davidsen%kbsvax.tcpip@GE-CRD.ARPA.UUCP (05/14/86)
In article <8605041048.AA06732@ucbvax.berkeley.edu> phil@amdcad.UUCP.UUCP writes: >In article <1703@sdcsvax.UUCP> brian@sdcsvax.UUCP (Brian Kantor) writes: >>With uucp, these modems work really well. However, the uucp transfers >>weren't much faster than those at 480 char/sec. I've seen (somewhere >>in the dark past of the net) a note that showed that normal uucp gained >>very little speed running above 4800 baud. > The problem is the turnaround time. We have been evaluating "Fastlink" modems, and have just gotten some new "fast turnaround" ROMS. Using a protocol which did not require a turnaround after each packet, we were able to run over 900cps with the old ones. uucp was very slow, <100cps. The limits in performance are due to the line, not uucp. Running 9600 baud from my (Xenix and PC/IX) micros to a loaded VAX, I regularly see rates of 850-880cps. On an unloaded system the rate will reach 920cps. Standard Kermit runs about 450-480cps wihtout windows. Windowed protocols can run at 90-98% of line speed, which can be combined with programs like compress to get very fast effective rates. Best transfer rate was obtained by: compressing the file using compress 4.0 using btoa to get a text file turning on logging and just listing the file with cat using atob and uncompress at the far end. Since the modems perform their own error checking, and atob will at least detect an error, this method is not likely to lead to incorrect files. Using this method, the observed line rate was 950cps, 820k bytes were transferred, and the effective transfer rate (using the size of the uncompressed data) was 12-13k cps. Obviously this is only reasonable over a modem which does error checking for you. At one time modem were available with a fast forward channel and a slow (110 or 300 bps) reverse channel for ACK/NAK. Perhaps someone can jolt my memory on this. At any rate, given a fast turnaround or windowed protocol, the existing modems will reach 90% of max line speed if the cpu can keep up. Has anyone tried the kilobuck modems in the back of PC Week? They claim 9600 baud.