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 
housekeeping.


--
Shmuel (Seymour J.) Metz
http://mason.gmu.edu/~smetz3


________________________________________
From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of 
Charles Mills <charl...@mcn.org>
Sent: Tuesday, January 14, 2020 10:23 AM
To: IBM-MAIN@LISTSERV.UA.EDU
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 
http://secure-web.cisco.com/1NJfAPk9CmbKpO7wNkHn9B6nE4DIuDh8VjmoRD6W14LTnkYRS8mUF9pSaMLpoFNQw1X7bKTufSQxpDFbxWiK_GJYC4fCTMeYoNXrWdY006d3QvNX5gwLKr_Tddhqv6hARKpUa2Ww_M-j3EtEtqgNXVwwhqxhBwkNHfbHZNfctAXcxWr7RaxxyYllBigY0HWHt1hks74ObW0Emd3pHjWjCQHpzxYI6aytGZbSKExfPlNvoHUHfwOnPOHU_wmz_J3R0OqSaVHen3cuw0dZztcIwamLWVnT8OOQTiI77EDcb1tWEj5cBj7OzyBwA6w6iZON7Ri3ukxOmPLHqij2zcSk4cUnQ_K-sX-tj8NSLSBvFxasoFny16vytF4hNgcCM-jBg6miye3bvKK4X5b8TCMWs7yI2ByD6-70MEZGk2McpqNsWtMdhCMLw_4RLIurdIAR8/http%3A%2F%2Fruelgnoj.co.uk%2F3270%2F3270.pdf
 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
(https://secure-web.cisco.com/18c0BA4dtXGJ3jrmHxOb0fQfMOn7KsS3MCPwA3S8XLeEpnbvImAU6lrPFliVgZUwfdITCv2vD8QAyQIst3e9t4oQBI5fw6kn3Z5zvTgtodVYMWXfgRrZ_rDOHCTuoC9voavt2oVRuk2rXTFzrTcGuqP2njC-JbLJOzNAFUOz_790kOT5eusVJPhfplzNyOqiC-BBSmblQkv6CG1UkI3YxnfLa6Bh_I3qU4A1_sCKjFd31oN7FM6cohvAz-j8TsK3jjrajkQ4gi3GT8bcI4tjYJ4-8v0X7FsTJ9-lesmTEaWHX0JEhBPROGC5-Psii1-zu50IIMKHtMOJ68yp_bmrKiDcLeI-jUnK_rg6t38XQ7mp3DWnrpndTasniJpzPJ4yk1XewnqlxgXQ_oMJ423_1em3a2ThaJg9sIN_pZIMYnHPGn7lUOGfPv6DNpk7G8fpp/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSynchronous_Data_Link_Control%29.

Good luck! Sounds like fun.

Charles

-----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
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Talking to 3270 terminals?

Hi

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

* 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 ibm.com 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
  though.

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
layers.

* 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.

-Alex

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