topologies & hardware student

7/28/2019 Topologies & Hardware Student

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Carol Tilden


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Topologies and Ethernet StandardsDescribe the basic and hybrid LAN physical topologies, and

their uses, advantages, and disadvantagesDescribe the backbone structures that form the foundation for

most LANsUnderstand the transmission methods underlying Ethernetnetworks

Compare the different types of switching used in datatransmission

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Physical TopologiesPhysical topology

Physical layout of network nodesDepicts broad scope

Does not specify:Device typesConnectivity methodsAddressing schemes

Fundamental shapesBus, ring, starHybrid

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Bus Topology

Single cable, connecting all network nodes- No intervening connectivity devices

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Bus TopologyOne shared communication channel

Physical medium - Coaxial cablePassive topology

Node listens for, accepts dataUses broadcasts to send

Broadcast domainNode communicates using broadcast transmissionTerminators

50-ohm resistorsStops signal at end of wire

Signal bounce

Signal travel endlessly between two network endsOne end groundedRemoves static electricity

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Bus Advantages/Disadvantages

AdvantagesRelatively inexpensive

Disadvantage

Does not scale wellDifficult to troubleshootNot very fault tolerant

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Ring Topology

Node connects to nearest two nodes in circular network

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Ring Topology

Clockwise data transmissionOne direction (unidirectional) around ring

Active topologyWorkstation participates in data deliveryData stops at destination

Physical mediumTwisted pair or fiber-optic cabling

Drawback

Malfunctioning workstation can disable networkNot flexible or scalable

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Star Topology

Nodes connects through central device

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Star Topology

Physical mediumTwisted pair or fiber-optic cablingSingle cable connects two devicesRequire more cabling, configuration

AdvantageFault tolerance

Centralized connection point affects LAN segmentScalable

Most popular fundamental layout:Ethernet networks based on star topology1024 addressable logical network nodes maximum

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Hybrid Physical Topologies

Pure bus, ring, star topologiesRarely exist - Too restrictive

Hybrid topologyMore likelyComplex combination of puretopologies

Star-wired ringtopology

Star physical topologyRing logical topology

BenefitStar fault tolerance

Network useToken Ring networks

IEEE 802.5

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Star-wired BusStar-wired bus topology

Workstation groupsStar-connected devices

Networked via single busAdvantageCover longer distancesEasily interconnect, isolate different segments

Drawback

Cabling, connectivity device expenseBasis for modern Ethernet networks

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Star-wired Bus

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Backbone Networks

Cabling connecting hubs, switches, routersMore throughputLarge organizations

Fiber-optic backboneCat 5 or better for hubs, switches

Enterprise-wide network backbonesComplex, difficult to plan

EnterpriseEntire organizationSignificant building block: backbone

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Serial BackboneSimplest backbone

Two or more internetworkingdevicesConnect using single daisy-chain cable

BenefitLogical growth solution

Modular additionsLow-cost LANinfrastructure

expansionEasily attach hubs

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Distributed BackboneConnected to hierarchy of central connectivity devicesConnects multiple LANs, LAN segments, using switches

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Distributed BackboneConnected to hierarchy of central connectivity devicesConnects multiple LANs, LAN segments, using switches and routers

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Collapsed BackboneUses router or switch

Single central connection point for multiple subnetworksHighest layer

Router with multiprocessors

Central router failure riskRouters may slow data transmissionAdvantages

Interconnect different subnetwork typesCentral management

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CollapsedBackbone

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Parallel Backbone

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Most robust networkbackboneMore than one centralRouter connects to eachnetwork segment

Requires duplicateconnections betweenconnectivity devices

AdvantageRedundant linksIncreased performanceBetter fault tolerance


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SwitchingCircuit switching - Message switching - Packet switching

CircuitConnection established before transmitting data between two network nodesDedicated bandwidth - Data follows same initial path selected by switch

