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  1. 1. Tutorial T4: ATM Basics Joseph D. Robinson Advisory Networking Specialist Network Computing Systems Center International Business Machines Corporation 1001 Winstead Drive Cary, NC 27513 919-301-3882 Fax: 919-301-3794 Internet: joerobin@vnet.ibm.com
  2. 2. Joseph D. Robinson is an Advisory Marketing Support Representative at the IBM Network Computing Systems Center in Cary , North Carolina. He works with IBM Networking Services Specialists and IBM Customers planning and implementing Campus ATM Networks. Joe has implemented both Classic IP and ATM LAN Emulation products for the past 4.0 years. These products include the 8260 ATM Switch, 8210 Multiprotocol Switch Server (MSS), the 827X LAN Switches, the 8285 Workgroup Switch, the 8281 ATM LAN Bridge, ATM Campus Manager, Classic/IP for the RS/6000 and LAN Emulation for Netware, DOS, and Windows. Prior to his work at the Network Computing Systems Center Joe was a Networking Systems Engineer for 7 years in Tampa, Florida. Biography
  3. 3. What is switching? Why cell switching? What is ATM? This tutorial is for professionals who are not familiar with ATM. It focuses on ATM (Asynchronous Transfer Mode) communication technology. The ATM layered model is presented along with ATM terminology and traffic descriptors. Basic ATM concepts such as Permanent Virtual Circuits, Switch Virtual Circuits, and Network to Network interfaces are also covered. This is a technical discussion of basic ATM standards. Abstract
  4. 4.  Introduction to ATM  Layered Model  Physical Layer  ATM Layer  ATM Adaptation Layer  ATM Addressing  ILMI Registration  Permanent Virtual Circuits  Switched Virtual Circuits  QoS  Connection Types  Conclusion Agenda
  5. 5. An industry group that formulates implementations of standards for ATM Networking equipment vendors Service providers Network users Over 600 total members IBM is a Principal Member IBM/ISSC and IBM Global Network (Advantis) are User Members Many Auditing Members Contributions IBM has made over 10 % of the technical contributions http://www.atmforum.com ATM Forum
  6. 6. Current LAN technologies have reached their limit: Available bandwidth is shared Fewer users per LAN segment increases topology complexity Time dependent traffic incompatible with shared media Shared media is leaving the stage to switching: Provides dedicated bandwidth for high-demand WS Static switching: per module - per port Dynamic switching: based on LAN address Ultimate: cell switching - ATM Why ATM?
  7. 7. New High Speed Environment New Network Architecture High-Bandwidth Applications New Technology Different Traffic Types Voice, video, data integration Bursty traffic Isochronous Timing sensitive Multipoint PDH Sonet/SDH (OCx, STM-1) Cell Relay (ATM) SMDS/CBDS Lower Costs / High Quality Fiber LAN Interconnect Client/Server Image Distributed Computing Multimedia Medical Imaging Video Distribution
  8. 8. Multimedia Applications Kiosks  Retail merchandizing  Public information services Business Desktop  Annotated mail documents  Image, video archives  Conferencing  Training  News bulletins Audio/Video Distribution (Media on Demand)  Entertainment  News  Education  Information  Business Simulation & Imaging Medical  Patient records  Diagnosis Engineering  Design  Modeling Manufacturing  Process control  Monitoring  Training Media production  Animation  A/V Development  Entertainment  Advertising  Theme Parks The World Wide Web
  9. 9. Multimedia Isochronous Requirements FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME FRAME t t t t T= / Latency Latency Jitter Skew Sender Receiver Receiver Video Audio Skew Network delay Synchronization between flows Uneven arrival
