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Chapter 9. Local Area Networks. Introduction. Network- a set of two or more interconnected devices or computers LAN may consist of PCs and/or MACs, mainframes, minicomputers, etc.

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Chapter 9

Local Area Networks


  • Network- a set of two or more interconnected devices or computers

  • LAN may consist of PCs and/or MACs, mainframes, minicomputers, etc.

  • Local area is typically within an office, a building, or a group of buildings. The distance among the computers and devices is only one characteristic that makes a network a local area network.

  • Due to new technologies, LANs now often span much longer distances, up to many miles in some cases.

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Figure 9.1 a networked arrangement and a single multi-user system

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Introduction Continued

  • What features differentiate a LAN from a wide area, WAN?

    • Generally, WANs are geographically larger than LANs.

    • Often WANs are used to connect many more computers than LANs

    • LANs are owned and operated by a single company mostly, and their wiring, systems, and devices are on the company's premises

    • WAN is often provided by common carriers such as the telephone companies

    • However, many companies provide their own private WANs by leasing or purchasing transmission equipment.

    • LANs make use of media access techniques that are different than the physical interfaces to WAN. LANs may use different protocols from WANs

    • The interconnection of LANs over WANs is very common in corporations today

    • New networking and switching technologies are blurring the lines between the two types of networks.

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Motivation for Using a LAN

  • Two primary reasons:

    • to share resources such as printers or files

    • to improve communications between users in a workgroup, office, department, or company

  • Disk sharing:

    • provides access to commonly used programs reducing total disk space requirements

    • provides access to commonly needed data.

    • With only a shared "copy" of the information, each user is assured that it is always accurate and up-to-date.

    • allows centralized backup of files

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Figure 9.2: In addition to saving on hardware, LAN also results in software savings

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Motivation for Using a LAN Continued

  • LAN can also offer improved security.

    • Security features such as passwords are built into the servers

  • System attached to the LAN could be diskless workstation (no floppy disk drive).

    • No software or data resides on the system, and none can be copied to a floppy disk and taken away.

    • Also limits the introduction of viruses or loading unauthorized programs.

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Motivation for Using a LAN Continued

  • Improves communications

  • Electronic mail and workgroup applications

  • Documents, programs, and data files exchanged as attachments using electronic mail among LAN users.

  • Workgroup applications allow multiple users to cooperate in performing various tasks

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Components of Local Area Networks

  • Often consist of interconnected computers including personal computers, UNIX workstations, multi-user systems, and even large mainframe computers.

  • Computers containing shared resources are called servers.

  • The users and applications running on other systems access these servers over the LAN, and are called clients, hence the name client server computing

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  • Standalone workstation - a workstation that is not connected to a network, but relies on its own hard disk for data storage and applications.

  • Client - a workstation connected to a network. A person whose workstation is part of a network may also be called a client, or that person may be known more informally as a user.

  • Servers - store shared data and programs on their hard disks. They can also perform management functions, such as determining which users have access to certain programs.

  • Client-server - a network that uses a server to enable clients to share data, data storage space, and devices.

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Figure 9-3: Client Server LAN Configuration

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Components of Local Area Networks Continued

  • Print server- this computer accepts print requests from other systems on the LAN, temporarily writes the data to be printed onto its disk storage, then sends the data to the printer.

    • The print server manages the print streams from several systems concurrently

    • A directly attached printer acts as a print server. Other systems on the LAN can direct print streams to the printer.

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Components of Local Area Networks Continued

  • A LAN adapter is a hardware board (e.g., a PC adapter card) that can be inserted into an expansion slot in the PC.

    • LAN adapters are commonly called network interface adapters (NIAs) or network interface cards (NICs).

    • The adapter provides the interface to the PC or device on one side and the network on the other side.

    • The adapter provides a socket into which the LAN medium, such as a cable, can plug.

    • The adapter has to translate the signals used within the PC or printer into signals used on the LAN cable.