Monopolizes bandwidth while connected, wastes resourcesUses: Live audio, videoconferencing, home modem connecting to ISP

MessageConnection established between two devices, data transferred then connection broken,information stored and forwarded in second device

Repeat store and forward routine until destination reachedAll information follows same physical pathConnection not continuously maintainedDevice requirements

Sufficient memory, processing power

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SwitchingPacket switchingMost popularBreaks data into packets before transportingPackets

Travel any network path to destination

Find fastest circuit available at any instantNeed not follow each otherNeed not arrive in sequenceReassembled at destination

Requires speedy connections for live audio, videotransmission

AdvantagesNo wasted bandwidthDevices do not process information

Examples: Ethernet networks, Internet

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MPLS (Multiprotocol Label Switching)IETF - Introduced in 1999Multiple layer 3 protocols

Travel over any one of several connection-oriented layer 2 protocolsSupports IP - Layer 2 WAN protocols

AdvantagesUse packet-switched technologies over traditionally circuit switched

networksCreate end-to-end paths

Act like circuit-switched connectionsAddresses traditional packet switching limitationsBetter QoS (Quality of Service)

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EthernetDeveloped by Xerox: 1970s

Improved by: Digital Equipment Corporation (DEC), Intel, Xerox (DIX)Benefits

FlexibleExcellent throughput - Reasonable cost

All variations share common access method: CSMA/CD

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

Network access methodControls how nodes access communications channel, share finitebandwidth

Carrier sense - Ethernet NICs listen, wait until free channel detected

Multiple access - Ethernet nodes simultaneously monitor traffic, access mediaCollision detection - nodes respond to collisionRequires collision detection routine

Enacted if node detects collisionJamming - NIC issues 32-bit sequence, indicates previous message faulty

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EthernetCollision domain

Portion of network where collisions occur

Ethernet network designRepeaters repeat collisions

Result in larger collision domain

Switches and routersSeparate collision domains

Collision domains differ from broadcast domains

Data propagation delay - Time for data to travel from one segment point toanother point

Too long - Cannot identify collisions accurately100 Mbps networks - Three segment maximum connected with twohubs10 Mbps buses - Five segment maximum connected with four hubs

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Network Hardware

OBJECTIVES of CHAPTER 6:

Identify the functions of LAN connectivity hardwareInstall, configure, and differentiate between network devices

such as, NICs, hubs, bridges, switches, routers,and gateways

Explain the advanced features of a switch and understandpopular switching techniques, including VLAN management

Explain the purposes and properties of routing

Describe common IPv4 and IPv6 routing protocols

This is really where it all happens!!

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NICs (Network Interface Cards)NICs - Connectivity devices that enable device transmission

Transceiver - Transmits and receives data

Operates at Physical layer and Data Link layer (OSI Model)

Issues data signals

Assembles and disassembles data framesInterprets physical addressing information

Determines the right to transmit data (collisions)

Some NICs perform prioritization, network management,

buffering, traffic-filtering

Does not analyze informat ionAdded by layers 3 through 7 OSI model protocols

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Types of NICs

Before ordering or installing a NIC

Know device inter face type

NIC dependenc ies:

Access method

Network transmission speed

Connector interfaces

Compatible motherboard or device typeManufacturer

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Internal Bus StandardsExpansion slots - Multiple electrical contacts on motherboardExpansion card (expansion board)

Circuit board for additional devicesInserts into expansion slot, establishes electrical connectionComputer centrally controls device

Multiple Bus TypesPCI bus: most popular expansion board NIC PCI (PeripheralComponent Interconnect)

32- or 64-bit bus, Clock speeds rated at 33-, 66- or 133-MHzMaximum data transfer rate: 1 GbpsLatest official version: 3.0 (2004) Older version, ISA (Industry

Standard Architecture) Original PC bus type (early 1980s), supportfor 8- and 16-bitPCI bus characteristics

Shorter connector length, faster data transmissionPCs and Macintosh compatible

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Figure 6-1 PCI NIC Figure 6-2 PCIe NIC


