NETWORK CABLING
What is Network Cabling?
Cable is the medium through which information usually moves from
one network device to another. There are several types of cable which are
commonly used with LANs. In some cases, a network will utilize only one type of
cable, other networks will use a variety of cable types. The type of cable
chosen for a network is related to the network's topology, protocol, and size.
Understanding the characteristics of different types of cable and how they
relate to other aspects of a network is necessary for the development of a
successful network.
Network Cabling is a universal system; that supports digital as
well as analog signal transmissions, in which the telecommunication outlets are
installed even in locations where they are not needed at the moment of
installation, that use data cables with four twisted pairs and fiber cables, in
which long technical and also moral service life is expected, and whose correct
functionality is as important for a company as the functioning of the
electrical distribution system or any other system in company’s infrastructure.
The
following sections discuss the types of cables used in networks and other
related topics.
- Unshielded
Twisted Pair (UTP) Cable
- Shielded Twisted
Pair (STP) Cable
- Coaxial Cable
- Fiber Optic
Cable
- Cable
Installation Guides
- Wireless LANs
- Unshielded
Twisted Pair (UTP) Cable
Twisted
pair cabling comes in two varieties: shielded and unshielded. Unshielded
twisted pair (UTP) is the most popular and is generally the best option for
school networks (See fig. 1).
Fig.1.
Unshielded twisted pair
The quality of UTP may vary from telephone-grade wire to extremely
high-speed cable. The cable has four pairs of wires inside the jacket. Each
pair is twisted with a different number of twists per inch to help eliminate
interference from adjacent pairs and other electrical devices. The tighter the
twisting, the higher the supported transmission rate and the greater the cost
per foot. The EIA/TIA (Electronic Industry Association/Telecommunication
Industry Association) has established standards of UTP and rated six categories
of wire (additional categories are emerging).
Categories of Unshielded Twisted Pair
|
Category
|
Speed
|
Use
|
|
1
|
1 Mbps
|
Voice Only (Telephone Wire)
|
|
2
|
4 Mbps
|
Local Talk & Telephone (Rarely used)
|
|
3
|
16 Mbps
|
10BaseT Ethernet
|
|
4
|
20 Mbps
|
Token Ring (Rarely used)
|
|
5
|
100 Mbps (2 pair)
|
100BaseT Ethernet
|
|
1000 Mbps (4 pair)
|
Gigabit Ethernet
|
|
|
5e
|
1,000 Mbps
|
Gigabit Ethernet
|
|
6
|
10,000 Mbps
|
Gigabit Ethernet
|
Unshielded Twisted Pair Connector
The
standard connector for unshielded twisted pair cabling is an RJ-45 connector.
This is a plastic connector that looks like a large telephone-style connector
(See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands
for Registered Jack, implying that the connector follows a standard borrowed
from the telephone industry. This standard designates which wire goes with each
pin inside the connector.
Fig. 2.
RJ-45 connector
Shielded
Twisted Pair (STP) Cable
Although
UTP cable is the least expensive cable, it may be susceptible to radio and
electrical frequency interference (it should not be too close to electric
motors, fluorescent lights, etc.). If you must place cable in environments with
lots of potential interference, or if you must place cable in extremely
sensitive environments that may be susceptible to the electrical current in the
UTP, shielded twisted pair may be the solution. Shielded cables can also help
to extend the maximum distance of the cables.
Shielded
twisted pair cable is available in three different configurations:
1.
Each pair of wires is individually shielded with foil.
2.
There is a foil or braid shield inside the jacket covering all
wires (as a group).
3.
There is a shield around each individual pair, as well as around
the entire group of wires (referred to as double shield twisted pair).
Coaxial
Cable
Coaxial
cabling has a single copper conductor at its center. A plastic layer provides
insulation between the center conductor and a braided metal shield (See fig.
3). The metal shield helps to block any outside interference from fluorescent lights,
motors, and other computers.
Fig. 3.
Coaxial cable
Although
coaxial cabling is difficult to install, it is highly resistant to signal
interference. In addition, it can support greater cable lengths between network
devices than twisted pair cable. The two types of coaxial cabling are thick
coaxial and thin coaxial.
