LAN/WAN InterconnectivityLAN/WAN Interconnectivity

Learning ObjectivesLearning Objectives

Explain the OSI reference model, which Explain the OSI reference model, which sets standards for LAN and WAN sets standards for LAN and WAN communicationscommunications

Discuss communication between OSI Discuss communication between OSI stacks when two computers are linked stacks when two computers are linked through a networkthrough a network

Apply the OSI model to realistic Apply the OSI model to realistic networking situationsnetworking situations

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Learning ObjectivesLearning Objectives

Describe the types of networks as represented Describe the types of networks as represented through LAN topologiesthrough LAN topologies

Describe major LAN transmission methods, Describe major LAN transmission methods, including Ethernet, token ring, and FDDIincluding Ethernet, token ring, and FDDI

Explain basic WAN network communications Explain basic WAN network communications topologies and transmission methods, including topologies and transmission methods, including telecommunications, cable TV, and satellite telecommunications, cable TV, and satellite technologiestechnologies

LAN/WAN InterconnectivityLAN/WAN Interconnectivity

Intense competition between three Intense competition between three sectors:sectors:Telecommunications companiesTelecommunications companiesCable TV companiesCable TV companiesSatellite communications companiesSatellite communications companies

OSI Reference ModelOSI Reference Model

Foundation that brings continuity to LAN Foundation that brings continuity to LAN and WAN communicationsand WAN communications

Product of two standards organizations:Product of two standards organizations: ISOISOANSIANSI

Developed in 1974Developed in 1974Set of communication guidelines for Set of communication guidelines for

hardware and software designhardware and software design

OSI Guidelines Specify…OSI Guidelines Specify…

How network devices contact each other; How network devices contact each other; how devices using different protocols how devices using different protocols communicatecommunicate

How a network device knows when to How a network device knows when to transmit and not transmit datatransmit and not transmit data

How physical network network devices are How physical network network devices are arranged and connectedarranged and connected

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OSI Guidelines Specify…OSI Guidelines Specify…

Methods to ensure that network Methods to ensure that network transmissions are received correctlytransmissions are received correctly

How network devices maintain a How network devices maintain a consistent rate of data flowconsistent rate of data flow

How electronic data is represented on How electronic data is represented on network medianetwork media

OSI LayersOSI Layers

OSI LayersOSI Layers

Bottom layersBottom layers Support for physical connectivity, frame formation, Support for physical connectivity, frame formation,

encoding, and signal transmissionencoding, and signal transmission

Middle layersMiddle layers Establish and maintain a communication session Establish and maintain a communication session

between two network nodesbetween two network nodes Monitor for error conditionsMonitor for error conditions

Uppermost layersUppermost layers Application/software support for encrypting data and Application/software support for encrypting data and

assuring interpretation/presentation of dataassuring interpretation/presentation of data

Physical Layer FunctionsPhysical Layer Functions

Provides transfer medium (eg, cable)Provides transfer medium (eg, cable) Translates data into a transmission signalTranslates data into a transmission signal Sends signal along the transfer mediumSends signal along the transfer medium Includes physical layout of networkIncludes physical layout of network Monitors for transmission errorsMonitors for transmission errors Determines voltage levels for data signal Determines voltage levels for data signal

transmissions and to synchronize transmissions and to synchronize transmissionstransmissions

Determines signal type (eg, digital or analog) Determines signal type (eg, digital or analog)

Analog SignalsAnalog Signals

Digital SignalsDigital Signals

Data Link Layer FunctionsData Link Layer Functions

Constructs data framesConstructs data framesCreates CRC information; checks for Creates CRC information; checks for

errorserrorsRetransmits data if there is an errorRetransmits data if there is an error Initiates communications link; makes sure Initiates communications link; makes sure

it is not interrupted (ensures node-to-node it is not interrupted (ensures node-to-node physical reliability)physical reliability)

Examines device addressesExamines device addressesAcknowledges receipt of a frameAcknowledges receipt of a frame

Data Link LayerData Link Layer

Data link frame contains fields consisting Data link frame contains fields consisting of address and control informationof address and control information

Two important sublayersTwo important sublayersLogical link control (LLC)Logical link control (LLC)Media access control (MAC)Media access control (MAC)

Connectionless service versus connection-Connectionless service versus connection-oriented serviceoriented service

Network Layer FunctionsNetwork Layer Functions

Determines network path for routing Determines network path for routing packetspackets

Helps reduce network congestionHelps reduce network congestionEstablishes virtual circuitsEstablishes virtual circuitsRoutes packets to other networks, Routes packets to other networks,

resequencing packet transmissions when resequencing packet transmissions when neededneeded

