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.
- Unshielded Twisted Pair (UTP) Cable
- Shielded Twisted Pair (STP) Cable
- Coaxial Cable
- Fiber Optic Cable
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.
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) | 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. 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.
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. 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.
- There is a shield around each individual pair, as well as around the entire group of wires.
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.
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. 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 connectorFiber Optic Cable
Fiber optic cabling consists of a center glass core surrounded by
several layers of protective materials. 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. 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.
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.
VIDEO!!!!
| 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 |
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