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

Documents

theory slide

lans information technology

information flows

lans physical topology

laura denardis slide

metropolitan area networks

lans lana network

network token