Need help! Transfer large binary files amone private network group without FTP, maybe P2P?

[Alan]

I am looking for a solution that can do:

Situation:
I have a Linux at home and my friends have Linux at home as well, we
all use ADSL, So, no fix IP.
I would like to build a "private large binary file transfer network"
thru internet, as soon as I have created
a file (say, 700MB) and saved it into a share folder and assign a
counter party name, say, John. Then after a while, this file will be
in John's share folder.

The solution should do:
1, recovery after disconnect
2, as fast as possible
3, background process or batch process, no human interaction. user can
config the process in advance, but it has to be automatic.
4, Users only recognized by user name or id, no IP address. (Sounds
like P2P?)

I know someone splitting the larget file into chunks and FTP,
but I would like this whole process to be automatic,
and a complete file in other party's share folder, not chunks.
And I don't want to install FTP server and manage it.

I have been thinking about private P2P, but how?

Alan