Chapter 7 Chapter 7 Introduction to Introduction to

Local Area Local Area NetworksNetworks

Part II: Understanding Internet Access Part II: Understanding Internet Access TechnologiesTechnologies

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Topics Addressed in Chapter Topics Addressed in Chapter 77

• What is a local area network?• Business rationale for LANs• LAN alternatives• Emerging alternatives to full-fledged LANs• LAN components• Communication media• Wiring center options and LAN adapters• Print servers and backup devices• Storage area networks• LAN-to-host interfaces

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What is a Local Area What is a Local Area Network?Network?

• A local area network (LAN) is a data communication network that serves users in a confined geographic area and uses high transmission speeds (typically 10 mbps to 1 gbps)

• Major LAN components include servers, workstations, network operating systems, communication links, and wiring center technologies

• LANs are fundamental building blocks for enterprise-wide networks

• LANs are the a primary means for business users to access and leverage the Internet

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Business Rationale for LANsBusiness Rationale for LANs

• Some of the major drivers of business interest in LANs are:– cost-effective via resource sharing– support of work groups– potential for management control over

computing resources– modular expansion– ability to adapt to changing hardware and

software requirements– wide variety of LAN alternatives

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LAN AlternativesLAN Alternatives• LAN alternatives include

– full-fledged LANs with dedicated servers– peer-to-peer LANs with non-dedicated servers– centralized host-based networks with terminals (see

Figure 7-1)– interconnections via service bureaus or application

service providers– zero-slot LANs– sub-LANs with data switches (see Figure 7-2 and Figure

7-3)

• Table 7-1 compares several of these alternatives on a variety of dimensions

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Figure 7-Figure 7-33

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Table 7-1Table 7-1

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Emerging Alternatives to Emerging Alternatives to Full-Fledged LANsFull-Fledged LANs

• Additional alternatives to full-fledged LANs have become increasingly popular. These include:– cable-based home (and SOHO) networks

• CEBus (Consumer Electric Bus) and HomePnP networks• HomePNA (Home PhoneLine Networking Alliance) networks

– wireless home networks• HomeRF• WiFi & other IEEE 802.11 WLANs

– personal area networks (PANs)• wireless PANs (WPANs)

– Bluetooth– IrDA

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LAN ComponentsLAN Components• Full-fledged LANs have several major

components (see Figure 7-4):– servers– workstations (clients)– communication media– wiring center technologies– network interface cards (LAN adapters)– LAN software

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Figure 7-4Figure 7-4

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ServersServers• Servers enable network users to access shared computing

and communication services. A variety of servers are found in LANs including:– File servers– Print servers– Database servers– Application servers– Fax servers– Remote access servers– Communication servers– Terminal servers– Thin client servers– Citrix™ servers

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File, Database, and File, Database, and Application ServersApplication Servers

• File servers are used to provide user access to data, programs, and other files stored on the server’s disk drives (see Figure 7-5)– When a user requests a file on a file server, the entire file is

sent to the user over the LAN’s communication medium• Database servers enable users to access records and also

performs some database processing. For example, in response to a user’s request for a count of the total number of records in the database that meet certain conditions, a database server would send the total, not copies of all the records– SQL Server is an example of a database server (see Figure

7-6)• Application servers provide server-side application processing

for network users

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Server ConfigurationServer Configuration• A server is a combination of hardware and

software. Key aspects of server hardware include:– Disk drive capacity and performance capabilities (access

time, disk controllers [EIDE vs. SCSI], etc.)– Memory (including sufficient RAM and cache memory;

virtual memory management; ECC [error-correcting code] memory, etc.)

– Processor(s) and processor speed (including SMP [symmetrical multiprocessing])

– Expansion capabilities (ability to add new peripherals or to create server clusters)

– System bus speed and architecture– Expansion bus architecture (EISA vs. PCI vs. Infiniband,

etc.)

