Upgrading and Repairing Networks

Structured Wiring

In the 1980s, the Telecommunications Industry Association (TIA) and the Electronics Industries Association (EIA) formed a task force to establish a set of standards for installing network wiring in buildings. The first draft was completed in 1991 and became known as EIA/TIA-568 (referred to in this chapter as 568). A more recent standard is named ANSI/TIA/EIA-569-A (referred to in this chapter as 569-A). These standards documents encompass structured wiring, cables, network topology, connectors and hardware, electrical performance specifications, physical termination, and support mechanisms.

The 568 and 569-A standards describe the physical layout and specifications for the physical plant as it relates to the various topological standards. The physical plant, in this context, comprises everything having to do with what leads up to your desktop, from routers, cables, patch panels, and so on.

These are the basic topics covered in the standards:

• The work area The termination point of the network at a user's work space.

• The backbone cabling system structure Connections between multiple telecommunication rooms, equipment rooms, and entrance facilities.

• The horizontal cabling system structure Connection from the telecommunications outlet in the work area, terminating in the telecommunications room.

• The telecommunications closet The central wiring point for a floor. The telecommunications closet can contain both network devices and concentrators (such as switches), as well as telephone equipment.

• Other specifications Such issues as intrabuilding connections and such factors as electromechanical interference.

In the following sections you will learn about these topics, as well as others. For a more complete explanation of the standards, it is suggested that you obtain the standards and read them. It is beyond the scope of this book to describe the standards in detail. Instead, those that apply to networks are discussed. In addition, several terms are defined for those who are not well versed in the terminology used by these standards. Many of these terms are also used throughout other chapters in this book. Between this chapter and the glossary, you should be able to locate the definition of almost any word used by network administrators, and those who put together LANs, MANs, and WANs.

The Work Area

The work area includes the telecommunications outlet (that is, the faceplate into which you plug your computer's network cable at your desk), which serves as the work area interface to the entire network cabling system. Work area equipment includes cables used to connect to the telecommunications outlet. The following are the work area cabling specifications:

• Equipment cords are assumed to have the same performance as patch cords (in the telecommunications closet) in the same typing category, for example, Category 5, 5e, and 6 network cables.

• When used, adapters are assumed to be compatible with the transmission capabilities of the equipment to which they connect.

• Horizontal cable links are specified with the assumption that a maximum cable length of 5 meters (16 feet) is used for equipment cords in the work area. This can depend on the actual length of cabling used to connect the work area back to the telecommunicatons closet. The important factor to remember is that there is a maximum distance that all cables can add up to, depending on your topology. Thus, if the cable from the telecommunications closet is less than the specified length allowed by the standards, you can use a longer cable from the termination point at the work area.

The Backbone Cabling System Structure

The backbone cabling system of the standard provides interconnections between telecommunication rooms, equipment rooms, and entrance facilities (see Figure 6.1).

This cabling system includes backbone cables, intermediate and main cross connects, mechanical terminations, and patch cords or jumpers used for backbone-to-backbone cross connections. The backbone also extends between buildings in a campus environment.

There are some points specified for the backbone of the cabling system:

• Equipment connections to the backbone cabling should be made with cable lengths of 30 meters or less.

• The backbone of cabling should be configured as a star topology.

• The backbone is limited to no more than two hierarchical levels of cross connectsmain and intermediate. No more than one cross connect can exist between a main and a horizontal cross connect, and no more than three cross connects can exist between any two horizontal cross connects.

• A total coax backbone distance of 90 meters is specified for high-bandwidth capability over copper. This distance is for uninterrupted backbone runs.

• The distance between terminations in the entrance facility and main cross connect should be documented and made available to a service provider.

• Recognized media can be used individually or in a combination, as required by the installation.

• Multipair cable is allowed, as long as it satisfies the requirement of a minimum of cross-talk.

• The proximity of cabling to sources of electromagnetic interference should be taken into account.

• Cross connects for different cable types must be located in the same facility.

Note that in these specifications, bridge taps and splitters are not allowed.

The Horizontal Cabling System Structure

The horizontal cabling system (shown in Figure 6.2) extends from the telecommunications outlet in the work area and terminates in a horizontal cross connect in the telecommunications room. It includes the telecommunications outlet.

The distance covered by the horizontal cabling is limited by the network topology chosen for your network. For example, in most Ethernet networks, this distance is 90 meters. Token-Ring has various specifications, depending on the cables used. For more information about Token-Ring, see the chapter "Token-Ring Networks," located on the upgradingandrepairingpcs.com Web site.

The Telecommunications Closet

Telecommunications rooms generally are considered to be floor-serving facilities for horizontal cable distribution. They also are used for intermediate and main cross connects. The telecommunications room is where you place patch panels, as well as hubs or switches that are used to connect individual workstations or servers to the network backbone.