1 guide to network cabling fundamentals chapter 5

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Guide to Network Cabling Fundamentals

Chapter 5

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Chapter 5 - Backbone and Horizontal Distribution Systems

Understand backbone distribution systems Discuss the types of cross-connection in a

backbone system Differentiate between interbuilding and intrabuilding

backbone systems

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Chapter 5 - Backbone and Horizontal Distribution Systems

Understand horizontal distribution systems Discuss design guidelines and work areas in

horizontal distribution systems Document the cable plant Document equipment rooms

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Backbone distribution systems connect the equipment rooms, telecommunications rooms (TRs), and entrance facilities Two types of connections exist: intrabuilding, are made

between the floors of multistory buildings; and interbuilding, those made between buildings

Intrabuilding backbones link all of a building’s cross-connects, which mechanically terminate and administer building wiring

Interbuilding backbones link intermediate cross-connects in other buildings to the main cross-connect

Backbone Distribution Systems

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All backbone cabling in the distribution system links three types of cross-connects: Horizontal cross-connects (HCs), which consist of horizontal

cabling using jumpers, patch cords and other hardware; main cross-connects (MCs), the primary connection and flexibility point within a network; and intermediate cross-connects (ICs) between first- and second-level backbones

Backbone cabling connects the equipment and runs from the equipment room to the various TRs; depending on the size of the building(s) involved, these TRs house either the ICs or the HCs


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Intrabuilding backbones: Consist of multipair copper or optical-fiber cables and

their supporting hardware Connect all the HCs or ICs in a building to the MC ANSI/EIA/TIA-568-A standard requires all backbone

cabling to be a star or hierarchical star topology Backbone topology differs from that of a network in the

following ways: they connect multiple network segments; they can connect and support different topologies; they provide support for all modes of communication


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Intrabuilding backbones (cont.): In the star topology, individual nodes are linked to the HC,

which is connected directly to the MC In hierarchical star, some or all of the HCs are linked to an

IC, which in turn is linked to the building’s MC In general, the star topology is the better design choice,

unless in large buildings, such as high-rises Choose the topology based on: the types and sizes of

cable available; the hardware necessary; the size of the site and number of end users; the installation labor required; the applications used


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Interbuilding backbones: Link the HC or IC in various buildings to the MC Is the network segment that gives distributions designers

and users the most options, but is also most affected by physical considerations

ANSI/EIA/TIA-568-A standard requires interbuilding backbones to be the hierarchical star topology

The better design for small networks is a single-level hierarchical star because: it provides a single point of control; allows testing and reconfiguration; easier maintenance and security; increased flexibility


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Selecting backbone distribution media considerations: The recognized cable types are: multimode optical fiber;

single-mode optical fiber; 100-ohm twisted-pair Often a single cable type will not satisfy all user

requirements and if more that one medium is used, make sure they all use the same facility architecture

Consider the following factors when choosing medium: its flexibility with respect to the supported services; the required useful life; the size of the site and number of users


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Selecting backbone distribution media (cont.): Whenever possible, first determine the different service

requirements, then group them into similar services, such as voice, display terminal, LAN, and other digital connections; next identify the individual media types and project each group’s quantities

When deciding on backbone cable size, first know how many workstations are served by each TR and how many pairs the horizontal cabling provides

When selecting backbone cable, know the maximum backbone distances for each medium


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Selecting backbone distribution media (cont.): Fiber cables are available with different sheaths for indoor

(intrabuilding) and outdoor (interbuilding) Backbone fiber cable consists of optical fibers with

individually colored buffer jackets of flame-retardant polymer; the cable is stranded around central strength member, providing a rugged cable

When using fiber for the backbone, plan to use at least a six-fiber cable for each TR, however, a 24-fiber cable is highly recommended; typically fibers reserved are: six for LANs, six for redundancy, and twelve for growth


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Selecting backbone distribution media (cont.): Plastic insulated conductor (PIC) cable is twisted-pair

designed to ease cable-pair identification Each pair is color-coded in groups of 25 pairs; these pairs

are placed together in a binder group, which is identified by a color-coded binder wrapping

PIC cables are usually available in sizes ranging from 6 to 4200 pairs

The cables are manufactured in various designs for aerial, buried, underground, and in-building applications


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Selecting the main cross-connect hardware: The main cross-connect is the primary connection and

flexibility point within a network Depending on the number of copper pairs necessary to

terminate at the main cross-connect, the cross-connection hardware can be wall- or rack-mounted

The main cross-connect is generally located in the equipment room; when selecting the location for this room, consider that the room should be: accessible for large equipment delivery, not constricted for expansion, not below the water level


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This cabling system provides: The physical means for transporting signals between the

telecommunications outlet/connector in the work area and the HC in the TR

The cabling and its associated connecting hardware make up the horizontal pathways

These pathways include the cable pathway itself, as well as the related spaces, such as pull boxes, splice boxes, and intermediate consolidation points

The pathway design should allow for at least three cable runs per work area

Horizontal Distribution Systems

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Horizontal distribution design guidelines: The horizontal cabling is usually less accessible than

other cabling, and is subject to the greatest amount of activity, so good design is crucial

A star topology must be used Each telecommunications outlet in the work area must

be directly connected to an HC in a TR on the same floor; the maximum distance for this is 90 m

For each horizontal cable, a maximum distance of 10 m is permitted for work area cords, patch cords, and jumpers, and any equipment cords