Thin
coaxial cable is also referred to as thinnet. 10Base2 refers to the
specifications for thin coaxial cable carrying Ethernet signals. The 2 refers
to the approximate maximum segment length being 200 meters. In actual fact the
maximum segment length is 185 meters. Thin coaxial cable has been popular in
school networks, especially linear bus networks.
Thick
coaxial cable is also referred to as thicknet. 10Base5 refers to the
specifications for thick coaxial cable carrying Ethernet signals. The 5 refers
to the maximum segment length being 500 meters. Thick coaxial cable has an
extra protective plastic cover that helps keep moisture away from the center
conductor. This makes thick coaxial a great choice when running longer lengths
in a linear bus network. One disadvantage of thick coaxial is that it does not
bend easily and is difficult to install.
Coaxial Cable Connectors
The most
common type of connector used with coaxial cables is the Bayone-Neill-Concelman
(BNC) connector (See fig. 4). Different types of adapters are available for BNC
connectors, including a T-connector, barrel connector, and terminator.
Connectors on the cable are the weakest points in any network. To help avoid
problems with your network, always use the BNC connectors that crimp, rather
screw, onto the cable.
Fig. 4.
BNC connector
Fiber
Optic Cable
Fiber
optic cabling consists of a center glass core surrounded by several layers of
protective materials (See fig. 5). It transmits light rather than electronic
signals eliminating the problem of electrical interference. This makes it ideal
for certain environments that contain a large amount of electrical
interference. It has also made it the standard for connecting networks between
buildings, due to its immunity to the effects of moisture and lighting.
Fiber
optic cable has the ability to transmit signals over much longer distances than
coaxial and twisted pair. It also has the capability to carry information at
vastly greater speeds. This capacity broadens communication possibilities to
include services such as video conferencing and interactive services. The cost
of fiber optic cabling is comparable to copper cabling; however, it is more
difficult to install and modify. 10BaseF refers to the specifications for fiber
optic cable carrying Ethernet signals.
The
center core of fiber cables is made from glass or plastic fibers (see fig 5). A
plastic coating then cushions the fiber center, and Kevlar fibers help to
strengthen the cables and prevent breakage. The outer insulating jacket made of
Teflon or PVC.
Fig. 5.
Fiber optic cable
There are
two common types of fiber cables -- single mode and multimode. Multimode cable
has a larger diameter; however, both cables provide high bandwidth at high
speeds. Single mode can provide more distance, but it is more expensive.
|
Cable Type
|
|
|
10BaseT
|
Unshielded Twisted Pair
|
|
10Base2
|
Thin Coaxial
|
|
10Base5
|
Thick Coaxial
|
|
100BaseT
|
Unshielded Twisted Pair
|
|
100BaseFX
|
Fiber Optic
|
|
100BaseBX
|
Single mode Fiber
|
|
100BaseSX
|
Multimode Fiber
|
|
1000BaseT
|
Unshielded Twisted Pair
|
|
1000BaseFX
|
Fiber Optic
|
|
1000BaseBX
|
Single mode Fiber
|
|
1000BaseSX
|
Multimode Fiber
|
Network Cabling Testing
Testing
has a major significance for the correct functionality of network cabling.
Testing devices are able to measure installed components and determine whether
all requirements defined in the international standards necessary for reliable
operation have been met. For category 5e and Category 6 the following main
parameters are measured:
Wire Map
This
parameter checks the correct termination of cable wires in telecommunication
outlets and patch panels, including the shielding in STP cabling. At the same
time, it checks the signal throughput on the whole cable length-i.e.; it is
able to show any open-circuit or short circuit faults. The Wire Map parameter
is very important but in itself it cannot ensure the correct functionality of
an installed computer network.
T568A and T568B map schemes:
T568A T568B
1. White-green 1. White-orange
2. Green 2. Orange
3. White-orange 3. White-green
4. Blue 4. Blue
5. White-Blue 5. White-blue
6. Orange 6. Green
7. White Brown 7. White-brown
8. Brown 8. Brown
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