From: utzoo!decvax!harpo!npois!ucbvax!C70:editor-people Newsgroups: fa.editor-p Title: Re: ^S/^Q but not DTR Article-I.D.: ucb.1385 Posted: Sat Jun 19 02:41:28 1982 Received: Sun Jun 20 01:03:29 1982 Reply-To: ople >From Frankston.SoftArts@MIT-MULTICS Sat Jun 19 02:39:12 1982 editor-people at SU-SCORE, Goldberg at RUTGERS Remailed-date: 19 Jun 1982 0001-PDT Remailed-from: J.Q. JohnsonRemailed-to: Editor People: ; {More discussing Xon/Xoff issues, skip this if you are not interested} There is a big difference between something that just happens to work in one case for random reasons and some that works. A propeller airplane is a lousy means of getting to the moon. DTR might just happen to work between two pieces of hardware. On the other hand it is more likely to hangup your phone. At least ^S/^Q can be passed over a communication line. I would guess that Xon/Xoff is considered much harder to implement because you are speaking to hardware people who seem to be unable to deal with things that are not implemented solely in chips. All it takes is an interrupt handler that is able to operate within the skid time of your terminal. For a VT100 that is about 16 character times which as 19200 is 1/19200*10*16 seconds which 8.32 milliseconds. To be conservative, let's assume 4 milliseconds. That is a very long period of time. A real VT100 is closer to operating at 4800 baud anyway so that cranking it up to 19200 doesn't really help you. Probably 9600 is better for it. This is not to say that Xon/Xoff is a good protocol. It is a rather poor one, but it is available on many terminals. If we were redoing the world, then there would be a transport level that deals with such matters and does it out of band. Such mechanisms to exist, but are not in the domain of this discussion.