RFC 1109: Report of the Second Ad Hoc Network Management Review Group.
It was recognized in this process that the definition of the layer BELOW IP was a difficult task. IP is sufficiently simple and general that it has been moved in encapsulated form over many media including the MAC level of various local nets, X.25 packet level, serial line protocols, multiplexors, tunnels and, it is rumored, tin cans and string.
Don't mess with The Phone Company. If you piss them off, whaddaya gonna do? Get two tin cans and a piece of string? They got you and they know it and so do you.
-- Paraphrase of comedian and social critic Lenny Bruce.
IP over Two Tin Cans and a Piece of Wet String
Nokia Unveils "Tin Can and String" Network.