CS2005 - Lecture 4 - Distributed Systems

Distributed System

A collection of loosely coupled nodes interconnected by a communication network

Nodes in a Distributed System

An individual computer or server that is part of a larger system

Advantages of Distributed Systems

Scalability, Speedup, High performance, Openness, Reliability, Flexibility

Disadvantages of Distributed Systems

Difficult troubleshooting, Less software support, High network infrastructure costs, Security issues

Resource Sharing

A user at one site may be able to use the resources available at another

Computation Speedup

Sub-computations can be distributed among the various sites and run simultaneously

Reliability

If one site fails in a distributed system, the remaining sites can continue operating

Communication

Users at various sites can exchange information at different levels

Process in a Distributed System

A program being executed

How Processes Communicate

Using inter-process communication if within same host. Exchange messages across network if in different end systems

Client

The process that initiates the communication

Server

The process that waits to be contacted to begin the session

Sockets

Where a client and server process communicate with each other by reading from and writing to

Two Socket Types

UDP and TCP

UDP (User Datagram Protocol)

Is connectionless, unreliable where group of bytes (datagram) is sent through the socket

TCP (Transmission Control Protocol)

Is connection-oriented, reliable where a stream of bytes is sent through the socket

Echo Server Network Application

Simple client server program that sends and received echoes from client to server

Single Client Knock-Knock Network Application

Client-server program that implements the knock-knock jokes

RPCs (Remote Procedure Calls)

Allows a client to call a procedure on a remote host

Pipes

Acts as a channel allowing two processes to communicate

Ordinary Pipes

Allow communication in standard producer-consumer style

How Ordinary Pipes Work

Producer write to one end and consumer reads from other end. They are unidirectional and require parent-child relationship

Named Pipes

Several processes can use the pipe for communication and allows inter-process communication over a network. They are bidirectional