The document provides an introduction to networking and local area networks (LANs). It discusses network fundamentals including different types of networks such as WANs, MANs, LANs and PANs. It also covers common LAN topologies like star, ring, bus and mesh. The document then describes various LAN hardware components including cables, connectors, repeaters, hubs, bridges, switches and routers.

1. 1
Introduction to Networking
and Local-Area Networks
© 2008 The McGraw-Hill Companies

2. 2
Topics Covered
 Network Fundamentals
 LAN Hardware
 Ethernet LANs
 Token-Ring LAN
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12-1: Network Fundamentals
 A network is a communication system with two or
more stations that can communicate with one another.
 When it is desired to have each computer
communicate with two or more additional computers,
the interconnections can become complex.
 The number of links L required between N PCs
(nodes) is determined by using the formula
L = N(N−1) / 2
 The number of links or cables increases in proportion
to the number of nodes involved
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Network Fundamentals
 Each computer or user in
a network is referred to
as a node.
 The interconnection
between the nodes is
referred to as the
communication link.
A network of four PCs.
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Network Fundamentals
Types of Networks
 There are four basic types of networks:
 Wide-area networks (WANs),
 Metropolitan-area networks (MANs)
 Local-area networks (LANs)
 Personal-area networks (PANs)
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Network Fundamentals
Wide-Area Networks (WANs)
 A WAN covers a significant geographical area.
 Local telephone systems are WANs, as are the many
long-distance telephone systems linked together across
the country and to WANs in other countries.
 The nationwide and worldwide fiber-optic networks set
up since the mid-1990s to carry Internet traffic are also
WANs.
 Known as the Internet core or backbone, these high-
speed interconnections are configured as either direct
point-to-point links or large rings with multiple access
points
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Network Fundamentals
Metropolitan-Area Networks (MANs)
 MANs are smaller than WANs and generally cover a
city, town, or village.
 Cable TV systems are MANs.
 Other types of MANs, or metro networks as they are
typically called, carry computer data.
 MANs are usually fiber-optic rings encircling a city that
provide local access to users. Businesses,
governments, schools, hospitals, and others connect
their internal LANs to them.
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Network Fundamentals
Local-Area Networks (LANs)
 A LAN is the smallest type of network in general use.
 A LAN consists primarily of personal computers
interconnected within an office or building.
 LANs can have as few as three to five users, although
most systems connect to several thousand users.
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Network Fundamentals
Personal-Area Networks (PANs).
 A PAN is a short-range wireless network that is set up
automatically between two or more devices such as
laptop computers, personal digital assistants (PDAs),
peripheral devices, or cell phones.
 The distance between the devices is very short, no
more than about 10 m and usually much less.
 PANs are referred to as ad hoc networks that are set up
for a specific single purpose, such as the transfer of
data between the devices as required by some
application.
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Network Fundamentals
Storage-Area Networks (SANs)
 SANs are an outgrowth of the massive data storage
requirements developed over the years
 These networks usually attach to a LAN or Internet
server and store and protect huge data files.
 The SAN also provides network users access to
massive data files stored in mass memory units, called
redundant arrays of independent disks (RAIDs).
 RAIDs use many hard drives interconnected to the
network and may be located anywhere since access
can be via the Internet or a fiber-optic WAN or MAN.
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Network Fundamentals
Network Topologies
 The topology of a network describes the basic
communication paths between, and methods used to
connect, the nodes on a network.
 The three most common topologies used in LANs are
star, ring, and bus.
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Network Fundamentals
Star Topology
 A basic star configuration
consists of a central
controller node and multiple
individual stations
connected to it.
 The central or controlling
PC, often referred to as the
server, is typically larger
and faster than the other
PCs and contains a large
hard drive where shared
data and programs are
stored.
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Network Fundamentals
Star Topology
 A star-type LAN is extremely simple and
straightforward.
 New nodes can be quickly and easily added to the
system, and the failure of one node does not disable the
entire system.
 If the server node goes down, the network is disabled
but individual PCs will continue to operate
independently.
 Star networks generally require more cable tha other
network topologies
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Network Fundamentals
Ring Topology
 In a ring configuration,
the server or main
control computer and all
the computers are simply
linked together in a
single closed loop.
 Usually, data is
transferred around the
ring in only one direction,
passing through each
node.
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 The ring topology is easily implemented and low in
cost.
 The downside of a ring network is that a failure in a
single node generally causes the entire network to go
down.
 It is also difficult to diagnose problems on a ring.
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Network Fundamentals
Bus Topology
 A bus is a common cable to
which all of the nodes are
attached.
 The bus is bidirectional in that
signals can be transmitted in
either directions between any
two nodes.
 Only one node can transmit at
a given time.
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 A signal to be transmitted can be destined for a single node, or
transmitted or broadcast to all nodes simultaneously.
 The bus is faster than other topologies, wiring is simple, and the bus
can be easily expanded
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Network Fundamentals
Mesh Topology
 A mesh network is one
in which each node is
connected to all other
nodes.
 In a full mesh, every
node can talk directly to
any other node.
