Remote job submission from PDP-11

Stefan Skoglund stefan.skoglund at
Sat Oct 10 06:11:46 CDT 2020

ons 2020-10-07 klockan 14:08 -0400 skrev Paul Koning via cctalk:
> Not flags, that's an HDLC concept.  Bisync uses sync characters (as
> DDCMP does) but instead of doing framing by byte counts it does it by
> a frame terminator, and for transparency if that occurs inside the
> data it has to be escaped.

Bit stuffing ? ie if the payload contains a sequence which is reserved
add a an escape for example an A after three consecutive spaces.

ON the receiving end remove the A, if it came after three spaces.

Four consecutive spaces in the wire stream, that is a frame marker...

> Bisync is usually associated with older IBM protocols like 2780, but
> it's occasionally found elsewhere.  One of my nightmare memories is
> debugging the communication between a PDP-11/70 running Typeset-11
> (on IAS) and a Harris 2200 display advertising graphics editing
> workstation.  That runs Bisync, half duplex, multipoint, with modem
> control, on an async comm link -- DL11-E devices at the PDP-11
> end.  Yikes.  At our customer site in downtown Philadelphia, it
> tended to lock up, but only during the "lobster shift" -- midnight to
> 8 am.
> I don't really know anything about that particular protocol beyond
> what I just mentioned, but I'm fairly sure it didn't have anything to
> do with IBM products.
> 	paul

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