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Network Interface Cards (NICs)

Types of NICs

  • Industry Standard Architecture (ISA)

  • MicroChannel Architecture (MCA)

  • Extended Industry Standard Architecture (EISA)

  • Peripheral Component Interconnect (PCI)

FIGURE: Four primary bus architectures

Network Interface Cards (NICs)

FIGURE : Three kinds of bus connections on the same board

Network Interface Cards (NICs)

  • NICs may connect to interfaces other than a PC’s bus

  • For laptop computers, Personal Computer Memory Card International Association slots may be used to connect NICs

    • PCMCIA

    • Also called PC card

    • Developed in the early 1990s to provide a standard interface for connecting any type of device to a portable computer

Network Interface Cards (NICs)


FIGURE : Parallel port NIC

Network Interface Cards (NICs)

FIGURE : Wireless NIC and transceiver

FIGURE : Ethernet NICs for printers

Basics of Local Area Networks

  • IEEE 802-series of standards is focused on LAN interconnection and operation

  • The IEEE LAN standards are specific set of standards that conform to the lower layers of the OSI reference Model

  • The most popular types of LAN physical media are coaxial cable, twisted-pair wire, and fiber optic cable

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Coax in LANs

  • The original type of coaxial cable used in Ethernet LANs is known as thick coax, approximately 1/2 inch thick and is relatively inflexible and difficult to install.

    • Main advantage of coaxial cable - less susceptible to interference than twisted-pair wire, and supports relatively high rates of data transmission over greater distances.

    • The main disadvantage - more expensive that other media, and in the case of thick coax, its size and inflexibility makes it more difficult to install.

    • Typical data rates over coaxial cable LANs is 10 Mbps with distances ranging from 100's to 1000's of feet.

  • "thin" coax came into widespread use because it is less expensive than thick coax, and easier to work with.

    • It is approximately 1/4 inch (0.63 cm) thick and very similar to the coax used for cable TV.

    • But, this coax supports shorter distances than the thick coax.

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Twisted-pair Cables in LANs

  • Unshielded twisted-pair (UTP) is the standard telephone cable

  • Main advantages of UTP wiring - inexpensive, flexible, easy to install and available

  • In the past, only relatively low speed transmissions were possible over UTP but newer techniques are now in use that will support UTP speed in the 100 megabits per second range.

  • Disadvantages:

    • more susceptible to electrical interference. Not a huge problem in offices, but can be a problem in factories where electrical machinery is in use.

    • Another problem is that signals lose their strength as they are transmitted over UTP, high attenuation.

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Twisted-pair Cables in LANs Continued

shielded twisted-pair, STP:

  • shield provides protection from noise, thus eliminating somewhat the problems associated with susceptibility to noise that plagues UTP

  • shield also helps keep signals from emanating out of the wire, important in certain environments.

  • A negative of STP though, is that the shield increases the cost of the wire so it is typically more expensive than UTP

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Fiber Optic cabling in LANs

  • Advantages:

    • high transmission rates, up to 100 Mbps and therefore greater bandwidth

    • immune to electrical interference because they use light rather than electricity

    • very thin and flexible. Thus, a fiber optic cable is easy to install, and ideal for bundling many fibers together to create a cable that carries very large amount of traffic.

    • Less attenuation than copper wiring (longer length of a fiber optic cable before repeaters are required).

    • Very secure. Any tap into the cable interrupts the flow of light and is easily detected.

    • Disadvantages: cables and adapters more expensive

  • Commonly used for high speed backbones

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Transmission Techniques

  • Baseband:

    • Signals placed directly onto the transmission medium (not modulated by a carrier)

    • A stream of such digital pulses represents the information being transmitted.

    • The signal takes up the entire bandwidth of the transmission medium.

    • Signals from multiple sources can be transmitted via the technique known as Time Division Multiplexing or TDM as seen in Chapter 2.

    • Relatively inexpensive. No special equipment is required to modify the signals.

    • One problem -signals lose strength as they are carried over longer distances and must be regenerated.

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Figure 9.5: Baseband Transmission

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Transmission Techniques Continued

  • Broadband:

  • signals modulated to different frequency ranges typically provided using radio frequency modems.