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WorkstationsWorkstations• Most LAN workstations are microcomputers. Like

servers, workstation configuration is an important determinant of performance. Key configuration considerations include:– Memory– Processor version and speed– System bus architecture– Expansion bus architecture

• Thin clients, diskless workstations, and terminals may also be found in LANs

• Docking stations and wireless connections can be used to enable notebooks, PDAs, and handheld computers to function as LAN workstations

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Communication MediaCommunication Media• Data communication media,

including that used in LANs can be broken down into two major classes:– Conducted media that use a conductor

such as a wire or fiber optic cable to move a signal from sender to receiver

– Radiated media are wireless media such as radio frequencies and infrared light

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WiresWires

• Wires are the most widely used data transmission medium in LANs– Advantages include availability and low cost

• Some support transmission speeds up to 1 gbps– Disadvantages include susceptibility to signal distortion

and transmission errors– Per foot costs depend on shielding, gauge, and number of

conducting wires in the cable• In the U.S., (AWG) gauges of 19, 22, 24, 26, and 28 are most

common; the lower the gauge, the thicker the wire and the higher the bandwidth

• The number of conducting strands in data communication wires varies with 4, 7,8, 10, 12, 15, and 25 being most common

– Examples are illustrated in Figure 7-8

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Figure 7-8Figure 7-8

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Twisted-Pair WiresTwisted-Pair Wires• Twisted-pair wires are currently the most

common media in LANs. These are classified in several ways including:– AWG rating (gauges from 22 to 26 are most common)– Unshielded (UTP) or shielded (STP); UTP is most

common, STP is more expensive than UTP.– EIA/TIA category (see Table 7-2 and Table 7-3); Cat 5 or

higher is most common– PVC vs. plenum. PVC (polyvinyl chloride) insulation is

most common; plenum is more expensive

• RJ-45 connectors are the most common twisted-pair connectors in LANs (see Figure 7-18)

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Table 7-3Table 7-3

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Figure 7-18Figure 7-18

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Coaxial CableCoaxial Cable• Coaxial cable was the most widely used communication

medium in early LANs and is still used in some networks, sometimes alongside other wires (see Figure 7-9)

• Figure 7-10 illustrates the typical make-up of coaxial cable. The insulation can be PVC or plenum

• RG58 and RG59 are the two most common kinds of coaxial cable found data communication networks

• T-connectors and AUI connectors are most common• Data transmission over coaxial cable involves two basic

techniques broadband or baseband (see Figure 7-11) – Baseband is more common in LANs

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Figure 7-10Figure 7-10

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Figure 7-11Figure 7-11

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Fiber Optic CableFiber Optic Cable• Fiber optic cable comes in three varieties, each

with a different way of guiding light pulses from source to destination:– Multimode step-index (see Figure 7-13)– Multimode graded-index (see Figure 7-14)– Single-mode (see Figure 7-15)

• All three have the same basic form and characteristics (see Figure 7-12), however, single mode has the smallest diameter core and greatest bandwidth (see Figure 7-16); single mode is also the most expensive

• Several types of connectors exist (see Figure 7-17), but ST and SC are most common in LANs

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Figure 7-12Figure 7-12

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Figure 7-13, 7-14, 7-15Figure 7-13, 7-14, 7-15

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Figure 7-16Figure 7-16

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Figure 7-17Figure 7-17

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Radiated MediaRadiated Media• The two most common kinds of radiated media used in wireless

LANs are spread-spectrum radio (SSR) and infrared light; SSR is the most widely used

• There are two major types of SSR:– Frequency hopping: this SSR technique changes the

transmission frequency at regular intervals over a fixed spectrum; data are transmitted at one frequency, then the data are transmitted at a different frequency. Each piece of data is transmitted over several frequencies to increase the probability that it will be successfully received. Both Bluetooth and HomeRF rely on frequency hopping SSR

– Direct sequencing: this SSR transmission technique simultaneously transmits the same data on different frequencies in order to increase the probability of success. Most 802.11 WLANs use direct sequencing

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Wiring Center OptionsWiring Center Options

