all of the applicationprocessing and data management is carried outon the server. The client is simply responsiblefor running the presentation software.c3, c4ServerDatamanagementThin client model16 Used when legacy systems aremigrated to client serverarchitectures.– The legacy system acts as a server in itsown right with a graphical interfaceimplemented on a client A major disadvantage is that it placesa heavy processing load on both theserver and the network4
Fat client model17 More processing is delegated to the clientas the application processing is locallyexecuted Most suitable for new C/S systems wherethe capabilities of the client system areknown in advance More complex than a thin client modelespecially for management. New versions ofthe application have to be installed on allclientsLayered application architectureA client-server ATM system18ATMATMAccount serverTeleCustomerprocessing accountmonitordatabaseATMATM19Application layers20 Presentation layer– Concerned with presenting the results of acomputation to system users and with collectinguser inputsPresentation layer Application processing layer– Concerned with providing application specificfunctionality e.g., in a banking system, bankingfunctions such as open account, close account,etc. Data management layer– Concerned with managing the system databasesApplication processinglayerData managementlayer5
Three-tier architectures21 In a three-tier architecture, each of theapplication architecture layers mayexecute on a separate processor Allows for better performance than a thinclient approach and is simpler to managethan a fat-client approach A more scalable architecture - as demandsincrease, extra servers can be addedAn internet banking ationprocessingDatamanagementUse of C/S architectures24HTTP interactionDatabase serverWeb serverClientA 3-tier C/S architecture22Account serviceprovisionSQL querySQLCustomeraccountdatabaseClientClient6
Distributed object architectures25 There is no distinction in a distributedobject architectures between clients andservers Each distributable entity is an object thatprovides services to other objects andreceives services from other objects Object communication is through amiddleware system called an objectrequest broker (software bus) However, more complex to design than C/SsystemsAdvantages of distributed objectarchitecture It allows the system designer to delaydecisions on where and how services shouldbe provided It is a very flexible and scaleable systemarchitecture that allows new resources tobe added to it as required It is possible to reconfigure the systemdynamically with objects migrating acrossthe network as requiredDistributed object architectureo1o2o3o4S (o1)S (o2)S (o3)S (o4)26Software bus27o5o6S (o5)S (o6)Uses of distributed objectarchitecture28 As a logical model that allows you tostructure and organize the system. In thiscase, you think about how to provideapplication functionality solely in terms ofservices and combinations of services As a flexible approach to theimplementation of client-server systems.The logical model of the system is a clientserver model but both clients and serversare realized as distributed objectscommunicating through a software bus7
Middleware29 Software that manages and supportsthe different components of adistributed system. In essence, it sitsin the middle of the system Middleware is usually off-the-shelfrather than specially writtensoftwareApplication structure Application objects Standard objects, defined by the OMG,for a specific domain e.g. insurance Fundamental CORBA services such asdirectories and security management Horizontal (i.e. cutting across applications)facilities such as user interface facilities30CORBA Common Object Request BrokerArchitecture (CORBA) is an internationalstandard for an Object Request Broker middleware to manage communicationsbetween distributed objects Several implementation of CORBA areavailable Distributed Component Object Model(DCOM) is an alternative approach byMicrosoft to object request brokers CORBA has been defined by the ObjectManagement Group (OMG)31CORBA application ontalCORBA facilitiesObject request brokerCORBA services8
CORBA standards33 CORBA objects are comparable, inprinciple, to objects in C and Java They MUST have a separate interfacedefinition that is expressed using acommon language (IDL) similar to C There is a mapping from this IDL toprogramming languages (C , Java, etc.) Therefore, objects written in differentlanguages can communicate with each other An object model for application objects– A CORBA object is an encapsulation of statewith a well-defined, language-neutral interfacedefined in an IDL (interface definitionlanguage) An object request broker that managesrequests for object services A set of general object services of use tomany distributed applicationsObject request broker (ORB) The ORB handles object communications.It knows of all objects in the system andtheir interfaces Using an ORB, the calling object binds anIDL stub that defines the interface of thecalled object Calling this stub results in calls to the ORBwhich then calls the required objectthrough a published IDL skeleton (links theinterface to the service implementation)CORBA objects343536ORB-based object communicationso1o2S (o1)S (o2)IDLstubIDLskeletonObject Request Broker9
Inter-ORB communications37 ORBs handle communications betweenobjects executing on the samemachine Several ORBS may be available andeach computer in a distributedsystem will have its own ORB Inter-ORB communications are usedfor distributed object calls38Inter-ORB communicationso1o2o3o4S (o1)S (o2)S (o3)S (o4)IDLIDLIDLIDLObject Request BrokerObject Request BrokerNetworkCORBA services Naming and trading services– These allow objects to discover and refer toother objects on the network Notification services– These allow objects to notify other objectsthat an event has occurred Transaction services– These support atomic transactions and rollbackon failure39Additional Resources on CORBA40 http://www.corba.org/ CORBA Success Storieshttp://www.corba.org/success.htm– The Weather Channel (TWC) used CORBA andLinux to develop a system that providesreliability, doesn't require a high level ofoperational support and offers the ability tohave detailed data logging. They were able tomeet these needs and slash their softwaredevelopment time from months to weeks.– http://www.corba.org/industries/publish/twc.htm10
Distributed systems where the system software runs on a loosely integrated group of cooperating processors linked by a network 2 Distributed systems Virtually all large computer-based systems are now distributed systems Information processing is distributed over several computers rather than confined to a single machine
Distributed Database Design Distributed Directory/Catalogue Mgmt Distributed Query Processing and Optimization Distributed Transaction Mgmt -Distributed Concurreny Control -Distributed Deadlock Mgmt -Distributed Recovery Mgmt influences query processing directory management distributed DB design reliability (log) concurrency control (lock)
Distributed Control 20 Distributed control systems (DCSs) - Control units are distributed throughout the system; - Large, complex industrial processes, geographically distributed applications; - Utilize distributed resources for computation with information sharing; - Adapt to contingency scenarios and
A distributed system is a collection of independent computers, interconnected via a network, capable of collaborating on a task. Distributed computing is computing . 1.2 Introduction of Distributed System High degree of scalability A distributed system is functionally equivalent to the systems of which it is composed. .
Operating System Concepts – 10th Edition 19.3 Silberschatz, Galvin and Gagne 2018 Chapter Objectives Explain the advantages of networked and distributed systems Provide a high-level overview of the networks that interconnect distributed systems Define the roles and types of distributed systems in use today Discuss
Of course, the distributed systems community has been developing general distributed systems platforms for many years, and there are currently a number of contenders for distributed systems standards including ISO's Open Distributed Processing (ODP) [ISO90, Bence93], OMG's Object Management Architecture,
the proposed distributed MPC framework, with distributed estimation, distributed target cal- culation and distributed regulation, achieves offset-free control at steady state are described. Finally, the distributed MPC algorithm is augmented to allow asynchronous optimization and
8. Distributed leadership as a companion to continuous improvement, 29 a. Distributed leadership in problem diagnosis, 31 b. Distributed leadership in solution design and enactment, 34 c. Distributed leadership in action review, 38 9. Managing the risks of using distributed leadership for improvement, 38 a. The discomfort of public disagreement .
Evaluating community projects A practical guide Marilyn Taylor, Derrick Purdue, Mandy Wilson and Pete Wilde These guidelines were initially developed as part of the JRF Neighbourhood Programme. This programme is made up of 20 community or voluntary organisations all wanting to exercise a more strategic influence in their neighbourhood. The guidelines were originally written to help these .