  10. 10. Bandwidth Scalable speed up to 1.2 Gbps (and higher) Dedicated bandwidth Full duplex Topology Scalable Physical logical segmentation Multimedia requirements Isochronous Bandwidth on demand Deployment Industry driven standard evolution (ATM Forum) Aggressive price/performance expectations ATM Meets New Requirements
  11. 11. ATM supports voice, data, video Cell switching 53-byte cells (5-byte header + 48 bytes data) Small cells to minimize cell delay Low-error rate links (primarily optical) Defined as part of Broadband-ISDN standards No error recovery in network Only error detection and some correction Error recovery is responsibility of end device Connection oriented Guaranteed sequential delivery No room in a cell header for a destination ATM address Instead using circuit identifier (VPI/VCI) Key Concepts
  12. 12. One Network for All Information Data Video Voice Multimedia Integrated Services Digital Pipe Up To Gigabit Speeds Cells Voice Data Video  ATM Moves Cells  Low Delay  Low Delay Variation  Very High Speeds
  13. 13. Why 53 Bytes? 64 + 5 32 + 4 48 + 5 U.S. Telco wanted 64 Bytes for Efficiency Europe wanted 32 Bytes to avoid echo cancellation equipment Compromise reached in ITU-TS Study Group in 1989
  14. 14. ATM Layered Architecture Adaptation Layer ATM Layer Physical Layer ATM Switch C P S w ATM User Device ATM User Device Adaptation Layer ATM Layer Physical Layer
  15. 15. Consists of two sublayers: Transmission Convergence Sublayer HEC Generation Cell Scrambling/Descrambling Cell Delineation (HEC) Path Signal Identification Frequency Justification/ Pointer Processing Multiplexing Scrambling Descrambling Transmission frame generation/recovery Physical Media Dependent Sublayer Encoding for transmission Timing and synchronization Transmission (electrical/optica) Physical Layer 155 Mpbs
  16. 16. OVERHEAD Maintenance & Operations CELL CELL CELL CELL CELL CELL CELL CELL CELL CELL CELL CELL CELL .... .... SDH or SONET Framing - STS 3C 270 Columns 9 Rows 9 Bytes 125 U secs 1 Synchrounous Payload Data Envelope (1 floating column of overhead) 9 x 260 x 8 / 125 u secs = 149.76 Mpbs May be interleaved to get STS 12 and higher
  17. 17. ATM Forum Physical Interfaces
  18. 18. Cell creation (53 Octets) Transfer of fixed size ATM Service Data Units (SDU) Data - 48 Bytes SDU Type - PTI Requested/Received Cell Loss Priority - CLP Congestion Experience - EFCN According to traffic contract QoS traffic parameters conformance definition Multiplexing/demultiplexing - multiple ATM connections with QoS requirements Generic flow control ATM Layer
  19. 19. ATM User-Network Interface (UNI) Cell BIT 1 2 3 4 5 6 53 GFC VPI VPI VCI VCI VCI PT CLP HEC CELL PAYLOAD (48 OCTETS) 1 4 5 8 GFC - Generic Flow Control VPI - Virtual Path Identifier VCI - Virtual Channel Identifier PT - Payload Type CLP - Call Loss Priority HEC - Header Error Control
  20. 20. ATM Network to Network Interface (NNI) Cell BIT 1 2 3 4 5 6 53 VPI VPI VPI VCI VCI VCI PT CLP HEC CELL PAYLOAD (48 OCTETS) 1 4 5 8 VPI - Virtual Path Identifier VCI - Virtual Channel Identifier PT - Payload Type CLP - Call Loss Priority HEC - Header Error Control
  21. 21. 5 classes defined  A - circuit emulation (e.g. voice)  Constant bit rate, connection oriented, timing  Emulates a leased line  Iintended for constant rate voice and video applications.  B - variable bit-rate service (e.g. compressed voice and video)  Variable bit rate, connection oriented, timing  Intended for voice and video traffic  Basically isochronous at the level of end-user presentation  May becoded as variable-rate information.  C - connection-oriented data  Variable bit rate, connection oriented  traditional data traffic as known in an SNA or X.25 network  D - connectionless data  Variable bit rate, connectionless  could beused for example to carry TCP/IP or LAN interconnection traffic where the protocol in use is inherently connectionless  X - connection oriented  User defined bandwidth and QoS, VBR or CBR ATM Adaptation Layer
