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Atm

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Atm

  1. 1. AsynchronousAsynchronous Transfer ModeTransfer Mode (ATM)(ATM)
  2. 2. Asynchronous Transfer ModeAsynchronous Transfer Mode One man had a vision of railways that would link all theOne man had a vision of railways that would link all the mainline railroad termini. His name was Charles Pearsonmainline railroad termini. His name was Charles Pearson and, though born the son of an upholsterer, he becameand, though born the son of an upholsterer, he became Solicitor to the city of London. There had previously been aSolicitor to the city of London. There had previously been a plan for gaslit subway streets through which horse-drawnplan for gaslit subway streets through which horse-drawn traffic could pass. This was rejected on the grounds that suchtraffic could pass. This was rejected on the grounds that such sinister tunnels would become lurking places for thieves.sinister tunnels would become lurking places for thieves. Twenty years before his system was built, Pearson envisaged aTwenty years before his system was built, Pearson envisaged a line running through "a spacious archway," well-lit and well-line running through "a spacious archway," well-lit and well- ventilated.ventilated. His was a scheme for trains in a drain.His was a scheme for trains in a drain. —King Solomon's Carpet, Barbara Vine (Ruth Rendell)
  3. 3. ATMATM  a streamlined packet transfer interfacea streamlined packet transfer interface  similarities to packet switchingsimilarities to packet switching  transfers data in discrete chunkstransfers data in discrete chunks  supports multiple logical connections over asupports multiple logical connections over a single physical interfacesingle physical interface  ATM uses fixed sized packets called cellsATM uses fixed sized packets called cells  with minimal error and flow controlwith minimal error and flow control  data rates of 25.6Mbps to 622.08Mbpsdata rates of 25.6Mbps to 622.08Mbps
  4. 4. Protocol ArchitectureProtocol Architecture
  5. 5. Reference Model PlanesReference Model Planes  user planeuser plane  provides for user information transferprovides for user information transfer  control planecontrol plane  call and connection controlcall and connection control  management planemanagement plane  plane managementplane management • whole system functionswhole system functions  layer managementlayer management • Resources and parameters in protocol entitiesResources and parameters in protocol entities
  6. 6. ATM Logical ConnectionsATM Logical Connections  virtual channel connections (VCC)virtual channel connections (VCC)  analogous to virtual circuit in X.25analogous to virtual circuit in X.25  basic unit of switching between two end usersbasic unit of switching between two end users  full duplexfull duplex  fixed size cellsfixed size cells  also foralso for  user-network exchange (control)user-network exchange (control)  network-network exchange (network mgmt & routing)network-network exchange (network mgmt & routing)
  7. 7. ATM Virtual Path ConnectionATM Virtual Path Connection  virtual path connection (VPC)virtual path connection (VPC)  bundle of VCC with same end pointsbundle of VCC with same end points
  8. 8. Advantages of Virtual PathsAdvantages of Virtual Paths  simplified network architecturesimplified network architecture  increased network performance andincreased network performance and reliabilityreliability  reduced processingreduced processing  short connection setup timeshort connection setup time  enhanced network servicesenhanced network services
  9. 9. CallCall EstablishEstablish mentment Using VPsUsing VPs
  10. 10. Virtual Channel ConnectionVirtual Channel Connection UsesUses  between end usersbetween end users  end to end user dataend to end user data  Control signalsControl signals  VPC provides overall capacityVPC provides overall capacity • VCC organization done by usersVCC organization done by users  between end user and networkbetween end user and network  control signalingcontrol signaling  between network entitiesbetween network entities  network traffic managementnetwork traffic management  routingrouting
  11. 11. VP/VC CharacteristicsVP/VC Characteristics  quality of servicequality of service  switched and semi-permanent channelswitched and semi-permanent channel connectionsconnections  call sequence integritycall sequence integrity  traffic parameter negotiation and usagetraffic parameter negotiation and usage monitoringmonitoring  VPC onlyVPC only  virtual channel identifier restriction within VPCvirtual channel identifier restriction within VPC
