Post on 14-Dec-2015
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
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