  22. 22. AAL-1: Constant bit rate services (circuit emulation) Voice, video,... AAL-2: Variable bit rate Compressed voice, coded video Not yet defined AAL-3/4: Traditional data and image Very complex (derived from SMDS) AAL-5: Traditional data and image Simple - what everyone will use AAL Types
  23. 23. AAL 5 Operation User Data User Data Fill Trailer SAR PDU SAR PDU SAR PDU ATM Adaptation Layer ATM Layer SAR PDU SAR PDU 5 Bytes 5 Bytes 5 Bytes SAR PDU Step 1 1.) Pad such that SDU PLUS 8-byte trailer will be a multiple of 48 2) Add Trailer Step 2 Segment into 48 Bytes Step 3 Add 5 Byte Header and mark the last one with an EOM bit x Service Interface
  24. 24. ATM Layered Model Management Plane User Plane Control Plane User Layer ATM Standard ATM Adaption Layer ATM Layer Physical Layer Signalling & Control Class A Class B Class C Class D Constant Bit Rate Circuit Emulation Variable Bit Rate Audio/Video Connection Oriented Services Connection- less Services AAL1 AAL2 AAL3/4 or AAL5  ATM Adaptation Layer takes frames and adds header/trailer to create 48-byte PDU to have ATM Layer create 53-byte cell  Protocols above ATM Adaptation Layer not defined by ATM standards
  25. 25. CONTROL PLANE FUNCTIONS  ATM Forum V3.0 ,V3.1 (UNI) – SVC, PVC – Point to point and Point to multipoint – Anycast addresses (4.0 feature) – Interworking 3.0 3.1  PNNI Phase 1 – Single level hierarchy – Soft PVCs – Crankback  Path Selection – Generic CAC – On demand and Precomputed routing – Widest Path and Shortest path – Load balancing – Tuneable to specific network conditions
  26. 26. LANE Software Layer Layered Interfaces Higher Layer Protocols LLC or Bridge Relay function LAN Emulation Entity Q2931 Connection Mgt. SAAL AAL (NULL SSCS) AAL5 Common Part ATM PHY Layer Mgt. LUNI Network Layer Data Link Layer Physical Layer
  27. 27. LE will use ATM Adaptation Layer 5 (AAL5) to segment and reassemble its Protocol Data Units (PDU) AAL5 Message Mode Service and non-assured operation Service Specific CS is NULL QoS class 0 (best effort) (not required)  Bearer Classes BCOB-X or BCOB-C for incoming calls  BCOB-X for outgoing calls Point to point VCCs (SVC) Point-to-multipoint services (if available) for multicast services End system must "initialize" to find its ATM @ ATM Network Assumptions
  28. 28. ATM Address AFI DCC HO DSP ESI S E L AFI ICD HO DSP ESI S E L 39 - DCC Data Country Code ISO-3166 47 - ICD International Code Descriptor ISO-6523 AFI E.164 telephone number HO DSP ESI S E L 45 - E.164 ISDN in their International Format AFI authority and format identifier HO DSP high order domain specific part ESI end system identifier SEL vendor selector
  29. 29. ICD / GOSIP Encodings AFI ICD HO DSP ESI S E L 47 - ICD International Code Descriptor ISO-6523 D F I AA reserved RDN Area 470005 80FFEA000000xxxxyyyy DFI Domain Format Identifier AA Administrative Authority RDN Routing Domain Number
  30. 30. SNMP Interface Access UNI V3.X MIB Address Registration ATM UNI V3.X MIB Physical Layer ATM Layer ATM Layer Statistics Virtual Path Connection Virtual Channel Connection Default VPI=0 VCI=16 Interim Local Management Interface
  31. 31. Address Registration Using ILMI Network Prefix Table Address Table User Side Network Side UNI 1) Initialize Network Prefix Table 2) Issue ColdStart trap 3) Issue GET Address Table 4) Update Network Prefix Table 5) Append ESI/SEL 6) SET ATM Address 1) Initialize Address Table 2) SET Network Prefix 3) Update Address Table C P S w 40.00.03.50.00.01 39.99.99.99.99.99.99.00.00.99.99.01.05 39.99.99.99.99.99.99.00.00.99.99.01.05.40.00.03.50.00.01.00
  32. 32. Connection Relationships Physical Link VP VC VP = Virtual Path VC = Virtual Channel VC VC VC VC VC VP VP VP VP VP - A bundle of Virtual Channels - All the Virtual Channels have the same endpoints - A unidirectional communication capability for the transport of ATM cells