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Internal Bus Standards(continued)

PCIe (PCI Express)32- or 64-bit bus, maximum 133-MHz clock speedTransfer rate

500 Mbps per data path (full-duplex transmission)

PCIe advantages over PCIMore efficient data transferQuality of service distinctions supportError reporting, handlingCurrent PCI software compatiblePCIe slots differ from conventional PCI

Vary by data path or lanes supportedLanes offers full-duplex throughput of 500 MbpsSupport up to 16 lanesx16 slot : 8 Gbps throughput

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Peripheral Bus StandardsExternally Attached - simple installationPersonal Computer Memory Card International Association or PCMCIA

Sets standards for externally attached cards

PC Card - first standardPCMCIA-standard adapter, 16- bit interface running at 8 MHz

CardBus standard (1990s)32-bit interface running at 33 MHz - PCI expansion board standard

ExpressCard standardDifferent types of external devices connect to portable computers26-pin interfaceData transfer rates: 250 Mbps in each direction, 500 Mbps totalSame data transfer standards as PCIe specification (two sizes

34 mm, 54 mm wide)

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Peripheral Bus Devices

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Peripheral Bus Standards (continued)USB (universal serial bus) port

USB standardsDifference: speedUSB 1.1: transfer rate of 12 Mbps

USB 2.0: transfer rate of 480 MbpsUSB 3.0 (SuperSpeed USB): transfer rate: 5.0 Gbps

USB 3.0 arrives January 2010The theoretical throughput improvement offered by USB 3.0 is dramatic -- a theoretical10X jump over existing USB 2.0 hardware. USB 2.0 maxed out at a theoretical

480Mbps, while USB 3.0 can theoretically handle up to 5Gbps. (PCWorld, 2010)http://www.pcworld.com/article/186566/usb_30_finally_arrives.html

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Peripheral Bus Standards (continued)Firewire

Apple Computer (1980s), IEEE 1394 standard (1995)Traditional Firewire connection: 400 Mbps (max)Newer version: 3 GbpsConnects most peripheral types

Connects small networkTwo or more computers using bus topology

FireWire-connected peripheralsSimilar to USB- and PCMCIA-connected peripherals

Simple installationTwo connector varieties: 4-pin and 6-pin6-pin connector

Two pins supply powerInterconnect computers

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On-Board NICs and Wireless NICsOn-board NIC is connected through an on-board port

Connects device directly to the motherboardOn-board ports: mouse, keyboard

New computers, laptops use onboard NICs integrated intomotherboard

Advantages: Saves space, Frees expansion slots

Wireless NICsContain antennas

Send, receive signalsAll bus types supported

Disadvantages over wire-bound NICsMore expensiveBandwidth and security limitations

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NIC Installation Device DriversOperating system built-in drivers

Automatically recognizeshardware and installs drivers

Computer startup - Device drivers

loaded into RAM

Drivers not available fromoperating system

Install and configure NICsoftware (most current from the

manufacturers web site)

Use operating system interface

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Repeaters and HubsRepeater

Simplest connectivity device for regenerating signalsOperates at Physical layer - no means to interpret dataLimited scope: One input port, one output port

Receives and repeats single data streamSuitable for bus topology networks to extend network inexpensively

Rarely usedon modern networks due to limitations; other devices decreasingcostsHub

A repeater with multiple data ports and an uplink portRepeats signal in broadcast fashion - Operates at Physical layerEthernet network hub, star or star-based hybrid central connectionpointConnect workstations, print servers, switches, file servers, other devicesPassive hubs, Intelligent hubs (managed hubs), Stand-alone hubs(workgroup hubs)Replaced by switches, and routers

Limited features - merely repeat signals

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Bridges (almost extinct)Connects two network segments - Analyzes incoming frames and decides where tosend based on a frames MAC addressOperates at Data Link layer - Single input port and single output portInterprets physical addressing information

