ANSI/TIA-568-D 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 (
ICCs) and
horizontal cross-connects (
HCCs). Telecommunications design traditions utilized a similar topology. Many people refer to cross-connects by their telecommunications names:
distribution frames (with the various hierarchies called
main distribution frames (
MDFs),
intermediate distribution frames (
IDFs) and
wiring closets). Backbone cabling is also used to interconnect entrance facilities (such as telco
demarcation points) to the main cross-connect. 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 is 90 meters of installed twisted-pair cabling, with 100 meters of maximum total length including patch cords. No patch cord should be longer than 5 meters. Optional consolidation points are allowable in horizontal cables, often appropriate for open-plan office layouts where consolidation points or media converters may connect cables to several desks or via partitions. At the work area, equipment is connected by patch cords to horizontal cabling terminated at jack points. TIA/EIA-568 also defines characteristics and cabling requirements for entrance facilities, equipment rooms and telecommunications rooms. ==T568A and T568B termination== Perhaps the most comprehensively known and most discussed feature of ANSI/TIA-568 is the definition of the pin-to-pair assignments, or
pinout, between the pins in a connector (a plug or a socket) and the wires in a cable. Pinouts are critical because cables do not function if the pinouts at their two ends aren't correctly matched. The standard specifies how to connect eight-conductor 100-ohm
balanced twisted-pair cabling, such as
Category 5 cable, to
8P8C modular connectors (often incorrectly referred to as
RJ45 connectors). The standard defines two alternative pinouts: T568A and T568B. ANSI/TIA-568 recommends the T568A pinout for horizontal cables. This pinout is compatible with the 1-pair and 2-pair Universal Service Order Codes (USOC) pinouts. The U.S. Government requires it in federal contracts. The standard also allows, only in certain circumstances, the T568B pinout "if necessary to accommodate certain 8-pin cabling systems", i.e. when, and only when, adding to an existing installation that used the T568B wiring pattern before it was defined, being those that pre-dated ANSI/TIA-568 and used the previous AT&T 258A (Systimax) standard. In the 1990s, when the original TIA/EIA-568 was published, the most widely installed wiring pattern in UTP cabling infrastructure was that of AT&T 258A (Systimax), hence the inclusion of the same wiring pattern (as T568B) as a secondary option for use in such installations. Many organizations still use T568B out of inertia. The colors of the wire pairs in the cable, in order, are blue (for pair 1), orange, green, and brown (for pair 4). Each pair consists of one conductor of solid color and a second conductor, which is white with a stripe of the other color. The difference between the T568A and T568B pinouts is that pairs 2 and 3 (orange and green) are exchanged.
Wiring See
modular connector for numbering of the pins. wall sockets indicate T568A and T568B termination schemes internally.|alt=Eight-position eight-conductor wall socket internals showing T568A and T568B termination schemes Both T568A and T568B 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 connect to the opposite ends that are paired in both configurations: pins 1 and 2 form a pair, as do 3 and 6, 4 and 5, and 7 and 8. One can use cables wired according to either configuration in the same installation without significant problems if the connections are the same on both ends. A cable terminated according to T568A on one end and T568B on the other is a
crossover cable when used with the earlier twisted-pair Ethernet standards that use only two of the pairs because the pairs used happen to be pairs 2 and 3, the same pairs on which T568A and T568B differ. Crossover cables are occasionally needed for 10BASE-T and 100BASE-TX Ethernet. Swapping two wires between different pairs causes
crosstalk, defeating one of the purposes of twisting wires in pairs.
Use for T1 connectivity In
Digital Signal 1 (T1) service, pairs 1 and 3 (T568A) are used, and the USOC-8 jack is wired according to the
RJ-48C specification. The termination jack is often wired according to the
RJ-48X specification, providing 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 or 4 and 5 reversed. This does not affect the quality of the T1 signal, which is fully differential and uses the
alternate mark inversion (AMI) signaling scheme.
Backward compatibility Conventional
plain old telephone service up to four lines can use
six-position (6P) and
eight-position (8P) plugs and jacks, with
line 1 on the center pins,
line 2 straddling the center pair, and subsequent pairs proceeding outward, this pattern is often called
USOC. One-, two-, and three-line service can use six-position jacks (respectively RJ11, RJ14, and RJ25), and four-line service eight-position jacks (RJ61). Because pair 1 is on the center pins (4 and 5) of the 8P8C connector in USOC and both T568A and T568B, a telephone will connect to
line 1 of both T568A and T568B as well as all of the above
registered jacks, but if a second line is used (3 and 6) is used, it connects to line 2 (pair 2) of USOC and T568A jacks, but to pair 3 of T568B jacks. This makes T568B potentially confusing in telephone applications. Because of different wire pairings of the outer pins, USOC plugs cannot connect to pair 3 or 4 from T568A, or pair 2 or 4 from T568B, without splitting pairs. This means either the lines don’t connect at all or likely unacceptable levels of hum, crosstalk, and noise.
Optical fiber To maintain polarity for duplex connector the cabling shall be installed with alternating Position A at one end and Position B at the other.
Theory The original idea in wiring modular connectors, as seen in the
Bell System registered jacks, was that the first pair would go in the center positions, the next pair on the next-innermost ones, and so on. Also, signal shielding would be optimized by alternating the
live and
earthy pins of each pair. The TIA-568 terminations diverge from this concept by placing a pair on pins 1 and 2 and one on 7 and 8 because, on the eight-position connector, the original arrangement of conductors would separate the outer pairs substantially, impairing
balanced line performance too much to meet the electrical requirements of high-speed LAN protocols. ==Standards ==