SUPDUP
SUPDUP is a network protocol for display terminals. The character set can be standard ASCII, or optionally, an extended version which is based on Stanford Extended ASCII but closer to ASCII 1967.
The name means "super-duper image mode". The explanation behind this is that ITS can open files in various modes; the .OPEN system call offers a choice between ASCII mode and image mode. Opening a terminal in ASCII mode means various control characters are interpreted the conventional way. In image mode, most characters are passed through uninterpreted, but not all; e.g. ^Z is still trapped by the operating system. Using special system calls, a file channel can be set to super image mode in which all characters with no exception are treated verbatim. SUPDUP takes this to yet another level by sending display codes as-is from internal ITS buffers, thus they are "super-duper" image.
