gandrews@netcom.COM (Greg Andrews) (04/13/91)
In article <1991Apr9.161637.12059@oswego.oswego.edu> ostroff@oswego.Oswego.EDU (Boyd Ostroff) writes: > >The only problem I've noticed is that there are often a bunch of NULLs >appended to the end of the file, as though the two programs couldn't agree >on where the file ends... > XMODEM doesn't send any file name or file length information to the receiver, and the data packets are 128 bytes in size, period. If the file size doesn't match up to an exact multiple of 128 bytes, the last packet will be only partly full of file data. The protocol has to put SOMEthing into the packet to fill it out, and nulls are often used. -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
dnichols@ceilidh.beartrack.com (DoN Nichols) (04/14/91)
In article <1991Apr13.014747.7144@netcom.COM> gandrews@netcom.COM (Greg Andrews) writes: >In article <1991Apr9.161637.12059@oswego.oswego.edu> ostroff@oswego.Oswego.EDU (Boyd Ostroff) writes: >> >>The only problem I've noticed is that there are often a bunch of NULLs [ ... ] >If the file size doesn't match up to an exact multiple of 128 bytes, the >last packet will be only partly full of file data. The protocol has to >put SOMEthing into the packet to fill it out, and nulls are often used. Also VERY frequently used is the '^Z' character, since it is interpreted as 'EOT' by text-mangling utilities under CP/M (where the xmodem protocol originated), and, by extension, MS-DOS. The packet size was chosen to be a single sector on then-popular implementations of CP/M. (I don't know whether CP/M ever had any other size sectors, alghough probably CP/M-86 which ran on IBM-PC hardware probably used larger sectors, at least as an option. At least there are never more than 127 of them, so I can get rid of them using JOVE, and not have to resort to emacs. :-) Kermit is a MUCH nicer protocol, it's a pity that it has so much overhead :-) (Although two of the newer ones talking to each other are not bad at all. -- Donald Nichols (DoN.) | Voice (Days): (703) 664-1585 D&D Data | Voice (Eves): (703) 938-4564 Disclaimer: from here - None | Email: <dnichols@ceilidh.beartrack.com> --- Black Holes are where God is dividing by zero ---