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- Hi Tom -
-
- IMAP can be run over any link which provides reliable, flow-controlled
- transmission that does not intercept any characters. It does not require any
- specific lower-level protocol.
-
- In theory, an error-correcting (e.g. V.42 or MNP) modem with hardware
- (CTS/RTS) flow control connected to a serial port that respects (and uses!)
- hardware flow control will suffice for this purpose. In actuality, there are
- various conditions which make this less than fully perfect; I've seen
- transmission errors and dropped characters. So, it is preferable that there
- be some layer between the serial line and raw data to ensure a reliable link.
-
- Some people have run POP successfully without a reliable link. They just
- accept as ``sh*t happens'' the possibility of dropped characters or line
- noise, since error-correcting modems do reduce this greatly. The problem is
- that POP uses a data marker (a line with only a period) whereas IMAP uses byte
- counts; consequently IMAP is more dependent upon the stream being reliable.
-
- There has been some talk of a lightweight protocol (something that could
- run as a small user program on UNIX) that can be used in place of SLIP. One
- possibility is TCP without IP. The advantage is that you could run other
- protocols as well. Another possibility is reviving my old (1977) Dialnet
- protocol.
-
- The question with either of these is: do we want them to work over links
- which intercept characters? You mentioned Telnet; the UNIX telnet client
- intercepts lots of control characters in various evil ways and on top of that
- certain UNIX telnet servers adds their own bizarreness (some, but not all,
- systems have fixed this). To be reliable, you need a protocol such as Kermit
- or Cafard (my 1985 work for TOPS-20 mail interchange over dialups, designed to
- work over even the most cretinous X.25 PADs).
-
- My suspicion is that no single solution is really best for all dialup
- applications, and more research work is needed in this area. I might be doing
- some of this research later this year.
-
- -- Mark --
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