Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uwm.edu!rpi!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!uunet!mcsun!ukc!cam-cl!nmm From: nmm@cl.cam.ac.uk (Nick Maclaren) Newsgroups: comp.windows.x Subject: Re: X over long haul net ? Message-ID: <1730@gannet.cl.cam.ac.uk> Date: 17 Jan 90 14:35:13 GMT References: <9001162320.AA20905@Morgan.COM> Sender: news@cl.cam.ac.uk Reply-To: nmm@cl.cam.ac.uk (Nick Maclaren) Organization: U of Cambridge Comp Lab, UK Lines: 38 I did not see the original question, but a follow-on had this: > Paul O. Perry asks: > I was wondering if people thought that using X over a long-haul > network (T1) was an adequate design for an operational system > or whether it would be just infeasible. Some measurements by people at Edinburgh and elsewhere indicate that you need to transfer about 9.6Kbits/second in both directions to achieve reasonable response. This is a problem for those of us where dial-up means 2400/2400 at most (and often 1200/75), but is not a design problem with X. Ditto requirements for local store, fast access to a font server, etc. The fundamental design problem that I know of (in X11.3, at least) is this: The X design requires at least one packet to do the round trip from the keyboard to the application and back per character typed, and may require four (or, rarely, more). If the application supports auto-repeat, the minimum is two. This must happen BEFORE reflection. The people at Edinburgh measured about 5 packets/second for ordinary users doing ordinary work. Fast typists or graphics work could easily be 5-10 times as much, depending on the use and application. This is a serious strain on almost all switching systems, and is likely to remain so for the forseeable future. If you are sufficiently unfortunate as to want to use your local X-server to a client in a far country (e.g. from Europe to the U.S.A.) and get switched via a satellite, there is some 0.6 second delay on each character reflected (5 characters at a normal fast typing speed). With the X11.3 design, this is fundamental and cannot be removed without changing the speed of light! Nick Maclaren University of Cambridge Computer Laboratory nmm@cl.cam.ac.uk