Translates between protocolsTranslates between protocols

Transport Layer FunctionsTransport Layer Functions

Ensures reliability of packet transmissionsEnsures reliability of packet transmissions Ensures data is sent and received in the same Ensures data is sent and received in the same

orderorder Sends acknowledgement when packet is Sends acknowledgement when packet is

receivedreceived Monitors for packet transmission errors and Monitors for packet transmission errors and

resends bad packetsresends bad packets Breaks large data units into smaller ones and Breaks large data units into smaller ones and

reconstructs them at the receiving end for reconstructs them at the receiving end for networks using different protocolsnetworks using different protocols

Session Layer FunctionsSession Layer Functions

Establishes and maintains Establishes and maintains communications linkcommunications link

Determines which node transmits at any Determines which node transmits at any point in timepoint in time

Disconnects when communication session Disconnects when communication session is overis over

Translates node addressesTranslates node addresses

Presentation Layer FunctionsPresentation Layer Functions

Translates data to a format the receiving Translates data to a format the receiving node understands (eg, from EBCDIC to node understands (eg, from EBCDIC to ASCII)ASCII)

Performs data encryptionPerforms data encryptionPerforms data compressionPerforms data compression

Application Layer FunctionsApplication Layer Functions

Enables sharing remote drivers and Enables sharing remote drivers and printersprinters

Handles e-mail messagesHandles e-mail messagesProvides file transfer servicesProvides file transfer servicesProvides file management servicesProvides file management servicesProvides terminal emulation servicesProvides terminal emulation services

Communicating Between Communicating Between StacksStacks

OSI model provides standards for:OSI model provides standards for:Communicating on a LANCommunicating on a LANCommunicating between LANsCommunicating between LANs Internetworking between LANs and WANs Internetworking between LANs and WANs

and between WANs and WANsand between WANs and WANs

Peer ProtocolsPeer Protocols

PrimitivesPrimitives

Layered CommunicationsLayered Communications

Applying the OSI ModelApplying the OSI Model

Types of NetworksTypes of Networks

Three main topologiesThree main topologiesBusBusRingRingStarStar

Bus TopologyBus Topology

Built by running cable Built by running cable from one PC or file from one PC or file server to the nextserver to the next

Terminators signal Terminators signal the physical end to the physical end to the segmentthe segment

Advantages of Bus TopologyAdvantages of Bus Topology

Works well for small networksWorks well for small networksRelatively inexpensive to implementRelatively inexpensive to implementEasy to add to itEasy to add to it

Disadvantages ofDisadvantages ofBus TopologyBus Topology

Management costs can be highManagement costs can be highPotential for congestion with network Potential for congestion with network

traffictraffic

Ring TopologyRing Topology

Continuous path for Continuous path for data with no logical data with no logical beginning or ending beginning or ending point, and thus no point, and thus no terminatorsterminators

Advantages of Ring TopologyAdvantages of Ring Topology

Easier to manage; easier to locate a Easier to manage; easier to locate a defective node or cable problemdefective node or cable problem

Well-suited for transmitting signals over Well-suited for transmitting signals over long distances on a LANlong distances on a LAN

Handles high-volume network trafficHandles high-volume network trafficEnables reliable communicationEnables reliable communication

Disadvantages ofDisadvantages ofRing TopologyRing Topology

ExpensiveExpensiveRequires more cable and network Requires more cable and network

equipment at the startequipment at the startNot used as widely as bus topologyNot used as widely as bus topology

Fewer equipment optionsFewer equipment optionsFewer options for expansion to high-speed Fewer options for expansion to high-speed

communicationcommunication

Star TopologyStar Topology

Oldest and most Oldest and most common network common network designdesign

Multiple nodes Multiple nodes attached to a central attached to a central hubhub

Advantages of Star TopologyAdvantages of Star Topology

Good option for modern networksGood option for modern networksLow startup costsLow startup costsEasy to manageEasy to manageOffers opportunities for expansionOffers opportunities for expansionMost popular topology in use; wide variety Most popular topology in use; wide variety

of equipment availableof equipment available

Disadvantages ofDisadvantages ofStar TopologyStar Topology

Hub is a single point of failureHub is a single point of failureRequires more cable than the busRequires more cable than the bus

Bus Networks in a Physical Star Bus Networks in a Physical Star LayoutLayout

No exposed terminatorsNo exposed terminatorsCapability for connecting multiple hubs to Capability for connecting multiple hubs to

expand network in many directionsexpand network in many directionsExpansion opportunities for implementing Expansion opportunities for implementing

high-speed networkinghigh-speed networkingPopular design; wide range of equipment Popular design; wide range of equipment

availableavailable

LAN Transmission MethodsLAN Transmission Methods

EthernetEthernet IEEE 802.3 specificationsIEEE 802.3 specificationsBroadest options for expansion and high-Broadest options for expansion and high-

speed networkingspeed networkingToken ringToken ring

IEEE 802.5 specificationsIEEE 802.5 specificationsFDDI (Fiber Distributed Data Interface)FDDI (Fiber Distributed Data Interface)

