scasterg@magnus.acs.ohio-state.edu (Stuart M Castergine) (04/29/91)
I have recently ben testing out an MNP error-correctin gmodem. It works great except for the fact that I can't get zmodem protocol to work while MNP protocol is in effect. Consultant here says the two can't co-exist. Is that true? I can't seem to get xmodem to work, either. Is kermit the only protocol that will work in conjuntion with MNP? What kind of performance are you getting from it? -- scasterg@magnus.ircc.ohio-state.edu Stuart M Castergine "The sound of gunfire off in the distance; I'm getting used to it now." -- The Talking Heads, Life During Wartime
labc-1ic@e260-1f.berkeley.edu (Willy S. Liao) (04/30/91)
In article <1991Apr29.153954.1661@magnus.acs.ohio-state.edu> scasterg@magnus.acs.ohio-state.edu (Stuart M Castergine) writes: > >I have recently ben testing out an MNP error-correctin gmodem. It >works great except for the fact that I can't get zmodem protocol to >work while MNP protocol is in effect. > >Consultant here says the two can't co-exist. Is that true? >I can't seem to get xmodem to work, either. > >Is kermit the only protocol that will work in conjuntion with MNP? >What kind of performance are you getting from it? > >-- >scasterg@magnus.ircc.ohio-state.edu Stuart M Castergine > "The sound of gunfire off in the distance; I'm getting used to > it now." -- The Talking Heads, Life During Wartime Well, I use Zmodem with MNP 5 and it does work, sort of. I have to watch out for nasty flow-control problems because the modem I'm connecting to can't pass on flow-control signals to the UNIX host (so I'm told). Anyway, with sz 3.07 I've gotten over 300 cps on text files routinely (I usually use only MNP 4 when transferring .sit or .cpt files). If flow control is a problem on your system, try something like 'sz -w 1536', which means "do not send more than 1536 bytes unacknowledged" so if your Mac does something under MultiFinder which hogs the CPU, the UNIX host will stop sending after 1536 bytes have gone through w/o a reply from your Mac. Anyway I do recall reading in my modem manual that xmodem absolutely does not work without XON/XOFF flow control, so this implies it will never work with MNP 5 & RTS/CTS. But zmodem I know will work, if you can figure out how to force it to... This specifics may also have to do with whether you're talking to a BSD host or a SysV host, or one that's not even UNIX... Willy Liao labc-1ic@web.berkeley.edu
dplatt@ntg.com (Dave Platt) (05/01/91)
In article <1991Apr29.193312.16542@agate.berkeley.edu> labc-1ic@e260-1f.berkeley.edu (Willy S. Liao) writes: >Well, I use Zmodem with MNP 5 and it does work, sort of. I have to watch out >for nasty flow-control problems because the modem I'm connecting to can't >pass on flow-control signals to the UNIX host (so I'm told). Anyway, with >sz 3.07 I've gotten over 300 cps on text files routinely (I usually use >only MNP 4 when transferring .sit or .cpt files). If flow control is a >problem on your system, try something like 'sz -w 1536', which means >"do not send more than 1536 bytes unacknowledged" so if your Mac does >something under MultiFinder which hogs the CPU, the UNIX host will stop >sending after 1536 bytes have gone through w/o a reply from your Mac. I've had similar results, running the ZMODEM protocol over a modem-link which uses V.42 error control and V.42bis compression. I've found that it's not a good idea to try to use XON/XOFF software flow control... although the ZMODEM protocol is smart enough to avoid use of these characters in its packets, Unix systems frequently won't honor XON/XOFF flow control when they're sending/receiving data in "raw" mode. To make matters more annoying, many Unix system's don't honor RTS/CTS hardware flow control... meaning that there is _no_ reliable out-of-band flow control available! I've found that the ZMODEM "sliding window" mode, invoked by the -w option in sz and the "window size" option in ZTerm, is really the ticket to getting ZMODEM to work well over modems that support error control and/or compression. It costs a percent or so of line throughput, but it almost entirely eliminates data overruns and similar nasty things. It implements a true end-to-end flow control within the ZMODEM protocol, and is thus more reliable than flow control that's implemented solely at the host-to-modem level. Using a V.32 modem with V.42bis compression, I've seen ZMODEM throughput as high as 2500 character/second when sending ASCII text files. >Anyway I do recall reading in my modem manual that xmodem absolutely does >not work without XON/XOFF flow control, so this implies it will never work >with MNP 5 & RTS/CTS. It's the other way around, actually. XMODEM requires a clean, transparent 8-bit data link... modems which implement XON/XOFF flow control will "eat" these characters, corrupt the XMODEM packets, and cause the file transfer to abort. XMODEM is compatible with both MNP 5 and RTS/CTS flow control. However, if you're using vanilla XMODEM (128-byte packets), MNP of any persuasion will probably hurt more than it helps... it introduces some delay into the transmission, and increases the end-of-packet turnaround delay... already a bottleneck in many situations. -- Dave Platt VOICE: (415) 813-8917 Domain: dplatt@ntg.com UUCP: ...apple!ntg!dplatt USNAIL: New Technologies Group Inc. 2468 Embarcardero Way, Palo Alto CA 94303