I'm under the impression that a cable is something of a formalized document format - like when an enterprise has a formal template for a memo. Link wise, I'm pr

I'm under the impression that a cable is something of a formalized document format - like when an enterprise has a formal template for a memo. Link wise, I'm pretty sure embassies use a combination of leased lines and satellites, with link layer hardware encryption and one time pads for messages deemed sufficiently sensitive. They may well get delivered using smtp but every email wouldn't get called a cable, and definitely not over public networks. The name cable obviously just stuck from historical use.