An HPUX 11i network, running on new hardware, for what they call “mission critical” operations at a unique business, terminates for the user at Sherwood 7000STs. While functional (and lightning fast compared to the Web 2.0 systems I grew up with), the terminals connecting via DB-25 (thanks @grawity) RS232 all over the office must be decommissioned. They’ll be replaced with modern Ethernet over RJ45 connections going into a switch with server on a single subnet, and I need to understand how our application will be affected.


Serving an application serially is working fine.

Telnet and SSH are installed.

There are both NIC and COM PCI cards. (LMK if terminology is inaccurate — I will run dmesg tomorrow and update post.)


There are many possible configurations of serial terminal.

Telnet and SSH run in terminal emulators when connecting across Ethernet in normal usage.

No firm basis exists for me to expect this application to flawlessly transition.

Previously, server upgrades caused terrible dysfunction between apparently compatible hardware when proprietary wiring meant that our (serial) RJ45 to 25-pin RS232 to 9-pin RS232 conversions had literal crossed wires, as hardware deviated from the spec. Analogies to software are here easy to concieve of, but they should be equally hard to encounter in production!

@Bob - a switch will be in place. What other considerations must I make? See below.


  1. Should I expect telnet to “just work” on a new Linux box (like Raspberry Pi), going into the server? It will be going through a switch, of course. But can Ethernet networks replace serial networks as a drop-in at every layer, up to and including applications?

  2. Baud rate will obviously no longer be necessary, but what about other configurable settings such as escape characters?

  3. Line wrapping?

  4. Paging?

  5. Important: What about programs that define terminal display (such as Unibasic)?

  6. Important: Will RJ45 run the risk of being somehow “incompatible” with the existing system?


I am confused where processing takes place, and any deeper characterization of the issues above in this context would be appreciated. Mods, please accept this vague question due to the lack of existing discussion on Stack Exchange. I have carefully looked before posting. I am happy to document my research of the existing lit.

Thank you so much.

  • 1
    I don't understand what exactly you're replacing it with. RJ45 is not a communications protocol – it is just a physical jack type; it could mean the same RS232 serial or it could mean Ethernet or Token Ring or analog phone lines... Which one did you mean? – grawity Aug 8 '18 at 4:03
  • @grawity that’s a good question. Ethernet over twisted pair is where we are heading, and the majority of the consumer world is already. Does RS232 over RJ45 entail no configuration on the terminal emulator end, such that Linux boxen could consume the same – lettucehead Aug 8 '18 at 5:23
  • ... (stupid time limit) ... protocol as our DB-25 headed terminals? I had assumed they were mutually exclusive and appreciate the clarification. Re: the others: Token Ring finds sexiness only in an expensive obscurity, whereas being ubiquitous doesn’t bring telnet to bare phones (that would be a sick research project). If TL;DR: lmk cmd to dump info 4u. – lettucehead Aug 8 '18 at 5:39
  • One thing that isn't clear (and I'm kinda scared that the question actually leaves it open)... do you have a proper TCP/IP network set up (preferably, switched) or do you intend to plug your clients directly into the server via an ethernet cable? The former is a fairly typical config. The latter ... not so much. – Bob Aug 8 '18 at 5:59
  • @Bob No, and yes. Another thing that isnt clear is your question ;) The tcp/ip will be added in, just isnt already there. We intend to plug in via switch, not directly. Ty – lettucehead Aug 8 '18 at 6:01

You need to be aware that on the HP-UX side, RS-232 interfaces are totally different from network interfaces, which are again different from the telnet API.

If all you use your terminals for is to log in into the HPs, then you can replace that by telnet, or by ssh if you want it to be more secure.

If you have custom software that these terminals connect, then this could be a major problem: You'll have to adapt the software to deal with the new kind of connection. Which, depending on the software, may be easy, hard or impossible, but it's the major concern here.

To the questions:

1) Yes.

2) Won't matter, everything is passed through. If you use it to log in, you can still change backspace/del etc. via stty (if that's what it's also called on the HPs, been too long since I used one).

3,4,5) Is a function of the way the application and the terminal program interpret control sequences. Transport doesn't affect this.

6) See above.

You should keep in mind that processing works on layers.

RS-232 and Ethernet ("RJ-45") are very different transport technologies, as are protocols (telnet, ssh) that work over Ethernet. You should have someone who is familiar with modern network technology, and can install all this for you. If you don't have one, hire one, or ask another company to do it for you.

Above this transport layer, when the software on both sides just sees a character stream, the differences are minimal.

  • You should have someone who is familiar with modern network technology, and can install all this for you. How hard could it be? I appreciate this answer, except for the “all this,” indicating there’s (A) more being left unsaid or (B) a dubious limit to one’s ability to plug connectors into sockets and run apt-get. pI am asking about concrete details. I’m doing my due diligence and will see it through - if a professional needs to come, please advise the actual content of their expertise in this regard. I sincerely appreciate your informative answer. – lettucehead Aug 8 '18 at 6:14
  • From your questions: It's all doable, but you'll spend a lot of time figuring things out, you'll make mistakes along the way, etc. One can learn everything, but one has to invest this time. How much would you think your time is worth? How critical is this infrastructure for your business? How much would it cost to recover from mistakes? Compare this to how much it would cost to pay someone else for knowledge already acquired. – dirkt Aug 8 '18 at 6:20
  • If I had to hire a professional for this, I'd look for some one familiar enough with HP-UX to configure things if necessary. The networking infrastructure is not that hard, but there are plenty of mistakes you can make when laying cables etc. So leave at least that to a professional. The most critical part is the software used, where you haven't said yet if it's a simple login, or custom software. – dirkt Aug 8 '18 at 6:23
  • $17/hr; mission-critical; thousands of dollars. But we were quoted for $40-50k. What were they gonna do, mine the rare earth metals for our I2Cs? – lettucehead Aug 8 '18 at 6:24
  • The software is all served from the server - the terminals are completely dumb. Login and text input is needed. And text display, go figure. There are some facile macros but Prometheus gave us vi for a reason. – lettucehead Aug 8 '18 at 6:25

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