ATM Technologies

Chapter 8

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

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

Advantages of ATMScalable

Solves congestion problems

Helps segment networks

Provides high-speed connectivity to desktop

Contributors to ATMATM Forum

Internet Engineering Task Force (IETF)

Frame Relay Forum

Switched Multimegabit Data Service Special Interest Group (SMDS SIG)

Technologies Compatiblewith ATM

B-ISDN

DSL

FDDI

Frame relay

Gigabit and 10 Gigabit Ethernet

SONET and SDH

SMDS

Wireless communication

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

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

ATM Layers

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

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

ATM QoS Service Attributes

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

AAL Types

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)

ATM Services and Applications Layer Service Types

ATM Cell StructureFixed-length cell

5-byte headerProvides each cell with channel and path information

48-byte payload

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)

ATM Cell Header

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)

PVCDedicated between two endpoints

Preassigned path and fixed allocated bandwidth between endpoints

SVCCreated on an as-needed basis only for as long as devices are communicating

SPVCCombines characteristics of PVCs and SVCs

Must be manually configured (like PVC)

Each transmission has its own defined path (like SVC)

ATM Transmission Characteristics

Logical connection-oriented technology

Virtual circuits define logical channelsVirtual channels (VCs)

Virtual paths (VPs)

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

ATM Design ConsiderationsATM components

ATM switch

ATM switch characteristics and types

ATM interface types

ATM Components

ATM Switch CharacteristicsNumber and size of cell buffersPort contention and management of port parametersConnection managementLatencyTypes of physical and internetworking interfacesTraffic and congestion control options

ATM Switch TypesATM LAN switches

ATM modules for existing multiprotocol network hubs

Multiprotocol hubs

ATM Interface TypesUser-Network Interface (UNI)

End node-to-switch connection

Network Node Interface (NNI)Connection between two ATM switches

Uses of ATMLAN backbone

LAN design uses

High-speed LAN access to servers

Connections to desktop

WAN design uses

Uses of ATM

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

ATM on a Legacy LAN

ATM on a Large Multi-LAN

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

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

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)

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

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)

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

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

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

Transporting Frame Relay over ATM

Transporting Frame Relay over ATM

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

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

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