  • Frequency Division Multiplexing (FDM) is used where each signal occupies a different frequency range.

    • The different frequency ranges called logical channels.

    • Therefore, multiple channels are available using broadband transmission. (technique used in standard cable TV).

    • Each logical FDM channel could also be shared by multiple applications by using TDM within the channel.

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Transmission Techniques Continued

  • Broadband provides:

    • greater bandwidth than baseband and is, therefore, able to carry more information and support greater distances than baseband.

    • ability to carry voice, data, and video at the same time.

  • Disadvantages:

    • Typically more expensive than baseband transmission.

    • more difficult to configure and costly to modify.

  • Best suited to large installations

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Figure 9.6: Broadband Transmission

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Media Access Methods

  • All devices attached to a LAN share the transmission medium.

  • What happens if multiple devices attempt to send data onto the LAN at the same time?

  • A media access control (MAC) method determines how multiple devices share the transmission medium.

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Media Access Methods Continued

  • Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

    • Devices must sense the presence of a carrier signal (presence of a carrier signal indicates that information is currently being transmitted)

    • If a carrier signal is not detected, it is an indication that the LAN is free and the device can attempt to send.

    • If another device had sent information at the same time, though, the listening devices would detect a collision. This is where the "collision detection" part of the name comes from.

    • When such a collision is detected, the devices stop transmitting and wait for some period of time before attempting to transmit again.

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Media Access Methods CSMA/CD Continued

  • CSMA/CD is the access method used in Ethernet and 802.3 LANs and became an international standard when IEEE 802.3 was approved.

  • Traffic increases may result in much more frequent collisions degrading network performance.

  • Rule of thumb: CSMA/CD LANs (Ethernet) work fine with constant traffic load of 30 percent of capacity and traffic bursts of about 60 percent of capacity;

    • otherwise divide the Ethernet into additional segments to reduce the number of stations that are sharing a given segment's bandwidth.

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CSMA/CD continue

  • CSMA/CD is a probabilistic access control method (the opportunity to transmit is not guaranteed).

  • The possibility that a device might not gain access to the network at a critical time is unacceptable.

  • This is one reason why IBM invented the Token-Ring network.

  • Token passing is the media access technique used in token ring LANs:

    • A token ring operates as a logical ring.

    • The transmitter of each device is connected to the receiver of the next device in the ring enabling devices to pass messages around the ring.

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Figure 9.8: Token Passing

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Token Ring continued

  • Token: special type of data frame that circulates around the ring.

    • A device can transmit only when it is in possession of the token

    • After a data frame is transmitted, the device releases the token to the network so that other devices can transmit.

  • Apparently simple method but:

    • How is the loss of a token detected and how is a new token created?

    • What steps should a station take if it stops receiving data?

    • What if a station that was to receive a frame goes off the network?

    • How is the network to identify frames that have circulated the network too many times?

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Token Ring continued

  • Ring error monitor (REM) can regenerate lost tokens and remove bad frames from the network.

  • Additionally, each device is capable of signaling certain problems by transmitting a beacon signal.

  • Error detection and diagnostic tools available on a token ring are quite extensive. By contrast, no such tools are built into Ethernet (CSMA/CD) networks.

  • The mechanism that controls a token ring network is much more involved and expensive than that required for Ethernet.

  • Token ring is deterministic (every device is guaranteed a chance to transmit each time the token circulates the ring ) while Ethernet is probabilistic.

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Token Ring vs. CSMA/CD

  • Token passing may suffer less performance degradation than CSMA/CD in very large LANs.

    • Because contention for the transmission medium is more orderly than with CSMA/CD, eliminating collisions, timeouts, and subsequent retries.

    • Token passing allows stations to transmit whenever a free token is available, but they may have to wait a while to get a token.

  • A potential problem is that stations that get a token can "hog" the LAN.

    • Implementations attempt to minimize this by placing a limit on the amount of time a single station can send before passing on the token.