• Most LAN architectures use wiring hubs to provide device interconnection– A wiring hub is a central interconnection point for

workstations, servers, and other network equipment that is used in numerous LAN implementations to provide node-to-node connections (see Figure 7-19)

• Hubs vary in terms of:– LAN architecture (e.g. Ethernet vs. token ring)– number of ports– stand-alone vs. stackable– unmanaged vs. managed

• Because hubs do not process the frames transmitted by network-attached computers, they are often considered to be physical layer devices

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Figure 7-19Figure 7-19

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LAN SwitchesLAN Switches• LAN switches physically resemble hubs and like

hubs, they vary in number of ports, stand-alone vs. stackable, and managed vs. unmanaged

• However, because they must read and process transmitted frames in order to provide a switched connection between network-attached devices, they are found at the data link layer (or higher)

• Some switches support virtual LANs (VLANs). A VLAN is a logical group of workstations interconnected by one or more LAN switches that function as a self-contained LAN or workgroup

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Wireless LAN HubsWireless LAN Hubs• Wiring center options for wireless LANs

depend on the kind of communication medium that is used (see Figure 7-20)

• When SSR is used (e.g. in IEEE 802.11) in WLANs, the wireless hubs are called access points

• Access points are often used to create wireless segments of cable-based networks (see Figure 7-20b)

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Figure 7-20aFigure 7-20a

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Figure 7-20bFigure 7-20b

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LAN AdaptersLAN Adapters• LAN adapters, also called network interface cards

(NICs), provide the connection between the communication medium and a workstation or server bus (see Figure 7-21 and 7-22)

• Adapters are designed to support a specific LAN architecture (e.g. Ethernet or token ring) and support one or more physical connection interfaces. They must be compatible with the computer’s bus architecture

• PC cards (PCMCIA) adapters are available for notebook computers and wireless LAN adapters are needed for WLANs

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Figure 7-21Figure 7-21

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Figure 7-22Figure 7-22

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NIC FunctionsNIC Functions• LAN adapters have their own onboard

architectures (see Figure 7-23) and they carry out several important functions including:– monitoring activity on the communication medium– providing each workstation/server with a unique

identification address– recognizing and receiving data transmitted to the

computer– creating (building) the frames needed to transmit data

on the communication medium– controlling LAN transmission speed– transmission error detection and recovery

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Figure 7-23Figure 7-23

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Other Important LAN Other Important LAN HardwareHardware

• Other key LAN hardware components include:– printers and print servers– backup devices and media including

• duplexed servers• high-capacity removable disks• mirrored disks• RAID (redundant arrays of independent disks)• optical disk systems• virtual disk systems• magnetic tape backup systems

– uninterruptible power supplies (UPSs)

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Print ServersPrint Servers• Print servers manage shared printers and print

queues• Some file servers also function as print servers,

however, dedicated print servers are very common• Most print servers are capable of managing

multiple printers• Primary print server functions include job

distribution (routing print jobs to the printers controlled by the print server) and job sequencing (managing the print queues for the individual printers controlled by the print server)

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Storage Area NetworksStorage Area Networks• Storage area networks (SANs) enable storage to

be physically separated from an organization’s servers and to be managed as a central resource while still logically controlled by each server’s application software– There are two main ways of implementing SANs (see

Figure 7-24):• centralized• decentralized

• Network attached storage systems (NASs) are similar to centralized SANs, but connect to LANs much like a server

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Figure 7-24Figure 7-24

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LAN-to-Host InterfacesLAN-to-Host Interfaces• Today’s LAN-to-host interfaces include:

– Installing a LAN adapter in the host and establishing node-to-host connections via LAN wiring center technologies

– Dedicated point-to-point connections between LAN nodes and the host

– Switched or dedicated connections via modems– Shared/multiplexed connections between LAN nodes and

the host– Shared connections via a communication server– Connections via distributed or collapsed backbone

networks– LAN-to-host gateways

Chapter 7 Chapter 7 Introduction to Introduction to

Local Area Local Area NetworksNetworks

Part II: Understanding Internet Access Part II: Understanding Internet Access TechnologiesTechnologies