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Horizontal distribution design guidelines (cont): Horizontal distribution system recommended media:

four-pair, 100-ohm UTP cable; two-pair, 150-ohm STP-A; two-fiber fiber-optic cable

Hybrid cables contain multiple types of media under a single sheath; one that contains both fiber cable and copper conductors is called a composite cable

Points to consider when using hybrid cables: 100-ohm UTP cables of mixed categories should not reside within the same sheath; the cables of a hybrid cable must meet cross-talk specifications


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Work area components for horizontal distribution: Work area cables are the modular cords that connect the

telecommunications outlet to the work area equipment The modular cord in the work area should have a

maximum length of 3 m, and all four-pair UTP cables must be terminated in eight-position modular jacks (RJ-45) in the work area, following T-568

The connector must be mounted on the outlet faceplate to make it accessible for work area connectors


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Horizontal cables and their cross-connects: Link each telecommunications outlet to the HC with a

dedicated 4-pair, 24-AWG, Cat 5 UTP cable; the length of this cable should not exceed 90 m

The HC consists of cable terminations and cabling hardware to help link the horizontal cables to the telecommunications and control equipment

Use the BIX or 110 IDC cross-connect system with modular RJ-45 patch panels to connect voice/data

The HC is located in the TR; each floor should have at least one TR


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The cable plant: Includes all cables and termination points in an

installation, such as the work area outlets, patch panels, and punch-down blocks

This information is probably the most useful and important component of the documentation - once cables are run through ceilings and floors and terminated, finding a particular cable that is causing problems is next to impossible if it wasn’t labeled; also it tells you which cables can and cannot be disconnected when you move equipment

Documenting the Cable Plant

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Documenting cable types and Terminators: Begin the cable plant documentation by describing the

types of cables in use, their purposes, and the types of terminators used

In addition, list any exceptions that were made during installation

Use a cut sheet to include information on the connection made by the cable, the length of the run, the cable ID and type of cable, the patch-panel port, whether the cable is in use or not, and any testing done and the results of such


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Labeling: Label all cable runs, equipment, patch panels, and jacks

with a name/number clearly identifying them

Document cable test results and problems with the cable plant Once a cable passes its requisite tests, label it and move

on to the next cable When there are any concerns about the cable plant,

include them in the documentation


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Equipment rooms must be documented: Include the room location and room dimensions, as well

as the types of doorways, ceilings, walls, cooling, heating, and lighting used

All of the cables in the equipment room must be documented, as well as those in the building areas each room serves

Describe devices and their location in each room, including their capacities; before adding workstations in any area, determine whether patch panels, hubs, and switches have available ports

Documenting Equipment Rooms

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Documenting power considerations: Many network devices require considerable power to

operate, and some even have special electrical outlet requirements; most major equipment comes with redundant power supplies

Examine each equipment room to determine the type and number of power outlets, document the power budget, including total power, and how much power is in use

Most equipment rooms use an uninterruptible power supply (UPS); document each UPS


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Diagramming equipment racks and installed equipment: Provide detailed drawings of your equipment racks, with

the installed devices shown and labeled Include the rack name and location; the patch panel

name, type and ports; the hub name, type and ports; the UPS name and type

Documenting known problems or concerns with equipment rooms Include information about any rooms that do not meet

specifications for cooling, power, or lighting


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Chapter Summary

Backbone distribution systems provide the interconnections between telecommunications rooms, equipment rooms, and entrance facilities. The two types of backbone distribution systems are the interbuilding system, which connects other buildings to the main cross-connect, and the intrabuilding system, which provides connections between the floors of a multistory building

The maximum recommended distances for backbone cables depend on their application. For example, the maximum distance for data applications is 90 m. For voice applications, the maximum distances vary

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Chapter Summary

When planning multipair (backbone) cable spaces, you should stay as far away as possible from power cables, transformers, electrical motors, and fluorescent lighting

A typical fiber backbone installation consists of one fiber-optic cable, usually in counts of 6, 12, or 24 fibers, that runs between the main cross-connect and each TR

Backbone distribution systems usually employ a hierarchical star topology with one or more levels. Horizontal distribution systems use a simple star topology

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Chapter Summary

The horizontal distribution is the part of the cabling system used to distribute, support, and provide access to the horizontal cabling. This cabling system provides the physical means for transporting signals between the telecommunications outlet/connector in the work area and the horizontal cross-connect in the TR. The cabling and its associated connecting hardware make up the content of the horizontal pathway and related space

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Chapter Summary

Work area components for horizontal distribution include telephones, fax, data terminals, and computers, plus any other items located between these components and the telecommunications outlet

Your cable plant documentation includes all the cables and termination points in an installation, such as work area outlets, patch panels, and punch-down blocks. The cable plant information is probably the most useful and important components of your documentation - once cables are run through ceilings and floors and terminated, finding a particular cable that is causing problems can be almost impossible if you didn’t label it

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Chapter Summary

Describe each equipment room in detail in your documentation. Include information for all cable runs, devices, racks, power considerations, and known problems or concerns. This documentation makes additions and changes easier, provides port information to accommodate additions, and identifies all equipment and its locations

1 guide to network cabling fundamentals chapter 5

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buildings cross

horizontal cross

types of cross

horizontal cabling

distribution system

intermediate cross

various buildings

backbone systemdifferentiate