Yes, you can. I already told you how you can - you can use FTP's resume feature! And if you don't want to do that, you can implement the same sort of scheme yourself. The wise old coders behind the FTP system have even given you a head start - you don't have to come up with a new system yourself, you can copy theirs.

Of course, it would be much easier to just use an existing client and server that supports resuming. I don't know why you don't want to do that, and I don't especially care.

-sam