I'd like to take this opportunity to point out the misuse of the "RJ-45" name when really what is meant is an 8-position modular jack. RJ-45 refers to a specific T1 wiring scheme using an 8 position modular jack (8P4C). Similarly, we often see RJ-11 misused as well. RJ-11 is a 2 wire connection utilizing a 6-position modular jack (6P2C) and RJ-14 is a 4 wire connection also utilizing a 6-position modular jack (6P4C).
These all date back to the Bell System USOC (Universal Service Ordering Codes) that have been used and misused for years. I cringe every time RJ-45 is used when referring to Ethernet. I'm not an old Bell System guy who wrote these specs originally, but I guess it is a pet peeve of mine! I'm constantly correcting the engineers I work with. :-) Dan Roman Dialogic From: [email protected] [mailto:[email protected]] On Behalf Of Powell, Doug Sent: Thursday, December 14, 2006 11:25 AM To: [email protected]; Grasso, Charles Cc: Carpentier Kristiaan; Emc-Pstc Subject: RE: Ethernet cable: 2 versus 4 pairs. An interesting discussion, Of course, the 2-pair is for the RJ-11 connector and the 4-pair is for the RJ-45. I was always under the impression that the choice in pairs and colors was a result of a choice made at Bell Labs (part of the Bell System). And this was a carry-over from the 4-pair cable that I saw elsewhere in the Bell System. Also, this cable was physically compatible with punch blocks found in telephone equipment rooms. One of the things I observed in the original 2-pair voice-grade wire was the practice of using the yellow conductor as a telephone set ground. Since digital networks needed a second data pair, the jump to the already available 4-pair cable made sense, in order to keep a grounding conductor available in the cable. Besides the Telco system was famous for keeping spare pairs of wire handy, making service and upgrades easier. I can't begin to imagine how much length of this cable has been made over the years. So with the availability of this cable it may have been a choice based in economics as much as anything else. What I cannot begin explain is the seeming inconsistency in not pairing up the green and white wires in the RJ-45 connector. RJ-11 Pin color name 1 n.c. 2 blk 3 red ring 4 grn tip 5 yel often used for ground 6 n.c. RJ-45 Pin color pair name 1 wht/org 2 TX Data + 2 org/wht 2 TX Data - 3 wht/grn 3 Recv Data + 4 blu/wht 1 5 wht/blu 1 6 grn/wht 3 Recv Data - 7 wht/brn 4 8 brn/wht 4 Regards, -doug Douglas E. Powell Staff Engineer Corporate Compliance Department Advanced Energy Industries, Inc. Fort Collins, Colorado USA 80525 From: [email protected] [mailto:[email protected]] On Behalf Of Doug Smith Sent: Wednesday, December 13, 2006 4:47 PM To: Grasso, Charles Cc: Carpentier Kristiaan; Emc-Pstc Subject: Re: Ethernet cable: 2 versus 4 pairs. Hi Charles and the Group, I think you found it faster than me! I did an archeological dig today to find it. The patent, 4,751,607 dated June 14, 1988, was titled "Communication Line Transient Protection." Despite the title it has nothing to do with classical device protection but data signal integrity protection. The date puts it just before the extinction of coax cable for data transmission in an IT environment. Given the date, I suspect the patent is expired by now although I am not sure. Doug Grasso, Charles wrote: > The US Patent number is 4751607. > Its still there Doug!! > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications Corp. > Tel: 303-706-5467 > Fax: 303-799-6222 > Cell: 303-204-2974 > Pager/Short Message: [email protected] > Email: [email protected] > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Doug > Smith > Sent: Wednesday, December 13, 2006 9:37 AM > To: Carpentier Kristiaan > Cc: Emc-Pstc > Subject: Re: Ethernet cable: 2 versus 4 pairs. > > 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. 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