Toward reliable operation of minicomputer-based terminals on a TIP

The present protocol for communication between a TIP and attached terminals requires character-oriented transmission and provides for no error control. In the design of this protocol, it was apparently assumed that the majority of terminals attached to a TIP would be interactive, be normally used in a character-by-character mode both for transmission to and from the terminal, and normally support a human user who would in effect be in the communication loop. The human user would thus be in a position to detect any significant telecommunication-induced errors both by direct observation of the character stream and, more importantly, by examining the computer output in the context of his ongoing interaction. The effectiveness of this means for error detection and initiation of corrective measures when necessary is not adequate in the following cases: a. For terminal-TIP communication at a medium or higher data rate (say 1200 bps or higher) it is quite possible that the human will skim computer output and not be an effective character-by-character error detector. In particular, when both user input and computer output contain numerical data it is possible that significant undetected errors could occur. b. For terminals located at a distance from the TIP and connected either by a private line or the switched network more errors may be introduced than with a terminal local to the TIP (see Note 1). When a large number of user terminals are connected to TIP's through telecommunications facilities, whether within a single organization or, even more likely, when users and user groups not needing the full TIP capability are connected to a remote TIP, this problem may arise.