  33. 33. Permanent Virtual Circuits (PVC) C P S w 1 5 5 1 5 5 Similar to LEASED Lines Statically Defined No Standard for Defining VPI=0, VCI = 33 VPI=0, VCI = 33 VPI=0, VCI = 33 VPI=0, VCI = 34 Connection Table Port VPI/VCI Port VPI/VCI 1, 1 0/33 15, 1 0/33 1,2 0/33 17,2 0/34
  34. 34. Switched Virtual Circuits (SVC) C P S w 6 2 2 1 5 5 C P S w 1 5 5 6 2 2 PNNI-1 VP=2 ATM Address 39.01.01.....01 ATM Address 39.01.02.....02 Switch A Switch B Connection Table A Port VPI/VCI Port VPI/VCI 1, 2 0/33 17, 2 2/305 Connection Table B Port VPI/VCI Port VPI/VCI 1, 2 2/305 17, 2 0/34 Call (39.01.02.....02) VPI=0, VCI=33 VPI=0, VCI=34 VPI=2, VCI=305  Similar to Dial Up Lines  Dynamically Defined  Q2931 Signaling Standard OC-12
  35. 35. ATM CALL SET UP / CALL RELEASE RELEASE COMPLETE CONNECT SET UP SET UP CONNECT CONNECT ACK CONNECT ACK RELEASE RELEASE COMPLETE RELEASE CALL PROCEEDING CALL PROCEEDING C P S w
  36. 36. POINT to MULTIPOINT C P S w SET UP SET UP SET UP CONNECT CONNECT CONNECT ADD PARY ACK ADD PARTY
  37. 37. Quality of Service Reserved Bandwidth (RB) Used by ATM native applications: At call setup application knows how much is needed and how The network:  Guarantees the bandwidth  Assigns priorities  Performs policing and reshaping Non-Reserved Bandwidth (NRB) Used for support of current (LAN) applications The network:  Performs "best effort" switching  Packets transmitted after service for RB  Applies back-pressure to sender Flow Control is for NRB Only!!!  If a RB connection sticks with its traffic contract it has guarenteed bandwidth.  If a RB connection violates its traffic contract and the queue backs up POLICING takes place. Cells are discarded.
  38. 38. Constant Bit Rate (CBR) - circuit emulation  Continuous stream of bits -- 64 kbps, for example  Very low delay and very low delay variation Real-Time Variable Bit Rate (rt-VBR)  Very tight bounds on delay  Not have very tight bounds on cell loss Non-Real-Time Variable Bit Rate (nrt-VBR)  Complement of rt-VBR  Not as interested in delay  No Cell Loss Unspecified Bit Rate (UBR)  No guarantees Available Bit Rate (ABR)  Flow control  Very low cell loss within the network General QoS Service Catagories
  39. 39. Buffer Management and Traffic Management Determine: What Traffic Enters the Network,  At What Rate, and  Whether the Traffic Gets to Its Destination(s) Actual Throughput Seen By the Users Quality of Service Seen By the Users Throughput and QoS
  40. 40. Reshaping Traffic Reshaping - Evenly spacing ATM cells to conform to allocated bandwidth rates 25Mbps 25Mbps 100Mbps Queue 90 Mbps
  41. 41. Policing Traffic Policing - associated with RB traffic. Throwing away cells that do not meet the Traffic contract. 100 Mbps peak shallow queue 90 Mbps Traffic Contract BIT Bucket
  42. 42. Policing, Tagging, and Discarding Are Determined By: Cell Loss Priority (CLP) Traffic Control Descriptors Traffic Contract Enforcement Methods Congestion Thresholds Are Not User Setable Discard Methods: EPD - Early Packet Discard PPD - Partial Packet Discard RED - Random Early Detect Traffic Enforcement
  43. 43. GCRAs Are Also Referred to as Dual Leaky Buckets Each Virtual Circuit Has Two GCRAs Defined A GCRA Is Defined to Monitor One of the Following Options: CLP=0, CLP=1, or CLP=0+1: For the Following Characteristics (Based on QoS):  PCR  PCR + SCR  PCR + SCR + MBS  SCR + MBS For Each GCRA, an Enforcement Mode Is Also Selected: Static Enforcement - Discards Cells Regardless of Available Bandwidth Congestion Based Enforcement - Discards Cells Only If There Is Congestion Generic Cell Rate Algorithms (GCRAs)
  44. 44. Dual Leaky Buckets (GCRAs) VCC VCC PCR Dependent on Traffic Descriptor or Class #1 #2 Monitor  Based on CLP = 0, 1, or 0+1 Enforcement  Static or Congestion Based
  45. 45. BASIC CONTROL POINT FUNCTIONS ROUTING B CALL B ? ? SIGNALLING ?
