SOCKET SYSTEM CALLS
     #include <sys/types.h>
     #include <sys/socket.h>

     int socket(int domain, int type, int protocol)
         values for domain   AF_LOCAL    Host-internal protocols, formerly  AF_UNIX,
	                     AF_INET     Internet version 4 protocols,
	                     AF_INET6    Internet version 6 protocols,
                             (lots of others, see the man page for details)
         values for type     SOCK_STREAM
                             SOCK_DGRAM
                             SOCK_RAW

     int bind(int s, const struct sockaddr *addr, int addrlen)

     int listen(int s, int backlog)

     int accept(int s, struct sockaddr *addr, int *addrlen)

     int connect(int s, const struct sockaddr *name, int namelen)  /* client only */

     ssize_t recv(int s, void *buf, size_t len, int flags)
     flags can be  MSG_OOB        process out-of-band data
                   MSG_PEEK       peek at incoming message
                   MSG_WAITALL    wait for full request or error

    ssize_t send(int s, const void *msg, size_t len, int flags)
    flags can be   MSG_OOB        process out-of-band data 

    ssize_t sendto(int s,  const  void  *msg,  size_t  len,  int
     flags, const struct sockaddr *to, socklen_t tolen); /* datagrams */

    ssize_t recvfrom(int s, void *buf, size_t  len,  int  flags,
     struct sockaddr *from, socklen_t *fromlen); /* datagrams */

    char *inet_ntoa(struct in_addr addr)  /* returns string in dotted decimal notation

    struct hostent *gethostbyname(char *hostname)