UDP(ADMP)                                  UNIX System V



     Name
          udp - Internet User Datagram Protocol


     Syntax
          #include <sys/socket.h>
          #include <netinet/in.h>

          s = socket(AFINET, SOCKDGRAM, 0);


     Description
          UDP is a simple, unreliable datagram protocol that  is  used
          to  support  the  SOCK_DGRAM  abstraction  for  the Internet
          protocol family.  UDP sockets are  connectionless,  and  are
          normally  used  with  the  sendto  and  recvfrom  calls; the
          connect(SSC) call may also be used to  fix  the  destination
          for future packets (in which case, the recv(SSC), or read(S)
          and send(SSC),  or  write(S)  system/library  calls  may  be
          used).   In addition, UDP is available as TLI connectionless
          transport via the special file /dev/inet/udp.

          UDP address formats are identical to those used by TCP.   In
          particular,  UDP  provides  a port identifier in addition to
          the normal Internet address format.  Note that the UDP  port
          space  is  separate  from the TCP port space (that is, a UDP
          port may not be ``connected'' to a TCP port).  In  addition,
          broadcast  packets  may  be  sent  (assuming  the underlying
          network  supports  this)  by  using  a  reserved   broadcast
          address; this address is network interface-dependent.

          Options at the IP transport level may be used with UDP;  see
          ip(ADMP).


     Diagnostics
          A socket operation may fail with one of the following errors
          returned:

     [EISCONN]
                         when trying to establish a  connection  on  a
                         socket  which already has one, or when trying
                         to  send  a  datagram  with  the  destination
                         address  specified  and  the  socket  already
                         connected;

     [ENOTCONN]
                         when  trying  to  send  a  datagram,  but  no
                         destination  address  is  specified,  and the
                         socket has not been connected;

     [ENOSR]
                         when the system runs out  of  memory  for  an
                         internal data structure;

     [EADDRINUSE]
                         when an attempt is made to  create  a  socket
                         with a port that has already been allocated;

     [EADDRNOTAVAIL]
                         when an attempt is made to  create  a  socket
                         with  a  network address for which no network
                         interface exists.


     Files
          /dev/inet/udp


     See Also
          getsockopt(SSC),    recv(SSC),    send(SSC),    socket(SSC),
          intro(ADMP), inet(ADMP), ip(ADMP), RFC768.


     (printed 8/17/89)                                  UDP(ADMP)