A transaction in transaction? Possible?

Is it possible to have another transatction in a transaction??? In the following example the last ROLLBACK is totally ignored(transaction1).

//connect to database
$database = dbConnect($dbhost, $dbuser, $dbpass, $dbname);
dbExec($database, "BEGIN"); //transaction1

//*
dbExec($database, "BEGIN");//transaction2
$sql = "UPDATE orders SET technikernotiz='51' WHERE id=16143";
dbExec($database, $sql);
dbExec($database, "COMMIT");//transaction2
/**/

$sql = "UPDATE orders SET reklamationsdetail='51' WHERE id=16143";
dbExec($database, $sql);
dbExec($database, "ROLLBACK");//transaction1

dbClose($database);