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ATM (asynchorounus transfer mode)network


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ATM network with full details: all layers description: full class lecture :))

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ATM (asynchorounus transfer mode)network

  1. 1. ATM (Asynchronous Transfer Mode) Presented By- Surbhi & Vasundhara
  2. 2. Content:  What is ATM Network?  ATM Protocol Architecture  ATM Devices and the Network Environment  ATM network interfaces  ATM Cell Format  ATM switching operation  ATM Service Categories  ATM Adaption Layer (AAL 1 to AAL 5)  Advantages of ATM Network
  3. 3. What is ATM? • ATM Net = Data Net + Phone Net • Combination of Internet method of communication (packet switching) and phone companies’ method (circuit switching) • International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay • ATM networks are connection-oriented. • ATM virtual circuit: which is an end-to-end connection that has defined end points and routes but does not have bandwidth dedicated to it. • Bandwidth is allocated on demand by the network as users have traffic to transmit
  4. 4. ATM Protocol architecture
  5. 5. ATM Protocol architecture(cont.)  ATM cell: fixed size packets for information flow  Reduces overhead of processing and space (support high rate)  Planes in ATM network:  User plane: Provides for user information transfer, along with associated flow and error control  Control plane: Performs call control and connection control functions  Management plane: plane mgmt. & resources management as per parameter of protocol entities.
  6. 6. ATM Protocol architecture(cont.)  Physical layer :  Cells are converted into a bit stream  The transmission and receipt of bits on the physical medium are controlled.  ATM cell boundaries are tracked.  Cells are packaged into the appropriate types of frames for the physical medium.  Min data rate: 155.52 mbps : Max data rate: 622.08 Mbps  ATM Layer:  independent of service demanded (common to all)  Deals with AT cell transmission & use of logical connections
  7. 7. ATM Devices and the Network Environment  An ATM network is made up of an ATM switch and ATM endpoints.  An ATM switch is responsible for cell transit  reads and updates the cell header information and quickly switches the cell to an output interface towards its destination.  Examples of ATM endpoints are workstations, routers, digital service units (DSUs), LAN switches, and video coder-decoders (Codec’s).
  8. 8. ATM Network Interfaces ATM network interfaces UNI(connects ATM end systems (such as hosts and routers) to an ATM switch ) Public UNI Private UNI NNI(Connects two ATM switches) Public UNI Private UNI
  9. 9. ATM Cell Format  Each cell consists of 53 octets  Small, fixed-length cells are well suited to transfer voice and video traffic. Header (5 Bytes) Payload (48 bytes)
  10. 10. CELL format in ATM Header(UNI) GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) Generic Flow Control (GFC)— Provides local functions, such as identifying multiple stations that share a single ATM interface. This field is typically not used and is set to its default value of 0 (binary 0000).
  11. 11. CELL format in ATM Header(UNI) GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) Virtual Path Identifier (VPI)— In conjunction with the VCI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination
  12. 12. CELL format in ATM Header(UNI) GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) Virtual Channel Identifier (VCI)— In conjunction with the VPI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination.
  13. 13. ATM Logical connection  Two levels of ATM connections: • virtual path connections • virtual channel connections  Indicated by two fields in the cell header: • virtual path identifier VPI (identifies a particular VP link) • virtual channel identifier VCI (numerical tag to identifies a particular VC) Physical Link Virtual Paths Virtual Channels
  14. 14. ATM switching operations
  15. 15. CELL format in ATM Header(UNI) GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) • Payload Type (PT)—Indicates in the first bit whether the cell contains user data or control data. If the cell contains user data, the bit is set to 0. If it contains control data, it is set to 1. • The second bit indicates congestion (0 = no congestion, 1 = congestion). • The third bit indicates whether the cell is the last or not.
  16. 16. CELL format in ATM Header(UNI) GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) Cell Loss Priority (CLP)— Indicates whether the cell should be discarded if congestion as it moves through the network. If the CLP bit equals 1, the cell should be discarded in preference.
  17. 17. CELL format in ATM Header(UNI) GFC (4 bits) VPI (4 bits) VPI (4 bits) VCI (4 bits) VCI (8 bits) VCI (4 bits) PT (3 bits) CLP (1 bit) HEC (8 bits) ATM cell header Payload (48 bytes) Header Error Control (HEC)— Calculates checksum only on the first 4 bytes of the header. HEC can correct a single bit error in these bytes, thereby preserving the cell rather than discarding it.
