Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 beta 3/9/83; site sdcrdcf.UUCP Path: utzoo!watmath!clyde!floyd!harpo!seismo!hao!hplabs!sdcrdcf!darrelj From: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Newsgroups: net.lan Subject: Re: Ethernet cable length query Message-ID: <928@sdcrdcf.UUCP> Date: Wed, 21-Mar-84 11:24:25 EST Article-I.D.: sdcrdcf.928 Posted: Wed Mar 21 11:24:25 1984 Date-Received: Fri, 23-Mar-84 21:01:16 EST References: <1115@cbosgd.UUCP> Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Organization: System Development Corporation, Santa Monica Lines: 18 The Ethernet specification requires random pieces of Ethernet cable to be 1 or 3 or 5 times 23.4 meters (76.8 feet) in length. The rules are less stringent for a single piece of cable or cable entirely from a single lot. The rationale is that different lots of cable have slightly different impedences, resulting in reflections at each splice. 23.4 meters is one bit time, so this keeps reflections on bit boundaries, or even provide destructive interference with the reflections. (By the way, these guidelines are not guaranteed; if you want to be SURE of a given cable assembly, sweep testing of SWR is recommended) -- Darrel J. Van Buer, PhD System Development Corp. 2500 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,sdccsu3,trw-unix}!sdcrdcf!darrelj VANBUER@USC-ECL.ARPA