E Lesson 4 635

IDOL Institute of Distance and Online Learning ENHANCE YOUR QUALIFICATION, ADVANCE YOUR CAREER.

M.C.A 2 All right are reserved with CU-IDOL PARALLEL AND DISTRIBUTED COMPUTING Course Code: MCA635 Semester: Third SLM Unit : 4 eLession: 4 www.cuidol.in Unit-4 (MCA635)

Introduction to Distributed Systems 33 OBJECTIVES INTRODUCTION Student will be able to : In this unit we are going to learn about the Define Distributed System Distributed System . Describe types of Distributed System Under this unit you will also understand the Elaborate Distributed System Models types and models of Distributed System. Describe Client Server Model This Unit will also make us to understand Hardware concepts and Software concepts. Describe Hardware concepts and Software Concepts www.cuidol.in Unit-4 (MCA635) INASllTITriUgThEt aOrFeDreISsTeArNveCdE AwNitDh OCNUL-IIDNOE LLEARNING

TOPICS TO BE COVERED 4 > Introduction to Distributed System > Types of Distributed System > Distributed System Models > Hardware Concepts and Software Concepts > Models of Middleware > Client Server Model www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISTRIBUTED 5 SYSTEM  A distributed system is a network that consists of autonomous computers that are connected using a distribution middleware. They help in sharing different resources and capabilities to provide users with a single and integrated coherent network.  A distributed database is basically a database that is not limited to one system, it is spread over different sites, i.e., on multiple computers or over a network of computers.  A distributed database system is located on various sited that don’t share physical components. This maybe required when a particular database needs to be accessed by various users .globally. It needs to be managed such that for the users it looks like one single database www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

FEATURES OF 6 DISTRIBUTED SYSTEM  Components in the system are concurrent. A distributed system allows resource sharing, including software by systems connected to the network at the same time.  There can be multiple components, but they will generally be autonomous in nature.  A global clock is not required in a distributed system. The systems can be spread across different geographies.  Compared to other network models, there is greater fault tolerance in a distributed model.  Price/performance ratio is much better. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

GOALS OF DISTRIBUTED 7 SYSTEM  Transparency: Achieving the image of a single system image without concealing the details of the location, access, migration, concurrency, failure, relocation, persistence and resources to the users  Openness: Making the network easier to configure and modify  Reliability: Compared to a single system, a distributed system should be highly capable of being secure, consistent and have a high capability of masking errors.  Performance: Compared to other models, distributed models are expected to give a much-wanted boost to performance.  Scalability: Distributed systems should be scalable with respect to geography, administration or size. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

CHALLENGES OF 8 DISTRIBUTED SYSTEM • Security is a big challenge in a distributed environment, especially when using public networks. • Fault tolerance could be tough when the distributed model is built based on unreliable components. • Coordination and resource sharing can be difficult if proper protocols or policies are not in place. • Process knowledge should be put in place for the administrators and users of the distributed model. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

ADVANTAGES OF 9 DISTRIBUTED SYSTEM • All the nodes in the distributed system are connected to each other. So nodes can easily share data with other nodes. • More nodes can easily be added to the distributed system i.e. it can be scaled as required. • Failure of one node does not lead to the failure of the entire distributed system. Other nodes can still communicate with each other. • Resources like printers can be shared with multiple nodes rather than being restricted to just one. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISADVANTAGES OF 10 DISTRIBUTED SYSTEM • It is difficult to provide adequate security in distributed systems because the nodes as well as the connections need to be secured. • Some messages and data can be lost in the network while moving from one node to another. • The database connected to the distributed systems is quite complicated and difficult to handle as compared to a single user system. • Overloading may occur in the network if all the nodes of the distributed system try to send data at once. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISTRIBUTED SYSTEM 11 MODELS In distributed architecture, components are presented on different platforms and several components can cooperate with one another over a communication network in order to achieve a specific objective or goal. • In this architecture, information processing is not confined to a single machine rather it is distributed over several independent computers. • A distributed system can be demonstrated by the client-server architecture which forms the base for multi-tier architectures; alternatives are the broker architecture such as CORBA, and the Service- Oriented Architecture (SOA). www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISTRIBUTED SYSTEM 12 MODELS • There are several technology frameworks to support distributed architectures, including .NET, J2EE, CORBA, .NET Web services, AXIS Java Web services, and Globus Grid services. • Middleware is an infrastructure that appropriately supports the development and execution of distributed applications. It provides a buffer between the applications and the network. • It sits in the middle of system and manages or supports the different components of a distributed system. Examples are transaction processing monitors, data convertors and communication controllers etc. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

