[ns] 0 throughput for FTP connection...

[Salvo Danilo Giuffrida]

Hello, I've tried, both in a wireless and wired scenario, to setup an
FTP connection between two nodes. Everything works, except for the
fact that, if during the simulation I try to print some statistics
about the TCP or TCPSink agent, such as the values of variables...
ndatapack_
ndatabytes_
nackpack_

The only value always reported is 0, despite the fact that there is
traffic going on between the FTP source and its destination? The
reason I'm trying to do this, is to calculate the total amount of data
correctly transfered (that is, not counting duplicated packets).
What am I doing wrong? Thanks