  12. 12. Control Signaling - VCCControl Signaling - VCC  to establish or release VCCs & VPCsto establish or release VCCs & VPCs  uses a separate connectionuses a separate connection  methods are:methods are: 1.1. semi-permanent VCCsemi-permanent VCC 2.2. meta-signaling channelmeta-signaling channel 3.3. user to network signaling virtual channeluser to network signaling virtual channel 4.4. user to user signaling virtual channeluser to user signaling virtual channel
  13. 13. Control Signaling - VPCControl Signaling - VPC  methods for control signalling for VPCs:methods for control signalling for VPCs: 1.1. Semi-permanentSemi-permanent 2.2. Customer controlledCustomer controlled 3.3. Network controlledNetwork controlled
  14. 14. ATM CellsATM Cells
  15. 15. ATM Header FieldsATM Header Fields  generic flow controlgeneric flow control  Virtual path identifierVirtual path identifier  Virtual channel identifierVirtual channel identifier  payload typepayload type  cell loss prioritycell loss priority  header error controlheader error control
  16. 16. Generic Flow Control (GFC)Generic Flow Control (GFC)  control traffic flow at user to network interfacecontrol traffic flow at user to network interface (UNI) to alleviate short term overload(UNI) to alleviate short term overload  two sets of procedurestwo sets of procedures  uncontrolled transmissionuncontrolled transmission  controlled transmissioncontrolled transmission  every connection subject to flow control or notevery connection subject to flow control or not  if subject to flow controlif subject to flow control  may be one group (A) defaultmay be one group (A) default  may be two groups (A and B)may be two groups (A and B)  flow control is from subscriber to networkflow control is from subscriber to network
  17. 17. GFC - Single Group ofGFC - Single Group of ConnectionsConnections 1.1. If TRANSMIT=1 send uncontrolled cells anyIf TRANSMIT=1 send uncontrolled cells any time. If TRANSMIT=0 no cells may be senttime. If TRANSMIT=0 no cells may be sent 2.2. If HALT received, TRANSMIT=0 untilIf HALT received, TRANSMIT=0 until NO_HALTNO_HALT 3.3. If TRANSMIT=1 & no uncontrolled cell to send:If TRANSMIT=1 & no uncontrolled cell to send: 1.1. If GO_CNTR>0, TE may send controlled cell andIf GO_CNTR>0, TE may send controlled cell and decrement GO_CNTRdecrement GO_CNTR 2.2. If GO_CNTR=0, TE may not send controlled cellsIf GO_CNTR=0, TE may not send controlled cells 4.4. TE sets GO_CNTR to GO_VALUE uponTE sets GO_CNTR to GO_VALUE upon receiving SET signalreceiving SET signal
  18. 18. Use of HALTUse of HALT  to limit effective data rate on ATMto limit effective data rate on ATM  should be cyclicshould be cyclic  to reduce data rate by half, HALT issuedto reduce data rate by half, HALT issued to be in effect 50% of timeto be in effect 50% of time  done on regular pattern over lifetime ofdone on regular pattern over lifetime of connectionconnection
  19. 19. Two Queue ModelTwo Queue Model  uses two counters each with current &uses two counters each with current & initial values:initial values:  GO_CNTR_AGO_CNTR_A  GO_VALUE_AGO_VALUE_A  GO_CNTR_BGO_CNTR_B  GO_VALUE_BGO_VALUE_B
  20. 20. Header Error ControlHeader Error Control
  21. 21. Effect ofEffect of Error inError in CellCell HeaderHeader
  22. 22. Impact of Random Bit ErrorsImpact of Random Bit Errors on HEC Performanceon HEC Performance
  23. 23. Transmission of ATM CellsTransmission of ATM Cells  I.432 specifies several data rates:I.432 specifies several data rates:  622.08Mbps622.08Mbps  155.52Mbps155.52Mbps  51.84Mbps51.84Mbps  25.6Mbps25.6Mbps  two choices of transmission structure:two choices of transmission structure:  Cell based physical layerCell based physical layer  SDH based physical layerSDH based physical layer
  24. 24. Cell Based Physical LayerCell Based Physical Layer  no framing imposedno framing imposed  vontinuous stream of 53 octet cellsvontinuous stream of 53 octet cells  cell delineation based on header errorcell delineation based on header error control fieldcontrol field
  25. 25. Cell Delineation StateCell Delineation State DiagramDiagram
  26. 26. Impact of Random Bit ErrorsImpact of Random Bit Errors on Cell Delineationon Cell Delineation PerformancePerformance
  27. 27. Acquisition Time v Bit ErrorAcquisition Time v Bit Error RateRate
