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 UDP(7P)							     UDP(7P)

      UDP - Internet User Datagram Protocol

      #include <&lt&lt&lt;sys/types.h>&gt&gt&gt;
      #include <&lt&lt&lt;sys/socket.h>&gt&gt&gt;
      #include <&lt&lt&lt;netinet/in.h>&gt&gt&gt;

      s = socket(AF_INET, SOCK_DGRAM, 0);

      UDP is a simple, unreliable datagram protocol used to support the
      SOCK_DGRAM socket type for the internet protocol family.	UDP sockets
      are connectionless, and are normally used with the sendto() and
      recvfrom() calls (see send(2) and recv(2).  The connect() call can
      also be used to simulate a connection (see connect(2).  When used in
      this manner, it fixes the destination for future transmitted packets
      (in which case the send() or write() system calls can be used), as
      well as designating the source from which packets are received.  The
      recv() and read() calls can be used at any time if the source of the
      message is unimportant.

      UDP address formats are identical to those used by TCP.  In
      particular, UDP requires a port identifier in addition to the normal
      Internet address format.	Note that the UDP port domain is separate
      from the TCP port domain (in other words, a UDP port cannot be
      connected to a TCP port).

      The default send buffer size for UDP sockets is 65535 bytes.  The
      default receive buffer size for UDP sockets is 2147483647 bytes.	The
      send and receive buffer sizes for UDP sockets can be set by using the
      SO_SNDBUF and SO_RCVBUF options of the setsockopt() system call or the
      XTI_SNDBUF and XTI_RCVBUF options of the t_optmgmt() system call.	 The
      maximum size for these buffers is 2147483647 bytes. The maximum
      receive buffer size may be lowered using the ndd parameter

      The maximum message size for a UDP datagram socket is limited by the
      lesser of the maximum size of an IP datagram and the size of the UDP
      datagram socket buffer.  The maximum size of an IP datagram limits the
      maximum message size of a UDP message to 65507 bytes.  Therefore,
      using the maximum socket buffer size will allow multiple maximum-sized
      messages to be placed on the send queue.	The default inbound and
      outbound message size limit for a UDP datagram socket is 65535 bytes.

      The maximum message size for a UDP broadcast is limited by the MTU
      size of the underlying link.

      One of the following errors may be returned in errno if a socket
      operation fails.	For a more detailed list of errors, see the man

 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000

 UDP(7P)							     UDP(7P)

      pages for specific system calls.

	   [EISCONN]		 Attempt to send a datagram with the
				 destination address specified, when the
				 socket is already connected.

	   [ENOBUFS]		 No buffer space is available for an
				 internal data structure.

	   [EADDRINUSE]		 Attempt to create a socket with a port
				 which has already been allocated.

	   [EADDRNOTAVAIL]	 Attempt to create a socket with a network
				 address for which no network interface

      The socket interfaces to UDP were developed by the University of
      California, Berkeley.

      ndd(1M).	getsockopt(2), recv(2), send(2), socket(2), t_open(3),
      t_optmgmt(3) inet(7F), socket(7),

      RFC 768	     User Datagram Protocol
      RFC 1122	     Requirements for Internet hosts

 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000