> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Jay Hennigan > Sent: Friday, May 18, 2007 3:02 PM > To: Janet Plato > Cc: [email protected] > Subject: Re: [c-nsp] T1 Cables > > > Janet Plato wrote: > > DS1 cabling does not use the normal USOC pairing, so you forgo > > common mode rejection of noise. > > Sure it does, USOC RJ48. This is also the standard EIA pairing, same as > just about everything else. Pairs 1 and 3 of 568A or 1 and 2 of 568B. > Regular "ethernet" jumpers are also EIA 568, so the pairing is correct, > although one of the active pairs for DS1 is different from 10-base-T or > 100-base-T. > > There are several different USOC pairing schemes for 8-pin plug/jack > combinations. USOC RJ48 *IS* the DS1 standard. USOC RJ45 (which is > what the physical jack/plug format is often erroneously called) is > something completely different, no it's not ethernet, but the pairing is > still compatible. USOC RJ61 is VERY rare, pairing NOT compatible. USOC > RJ31X also not compatible, used for alarm jacks. > > http://www.hotlinkdata.com/wiring_diagram.htm > > > When a signal pin and that > > signal's ground share a common path with normal spacing, for > > example in a single twisted pair, they pick up the same amount of > > noise from the environment. The noise is common to both wires, > > and since the receiver is expecting to see the signal expressed as > > a difference in voltage between signal pin and ground pin, not > > an absolute voltage difference, the noise that is common to both > > wires is rejected. > > But T-1 is a balanced differential signal, so there is no signal pin and > ground but instead two signal pins per direction of transmission. > Regular "ethernet whips" indeed have the correct wires in twisted pairs > for T-1, pins 1 and 2 are a pair and pins 4 and 5 are a pair. > > > Having said that, I've run T1 short distances in a normal data > > center environment on some really crappy wire without problems. > > I suspect you either have a problem not related to your cabling, > > or enough noise that you really need the common-mode noise > > rejection afforded by correct pairing. > > The pairing of generic 8-pin UTP data cables is correct for T-1. I > agree that the original poster's issue is not with using conventional > "ethernet whip" jumpers for DS1. He may indeed have a layer one > problem, but EIA 568A or 568B jumpers (as long as both ends are the > same) aren't it. > > > I do not have a source of such cables, I've not used such things > > in a long time. > > You may be thinking of the old-school individually shielded twisted pair > 22-gauge T-1 cable. This was a special low-capacitance cable with two > pairs, insulated with a large diameter foam plastic dielectric, each > pair individually shielded. This cable was designed to carry T-1 > signals for thousands of feet without repeaters or CSU/DSU equipment. > > Occasionally I've seen a telco use this stuff as a ten-foot jumper from > a protector terminating a half-mile or so of 600-pair copper to a > smartjack on the backboard. I guess this gave them a warm fuzzy feeling > that at least the last ten feet was cabled better than the first > half-mile. > > This cable pre-dates the use of 8-pin modular plugs for T-1 > terminations. It was sometimes used with D-sub 15 pin plugs and jacks. > It is very difficult to terminate it correctly into an 8-pin modular > plug because the insulation is too thick.
Go to any wire distributor and ask for the "klingon bird of prey" plug, this is an RJ45 plug that has a back end that is 2 pieces that use a screw to hold them together. Ted _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
