### Satellite links ¶

Satellite links have very high delays together with high bandwidths. You can send several megabits of data per second, but they will reach the remote side only after half a second! Most file sharing protocols like FISH, FTP, scp, XMODEM will perform very badly because of round-trips quantity. Each file transmission explicitly generates request and acknowledgement packets that are send over the link. Remote side won’t do anything until it receives them. Moreover not all protocols allow duplex data transmission (when both sides are sending data simultaneously).

NNCP’s synchronization protocol (SP) tries to mitigate all that issues by reducing number of round-trips, number of packets passing through. All file lists, file download requests are grouped together (pipelined) in one huge packet. Only transmission halt and successful file download acknowledgements are sent explicitly. SP could be asked only either to upload or download packets for our node. SP could ignore files with low priority. Full files listing is passing even during the handshake procedure.