Advantages over repeaters and hubs: Protocol independence, add length beyond

maximum segments limits and can improve network performance

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SwitchesSwitches subdivide the network into segmentsOperate at Data Link layer (traditional)- Operate at layers 3 and 4(advanced)Interpret MAC address informationComponents: Internal processor, OS, memory, and portsMultiport switch:

Advantages over bridge:Better bandwidth use, more cost-efficientEach port acts like a bridgeEach device effectively

receives own dedicated channelEthernet perspective: Dedicated channel

represents one collision domainDisadvantages: Can become overwhelmeddespite buffers

UDP collisions mount: network traffic halts

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Switching MethodsSwitches differ in how they interpret incoming frames

Frame forwarding decision making

Four switching modes exist - the two most common are:

Cut Through ModeSwitch reads frames header

Forwarding decision made before receiving entire packetUses frame header: first 14 bytes contains destination MAC addressCannot verify data integrity using frame check sequenceCan detect runts - erroneously shortened packets

Runt detected: waits for integrity check

Store-and-Forward ModeSwitch reads entire data frame into memory

Checks for accuracy before transmitting information

Advantage over cut-through mode - transmits data more accuratelyDisadvantage over cut-through mode - more time consumingBest use

Larger LAN environments; mixed environmentsCan transfer data between segments running different transmission speeds

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VLANs and Trunking

VLANs (virtual local area networks)Logically separate networks withinnetworks (notice blue dotted lines)

Groups ports into broadcast domainBroadcast domain (subnet)

A port combination makes a layer 2segment. Ports rely on layer 2 device toforward broadcast frames.

Collision domainPorts in same broadcast domain

do not share single channel

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Spanning Tree ProtocolIEEE standard 802.1DOperates in Data Link layer

Prevents traffic loopsCalculating paths avoids potential loopsArtificially blocks links completing loop

Three steps:Select root bridge based on Bridge ID

Examine possible paths between

network bridge and root bridgeDisables links not part of shortest path

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Content and Multilayer Switches

Layer 3 switch (routing switch) - Interprets Layer 3 dataLayer 4 switch - Interprets Layer 4 dataContent switch (application switch)

Interprets Layer 4 to Layer 7 data

AdvantagesAdvanced filtering, statistics keeping, security functions

DisadvantagesNo agreed upon standard

Layer 3 and Layer 4 switch features vary widely

Distinguishing between Layer 3 and Layer 4 switchManufacturer dependent

Higher-layer switchesCost three times what Layer 2 switches cost, used in backbones

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RoutersMultiport connectivity devices that direct data betweennetwork nodes

Integrate LANs and WANs with different transmission speeds andprotocols, operate at Network layer (Layer 3)Routers direct data from one segment or network to another

Use logical addressing, routing tables with IP addresses (route print)Protocol dependent

Slower than switches and bridgesNeeds to interpret Layer 3 and higher informationTraditional stand-alone LAN routers being replaced by Layer 3 routing

switchesNew niche: Specialized applications

Linking large Internet nodes, completing digitized telephone calls

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Routing ProtocolsBest path

Most efficient route from one node to anotherDependent on: Hops between nodes, current network activity,unavailable link, network transmission speed and topologyDetermined by routing protocol

Routing protocolRouter communicationCollects current network status data

Contribute to best path selectionRouting table creation

Examples of routing protocols: Distance-Vector, Link-State andHybrid (EIGRP)Router convergence time - Time router takes to recognize best path

Distinguishing feature - overhead; burden on network to supportrouting protocol

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Gateways and Other MultifunctionDevicesGateway

Combinations of networking hardware and softwareConnecting two dissimilar networks

Connect two systems using different formatting,

communications protocols, architectureRepackages information

Reside on servers, microcomputers, connectivity devices,mainframes

Popular gatewaysE-mail gateway, Internet gateway, LAN gateway,Voice/data gateway, Firewall

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