Information Technology in Theory
By Pelin Aksoy and Laura DeNardis
Chapter 11
Local Area Networks
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
Information Technology in Theory
2
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
Information Technology in Theory
3
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)
Information Technology in Theory
4
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
Information Technology in Theory
5
Resources Accessed via LANs
Information Technology in Theory
6
LAN Design Characteristics
•
•
•
•
•
Physical topology
Logical topology
Access control and LAN switching
LAN physical media and equipment
LAN operating systems
Information Technology in Theory
7
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
Information Technology in Theory
8
Star Topology
Information Technology in Theory
9
Ring Topology
Information Technology in Theory
10
Star-Wired Ring Topology
Information Technology in Theory
11
Bus Topology
Information Technology in Theory
12
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
Information Technology in Theory
13
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
Information Technology in Theory
14
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
Information Technology in Theory
15
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
Information Technology in Theory
16
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
Information Technology in Theory
17
Gigabit LAN Switches
Information Technology in Theory
18
LAN Switching
Information Technology in Theory
19
LAN Physical Media and
Equipment
•
•
•
•
•
•
Network interface controller
Transmission media
Wiring hubs
High-speed switches
Routers
Servers
Information Technology in Theory
20
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
Information Technology in Theory
21
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 fiberoptic cable
• WLANs use radio frequency communications
rather than fiber-optic cable or copper cable
Information Technology in Theory
22
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
Information Technology in Theory
23
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
Information Technology in Theory
24
LAN Types
•
•
•
•
Information Technology in Theory
Ethernet
Token ring
FDDI
Wireless LANs
25
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
Information Technology in Theory
26
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
Information Technology in Theory
27
10/100-Mbps Switch
Information Technology in Theory
28
Ethernet Frame Format
Information Technology in Theory
29
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
Information Technology in Theory
30
Token Structure
Information Technology in Theory
31
Token Ring Network
Information Technology in Theory
32
Token Ring Frame Format
Information Technology in Theory
33
FDDI LAN
Information Technology in Theory
34
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
Information Technology in Theory
35
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
Information Technology in Theory
36
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
Information Technology in Theory
37
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
Information Technology in Theory
38
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
Information Technology in Theory
39
Home LAN Implementation
Information Technology in Theory
40
Business WLAN Implementation
Information Technology in Theory
41
WLAN Advantages
• Mobility
• Flexibility
Information Technology in Theory
42
WLAN Disadvantages
• Security
• Range limitations
• Bandwidth
• Manageability
Information Technology in Theory
43
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
Information Technology in Theory
44
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)
Information Technology in Theory
45
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
Information Technology in Theory
46
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
47