  46. 46. UNI 3.0 & 3.1 User Network Interface PNNI Phase 1.0 (Single Peer Group) Network to Network Interface Network Node Interface Establish VCs That Meet Requested Bandwidth and QoS Enable the Network to Scale to Hundreds (or Thousands) of Nodes Interim Inter-Switch Signaling Protocol (IISP) Interoperability With Older ATM Switches No topology or resource information gets passed Manually configure Static routing only. PNNI Phase Zero Connection Types
  47. 47. Current PNNI-1 CLUSTERING : 2 LEVELS HIERARCHY STANDARD or PRE-STANDARD INTERFACES UNI UNI IISP SSI -Signalling:UNI* -Routing:OSPF -Signalling:UNI* -Routing:Static
  48. 48. PATH SELECTION CBR, VBR A D C B x 5040 510 2520 510 x 'On demand routing' Path computation is done at Call set up time 1-Links not satisfying QOS are pruned (GCAC) Pruning takes in account asymmetry 2-Shortest path on the Administrative weight Network designer control 3-If equal shortest paths : Widest path on AvCR Load balancing Widest path: width of path determined by narrowest link in path AvCR: Available Cell Rate
  49. 49. PATH SELECTION UBR 'Precomputed routing' Paths are precomputed as a background task optimise Call Set-up late Network designer can select either: - Widest path on MaxCR optimise load balancing or - Shortest path on Admin. weight followed by Widest path optimise network resources and allow network designer control A D C B 5040 5040 5040 5040 5040 Widest path: width of path determined by narrowest link in path MaxCR: Maximum Cell Rate
  50. 50. The Future!!! L L L TOPOLOGY AGGREGATION CONCEPT OF 'HIERARCHY'
  51. 51. Conclusion ATM provides: Scalable network bandwidth Simplified network design Consolidation of disparate networks Seamless connectivity from LAN to WAN Multi-media support Migration from installed base Concerns Standards still emerging  Multimedia Public WAN deployment lagging
  52. 52.  AAL. ATM Adaptation Layer  AIX . IBM's implementation of the UNIX operating system  ARP Address Resolution Protocol  API. Application Programming Interface  ATM. Asynchronous Transfer Mode  BUS. Broadcast and Unknown Server  IP. Internet Protocol  ILMI. Interim Local Management Interface  LAN. Local Area Network  LANE. LAN Emulation  LEC. LAN Emulation Client  LES. Lan Emulation Server  LIS Logical IP Subnet  MAC. Part of Data Link Layer  MIB. Management Information Base  MSS. Multiprotocol Switch Services  NDIS. Network Driver Interface Specification  NNI. Network Node Interface  ODI. Open Data-link Interface Acronyms
  53. 53.  PVC. Permanent Virtual Connection  QOS Quality of Service  RFC. Request For Comments  RISC. Reduced Instruction-Set Computer SNMP. Simple Network Management Protocol SSCS Service Specific Convergence Subsystem SSI. Switch-to-Switch Interface SVC. Switched Virtual Connection SVN. Switched Virtual Networking TCP/IP. Transmission Control Protocol/Internet Protocol UNI. User-Network Interface VC. VIRTUAL CONNECTION VCC. Virtual Channel Connection VCI. Virtual Channel Identifier (in ATM cell header) VPI. Virtual Path Identifier WAN. Wide Area Network WG. Work Group Acronyms (continued)

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