[Click] Using udpgen.click without polling device patch???

[shule ney]

*HI all:*
  The udpgen.click is as below:

// UDPGen($device, $rate, $limit, $seth, $sip, $sport, $deth, $dip, $dport);
//
//	$device		name of device to generate traffic on
//	$rate		rate to generate traffic (packets/s)
//	$limit		total number of packets to send
//      $size		bytes per packet
//	$seth		source eth addr
//	$sip		source ip addr
//	$sport		source port
//      $deth		destination eth addr
//	$dip		destination ip addr
//	$dport		destination port

elementclass UDPGen {
  $device, $rate, $limit, $size,
  $seth, $sip, $sport, $deth, $dip, $dport |

  source :: FastUDPSource($rate, $limit, $size, $seth, $sip, $sport,
                                                $deth, $dip, $dport);
 * **pd :: PollDevice($device) -> ToHost;*
  source -> td :: ToDevice($device);
}

// create a UDPGen

u :: UDPGen(eth1, 82000, 820000, 1500,
	    00:e0:29:05:e2:d4, 2.0.0.2, 1234,
	    00:c0:95:e2:09:14, 1.0.0.2, 1234

1.So what does pd used for??? If I don't have polling device patch,
will it send much slower??

2.When I don't commented out this line， it also works, and the rate of
u is 0, is it common???