 There are major costs
and complications as the
number of nodes
increases
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Network Fundamentals
Other Topologies.
 The daisy chain topology is
a ring that has been broken.
 The tree topology is a bus
design in which each node
has multiple interconnections
to other nodes through a star
interconnection.
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Network Fundamentals
Client-Server and Peer-to-Peer LANs
 Most LANs conform to one of two general
configurations: client-server or peer-to-peer.
 In the client-server type, one of the computers in the
network, the server, essentially runs the LAN and
determines how the system operates.
 The server manages printing operations of a central
printer and controls access to a very large hard drive or
bank of hard drives containing databases, files, and
other information that the clients—the other computers
on the network—can access.
 The server also provides Internet access.
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Network Fundamentals
 In a peer-to-peer system, any PC can serve as either
client or server; any PC can have access to any other
PC’s files and connected peripherals.
 Peer-to-peer LANs are smaller and less expensive than
the client-server variety, and provide a simple way to
provide network communication.
 Disadvantages include:
 Lower performance (lower-speed transmission capability).
 Manageability and security problems (any user may
access any other user’s files).
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LAN Hardware
 All LANs are a combination of hardware and software.
 The primary hardware devices are the computers,
cables, and connectors.
 Additional hardware includes:
 Network interface cards (NICs)
 Repeaters
 Hubs and concentrators
 Bridges
 Routers
 Gateways
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LAN Hardware
Cables
 Most LANs use some type of copper wire cable to
carry data from one computer to another via baseband
transmission.
 The three basic cable types are:
1. Coaxial cable
2. Twisted pair
3. Fiber-optic cable
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LAN Hardware
: Coaxial cable.
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LAN Hardware
Types of twisted-pair cable. (a) Twisted-pair unshielded (UTP) cable. (b) Multiple
shielded twisted-pair (STP) cable.
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12-2: LAN Hardware
Twisted-Pair Cable
 The most widely used UTP is category 5 (CAT5). It can
carry baseband data at rates up to 100 Mbps at a range
up to 100 m.
 Twisted-pair cable specifications also include
attenuation and near-end cross talk figures.
 Attenuation means the amount by which the cable
attenuates the signal. The longer the cable, the greater
the amount of loss in the cable and the smaller the
output.
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LAN Hardware
Twisted-Pair Cable
 Cross talk refers to the signal
transferred from one twisted pair
in a cable to another by way of
capacitive and inductive coupling.
Near-end cross talk is the signal
appearing at the input to the
receiving end of the cable.
 Many newer office buildings are
constructed with special vertical
channels or chambers, called
plenums, through which cables
are run between floors or across
ceilings.
 Cable used this way, called
plenum cable, must be made of
fireproof material that will not emit
toxic fumes if it catches fire.
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LAN Hardware
Fiber-optic cable.
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LAN Hardware
Coaxial Cable Connectors
 Coaxial cables in networks use two types of
connectors:
1. N connectors are widely used in RF applications
2. BNC (Bayonet Neill-Concelman )connectors are
commonly used for attaching test leads to
measuring instruments such as oscilloscopes.
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LAN Hardware
Connectors: Coaxial Cable Connectors
 BNC T connectors are used to interconnect two cables
to the network hardware.
 The barrel connector provides a convenient way to
connect two coaxial cables.
 A terminator is a special connector containing a
resistor whose value is equal to the characteristic
impedance of the coaxial cable (typically 50Ω).
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LAN Hardware
Common coaxial connectors.
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LAN Hardware
BNC connector accessories and adapters. (a) T connector. (b) Barrel connector.
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LAN Hardware
Connectors: Twisted-Pair and Fiber-Optic Connectors
 Most telephones attach to an outlet by way of an RJ-11
connector or modular plug.
 RJ-11 connectors are used to connect PC modems to
the phone line but are not used in LAN connections.
 A larger modular connector known as the RJ-45 is
widely used in terminating twisted pairs.
 A wide range of connectors are available to terminate
fiber-optic cables.
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LAN Hardware
Modular (telephone) connectors used with twisted-pair cable. (a) RJ-11. (b) RJ-45.
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LAN Hardware
Repeater
 A repeater is an electronic circuit that takes a partially
degraded signal, boosts its level, shapes it up, and
sends it on its way.
 Repeaters are small, inexpensive devices that can be
inserted into a line with appropriate connectors or built
into other LAN equipment.
 Most repeaters are really transceivers, bidirectional
circuits that can both send and receive data.
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LAN Hardware
Concept of a repeater.
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LAN Hardware
Hub
 A hub is a central connecting box designed to receive
the cable inputs from the various PC nodes and to
connect them to the server.
 In most cases, hub wiring physically resembles a star
because all cabling comes into a central point, or hub.
 Hubs are usually active devices containing repeaters.
They amplify and reshape the signal and transmit it to
all connection parts.
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LAN Hardware
A hub facilitates interconnections to the server.
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LAN Hardware
Bridges
 A bridge is a network device that is connected as a
node on a network and performs bidirectional
communication between two LANs.
 A bridge is generally designed to interconnect two LANs
with the same protocol, for example, two Ethernet
networks, although some perform protocol conversion.
