
			< Lecture note (Feb.11,`97) >
				- CMSC 417 -
					- Kyung Dong Ryu (TA)

		Overview of socket interface & project #1
		=========================================

1. What's the difference bet'n TCP and UDP.
	. connection-oriented
		- first, connection is established bet'n two ends.
		- then, they communicate each other thru the connection.
	. connectionless (datagram)
		- whenever, one sends message to the other, dest. address
		is included. (no connection).
		- packet could be lost or delivered out of order.

2. Socket system calls for connection-oriented protocol (TCP)
	- server		- client
	. socket()		socket()
	. bind()
	. listen()
	. accept()
		  <------------	connect()
	. read()  <------------	write()
	. (process req)
	. write()  ----------->	read()

3. Socket system calls for connectionless protocol (UDP)
	- server		- client
	. socket()		socket()
	. bind()		bind()
	. recvfrom() <---------	sendto()
	. (process req)
	. sendto()   ---------> recvfrom()

4. Elementary Socket System Calls
	. int socket(int family, int type, int protocol);
		- open a socket, specifying the type of protocol desired

	. int bind(int sockfd, struct sockaddr *myaddr, int addlen);
		- assignes a name (local address) to a socket

	. int connect(int sockfd, struct sockaddr *servaddr, int addrlen);
		- a client establish a connection with a server

	. int listen(int sockfd, int backlog);
		- indicate it is willing to receive connections

	. int accept(int sockfd, struct sockaddr *peer, int *addrlen);
		- wait and accept the connection request (blocking)

	. int send(int sockfd, char *buff, int nbytes, int flags);
		- send message to the other end of connection (TCP)

	. int sendto(int sockfd, char *buff, int nbytes, int flags,
		     struct sockaddr *to, int addrlen);
		- send message to the specified receiver (UDP)

	. int recv(int sockfd, char *buff, int nbytes, int flags);
		- receive message from the other end of connection (TCP)

	. int recvfrom(int sockfd, char *buff, int nbytes, int flags,
		     struct sockaddr *from, int addrlen);
		- recevie message from any sender (UDP)

	. int read(int fdesc, char *buff, int nbytes);
		- read(receive) the message

	. int write(int fd, char* buff, int nbytes);
		- write(send) the message

	. htons(), htonl(), ntohs(), ntohl().
		- translate host byte ordering to network byte ordering
		  or vice versa.

5. Other System Calls for Request Processing
	. struct hostent *gethostbyname(char *name);
		- get host addr info using string host name.
		- may contains more than one inet address.
		- only h_addr field will be used for the project.

	. char *inet_ntoa(struct in_addr in);
		- turn in_addr type address into string.

	. int stat(char *path, struct stat *buf);
		- get all info for the specified file.
		- only st_size field will be used for the project.

	. netstat 
		- unix command - /usr/sbin/netstat in CSC class alpha cluster
		- netstat -f inet (limits reports to the inet address family)

6. Requirements
	. names of the executables should be server and client.
	. show everything your program can do in your transcript.
	. how to submit.
		1) tar all the source files, transcript and Makefile.
			> tar cvf prog1.tar *.*
			  (pls, don't include binary or object files)
		2) submit it using submit program
			> ~jh01/BIN/submit 1 prog1.tar	
		3) no late submission will be accepted and repeated submission
		   will overwrite the previous one.

7. Q&A session.
	. reliable transfer	- not required
	. data representation mismatch problems on different platforms
			- not required, but worth doing.