BSD 4_1c_2 development

Work on file usr/man/man4/udp.4p

Synthesized-from: CSRG/cd1/4.1c.2

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+.TH UDP 4P "25 March 1982"
+.UC
+.SH NAME
+udp \- Internet User Datagram Protocol
+.SH SYNOPSIS
+.B #include <sys/socket.h>
+.br
+.B #include <netinet/in.h>
+.PP
+.B s = socket(AF_INET, SOCK_DGRAM, 0);
+.SH DESCRIPTION
+UDP is a simple, unreliable datagram protocol which is used
+to support the SOCK_DGRAM abstraction for the Internet
+protocol family.  UDP sockets are connectionless, and are
+normally used with the
+.IR sendto (2)
+and
+.IR recvfrom (2)
+calls, though the
+.IR connect (2)
+call may also be used to fix the destination for future
+packets (in which case the 
+.IR recv (2)
+or
+.IR read (2)
+and 
+.IR send (2)
+or
+.IR write(2)
+system calls may be used).
+.PP
+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 (i.e. a UDP port
+may not be \*(lqconnected\*(rq to a TCP port).  In addition broadcast
+packets may be sent (assuming the underlying network supports
+this) by using a reserved \*(lqbroadcast address\*(rq; this address
+is network interface dependent.
+.SH DIAGNOSTICS
+A socket operation may fail with one of the following errors returned:
+.TP 15
+[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 is already connected;
+.TP 15
+[ENOTCONN]
+when trying to send a datagram, but
+no destination address is specified, and the socket hasn't been
+connected;
+.TP 15
+[ENOBUFS]
+when the system runs out of memory for
+an internal data structure;
+.TP 15
+[EADDRINUSE]
+when an attempt
+is made to create a socket with a port which has already been
+allocated;
+.TP 15
+[EADDRNOTAVAIL]
+when an attempt is made to create a 
+socket with a network address for which no network interface
+exists.
+.SH SEE ALSO
+intro(4N), inet(4F)