1 Computer Networks and Internets

2 Internet Growth

3 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

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

5 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

6 Ping program

7 Ping Program – Con’t

8 Traceroute Program

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

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

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

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

13 Example API

14 Illustration of API Calls

15 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 recv(connection con, char* buffer, int length, int flags) int recvln(connection con, char* buffer, int length) int send_eof(connection con)

16 Summary of Example API

17 Illustration of Echo Application

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

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