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LAN Topologies

  • Topology of the LAN: actual physical layout of a LAN or the arrangement in which devices are interconnected.

  • Most widely used topologies:

    • bus

    • star

    • ring

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Bus Topology

  • All stations (systems and devices) directly connected to the same transmission medium, usually a physical cable.

    • simple, and as a result, often inexpensive.

    • very common on LANs

    • type of topology originally specified for Ethernet LANs.

  • Information on bus-based LANs is broadcast to all connected stations.

    • Transmissions go in both directions along the bus or cable.

    • All stations, thus, receive all transmissions.

    • Each station has a unique address assigned to it.

    • Station address included in the data frames that carry information on the bus.

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Figure 9.9: LAN BUS topology

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Star Topology

  • Each station connected to a central piece of equipment commonly called a hub.

  • All communications go through the hub which amplifies and retransmits signals providing connectivity among stations

  • Individual stations are not directly connected to one another but indirectly through the central hub.

  • One problem with a star is that if the central hub fails, the network is inoperable.

  • Redundancy features are often built into hubs making them very reliable. Also, hubs can be configured so that a bypass is possible in the event that a component fails.

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Figure 9.10: LAN STAR topology

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Ring Topology

  • Stations directly connected to other stations form what looks like a ring.

    • Unlike a star, adjacent stations on the ring are directly cabled to one another.

    • No central hub. Information flows in one direction around a ring. Each station receives all signals from the adjacent station, regenerates and retransmits frames to the next station on the ring.

  • Eliminates problem of depending on a central switch but dependent on each individual station on the ring.

  • If a station fails, or the link between stations fails, the ring can become inoperable

    • There are solutions to this problem such as redundant links and ways to bypass failed stations.

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Ring Topology Continued

  • As with other LAN topologies, each station on a ring has a unique address.

  • A station look at the destination address in a frame to determine if a frame is intended for it.

    • If so, the frame is pulled off the ring.

    • If not, the frame is retransmitted to the next station.

  • Token passing schemes are often used on ring-base LANs.

    • For example, IBM's token-Ring LAN uses a ring topology on which a token passing media access control method is used.

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Figure 9.11: LAN RING topology

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  • Jointly by Xerox, DEC, and Intel

  • One of the most popular types of LAN in use today.

  • Original Ethernet specification called for coaxial cable as the transmission medium.

  • Today, Ethernet LANs make use of other types of cabling such as twisted-pair wire as well.

  • Ethernet uses a bus topology

  • The main advantage of Ethernet is its relatively low cost.

  • Inexpensive Ethernet adapters are available for most PCs and Ethernet interfaces are supported in a wide range of computer equipment.

  • Multivendor support of Ethernet makes it a popular choice in many cases

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Figure 9.12: Ethernet uses LAN BUS topology

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Ethernet Continued

  • Ethernet LAN uses a CSMA/CD contention protocol (defined as part of IEEE 802.3 standard).

  • Ethernet and IEEE 802.3 specifications are similar, but not identical.

  • One difference: Ethernet frame headers include a type field that indicates the higher layer protocol in use.

    • For example, the type field could indicate that either TCP/IP or XNS (Xerox Network System) protocols were used across the Ethernet LAN.

  • Instead of a type field, the header of an 802.3 frame includes a length field indicating the length of the data contained in the information portion of the frame.

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IEEE Networking Specifications


IEEE 802 standards

Figure 9.13: Ethernet frame compared to IEEE 802.3 frame

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Ethernet Continued

  • Originally designed for transmission rates of 10 Mbps

  • Work going on for Ethernet-like LANs at higher speeds (fast Ethernet at 100 Mbps).

  • Ethernet LANs with large number of users and heavy traffic demands may result in performance problems

    • Primarily due to the characteristics of the CSMA/CD (collisions, forcing stations to wait before retrying their transmission).

  • An upper limit of 10 Mbps also becomes a problem:

    • when transmitting information requiring high bandwidth such as video images.

    • It also makes Ethernet less attractive as a backbone LAN to interconnect other LANs.