  28. 28. SDH Based Physical LayerSDH Based Physical Layer  imposes structure on ATM streamimposes structure on ATM stream  eg. for 155.52Mbpseg. for 155.52Mbps  use STM-1 (STS-3) frameuse STM-1 (STS-3) frame  can carry ATM and STM payloadscan carry ATM and STM payloads  specific connections can be circuitspecific connections can be circuit switched using SDH channelswitched using SDH channel  SDH multiplexing techniques can combineSDH multiplexing techniques can combine several ATM streamsseveral ATM streams
  29. 29. STM-1 Payload for SDH-STM-1 Payload for SDH- Based ATM Cell TransmissionBased ATM Cell Transmission
  30. 30. ATM Service CategoriesATM Service Categories  Real time - limit amount/variation of delayReal time - limit amount/variation of delay  Constant bit rate (CBR)Constant bit rate (CBR)  Real time variable bit rate (rt-VBR)Real time variable bit rate (rt-VBR)  Non-real time - for bursty trafficNon-real time - for bursty traffic  Non-real time variable bit rate (nrt-VBR)Non-real time variable bit rate (nrt-VBR)  Available bit rate (ABR)Available bit rate (ABR)  Unspecified bit rate (UBR)Unspecified bit rate (UBR)  Guaranteed frame rate (GFR)Guaranteed frame rate (GFR)
  31. 31. Constant Bit Rate (CBR)Constant Bit Rate (CBR)  fixed data rate continuously availablefixed data rate continuously available  tight upper bound on delaytight upper bound on delay  uncompressed audio and videouncompressed audio and video  video conferencingvideo conferencing  interactive audiointeractive audio  A/V distribution and retrievalA/V distribution and retrieval
  32. 32. Real-Time Variable Bit RateReal-Time Variable Bit Rate (rt-VBR)(rt-VBR)  for time sensitive applicationsfor time sensitive applications  tightly constrained delay and delay variationtightly constrained delay and delay variation  rt-VBR applications transmit data at a rate thatrt-VBR applications transmit data at a rate that varies with timevaries with time  eg. compressed videoeg. compressed video  produces varying sized image framesproduces varying sized image frames  original (uncompressed) frame rate constantoriginal (uncompressed) frame rate constant  so compressed data rate variesso compressed data rate varies  hence can statistically multiplex connectionshence can statistically multiplex connections
  33. 33. Non-Real-Time Variable Bit RateNon-Real-Time Variable Bit Rate (nrt-VBR)(nrt-VBR)  if can characterize expected bursty traffic flowif can characterize expected bursty traffic flow  eg. airline reservations, banking transactionseg. airline reservations, banking transactions  ATM net allocates resources based on thisATM net allocates resources based on this  to meet critical response-time requirementsto meet critical response-time requirements  giving improve QoS in loss and delaygiving improve QoS in loss and delay  end system specifies:end system specifies:  peak cell ratepeak cell rate  sustainable or average ratesustainable or average rate  measure of how bursty traffic ismeasure of how bursty traffic is
  34. 34. Unspecified Bit Rate (UBR)Unspecified Bit Rate (UBR)  may be additional capacity over and above thatmay be additional capacity over and above that used by CBR and VBR trafficused by CBR and VBR traffic  not all resources dedicated to CBR/VBR trafficnot all resources dedicated to CBR/VBR traffic  unused cells due to bursty nature of VBRunused cells due to bursty nature of VBR  for application that can tolerate some cell loss orfor application that can tolerate some cell loss or variable delaysvariable delays  eg. TCP based trafficeg. TCP based traffic  cells forwarded on FIFO basiscells forwarded on FIFO basis  best effort servicebest effort service
  35. 35. Available Bit Rate (ABR)Available Bit Rate (ABR)  application specifies peak cell rate (PCR)application specifies peak cell rate (PCR) and minimum cell rate (MCR)and minimum cell rate (MCR)  resources allocated to give at least MCRresources allocated to give at least MCR  spare capacity shared among all ARBspare capacity shared among all ARB sourcessources  eg. LAN interconnectioneg. LAN interconnection
  36. 36. ATM Bit Rate ServicesATM Bit Rate Services
  37. 37. SummarySummary  Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode (ATM)  architecture & logical connectionsarchitecture & logical connections  ATM Cell formatATM Cell format  transmission of ATM cellstransmission of ATM cells  ATM servicesATM services

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