83 Pair Numbers and Color Coding The conductors in a UTP cable are twisted in pairs and color coded so that each pair of wires can be easily identified and quickly terminated to the appropriate pin on the connecting hardware (patch panels or telecommunication outlets). With four-pair UTP cables, each pair of wire is coded with two colors, the tip color and the ring color (see also Insulation Colors in Chapter 1). In a four-pair cable, the tip color of every pair is white. To keep the tip conductors associated with the correct ring conductors, often the tip conductor has bands in the color of the ring conductor. Such positive identification (PI) color coding is not necessary in some cases, such as with Category 5 and higher cables, because the intervals between twists in the pair are very close together, making separation unlikely. You identify the conductors by their color codes, such as white-blue and blue. With premises (indoor) cables, it is common to read the tip color first (including its PI color), then the ring color. Table 2.3 lists the pair numbers, color codes, and pin assignments for T568A and T568B.
84 Chapter 2 Cabling Specifications and Standards TABLE 2.3 Four-Pair UTP Color Codes, Pair Numbers, and Pin Assignments for T568A and T568B Pair Number Color Code T568A Pins T568B Pins 1 White-Blue (W-Bl)/Blue (Bl) W-Bl=5/Bl=4 W-Bl=5/ Bl=4 2 White-Orange (W-O)/Orange (O) W-O=3/O=6 W-O=1/O=2 3 White-Green (W-G)/Green (G) W-G=1/G=2 W-G=3/G=6 4 White-Brown (W-Br)/Brown (Br) W-Br=7/Br=8 W-Br=7/Br=8 Backbone Cabling The next subsystem of structured cabling is called backbone cabling. (Backbone cabling is also sometimes called vertical cabling, cross-connect cabling, riser cabling, or inter cabling.) Backbone cabling is necessary to connect entrance facilities, equipment rooms, and telecommunications rooms. Refer to Figure 2.7 later in the chapter to see backbone cabling that connects an equipment room with telecommunications rooms. Backbone cabling consists of not only the cables that connect the telecommunication rooms, equipment rooms, and building entrance but also the cross-connect cables, mechanical terminations, or patch cords used for backbone-to-backbone cross-connection. Permanent Link versus Channel Link TIA/EIA-568-B defines two basic link types commonly used in the cabling industry with respect to testing: the permanent link and the channel link. The permanent link contains only the cabling found in the walls (horizontal cabling), one transition point, the telecommunications outlet, and one cross-connect or patch panel. It is assumed to be the permanent portion of the cabling infrastructure. The permanent link is illustrated here. Transition point (if used) Cross-connect or patch panel Horizontal cable outlet Basic link Continued on next page
85 The channel link includes the basic link, as well as installed equipment, patch cords, and the cross-connect jumper cable; however, the channel does not include phones, PBX equipment, hubs, or network-interface cards. Two possible channel link configurations are shown here; one is the channel link for a 10Base-T Ethernet workstation, and one is for a telephone. Voice system PBX to voice Transition point outlet Cross-connect Channel link Data system Hub to hub Patch panel Transition point outlet Permanent and channel link performance requirements are provided in Chapter 14. KEY TERM cross-connect A cross-connect is a facility or location within the cabling system that permits the termination of cable elements and the reconnection of those elements by jumpers, termination blocks, and/or cables to another cabling element (another cable or patch panel). Backbone cabling includes: Cabling between equipment rooms and building-entrance facilities In a campus environment, cabling between buildings entrance facilities Vertical connections between floors ANSI/TIA/EIA-568-B specifies additional design requirements for backbone cabling, some of which carry specific stipulations, as follows: Grounding should meet the requirements as defined in ANSI/TIA/EIA-607, the Commercial Building Grounding and Bonding Requirements for. Care must be taken when running backbone cables to avoid sources of electromagnetic interference or radio-frequency interference.
