ICOM 6115 Computer Networks and the WWW Manuel

ICOM 6115 – Computer Networks and the WWW Manuel Rodriguez-Martinez, Ph. D. Lecture 4 ICOM 6115 ©Manuel Rodriguez-Martinez

Lecture Objectives • Understand Network Programming – Socket abstraction • Stream Socket • Datagram Socket – Networking Support in the programming language • Java – Operating Systems support for Networking – Implementation options for servers ICOM 6115 ©Manuel Rodriguez-Martinez

Network Programming • Client-server and P 2 P are the models to organize application – Architectural Framework • How do we actually move data between the components of the application? – Sockets – Provide abstraction of a file to perform I/O • Send data to receiver • Read data from sender ICOM 6115 ©Manuel Rodriguez-Martinez

The idea of OS File Application File “My. Letter. doc” Disk ICOM 6115 ©Manuel Rodriguez-Martinez

The OS File • Provides mechanism to read related blocks of bytes from disk – Hides where they are on disk • OS must keep track of this information – File System • Operations on files – Create, Open, Close, Read, Write • Need more sophistication: use streams – Another layer on top of files • Provides access to int, string, bytes, object, etc ICOM 6115 ©Manuel Rodriguez-Martinez

The Idea of Socket • See the networks as a cable to which the applications can connect. • Socket is the place where the application “plugs” itself to the network – Every app. is using a socket to send/receive • Associate a socket with two files – One for reading from socket – One for writing to socket ICOM 6115 ©Manuel Rodriguez-Martinez

Socket Abstraction Client IN I/O Files OUT IN Socket OUT Socket Network ICOM 6115 Server ©Manuel Rodriguez-Martinez

Communication between sockets Client Server IN IN OUT Socket Network ICOM 6115 OUT ©Manuel Rodriguez-Martinez

Types of Sockets • Stream Socket – Provide a reliable bytes stream between the end-points – Connection oriented • TCP • Datagram Socket – Provide an unreliable byte stream between the end-points – Connectionless • UDP ICOM 6115 ©Manuel Rodriguez-Martinez

Creating a Socket in Java • Client sockets – Destination host – Port number • Server Socket – Port number • Many other flags can be set • Sockets can be encrypted – SSL – Custom-made ICOM 6115 ©Manuel Rodriguez-Martinez

Example Client and Server apps • Basic Application – Get the Date • My. Server 1. java • My. Client 1. java • Another toy application – Get the Date or nick name of the machine – Illustrates the need for protocols ICOM 6115 ©Manuel Rodriguez-Martinez

Iterative Server Client Server Listen Queue OS ICOM 6115 ©Manuel Rodriguez-Martinez

Iterative Server • One server to handle multiple requests – Simple to implement – Take some time to service each request • Bottleneck if I/O is needed – Should be used only to service small requests • Time • Name of a computer – Typically used for connectionless services • Datagrams ICOM 6115 ©Manuel Rodriguez-Martinez

Concurrent Server Master Server ICOM 6115 Client Slave Server ©Manuel Rodriguez-Martinez

Concurrent Server • Multiple serves to handle multiple requests – Each client has its own server • Master server – receives initial request and forwards it to slaver server • Slave server is the actual entity that interacts with the client • Issues ICOM 6115 ©Manuel Rodriguez-Martinez

Concurrent Servers (Issues) • Issues – More complex to implement – Provides parallelism • Good for I/O intensive applications – Should be used to service large requests • HTTP • Database requests – Typically used for connection-oriented services • TCP Applications ICOM 6115 ©Manuel Rodriguez-Martinez