s04 structured cabling - university of hong kongwork6000/s04 structured cabling.pdf · structured...

UNIVERSITY OF HONG KONG Faculty of Engineering

M.Sc.(Eng) in Building Services Engineering MEBS6000 2010 Utilities Services

K.F. Chan (Mr.) of 17 Sept 2010

Structured cabling

In the early 1980s a range of different cabling systems were used for communication

system within buildings. These included various types of coaxial cables for CABD

(communal antenna and broadcasting distribution), multi-core twisted pairs for

telephone and fax lines, later on cable TV, RS232 and Ethernet data cables.

The lack of standardization caused considerable inconvenience, but from the

competing technologies emerged a high performance generic cabling system that

could be used for both voice and data applications. This is the origin of structured

cabling: a single cabling system that supports all voice, data and video applications

within a building. Nowadays, all new network installations of any size use a

structured cabling system because it provides a standardized way to wire a building

for all types of networks.

(Adopted from HASTING, P. The illustrated guide to electrical building services)




Key components of structured cabling systems

Backbone cable

The main distribution frame (MDF) links all the building’s interior wiring and

provides an interface connection to circuits coming from outside sources such as the

local phone companies and ISP’s. This interface point is equipped with surge

protectors to guard the building wirings.

(Adopted from DEAN, T. Network+ Guide to Network)

Vertical cables carry the Internet and private network connections up to cross-connect

panels in wiring closets on each floor. Vertical “risers” or backbone of a data network

are mostly optical fibre cables. A minimum of two optical fibres is needed to send and

receive data, and cables typically have a combination of 4, 8, 12 and 16 or more fibre

cores. Multi-mode cable is used in most buildings. It is straightforward to install and

is a relatively cheap option compared to systems that use single-mode fibre. Single

mode fibre is installed in backbone campus applications for long distance

transmission. Horizontal fibre is still a minority. Hubs enable optical fibre cables to

interface with copper cables. Backbone cable connects to floor distributors.





Fibre optic cables come in two primary types:

� single mode which include only one glass fibre at the core, generally works with

laser based emitters (1310 or 1550nm), more costly but spans the longest

distances;

� multimode cables, which incorporate two or more glass fibres at their cores,

generally works with LEDs (850 or 1300nm), less costly but span shorter

distances




The smaller the core, the lower the attenuation, the higher the bandwidth, but more

difficult to terminate and measure. So, small core fibres such as 9/125mµ are usually

used in long distance telecomm applications, while 50/125 mµ and 62.5/125mµ

fibres are usually used in short haul datacomms applications, typically up to 2km


There are also a number of fibre optic connectors, the more common ones are:

� ST – straight tip connectors join individual fibres at interconnects or to optical

devices, appear often in Ethernet network backbones. ST connector locks onto

the jack when twisted.

� SC – straight connection – this type of connectors pushes on, which makes them

easy to install and require less space. SC connectors make a strong connection

and may be used when splicing fibres. An SC connector is an one piece

component, with two receptacles for sending and receiving fibres. A notch in its

jacket ensures proper orientation when inserted.




Vertical backbones carry the network up to cross connects panels in wiring closets on

each floor. The wiring closet is the place where hubs and switches interconnect to the

horizontal cables going out to each floor.

Floor distributors and patch panels

A floor distributor connects the backbone to horizontal cables. A floor distributor

comprises one or more patch panels from which individual connections can be made

to either a data or voice hub, depending on which service is needed. Multiple RJ45

sockets on the front of patch panels and network hubs allow individual patching using

short patch cords.


Patch panels and network hubs are generally mounted together in a standard wall

mounted or free standing rack. Large structured cabling systems will have multiple

floor distributors, with rack systems located on each floor of the buildings.

(Adopted from HALSALL, F. Computer networking and the Internet)

It is now getting more and more common to use “switching hubs” instead of “repeater

hubs” to improve network throughput.




(Adopted from HALSALL, F. Computer networking and the Internet)




Horizontal cabling

Horizontal cabling brings the network from the floor distributors to individual outlets.

Outlets are invariably RJ45 sockets although RJ11 jacks still used for phones and fax

machines. Various types of cable can be used for horizontal cabling, but unshielded

twisted pair (UTP) cable is the most widely used.

RJ45

Unshielded - UTP




In environments where there is a significant risk of electromagnetic interference,

foiled twisted pair (FTP) or shielded twisted pair (STP) can be used. In most

installations (using Ethernet as the data link technology) length of horizontal cable

from a telecommunication outlet back to the floor distributor must not exceed 90m

(with 10m for patch cords).

