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DISTRIBUTED COMPUTING

Sunita Mahajan, Principal, Institute of Computer Science, MET League of Colleges, Mumbai

Seema Shah, Principal, Vidyalankar Institute of Technology, Mumbai University

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Chapter - 4�Remote Communication

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Topics

Introduction to Remote Communication
Remote Procedural Call Basics
RPC Implementation
RPC Communication
Other RPC Issues
Case Study: Sun RPC
Remote invocation Basics
RMI Implementation

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Introduction to Remote Communication �

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Introduction

Middleware

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Remote Procedural Call Basics

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Local Procedure Call

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�Remote Procedure Call

Basic RPC operation

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RPC operation

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Elements of RPC mechanism implementation

Client
Client stub
RPC Runtime
Server stub
Server

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RPC Execution

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Stub generation

Manual generation
Auto generation using Interface Definition Language (IDL)

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RPC Compilation

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RPC Implementation

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RPC implementation

RPC messages:

Call / Request
Reply

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RPC Call/ Request message

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RPC reply conditions

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RPC reply message

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Parameter Passing Semantics

Call-by-value semantic

Marshalling

Call-by –reference semantic
Call-by-copy/restore semantic

Call-by-value copies all parameters into a message before transmission . Call-by-reference passes pointers to the parameters that are passed from the client to the server. Call-by-copy/restore uses temporary storage accessible to both programs

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Call-by-value semantic

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Byte ordering

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Other semantics

Call-by –reference semantic
Call-by-copy/restore semantic

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Server management

Server implementation

Stateless server
Stateful server

Server management

Instance per call
Instance per session
Persistent servers

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RPC communication

RPC call semantics

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Orphan calls

Calls whose caller has expired due to a node crash
Handle orphan calls by using:

Extermination
Reincarnation
Gentle reincarnation
Expiration

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RPC communication protocols

Request protocol
Request/Reply protocol
Request/Reply/ Acknowledge- Reply protocol

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Request protocol

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Asynchronous RPC

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Request/Reply protocol

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Request/Reply/ Acknowledge- Reply protocol

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Client server binding process

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Client Server binding

Issues

Server naming
Server locating

Binding agent primitives

Register
Deregister
Lookup

Types of binding

Static binding
Dynamic binding

At compile time
At link time
At run time

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Other RPC Issues

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Other issues in RPC implementation

Exception handing and security
Failure handling
Optimizing RPC execution
Various types of complicated RPCs

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RPC in heterogeneous environment

Data presentation
Transport protocol
Control protocol

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Failure handling mechanism in RPC

Client cannot find the server
Request from client to the server is lost
Reply from server to the client is lost
Server crashes after getting the request
Client crashes after sending the request

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RPC Optimization

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Concurrent access to multiple servers

Use of threads
Early reply technique
Call buffering approach

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Early Reply technique

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Call buffer approach

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RPC Optimization

Serving multiple requests simultaneously
Reducing call workload of server
Using reply cache for idempotent RPC
Selection of the Timeout value

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Complicated and special RPCs

Complicated RPCs

RPCs with long duration calls or with gaps between calls
RPCs with long messages

Special RPCs:

Call back RPC
Broadcast RPC
Batch mode RPC

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Call back RPC

Client handle is provided to the server
Client process should wait for callback RPC
Handle callback deadlocks

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Special RPCs

Broadcast RPC
Batch mode RPC

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Case Study: Sun RPC

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Case Study- Sun RPC

Uses rpcgen compiler which generates

Header file
XDR filter file
Client stub file
Server stub file

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Remote Method Invocation Basics

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Remote Object Invocation

Distributed object concept

Remote objects reference
Remote interface

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RMI

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RMI vs LMI

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RMI Implementation

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RMI implementation �Design issues in RMI�

RMI invocation semantics
Level of transparency

Marshalling
Message passing
Task of locating and contacting the remote object for the client

RMI invocation semantics

Maybe semantics
At-least-once semantics
At-most-once semantics

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Invocation semantics

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Level of Transparency

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Components of RMI

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RMI execution components

Communication module
Remote reference module
RMI software
Server program
Client program
Binder

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RMI execution

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RMI software

Proxy
Dispatcher
Skeleton

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Types of objects

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Remote invocation readiness

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RMI binding

Implicit binding
Explicit binding

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Parameter passing in RMI

Pass by value
Pass by reference

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Case study: Java RMI

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Java RMI layer

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Summary

Introduction to Remote Communication
Remote Procedural Call Basics
RPC Implementation
RPC Communication
Other RPC Issues
Case Study: Sun RPC
Remote invocation Basics
RMI Implementation