1. Network and Sockets Today: Get started doing network programming
Reliable socket programming
Aka TCP programming

2. setup A number of PCs running XP and cygwin (tested)
Vista/W7 and cygwin (not ! tested)
Linux/ubuntu/ (tested)
Mac OSX (not tested but …)
Or linux livecd on PC (tested)
Why ? Because !

3. How ? Short !!! lecture Back and programming !!! :-)
You can only programming by programming !

4. A TCP socket is A reliable connection You get data correct transferred
Or not valid data through
No size limit of data – you can “stream” a movie
Although size of buffers matters
A unreliable link is a UDP socket
Unreliable – no check on data and on if they were received ok
64 B limit on each transaction (read/write)

6. TCP – the reliable one

7. UDP socket – the unreliable

8. Compared to … files file_handle = fopen (“jens”,..)
write(file_handle,” ost\n”);
read(file_handle,...)
Etc
/* so close to file operations ! */

9. Sockit ;-) fgets(buffer,255,stdin);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0)
error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);

10. Server versus client SERVER
The server shall be ready to accept a call from a client
IS not aware of clients IP address prior to call
Server and client must agree on ping pong protocol
Normally at design stage !
Server may be able to handle more than one call at a time (call desk :-)

11. Server versus client CLIENT
Try to connect to a server
Must know server IP and port( )
Your server should use ports above 10000
Some ports: (from /etc/services)
finger /tcp
www /tcp http
www /udp
link /tcp ttylink
kerberos /tcp kerberos5 krb5
kerberos /udp kerberos5 krb5

12. int sockfd;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
bzero((char *) &serv_addr, sizeof(serv_addr));
portno = atoi(argv[1]);
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
if (bind(sockfd, (struct sockaddr *) &serv_addr,
sizeof(serv_addr)) < 0)
error("ERROR on binding");
listen(sockfd,5);
clilen = sizeof(cli_addr);
newsockfd = accept(sockfd,
(struct sockaddr *) &cli_addr,
&clilen);
if (newsockfd < 0)
error("ERROR on accept");

13. if (newsockfd < 0)
error("ERROR on accept");
bzero(buffer,256);
n = read(newsockfd,buffer,255);
if (n < 0) error("ERROR reading from socket");
printf("Here is the message: %s\n",buffer);
n = write(newsockfd,"I got your message",18);