MIDDLEWARE AS AN INFRASTRUCTURE FOR 13 DISTRIBUTED SYSTEM www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

MIDDLEWARE AS AN INFRASTRUCTURE FOR 14 DISTRIBUTED SYSTEM  Advantages: • Resource sharing − Sharing of hardware and software resources. • Openness − Flexibility of using hardware and software of different vendors. • Concurrency − Concurrent processing to enhance performance. • Scalability − Increased throughput by adding new resources. • Fault tolerance − The ability to continue in operation after a fault has occurred. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

MIDDLEWARE AS AN INFRASTRUCTURE FOR 15 DISTRIBUTED SYSTEM  Disadvantages: • Complexity − They are more complex than centralized systems. • Security − More susceptible to external attack. • Manageability − More effort required for system management. • Unpredictability − Unpredictable responses depending on the system organization and network load. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

CENTRALISED SYSTEMS vs. 16 DISTRIBUTED SYSTEM Criteria Centralized system Distributed System Economics Low High Availability Low High Complexity Low High Consistency Simple High Scalability Poor Good Technology Homogeneous Heterogeneous Security High Low www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

CLIENT -SERVER 17 ARCHITECTURE The client-server architecture is the most common distributed system architecture which decomposes the system into two major subsystems or logical processes − • Client − This is the first process that issues a request to the second process i.e. the server. • Server − This is the second process that receives the request, carries it out, and sends a reply to the client. In this architecture, the application is modelled as a set of services that are provided by servers and a set of clients that use these services. The servers need not know about clients, but the clients must know the identity of servers, and the mapping of processors to processes is not necessarily 1 : 1 www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

CLIENT -SERVER ARCHITECTURE 18 www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

THIN CLIENT MODEL 19 • In thin-client model, all the application processing and data management is carried by the server. The client is simply responsible for running the presentation software. • Used when legacy systems are migrated to client server architectures in which legacy system acts as a server in its own right with a graphical interface implemented on a client • A major disadvantage is that it places a heavy processing load on both the server and the network. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

THICK/FAT CLIENT 20 MODEL Advantages: Disadvantages: • Separation of responsibilities such as user • Lack of heterogeneous infrastructure to deal interface presentation and business logic with the requirement changes. processing. • Security complications. • Reusability of server components and potential for • Limited server availability and reliability. concurrency • Limited testability and scalability. • Simplifies the design and the development of • Fat clients with presentation and business logic distributed applications • It makes it easy to migrate or integrate existing together. applications into a distributed environment. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

MULTI-TIER 21 ARCHITECTURE • Multi-tier architecture is a client–server architecture in which the functions such as presentation, application processing, and data management are physically separated. By separating an application into tiers, developers obtain the option of changing or adding a specific layer, instead of reworking the entire application. It provides a model by which developers can create flexible and reusable applications. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

22  Presentation Tier: Presentation layer is the topmost level of the application by which users can access directly such as webpage or Operating System GUI (Graphical User interface). The primary function of this layer is to translate the tasks and results to something that user can understand. It communicates with other tiers so that it places the results to the browser/client tier and all other tiers in the network.  Application Tier (Business Logic, Logic Tier, or Middle Tier):Application tier coordinates the application, processes the commands, makes logical decisions, evaluation, and performs calculations. It controls an application’s functionality by performing detailed processing. It also moves and processes .data between the two surrounding layers www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DATA-TIER 23 ARCHITECTURE • In this layer, information is stored and retrieved from the database or file system. The information is then passed back for processing and then back to the user. It includes the data persistence mechanisms (database servers, file shares, etc.) and provides API (Application Programming Interface) to the application tier which provides methods of managing the stored data. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DATA-TIER 24 ARCHITECTURE Advantages: Disadvantages: • Better performance than a thin-client approach and is • Unsatisfactory Testability due to lack of testing simpler to manage than a thick-client approach. tools. • Enhances the reusability and scalability − as demands • More critical server reliability and availability. increase, extra servers can be added. • Provides multi-threading support and also reduces network traffic. • Provides maintainability and flexibility www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

