[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 > >Hi, > >> I am new to this list and would like to discuss an idea and ask several >> questions. > >Welcome. > >> * Did anybody ever attempt to 'talk' to 3270 terminals with something >> different than an IBM mainframe? > >Yes* > >* 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 > >Agreed. > >> 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. > >SNA is a *FULL* *PROTOCOL* *STACK* / *SUITE*. > >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 >disservice. > >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. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
