Chapter 08
Transcript of Chapter 08
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ATM Technologies
Chapter 8
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Learning ObjectivesExplain the general characteristics of ATMDescribe ATM layered communicationsExplain the ATM cell structureExplain how ATM worksDiscuss ATM design considerationsDescribe ATM applications on LANs and WANsDiscuss virtual LANs and ATMDiscuss network management issues for ATM LANs and WANs
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Introduction to ATMHigh-speed transport technology that handles voice, video, data, and multimedia transmissions
Transmits fixed-length cells rather than packets over virtual circuits
Uses cell-switching
Has QoS capabilities
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Advantages of ATMScalable
Solves congestion problems
Helps segment networks
Provides high-speed connectivity to desktop
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Contributors to ATMATM Forum
Internet Engineering Task Force (IETF)
Frame Relay Forum
Switched Multimegabit Data Service Special Interest Group (SMDS SIG)
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Technologies Compatiblewith ATM
B-ISDN
DSL
FDDI
Frame relay
Gigabit and 10 Gigabit Ethernet
SONET and SDH
SMDS
Wireless communication
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ATM CharacteristicsTransports wide range of information transmissions at high speeds
Divides data into equal-sized cellsAttaches a header to ensure that each cell is routed to its destination
Transports voice, video, and data equally wellEasily scalable; switch-based technologyPhysical links operate over many cable typesMany possible ATM transmission speeds
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ATM Layered Communications
ATM Protocol Reference ModelFour-layer architectureEnables multiple services to function at same time on single network
ATM MAC equivalent sublayer operates independently of upper layersATM layer and ATM Adaptation layer (AAL) specifically perform ATM functions
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ATM Layers
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ATM Physical LayerConverts cell stream into transportable bitsHandles functions at physical medium (cable)Defines electrical and physical interfaces, line speeds, and transmission controlTwo sublayers
Transmission Convergence (TC) sublayerPhysical Medium Dependent (PMD) sublayer
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ATM LayerCreates the ATM cell
Determines cell structure, how cell is routed, and error-control techniques
Ensures QoS of virtual circuit or channel
Functions performed by:ATM switch
ATM attached device
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ATM QoS Service Attributes
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ATM Adaptation Layer (AAL)Responsible for segmentation and reassembly of data into and out of ATM cell format
Ensures that different traffic types are assigned correct QoS level
Provides support for four classes of service
Two sublayersConvergence sublayer
Segmentation and Reassembly (SAR) sublayer
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AAL Types
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ATM Services and Applications Layer
Determines class of service needed for a transmissionEstablishes link between node generating the data stream and the ATM Adaptation layerFour service classes
Constant bit-rate service (CBR)Variable bit-rate service (VBR)Unspecified bit-rate service (UBR)Available bit-rate service (ABR)
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ATM Services and Applications Layer Service Types
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ATM Cell StructureFixed-length cell
5-byte headerProvides each cell with channel and path information
48-byte payload
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Fields in ATM Cell HeaderGeneric Flow Control (GFC)
Virtual Path Identifier (VPI)
Virtual Channel Identifier (VCI)
Payload Type Indicator (PTI)
Cell Loss Priority (CLP)
Header Error Control (HEC)
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ATM Cell Header
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How ATM WorksCreates virtual circuits as pathways between sending and receiving nodes
Permanent virtual circuit (PVC)
Switched virtual circuit (SVC)
Smart permanent virtual circuit (SPVC)
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PVCDedicated between two endpoints
Preassigned path and fixed allocated bandwidth between endpoints
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SVCCreated on an as-needed basis only for as long as devices are communicating
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SPVCCombines characteristics of PVCs and SVCs
Must be manually configured (like PVC)
Each transmission has its own defined path (like SVC)
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ATM Transmission Characteristics
Logical connection-oriented technology
Virtual circuits define logical channelsVirtual channels (VCs)
Virtual paths (VPs)
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Advantages of ATM Network Design
Cells arriving at incoming port can be easily directed to appropriate outgoing portGrouped/shared connections along a common virtual path require only one set of management servicesEasy to add virtual circuitsAutomatic adjustment of all channels in a path to compensate for a problem
