[ns] Difference between two simplex-links and one duplex-link?

[Pan Li <panli@info.sh.cn>]

Hi all:
     I want to create a congestion link between node1 and node2.
Data(TCP connections) are send from
node1 to node2.
One way is:
$ns simplex-link $n1 $n2 1.5Mb 10ms DropTail
$ns simplex-link $n2 $n1 1.5Mb 10ms DropTail
Another way is:
$ns duplex-link $n1 $n2 1.5Mb 10ms DropTail
I don't know the difference between them. I wonder that the ACK packets
will intefere
the transmission of data packets from $n1 to $2 in the duplex-link mode.

Thank you.