PHP で APNS 経由で複数のプッシュ通知を送信するにはどうすればよいですか?

<code class="php">function sendNotification($deviceToken, $message, $passphrase) {
    $ctx = stream_context_create();
    stream_context_set_option($ctx, 'ssl', 'local_cert', 'ckipad.pem');
    stream_context_set_option($ctx, 'ssl', 'passphrase', $passphrase);

    $fp = stream_socket_client('ssl://gateway.sandbox.push.apple.com:2195', $err, $errstr, 60, STREAM_CLIENT_CONNECT | STREAM_CLIENT_PERSISTENT, $ctx);

    if (!$fp) {
        echo "Failed to connect: $err $errstr" . PHP_EOL;
        return false;
    }

    $body = [
        'aps' => [
            'badge' => +1,
            'alert' => $message,
            'sound' => 'default'
        ]
    ];

    $payload = json_encode($body);
    $msg = chr(0) . pack('n', 32) . pack('H*', $deviceToken) . pack('n', strlen($payload)) . $payload;

    $result = fwrite($fp, $msg, strlen($msg));

    if (!$result) {
        echo 'Message not delivered' . PHP_EOL;
        return false;
    } else {
        echo 'Message successfully delivered: ' . $message . PHP_EOL;
        return true;
    }

    fclose($fp);
}</code>

<code class="php">if ($teacherReply) {
    sendNotification($studentDeviceToken, "New response from teacher", $passphrase);
} else {
    sendNotification($teacherDeviceToken, "New question from student", $passphrase);
}</code>