Why does TCP work, when UDP does not?

Question

The code:

<?php
error_reporting(E_ALL);

/* Allow the script to hang around waiting for connections. */
set_time_limit(0);

/* Turn on implicit output flushing so we see what we're getting
 * as it comes in. */
ob_implicit_flush();

$address = '127.0.0.1';
$port = 11100;

if (($sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UP)) === false) {
    echo "socket_create() failed: reason: " . socket_strerror(socket_last_error()) . "\n";
}

if (socket_bind($sock, $address, $port) === false) {
    echo "socket_bind() failed: reason: " . socket_strerror(socket_last_error($sock)) . "\n";
}

if (socket_listen($sock, 5) === false) {
    echo "socket_listen() failed: reason: " . socket_strerror(socket_last_error($sock)) . "\n";
}

do {
    if (($msgsock = socket_accept($sock)) === false) {
        echo "socket_accept() failed: reason: " . socket_strerror(socket_last_error($sock)) . "\n";
        break;
    }
    do {
    $out = socket_read($msgsock, 2048);

    if (!empty($out)) {
     if ($out == 'quit') {
            break;
        }
        elseif ($out == 'shutdown') {
            socket_write($msgsock, 'plc down', 8);
      socket_close($msgsock);
            break 2;
        }
     else {
      switch ($out) {
       case "KABBE": $response = "Kabbe te!"; break;
       case "SZOPJ": $response = "Szopjal te!"; break;
       default: $response = "Ismeretlen parancs";
      }
      socket_write($msgsock, $response, strlen($response));
      break;
     }
    }
    } while (true);
socket_close($msgsock);
} while (true);

socket_close($sock);
?>

It works with TCP:

$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);

but with UDP it's not working:

$sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);

The errors:

Warning: socket_listen() [function.socket-listen]: unable to listen on socket [0]: The attempted operation is not supported for the type of object referenced. in C:\wamp\www\socket\socket.php on line 22 socket_listen() failed: reason: The attempted operation is not supported for the type of object referenced.

Warning: socket_accept() [function.socket-accept]: unable to accept incoming connection [0]: The attempted operation is not supported for the type of object referenced. in C:\wamp\www\socket\socket.php on line 27 socket_accept() failed: reason: The attempted operation is not supported for the type of object referenced.

Answer 1

Because TCP is connection oriented and UDP is not, and there are different APIs for UDP sockets. Have a look at socket_recvfrom and socket_sendto.