Cabling Standards  

Present networking trends favor an integrated network that can support data, multimedia, voice, and video. Fortunately, new structured wiring and networking standards have been defined to help network designers to plan, install, and test cable systems that support gigabit- and multi-gigabit-per-second data rates.

In the 1970s and 1980s, coaxial cable was the preferred LAN medium. But by the late 1980s, data-capable twisted-pair wiring emerged as the predominant network cabling scheme. While twisted-pair wire has cable distance limitations, a hierarchical wiring scheme, initially built around hubs (and more recently switches), overcomes those limitations. Workstations are attached to workgroup hubs/switches in nearby wiring closets and those hubs/switches are attached to wiring hubs/switches at centralized data centers via twisted-pair cable, or via fiber-optic cable over long distances.

Today, there are a variety of standards that define cable and component specifications, including the configuration, implementation, performance, conformance, and verification of cabling systems. The most prominent standards are listed here:

United States: TIA/EIA-568-A (Telecommunications Industry Association/Electronic Industries Association-568-A), defines how to design, build, and manage a structured wiring system. Note that the specification is also called the EIA/TIA-568 in some references.

Europe: Cenelec EN 50173 was derived from ISO 11801 and defines generic cabling and open-market cabling components.

In the mid-1980s, the TIA (Telecommunications Industry Association) and the EIA (Electronic Industries Association) began developing methods for cabling buildings, with the intent of developing a uniform wiring system that would support multi-vendor products and environments. In 1991, the TIA/EIA released the TIA/EIA 568 Commercial Building Telecommunication Cabling standard. Note that the ISO/IEC-11801 Generic Customer Premises Cabling standard is an international cabling standard that is based on the ANSI/TIA/EIA-568 cabling standard.

The TIA/EIA structured cabling standards define how to design, build, and manage a cabling system that is structured, meaning that the system is designed in blocks that have very specific performance characteristics. The blocks are integrated in a hierarchical manner to create a unified communication system. For example, workgroup LANs represent a block with lower-performance requirements than the backbone network block, which requires high-performance fiber-optic cable in most cases. The standard defines the use of fiber-optic cable (single and multimode), STP (shielded twisted pair) cable, and UTP (unshielded twisted pair) cable.

The initial TIA/EIA 568 document was followed by several updates and addendums as outlined below. A major standard update was released in 2000 that incorporates previous changes.

• TIA/EIA-568-A-1995 (Commercial Building Telecommunications Wiring Standards)    Defines a standard for building cable system for commercial buildings that support data networks, voice, and video. It also defines the technical and performance criteria for cabling.
  
• TIA/EIA-568-A updates (1998-1999)    The TIA/EIA-568 was updated several times through this time period. Update A1 outlined propagation delay and delay skew parameters. Update A2 specified miscellaneous changes. Update A3 specified requirements for bundled and hybrid cables. Update A4 defined NEXT and return loss requirements for patch cables. Finally, update A5 defined performance requirements for Enhanced Category 5 (Category 5E).
  
• TIA 568-B.1-2000 (Commercial Building Telecommunications Wiring Standard)    The year 2000 update packages all the previous addendums and service updates into a new release and, most important, specifies that Category 5E cable is the preferred cable type that can provide minimum acceptable performance levels. Several addendums were also released that specify technical information for 100-ohm twisted-pair cable, shielded twisted-pair cable, and optical fiber cable.
  
• TIA/EIA-569-A-1995 (Commercial Building Standard for Telecommunications Pathways and Spaces)    This standard defines how to build the pathways and spaces for telecommunication media.
  
• TIA 570-A-1998 (Residential and Light Commercial Telecommunications Wiring Standard)    This standard specifies residential cabling.
  
• TIA/EIA-606-1994 (Building Infrastructure Administration Standard)    This standard defines the design guidelines for managing a telecommunications infrastructure.
  
• TIA/EIA-607-1995 (Grounding and Bonding Requirements)    This standard defines grounding and bonding requirements for telecommunications cabling and equipment.

The current trend is to evolve the standards to support high-speed networking such as Gigabit Ethernet and define advanced cable types and connectors such as four-pair Category 6 and Category 7 cable. Category 6 is rated for channel performance up to 200 MHz, while Category 7 is rated up to 600 MHz. 

The remainder of this section discusses the TIA/EIA-568 standard in general, rather than any specific release. According to TIA/EIA 568 documents, the wiring standard is designed to provide the following features and functions:

• A generic telecommunication wiring system for commercial buildings
  
• Defined media, topology, termination and connection points, and administration
  
• Support for multi-product, multi-vendor environments
  
• Direction for future design of telecommunication products for commercial enterprises
  
• The ability to plan and install the telecommunication wiring for a commercial building without any prior knowledge of the products that will use the wiring

The layout of a TIA/EIA 568-A structured cable system as the hierarchical structure is apparent in the multi-floor office building. A vertical backbone cable runs from the central hub/switch in the main equipment room to a hub/switch in the telecommunication closet on each floor. Work areas are then individually cabled to the equipment in the telecommunication closet. 

The TIA standard defines the parameters for each part of the cabling system, which includes work area wiring, horizontal wiring, telecommunication closets, equipment rooms and cross- connects, backbone (vertical) wiring, and entrance facilities. 

The work area wiring subsystem consists of the communication outlets (wall-boxes and faceplates), wiring, and connectors needed to connect the work area equipment (computers, printers, and so on) via the horizontal wiring subsystem to the telecommunication closet. The standard requires that two outlets be provided at each wall plate-one for voice and one for data.

The horizontal wiring system runs from each workstation outlet to the telecommunication closet. The maximum horizontal distance from the telecommunication closet to the communication outlets is 90 meters (295 feet) independent of media type. An additional 6 meters (20 feet) is allowed for patch cables at the telecommunication closet and at the workstation, but the combined length cannot exceed 10 meters (33 feet). The work area must provide two outlets. The horizontal cable should be four-pair 100-ohm UTP cable (the latest standards specify Category 5E), two-fiber 62.5/125-mm fiber-optic cable, or multimode 50/125-mm multimode fiber-optic cable. Coaxial cable is no longer recommended.

The telecommunication closet contains the connection equipment for workstations in the immediate area and a cross-connection to an equipment room. The telecommunication closet is a general facility that can provide horizontal wiring connections, as well as entrance facility connections. There is no limit on the number of telecommunication closets allowed. Some floors in multistory office buildings may have multiple telecommunication closets, depending on the floor plan. These may be connected to an equipment room on the same floor.

An equipment room provides a termination point for backbone cabling that is connected to one or more telecommunication closets. It may also be the main cross-connection point for the entire facility. In a campus environment, each building may have its own equipment room, to which telecommunication closet equipment is connected, and the equipment in this room may then be connected to a central campus facility that provides the main cross-connect for the entire campus.

The backbone wiring runs up through the floors of the building (risers) or across a campus and provides the interconnection for equipment rooms and telecommunication closets. The distance limitations of this cabling depend on the type of cable and facilities it connects. Refer to the following table. Note that UTP is limited to 90 meters.

The entrance facility contains the telecommunication service entrance to the building. This facility may also contain campus-wide backbone connections. It also contains the network demarcation point, which is the interconnection to the local exchange carrier's telecommunication facilities. The demarcation point is typically 12 inches from where the carrier's facilities enter the building, but the carrier may designate otherwise.