Chapter 11 Local Area Networks Information Technology in Theory By Pelin Aksoy and Laura DeNardis.

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

• 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


Chapter 11 Local Area Networks Information Technology in Theory By Pelin Aksoy and Laura DeNardis.

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