Computer Networks and Internets 1 Internet Growth 2

Computer Networks and Internets 1

Internet Growth 2

What a Network Include • Transmission hardware • Special-purpose hardware device – Interconnect transmission media – Control transmission – Run protocol software • Protocol software – Encodes and format data – Detects and corrects problems 3

What a Network Does • Provide communication that is – Reliable – Fair – Efficient – Secure – From one application to another 4

What a Network Does – Con’t • Automatically detect and corrects – Data corruption – Data loss – Duplication – Out-of-order delivery • Automatically finds optimal path from source to destination 5

Ping program 6

Ping Program – Con’t 7

Traceroute Program 8

Network Programming • Network allows arbitrary applications to communicate • Programmer does not need to understand network technologies • Network facilities accessed through an Application Program Interface 9

Basic Paradigm for Internet Communication • Establish contact • Exchange data (bi-directional) • Terminate contact 10

Establishing Contact • Performed by pair of applications • One application starts and wait for contact (called server) • Other applications initiate contact (called client) 11

Representations and Translations • Humans use names such as: – www. netbook. cs. purdue. edu (computer) – ftp (applications) • Network protocols require binary values • Library routines exist to translate from names to numbers 12

Example API 13

Illustration of API Calls 14

Definition of the API • • • connection await_contact (appnum a) connection make_contact (computer c, appnum a) appnum appname_toappnum(char* a) computer cname_to_comp(char* a) int send(connection con, char* buffer, int length, int flags) • int recvln(connection con, char* buffer, int length) • int send_eof(connection con) 15

Summary of Example API 16

Illustration of Echo Application 17

Examples • echoserver. c and echoclient. c • chatserver. c and chatclient. c • webclient. c and webserver. c 18

Summary • Studying networks is important because – The world is interconnected – Applications now operate in a distributed environment 19