  • But, multiple Ethernet LANs can be easily interconnected by devices called bridges forming large logical LANs.

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Thick Ethernet (or thicknet) Cabling

  • Thick Ethernet or thicknet.

  • IEEE label 10BASE5 summarizes these cable characteristics: 10-Mbps bandwidth, baseband operation, and 500 meters segments

  • Workstations don't connect directly to the thick coaxial cable.

    • They attach by way of multistation access unit (MAUs).

    • Pins in a clamp-on MAU penetrate the cable to make contact with the shielded center conductor. (vampire taps).

    • MAUs should attach to the thick coaxial cable at intervals that are even multiple of 2.5 meters.

  • Both MAUs and device network interfaces are equipped with a special 15-pin connector called an attachment unit interface (AUI) connector.

  • A multi-conductor AUI cable of up to 50 meters can be used to connect the device to the MAU.

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Figure 9.14: Components of a thick Ethernet

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Thick Ethernet (or thicknet) Cabling Continued

  • Note in Figure 9.14 the ends of an Ethernet bus must be equipped with termination-connectors incorporating a 50-ohm resistor to match the characteristic impedance of the cable.

    • The terminator absorbs the signal that reaches it preventing the signal from being reflected back into the cable as noise.

    • One of the terminators must be connected to an electrical ground.

    • Without the ground connection, the cable's shield might not do an effective job of preventing against EMI (electromagnetic interference).

    • Only one termination should be grounded.

  • the IEEE 802.3 standard refers to the cable interface as a medium attachment unit, it is more commonly called a transceiver when used in an Ethernet II environment.

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Thick Ethernet (or thicknet) Cabling Continued

  • Apart from naming conventions, cabling is identical for Ethernet II and IEEE Ethernet 802.3.

  • A segment consists of the coaxial cable between two terminators.

    • Maximum length of a thick Ethernet segment is 500 meters

    • Each segment can support a maximum of 100 connections.

    • As shown in Figure 9.15, Segments can be connected using repeaters.

    • Repeaters serve several purposes. They:

      • Electrically isolate the coaxial segments

      • Amplify signals that pass between segments

      • Reshape waveforms to correct distortions that arise as signals travel through cables.

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Figure 9.15: Expanding a thick Ethernet with a link segment

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Thick Ethernet (or thicknet) Cabling Continued

  • A repeater segment is called a link segment.

    • At most, an Ethernet can include three coaxial cable segments and two link segments.

    • Repeaters connect to coax segments using AUI cables, which are limited to 50 meters.

    • Thus, the maximum length of a link segment is 100 meters.

    • For longer link segments, fiber-optic cable can be used to create a fiber-optic repeater link segment (up to 1 kilometer).

  • Thick Ethernet is seldom used in new installations.

    • The cable is expensive and bulky.

    • Network components are also expensive and difficult to install.

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Thin Ethernet (10BASE2)

  • 10-Mbps bandwidth

  • baseband operation

  • segment length of approximately 200m (precisely 185)

  • Coax used considerably thinner than thicknet

  • Attach to the network by means of T connectors, which connect directly to the NIC.

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Thin Ethernet (10BASE2) Continued

  • Thinnet coaxial cable must have a terminator at each end with only one of the terminators should be grounded

  • Segment should not exceed 185 meters or include more than 30 attached devices.

  • For best performance, devices should be spaced even multiples of one-half meter.

  • Manufactured cables have two advantages:

    • connectors are securely installed

    • cable lengths conform to the rule of one-half meter multiples.

  • Thin Ethernet is easy to install in most situations.

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Figure 9.16: Components of a thin Ethernet

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Thin Ethernet (10BASE2) Continued

  • Like thick Ethernet, thinnet networks can be extended using repeater links. SEE Figure 9.17.

  • Each work station connection involves three separate BNC connectors; these are the cause of most problems with thin Ethernet.

    • Common for users to accidentally dislodge connectors or to pull the cable out of a connector

    • A break in the coaxial can disrupt the network communications for the entire segment.

