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Intro to ATM Asynchronous Transfer Mode Text References –Sect 2.6 –Sect 3.6.3 –Sect 5.6 –Sect 6.5

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  • Slide 1
  • Intro to ATM Asynchronous Transfer Mode Text References Sect 2.6 Sect 3.6.3 Sect 5.6 Sect 6.5
  • Slide 2
  • ATM Background Outgrowth of TELCO transition to integrated services Only real >100Mbit standard Offers multiservice (voice video data) potential Switched architecture familiar to TELCOs, not to high speed data networks
  • Slide 3
  • What is ATM? Note: Tanenbaum considers this more a network layer technology.
  • Slide 4
  • ATM - A layered standard AAL - ATM Adaptation Layer Assembles and disassembles broadband servicesinto a stream of cells Each cell has a header that contains routing information ATM - Asynchronous Transfer Mode Switches the cells around the network based on the routing information in the header Physical Layer Provides the physical transportation of cells across the network (Note: CCITT reference model, p. 63)
  • Slide 5
  • ATM - A Switched Architecture Cells (small, fixed length packets) are switched in a connection-oriented manner but not using circuits like todays voice. Switch Edge Device Edge Device
  • Slide 6
  • What is ATM Switching? Why small cells? (32+64)/2=48 + 5 header bytes Mixed Traffic Packet (random)vs Circuit (TDM) Switching Q.2931 SVC, PVC
  • Slide 7
  • Physical Layer Options SONET (US)/ SDH (Europe) SMDS DQDB Speeds from DS3 on up! (45Mbs to Gbps) OC-3c => 155.52Mbps => 149.76Mbps ^ optical carrier ^ 3rd level in heirarchy ^ full duplex (two strands of fiber) Also OC-12c (622Mbps), OC-48c (2048Mbps) [Look at the interesting way to frame cells]
  • Slide 8
  • ATM Adaptation Layer (AAL) Classes of Service: 1, 2, 3/4, 5 1: circuit emulation 2: variable bit rate service 3/4: connection oriented data service 5: connectionless data service SAR - Segmentation and Reassembly Convergence Sublayer the miscellaneous category
  • Slide 9
  • ATM Cell ATM cells are constant size packets of 53 bytes size. -- 48 bytes payload, 5 bytes header/overhead. VPI - Virtual Path ID VCI - Virtual Channel ID Type - Payload type (internal) Res - reserved CLP- Cell loss priority HEC- Header Error Control
  • Slide 10
  • VCI/VPI Operation A Virtual Channel exists between two switching points A Virtual Path contains 'bundles' of VCs
  • Slide 11
  • ATM Switch Architecture Crossbar Banyan TDM busses Buffering Input Output Both?
  • Slide 12
  • ATM Protocols UNI, NNI Services LAN Stuff
  • Slide 13
  • ATM Services CBR VBR (RT, NRT) UBR ABR
  • Slide 14
  • ATM Quality of Service QoS: A contract Traffic Descriptors Cell Rate Options (pg 462) Traffic Shaping Traffic Policing
  • Slide 15
  • ATM Congestion Control Admission Policy Reservation System Rate Based Control Other
  • Slide 16
  • ATM Flow Control The leaky bucket algorithm CLP in ATM header Frame Relay comparisons
  • Slide 17
  • Routing IISP (Interim Inter-switch Signaling Protocol) PNNI (Private Network-Network Interface) Phase 1 Phase 2
  • Slide 18
  • IISP Interim Allowed multi-vendor interoperability before completion of NNI Signaling Routing via manually configured NSAP prefixes
  • Slide 19
  • PNNI Topology abstraction Peer group(group of nodes) One switch elected Peer Group Leader All nodes in group have identical view of group Hierarchy of logical groups Up to 105 levels of hierarchy
  • Slide 20
  • PNNI Routing A117 A13 A12 A11 B25 A1 B A2 B3 B2B1 A23 A22 A21 NSAP Domain A11 A12 A13 A2 B View from A117 at A11
  • Slide 21
  • Sequence of Events A117 -> B25 Forward to switch (A11) Switch knows topology of A1 group B reachable by A2 - A2 reachable by either A12 or A13 DTL (Designated Transit List) [A12][A2][B] [A22][A23][B] [B2]
  • Slide 22
  • ATM LAN Stuff LAN == Link Layer Domain ELANs & VLANs LANE & MPOA LECS, LES, BUS
  • Slide 23
