9781423901402_PPT_Ch11

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Oct 26, 2013 (3 years and 9 months ago)

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Chapter 11

Local Area Networks

Information Technology in Theory

By Pelin Aksoy and Laura DeNardis

2

Objectives


Gain familiarity with the most popular types of
local area networks (LANs), with a focus on
Ethernet


Understand LAN design characteristics, including
topology, access mechanism, physical
transmission media, and equipment

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Objectives (continued)


Explain what a frame format is and what purpose
it serves in LANs


Define the functions of LAN operating systems


Understand the technical architecture of Wi
-
Fi

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Network Categories


Local area networks (LANs)


Wide area networks (WANs)


Personal area networks (PANs)


Metropolitan area networks (MANs)


Campus area networks (CANs)


Storage area networks (SANs)


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Defining LANs


LAN

a network that spans a confined
geographical distance, such as a building or home


WAN

a network that spans a larger geographical
area, such as a city, nation, or the world at large


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Resources Accessed via LANs

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LAN Design Characteristics


Physical topology


Logical topology


Access control and LAN switching


LAN physical media and equipment


LAN operating systems

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Physical Topology


A LAN’s
physical topology

refers to how the
multiple devices (often called network
nodes
) are
physically connected to each other


Star


Ring


Star
-
Wired Ring


Bus


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Star Topology

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Ring Topology

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Star
-
Wired Ring Topology

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Bus Topology

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Logical Topology


While the physical topology describes how
network nodes are connected within the LAN, the
logical topology

dictates how information flows
among the nodes


Common logical topologies for LANs


Bus


Ring


Star

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Access Control and LAN
Switching


Access control mechanism


A procedure that specifies and enforces rules
for when each device may transmit or receive
information over a network


Token passing


CSMA/CD


CSMA/CA

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Token Passing


Uses a
deterministic

access method


Each node communicates only during its specified
turn


A
token
, which is just a signal that comprises a
specific bit pattern, is transmitted from one device
to the next in a sequential pattern


When a device receives this signal, it “possesses
the token,” meaning it may transmit information

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CSMA/CD


CSMA/CD is
nondeterministic


Any device may transmit information at any given
moment, provided that no signals are already being
transmitted over the LAN


A node preparing to transmit information first
“listens” to the network to determine whether
transmissions are occurring


The node starts to transmit only if it detects that
the network is free of transmissions

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CSMA/CA


In some LANs, such as wireless LANs, collisions
cannot be detected


Using CSMA/CA, a node that has information to
transmit first listens to the network to see if
another node is transmitting


If the network is idle, it sends a “request to send”
(RTS) packet to other nodes


The other nodes can then send a “clear to send”
(CTS) packet, alerting the transmitting node that it
is free to send data

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Gigabit LAN Switches

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LAN Switching

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LAN Physical Media and
Equipment


Network interface controller


Transmission media


Wiring hubs


High
-
speed switches


Routers


Servers

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Network Interface Controller


Built into the computer’s motherboard


Basically a small card with a couple of integrated
circuits and other electronic components


Provides the physical interface to a network
medium or wireless LAN and supports an
addressing system that is critical to the LAN’s
operation

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Transmission Media


The most common LAN transmission media are
free space, fiber
-
optic cable, twisted pair, or
some combination


Many LANs connect devices using a
combination of twisted pair cable and fiber
-
optic cable


WLANs use radio frequency communications
rather than fiber
-
optic cable or copper cable

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LAN Operating Systems


Software


Sometimes called a network operating system
(NOS) or a server operating system


Some computer operating systems, like UNIX,
Linux, and Windows NT have built
-
in
networking features


Other software, like Novell’s Netware, has
specifically been designed as a
LAN operating
system

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LAN Operating Systems (continued)


Manage and control networked access to LAN
resources such as printers, files, applications,
and messaging services


Provide security by managing user directories,
monitoring remote LAN access, and
incorporating encryption and other security
features


