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Chapter 11 Local Area Networks

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Title: Chapter 11 Local Area Networks


1
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

3
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

4
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)

5
Defining LANs
  • LANa network that spans a confined geographical
    distance, such as a building or home
  • WANa network that spans a larger geographical
    area, such as a city, nation, or the world at
    large

6
Resources Accessed via LANs
7
LAN Design Characteristics
  • Physical topology
  • Logical topology
  • Access control and LAN switching
  • LAN physical media and equipment
  • LAN operating systems

8
Physical Topology
  • A LANs physical topology refers to how the
    multiple devices (often called network nodes) are
    physically connected to each other
  • Star
  • Ring
  • Star-Wired Ring
  • Bus

9
Star Topology
10
Ring Topology
11
Star-Wired Ring Topology
12
Bus Topology
13
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

14
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

15
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

16
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

17
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

18
Gigabit LAN Switches
19
LAN Switching
20
LAN Physical Media and Equipment
  • Network interface controller
  • Transmission media
  • Wiring hubs
  • High-speed switches
  • Routers
  • Servers

21
Network Interface Controller
  • Built into the computers 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 LANs operation

22
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

23
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 Novells Netware, has
    specifically been designed as a LAN operating
    system

24
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

25
LAN Types
  • Ethernet
  • Token ring
  • FDDI
  • Wireless LANs

26
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

27
Ethernet LANs
  • Originally developed in 1976 by Bob Metcalfe at
    Xeroxs Palo Alto Research Center (PARC)
  • IEEE 802.3 standard
  • Commonly implemented over free space, twisted
    pair cable, or fiber-optic cable

28
10/100-Mbps Switch
29
Ethernet Frame Format
30
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

31
Token Structure
32
Token Ring Network
33
Token Ring Frame Format
34
FDDI LAN
35
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

36
Wi-Fi
  • Predominant WLAN implementation is known as Wi-Fi
    (wireless fidelity)
  • A catchy designation indicating that a product
    complies with the IEEEs 802.11 wireless Ethernet
    specifications
  • Uses a carrier radio frequency in the unlicensed
    2.4-GHz or 5-GHz range

37
WLAN Standards
  • IEEE 802.11aWireless technology operating at a
    frequency of 5 GHz with a maximum data rate of 54
    Mbps
  • IEEE 802.11bWi-Fi wireless technology operating
    at a frequency of 2.4 GHz with a maximum data
    rate of 11 Mbps
  • IEEE 802.11gBackward compatible with 802.11b,
    operating at a frequency of 2.4 GHz and a maximum
    data rate of 54 Mbps

38
WLAN Standards (continued)
  • IEEE 802.11iStandards for wireless security
    mechanisms
  • IEEE 802.15Known as WPAN, or wireless personal
    area networks
  • IEEE 802.16WiMAX, an emerging technology that
    seeks to provide high-speed wireless access over
    much longer distances than implementations of the
    IEEE 802.11 standards

39
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

40
Home LAN Implementation
41
Business WLAN Implementation
42
WLAN Advantages
  • Mobility
  • Flexibility

43
WLAN Disadvantages
  • Security
  • Range limitations
  • Bandwidth
  • Manageability

44
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

45
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)

46
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

47
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
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