RFC 357 (rfc357) - Page 2 of 13
Echoing strategy for satellite links
Alternative Format: Original Text Document
RFC 357 An Echoing Strategy For Satellite Links June 1972 knows the syntax of the string it expects, it can specify to the Terminal Handler those characters which delimit completed parameters. Such characters are called 'Wakeup Characters' since the user process is awakened as they are echoed. Certain commands keyed by the user will require an output response from the process. In order that the typed commands be followed by its response and be separated from succeeding commands, the Terminal Handler must suspend echoing of user type-ahead. It can resume echoing (starting for type-ahead - with the unechoed characters in the buffer) as soon as the process has stated (implicitly or explicitly) that it has completed the output response. Characters which cause the Terminal Handler to suspend echoing are called 'break characters' They are specified by the user process based upon the syntax of the expected input. Normally break characters are also wakeup characters. As examples: 1. A text editor may gobble up typed English sentences every time a period or question mark is echoed. The two characters are wakeup characters only. There is no need to suspend echoing. 2. In some systems, an ESC character is used to invoke command recognition. The user who types CO [ESC] ABC [ESC] XYZ should see as output COPY (FROM FILE) ABC (TO FILE) XYZ The ESC is both a break and a wakeup. The printout should be the same no matter how fast the user types. The server must provide a means for each user process to communicate the following to the Terminal Handler: 1. the set of wakeup characters, 2. the set of break characters, 3. which break characters should and which should not be echoed, (Some break characters - such as ESC in example 2 - should not be echoed). 4. completion of an output response, 5. whether or not to echo characters. (Not echoing is useful in "hide your input" applications.) Davidson
