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Very neat. I recall in the dusty recesses of my mind various settings that you could pass to a modem at call initialisation to force certain speeds, modes, and other parameters. Did it have to be an actual 2400 baud modem or could you just "step down" the 56k for the same effect?

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Usually yes, with an AT command: http://www.messagestick.net/modem/Hayes_Ch1-1.html

Knowledge of AT commands is still useful today, but the modems are cellular: https://www.twilio.com/docs/iot/supersim/introduction-at-com...

Just finished a project last summer with a cell modem, actually. Felt weird using AT commands to make an http connection.

It was a one-off I built for a water utility in Connecticut. I'm pretty sure it was an embedded XECOM 2,400bps modem, but I don't remember how I figured out it was faster to do that than to use a 56.6k modem which I would have expected to be faster.

Since at 28.8k and higher the modems are negotiating more than just frequencies (phase shifts and bit compression are also negotiated, IIRC), telling a 56k to run at 2.4k should have the same effect.

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