UDP is a connectionless protocol running over IP that is mainly used for broadcasting messages, popular services that use UDP include NFS, SNMP and DNS.

<?php
$sock = socket_open(AF_INET, SOCK_DGRAM, 0);
if($sock < 0) {
    echo "socket() failed, error:" . strerror($sock) . "\n";
}

$opt_ret = socket_set_option($sock, SOL_SOCKET, SO_BROADCAST, 1);
if($opt_ret < 0) {
    echo "setsockopt() failed, error: " . 
         strerror($opt_ret) . "\n";
}

$send_ret = socket_sendto($sock, 
                          $broadcast_string, 
                          strlen($broadcast_string),
                          0, 
                          '255.255.255.255', 
                          4096);
if($send_ret < 0) {
    echo "sendto() failed, error:" . strerror($send_ret) . "\n";
}

socket_close($sock);
?>