Terminal output: parity, etc. (Comm. protocol issues)

[rf at wu1.UUCP]

Eight bit data transfer is likely to upset some terminals and
some data transport networks.  Unfortunately, the nearest to a
standard Ascii asynchronous protocol we have is seven-bit, even
parity, xon/xoff flow control (control-s/control-q).  There are
numerous programs likely to be upset by the receipt of eight bit
data (csh and ingres to name two).  Some older terminals much
prefer parity.

>>> FLAME ON <<<

I'm going to use the space to plead for cleaner communications
interface design.  The hopeless lack of standardization in the
terminals and line interfaces used with Unix systems means that
any code we write to handle communications is device dependent.

I want a terminal handler which is flexible enough to be
customized to *any* protocol.  If this means that we have to
devise a method of dynamically loading kernel code, so be it.

What are called "tty" ports are used for four things:

  1. Local connections to keyboard terminals at speeds of 9600
     bits per second or more.

  2. Local connections to fast printers at speed of 9600 bps or
     more.

  3. Remote connections to keyboard terminals at speed of 110 to
     9600 bps (since 9600 bps requires a dedicated line -- or
     true half-duplex operation -- this speed is unusual).

  4. Remote connections to computers at speeds of 300 to 56,000
     bits per second.

Unix handles local connections reasonably well.  Type 103 and
212 modems are handled passably in asynchronous answer mode,
though many 68,000 Unices do not properly recognize some RS-232
signals.  Dialout modems are handled somewhat awkwardly, and
*no* synchronous or half-duplex modems are supported without
extensive hacks to the kernel.  The reception of data at high
speeds is handled by the same code which handles keyboard input
-- an appalling waste of CPU capacity.

Unix is a product of the company which *invented* the modem.
Come on!  Can't we do a little better?

One final flare: the term "baud" refers to state changes on a
transmission line -- *NOT* "bit rate".  A 9600 bit per second
modem operates at 2400 baud.

decvax!philabs!wu1!rf		Randolph Fritz
				Western Union Telegraph