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Thread: Dial-Up at Home With a Line Simulator

  1. #1
    Join Date
    Jan 2010
    Central VA

    Default Dial-Up at Home With a Line Simulator


    I finally got around to trying an experiment yesterday: I've had a little Teltone TLS2 line simulator for a while, and while it worked with regular phones, I wanted to see if it'd work on a modem connection. The TLS2 is an analog two-port line simulator, which is sort of like a very minimal PBX: there are two ports, the TLS2 provides dialtone and ringing, and will let you dial one port from the other. You dial 40 to ring the port on the left, and 29 to ring the port on the right. Teltone made newer and more complicated versions. They're popular with folks traveling to telephone shows, apparently.

    Hardware/software used for the setup:

    * Sun SPARCstation 2 running SunOS 4.1.4, ttya configured as a modem line
    * Teltone TLS2 Line Simulator
    * Microcom AX/2400 external 2400 bps modem, set for auto answer, AT mode, on the SS2's ttya port
    * IQ Technologies SmartCable (in straight through mode, mostly just for blinkenlights )
    * Leading Edge Model D "mostly XT compatible" computer running MS-DOS 3.30
    * ProComm 2.4.2
    * Practical Peripherals 2400 bps internal 8-bit ISA modem
    * Various cables

    The "ISP" end of the setup is the SPARCstation 2. Here's a picture of it up and running:

    Check out Celeste's Tutorial on SunOS 4.1.x Modems & Terminals for pointers on getting a serial port set up for a modem line under SunOS 4.1.x -- you don't need to use a Sun or SunOS, I just happened to have one on the bench this week. A closeup of the SS2 and related equipment:

    The SPARCstation 2 is connected to my DEChub 90 system via 10base2/ThinNet, and links back to the main network through a DECbrouter 90T1 over V.35 sync serial to my Cisco 2801 router. As you can see from the modem lights, there's a client connected when the picture was taken. A picture with no flash, to better show off the blinkenlights:

    This is the client end of the setup:

    The Leading Edge Model D is running MS-DOS 3.30 from a floppy in the A: drive, with a Procomm 2.4.2 working disk in the B: drive. The Practical Peripherals modem is set up as COM2. Just give an ATDT29 and it dials the SPARCstation and connects! This is actually pretty similar to my first ISP account growing up: I dialed in to Grex in Ann Arbor, MI (usually through calling cards!). Grex was running SunOS 4 on a Sun4 SPARC VME chassis at the time. I forget what speed modem I had in my IBM 5160 PC/XT but it was probably 1200 or 2400 bps.

    And yes, I did reattach my screen session and IRC over the link

    So, that was a success: you can in fact at least run 2400 bps over a Teltone line simulator! Avoids the cost and hassle of having two phone lines to call within your own house, and it's a much simpler device than running Asterisk with FXS ports. Might even be very slightly practical if you have a laptop or other portable that has an internal modem but no serial port!

  2. #2


    I'll have to give that a try. I'm interested in getting my DEC PRO 380 "online" and serial port just seems simplest (it runs Venix, which makes it harder).
    I use my C128 because I am an ornery, stubborn, retro grouch. -- Bob Masse
    Various projects and oddities:
    Machine room:

  3. #3


    In 2005 the community college I attended used these for the modems segment of the computer networking classes. They replaced a Mitel PBX, whose tape drive had finally died.

    My Site (under construction!) | My Apple Lisa 2/10

  4. #4
    Join Date
    Mar 2017
    New Jersey, USA


    I have been wanting to do something like this for a while, but since I don't have a line simulator I was considering a software PBX like asterisk, with some line cards in a pc. The lack of cards with OpenBSD driver support has been an impediment -- I don't want to run Linux for just this one thing.

  5. #5


    amazing setup. and I saw Floppy, when I was in school. Those days. so, how did you set modem up?? guide us in brief!!


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