In reply to a post by BatBoy:

The modem is acting as a handset

Are you still on dial-up? I don't recall seeing anything relating to an acoustic coupler.... and on what basis, barring flexibility, is a stranded core better than a solid conductor for power or data in the usage case originally posted?

The difference is clearly illustrated in this diagram https://upload.wikimedia.org/wikipedia/en/thumb/4/4b...

Serial interface? Really?
I refuse to have a battle of wits with an unarmed person.
goodnight.

Really. You didn't actually think the data arrive all at the same time, did you?

Due to pedantry and original question was answered a long time ago.

Pedantry is something that will often discourage new posters from posting, as they will worry about being 'shamed' by those who are either having a bit of fun or genuinely believe everything has to be just so.