Figure 1 XMODEM File Transfer

SENDER                         RECEIVER
---------------------------------------
           Start Character (NAK or 'C')
Packet 1
              ACK (Packet Received OK)
Packet 2
                   NAK (Packet NOT OK)
Packet 2
                       ACK (Packet OK)
              ·
              ·
              ·
Packet n
                                   ACK
EOT
                                   ACK
--------------------------------------