  18. 18. ATM Service Categories ATM Service Categories Real-Time Service Constant bit rate(CBR) Real-Time Variable bit rate(rt-VBR) NON-REAL- TIME service Non real- time variable bit rate(nrt- VBR) Available Bit rate(ABR) Unspecified BIT Rate(UBR) Guaranteed Frame Rate(GFR) Tolerance of JITTER matters here (tight constraints of delay) Busty traffic characteristics (un-tight constraints of delay) Fixed rate throughout lifetime of connection(telep hony, video conf) Time sensitive application (video compression effect rate) Data rate varies Relative low delay and minimal loss cell (End system have specify peak cell rate) FIFO based transmission acc. To left resources (variable delay and data rate) Fair distribution of resources among ABR sources(if left given to UBR) Used for IP and Ethernet based sub networks (sp. For frame based network)
  19. 19. ATM Adaption layer Higher Layers ATM Adaptation Layer (AAL) Convergence Sub layer (CS) Segmentation and Reassembly Sub layer (SAR) ATM Layer (ATM) Virtual Channel (VC) Virtual Path (VP) Physical Layer (PL) Transmission Convergence Sub layer (TC) Physical Medium Sub layer (PM)
  20. 20. ATM Adaptation Layer  Defines the rules for breaking up a higher level protocol data unit (PDU) into ATM cells for transmission on the network, and for reassembling the PDU at the other end.  Segmentation and reassembly (SAR): breaks data into cells at the sender and reassembles cells into larger data units at the receiver.  Convergence sub layer: adds sequencing and control information to aid SAR process TCP IP AAL ATM TCP IP AAL ATM ATM Network
  21. 21. PDU PDUCS-header Pad CS-trailer Cell header Cell payload SAR-PDU header SAR-PDU payload SAR-PDU trailer SAR-PDU header SAR-PDU payload SAR-PDU trailer Higher layer CS layer SAR layer ATM layer Cell header Cell payload Adaptation Layer : A detailed view
  22. 22. ATM Adaptation Layer Connectionless Date Transfer Bit Rate Connection Mode Examples of Services Circuit Emulation Constant Bit Rate Video and Audio Constant Variable Connection Oriented Connectionless Variable Bit Rate Video and Audio Connection- oriented Data Transfer AAL TYPE AAL 1 AAL 2 AAL 3/4 AAL 5 Class A Class B Class C Class D Related Not Related Service Timing between Source and Destination AAL3/4 AAL 5
  23. 23. AAL Type 1 Protocol  Supports Class A traffic, i.e., constant bit rate data with specific requirements for delay, delay jitter, and timing, e.g., PCM voice.  Summary of AAL 1 functions  CS Functions  Handling of cell delay variation  Forward error correction for high quality video and audio  Report end-to-end performance status  SAR FUNCTIONS  Segmentation and reassembly of user information  Sequence numbering  Error protection  Mapping between CS PDU and SAR PDU
  24. 24.  Consists of 1 octet header (PCI) and 47 octets of payload  Sequence Number (SN): A 1-bit Convergence Sub layer Indication and 3-bit sequence count to detect deletion or miss insertion of cells  Sequence Number Protection (SNP): 3-bit CRC with even parity for detecting and correcting SN error  The 4 bit RTS is transferred by the CSI bit in successive SAR-PDU headers with an odd SN (SN = 1, 3, 5, 7)  For P format operations, the CSI value in SAR-PDU headers with an even SN (SN = 0, 2, 4, 6) is set to 1 SN SNP SAR-PDU Payload 4 bits 4 bits 47 Octets Cyclic Redundancy Check Even Parity 1 bit3 bit 1 bit 3 bits Convergence Sub layer Indication (CSI) Sequence Number (SN)
  25. 25. AAL Type 2 protocol  Deals with variable bit-rate information  Intended for analog applications ,such as video and audio(CBR not required)  Supports variable bit rate data where there is no timing relationship between source and destination, e.g., X.25, frame relay.  Convergence sublayer divided into two parts:  Common Part Convergence Sublayer (CPCS)  Service Specific Convergence Sublayer (SSCS) AAL Type 3/4 protocol
  26. 26. AAL Type ¾ protocol Types of services provided by AAL ¾ • Connectionless(independent packet) & connection- oriented(multiple SAR logical connection) • Message mode(cell mode) & stream mode(block mode) CPCS-PDU payloadCpcs header Cpcs-pdu trailerpad CPI Btag BAsize AL ETag Length of payload 1 octet1 octet 1 octet 2 octet 2 octet1 octet
  27. 27. CPCS= common part convergence sub layer SAR= Segmentation & Reassembly PDU= protocol data unit CPCS-H= caps header CPCS-T = cpcs trailer Sar-H= Sar header SAR- H = SAR Tailer ATM-H = Atm header BOM= beginning of msg COM = continuation of message
  28. 28. AAL Type 5 Protocol  AAL5 is a simple and efficient AAL (SEAL) to perform a subset of the functions of AAL3/4  The CPCS-PDU payload length can be up to 65,535 octets and must use PAD (0 to 47 octets) to align CPCS-PDU length to a multiple of 48 octets CPCS-PDU Payload PAD CPI Length 1 2 40 - 47 CPCS UU 1 CRC-32 PAD Padding CPCS-UU CPCS User-to-User Indicator CPI Common Part Indicator Length CPCS-PDU Payload Length CRC-32 Cyclic Redundancy Chuck
  30. 30. Advantages of ATM  Dynamic bandwidth for bursty traffic :meeting application needs and delivering high utilization of networking resources  Smaller header with respect to the data to make the efficient use of bandwidth.  Can handle Mixed network traffic very efficiently fixed size cell.  Cell network: All data is loaded into identical cells that can be transmitted with complete predictability and uniformity.  Class-of-service support for multimedia traffic allowing applications with varying throughput and latency requirements to be met on a single network.  Scalability in speed and network size supporting link speeds of (622 Mbps).  Common LAN/WAN ATM technology can be used either as a LAN technology or a WAN technology.
  31. 31. “Thank you for being connected”