Owens-Christopher@cs.yale.edu (Christopher Owens) (07/26/89)
Maybe someone out there has some insight into what is happening here. I use a Macintosh running Red Ryder 10.3, connected to a Practical Peripherals 2400 MNP level 5 modem, dialing into a Vax running Ultrix, via a Racal modem (model unavailable) that supports MNP level 3. For file transfer, I use mbget and mbput, which use the XMODEM, (128-byte packet with CRC) protocol plus some extra info in the headers to handle Macintosh's file format. When I use a generic 2400 baud (no MNP) connection, everything works fine. When I try to use a reliable (MNP) connection, which I assume is being negotiated at MNP level 3, I get fine behavior during my interactive session, but all kinds of problems with file transfer. Uploading files from the Mac to the Vax works OK, but downloading files from the Vax to the Mac causes either of two problems: Either the transfer never gets going -- times out before the first block is sent, or the transfer wedges after block 6. At this point, the connection is wedged. If I hang up and dial back in, the modem answers, this time in regular 2400 baud (No MNP) mode, and starts spewing ~?~?~?~?~?~?~?~?~?~?~?~?~ as soon as the connection is established. Apparently something in the data stream is causing the modem to go into a strange state. Any idea of what? This is a bit hard to debug. I'd appreciate any pointers. Thanks, -c P.S. I know that xmodem is redundant with MNP, but it happens to be embedded within a program that does other nice things for me, so "don't use xmodem" isn't really a good workaround.