Den lör 10 okt. 2020 kl 13:23 skrev Stefan Skoglund via cctalk < cctalk@classiccmp.org>:
> 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. > Bitstuffing is used in HDLC and SDLC and is where you insert a 0 after five consecutive ones. That is to differentiate it from the flag which has a zero followed by six ones and then yet another zero. > > 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... > BSC has the concept of escape character. They use the DLE which is 0x10 in EBCDIC. BSC can operate in transparent and non-transparent mode. Transparent mode text is initiated with DLE STX while non-transparent text is just STX. > > > > > Bisync is usually associated with older IBM protocols like 2780, but > > it's occasionally found elsewhere. BSC was widely used to connect various IBM terminals like 2260 and 3270. BSC has a polling concept with the ENQ character which is used to poll terminals on a shared line for data to send. > 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 > > > > > /Mattis