cabling can result in serious network disruption. Structured
cabling can be your answer to maximize network performance.
by Mahesh Rathod
cabling system provides a flexible cabling plan and can support
different computer and telephone systems from any vendor
networks becoming more complex and their requirements changing
constantly, having a good foundation for these networks is
crucial. Cabling, the backbone of any data communications
system is vital when it comes to determining performance and
reliability of any network. Structured cabling is the first
step towards achieving optimum performance from your network.
Origin of structured cabling
the early days of networking, various vendor-dependent cabling
systems existed for carrying data and voice. Troubleshooting
and managing these proprietary systems was very difficult
and time consuming as network managers had to maintain two
distinct networks (data and voice). This lead to the evolution
of structured cabling.
Structured cabling provides a flexible cabling plan and can
support computers and telephone systems from any vendor. Structured
cabling is a hierarchy based on backbone cables that carry
signals between telecommunication closets and floors of a
building, and on horizontal cables that deliver services from
telecom closets to work areas.
The central standard for structured cabling system is the
ANSI/TIA/EIA-568-A, "Commercial Building Telecommunications
Cabling Standard". This standard specifies a generic
telecommunications cabling system to support a multi-product
and multi-vendor environment.
Six Elements of a Structured Cabling System
The TIA/EIA 568 cabling standard specifies the six basic elements
of a structured cabling system.
Building entrance facilities: This is the service entrance
into the building including the cables, surge protection equipment
and connecting hardware that may be used to link the cabling
inside your building with the campus data network or public
Equipment room: This is a centralized space where telecommunications
equipment is located (e.g., PBX, computing equipment, video
Backbone cabling: In a Star topology backbone cabling is used
to provide connections between telecom closets, equipment
rooms and entrance facilities.
Telecommunications closet: The main role of the telecommunications
closet is to provide a location for the termination of the
horizontal cable on a given floor of a building. This closet
houses the mechanical cable termination and any cross-connects
for the horizontal and backbone cabling systems. It may also
house interconnection equipment like switches.
Horizontal cabling: It consists of physical media used to
connect each outlet to a closet. Various types of cables can
be used for horizontal distribution. Each type has its own
performance limitations, size, cost and ease-of-use.
Work Area: This is the area where computers and other equipment
are located. The work area components include patch cables
required to connect the computer and telephone to the communications
outlet on the wall.
Support for Star Topology
The structured cabling standard TIA/EIA 568 is based on a
Star topology. The standard specifies a backbone system with
a star cabling topology that has no more than two levels of
hierarchy within a building. This means that a cable should
not go through more than one intermediate cross-connect device
between the main cross-connect located in an equipment room
and the horizontal cross-connect located in a wiring closet.
There are many advantages to using star topology. The first
is that central equipment switches can be easily migrated
to new technologies. The second is the physical security that
can be provided for critical equipment preventing widespread
network failure as a result of tampering. Lastly the central
cabling points make it easier to troubleshoot networking problems.
Media types for Structured Cabling
The TIA/EIA 568 recognizes three different kinds of cables.
Unshielded Twisted Pair (UTP) is one of the media types. UTP
can be classified into three categories depending on their
performance. Category 3 is rated to 10 MHz, suitable for Ethernet
(10 Mbps). Category 4 is rated to 20 MHz, suitable for token
ring (16 Mbps). Category 5 is rated to 100 MHz, suitable for
Fast Ethernet (100 Mbps) and ATM (155 Mbps). Cat 5 or Category
5 is the de-facto standard now as it is easy to install and
has a lower installation cost. Cat 5 also has a most commonly
used variation: Cat 5e. This standard is used for Gigabit
The new upcoming standard is Cat 6.
Shielded Twisted Pair (STP) also known as the IBM Type 1 is
the other cable type. The 568-A standard for STP is known
as STP-A. This standard extends the system's rating through
300 MHz. But if installed properly STP-A structured cabling
system can run a 16 Mbps token ring signal and a 550 MHz broadband
video signal at the same time.
Fiber optic cable offers near infinite bandwidth and perfect
immunity to noise. Fiber offers more bandwidth than copper
cables. In fact, a single pair of fibers can handle the same
amount of voice traffic as 1400 pairs of copper. The trade-off
here is that fiber costs significantly more and installation
Installation and design practices
It is advisable to follow installation and design principals
laid down by the 568 standard to get optimal cabling performance.
The 568-A standard requires a minimum of two ports (voice
& data) per workstation. The first port must use 4-pair,
100 Ohm, Cat 3 or higher UTP cable. The second port can make
use of UTP, STP or optical fiber cable. The maximum length
for horizontal cabling between the switch and any outlet must
be 90 meters.
The first installation practice is pulling cables from the
telecommunications closet to each outlet location. The maximum
pulling tension for Category 5 is 25 lbf. Higher tension on
the cable may stretch the twists and can result in increased
attenuation. As per the 568, the pairs in a Category 5 cable
should never be untwisted more than half inch from the point
of termination. Any further untwisting of the pairs will increase
crosstalk and susceptibility to EMI/RFI (electromagnetic interference/radio
The next cable installation practice is to prepare the cable
for termination. This involves stripping away some of the
jacketing material and untwisting the conductors. After the
cables have been terminated, the cable must be dressed or
The initial investment for structured cabling is much more
than the traditional methods of cabling, but it is very important
to understand that structured cabling entails long-term investment.
Structured cabling is vendor independent. A standards-based
cable plant will support your applications and hardware even
after you change or mix and match any vendor. Structured cabling
maintains consistency and it simplifies troubleshooting.
Mahesh Rathod can be reached at firstname.lastname@example.org