3270 controller simulation

alan at alanlee.org alan at alanlee.org
Tue Nov 19 04:51:25 CST 2019

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 

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.


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