DISTRIBUTED COMPUTING PARADIGMS

Paradigm? A MODEL 2for notes

Distributed Computing Paradigms and their level of abstraction 3for notes

Paradigms for Distributed Applns Message passing Paradigm Client-Server Paradigm Peer-to-Peer Paradigm Message System Paradigm Remote Procedure call Paradigm 4for notes

Message Passing Paradigm The basic approach to interprocess communications is message passing. The data representing messages are exchanged between two processes, a sender and a receiver. A Process sends a message representing a request. The message is delivered to a receiver, which processes the request and sends a message in response. 5for notes

Message Passing Paradigm The basic operations required to support the message- passing paradigm are send and receive. The abstraction provided by this model, the interconnected processes perform input and output to each other, in a manner similar to file input and output. As with file I/O, the operations serve to encapsulate the detail of network communication at the operating system level, so that a programmer may make use of the operations to send and receive message without having to deal with underlying detail. 6for notes

Message Passing Paradigm 7for notes

Client-Server Paradigm The best known paradigm for network applications, the client-server model. One process, the server, plays the role of service provider, waiting passively for the arrival of requests. The Other process, the client issues specific requests to the server and awaits the servers response. 8for notes

Client-Server Paradigm The client-server model provides an efficient abstraction for the delivery of network services. Operations required include those for a server process to listen and to accept requests, and for a client process to issue requests and accepts responses. 9for notes

Client-Server Paradigm 10for notes

Peer-to-peer Paradigm The client – server paradigm has the role for server fixed to be a listener, it cannot initiate any action. The peer-to-peer paradigm, the participating processes play equal roles, with equivalent capabilities and responsibilities. Each participant may issue a request to another participant and receive a response.. 11for notes

PEER-TO-PEER 12for notes

Message System Paradigm(MOM) Also called as Message-Oriented Middleware(MOM) paradigm. In this paradigm a message system serves as an intermediary among separate, independent processes. The message system acts as a switch for messages through which processes exchange messages asynchronously, in a decoupled manner. 13for notes

Message System Paradigm A sender deposits a message with the message system, which forwards it to a message queue associated with each receiver. Once a message sent, the sender is free to move on to other tasks. 14for notes

Message System Paradigm 15for notes

Point-to-Point Message Model In this paradigm, a message system forwards a message from the sender to the receivers message queue. Unlike the basic message-passing model, the middleware provides a message repository and allows the sending and receiving to decoupled. Via the middleware, a sender deposits a message in the message queue of the receiving process. 16for notes

Point-to-Point Message Model A receiving process extracts the messages from its message queue and handles each message accordingly. Compared to the basic message-passing model, the point-to-point message paradigm provides an additional abstraction for asynchronous operations. 17for notes

Publish/subscribe Message Model In this model, each message is associated with a specific topic or event. Applications interested in the occurrence of a specific event may subscribe to messages for that event. When the awaited event occurs, the process publishes a message announcing the event or topic. 18for notes

Publish/subscribe Message Model The publish/subscribe message model offers a powerful abstraction for multicasting or group communcation. The publish operation allows a process to multicast to a group of processes, and the subscribe operation allows a process to listen for such a multicast. 19for notes

RPC Model The message passsing model works well for basic network protocols and for basic network applications. As applications grew increasingly complex, it became necessary for further abstractions to be provided for network programming. In particular, it was desirable to have a paradigm that allows distributed software to be programmed in a manner similar to convetional applications that run on a single processor. 20for notes

RPC Model The Remote Procedure Call(RPC) provides such an asbstraction. In this model, communication between two processes is carried out using a concept similar to that for a local procedure call, which is familiar to application programmers. 21for notes

RPC Model A remote procedure call involves two independent processes, which may reside on separate machines. A process A, wishing to make a request to another process B, issues a procedure call to B, passing with the call a list of argument values. A remote procedure call triggers a predefined action in a procedure provided by process B. 22for notes

RPC Model At the completion of the procedure, process B returns a value to process A. RPC allows programmers to build network applications using a programming construct similar to the local procedure call, providing a convenient abstraction for both interprocess communications and event synchronization. 23for notes

RPC Model 24for notes

Distributed Objects Paradigms RMI ORB The Object space Paradigm The Mobile Agent Paradigm The Network services Paradigm The Groupware Paradigm 25for notes

RMI Remote Method Invocation is the Object Oriented Equivalent of RPC. In this model, a process invokes the methods in an object, which may reside on the remote host. 26for notes

ORB Object Request Broker Paradigm A Process issues request to an appropriate object that provides the desired service. The paradigm closely resembles the RMI model in its support for remote objects. 27for notes

ORB The difference is that the object request broker in this paradigm functions as middleware, allowing an application, as an object requestor, to potentially access multiple remote objects. The request broker may also function as a mediator for heterogenous objects 28for notes

Object Space Paradigm The object space paradigm assumes the existence of logical entities known as object spaces. The participants of an application converge in a common object space. A provider places objects as entries into an object space, and requestor who subscribe to the space may access the entries. 29for notes

Mobile Agent Paradigm Mobile Agent is a transportable program or object. An agent is launched from an originating host. The agent then travels autonomously from host to host according to an itinerary that it carries. The paradigm offers the abstraction for a transportable program or object. 30for notes

Mobile Agent Paradigm In lieu of message exchanges, data is carried by the program/object as the program is itself transported among the participants. 31for notes

Network Services Paradigm Service providers register themselves with directory servers on a network. A process desiring a particular service contacts the directory server at runtime, and, if the service is available, the process will be provided a reference to the service. Using this reference the process interacts with the service. 32for notes

Network Services Paradigm This paradigm is essentially an extension of the Remote Method Invocation paradigm. The difference is that service objects are registered with a global directory service. 33for notes

Collaborative Application Model In this model for computer-supported cooperative work, Processes participate in a collaborative session as a group. The two categories of the groupware models are: Message Based Group ware White Based Group ware 34for notes

Message based groupware One participant initiates a group, to be joined and all the interested participants join in it. Message is multicasted among all the participants. 35for notes

Whiteboard based groupware All the participants share a virtual white board. One person writes a message on it. All other participants can view that message and responds to it. 36for notes

Choosing a Paradigm 37for notes