Why 568B? / Some Lucent is 568B?

[TelNetSystems]

From what I understand, 568A is the standard termination scheme, and 568B is an acceptable alternative for those who choose to use it. That is because 568A is compatible with USOC for pairs 1 and 2 which makes it easier to interface with 1 and 2 pair phone systems.

I see a great deal of posts claiming that 568B is "more common", "better", or "more compatible" with Lucent telephone systems. I haven't seen any compelling arguments to back up the "better" and "more compatible" arguments. How can a jack on a telephone system be A or B any more than a jack on a network switch? Pins x&x are this, pins x&x are that, etc. How would the Lucent phone system possibly know whether the cable was wired A or B as long as it was consistent? How is B "better" unless it is compatible with something A isn't?

When you interface telephone to 568B wiring, what do you use to cross-connect, blue and green 2-pair cross-connect? Or do you connect blue and green wiring with blue and orange cross-connect wire?

Can somebody help me out here??

 

[ANFPS26]

Here is some info:

thread575-555877

Jim

 

[TelNetSystems]

I saw that post. The vast majority of it seems to indicate 568A for new installs and match whatever is present for working on existing installs. At the very least, that post indicates no advantage to 568B over 568A. This would seem to agree with my premise. However, here are some exerpts from other posts:

>> Which AT&T system? Does it require two or four pairs
>> terminated at the jacks. If two, either terminate 568-A
>> or USOC 2-pair, if four, use 568-B.

>> But, the question was how to terminate it. Since you've
>> already prefaced it with ATT, the 568B may be the better
>> option depending on which phone it is. If you terminate
>> the wiring on 568B jacks, you should be able to plug ANY
>> phone into it (even those damn old Merlins).

>> Definately 568B for AT&T/Lucent/Avaya

These are only a few examples. There are many, many more on this board. These are the kind of people I was curious about. I don't presume to believe I know more than everyone else, so what are they thinking about when they write things like this? Do they know something I don't? Or is this merely a personal preference passing as informed opinion?

 

[DToolsDesigner]

One final point...

The Residential manufacturers use T568A only because T568B is NOT recognized in the EIA/TIA 570-A Residential Standard.

In my company we use A only unless specified by the owner or we are adding to a job that has T568B in place already.

I find it easier for everyone to stick with one for everything, which means T568A if you do any residential work.
Another point... there is no difference electronically.

The Residential manufacturers use T568A only because T568B is NOT recognized in the EIA/TIA 570-A Residential Standard.

In my company we use T568A only unless specified by the owner or we are adding to a job that has T568B in place already.

I find it easier for everyone to stick with one for everything, which means T568A if you do any residential work.

When we used T568B for commercial and T568A for residential we were having problems when my crews would help out on the opposite type job they were use to.

I urge all my students to use T568A since it is the standards choice, T568B is listed as an option when required by specific equipment. Government jobs are mandated to be T568A ONLY as well. So it makes no sense to use T568B.


Richard S. Anderson, RCDD

http://www.servamatic.net

 

[TouchToneTommy]

"How can a jack on a telephone system be A or B any more than a jack on a network switch? Pins x&x are this, pins x&x are that, etc. How would the Lucent phone system possibly know whether the cable was wired A or B as long as it was consistent?"

This assumes that the telephone system is modular, or that any punch downs are going to be extended to a patch panel. In the "old days", Merlin systems used 4-pair wiring, terminated 568-B, and the installer used an AT&T supplied premade cable with a 568-B plug on one end, and punched it down to the 66-block that held the station cable leading off to the jack. AT&T recommended that everything be terminated 4-pairs, 568-B to make it easy to migrate from the Spirit to Merlin to Legend. Now days, it just matters to pick one scheme and stick with it. Personally, we use 568-B, just because ALL of our embedded base is wired that way.

 

[TelNetSystems]

So, let me see if I understand this correctly. The Spirit systems came with a pre-manufactured cable that was terminated with a 568B plug on one end and loose cable on the other. Installers plugged the supplied cable into the modular jacks on the Spirit, then puched the other end down on 66 blocks for cross-connecting to the station wiring. Becuase the supplied cable was wired 568B, the wall jacks needed to be wired 568B as well in order to maintain the same wiring standard throughout the system. If the jacks were wired 568A, the cross connect wiring would have to cross orange to green and green to orange, which is obviously something to avoid if possible.

Evidently, after the adoption of 568A, people just stuck with what they had always done which was 568B. I am surprised that compatibility with USOC is not more of an issue, since using USOC requires reversing the orange and green pairs if the rest of your cabling is 568B. I suppose if all your equipment uses 8 position plugs, and everything is wired consistently, USOC compatibility is not any more of an issue than whether your cabling is 568A or 568B. If the correct pins match the correct pins then everything is happy.

If that is all correct, then I have two questions. Is most equipment compatible with 8 position plugs (excluding those that use 25 pair connectors, of course)? I know the Legend, Magix, and Partner ACS are, but what about systems like Panasonic, Nortel, and others I have seen but not worked on? Second, is all the reported "difficulty" of connecting the old Merlin systems to 568A wiring really as simple as replacing the supplied 568B cord with a 568A one?

I think I've got it.

Existing Installations: Modifications to existing installations should always maintain compatibility with the existing wiring standard.

New Installations: 568A will do everything 568B will do. 568A is the preferred commercial standard according to the TIA/EIA documents. 568A is the only residential standard. People who recommend using 568B on new installations because it is compatible with the installation cable originally supplied by AT&T with old Spirit systems could easily solve the problem by replacing the original cable with a 568A one. Finally, using 568B on new installations simply perpetuates the confusion of having two different, but similar, wiring standards to deal with.

Did I get any of that wrong?

 

[DToolsDesigner]

TelNet...Glad to see someone understands it.
I think you summed it up perfectly in your last couple of paragraphs.

Richard S. Anderson, RCDD

http://www.servamatic.net

 

[bobsou]

AT&T 568B was the standard that all Bell Systems techs used from late 70'sso that we could do any RJ from a 8 pin jack , so that why you find it all over, that is the way i was taught & is more comfortable, but now i always look to see what & how it is wired, but use the B standard , it probably was a political thing then as it is now

 

[PhoneGuy2000]

Just to clarify a few items, the standards don't favor one connection scheme over another. AT&T had a wiring scheme they pushed. The Committee proposed a second scheme and approved both. This way no one was being forced to use AT&T's scheme and thus that of their competitior. Both are recognized in the commercial standatd. Only T568A is trcognized in residential and it has to do with the compatibility of the jack to accept a 2 pair USOC connection. If you terminate your equipment on patch panels and jacks, either will operate identically. It is only when you terminate one end on a 66 or 110 or other style punch block to use cross connects that the scheme used comes into play. All of your comments of understanding are correct except that A was adopted after B. Before the T568 designations, the wiring scheme used on the Merlins was Bell 258A. Also, the name for the termination style (preceeded by a T) has no correlation to the current revision of the structured wiring standard EIA/TIA 568 which began as EIA/TIA 568A and in the next major rewrite became EIA/TIA 568B. As we have changes and improvements, in the next major rewrite we will have EIA/TIA 568C.

Larry McNeill, RCDD/BICSI Technician