High-speed variation of token ringHigh-speed variation of token ring

EthernetEthernet

Uses CSMA/CD access method for data Uses CSMA/CD access method for data transmission on a networktransmission on a network

Typically implemented in a bus or bus-star Typically implemented in a bus or bus-star topologytopology

Carrier senseCarrier senseCollisionCollision

Ethernet CommunicationsEthernet Communications

Ethernet IIEthernet II

Ethernet StandardsEthernet Standards

Token RingToken Ring

Developed by IBM in the 1970s; remains a Developed by IBM in the 1970s; remains a primary LAN technologyprimary LAN technology

Employs physical star topology with logic Employs physical star topology with logic of ring topologyof ring topology

Each node connects to a central hub, but Each node connects to a central hub, but the frame travels from node to node as the frame travels from node to node as though there were no starting or ending though there were no starting or ending pointpoint

Token Ring FrameToken Ring Frame

Token Ring TermsToken Ring Terms

Multistation access unit (MAU)Multistation access unit (MAU)BeaconingBeaconingBroadcast stormsBroadcast storms

FDDIFDDI

Fiber-optic data transport method capable of a Fiber-optic data transport method capable of a 100-Mbps transfer rate using a dual ring 100-Mbps transfer rate using a dual ring topologytopology

Synchronous versus asynchronous Synchronous versus asynchronous communicationscommunications

Nodes monitor network for error conditionsNodes monitor network for error conditions Long periods of no activityLong periods of no activity Long periods where the token is not presentLong periods where the token is not present

Class A and Class B nodesClass A and Class B nodes

WAN Network CommunicationsWAN Network Communications

Typical providers of WAN network servicesTypical providers of WAN network services Telecommunications companiesTelecommunications companies Cable TV companiesCable TV companies Satellite providersSatellite providers

Newer sources of WAN connectivityNewer sources of WAN connectivity Cable television networksCable television networks Satellite TV companiesSatellite TV companies Wireless WANsWireless WANs

Wide use of star topologyWide use of star topology

Telecommunications WANsTelecommunications WANs

Earliest source of WAN connectivityEarliest source of WAN connectivityRegional telephone companies, also Regional telephone companies, also

called:called:TelcosTelcosRegional bell operating companies (RBOCs)Regional bell operating companies (RBOCs)

Long-distance telecommunications Long-distance telecommunications companiescompanies

Plain old telephone service (POTS) or Plain old telephone service (POTS) or public switched telephone network (PSTN)public switched telephone network (PSTN)

General Topology Linking LATA General Topology Linking LATA and IXC Linesand IXC Lines

Connecting LANs throughConnecting LANs througha T-Carrier Linea T-Carrier Line

T-Carrier Services and Data T-Carrier Services and Data RatesRates

Cable TV WANsCable TV WANs

Also called cablecos or multiple system Also called cablecos or multiple system operators (MSOs)operators (MSOs)

Use a distributed architecture that consists Use a distributed architecture that consists of several star-shaped centralized of several star-shaped centralized locationslocations

Headend is the main focal point in the starHeadend is the main focal point in the star

Wireless WANsWireless WANs

Use radio, microware, and satellite Use radio, microware, and satellite communicationscommunications

Packet radio communicationsPacket radio communications

Topology of a Radio Wave Topology of a Radio Wave WAN Joining Two LANsWAN Joining Two LANs

WAN Transmission MethodsWAN Transmission Methods

Use different switching techniques to Use different switching techniques to create data paths (channels) for create data paths (channels) for transmitting datatransmitting data

SwitchingSwitchingEnables multiple nodes to simultaneously Enables multiple nodes to simultaneously

transmit and receive data, ortransmit and receive data, orEnables data to be transmitted over different Enables data to be transmitted over different

routes to achieve maximum efficiency in terms routes to achieve maximum efficiency in terms of speed and costof speed and cost

Switching TechniquesSwitching Techniques

Time division multiple access Time division multiple access (TDMA)(TDMA)

Divides channels into distinct time Divides channels into distinct time slotsslots

Frequency division multiple Frequency division multiple access (FDMA)access (FDMA)

Divides channels into frequenciesDivides channels into frequencies

Statistical multiple accessStatistical multiple access Dynamically allocates bandwidth Dynamically allocates bandwidth based on application needbased on application need

Circuit switchingCircuit switching Uses a dedicated physical circuitUses a dedicated physical circuit

Message switchingMessage switching Uses store-and-forward method Uses store-and-forward method of data transmissionof data transmission

Packet switchingPacket switching Combines circuit and message Combines circuit and message switchingswitching

Chapter SummaryChapter Summary

Open Systems Interconnection (OSI) Open Systems Interconnection (OSI) modelmodel

Basic network topologiesBasic network topologiesKey LAN transmission methodsKey LAN transmission methodsWAN communications optionsWAN communications optionsWAN transmission methodsWAN transmission methods