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.
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
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
|
LocalTalk & Telephone (Rarely used)
|
3
|
16 Mbps
|
10BaseT Ethernet
|
4
|
20 Mbps
|
Token Ring (Rarely used)
|
5
|
100 Mbps (2 pair)
1000 Mbps (4 pair)
|
100BaseT 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.
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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:
- Each pair of wires is
individually shielded with foil.
- There is a foil or braid shield
inside the jacket covering all wires (as a group).
- 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. The metal shield helps to block any outside interference from fluorescent
lights, motors, and other computers.
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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.
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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.
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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.
|
Specification
|
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
|
