stone@quest.UUCP (Scott Stone) (10/13/89)
>glen@aecom.yu.edu (Glen M. Marianko) writes: >In article <8909291306.AA06775@jvnca.csc.org>, aggarwal@JVNCA.CSC.ORG (Vikas Aggarwal none) writes: >> >> Just to collect one's views on Thinwire ethernet vs Thickwire ethernet, >> I am listing what I know about the topic: >> >> THINWIRE >> ... >> Max segment length - 185 meters (30 nodes per segment) >This posting reminded me of a question I had about thin ethernet and >the 30 nodes per segment limit. Why is this? I thought on thin >ethernet you can have a node every .5 meters (vs. thick which is >marked for much more). If so, then 185/.5=370 according to my >calculator with the weak battery :-). So why couldn't I have more >than 30 workstations? Tell ya, the only place I ever saw this in >print was in a DEC catalog. Maybe this is a DEC restriction? >-- ISO 8802-3 (which includes the ANSI/IEEE Std 802.3) states under the subsection "System Considerations" the following: p. 161 "A coax segment may contain a maximum of 185 m (600 ft) of coaxial cable and a maximum of 30 MAUs."..."The maximum end-to-end propagation delay for a coax segment is 950 ns"..."The maximum transmission path permitted between any two MAUs is limited by the number of repeater sets that can be connected in series".."The maximum number of segments connected in series is therefore five".."which shall consist of no more than three tapped coax segments" p. 159 "The sum of the center conductor, connectors, and shield resistance shall not exceed 10 ohms total per segment. Each in-line connector pair or MAU shall contribute no more than 10 mOhm." "The connection shall not disturb the transmission line characteristics of the cable significantly"..."Long (greater than 4cm) connections between the coaxial cable and the input of the MAU jeopardize this objective" p. 157 "The sum of the center conductor resistance plus the shield resistance measured at 20 degrees C shall not exceed 50 mOhms/m.".."are met by cable types RG 58 A/U or RG 58 C/U" It seems to me that the length limitation is truely based on the end-to-end propagation delay and the 30 node limitation based on limiting the total DC loop resistance. I am certain that you can vary from this standard in a multitude of ways, and still function normally (at least in appearance to the user). Since manufacturers of network equipment for 10 Base 2 follow this standard (or at least use it as a guideline) every deviation takes a chance of not working with equipment designed accordingly. The ISO 8802-3 ANSI/IEEE Std 802.3 is the currently accepted international standard, and is available from the IEEE service center (201) 981-0060 for $65.00 (less to IEEE members). Although it is about as exciting as most standards are, it does seem to have useful information in regards to many of the questions people ask in this newsgroup. Perhaps I, or some other engineer could post an article that states many of the more interesting parts, in simple terms. -- * * Scott T. Stone {rosevax,bungia}!quest!stone * (612) 894-7752 -- * * Scott T. Stone {rosevax,bungia}!quest!stone * (612) 894-7752