Path: utzoo!mnetor!uunet!husc6!ncar!ames!pasteur!agate!saturn!eshop From: eshop@saturn.ucsc.edu (Jim Warner) Newsgroups: comp.dcom.lans Subject: Re: Thinwire ethernet: Question about drop cables Message-ID: <2458@saturn.ucsc.edu> Date: 22 Mar 88 02:14:46 GMT References: <4491@june.cs.washington.edu> <13364@uflorida.cis.ufl.EDU> Reply-To: eshop@saturn.ucsc.edu (Jim Warner) Organization: University of California, Santa Cruz Lines: 44 In article <13364@uflorida.cis.ufl.EDU> mwn@beach.cis.ufl.edu () writes: >In article ron@topaz.rutgers.edu (Ron Natalie) writes: >>No, you can not place cable between the transciever and the T-adapter. >>The T adapter needs to be directly connected to the BNC jack on the >>integral transciever in the computer. Not only does it violate the >>specification, it doesn't work at all. > >Wrong. You can place cable between the T-connector and the transceiver jack. >On the workstation that I am typing this message from I just placed 12 feet >of cable between the T-connector and the transceiver on the back of the unit >and it is working just fine.... Using cable of any significant length violates the specification. Section 10.6.3 of 802.3 says: A BNC "T" adaptor provides a means of attaching a MAU to the coaxial cable. The connection shall not disturb the transmission line characteristics of the cable significantly; it shall present a low shunt capacitance and therefore a negligbly short stub length... Long (greater than 4 cm) connections between the coaxial cable and the input of the MAU jeopardize this objective. If you want to build and install a network that will work the first time without tuning, will work when you expand it to include the last station, and will continue to work after all the brand new components age and shift their values slightly, then you follow the rules. Tuning isn't, per se, bad. If you already own network diagnostic tools and can test your nonstandard configuration, and you decide this is the most cost effective solution to your networking needs, that's fine. My users want up front accurate estimates of how much they will pay me to install network access. For my estimates to be accurate, I need to know with high confidence that an installation will work the without doing a lot of tuning. So I opt to follow the rules. Beyond that, I want configuration rules that are the same for everybody. I'd be real interested to hear the results of a test where NM put 12 ft of stub coax between *every* station and the network cable. jim warner sr development engineer