cable are held side by side in the same
orientation, the colored wires will be seen in each. If the
order of the colored wires is the same at each end, then the
cable is straight-through as seen in Figure . With crossover,
the RJ-45 connectors on both ends show that some of the wires
on one side of the cable are crossed to a different pin on the
other side of the cable. Figure shows that pins 1 and 2 on one
connector connect respectively to pins 3 and 6 on the other.
Figure shows the guidelines for what type of cable to use when
interconnecting Cisco devices. Use straight-through cables for
the following cabling: - Switch to router
- Switch to PC or server
- Hub to PC or server
Use crossover cables for the following cabling:
- Switch to switch
- Switch to hub
- Hub to
hub
- Router to router
- PC to PC
- Router to PC
Figure illustrates how a variety
of cable types may be required in a given network. The category
of UTP cable required is based on the type of Ethernet that is
chosen. Lab Activity Lab Exercise: RJ-45 Jack Punch
Down This lab is to learn the correct process for terminating
or punching down an RJ-45 jack and to learn the correct
procedure for installing the jack in a wall plate
Interactive Media Activity PhotoZoom: Straight-Through
Cable In this PhotoZoom, the student will view a
straight-through cable. Interactive Media Activity
PhotoZoom: Crossover Cable In this PhotoZoom, the student will
view a crossover cable. Web Links Unshielded Twisted
Pair http://searchnetworking.techtarget.com/sDefinition/
0,,sid7_gci214167,00.html
Content 5.1
Cabling the LAN 5.1.6 Repeaters The term
repeater comes from the early days of long distance
communication. The term describes the situation when a person
on one hill would repeat the signal that was just received from
the person on the previous hill. The process would repeat until
the message arrived at its destination. Telegraph, telephone,
microwave, and optical communications use repeaters to
strengthen signals sent over long distances.A repeater receives
a signal, regenerates it, and passes it on. It can regenerate
and retime network signals at the bit level to allow them to
travel a longer distance on the media. The Four Repeater Rule
for 10-Mbps Ethernet should be used as a standard when
extending LAN segments. This rule states that no more than four
repeaters can be used between hosts on a LAN. This rule is used
to limit latency added to frame travel by each repeater. Too
much latency on the LAN increases the number of late collisions
and makes the LAN less efficient. Web Links Repeater
http://searchnetworking.techtarget.com/ sDefinition/0,,sid7_
gci212890,00.html
Content 5.1 Cabling
the LAN 5.1.7 Hubs Hubs are actually
multiport repeaters. In many cases, the difference between the
two devices is the number of ports that each provides. While a
typical repeater has just two ports, a hub generally has from
four to twenty-four ports. Hubs are most commonly used in
Ethernet 10BASE-T or 100BASE-T networks, although there are
other network architectures that use them as well. Using a hub
changes the network topology from a linear bus, where each
device plugs directly into the wire, to a star. With hubs, data
arriving over the cables to a hub port is electrically repeated
on all the other ports connected to the same network segment,
except for the port on which the data was sent. Hubs come in
three basic types: - Passive – A passive hub
serves as a physical connection point only. It does not
manipulate or view the traffic that crosses it. It does not
boost or clean the signal. A passive hub is used only to share
the physical media. As such, the passive hub does not need
electrical power.
- Active – An active hub must
be plugged into an electrical outlet because it needs power to
amplify the incoming signal before passing it out to the other
ports.
- Intelligent – Intelligent hubs are
sometimes called smart hubs. These devices basically function
as active hubs, but also include a microprocessor chip and
diagnostic capabilities. Intelligent hubs are more expensive
than active hubs, but are useful in troubleshooting situations.
Devices attached to a hub receive all traffic
traveling through the hub. The more devices there are attached
to the hub, the more likely there will be collisions. A
collision occurs when two or more workstations send data over
the network wire at the same time. All data is corrupted when
that occurs. Every device connected to the same network segment
is said to be a member of a collision domain. Sometimes hubs
are called concentrators, because hubs serve as a central
connection point for an Ethernet LAN. Lab Activity Lab
Exercise: Hub and NIC Purchase This lab is to introduce the
variety and prices of network components in the market Web
Links Hub http://searchnetworking.techtarget.com/
sDefinition/ 0,,sid7_ gci212294,00.html
Content
5.1 Cabling the LAN 5.1.8
Wireless A wireless network can be created with much less
cabling than other networks. Wireless signals are
electromagnetic waves that travel through the air. Wireless
networks use Radio Frequency (RF), laser, infrared (IR), or
satellite/microwaves to carry signals from one computer to
another without a permanent cable connection. The only
permanent cabling can be to the access points for the network.
Workstations within the range of the wireless network can be
moved easily without connecting and reconnecting network
cabling.A common application of wireless data communication is
for mobile use. Some examples of mobile use include commuters,
airplanes, satellites, remote space probes, space shuttles, and
space stations. At the core of wireless communication are
devices called transmitters and receivers. The transmitter
converts source data to electromagnetic (EM) waves that are
passed to the receiver. The receiver then converts these
electromagnetic waves back into data for the destination. For
two-way communication, each device requires a transmitter and a
receiver. Many networking device manufacturers build the
transmitter and receiver into a single unit called a
transceiver or wireless network card. All devices in wireless
LANs (WLANs) must have the appropriate wireless network card
installed. The two most common wireless technologies used for
networking are IR and RF. IR technology has its weaknesses.
Workstations and digital devices must be in the line of sight
of the transmitter in order to operate. An infrared-based
network suits environments where all the digital devices that
require network connectivity are in one room. IR networking
technology can be installed quickly, but the data signals can
be weakened or obstructed by people walking across the room or
by moisture in the air. There are, however, new IR technologies
being developed that can work out of sight. Radio Frequency
technology allows devices to be in different rooms or even
buildings. The limited range of radio signals restricts the use
of this kind of network. RF technology can be on single or
multiple frequencies. A single radio frequency is subject to
outside interference and geographic obstructions. Furthermore,
a single frequency is easily monitored by others, which makes
the transmissions of data insecure. Spread spectrum avoids the
problem of insecure data transmission by using multiple
frequencies to increase the immunity to noise and to make it
difficult for outsiders to intercept data transmissions. Two
approaches currently being used to implement spread spectrum
for WLAN transmissions are Frequency Hopping Spread Spectrum
(FHSS) and Direct Sequence Spread Spectrum (DSSS). The
technical details of how these technologies work are beyond the
scope of this course. Web Links Wireless
http://searchnetworking.techtarget.com/ sDefinition/0,,sid7_
gci213380,00.html
Content 5.1 Cabling