On 2019-11-18 19:42, Al Kossow via cctalk wrote:
I find it interesting that the field of comms interoperability with IBM mainframes was huge up until TCP/IP took over, and all traces of the software implementations have disappeared or were consolidated into a couple like Micro Focus.
In attempting to bridge the twinax world to something else, I guess I was naive coming from the ASCII/UNIX realm thinking 'how hard could it be?'
The electrical-wire and line framing and coding of the TwinAx data cable is pretty straight forward. 1 MSps differential Manchester coding with a fixed frame sync pattern. Then up to 256 bytes of payload per frame to 7 logical addresses. I was under a simplified-thinking impression the 5250'ish terminal and printer data protocols would live directly on top of that. Now it seems from my research, it's SNA/LU7 that sits on-top of TwinAx for early S/3x, correct? Then a 5250 data stream? Then 5250 display station specific commands?
Are there any ideal resources I should be looking at? I've browsed through the GC30-3073-1 SNA Technical Overview but it doesn't cover differences in LU types, for example... No wonder Big Blue was always so expensive.
-Alan
