[Default] On 14 Jan 2020 17:07:32 -0800, in bit.listserv.ibm-main
0000023065957af1-dmarc-requ...@listserv.ua.edu (Grant Taylor) wrote:

>On 1/14/20 2:52 AM, Alexander Huemer wrote:
>> Hi

There were both bus and tag 3174 terminals which could be used for
consoles and local SNA terminals which only worked with VTAM.

Clark Morris
>> 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?
>* because it's highly dependent on what you mean by "IBM mainframe". 
>More specifically if you mean the hardware and / or the software.
>I know that there are people actively working in the Hercules community 
>to drive (talk to) 3270 terminals.
>I think I've recently read some articles where someone is trying to use 
>a 3270 as a terminal for a Unix (Linux?) workstation.
>So, "It depends...."
>> 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.
>It doesn't sound completely crazy to me.  It does some completely 
>atypical.  But atypical can be entertaining and / or educational.
>> 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.
>I believe the article I recently read was talking about driving the 
>signal on the coax.
>I typically see some variation of the following discussed:
>1)  3270 terminal talks to the (remote) 3174 Control Unit (?).
>2)  The remote 3174 CU talks across Ethernet or Token Ring or RS-232 
>something else acting like a local 3174 CU.
>3)  This thing acting like a local 3174 usually talks TN3270 to a 
>mainframe OS, be it running on a physical mainframe or emulated.
>I believe that some later / feature rich 3174s have the ability to act 
>like primitive telnet clients.  Thus you could use the 3270 to talk to a 
>Unix box.
>> * What's the best available documentation regarding 3174 models and 
>> their features?
>I don't know.
>I've seen quite informative discussions about this type of thing on the 
>hercules-390 and cctalk mailing lists, plus a few newsgroups.
>> 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?
>I think it's highly dependent on if it's the "local" or "remote" 3174.
>I think that the "local" 3174 was exclusively Bus & Tag for northbound. 
>—  I've not heard of any ESCON interfaces for 3174.  —  The Token Ring / 
>Ethernet / SDLC / RS-232 was southbound to talk to "remote" 3174s.
>Similarly, the "remote" 3174 was Token Ring / Ethernet / SDLC / RS-232 
>for northbound and coax for southbound.
>The Token Ring / Ethernet / SDLC / RS-232 was used to connect "local" 
>and "remote" 3174s.
>> Bus&Tag doesn't seem to be a good candidate, it's difficult to interface 
>> with as far as I understand.
>Two things come to mind to interface with B&T.  The B&T cards that exist 
>for PCs running things like the PC/370 / P/390(-E) or something like a 
>big iron Cisco router with a Channel Interface Processor card.  But I 
>think even the CIP is a "grey" downstream device and can't pretend to be 
>a "black" host (mainframe) device.
>> Ethernet is way more common these days than Token Ring, though TR NICs 
>> are easy to procure second hand
>> protocol support under Linux (the OS I am most savvy with) is in place.
>Be careful there.  Contemporary Linux (4.x) no longer includes Token 
>Ring support.  I believe it was removed from 3.5.
>Even then, there are other protocols that I've not been able to find 
>support for in Linux.  SNA being the biggest contender.  There are 
>pieces that I think could be used to help support SNA.  But I'm not sure 
>that all of the requisite pieces are there.  LLC is questionable.  There 
>were a couple of implementations for some different things.  I don't 
>know if any of them were ever complete enough to support SNA.
>> RS232 is easy to interface with also, though then again, I am not sure 
>> if that interface really exists.
>I think that the 3174s did have RS-232 support.  But I'm not sure what 
>it's purpose was.  I don't know if it was for dial up SNA or if it was 
>for synchronous modems / X.25 networks.
>> * Did the LAN interfaces (Ethernet, TR) talk SNA on layers 2 and 3
>I think so.
>My understanding is that SNA on Ethernet / Token Ring used 802.2 LLC 
>frames (you can find the SSAP / DSAP numbers).  I don't think that SNAP 
>was used.
>SNA is as different from TCP/IP, IPX/SPX, AppleTalk, etc, as they were 
>from each other.
>You quickly get into the fact that traditional SNA thought it was the 