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Figure 9.17: A thin Ethernet that includes a repeater link segment

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Thin Ethernet Conclusion

  • Although gradually being replaced by UTP networks, thin Ethernet remains an excellent choice for small networks.

    • Connection cost is lowest of any network cabling system

    • No hubs are required, which can raise the cost of a network connection by $20 to more than $100 per device.

  • One problem: they can be difficult to reconfigure.

    • Adding a device requires you to add a T connector to the coax, which requires shutting network down.

    • For large network or networks that must be reconfigured frequently, choose an easier to configure and manage star-wired network with intelligent hubs.

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Twisted-Pair Ethernet (10BASE-T)

  • Uses unshielded twisted-pair cable.

  • Unlike coax Ethernet, 10BASE-T uses a star-wiring topology based on hubs.

  • Length of the cable that connects a device to the hub is limited to 100 meters.

  • Two twisted-pairs configured so that the transmitter of the device at one cable end connects to the receiver of the device at the other end.

  • See Figures 9-18 and 9-19

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Figure 9.18: Connecting workstations to a 10BASE-T hub

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Figure 9.19 Methods of crossing pairs in 10BASE-T connections

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Twisted-Pair Ethernet (10BASE-T) Continued

  • 10BASE-T networks require at least Category 3 UTP cable connected with RJ-45 connectors.

    • Do not use installed telephone wiring without determining whether it meets Category 3 specifications

    • Never use telephone-grade patch cables for connecting devices to hubs.

  • Physical topology of a 10BASE-T network does not alter the logical topology of Ethernet.

    • A 10BASE-T network remains a logical bus.

    • All devices share the 10-Mbps bandwidth of the network

    • only one device is can access the network at a given time.

  • The primary reason for choosing 10BASE-T:

    • should not be the goal of saving money with unshielded twisted-pair (UTP) cables

    • should focus on the advantage a star network offers in terms of reconfiguration and management.

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802.3 Ethernet versus Ethernet II

  • Summary of similarities and differences (see Figure 9.20):

    • 6-octet source and destination address fields. 802.3 Ethernet can operate with 2- octets (usually 6)

    • Manufacturer burns a unique 6-octet address into each Ethernet NIC (network interface card).

    • Ethernet II uses a Type field, the 802.3 replaces it with a Length field that describes the length in bytes of the LLC Data field. It is easy to distinguish an 802.3 frame from an Ethernet II frame by examining the value of the Type/Length field. If 1501 or greater, frame is an Ethernet II.

    • The data fields have different names but otherwise are identical.

      • minimum length of 46 octets

      • maximum length of 1,500 octets.

    • Frame Check Sequence field is used to detect transmission errors.

      • If the calculated (by the receiver) CRC matches the value in the CRC field of the received frame, then it is assumed that the frame was transmitted correctly.

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Figure 9.20: Frame formats for 802.3 Ethernet and Ethernet II

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High-Speed Ethernet

  • Fast Ethernet has taken off like mad, driven by dozens of vendors and hundreds of products.

  • Offers100-Mbps speed technologies similar to 10BASE-T.

  • Fast Ethernet is used for workstations that need greater LAN bandwidth and also for establishing high-speed backbones which interconnect servers.

  • Two technologies are competing in the 100-Mbps Ethernet area:

    • 100BASE-T, the IEEE standard derived from 802.3 Ethernet

    • 100VG-AnyLAN, which uses different technologies altogether

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High-Speed Ethernet Continued

  • 100 BASE-T

    • Standardized by IEEE 802.3 committee and is part of the established IEEE Ethernet standards. Three variations defined:

      • 100BASE-TX uses two pairs of Category 5 UTP cable

      • 100BASE-T4 uses four pairs of Category 3, 4 or 5 UTP

      • 100BASE-FX uses multimode optical fiber

  • 10-and 100-Mbps Ethernet can coexist on the same network.

    • 10/100-Mbps Ethernet switches can be used

    • to organize the network into different speed segments

    • as tools for migrating the network to100-Mbps speeds.

