This a container based on Alpine Linux running the TCPSER modem emulator.

TCPSER is a modem emulator, it emulates a Hayes compatible modem. It allows older systems to connect to services such as BBSes using a null-modem cable. The container also includes a preconfigured PPP to simulate a dialup ISP provider and connect to the internet.

It uses Alpine with TCPSER, PPP and Dnsmasq.

It is based on the PiModem project by PodSix, which uses a Raspberry Pi Zero W.

Features

• Uses the TCPSER fork by FozzTexx
• Includes PPP preconfigured to simulate a dialup ISP provider
• The PPP service accepts any username and password
• Uses Dnsmasq to share the host's DNS resolver

Requirements

• A retro computer with a serial port
• A modern computer running Docker with a serial port or an USB serial adapter
• A null-modem cable

How to build

git clone https://github.com/chris-l/docker-tcpser-modem-emulator.git
cd docker-tcpser-modem-emulator

docker build -t tcpser-modem-emulator .

Environment variables

• DEV: The serial device. Default: /dev/ttyS0
• BAUD: The baud rate to use. Default: 38400

For the fake dialup internet provider, the following additional variables are available:

• IP_SERVER: The IP assigned to the server. Default: 10.0.1.1
• IP_CLIENT: The IP assigned to the client. Default: 10.0.1.2
• PPP_PHONE: The phone number to use. Default: 5559000
• PROXY: Optional. Redirects all requests to port 80 to a proxy specified in the format IP:PORT, such as 172.17.0.1:8000. Unset by default.

Volumes

The container also supports the following volumes:

• /dev/<your serial device>: The serial device to be used. This is typically /dev/ttyUSB0 for USB adapters and /dev/ttyS0 for the first serial device (equivalent to "com1" on Windows)
• /phonebook.txt: A file containing lines in the format <phone number>=<ip/domain>:<port>. Example: 1701=bbs.fozztexx.com:23

Usage

The argument --privileged is required to allow the container to access the serial device.

In this example, its assuming the serial device is /dev/ttyUSB0, 115200 baud, a phonebook.txt file in the current directory and using --rm to remove the container after its closed.

docker run -it --rm --privileged -e BAUD=115200 -e DEV=/dev/ttyUSB0 -v /dev/ttyUSB0:/dev/ttyUSB0 -v $(pwd)/phonebook.txt:/phonebook.txt chrll/tcpser-modem-emulator

On the client, make sure to select the same baud as the container.

For the fake dialup provider, use the PPP_PHONE number. Any combination of username and password will work. For using a proxy, ideally use the client's browser settings to configure it. That way it can handle other request than those to port 80. If that is not possible, you can use the PROXY env var to redirect all port 80 requests through it.