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EIATIA Standards- EIA/TIA Wiring Standards- EIATIA 568A-EIA/TIA 568s

American Tech Supply has offered the following information to assist you in making you CAT 5e EIA/TIA wiring easy and stress -free. When you have completed your education- we hope you come back and purchase your Cat 5e and CAT 6 cables from us. We stock a complete array of CAT 6 patch cords and CAT 6 patch cables and includes our molded- booted CAT 6 Patch cords and patch cables. Our CAT 6 patch cords accommodate both T568A and T568B wiring applications, and are offered in several colors for easy circuit identification. High-quality CAT 6 patch cords are a critical, and sometimes overlooked, part of any high-performance cabling system. The only real way to guarantee modular CAT 6 patch cord performance is to test every CAT 6 patch cord across all pairs combinations, in both directions, after assembly. 100% factory transmission testing is critical to ensure the quality of the assembly process.

Maximum DISTANCE FOR 568A/B Wiring is 90 Meters or 300 Feet

 

Note that the only difference between T568A and T568B is that pairs 2 and 3 (orange and green) are swapped. Both configurations wire the pins "straight through", i.e., pins 1 through 8 on one end are connected to pins 1 through 8 on the other end. Also, the same sets of pins are paired in both configurations: pins 1 and 2 form a pair, as do 3 and 6, 4 and 5 and 7 and 8. However the different pairs in an Ethernet cable are identical, so one can use cables wired according to either configuration in the same installation without significant problem; problems involving crosstalk can occur (which is normally minimized by correctly twisting a pair together), but are usually insignificant in all but the most stringent specifications such as Category 6 cable. The primary thing one has to be careful of is not to accidentally wire the ends of the same cable according to different configurations (except if one intends to create an Ethernet crossover cable).

Use for T1 connectivity

In T1 service, the pairs 1 and 3 (T568A) are used, and the USOC-8 jack is wired as per spec RJ-48C. The Telco termination jack is often wired to spec RJ-48X, which provides for a Transmit-to-Receive loopback when the plug is withdrawn.

Vendor cables are often wired with Tip and Ring reversed -- i.e. pins 1 and 2 reversed, or pins 4 and 5 reversed. This has no effect on the signal quality of the T1 signal, which is fully differential, and uses the Alternate Mark Inversion (AMI) signaling scheme.

Backwards compatibility

Because pair 1 connects to the center pins (4 and 5) of the 8P8C connector in both T568A and T568B, both standards are compatible with the first line of RJ11, RJ14, RJ25, and RJ61 connectors that all have the first pair in the center pins of these connectors.

If the second line of an RJ14, RJ25 or RJ61 plug is used, it connects to pair 2 (orange/white) of jacks wired to T568A but to pair 3 (green/white) in jacks wired to T568B. This makes T568B potentially confusing in telephone applications.

Because of different pin pairings, the RJ25 and RJ61 plugs cannot pick up lines 3 or 4 from either T568A or T568B without splitting pairs. This would most likely result in unacceptable levels of hum, crosstalk and noise.

Theory

The original idea in wiring modular connectors, which you see exemplified in the registered jacks, was that the first pair would go in the center positions, the next pair on the next outermost ones, and so on. Also, signal shielding would be optimized by alternating the "live" and "earthy" pins of each pair. As you can see, the TIA/EIA-568-B terminations vary a little bit from this concept. That's because on the 8 position connector, this results in a pinout in which the outermost pair are too far apart to meet the electrical requirements of high-speed LAN protocols.

Structured cable system topologies

TIA/EIA-568-B defines a hierarchical cable system architecture, in which a main cross-connect (MCC) is connected via a star topology across backbone cabling to intermediate cross-connects (ICC) and horizontal cross-connects (HCC). Telecommunications design traditions utilized a similar topology, and many people refer to cross-connects by their older, nonstandard names: "distribution frames" (with the various hierarchies called MDFs, IDFs and wiring closets). Backbone cabling is also used to interconnect entrance facilities (such as telco demarcation points) to the main cross-connect. Maximum allowable backbone cable distances vary between 300 m and 3000 m, depending upon the cable type and use.

Horizontal cross-connects provide a point for the consolidation of all horizontal cabling, which extends in a star topology to individual work areas such as cubicles and offices. Under TIA/EIA-568-B, maximum allowable horizontal cable distance varies between 70 m and 90 m for twisted-pair cable types, depending upon patch cord length and gauge. Fiber optic horizontal cabling is limited to 90 m. Optional consolidation points or transition points are allowable in horizontal cables, although many industry experts discourage their use.

At the work area, equipment is connected to horizontal cabling by patch cords.

TIA/EIA-568-B also defines characteristics and cabling requirements for entrance facilities, equipment rooms and telecommunications room.

 

T568A and T568B termination

Perhaps the widest known and most discussed feature of TIA/EIA-568-B.1-2001 is the definition of pin/pair assignments for eight-conductor 100-ohm balanced twisted-pair cabling, such as Category 3, Category 5 and Category 6 unshielded twisted-pair (UTP) cables. These assignments are named T568A and T568B and they define the pinout, or order of connections, for wires in 8P8C (often incorrectly referred to as RJ45) eight-pin modular connector plugs and sockets. Although these definitions consume only one of the 468 pages in the standards documents, a disproportionate amount of attention is paid to them. This is because cables that are terminated with differing standards on each end will not function normally.

TIA/EIA-568-B specifies that horizontal cables should be terminated using the T568A pin/pair assignments, "or, optionally, per [T568B] if necessary to accommodate certain 8-pin cabling systems." Despite this instruction, many organizations continue to implement T568B for various reasons, chiefly associated with tradition (T568B is equivalent to AT&T 258A). The United States National Communication Systems Federal Telecommunications Recommendations do not recognize T568B.

The primary color of pair one is blue, pair two is orange, pair three is green and pair four is brown. Each pair consists of one conductor of solid color, and a second conductor which is white with a stripe of the same color. The specific assignments of pairs to connector pins varies between the T568A and T568B standards.

Mixing T568A-terminated patch cords with T568B-terminated horizontal cables (or the reverse) does not produce pinout problems in a facility. Although it may very slightly degrade signal quality, this effect is marginal and certainly no greater than that produced by mixing cable brands in-channel.

If we apply the 568A color code and show all eight wires, our pin-out looks like this:

Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard. Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing--they are just plain wasted.

However, the actual cables are not physically that simple. In the diagrams, the orange pair of wires are not adjacent. The blue pair is upside-down. The right ends match RJ-45 jacks and the left ends do not. If, for example, we invert the left side of the 568A "straight"-thru cable to match a 568A jack--put one 180° twist in the entire cable from end-to-end--and twist together and rearrange the appropriate pairs, we get the following can-of-worms:

This further emphasizes, I hope, the importance of the word "twist" in making network cables which will work. You cannot use an flat-untwisted telephone cable for a network cable. Furthermore, you must use a pair of twisted wires to connect a set of transmitter pins to their corresponding receiver pins. You cannot use a wire from one pair and another wire from a different pair.

Keeping the above principles in mind, we can simplify the diagram for a 568A straight-thru cable by untwisting the wires, except the 180° twist in the entire cable, and bending the ends upward. Likewise, if we exchange the green and orange pairs in the 568A diagram we will get a simplified diagram for a 568B straight-thru cable. If we cross the green and orange pairs in the 568A diagram we will arrive at a simplified diagram for a crossover cable. All three are shown below.

 

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