  • LANE v1 LAN Emulation No QoS (Quality of Service) Support Uses AAL5 signaling -optimized for data transport -entire cell payload available for user data LEC - LAN Emulation Client LAN Emulation Service -LECS - LAN Emulation Configuration Server -LES - LAN Emulation Server -BUS - Broadcast and Unknown Server STP (Spanning Tree Protocol) supported
  • Slide 24
  • LEC - LAN Emulation Client Software process on any ATM-connected LAN switch, router, PC, or workstation Layer 2 process Prior knowledge of certain parameters -LECs ATM address -LAN type to be emulated -maximum data frame size -any route descriptors (for SR bridging) -whether it is willing to proxy (respond to LE-ARP) -LAN name - SNMPv2 display string
  • Slide 25
  • LECS - LAN Emulation Configuration Server One per administrative domain Gives identity of ELAN (Emulated LAN) Returns ATM address of LES, type of LAN emulated, and maximum PDU size of ELAN Controls which physical LANs are combined to form VLANs (Virtual LAN) LECS address known via ILMI or its well-known NSAP address
  • Slide 26
  • LES- LAN Emulation Server Adds LECs to ELAN Assigns LECID to joining LEC Table of address information of LEC -MAC address -proxy for MAC address -Token Ring route descriptors LECs can communicate directly with each other only when they are connected to the same LES Multiple LESs on the same physical ATM LAN Answers LE-ARP requests from LECs
  • Slide 27
  • BUS- Broadcast and Unknown Server During address resolution LEC forwards all frames to the BUS -floods frames to all LECs -after address resolved flush protocol used to guarantee order of cells All multicast and broadcast traffic sent through BUS Traffic limited to 10 frames/second Intelligent BUS -resolve destinations -CLS- connectionless server
  • Slide 28
  • LANE Setup
  • Slide 29
  • Connections All SVC (switched virtual circuits) SVCs required: -LECs and LECS -LES and LECS -Control Direct - LECs and LES -pt-mpt Control Distribute - LES to LECs -Multicast Send - LECs and BUS -pt-mpt Multicast Forward - BUS to LECs -Data Direct - LEC and LEC PVC (permanent virtual circuit) possible to connect LEC and LECS
  • Slide 30
  • Virtual Channel Connections LANE Client (LEC) LANE Server (LES) LANE Configuration Server (LECS) ATM Host LAN Switch Configuration Direct VCC Control Direct VCC Control Distribute VCC LAN Switch ATM Host LANE Client (LEC) Multicast Forward VCC Data Direct VCC Multicast Send VCC Broadcast and Unknown Server (BUS)
  • Slide 31
  • NHRP Next Hop Resolution Protocol Grew out of ATMARP Only IP Allows shortcut routes (pt-pt) -direct VCCs across ATM network Address resolution across multiple IP networks If network unknown, request forwarded to other NHSs (Next-hop Server) -NHS with knowledge will forward response to source router Router must have ability to bypass default route
  • Slide 32
  • RSVP Resource Reservation Protocol Provides QoS (Quality of Service) guarantees Operates in simplex -each direction has separate reservation -maps well to ATM (two individual VCCs) Built on IP, but no data transport built-in Only if resources available and does not conflict with policy Flowspec (bandwidth and delay) and filterspec (type of packets) transmitted downstream -hop by hop
  • Slide 33
  • MPOA Multiprotocol over ATM EDFG (Edge Device Functional Groups) -existing LAN segments via LAN switches AHFG (ATM-attached Host Functional Groups) -ATM-connected host Layer 3 Only supports IP for now Uses LANE for Layer 2 forwarding within a single Layer 3 subnet Adaptation of NHRP to provide connectivity between hosts in different subnets
  • Slide 34
  • MPOA Operation
  • Slide 35
  • Competing Technologies Fast Ethernet 100BASE-TX, 100BASE-FX,100BASE-T4, 100BASE-VG FDDI, FDDI- II HPPI Gigabit Ethernet (IEEE 802.3z)
  • Slide 36
  • ATM Issues SONET/SDH duplication of services ATM overhead ATM granularity and bandwidth management ATM & connectionless service End point synchronization Flow Control !!! (bandwidth allocation, correlated traffic) ATM Forum

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