Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!seismo!munnari!moncskermit!trldeity!trlamct!tony From: tony@trlamct.UUCP Newsgroups: comp.dcom.lans Subject: Re: Thin Ethernet drop cables Message-ID: <273@trlamct.oz> Date: Thu, 23-Apr-87 23:57:52 EST Article-I.D.: trlamct.273 Posted: Thu Apr 23 23:57:52 1987 Date-Received: Sat, 25-Apr-87 08:31:43 EST References: <207@nih-csl.UUCP> Organization: Telecom Australia (Research), Applied Maths. & Computer Techniques. Lines: 31 Keywords: Ethernet thin-net cheapnet cheapernet Summary: Don't do it! -from a transmission line perspective. Re: > Comment on the use of a tee-connector on the thin ethernet segment with > a length of coax connected to the host? Will I grow warts if I try it? YES. The bus cable is a valuable shared resource that should be kept reliable. The wiring might be changed, such as adding another node, or someone lengthening their cable. Then prior sins could manifest themselves and GROW WARTS. Adding open circuit stubs of coax that are significant fractions of a wavelength long is liable to create highly reactive (capacitive or inductive) line characteristics, especially at multiples of a quarter wavelength. To avoid this, one could keep the stub less than say, a tenth of a wavelength, and the line will appear slightly capacitive. A 100MHz component has a wave- length of 3m ie. a cable of less than one foot. We have two wall connectors per node, and thus each host has two cables and a T piece. That is, lots of connectors per node and these are all in series with the bus. The user can also inadvertently unplug a connector and break the bus. Apart from direct cables machine to machine, and securing the connectors, there is no really neat way to implement thin ethernet that is simple and safe. The brochures (wrongly) make it sound trivial. -- Tony Thomas, Applied Mathematics & Computer Techniques Telecom Australia Research Laboratories, P.O. Box 249 Clayton, 3168. ACSnet tony@trlamct D D