Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site umcp-cs.UUCP Path: utzoo!linus!philabs!seismo!rlgvax!cvl!umcp-cs!chris From: chris@umcp-cs.UUCP Newsgroups: net.dcom Subject: XON/XOFF as flow control? Message-ID: <3636@umcp-cs.UUCP> Date: Sun, 6-Nov-83 21:50:32 EST Article-I.D.: umcp-cs.3636 Posted: Sun Nov 6 21:50:32 1983 Date-Received: Tue, 8-Nov-83 07:50:16 EST Organization: Univ. of Maryland, Computer Science Dept. Lines: 24 I can show how XON/XOFF flow control doesn't work over a network. Assume the terminal has a 32 character input FIFO. Now, the host writes a long escape sequence or whatever. Terminal sends an XOFF at 16 characters in FIFO. XOFF has to go over effective baud net connection, while terminal<->net connection is at least 2 baud. Unfortunately, the XOFF must have a packet constructed for it. This packet has a 40 byte header. Meanwhile, the next string written at the host is still coming across the connection (ie maybe 20 of those 40 header bytes have got through already with a large (20 character) text stream in the packet. By the time the host receives the XOFF, the entire 20 character packet has already gone through the net connection, and overflowed the FIFO. Of course, this problem goes away if you do the handshaking at the local net connection instead of the remote. (If only the flow control weren't on the "S"earch for and "Q"uote keys.... How about a new standard with untypeable flow control codes?) Chris -- In-Real-Life: Chris Torek, Univ of MD Comp Sci UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris CSNet: chris@umcp-cs ARPA: chris.umcp-cs@CSNet-Relay