1. TELE202 Lecture 15 Socket programming 1 Lecturer Dr Z. Huang Overview ¥Last Lecture »TCP/UDP (2) »Source: chapter 17 ¥This Lecture »Socket programming »Source: chapter 17 ¥Next Lecture »Internet applications (1) »Source: chapter 19

2. TELE202 Lecture 15 Socket programming 2 Lecturer Dr Z. Huang Socket programming ¥Socket is a UNIX construct and is the basis for UNIX network I/O »It is available under MS Windows as well, i.e. WinSock 2 ¥Developed by UC Berkeley ¥Originally used in UCB Unix as an API for TCP and UDP ¥Socket and its related primitives are transport interface to higher layer applications ¥Socket is a communication identifier consisting of a local port number and an Internet address

3. TELE202 Lecture 15 Socket programming 3 Lecturer Dr Z. Huang Socket programming ¥Client/server model »Involves two distinct programs running on different machines at different locations »They have network connections »The server provides services and responds to requests coming in from clients ¥Primitives for socket »socket: create a communication end point »bind: attach a local address to a socket »listen: announce number of connections »accept: waiting for a connection call »connect: attempt to establish a connection »send/write: send data over the connection »recv/read: receive data from the connection »close: close the connection

4. TELE202 Lecture 15 Socket programming 4 Lecturer Dr Z. Huang Data structures ¥Relevant data structures »Socket address struct sockaddr_in { u_short sin_family; /* protocol type * u_short sin_port; /* port number */ struct in_addr sin_addr; /* 4 bytes IP address */ char sin_zero[8]; /* unused, all zeros */ } struct in_addr { u_int s_addr } »Host information Struct hostent { char *h_name; /* domain name of a host */ char **h_alias; /* alternative names of a host */ int h_addrtype; /* address type */ int h_length; /* address length */ char **h_addr_list; /* address list */ }

5. TELE202 Lecture 15 Socket programming 5 Lecturer Dr Z. Huang Create/close a socket ¥The socket function creates sockets on demand »result = socket(pf, type, protocol) »pf specifies the protocol family to be used with the socket –PF_INET, TCP/IP internet –PF_UNIX, UNIX file system –PF_APPLETALK, AppleTalk network »type specifies the type of communication desired –SOCK_STREAM, reliable stream delivery service –SOCK_DGRAM, connectionless datagram delivery service –SOCK_RAW, a raw type that allows privileged programs to access low-level protocols or network interfaces »protocol is used to select a specific protocol in the protocol family if there are multiple protocols to support the same service type ¥The close function is called when a process finishes using a socket »close(socket) »socket specifies the descriptor of a socket to close

6. TELE202 Lecture 15 Socket programming 6 Lecturer Dr Z. Huang Socket inheritance

7. TELE202 Lecture 15 Socket programming 7 Lecturer Dr Z. Huang functions ¥Auxiliary functions »gethostbyname(char *hostname): return a hostent structure containing information about a host named by hostname »gethostname(char *hostname, int length): get the domain name of the local host and put it in hostname »getsockname(int sock, struct sockaddr *addr, int addr_length): after a socket is bound by bind, this function is used to get the address information of the socket sock, and put it into addr »bcopy(a1, a2, length): copy length bytes from a1 to a2 »htons(int port_number): convert the port_number into a standard format of port number

8. TELE202 Lecture 15 Socket programming 8 Lecturer Dr Z. Huang Summary