Editing YMODEM (section)

====Abort====
One problem with the original XMODEM was that there was no defined way to abort the transfer once started. The normal solution was to send {{mono|NAK}}s to every subsequent packet if the user requested it. Since the XMODEM protocol defined a limit of ten {{mono|NAK}}s to abort a send, and each packet might take a second to send, this meant there was a ten second delay where the sender continually sent data that was simply ignored.

Some implementations had added the ability to send a {{mono|CAN}} instead of {{mono|ACK}} or {{mono|NAK}} at the end of a received packet to indicate an abort. Unfortunately, there was the possibility that a {{mono|CAN}} could be generated by line noise and trigger an abort. YAM thus modified this slightly to require two {{mono|CAN}}s back-to-back, which would immediately perform a "graceful abort" on the sender end.