Chapter 11 Local Area Networks

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Chapter 11Local Area Networks

• Information Technology in Theory
• By Pelin Aksoy and Laura DeNardis

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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

• 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

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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 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

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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 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

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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 Novells 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
  Xeroxs 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 IEEEs 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 802.11aWireless 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

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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

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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