รบกวนสอบถามเกี่ยวกับการใช้เมดธอด REQUEST หน่อยครับ

<?php
echo $dbtype = $_REQUEST['dbtype'];
echo $sipuser = $_REQUEST['sipuser'];

$sessionuser= $_REQUEST['sessionuser'];
$sessionuser."<br>";
session_start();


	if (!isset ($_SESSION['sessionuser']))
	{
		header("Location:login.php");
		exit();
	}

header('Content-Type : text/html; charset=utf-8');
include "headermain.php";
include "dbconnect.php";

//$username = $_REQUEST['username'];
//$password = $_REQUEST['password'];
//$sipuser = $_REQUEST['sipuser'];
//$secret = $_REQUEST['secret'];
//$email = $_REQUEST['email'];

$sql = "select * from sipaccount where  sipuser='$sipuser'";
$query = mysql_query($sql);
$rs = mysql_fetch_array($query);
			$usertype = $rs['1'];
			$username = $rs['2'];
			$password = $rs['3'];
			$sipuser = $rs['4'];
			$secret = $rs['5'];
			$email = $rs['6'];

?>

<form name = regfrom method = post action = editinformation.php>
<table width="350" border="1" align = "center">
  
  <tr>
    <td align = "center"  > ข้อมูลส่วนตัว </td>
  </tr>
  
  <tr>
    <td height = "5" ></td>
  </tr>
  
  <tr>
    <td height = "5" ></td>
  </tr>

  <tr>
    <td align = "right"> ยูสเซอร์เนม :</td>
    <td width = "5"></td>
    <td>
		<input type = text name = username value = <?php echo $username?> readonly>
	</td>
  </tr>

  <tr>
    <td height = "5" ></td>
  </tr>

  <tr>
    <td align = "right"> พาสเวิร์ด :</td>
    <td width = "5"></td>
    <td>
		<input type = text name = password value = <?php echo $password?> readonly>
	</td>
  </tr>
  
  <tr>
    <td height = "5" ></td>
  </tr>

  <tr>
    <td align = "right"> เบอร์โทรศัพท์ :</td>
    <td width = "5"></td>
    <td>
		<input type = text name = "sipuser" value = <?php echo $sipuser?> size="10" maxlength="10" title="Telephone" readonly>
	</td>
  </tr>

  <tr>
    <td height = "5" ></td>
  </tr>

  <tr>
    <td align = "right"> พาสเวิร์ด :</td>
    <td width = "5"></td>
    <td>
		<input type = text name = secret value = <?php echo $secret?> readonly>
	</td>
  </tr>


  <tr>
    <td height = "5" ></td>
  </tr>

    <tr>
    <td align = "right"> อีเมลล์ :</td>
    <td width = "5"></td>
    <td>
		<input type = text name = email value = <?php echo $email?> readonly>
	</td>
  </tr>

<tr>
    <td align = "right"> ประเภทของผู้ใช้ :</td>
    <td width = "7"></td>
    <td>
	<input type = text name = typeuser value = <?php if ($usertype == '01'){echo "ผู้ดูแลระบบ";} else{echo "ผู้ใช้งานทั่วไป";} ?> readonly >
	</td>
  </tr>

  </tr>

  <tr>
	<td align = "center" >
		<input type =submit name = login value = ตกลง>
	</td>
  </tr>





</table>
<br></br>
</form>