file transfering through internet

[munna_dude]

hi all
i wud like to develop a free software for
file transfering through internet.
i tried for local machine (LAN) it suceeded.
but i am unable to send through internet.
if u odnt mine. i will tell the name of the software, just for example.
skype.
this software has the capability of transfer a file through internet, for a perticular peroson.(any where in the world), i complete these all. and strucked at file transfering.

can you please help me

thank you in advance.

[Smither]

Does it by any chance need to act as a server/ listen to ports? If so you'll need to set up port forwaring through your router if you have one.