RFC 559 Comments on TELNET August 1973 A quick investigation revealed that the above problem (of sending GA's reliably) is not confined to the ITS operating system alone. In fact TENEX (ref. conversation with Ray Tomlinson) and DEC-10 (ref. conversation with Ed Taft at Harvard) systems will encounter similar problems. Our solution to the GA sending problem was to have the server wait 2.5 seconds after sending output to see if there is more output to be sent. If the server has been "idle" for more than 2.5 seconds in the "output-sent" state it sends a GA and goes in an I/O wait state (looking for input or output). This scheme works most (but not guaranteed all) of the time and doesn't cause any noticeable delay. It is possible for the server to send an extra GA. Our experimentation revealed that 1-5 seconds was a good range for this "idling time constant". We do implement the "suppress GA" option and will not send GA to hosts who agree to negotiate out of it. Our server tries to negotiate these suppress GA option. C. Other Options and TELNET Control Sequences Our server will refuse all other options by sending the appropriate DONTs and WONTs. In addition to the ECHO and Suppress GA options we recognize the following TELNET "control sequences". 1. Interrupt Process (IP) - The server substitutes the system wide interrupt character (ACII SUB) which immediately interrupts the process, moving control to the immediately superior process. If the user is several levels down his process tree he may have to send several IP's to reach top level. It should be noted that the IP does not interrupt the running process in the sense a interrupts muddle but only passes control to the superior. 2. Erase Character (EC) - The server substitutes the system wide standard erase character (ACII DEL). The deletion however is done not by the server but by the receiving process. It is conceivable that some process (such as a user TELNET) take no action on receiving EC. Most processes will echo the deleted character(s). Several EC's will delete the several previous characters. (If the console is declared to be an IMLAC, the deleted character is removed from the screen). 3. Abort Output (AO) - The server substitutes the character (ACII DC3). The control-S convention is followed by many but not all of our programs. The action taken on receiving AO varies with the program. Bushan