 Remote bridges are special bridges used to connect
two LANs that are separated by a long distance.
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LAN Hardware
A bridge connects two LANs.
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LAN Hardware
Switch
 A switch is a hublike device
that is used to connect
individual PC nodes to the
network wiring.
 A switch provides a means to
connect or disconnect a PC
from the network wiring.
 Switches have largely
replaced hubs in most large
LANs because they greatly
expand the number of
possible nodes and improve
performance.
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LAN Hardware
Router
 Routers are designed to
connect two networks.
 The main difference between
bridges and routers is that
routers are intelligent devices
that have decision-making and
switching capabilities.
 The basic function of a router
is to expedite traffic flow on
both networks and maintain
maximum performance.
 Some routers are a
combination of a bridge and a
router.
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LAN Hardware
Gateway
 A gateway is another internetwork device that acts as
an interface between two LANs or between a LAN and
a larger computer system.
 The primary benefit of a gateway is that it can connect
networks with incompatible protocols and
configurations.
 The gateway acts as a two-way translator that allows
systems of different types to communicate.
 Most gateways are computers and are sometimes
referred to as gateway servers.
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LAN Hardware
A gateway commonly connects a LAN to a larger host computer.
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LAN Hardware
Modem
 Modems are interfaces between PCs and standard
telephone systems.
 Modems convert the binary signals of the computer into
audio-frequency analog signals compatible with the
telephone system and, at the other end, convert the
analog signals back into digital signals.
 The most common application is one in which remote
PCs use modems to connect to an Internet service
provider (ISP) which provides services such as Internet
access and e-mail.
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Ethernet LANs
 One of the oldest and by far the most widely used of all LANs is
Ethernet.
 Ethernet was originally developed by Xerox from an earlier
specification called Alohanet (for the Palo Alto Research Center Aloha
network) and then developed further by Xerox, DEC, and Intel
 Ethernet was named by Robert Metcalfe, one of its developers, for the
passive substance called "luminiferous (light-transmitting) ether" that
was once thought to pervade the universe, carrying light throughout.
Ethernet was so- named to describe the way that cabling, also a
passive medium, could similarly carry data everywhere throughout the
network
 The original versions of Ethernet used a bus topology. Today, most
use a physical star configuration.
 Ethernet uses baseband data-transmission methods.
 The serial data to be transmitted is placed directly on the bus media.
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Ethernet LANs
The Ethernet bus.
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Ethernet LANs
Speed
 The standard transmission speed for Ethernet LANs is
10 Mbps.
 The most widely used version of Ethernet is called Fast
Ethernet (100BASE-T). It has a speed of 100 Mbps.
 Other versions of Ethernet run at speeds of 1 Gbps or
10 Gbps, typically over fiber-optic cable but also on
shorter lengths of coaxial or twisted-pair cable.
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Ethernet LANs
Transmission Medium: Coaxial Cable
 The original transmission medium for Ethernet was
coaxial cable. However, today twisted-pair versions of
Ethernet are more popular.
 The two main types of coaxial cable used in Ethernet
networks are RG-8/U and RG-58/U.
 RG-8/U cable is known as thick cable, and large type-
N coaxial connectors are used to make the
interconnections.
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Ethernet LANs
Transmission Medium: Coaxial Cable
 Ethernet systems using thick coaxial cable are generally
referred to as 10Base-5 systems:
 10 means a 10-Mbps speed
 Base means baseband operation
 5 designates a 500-m maximum distance between
nodes, transceivers, or repeaters.
 Ethernet LANs using thick cable are also referred to as
Thicknet.
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Ethernet LANs
The Ethernet (10Base-5) bus.
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Ethernet LANs
Transmission Medium: Coaxial Cable
 Ethernet systems implemented with thinner coaxial
cable are known as 10Base-2, or Thinnet systems.
 The 2 indicates the maximum 200-m (actually, 185-m)
run between nodes or repeaters.
 The most widely used thin cable is RG-58/U.
 It is much more flexible and easier to work with than
RG-8/U cable.
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12-3: Ethernet LANs
10Base-2 coaxial Ethernet bus.
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12-3: Ethernet LANs
Transmission Medium: Twisted-Pair Cable
 More recent versions of Ethernet use twisted-pair cable.
 The twisted-pair version of Ethernet is referred to as a
10Base-T network, where the T stands for twisted-pair.
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12-3: Ethernet LANs
Transmission Medium: Gigabit Ethernet
 Gigabit Ethernet (1 GE) is capable of achieving 1000
Mbps or 1 Gbps over category 5 UTP or fiber-optic
cable.
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Token-Ring LAN
 In the Token-Ring configuration, all of the nodes or PCs in
the network are connected end to end in a continuous circle
or loop.
 Data in the network travels in only one direction on the ring.
 The transmitted information passes through the NICs of each
PC in the loop.
 Token Ring uses baseband transmission; the binary data is
placed directly on the cable.
 Token-ring LANs use twisted pair cable and connections are
made by using RJ-45 modular connectors.
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Token-Ring LAN
Token-Ring wiring.
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