UDP(7)                                                        UDP(7)


       NAME
             UDP - Internet User Datagram Protocol

       SYNOPSIS
             udp

       DESCRIPTION
             UDP is a simple datagram protocol which is layered directly
             above the Internet Protocol (IP).  Programs may access UDP
             using the socket interface, where it supports the SOCK_DGRAM
             socket type, or using the Transport Level Interface (TLI),
             where it supports the connectionless (T_CLTS) service type.

             Within the socket interface, UDP is normally used with the
             sendto, sendmsg, recvfrom, and recvmsg calls [see send(3N) and
             recv(3N)].  If the connect(3N) call is used to fix the
             destination for future packets, then the recv(3N) or read(2)
             and send(3N) or write(2) calls may be used.

             UDP address formats are identical to those used by the
             Transmission Control Protocol (TCP).  Like TCP, UDP uses a
             port number along with an IP address to identify the endpoint
             of communication.  The UDP port number space is separate from
             the TCP port number space (that is, a UDP port may not be
             ``connected'' to a TCP port).  The bind(3N) call can be used
             to set the local address and port number of a UDP socket.  The
             local IP address may be left unspecified in the bind call by
             using the special value INADDR_ANY.  If the bind call is not
             done, a local IP address and port number will be assigned to
             the endpoint when the first packet is sent.  Broadcast packets
             may be sent (assuming the underlying network supports this) by
             using a reserved broadcast address.  This address is network
             interface dependent.  Broadcasts may only be sent by the
             privileged user.

             Options at the IP level may be used with UDP; see IP(7).

             As the RFC allows, there are a variety of ways that a UDP
             packet can be lost or corrupted, including a failure of the
             underlying communication mechanism.  UDP implements a checksum
             over the data portion of the packet.  If the checksum of a
             received packet is in error, the packet will be dropped with
             no indication given to the user.  A queue of received packets
             is provided for each UDP socket.  This queue has a limited
             capacity.  Arriving datagrams which will not fit within its
             ``high-water'' capacity are silently discarded.


                           Copyright 1994 Novell, Inc.               Page 1

      UDP(7)                                                        UDP(7)


            As the RFC allows, UDP processes Internet Control Message
            Protocol (ICMP) error messages received in response to UDP
            packets it has sent.  See ICMP(7).  ICMP source quench
            messages are ignored.  ICMP destination unreachable, time
            exceeded and parameter problem messages disconnect the socket
            from its peer so that subsequent attempts to send packets
            using that socket will return an error.  UDP will not
            guarantee that packets are delivered in the order they were
            sent.  As well, duplicate packets may be generated in the
            communication process.

      REFERENCES
            bind(3N), connect(3N), ICMP(7), inet(7), IP(7), read(2),
            recv(3N), send(3N), TCP(7), write(2)
            RFC 768

































                          Copyright 1994 Novell, Inc.               Page 2