BROKER ARCHITECTURE 25 STYLE • Broker Architectural Style is a middleware architecture used in distributed computing to coordinate and enable the communication between registered servers and clients. Here, object communication takes place through a middleware system called an object request broker (software bus). • Client and the server do not interact with each other directly. Client and server have a direct connection to its proxy which communicates with the mediator-broker. • A server provides services by registering and publishing their interfaces with the broker and clients can request the services from the broker statically or dynamically by look-up. • CORBA (Common Object Request Broker Architecture) is a good implementation example of the broker architecture. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

COMPONENTS OF BROKER 26 ARCHITECTURE STYLE Broker:  Broker is responsible for coordinating communication, such as forwarding and dispatching the results and exceptions. It can be either an invocation-oriented service, a document or message - oriented broker to which clients send a message.  It is responsible for brokering the service requests, locating a proper server, transmitting requests, and sending responses back to clients.  It retains the servers’ registration information including their functionality and services as well as location information.  It provides APIs for clients to request, servers to respond, registering or unregistering server components, transferring messages, and locating servers. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

COMPONENTS OF BROKER 27 ARCHITECTURE STYLE Stub: • Stubs are generated at the static compilation time and then deployed to the client side which is used as a proxy for the client. Client-side proxy acts as a mediator between the client and the broker and provides additional transparency between them and the client; a remote object appears like a local one. • The proxy hides the IPC (inter-process communication) at protocol level and performs marshaling of parameter values and un-marshaling of results from the server. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

COMPONENTS OF BROKER 28 ARCHITECTURE STYLE Skeleton: • Skeleton is generated by the service interface compilation and then deployed to the server side, which is used as a proxy for the server. Server-side proxy encapsulates low-level system-specific networking functions and provides high-level APIs to mediate between the server and the broker. • It receives the requests, unpacks the requests, unmarshals the method arguments, calls the suitable service, and also marshals the result before sending it back to the client. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

COMPONENTS OF BROKER 29 ARCHITECTURE STYLE • Bridge • A bridge can connect two different networks based on different communication protocols. It mediates different brokers including DCOM, .NET remote, and Java CORBA brokers. • Bridges are optional component, which hides the implementation details when two brokers interoperate and take requests and parameters in one format and translate them to another format. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

BROKER IMPLEMENTATION 30 IN CORBA • CORBA is an international standard for an Object Request Broker – a middleware to manage communications among distributed objects defined by OMG (object management group). www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

SERVICE ORIENTED 31 ARCHITECTURE • Service-oriented architecture is a client/server design which support business-driven IT approach in which an application consists of software services and software service consumers (also known as clients or service requesters). www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

SERVICE ORIENTED 32 ARCHITECTURE • A service is a component of business functionality that is well-defined, self-contained, independent, published, and available to be used via a standard programming interface. The connections between services are conducted by common and universal message-oriented protocols such as the SOAP Web service protocol, which can deliver requests and responses between services loosely. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

FEATURES OF SOA 33  Distributed Deployment − Expose enterprise data and business logic as loosely, coupled, discoverable, structured, standard-based, coarse-grained, stateless units of functionality called services.  Composability − Assemble new processes from existing services that are exposed at a desired granularity through well defined, published, and standard complaint interfaces.  Interoperability − Share capabilities and reuse shared services across a network irrespective of underlying protocols or implementation technology.  Reusability − Choose a service provider and access to existing resources exposed as services. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

SOA 34 OPERATIONS www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

ADVANTAGES OF SOA 35 • Loose coupling of service–orientation provides great flexibility for enterprises to make use of all available service recourses irrespective of platform and technology restrictions. • Each service component is independent from other services due to the stateless service feature. • The implementation of a service will not affect the application of the service as long as the exposed interface is not changed. • A client or any service can access other services regardless of their platform, technology, vendors, or language implementations. • Reusability of assets and services since clients of a service only need to know its public interfaces, service composition. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