>center of the universe and the only form of intelligent life.  Then — as 
>I understand it — you start getting into APPN when systems are no longer 
>the center of the universe where there is something out there 
>intelligent like another host.
>> was there by any chance something going on with TCP/IP? I doubt it though.
>SNA is decidedly NOT TCP/IP.
>That being said, I know that TCP/IP can carry SNA traffic in a myriad of 
>ways.  TCP/IP can encapsulate SNA;  SNASw and Enterprise Extender come 
>to mind.  TCP/IP can gateway some of the higher SNA application layer 
>traffic and carry it more natively; TN3270 comes to mind.
>I've heard / read that SNA could carry TCP/IP traffic via things like 
>AnyNet from IBM.
>This quickly devolves into a quagmire where you need to really 
>understand what you do (not) have and what you want to (not) do.
>I believe you can substitute IPX/SPX in place of TCP/IP and have a 
>different quagmire too.  I know that Apple played in this space, but I'm 
>not sure how much they did on the network layers.
>> Talking SNA with custom software doesn't seem to be a low-hanging fruit.
>No, not at all.
>You really are talking about all of the layers of the OSI model.
>> From where I stand right now I cannot say how straight-forward the network 
>> traffic between the mainframe and a 3174 is
>I think that considering it to be a network protocol is probably a 
>The host sees things connected to it like a tree of devices.  Much like 
>USB on contemporary systems.
>Is it a protocol?  Probably.
>Is it a /network/ protocol?  I think not.
>> how difficult it would be to emulate that protocol with custom software 
>> over several layers.
>Probably quite.
>There is a *LOT* to SNA.
>> * 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 think anything like that over B&T is nigh impossible.
>Yes, it would be possible to get packet captures of SNA over Ethernet or 
>Token Ring.  But I've not seen such discussed anywhere.
>I suspect it would be problematic to find someone with the proper 
>equipment to configure an RS-232 based connection, much less capture it.
>I think that the further you get away from the host the less of the 
>protocol that you might actually see.
>I want to say that the host and it's 3174s had a symbiotic relationship. 
>   But that's not the case.  It's more that the host was the brain and 
>that everything else was a lowly appendage.  Some things like the 3174 
>control units were quite important, like the heart and lungs.  But they 
>were still functionally subservient to the host.
>> I would appreciate any thoughts regarding this topic, especially to the 
>> questions marked with asterisks.
>This is all my understanding that I've manged to pick up over the last 
>year or so.  It is quite likely that I'm misunderstanding things 
>completely or may have some subtle nuance wrong.  Please politely 
>correct me if I'm wrong.
>> Also, if anything is known regarding a similar thing with 5250 instead 
>> of 3170 terminals, that would be interesting as well.
>I  don't know if I've seen anyone trying to talk to 5250 terminals like 
>3270s.  But my ignorance doesn't preclude such from existing.
>I was recently involved in discussions about how to leverage different 
>Cisco routers with proper IOS support to get AS/400s talking to each 
>other across disparate networks.  Enterprise Extender running on a 
>contemporary machine & OS using an OSA to connect to one Cisco.  That 
>first Cisco gatewaying to something else across virtual Token Ring (?) 
>to another older Cisco.  That second Cisco was doing additional 
>gatewaying to talk to an older machine & OS on Token Ring.  It took the 
>combination of the two Ciscos, each doing a piece of the job, to allow 
>the two machines talk.
>Search for the "SNA and I Systems" thread in the comp.sys.ibm.as400.misc 
>newsgroup if you are interested to know more.
>Finally, I'll say that I'm somewhat surprised to see this type of 
>discussion in IBM-MAIN.  Not because I think it belongs elsewhere. 
>Because I think that IBM-MAIN is more day to day production support 
>related issues and virtually nobody is running anything like this in 
>production.  I would sort of expect to see this type of discussion in 
>hercules-390 / cctalk / newsgroups that are further off the beaten path.

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