Foiled - FTP

Screened - STP

Cat 5 cable together with microduct

for blowing optic fibre later on

Multi-core Cat 5 cable together with

microducts for future optic fibre blowing





Older installations may see Cat 3 cables, but most installations are Cat 5. Today, Cat

5e or even Cat 6 is the norm, with a trend of moving towards Cat 7.




Telecommunication outlets

Traditionally, BT type phone jacks were installed in Hong Kong.

A BT phone outlet – a RJ11 to BT adaptor is shown

Nowadays, with structured cable installation, each user is provided with a

telecommunication outlet into which both his/her computer and phone plugs in.

Typically, two outlets are mounted on a common wall plate or floor plate.

An EIA/TIA wall outlet





UTP cabling is rated according to a number of categories devised by the Electronic

Industries Alliance (EIA) and the Telecommunications Industries Association (TIA);

since 1991, the American National Standards Institute (ANSI) has also endorsed these

standards. A document known as the ANSI/EIA/TIA 568 Commercial Building

Wiring Standard defines standards that apply to the kinds of wiring used in

commercial environments. This set of standards helps ensure consistent performance

from wiring products that adhere to its requirements. The ANSI/EIA/TIA568 standard

currently includes the following categories:

Cat 1 telephone cabling for voice but not data. Most UTP installed prior to

1982 falls into this category.

Cat 2 bandwidth up to 4Mbps and consists of four pairs of wire.

Cat 3 bandwidth up to 10Mbps, with signaling rates up to 16MHz.

Cat 4 bandwidth up to 16Mbps with signaling rates up to 20MHz. This is

the first ANSI/EIA/TIA designation that labels the cables as datagrade

rather than voicegrade.

Cat 5 bandwidth up to 100Mbps with signaling rates up to 100MHz.

Cat 5E Cat 5 enhanced UTP. It differs primarily in the tests it must undergo

and was designed to correct some of the shortcomings in Cat 5

cabling, particularly in the areas of Gigabit Ethernet and full duplex

operation.

Cat 6 cabling for Gigabit Ethernet, use the same type of modular jack as

lower categories and backward compatible with Cat 5 and Cat 5E.

Cat 7 fully shielded twisted pair (each pair is shielded so is the outer jacket)

Cat 5 and Cat5E is by far the most popular types of data cables in use so far.




(Adopted from Janis, R, Tao, W. Mechanical and Electrical Systems in Buildings)




Item Wire-pair cable LOS microwave Satellite

communication

Fibre optic Coaxial cable

Bandwidth 2MHz to 400MHz 500/2500MHz 500/2500MHz 120GHz per band Up to 1GHz

Common bit

rates

1.544 / 2.048Mbps 155Mbps 2.048Mbps 2.4/10/40Gbps 100Mbps

Achievable bit

rates

1000Mbps 622Mbps 155Mbps 4000Gbps per fibre 1Gbps

limitations Length limited By statute, problem during

high humidity

By statute, delay Severing cable Severing cable

Applications LAN, telco

outside plant

Long distance/short

distance links, telco,

CATV, broadband

providers, private networks

VSAT networks,

long distance links,

video transport

For every broadband,

phone and

communication

terrestrial application

CATV last mile/last 100

feet; RF transport short

distances; otherwise

limited

(Table adopted from Freeman, R.L. Fundamentals of Telecommunications)




Copper and fibre in the subscriber loop (Adopted from HECHT, J. Understanding fiber optics)

A BNC (British Naval Connector) connector




The employment of coaxial cable in the telecommunication system is now practically

obsolete with the following exceptions:

- the last mile or last 100 feet in the cable television (CATV) plant,

- as an RF transmission line for short distances.

It is being replaced in the enterprise network with high quality twisted pair and fibre

optic cable connectivities. In the long distance network, the fibre optic solution is far

superior in nearly every respect.




Network connectors and their uses





Design consideration

Structured cabling is used to coordinate the transmission of data, voice, audio, and

video signals. A plan for the installation of structured cabling should cover seven

design elements:

1. Entrance facilities (i.e. conduits, draw pits and armored cables)

2. Equipment rooms, e.g. Main Distribution Frame (MDF), headend equipment.

3. Telecommunication rooms (telecom closets)

4. Backbone wiring

5. horizontal wiring

6. Work area

7. Administration

Specific recommendations for each design element are given in EIA/TIA Standard no.

568B. Cables are best connected and terminated at one or more telecommunication

rooms distributed strategically throughout each floor, preferably not more than 150m

apart.

(Text and figures mostly adopted from HASTING, P. The illustrated guide to

electrical building services, DERFLER, F. Jr. & FREED, L. How network works, and

Janis, R, Tao, W. Mechanical and Electrical Systems in Buildings)

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