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High-Speed Ethernet Continued

  • 100VG-AnyLAN

    • Not an Ethernet technology, but aimed at the 100BASE-T market. standardized by IEEE 802.12.

    • Access method used is Domain Based Priority Access, which eliminates collisions, enabling 100VG-AnyLAN networks to exceed the size limits imposed on 100BASE-T, and greatly reduces the need for repeater.

    • Supports Ethernet frame formats and can be integrated with standard Ethernet Networks.

    • Also supports token-ring frames, and can be used as a high-speed LAN that integrates Ethernet and token-ring network segments.

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High-Speed Ethernet Continued

  • Gigabit Ethernet

  • As more organizations move to 100BASE-T, increasing the traffic load on backbone networks, demand for Gigabit Ethernet has intensified.

  • In late 1995, the IEEE 802.3 began investigating means of transferring Ethernet packets at speeds in the Gbps range.

    • similar to those of the 10- and 100-Mbps Ethernets.

    • Retains the CSMA/CD media access method and the Ethernet frame format of its 10- and 100-Mbps predecessors.

    • compatible with 100BASE-T and 10BASE-T

    • use of optical fiber over relatively short distances, but unshielded and shielded twisted pairs are also allowed.

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network operating system--NOS

  • Typical NOS functions include:

    • Print Services

    • File and Database Services

    • Remote Access Services

    • Messaging Services

    • Network Management Services

    • Communications Services

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Figure 9.29: Printing Service of the Network Operating System

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LAN Protocols

  • The most popular protocols used in LAN environments are:

    • NetBIOS

    • TCP/IP

    • XNS

    • SPX/IPX

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  • DOS's BIOS offers services for accessing local devices such as disks and printers

  • NetBIOS provides a similar set of services for accessing devices connected to a LAN.

  • basic services include

    • general control services

      • name support services:

      • Add Names

      • Remove Names

      • Show List of Names

      • datagram support services

        • Send Packet

        • Receive Packet

    • session support servicesEstablish a connection ("call" another station)

      • Send Data

      • Receive Data

      • Terminate a Connection ("hang up”)

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Figure 9.32: Where NetBIOS fits within the DOS operating system

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Origins of TCP/IP

  • Transmission Control Protocol/Internet Protocol (TCP/IP)

    • Protocol suite whose invention and evolution resulted from a coordinated effort by the United States Department of Defense (DOD)

  • Advanced Research Projects Agency (ARPA)

    • DOD branch responsible for creation and proliferation of the Internet and TCP/IP protocol suite

    • Advanced Research Projects Agency Network (ARPANET)

      • Original name of the Internet

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Overview of the TCP/IP Protocol Suite

  • Four layers of the TCP/IP protocol suite :

    • Application

    • Transport

    • Internetwork

    • Network Interface

  • Series of documents called Requests for Comments (RFCs) define, describe, and standardize implementation of TCP/IP protocol suite

    • The Internet Network Information Center (InterNIC) is responsible for maintaining these standards

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Overview of the TCP/IP Protocol Suite

Figure 3-1: Protocol architecture comparison

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Application Layer

  • Protocols that exist at this layer include:

    • File Transfer Protocol (FTP)

    • Trivial File Transfer Protocol (TFTP)

    • Network File System (NFS)

    • Simple Mail Transfer Protocol (SMTP)

    • Terminal emulation protocol (telnet)

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Application Layer

  • Protocols that exist at this layer include (cont):

    • Remote login application (rlogin)

    • Simple Network Management Protocol (SNMP)

    • Domain Name System (DNS)

    • Hypertext Transfer Protocol (HTTP)

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Transport Layer

  • Two protocols reside at this layer:

    • TCP

    • User Datagram Protocol (UDP)

  • Ports

    • Both TCP and UDP use port numbers for communication between hosts

    • Well Known Port Numbers

      • TCP and UDP ports from 0 through 1023 on which client applications expect to find common Internet services

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Well Known TCP and UDP Port Numbers from RFC 1700