86 Chapter 2 Cabling Specifications and Standards No more than two hierarchical levels of cross-connects are allowed, and the topology of backbone cable will be a star topology. (A star topology is one in which all cables lead from their termination points back to a central location. Star topology is explained in more detail in Chapter 3.) Each horizontal cross-connect should be connected directly to a main cross-connect or to an intermediate cross-connect that then connects to a main cross-connect. No more than one cross-connect can exist between a main cross-connect and a horizontal cross-connect. Figure 2.5 shows multiple levels of equipment rooms and telecommunications rooms. Equipment connections to the backbone should be made with cable lengths of less than 30 meters (98 feet). For high-speed data applications, the total maximum backbone distance should not exceed 90 meters (295 feet) over copper wiring. This distance is for uninterrupted lengths of cable (cross-connects are not allowed). Bridge taps or splices are not allowed. Multi-pair (greater than four-pair) cable may be used as long as it meets additional performance requirements such as for power-sum crosstalk. These requirements are specified in the Standard. FIGURE 2.5 Star topology of equipment room and telecommunication rooms connected via backbone cabling 4th floor 3rd floor Backbone cabling to 2nd, 3rd, and 4th floor telecommunications s Equipment room and 1st floor telecommunications 2nd floor 1st floor
87 KEY TERM shared sheath Shared sheath a single cable that supports more than one application is permitted in ANSI/TIA/EIA-568-B.1, with guidelines specified in Annex B of the Standard. A shared sheath may occur, for example, when Ethernet data transmission and voice transmission are both placed in a cable with more than four pairs. However, a shared sheath is not advisable, as separate applications often have incompatible signal levels, and the signal of one application will interfere as noise with the signal of the other application(s). Recognized Backbone Media ANSI/TIA/EIA-568-B recognizes several types of media (cable) for backbone cabling. These media types can be used in combination as required by the installation. The application and the area being served will determine the quantity and number of pairs required. Table 2.4 lists the media types, applications, and maximum distances permitted. NOTE media The term media is used in the cabling business to denote the type of cabling used. Media can include fiber-optic cable, twisted-pair cable, or coaxial cable. The definition of media can also be broadened to include wireless networking. TABLE 2.4 Media Types, Applications, and Maximum Distances Permitted Media Application Distance 100-ohm UTP or ScTP Data 90 meters (295 feet) 100-ohm UTP or ScTP Voice 800 meters (2,624 feet) Single-mode 8.3/125-micron optical fiber Data 3,000 meters (9,840 feet) Multimode 62.5/125-micron or 50/125-micron optical fiber Data 2,000 meters (6,560 feet) The distances in Table 2.4 are the total cable length allowed between the main cross-connect and the horizontal cross-connect, allowing for one intermediate cross-connect. WARNING Coaxial cabling is not recognized by the ANSI/TIA/EIA-568-B version of the Standard. Work Area The work area is where the horizontal cable terminates at the wall outlet (telecommunications outlet). In the work area, the users and telecommunications equipment connect to the structured-cabling infrastructure. The work area begins at the telecommunications area and includes components such as the following: Patch cables, modular cords, fiber jumpers, and adapter cables
88 Chapter 2 Cabling Specifications and Standards Adapters such as baluns and other devices that modify the signal or impedance of the cable (these devices must be external to the information outlet) Station equipment such as computers, telephones, fax machines, data terminals, and modems The work-area wiring should be simple and easy to manipulate. In today s business environments, moves, additions, and removal of equipment are frequent. Consequently, the cabling system needs to be easily adaptable to these changes. Rooms The telecommunications room (along with equipment rooms, generically referred to as wiring s) is the location within a building where cabling components such as cross-connects and patch panels are located. These rooms are where the horizontal structured cabling originates. Horizontal cabling is terminated in patch panels or termination blocks and then uses horizontal pathways to reach work areas. The telecommunications room may also contain networking equipment such as LAN hubs, switches, routers, and repeaters. Backbone-cabling equipment rooms terminate in the telecommunications room. Figures 2.5 and 2.7 illustrate the relationship of a telecommunications room to the backbone cabling and equipment rooms. ANSI/TIA/EIA-569-A discusses telecommunications-room design and specifications, and a further discussion of this subsystem can be found in Chapter 5, Cabling System Components. ANSI/TIA/EIA 569-A recommends that telecommunications rooms be stacked
89 vertically between one floor and another. ANSI/TIA/EIA-568-B further dictates the following specifications relating to telecommunications rooms: Care must be taken to avoid cable stress, tight bends, staples, wrapping the cable too tightly, and excessive tension. You can avoid these pitfalls with good cable-management techniques. Use only connecting hardware that is in compliance with the specifications you want to achieve. Horizontal cabling should terminate directly not to an application-specific device but rather to a telecommunications outlet. Patch cables or equipment cords should be used to connect the device to the cabling. For example, horizontal cabling should never come directly out of the wall and plug in to a phone or network adapter. Entrance Facility The entrance facility (building entrance) defined by ANSI/TIA/EIA- 568-B specifies the point in the building where cabling interfaces with the outside world. All external cabling (campus backbone, interbuilding, antennae pathways, and telecommunications provider) should enter the building and terminate in a single point. carriers are usually required to terminate within 50 feet of a building entrance. The physical requirements of the interface equipment are defined in ANSI/TIA/EIA-569-A, the Commercial Building Standard for Pathways and Spaces. The specification covers telecommunications-room design and cable pathways. ANSI/TIA/EIA-569-A recommends a dedicated entrance facility for buildings with more than 20,000 usable square feet. If the building has more than 70,000 usable square feet, ANSI/TIA/EIA-569-A requires a dedicated, locked room with plywood termination fields on two walls. The ANSI/TIA/EIA-569-A Standard also specifies recommendations for the amount of plywood termination fields, based on the building s square footage. KEY TERM demarcation point The demarcation point (also called the demarc, pronounced deemark) is the point within a facility, property, or campus where a circuit provided by an outside vendor, such as the phone company, terminates. Past this point, the customer provides the equipment and cabling. Maintenance and operation of equipment past the demarc is the customer s responsibility. The entrance facility may share space with the equipment room, if necessary or possible. Telephone companies often refer to the entrance facility as the demarcation point. Some entrance facilities also house telephone or PBX (private branch exchange) equipment. Figure 2.6 shows an example of an entrance facility.