Hi Kris, Normally the extra pairs are not needed. I have some jumpers that have two pairs and I like the smaller size. Gigabit Ethernet uses all four pairs though.
Over 15 years ago, in the late 80s when Cat5 cable was new and dinosaurs roamed the earth, part of my funding at Bell Labs was from the group that designed and made Cat5 cable (before it was a commodity item). They were trying to use Cat5 cable on a computer/data network of the day that used coaxial cable as the medium. There were problems with immunity to ESD. I was able to design a circuit that sat at the ends of the cable that also used the extra pairs. The circuit made the Cat5 cable even more immune than the coax cable was. The engineers >from that company did not believe it and came to Bell Labs to check. They left convinced. The arrangement that worked so well connected the two extra pairs to ground on both ends as well as my circuitry which we patented (probably expired by now). The extra circuitry included a few features such as running both the grounded pairs and the signal pairs through small ferrite cores. That really confounded the "balun experts" of the day. If anyone is interested, I can probably find the patent number so they can look it up and read the details. The point is that the extra pairs can be used to help immunity if grounded and you are not planning to run Gigabit Ethernet. A long time ago at Bell Labs we were running something pretty close to Gigabit Ethernet over Cat5 cable as well! Doug Carpentier Kristiaan wrote: > Hello, > > Does anyone know why an Ethernet cable has 4 pairs where only 2 pairs > are used: 1 for TX, 1 for RX. > Is it possible to use ethernet cables with just 2 pairs and not have > performance or other issues? > > Best regards, > > Kris Carpentier > Regulatory & Approvals > > - ---------------------------------------------------------------- This > message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > -- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: [email protected] \ _ / ] \ _ / Web: http://www.dsmith.org - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
