udp(ADMP)                       19 June 1992                       udp(ADMP)


 Name

    udp - Internet User Datagram Protocol

 Syntax

    Programmer's interface:
    #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 avail-
    able 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 addi-
    tion, broadcast packets may be sent (assuming the underlying network sup-
    ports 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 is already connected

    [ENOTCONN]          when trying to send a datagram, but no destination
                        address is specified, and the socket hasn't been con-
                        nected

    [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 which 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), inet(ADMP), Intro(ADMP), ip(ADMP), recv(SSC), send(SSC),
    socket(SSC)