in case anyone was wondering what a 1995 era dial-up ISP might look like in 2025
nothing has been hooked up yet, as i need to craft a bunch of very arcane cables for the job.
this is how it works in theory:
that fat scsi-looking plug on the Mediatrix 4124 is to attach 24 plain old analog telephone lines via a fat octopus cable. the mediatrix is an ATA or Analog Telephone Adapter. it translates VOIP/voice-over-IP calls to plain old telephone service that you could hook up any old telephone to.
but we're after dial-up internet service, so - normally those 24 lines would go to external modems, but it'd be silly to have 24 black boxes with 24 power adapters plugged into the wall.
so, instead, the Mediatrix telephone lines run to that black US Robotics Total Control Modem Pool 16. it lets 16 modems ask for an internet connection via SLIP or PPP - the dial-up protocols you used in the 1990s.
the total control appliance has sixteen 33.6Kbaud internal modems inside (each on a small circuit board). the modems speak analog on the telephone line side, and speak digital on the serial side.
the serial side of the total control box then runs sixteen RS-232 serial cables to the box above it: a Cisco 2511 Access Server.
the access server has sixteen serial ports on the back, which accept the serial connections from the modem pool. this is where the internet magic happens.
the rear of the cisco 2511 has a port for connecting to the outside world on behalf of each modem line. it gives an IP address to each modem line, and routes all traffic to the internet. this is where the SLIP/PPP protocol is used.
so in essence:
your modem dials my number ->
mediatrix 4224 accepts the incoming call ->
total control mp16 accepts the call on one of its modem ports ->
cisco 2511 accepts the modem's request for an IP address and begins routing internet traffic back to you, via the exact same chain of hardware in the opposite direction.
(also pictured just for fun: a big yellow google search appliance, circa 2002 - back when the company featured useful tools like searching the web for things. the GSA is a fancy Dell server with a tool that lets you search document databases on an intranet. the kind of thing a medical firm, oil company or rich dentist office would have)