  • TCP port 20 – FTP data transfer

  • TCP port 21 – FTP control port

  • TCP port 23 – Telnet

  • TCP port 25 – SMTP

  • TCP & UDP port 53 – DNS

  • TCP (port 80) – HTTP Web services

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Well Known TCP and UDP Port Numbers from RFC 1700

  • TCP & UDP port 123 – Network Time Protocol (NTP)

  • TCP port 110 – Post Office Protocol version 3 (POP3)

  • TCP port 119 – Network News Transport Protocol (NNTP)

  • UDP port 69 – TFTP

  • UDP port 161 – SNMP

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Internetwork Layer

  • Four main protocols function at this layer:

    • Internet Protocol (IP)

    • Internet Control Message Protocol (ICMP)

      • Uses eight different message types to manage 11 different aspects of IP communications

    • Address Resolution Protocol (ARP)

    • Reverse Address Resolution Protocol (RARP)

      • In the case of a diskless workstation, a source host will know its MAC address but not its IP address

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  • IP, ARP, and RARP are all routed protocols associated with TCP/IP

  • ARP tables

    • Table used by a network device that contains MAC to IP address mappings

    • Maintained in volatile Random Access Memory (RAM)

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Network Interface Layer

  • Plays the same role as the Data Link and Physical layers of the OSI model

  • The MAC address, network card drivers, and specific interfaces for the network card function at this level of the TCP/IP protocol stack

  • No specific IP functions exist at this layer because the layer’s focus is on communication with the network card and other networking hardware

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IP Addressing

Table 3-2: Binary to decimal conversion

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MAC to IP Address Translation

  • The MAC address identifies a specific computer on a network, so each MAC address is unique

  • However, MAC address are not grouped logically, they cannot be modified, and they don’t give information about physical or logical network configuration

  • Therefore, another addressing scheme called IP addressing was devised for use on large networks

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Figure 9.34: TCP/IP protocols as they fit into layer 4 and layer 3 of the OSI reference model

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Figure 9.35: TCP/IP Applications

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  • Xerox Network Systems (XNS) is a suite of protocols introduced in the early 1980s,

  • Used in a wide variety of network equipment and applications.

    • five different levels of protocols similar to the layers of the OSI Reference Model.

    • Figure 9.37 shows the relationships between the OSI layers and the XNS protocol suite.

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Figure 9.37: XNS protocol suite in relation to the OSI reference model

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  • Internet Packet Exchange (IPX) and Sequenced Packet Exchange (SPX) are key networking protocols supported in Novell's NetWare.

    • Most widely used LAN protocol.

    • IPX (Internet Packet Exchange) is based on the XNS IDP protocol and the packet formats used by IPX are the same as those used with IDP.

    • IPX is a connectionless, datagram-oriented service that handles routing of data through an internetwork

    • Since IPX does not guarantee delivery of packets, higher layer protocols provide the services for reliable delivery:

      • Packet retransmission requests

      • packet acknowledgement,

      • flow control

      • error detection.

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Figure 9.38: Relationship between IPX/SPX and the OSI reference model

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IPX/SPX Continued

  • Relationship between SPX and IPX similar to the that between TCP and IP, and SPP and IDP of XNS.

  • Used in both LAN and WAN environments.

  • Because network protocols are "layered," many network applications can run independent of the underlying networking protocols used

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Figure 9.39: OSI Reference Model: TCP/IP, XNS, and IPX/SPX

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LAN Standards

  • 802.2: Logical Link Control

    • manage the exchange of information across a LAN.

  • 802.3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

    • includes the 10BASE-2, 10BASE-5, and 10BASE-T specifications

  • 802.4: Token Passing Bus

    • describes a token passing media access method for use on bus-based LANs

  • 802.5: Token Passing Ring

    • describes a token passing media access method for use on ring-based LANs.

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  • The intent of this chapter was to introduce the reader to:

  • Basics of LANs and the terminology

  • Motivations behind using a LAN

  • Components that make up a LAN.

  • LAN operations, topology, protocol

  • Specific implementations including Ethernet High speed LANs

chapter 9

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