wlj1@cunixb.cc.columbia.edu (Wayne L Jebian) (07/17/90)
2 more questions: 1 will desterm have Zmodem as a Xfer protocol? its my understanding that Zmodem is the best Xfer protocol as far as reliability and speed are concerned if not, what terms use Zmodem on the 128/64? 2- what exactly does FTP mean? again, thanks -Mark Dolengo
dg@pallio.UUCP (David Goodenough) (10/21/90)
root@zswamp.fidonet.org (Geoffrey Welsh) says: > I have argued over ZMODEM implementation with more people than I can count. > The main advantage of ZMODEM is the ability to transmit non-stop. This > requires that the receiver be able to continue RS-232 input while writing > to disk. In the vast majority of Commodore configurations, this is not > possible; the timing of both the serial bus and the RS-232 port is to > sensitive to allow them to coexist at useful speeds (i.e., 2400 or 9600). This is not strictly true - Zmodem exists for CP/M, and the bulk of CP/M systems can't overlap serial I/O and disk I/O. When Chuck F. designed Zmodem he put in provision for these systems. Basically, if the receiver has to stop every so often to write to disk, then it tells the transmitter how often to stop, and then it has the option to write to disk, and then send an ACK when it's done. I've got a copy of Chuck F.'s document about Zmodem, and can dig up the packet types for those that are really interested. > I submit that ZMODEM, if implemented with the pauses > necessary to make it work with common drives, would offer *NO SIGNIFICANT > ADVANTAGES* over YMODEM. On a regular dialup line, this would be a close call, however I'd still put my money on Zmodem. But only by a very short head. QTERM (a term program I wrote), can get up to about 224 CPS on a 2400 BPS line with Ymodem, and this is only about 93% efficiency. With Zmodem being able to send 8K or larger chunks at a time I'd expect this to jump a bit. However the _REAL_ advantage will be when using a packet switched network. I've seen QTERM doing Ymodem over PC-Pursuit, and it's pitiful: about 70% throughput. With Zmodem, this would jump to something closer to the 90% range, even with the the segmented approach that would be needed. Note that this is lower than Ymodem on a dialup line, but even Zmodem will take a hit because of the long "turnaround" time of P.S.N.'s (four seconds or worse on a bad day). If anyone wants a real analysis of these times and percentages, I can post one. I agree that on a regular phone line, it's hardly worth it, but on a P.S.N. it would make a difference. Come to that, the turnaround time on GEnie (a service I call into regularly), can get almost as bad as PC-P., so I'd like to be able to to get Zmodem for uploading and downloading from there. But I guess that'll have to wait till I get a UNIX or DOS machine. -- dg@pallio.UUCP - David Goodenough +---+ IHS | +-+-+ ..... !harvard!xait!pallio!dg +-+-+ | AKA: dg%pallio.uucp@xait.xerox.com +---+