DISTRIBUTED COMPUTING PARADIGMS. Paradigm? A MODEL 2for notes
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Transcript of DISTRIBUTED COMPUTING PARADIGMS. Paradigm? A MODEL 2for notes
DISTRIBUTED COMPUTING PARADIGMS
Paradigm?
A MODEL
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Distributed Computing Paradigms and
their level of abstraction
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Paradigms for Distributed Appl’nsMessage passing ParadigmClient-Server ParadigmPeer-to-Peer ParadigmMessage System ParadigmRemote Procedure call Paradigm
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Message Passing ParadigmThe 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.
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Message Passing ParadigmThe 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.
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Message Passing Paradigm
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Client-Server ParadigmThe 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 server’s response.
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Client-Server ParadigmThe 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.
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Client-Server Paradigm
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Peer-to-peer ParadigmThe 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..
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PEER-TO-PEER
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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.
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Message System ParadigmA 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.
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Message System Paradigm
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Point-to-Point Message ModelIn this paradigm, a message system forwards
a message from the sender to the receiver’s 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.
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Point-to-Point Message ModelA 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.
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Publish/subscribe Message ModelIn 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.
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Publish/subscribe Message ModelThe 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.
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RPC ModelThe 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.
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RPC ModelThe 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.
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RPC ModelA 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.
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RPC ModelAt 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.
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RPC Model
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Distributed Objects ParadigmsRMIORBThe Object space ParadigmThe Mobile Agent ParadigmThe Network services ParadigmThe Groupware Paradigm
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RMIRemote 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.
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ORBObject 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.
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ORBThe 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
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Object Space ParadigmThe 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.
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Mobile Agent ParadigmMobile 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.
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Mobile Agent ParadigmIn lieu of message exchanges, data is carried
by the program/object as the program is itself transported among the participants.
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Network Services ParadigmService 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.
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Network Services ParadigmThis paradigm is essentially an extension of
the Remote Method Invocation paradigm.
The difference is that service objects are registered with a global directory service.
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Collaborative Application ModelIn 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 wareWhite Based Group ware
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Message based groupwareOne participant initiates a group, to be joined
and all the interested participants join in it.
Message is multicasted among all the participants.
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Whiteboard based groupwareAll 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.
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Choosing a Paradigm
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