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ATM Technologies Chapter 8 Learning Objectives Explain the general characteristics of ATM Describe ATM layered communications Explain the ATM cell structure Explain how ATM works Discuss ATM design considerations Describe ATM applications on LANs and WANs Discuss virtual LANs and ATM Discuss network management issues for ATM LANs and WANs Introduction to ATM High-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 ATM Scalable Solves congestion problems Helps segment networks Provides high-speed connectivity to desktop Contributors to ATM ATM Forum Internet Engineering Task Force (IETF) Frame Relay Forum Switched Multimegabit Data Service Special Interest Group (SMDS SIG) Technologies Compatible with ATM B-ISDN DSL FDDI Frame relay Gigabit and 10 Gigabit Ethernet SONET and SDH SMDS Wireless communication ATM Characteristics Transports wide range of information transmissions at high speeds Divides data into equal-sized cells Attaches a header to ensure that each cell is routed to its destination Transports voice, video, and data equally well Easily scalable; switch-based technology Physical links operate over many cable types Many possible ATM transmission speeds ATM Layered Communications ATM Protocol Reference Model Four-layer architecture Enables multiple services to function at same time on single network ATM MAC equivalent sublayer operates independently of upper layers ATM layer and ATM Adaptation layer (AAL) specifically perform ATM functions ATM Layers ATM Physical Layer Converts cell stream into transportable bits Handles functions at physical medium (cable) Defines electrical and physical interfaces, line speeds, and transmission control Two sublayers Transmission Convergence (TC) sublayer Physical Medium Dependent (PMD) sublayer ATM Layer Creates 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 sublayers Convergence sublayer Segmentation and Reassembly (SAR) sublayer AAL Types ATM Services and Applications Layer Determines class of service needed for a transmission Establishes link between node generating the data stream and the ATM Adaptation layer Four 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 Structure Fixed-length cell 5-byte header Provides each cell with channel and path information 48-byte payload Fields in ATM Cell Header Generic 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 Works Creates virtual circuits as pathways between sending and receiving nodes Permanent virtual circuit (PVC) Switched virtual circuit (SVC) Smart permanent virtual circuit (SPVC) PVC Dedicated between two endpoints Preassigned path and fixed allocated bandwidth between endpoints SVC Created on an as-needed basis only for as long as devices are communicating SPVC Combines 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 channels Virtual channels (VCs) Virtual paths (VPs) Advantages of ATM Network Design Cells arriving at incoming port can be easily directed to appropriate outgoing port Grouped/shared connections along a common virtual path require only one set of management services Easy to add virtual circuits Automatic adjustment of all channels in a path to compensate for a problem ATM Design Considerations ATM components ATM switch ATM switch characteristics and types ATM interface types ATM Components ATM Switch Characteristics Number and size of cell buffers Port contention and management of port parameters Connection management Latency Types of physical and internetworking interfaces Traffic and congestion control options ATM Switch Types ATM LAN switches ATM modules for existing multiprotocol network hubs Multiprotocol hubs ATM Interface Types User-Network Interface (UNI) End node-to-switch connection Network Node Interface (NNI) Connection between two ATM switches Uses of ATM LAN backbone LAN design uses High-speed LAN access to servers Connections to desktop WAN design uses Uses of ATM ATM as a LAN Backbone Simplifies 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 Uses LAN 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 LANE Compatible 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 Components LAN 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 ATM Transport of IP over ATM; focuses strictly on IP support Each subnet must have its own ARP server Simpler implementation than LANE; generates less network overhead Any 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 Connections to 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 Uses Connecting 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 LANs Benefits 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 goal Monitor network congestion and flow control for optimal traffic patterns Chapter Summary Characteristics of ATM networks ATM layered communications ATM’s use of cells instead of packets How ATM works ATM design elements How ATM is applied to LANs and WANs Link between ATM and virtual LAN configurations Basic ATM network management considerations