Provide network management, including
diagnostic tools

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LAN Types


Ethernet


Token ring


FDDI


Wireless LANs

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LAN Characteristics


Shared or switched access method


Topology (ring, bus, star)


Medium (twisted pair, free space, fiber)


Speed, distance


Cost


Performance, mobility


Manageability


Number of devices supported


Frame format

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Ethernet LANs


Originally developed in 1976 by Bob Metcalfe at
Xerox’s Palo Alto Research Center (PARC)


IEEE 802.3 standard



Commonly implemented over free space, twisted
pair cable, or fiber
-
optic cable

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10/100
-
Mbps Switch

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Ethernet Frame Format

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Token Ring and FDDI


Not as popular as Ethernet


Token Ring


Ring configuration


Token passing access method


FDDI


Dual ring configuration


Fiber


Token passing access method

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Token Structure

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Token Ring Network

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Token Ring Frame Format

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FDDI LAN

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Wireless LANs


WLAN: wireless local area network


Use radio
-
frequency signals, rather than light or
electricity over cables, to connect users within a
limited geographical range


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Wi
-
Fi


Predominant WLAN implementation is known as
Wi
-
Fi

(wireless fidelity)


A catchy designation indicating that a product
complies with the IEEE’s 802.11 wireless Ethernet
specifications


Uses a carrier radio frequency in the unlicensed
2.4
-
GHz or 5
-
GHz range

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WLAN Standards


IEEE 802.11a

Wireless technology operating at
a frequency of 5 GHz with a maximum data rate
of 54 Mbps


IEEE 802.11b

Wi
-
Fi wireless technology
operating at a frequency of 2.4 GHz with a
maximum data rate of 11 Mbps


IEEE 802.11g

Backward compatible with
802.11b, operating at a frequency of 2.4 GHz and
a maximum data rate of 54 Mbps

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WLAN Standards (continued)


IEEE 802.11i

Standards for wireless security
mechanisms


IEEE 802.15

Known as WPAN, or wireless
personal area networks


IEEE 802.16

WiMAX, an emerging technology
that seeks to provide high
-
speed wireless access
over much longer distances than implementations
of the IEEE 802.11 standards


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Personal WLANs


A home
-
based wireless LAN uses a
wireless
access point
(WAP)


A device that connects wireless computers to a wired
network to enable high
-
speed Internet access and other
services


Laptops with an installed wireless adapter then
communicate with the WAP over the 2.4
-
GHz or
5
-
GHz frequency range

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Home LAN Implementation

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Business WLAN Implementation

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WLAN Advantages


Mobility


Flexibility

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WLAN Disadvantages


Security


Range limitations


Bandwidth


Manageability


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Municipal Broadband Wireless


Some cities and municipalities offer public
Internet access via Wi
-
Fi network access points in
parks, libraries, and other public locations


These networks are driven by economic, political,
and technical factors

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Summary


A network shares information using a set of
hardware and software designed to interconnect
multiple computers, communication devices, and
other types of devices


Categorizing networks is somewhat arbitrary, but
in the networking industry, the most common
categories are local area networks (LANs) and
wide area networks (WANs)


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Summary (continued)


LANs are networks that span a relatively small
geographical area, such as the floor of an office or
a house; LANs interconnect local computing
resources and provide WAN access


WANs are networks that span a large geographical
area such as a city, a country, or the world at large


The Internet is the most important example of a WAN


Chapter 12 discusses WANs in detail


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Summary (continued)


Some design characteristics of LANs include
topology (such as bus, star, and ring), access
method (such as CSMA/CD, CSMA/CA, or token
passing), and type of medium (wireless, fiber,
twisted pair)


Ethernet, including switched Ethernet, has become
the most prevalent type of local area network


Some wireless local area networks (WLANs)
include the IEEE 802.11b and IEEE 80211g
standards, more commonly called Wi
-
Fi


WLANs have great advantages, including mobility and
flexibility, but they also present security challenges

Information Technology in Theory