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ATM Design ConsiderationsATM components
ATM switch
ATM switch characteristics and types
ATM interface types
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ATM Components
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ATM Switch CharacteristicsNumber and size of cell buffersPort contention and management of port parametersConnection managementLatencyTypes of physical and internetworking interfacesTraffic and congestion control options
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ATM Switch TypesATM LAN switches
ATM modules for existing multiprotocol network hubs
Multiprotocol hubs
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ATM Interface TypesUser-Network Interface (UNI)
End node-to-switch connection
Network Node Interface (NNI)Connection between two ATM switches
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Uses of ATMLAN backbone
LAN design uses
High-speed LAN access to servers
Connections to desktop
WAN design uses
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Uses of ATM
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ATM as a LAN BackboneSimplifies network management by reducing complexity of internetworking environments
Able to increase backbone speeds incrementally
Allows “future-proofing” of network
Common in campus environment
Works well for:Small to medium-sized legacy backbones
As a backbone for large multi-LAN designs
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ATM on a Legacy LAN
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ATM on a Large Multi-LAN
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ATM LAN Design UsesLAN Emulation (LANE)
Technique used to adapt ATM to Ethernet network by creating a multicast network to enable preassigned groups of Ethernet nodes to receive transmissions
Vital for integrating ATM with non-ATM networks
Uses ATM’s connection-oriented technology without requiring hardware or software changes within legacy LAN
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Benefits of LANECompatible with legacy LAN equipment
Application software and upper-layer protocols can communicate over LANE
Client can be anywhere; not bound by distance limitations of legacy LAN
Network traffic congestion not a problem
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LANE ComponentsLAN Emulation Client (LEC) software
LAN emulation software; implemented on three logical servers
LAN Emulation Server (LES)
Broadcast and Unknown Server (BUS)
LAN Emulation Configuration Server (LECS)
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Classical IP over ATMTransport of IP over ATM; focuses strictly on IP supportEach subnet must have its own ARP serverSimpler implementation than LANE; generates less network overheadAny device with a legacy LAN connection must pass through a router to reach destination device
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Multiprotocol over ATM (MPOA)
Communications technique that enables multiprotocol traffic to be routed over ATM
Network layer protocols use routers to communicate across subnet boundaries
Can produce performance problems
Integrates LANE and the Next Hop Resolution Protocol (NHRP)
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ATM High-Speed LAN Access to Servers
Alternative when Fast Ethernet no longer able to handle traffic to heavily used LAN servers
Benefits of a “server farm”Easy to connect to ATM switches on network backbone
Cheaper and easier bandwidth upgrades
Easier for administrator to control access to servers
Enables servers to be secured
Easier to place servers on conditioned power and UPS
Multiple servers can share one display monitor
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ATM for Connectionsto the Desktop
To relieve congestion caused by more demanding software applications
To achieve full QoS
Each end device must be equipped with an ATM adapter o NIC
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ATM WAN Design UsesConnecting two or more LANs using an ATM WAN
Transporting ATM over SONET
Connecting frame relay WANs using an ATM WAN
Connecting SMDS WANs using an ATM WAN
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Transporting Frame Relay over ATM
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Transporting Frame Relay over ATM
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Virtual LANsBenefits of VLANs over ATM networks
Enable logical segmentation of a network regardless of physical network constraints
Enhanced network performance
Advanced network management features
Capability for reducing number of router hops and amount of required bandwidth
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Network Management Issues for ATM LANs and WANs
Monitoring and controlling all virtual circuits (PVCs and SVCs)
Network topology
Status of ATM network devices
Overall goalMonitor network congestion and flow control for optimal traffic patterns
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Chapter SummaryCharacteristics of ATM networksATM layered communicationsATM’s use of cells instead of packetsHow ATM worksATM design elementsHow ATM is applied to LANs and WANsLink between ATM and virtual LAN configurationsBasic ATM network management considerations