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 (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).
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
(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
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
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 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
|
More and
more networks are operating without cables, in the wireless mode. Wireless LANs
use high frequency radio signals, infrared light beams, or lasers to
communicate between the workstations, servers, or hubs. Each workstation and
file server on a wireless network has some sort of transceiver/antenna to send
and receive the data. Information is relayed between transceivers as if they
were physically connected. For longer distance, wireless communications can
also take place through cellular telephone technology, microwave transmission,
or by satellite.
Wireless
networks are great for allowing laptop computers, portable devices, or remote
computers to connect to the LAN. Wireless networks are also beneficial in older
buildings where it may be difficult or impossible to install cables.
The two
most common types of infrared communications used in schools are line-of-sight
and scattered broadcast. Line-of-sight communication means that there must be
an unblocked direct line between the workstation and the transceiver. If a
person walks within the line-of-sight while there is a transmission, the
information would need to be sent again. This kind of obstruction can slow down
the wireless network. Scattered infrared communication is a broadcast of
infrared transmissions sent out in multiple directions that bounces off walls
and ceilings until it eventually hits the receiver. Networking communications
with laser are virtually the same as line-of-sight infrared networks.
Wireless standards and speeds
The Wi-Fi
Alliance is a global, non-profit organization that helps to ensure standards
and interoperability for wireless networks, and wireless networks are often
referred to as WiFi (Wireless Fidelity). The original Wi-Fi standard (IEEE
802.11) was adopted in 1997. Since then many variations have emerged (and will
continue to emerge). Wi-Fi networks use the Ethernet protocol.
Standard
|
Max Speed
|
Typical Range
|
802.11a
|
54 Mbps
|
150
feet
|
802.11b
|
11 Mbps
|
300
feet
|
802.11g
|
54 Mbps
|
300
feet
|
802.11n
|
100
Mbps
|
300+
feet
|
Wireless Security
Wireless
networks are much more susceptible to unauthorized use than cabled networks.
Wireless network devices use radio waves to communicate with each other. The
greatest vulnerability to the network is that rogue machines can
"eves-drop" on the radio wave communications. Unencrypted information
transmitted can be monitored by a third-party, which, with the right tools
(free to download), could quickly gain access to your entire network, steal
valuable passwords to local servers and online services, alter or destroy data,
and/or access personal and confidential information stored in your network
servers. To minimize the possibility of this, all modern access points and
devices have configuration options to encrypt transmissions. These encryption
methodologies are still evolving, as are the tools used by malicious hackers,
so always use the strongest encryption available in your access point and
connecting devices.
Encryption.
Enable the strongest encryption
supported by the devices you will be connecting to the network. Use strong
passwords (strong passwords are generally defined as passwords containing
symbols, numbers, and mixed case letters, at least 14 characters long).
Isolation.
Use a wireless router that places
all wireless connections on a subnet independent of the primary private
network. This protects your private network data from pass-through internet
traffic.
Hidden
SSID.
Every access point has a Service
Set IDentifier (SSID) that by default is broadcast to client devices so that
the access point can be found. By disabling this feature, standard client
connection software won't be able to "see" the access point. However,
the eves-dropping programs discussed previously can easily find these access
points, so this alone does little more than keep the access point name out of
sight for casual wireless users.
Advantages of wireless networks:
- Mobility - With a laptop computer or mobile device, access can be available throughout a school, at the mall, on an airplane, etc. More and more businesses are also offering free WiFi access ("Hot spots").
- Fast setup - If your computer has a wireless adapter, locating a wireless network can be as simple as clicking "Connect to a Network" -- in some cases, you will connect automatically to networks within range.
- Cost - Setting up a wireless network can be much more cost effective than buying and installing cables.
- Expandability - Adding new computers to a wireless network is as easy as turning the computer on (as long as you do not exceed the maximum number of devices).
Disadvantages of wireless networks:
- Security - Be careful. Be vigilant. Protect your sensitive data with backups, isolated private networks, strong encryption and passwords, and monitor network access traffic to and from your wireless network.
- Interference - Because wireless networks use radio signals and similar techniques for transmission, they are susceptible to interference from lights and electronic devices.
- Inconsistent connections - How many times have you hears "Wait a minute, I just lost my connection?" Because of the interference caused by electrical devices and/or items blocking the path of transmission, wireless connections are not nearly as stable as those through a dedicated cable.
- Speed - The transmission speed of wireless networks is improving; however, faster options (such as gigabit Ethernet) are available via cables. If you are only using wireless for internet access, the actual internet connection for your home or school is generally slower than the wireless network devices, so that connection is the bottleneck. If you are also moving large amounts of data around a private network, a cabled connection will enable that work to proceed much faster.
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