ADVANTAGES OF 36 SOA • SOA based business application development are much more efficient in terms of time and cost. • Enhances the scalability and provide standard connection between systems. • Efficient and effective usage of ‘Business Services’. • Integration becomes much easier and improved intrinsic interoperability. • Abstract complexity for developers and energize business processes closer to end users. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 37 DISTRIBUTED SYSTEM • All distributed systems consist of multiple CPUs. There are several different ways the hardware can be arranged. The important thing related to hardware is that how they are interconnected and how they communicate with each other. It is important to take a deep look at distributed system hardware, in particular, how the machines are connected together and how they interact. • Many classification schemes for multiple CPU computer systems have been proposed over the years, but none of them have really implemented. Still, the most commonly used taxonomy is Flynn's (1972), but it was in basic stage. In this scheme, Flynn took only two things to consider i.e. the number of instruction streams and the number of data streams. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 38 DISTRIBUTED SYSTEM Single Instruction, Single Data Stream (SISD): A computer with a single instruction stream and a single data stream is called SISD. All traditional uni-processor computers (i.e., those having only one CPU) fall under this category, from personal computers to large mainframes. SISD flow concept is given in the figure below. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 39 DISTRIBUTED SYSTEM Single Instruction, Multiple Data Stream (SIMD): This type uses an array of processors with only one instruction unit that fetches an instruction, and multiple data units which work in parallel. These machines are used where there need to apply the same instruction for multiple data example, adding up all the elements of 64 independent vectors. Some supercomputers are SIMD. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 40 DISTRIBUTED SYSTEM Multiple Instruction, Single Data Stream (MISD): The next category is MISD i.e. multiple instruction streams, single data stream. This structure was worked when there are multiple different instructions to operate on the same type of data. In general MISD architecture is not use more in practical. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 41 DISTRIBUTED SYSTEM Multiple Instruction, Multiple Data Stream (MIMD): The next category is MIMD, which has multiple instructions performances on multiple data units. This means a group of independent computers; each has its own program counter, program, and data. All distributed systems are MIMD, so this classification system is not more useful for simple purposes. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 42 DISTRIBUTED SYSTEM Taxonomy of parallel and distributed computer systems www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS IN 43 DISTRIBUTED SYSTEM  In the bus, there is a single network, backplane, bus, cable, or another medium that connects all the machines. In a cable television system, the cable company runs a wire down the street, and other subscribers have taps running to it from their television sets.  Switched systems do not have a single backbone like cable television. But, there are individual wires from machine to machine, having different wiring patterns in use. Messages move through the wires, and the final switching decision is made at each routing stage to route the message to an outgoing destination. The public telephone system for the whole world is organized in this way. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

HARDWARE CONCEPTS 44 IN DISTRIBUTED SYSTEM  In a tightly-coupled system, delay is short for message passing, and also the data rate is high; that means, the number of bits per second that can be transferred is large.  In the loosely-coupled system, it is just the opposite of it. The inter-machine message delay is large and the data rate is low. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

SOFTWARE CONCEPTS IN DISTRIBUTED 45 SYSTEM The software concepts of the distributed system is nothing but selection of different operating system platforms. The operating system is the interaction between user and the hardware. There are three largely used operating system types:  Distributed operating system  Network operating system  Middleware operating system www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISTRIBUTED OPERATING 46 SYSTEM • Distributed Operating System is one of the important type of operating system. • Multiple central processors are used by Distributed systems to serve multiple real-time applications and multiple users. Accordingly, Data processing jobs are distributed among the processors.  Processors communicate with each other through various communication lines (like high-speed buses or telephone lines). These are known as loosely coupled systems or distributed systems. Processors in this system may vary in size and function. They are referred as sites, nodes, computers, and so on. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISTRIBUTED OPERATING 47 SYSTEM www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

DISTRIBUTED OPERATING 48 SYSTEM Advantages: • With resource sharing facility, a user at one site may be able to use the resources available at another. • Speedup the exchange of data with one another via electronic mail. • Failure of one site in a distributed system doesn’t affect the others, the remaining sites can potentially continue operating. • Better service to the customers. • Reduction of the load on the host computer. • Reduction of delays in data processing. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

NETWORK OPERATING SYSTEM 49  Network Operating System runs on a server and gives the server the capability to manage data, users, groups, security, applications, and other networking functions.  The basic purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks.  Some examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL

NETWORK OPERATING 50 SYSTEM  Advantages • Centralized servers are highly stable. • Security is server managed. • Upgradation of new technologies and hardware can be easily integrated into the system. • It is possible to remote access to servers from different locations and types of systems.  Disadvantages • High cost of buying and running a server. • Dependency on a central location for most operations. • Regular maintenance and updates are required. www.cuidol.in Unit-4 (MCA635) All right are reserved with CU-IDOL