The old internet, specifically the Dial-Up connection. It was one of the first point-to-access for the web. The user had to mark the phone number of his provider, and then the computer began to send auditory signals by line phone, this make the iconic noise and erratic sounds.
The provider received that call with another modem; in this process, they measured things like speed, compression. Something like a handshake.
The maximum speed of dial-up connection reached 56 kbps, but usually the speed would be between 40-50 kbps due to line quality.
The internet was so low in that times, any kind of activity felt so slow like loading an image or a song would take many minutes, also when you were using this connection, you couldn't use the phone for calls, any incoming call or noise would interrupt the connection, having to reconnect again. The latency was so high, making it so hard to play online games or make video calls.
Usually the rates charged was for the time you used the internet or the provider could give you a daily time or monthly time to use the connection.
With the arrival of new connection technologies like ADSL, coaxial, and optical fiber, dial-up was progressively forgotten, but we can't deny how useful it was in its time.