Session ID

[Anon]

I have this code on one of my page but everytime I refresh the page SID changes. Shouldn't it be same or am I doing something wrong ?

session_start();

echo "session id" . SID . "<br>";

$sc = $Session->session_code;

if (!isset($SESSION['sc']))
{
$SESSION['sc'] = $Session->session_code;
}

echo "session code=". $_SESSION['sc'];