You don't talk TN3270 to an emulator; all of the 3270 simulation is in the 
TN3270 client. Tn3270 just encapsulates 3270 data streams and associated 

Shmuel (Seymour J.) Metz

From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of 
Charles Mills <>
Sent: Tuesday, January 14, 2020 10:23 AM
Subject: Re: Talking to 3270 terminals?

Would talking the TN3270 protocol to a 3270 emulator do the job for you?
That solves all of the hardware issues: it is simply TCP out of your
implementation and into the emulator.

You could then if you wished "graduate" to a real 3270 terminal. If I were
doing it I would go SNA but that is because once upon a time I knew SNA at
the bit level, but little about how bus & tag worked at that level.

I can't speak much to physical connection or the layer immediately above
that but this book
 is the bible of the
byte stream going to the device.

There is no real reason you could not drive one from Linux or Windows. A
Raspberry Pi with a 3270 attached would be an amusing idea.

BTW, RS232 is a specification for the plug between a device and a modem. It
is at a lower level in the stack than most of the other things you mention.
Yes, it would be relevant to a dial-up SNA implementation. The "bits going
over the modem" layer of SNA is called SDLC

Good luck! Sounds like fun.


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
Behalf Of Alexander Huemer
Sent: Tuesday, January 14, 2020 1:52 AM
Subject: Talking to 3270 terminals?


I am new to this list and would like to discuss an idea and ask several

* Did anybody ever attempt to 'talk' to 3270 terminals with something
  different than an IBM mainframe?

This might sound like a strange idea, though I find it intriguing to be
able to display content on such a terminal and be able to receive
keyboard input from it.

I guess the most straight-forward way to attempt something like that is
to use a 3270 terminal attached to a 3174 or similar and try to talk to
that instead of the terminal itself. I wouldn't know how to interface
with the terminal directly over the coax.

* What's the best available documentation regarding 3174 models and
  their features?

I poked around on and google but wasn't able to find much. It
seems like there were several different physical-layer north-bound
interfaces for 3174. Bus&Tag, Token Ring, Ethernet, RS232 (if I am not
mistaken, for dial-up connections), maybe others?

Bus&Tag doesn't seem to be a good candidate, it's difficult to interface
with as far as I understand.
Ethernet is way more common these days than Token Ring, though TR NICs
are easy to procure second hand and protocol support under Linux (the OS
I am most savvy with) is in place.
RS232 is easy to interface with also, though then again, I am not sure
if that interface really exists.

* Did the LAN interfaces (Ethernet, TR) talk SNA on layers 2 and 3 or
  was there by any chance something going on with TCP/IP? I doubt it

Talking SNA with custom software doesn't seem to be a low-hanging fruit.
>From where I stand right now I cannot say how straight-forward the
network traffic between the mainframe and a 3174 is, how difficult it
would be to emulate that protocol with custom software over several

* Is anybody on the list here able to provide protocol traces from the
  link between mainframe and 3174 over any interface? pcap format is
  preferred, though anything would be valuable.

I would appreciate any thoughts regarding this topic, especially to the
questions marked with asterisks.
Also, if anything is known regarding a similar thing with 5250 instead
of 3170 terminals, that would be interesting as well.


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