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 > >
