How to connects to Linux machine via null-modem cable and cu command?

[Sun Zongjun-E5739C]

HI, all
 
I am a newbie to FreeBSD. I want to connect one my pc running FreeBSD
6.1 to another PC running Fedora core 5 via a null modem cable.
 
I can login the PC running the Fedora Core 5 from PC running Windows via
one NULL modem cable.
 
When I connect the two serial ports of two pc, one running FreeBSD6.1
and the other is FC5 which acts a server. 
 
I run the command on device running FreeBSD 6.1
 
Test# cu -l /dev/cuad0 
Connected
 
There is no response on the FreeBSD except the "Connected" string.  Such
string can occur even there is no cable available.
 
What happens to cu command on FreeBSD?
 
Thanks for your kind support.
 

Thanks
Regards
Zongjun