- A History of Cabling for Communications
- The
history of telecommunications spans slightly more than 150 years,
starting with the development of the telegraph in the early 19th
century. Telegraphy gave man the means to transmit a series of impulses
that represented letters, called Morse Code for Samuel F. B. Morse, who
is credited with the invention of telegraphy. When these letters were
received and decoded, they provided a way to convey messages over long
distances.
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- Naturally, the next step was
to consider whether sound might also somehow be electrically
transmitted. Alexander Graham Bell applied for his patent for
an "electrical speaking telephone" in 1876, beating Elisha Gray by only a few hours. In reality,
many people contributed to telephone improvements including Thomas Alva Edison, Lars Ericsson and David
Edward Hughes whose invention of the microphone became universally
used in telephones.
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- It is amazing how quickly the
use of the telephone spread. The first switchboard, an experiment,
was installed in Boston in 1877. Just four years later, there
were 54,000 telephones in the United States! The first connections from Boston to New York begain in 1884. Wireless communications developed from the work of Nikola Tesla and Guglielmo Marconi. In the first decade
of the 20th century, Dr. Lee deForest's invention of the vacuum
tube amplifier enabled long distance communications.
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- Technology
allowed the expansion of telecommunications. With the advent of the
space program in the 1960s, communications satellites expanded the
worldwide telecommunications network faster than could be done by
laying transoceanic cables. By the 1970s, integrated circuit technogy
and the microprocessor began to influence telecommunications and
computers. Experiments began in digital voice transmission and fiber
optics. Computer networks like Ethernet and the predecessor of the
Internet were developed.
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- The 1980s brought wide scale
use of digital telecom, computer networks and fiber optics, but
was also the era of the breakup of the Bell system. Users who
once depended on AT&T for telecom standards and IBM or other
computer companies for the "rules" they depended on
were left stranded.
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- Manufacturers assumed responsibility for standards
development to ensure interoperability of their products - under
the auspices of the IEEE for computer networking electronics
and EIA/TIA for cabling in the US and ISO and IEC worldwide. Thus was born the industry standards
that we all depend on for today's communications networks.
The
1990s to today are the era of computer LANs and the Internet. Although
not every
proposed usage of cabling has been successful, today every PC is
connected to a LAN or the Internet or both. Telephone systems are using
VoIP (Voice over Internet Protocol) over the Internet as well as
traditional telecom protocols, with wireless connection being used in
many cases instead of wiring. Internet access over cell phones has
added even more expansion to the market. Perhaps the biggest change of
the current era is the final expansion of fiber optic networks direct
to the subscriber, either homes or business (FTTx), using passive optical network (PON) technology.
But all telecommunications
and the Internet depend on cabling, even wireless. Typically it's all on a worldwide fiber
optic backbone connected into private networks that utilize a
combination of copper, fiber and wireless connections.
What is Premises Cabling?
By
premises cabling, we mean the cabling used inside buildings (and in
restricted geographic areas like campuses or among business facilities)
that follows industry standards. Mostly we are refering to structured
cabling systems defined by TIA-568 or ISO/IEC 11801 and related
standards that are used
for LANs, telephone systems and even other systems adapted to
structured cabling like CCTV, security or building management. Other
systems that depend on cabling such as security and building control
are migrating to structured cabing for its widespread availability and
predictability.
Other Uses For Standardized Premises Cabling
TIA-568
originally considered the use of structured cabling to be corporate
LANs, primarily Ethernet but some legacy IBM Token Ring. However the
large-scale adoption of UTP cabling standards has gained the attention
of many other applications. UTP is now used for CCTV cameras, security
systems, building management systems, etc. Some of these systems have
been redesigned for UTP cable while others require adapters, such as
BALUNs which convert coax to balanced UTP transmission. One can also
get adapters that allow multiple equipment to use separate pairs of the
UTP cable, for example for a POTS phone line and a Fast Ethernet
connection. Most of these applications will also use fiber optics where
the length or bandwidth exceeds the limitations of UTP copper cable.
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- What Are Cabling Standards?
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- Widespread
useage of any technology depends on the existence of acceptable
standards for components and systems. These standards are written as
minimum specifications for components and systems that will ensure interoperability of equipment from various
manufacturers. The most important "standard" and the only one that is
legally mandatory is the National Electrical Code developed by the
National Fire Protection Assn. that covers all aspects of electrical
and fire safety. Article 800 of the NEC covers communication circuits,
such as telephone systems and outside wiring for fire and burglar alarm
systems and Article 770 covers fiber optics. Also, all VDV wiring must
comply with building and electrical codes applicable in your state or
city.
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- But during the 1980s, technology changed rapidly. Phone
signals became digital, fiber proliferated, PCs became connected over LANs and new cables and
cabling architecture were needed. The goal was to make buildings
"smart," able to allow computer and phone conversations
over a standardized wiring system. By the early 90s, a scheme
of "structured cabling" was standardized by technical
committee of a trade association, the merged Electronic Industries
Association and Telecommunications Industry Association (hereafter
referred to as EIA/TIA) in the USA and ISO/IEC worldwide.
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- This
cabling standard, developed by what was then called the EIA/TIA TR 41.8 committee
- now renamed TR 42 - is referred to by the number of the primary
standard, EIA/TIA 568, although there are actually a number of
standards, technical advisories, etc. that cover all aspects
of structured cabling. When most people simply
say "568" when they mean the entire output
of the TR 42 committee (see below.)
The
model for premises cabling standards was AT&T’s design
guidelines for communications cabling developed originally from a
1982 survey of 79 businesses located in New York, California, Florida
and Arkansas involving over 10,000 cable runs. At the time, cabling was
used mainly for telephones to wiring closets and PBXes (Private Branch
Exchanges or local phone switches), but it established a baseline for
cable length requirements for commercial customers that was used
in creating TIA-568. The AT&T survey determined that 99.9% of
all stations were less than 300 feet (about 100 meters) from the wiring
closet, so that became the goal of the 568 standard. Much of the
terminology from the telephone industry also carried over into the
development of structured cabling standards, although some of that
terminology is being replaced by less telephone-specific terminology.
Today's premises cabling standards define cabling systems, using both copper and
fiber optic cables, that can support premises networks called LANs for
"local area networks" from 10 megabits per second to 10 gigabits per
second over 100 meter distances. Other premises systems such as
building management, HVAC, security systems including CCTV that
previously used coax cabling, etc. now are designed around structured
cabling standards.
Cabling
standards are not developed for end users or installers, but for
component and equipment manufacturers who need to develop products that
offer interoperability andthe mutliple sources of supply demanded by
users. The manufacturers develop
products around the standards specifications and are responsible for
telling installers and end users how to use these components. The
designers, installers and users of networks can rely on the instructions of the manufacturers on how to utilize these "standard products" correctly.
The
essence of standards for structured cabling is they provide a minimum
performance level for components and cabling systems that manufacturers
use to develop products for the marketplace. The competition in the
cabling marketplace requires companies to make cables that are better
than those standards in order to differentiate their products from
competitors. So using those standards, manufacturers make cables that
will be compatible with other cables meeting the same standards but
offer advantages in performance, installation or cost.
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- Many people think this standard is a mandatory, even legal, document
like the NEC. In fact, "568" is a voluntary interoperability
standard for communications cabling, developed by a number
of manufacturers of cabling components and networking equipment,
so that they might make equipment that could use any 568-compliant
cabling system and be upgraded in the future as long as it was
designed for the same cable plant. What
568 is, in fact, is a common sense approach to cabling that defines
component and cabling system specifications and offers
interoperability, upgradability and low cost due to the numerous
manufacturers offering compatible products.
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- Note: TIA-568 is a US standard. Worldwide, ISO/IEC writes
the standards and a summary of their standards is below.
- The Basics of "568"
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- The TIA "568" structured cabling standard calls for connecting
the desktop (work area) to a telecom closet (the "horizontal"
run) with up to 100 meters of cable (including 90 m of permanently installed cable (permanent link) and no more than 10
m total of patchcords), which is usually unshielded twisted pair - UTP - with 4 pairs of wires - called Cat 3, Cat 5, Cat5e,
Cat 6 or Cat 6A.
The "Cat" or "category" designation refers to a performance level or grade for UTP cabling,
which we will explain in the Cables section. Most copper installations
today use Cat 5e or Cat 6 exclusively, as they aren't that much more
expensive than Cat 3 and can support phones or any LAN on any outlet.
Screened twisted pair (foil shielded over the 4 pairs) and shielded
twisted pair (STP) are also acceptable and in fact widely used outside the USA.
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- The backbone cabling can be
either UTP or fiber optics. In larger networks, fiber is most
often used for its longer distance capability and higher bandwidth.
568 specifies two multimode fibers, 62.5/125 - the most common
MM fiber until recently, and 50/125 - a higher bandwidth fiber
rated for use with lasers for gigabit networks that is rapidly
overtaking 62.5/125 in popularity. Singlemode fiber is also specified
for longer backbone links, as in a campus, for high speed networks.
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- Fiber optics is also a horizontal
option in 568, but not often used because of the higher cost
except where high bitrate networks or future upgrades are expected.
However, a properly designed centralized fiber network that connects
the desktop directly to the computer room with no intermediate
electronics does not need a telecom closet and saves the cost
of conditioned power, data ground, AC and the floor space, which
may offset the additional cost of the fiber electronics.
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- Virtually
every corporate network now includes wireless, which is, of course, not
wireless since access points are connected into the network with copper
or fiber cabling. Issues for wireless include proper siting of the
wireless access points (antennas, also abbreviated as APs), providing
adequate bandwidth to the access points and ensuring network security
since wireless signals are easily intercepted.
- The telecom closet, or telecom room (TR) as it is now called, houses the
hubs for the computers in the work areas. These hubs are interconnected
on "backbone" wiring which is mostly fiber optics,
as it usually carries higher speed signals over longer distances
and provides isolation from ground loops, another problem with copper cabling in
LANs. The main cross-connect (MXC) or equipment room contains
the network and telco hardware. For the telephones, their lower
bandwidth requirements allow longer runs, so they are usually
simply connected to backbone cables in the telecom closet with
a punchdown and run straight to the MXC.
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- TIA 568 standards have also included IBM Type 1
cable, a shielded two pair cable, since it is still used in some
networks. However, it does not include coax cable, like RG-58 used in
some Ethernet LANs and RG-6 used in CATV and CCTV, except in the residential standard.
A
general restriction for structured cabling is the permissible distances
for cable runs. The table below lists cable distances for various types
of permitted cabling. The restrictions on fiber links in the horizontal
are arbitrary to be equal to copper cabling and may be exceeded for
many network uses as long as the equipment provider allows such use.
Fiber lengths in the backbone may be restricted by
the bandwidth of multimode fiber when used with high speed networks, so
the choice of fiber type may determine the actual length possible.
| Cable Type | Distance (Meters) | Distance (Feet) | | UTP copper (data) | 100 | 330 | | UTP copper (voice-POTS) | 800 | 2625 | | DSL/ADSL | 5000 | 16404 | | MM fiber (horizontal) | 100 | 330 | | MM fiber (centralized) | 300 | 1000 | | MM fiber (backbone) | 2000 | 6560 | | SM fiber (backbone) | 3000 | 9840 |
TIA-568-C revision proposes to change the nomenclature of structured cabling systems. Here is an explanation of the proposal, as of 12/2008.-
- Beyond "568"
- 568 is only part of the structured
cabling standards. It's a multi-part standard itself and there
are several more standards cover other areas of cabling:
- EIA/TIA 568: The main standard
document for structured cabling, usually referred to as simply
"568." It is now on the "C" revision, published in 2009. Always check with manufacturers for the latest revisions.
- EIA/TIA 569: Covers pathways
and spaces. Defines the "telecom closet" or telecom
room as it is now called.
- EIA/TIA 570: Residential
cabling.
- EIA/TIA 606: Cabling system
administration (documentation)
- EIA/TIA 607: Grounding and bonding
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- International Standards
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- The international equivalent
of EIA/TIA 568 is ISO/IEC 11801. The standards are written similarly
to what has been done by TR 42. Here are their relevant standards:
- ISO/IEC 11801 - Cabling for
customer premises - structured cabling similar to TIA 568
ISO/IEC 14763-1 - Administration, documentation - similar to TIA 606
ISO/IEC 14763-2 - Planning and Installation - similar to TIA 569
ISO/IEC 14763-3 - Testing optical fibre cabling - included in TIA 568
IEC 61935-1 - Testing copper cabling - included in TIA 568
Electrical Codes For Cabling
The most important "standards" and the
only ones that are legally mandatory are the local building and
electrical codes, such as the US National Electrical Code (NEC.) The
NEC is developed by the National Fire Protection Assn. and covers all
aspects of electrical and fire safety. Article 800 of the NEC covers
communication circuits, such as telephone systems and outside wiring
for fire and burglar alarm systems and Article 770 covers fiber optics.
All premises cabling must comply with building and electrical codes
applicable in your area. Below is a listing of current NEC articles
covering premises cabling.
NEC Articles Covering Cabling
| Chapter | Article | Topic |
| 6 | 640 | Sound Systems |
| 7 | 725 | Remote-Control, Signaling and Power-Limited Circuits |
| 7 | 760 | Fire Alarm Signaling Systems |
| 7 | 770 | Optical Fiber Cables and Raceways |
| 7 | 780 | "Smart House" Wiring |
| 8 | 800 | Telecommunications Circuits (Telephone and LAN) |
| 8 | 810 | Radio and TV Equipment |
| 8 | 820 | CATV Systems |
| 8 | 830 | Network-Powered Broadband Systems |
Learning More About Standards and Codes
There
are a number of ways of finding out more about cabling standards. You
can buy a complete copy of the EIA/TIA or ISO/IEC standards which can
be very expensive and wade through page after page of standards
language. You can also get catalogs and/or visit the websites of a
number of cabling manufacturers who have extremely complete
explanations of the standards which have been created for their
installers and end users. The second method is the recommended one.
Understanding
codes requires not only learning what codes cover but what codes are
applicable in the local area and who inspects installations.
Furthermore, codes change regularly, usually every 2-5 years, and
installers are required to keep up to date on the codes. Understand
what is required in the areas you do installations and know when the
codes are updated.
- The "Cables" of "Cabling"
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- The choice of cable in network cabling
(or communication medium as it is sometimes called) is rather
important because of the extremely high frequencies of the signals.
Sending a 60-cycle utility power through a wire rarely presents
a difficulty; but sending a 1 or 10 billion bits per second signal
can be a lot more difficult. For this reason, the method of sending
signals and the materials they are sent through can be important.
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- Network Cabling Types
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- A number of cabling options
have been developed over the history of communications and are still in use for networking connections.
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- Unshielded Twisted pair (UTP)
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UTP cable is the primary cable used for networks, as specified in the
EIA/TIA 568 standard. UTP was developed from the original phone wires
but refined to enhance its bandwidth capability. This cable type has
been widely used because it is inexpensive and simple to install. The
limited bandwidth of early UTP (which translates into slower
transmissions) has pushed development of new cable performance grades
(the "categories" of 568) but has created a more expensive product and
more complicated installation process.
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- Screened Twisted pair (ScTP)
- Same as UTP with an overall shield around the 4 pairs. While
not currently specified for any networks or covered in the EIA/TIA
568 standard (but not prohibited), it is used in many networks in Europe where EMI
is a greater concern. It tends to be more expensive, harder to
terminate and requires special shielded plugs and jacks.
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- Shielded Twisted Pair (STP)
- Like UTP but with a shield around every pair. Widely used in
IBM systems (IBM Type 1 cable) and included in early versions of 568.
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- Coaxial Cables
- The original Ethernet cable was coax and coax is still used in
video (CCTV, CATV) systems. This is familiar and easy to install, has
good bandwidth and lower attenuation but more expensive and bulky. Not
included in 568, but in 570 for residential video use. Coax is also
used in residential applications for LANs using a transmission scheme
called MoCA that works like a cable modem. Read more on coax.
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- Optical Fiber - Optional for
most networks, top performance, excellent bandwidth, very long
life span, excellent security but slightlly higher installed
cost than twisted pair cables, more expensive electronics interface
to them. Fiber can be cost efffective with optimal architecture. See FIber in Premises Cabling and the FOA Online Fiber Optic Reference Guide Table of Contents .
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- Other transmission options:
- Wireless
- no data transmission cables are required to connect any individual
terminal, but wireless requires cabling to every antenna (called an Access
Point.) Within the range of the radio
signals, a terminal can be moved anywhere. Usually wireless is more expensive but can be
used in locations where is would be difficult to install cables. In the
modern network, wireless is a requirement because so many users want
"mobility" - so they are not "tethered" to a desktop. More on wireless.
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- Infrared Transmission
- Also transmits data without wires or fibers using infrared (IR) light
but each transmitter requires cabling. By sending pulses of infrared
light in the same patterns as electronic pulses sent over cables, it is
possible to send data from one place to another. Networks based on IR
transmission have been developed for use in office and for
line-of-sight transmissions between buildings. It is generally limited
in range and can be interrupted by blocking or weather.
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- Powerline or Phone Line Transmission
- Networks using available power line cabling have been under
development for many years, but with mixed results due the
unpredictability of wiring performance and interference from power line
noise.
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We will focus only on the most popular types of cabling, UTP, coax and fiber optics, as well as cabling for wireless.
Test your comprehension with the section quiz.
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