of Structured Cabling
Training Programs and Equipment
- Structured Cabling for VDV
Communications - An Overview
- A Little History....
- The history of telecommunications
spans a mere 150 years, starting with the development of the
telegraph in the early 19th century. Telegraphy gave man the
means to transmit impulses that represent letters. When these
letters were received and decoded, they provided a way to convey
messages over long distances.
- 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" om 1876. In reality,
many men contributed to telephone improvements including David
Edward Hughes whose invention of the microphone became universally
used in telephones.
- 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! In the first decade
of the 20th century, Dr. Lee deForest's invention of the vacuum
tube amplifier enabled long distance communications.
- 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.
- 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.
- Manufacturers took up standards
development to insure interoperability of their products - under
the auspices of the IEEE for computer networking electronics
and EIA/TIA for cabling. Thus was born the industry standards
that we all depend on for today's communications networks.
- Mandatory or Voluntary Standards?
- Widespread useage of any technology
depends on the existence of acceptable standards. The most important
standard and the only one that is mandatory is the National Electrical
Code developed by the National Fire Protection Assn. that covers
all aspects of electrical 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.
- But during the 1980s, phone
signals became digital, LANs proliferated 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).
- Just to confuse everybody, this
cabling standard, developed by 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. We'll go along with the crowd and simply
say "568" when we generally mean the entire output
of the TR 42 committee!
- And to further confuse everybody,
many people think this standard is a mandatory, even legal, document
like the NEC. NO WAY! "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 offers interoperability, upgradability
and low cost due to the numerous manufacturers offering compatible
products. But it ain't code!
- Note: TIA-568 is a US standard. Overseas, ISO/IEC writes
the standards and a summary of their standards is below.
- The Basics of "568"
- "568" calls for connecting
the desktop (work area) to a telecom closet (the "horizontal"
run) with up to 100 meters of cable (including no more than 10
m total of patchcords), which is usually Cat 3, Cat 5 or Cat5e
UTP. The "Cat" or category designation refers to a
performance grade, which we will explain later in the Cables
section. Most copper installations today use Cat 5e or Cat 6
exclusively, as it isn't that much more expensive than Cat 3
and can support phones or any LAN on any outlet.
- 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 in recent history, 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 links, as in a campus, for high speed networks.
- 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.
- Virtually every network now
includes wireless, which is, of course, not wireless-access points
are connected into the network with copper or fiber cabling.
- The telecom closet 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 bugaboo of
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.
- 568 also includes IBM Type 1
cable, a shielded two pair cable, since it is still used in some
networks. However, it ignores coax cable, like RG-58 used in
some Ethernet LANs and RG-6 used in CATV and CCTV.
- 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 "B" revision and
includes sections for general specifications (B.1) and individual
sections for copper (B.2) and fiber optics (B.3)
- EIA/TIA 569 A: Covers pathways
and spaces. Defines the "telecom closet" or telecom
room as it is now called.
- EIA/TIA 570 A: For residential
- EIA/TIA 606: Cabling system
- EIA/TIA 607: Grounding and bonding
- International Standards
- 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
ISO/IEC 14763-1 - Administration, documentation
ISO/IEC 14763-2 - Planning and Installation
ISO/IEC 14763-3 - Testing optical fibre cabling
IEC 61935-1 - Testing copper cabling
- Learning More About Standards
- There are a number of ways of
finding out more about these cabling standards. You can buy a
complete copy of the EIA/TIA or ISO/IEC standards from Global
Engineering Documents for a lot of money and wade through
the strange standards language. Or you can get catalogs from
a number of companies that sell cabling products who have extremely
complete explanations of the standards. Guess which we recommend?!