Subsystems of a Structured Cabling System

The ANSI/TIA-568-C.1 standard breaks structured cabling into six areas:

• Horizontal cabling
• Backbone cabling
• Work area
• Telecommunications rooms and enclosures
• Equipment rooms
• Entrance facility (building entrance)

Interpreting Standards and Specifications

Standards and specification documents are worded with precise language designed to spell out exactly what is expected of an implementation using that specification. If you read carefully, you may notice that slightly different words are used when stating requirements.

If you see the word shall or must used when stating a requirement, it signifies a mandatory requirement. Words such as should, may, and desirable are advisory in nature and indicate recommended requirements.

In ANSI/TIA-568-C, some sections, specifically some of the annexes, are noted as being normative or informative. Normative means the content is a requirement of the standard. Informative means the content is for reference purposes only. For example, Category 5 cable is no longer a recognized media and Category 5 requirements have been placed in informative Annex M of 568-C.2 in support of "legacy" installations.

Tip

This chapter provides an overview of the ANSI/TIA-568-C standard and is not meant as a substitute for the official document. Cabling professionals should purchase a full copy; you can do so at the Global Engineering Documents website (www.global.ihs.com).

Horizontal Cabling

Horizontal cabling, as specified by ANSI/TIA-568-C.1, is the cabling that extends from horizontal cross-connect, intermediate cross-connect, or main cross-connect to the work area and terminates in telecommunications outlets (information outlets or wall plates). Horizontal cabling includes the following:

• Cable from the patch panel to the work area
• Telecommunications outlets
• Cable terminations
• Cross-connections (where permitted)
• A maximum of one transition point
• Cross-connects in telecommunications rooms or enclosures

Figure 1 shows a typical horizontal-cabling infrastructure spanning out in a star topology from a telecommunications room. The horizontal cabling is typically connected into patch panels and switches/hubs in telecommunications rooms or enclosures. A telecommunications room is sometimes referred to as a telecommunications closet or wiring closet. A telecommunications enclosure is essentially a small assembly in the work area that contains the features found in a telecommunications room.

Transition point ANSI/TIA-568-C allows for one transition point in horizontal cabling. The transition point is where one type of cable connects to another, such as where round cable connects to under-carpet cable. A transition point can also be a point where cabling is distributed out to modular furniture. Two types of transition points are recognized:

 
Figure 1: Horizontal cabling in a star topology from the telecommunications room

MUTOA This acronym stands for multiuser telecommunications outlet assembly, which is an outlet that consolidates telecommunications jacks for many users into one area. Think of it as a patch panel located out in the office area instead of in a telecommunications room.

CP CP stands for consolidation point, which is an intermediate interconnection scheme that allows horizontal cables that are part of the building pathways to extend to telecommunication outlets in open-office pathways such as those in modular furniture. The ISO/IEC 11801 refers to the CP as a transition point (TP).

If you plan to use modular furniture or movable partitions, check with the vendor of the furniture or partitions to see if it provides data-cabling pathways within its furniture. Then ask what type of interface it may provide or require for your existing cabling system. You will have to plan for connectivity to the furniture in your wiring scheme.

Application-specific components (baluns, repeaters) should not be installed as part of the horizontal-cabling system (inside the walls). These should be installed in the telecommunication rooms or work areas.

Is There a Minimum Distance for UTP Horizontal Cable?

The ANSI/TIA/EIA-568-B does not specify a minimum length for UTP cabling, except when using a multiuser telecommunications outlet assembly (MUTOA). A short-link phenomenon occurs in cabling links usually less than 20 meters (60′) long that usually support 100Base-TX applications. The first 20 to 30 meters of a cable is where near-end crosstalk (NEXT) has the most effect. In higher-speed networks such as 100Base-TX, short cables may cause the signal generated by crosstalk or return loss reflections to be returned back to the transmitter. The transmitter may interpret these returns as collisions and cause the network not to function correctly at high speeds. To correct this problem, try extending problematic cable runs with extra-long patch cords.