I recently came across a video that used a Teltone TLS-5 telephone simulator that was used as a dial up connection. I found a used one and decided to give it a shot.
Hardware used:
- Teltone TLS-5
- USROBOTICS USB modem
- IBM Thinkpad T42 running Windows 98
- Regular telephone for testing
What the TLS-5 is actually doing
The reason you need a box like this at all is that two modems cannot simply be wired together. A plain old telephone line is not a passive pair of wires; the exchange at the far end supplies power and signalling. Specifically it feeds around 48 volts DC across the loop so the equipment knows the line exists, drops that voltage when a handset goes off-hook, plays dial tone, collects the digits you dial as either pulses or DTMF tones, and then puts roughly 90 volts AC at 20 Hz down the other line to make the far phone ring.
The TLS-5 generates all of that on a desk. It is a miniature central office with a handful of ports, each with its own extension number, and it will do line current, dial tone, ring cadence, busy signal and ring-back without any connection to a telephone company. That is the whole trick, and it is why this is the standard piece of kit for anyone doing retro networking.
Steps involved.
- Connect Teltone TLS-5 to power outlet and switch to On position
- Install the USB modem to a Windows XP host (I currently have a 6 node Proxmox cluster with a Windows XP virtual machine that has the USB modem attached) to port 2
- Install USB modem drivers on host
- Connect the laptop to port 3
- Install modem drivers on to laptop host if the host is missing them
- On the Windows XP host create a new advanced internet connection and select the modem and user as the dial in user.
- On the laptop or host you want to dial in from, create a new dial up connection and use the username/password from step 6 and use number 102 as the phone number
- Click Connect and you should be connected.
What is happening on the wire
Once the carriers lock up you are running PPP. The answering side is Windows XP’s Routing and Remote Access doing the work an ISP’s terminal server used to do: it authenticates the dial-in user, assigns the client an IP address from its own pool, and bridges it onto the LAN. From the ThinkPad’s point of view it has just joined the internet through a phone line, which is exactly the illusion you want.
Do not expect 56k. That number was always asymmetric and always required the answering end to be digitally attached to the phone network, so the downstream path had no analog-to-digital conversion in it. Two ordinary analog modems talking to each other over a line simulator have a converter at both ends, which puts you on V.34 and a ceiling of 33.6k. In practice you will see less, and it will feel exactly right.
Gotchas In the tutorial I was using Netscape Navigator. The homepage was home.netscape.com. This is no longer a thing, and neither is most of what a 1998 browser wants to load: the sites are gone, the DNS records are gone, and the handful that answer now speak TLS versions Navigator has never heard of. An upcoming tutorial will use pihole as a DNS lookup so that going to old URLs still work, pointing the dead hostnames at local archives instead.
Video demonstration of someone else ring testing: