When communication link failures interrupt UUCP transmissions between SunOS release 4 systems, the transmission starts again from the beginning of the file as soon as communication resumes. Communication between two systems running Solaris 7 UUCP resumes where it was interrupted instead of returning to the beginning. This makes better throughput possible, especially on erratic or noisy transmission lines.
The systems use two new files to store sent and received data and to compare the sizes of the files to determine where to restart transmission. The systems use.P files to store received data and.D files to store transmitted data. These files replace the TM. files of previous UUCP versions. If only one system is running SunOS release 5.7 UUCP, no comparison can take place and transmission restarts from the beginning.