How do hotlines between nations work?

I was watching Dr Strangelove last night and couldn’t help to wonder how did the USSR-USA hotline look like in real life.
Was there an actual telephone cord from Kremlin to White House, or was there a more sophisticated method?

The hotline (Moscow-Washington Direct Communications Link) is actually a teleprinter (teletype) link. The US side is located at Fort Detrick, Maryland.

The famous "Red Telephone, " established between Moscow and Washington after the Cuban Missiel Crisis, actually was based on teleprinters, not voice. Teleprinters are essentially typewriter-like machines that print out text entered on the other end of the line and coded into signals that are transmitted. I recall reading (sorry, no cite) that in the beginning, it was an actual cable running from Russia to the USA; after an incident when the cable was damaged, it was supplemented with two satellites (one American, one Soviet). All three channels would simultaneously transmit the same information to reduce the risk of the link collapsing.

See also here.

I believe that Colin Powell’s book, which was published in the early 1990s, claims that the first actual telephone conversation between a President in the White House and a Soviet primier in the Kremlin occured in 1989. I don’t have the book handy, however, to cite the page.