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Chapter 5

Chapter 5. Asynchronous Transfer Mode (ATM). Introduction. ATM Protocol Architecture Logical connections ATM Cells Service categories ATM Adaptation Layer (AAL). ATM Protocol Architecture. Fixed-size packets called cells Streamlined: minimal error and flow control

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Chapter 5

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  1. Chapter 5 Asynchronous Transfer Mode (ATM) Chapter 5 Asynchronous Transfer Mode

  2. Introduction • ATM Protocol Architecture • Logical connections • ATM Cells • Service categories • ATM Adaptation Layer (AAL) Chapter 5 Asynchronous Transfer Mode

  3. ATM Protocol Architecture • Fixed-size packets called cells • Streamlined: minimal error and flow control • 2 protocol layers relate to ATM functions: • Common layer providing packet transfers • Service dependent ATM adaptation layer (AAL) • AAL maps other protocols to ATM Chapter 5 Asynchronous Transfer Mode

  4. Protocol Model has 3 planes • User • Control • Management Chapter 5 Asynchronous Transfer Mode

  5. Figure 5.1 Chapter 5 Asynchronous Transfer Mode

  6. Logical Connections • VCC (Virtual Channel Connection): a logical connection analogous to virtual circuit in X.25 • VPC (Virtual Path Connection): a bundle of VCCs with same endpoints Chapter 5 Asynchronous Transfer Mode

  7. Figure 5.2 Chapter 5 Asynchronous Transfer Mode

  8. Advantages of Virtual Paths • Simplified network architecture • Increased network performance and reliability • Reduced processing and short connection setup time • Enhanced network services Chapter 5 Asynchronous Transfer Mode

  9. VPC/VCC Characteristics • Quality of Service (QoS) • Switched and semi-permanent virtual channel connections • Cell sequence integrity • Traffic parameter negotiation and usage monitoring • (VPC only) virtual channel identifier restriction within a VPC Chapter 5 Asynchronous Transfer Mode

  10. Control Signaling • A mechanism to establish and release VPCs and VCCs • Methods to request for a VC: • Semi-permanent VCCs • Request as needed Chapter 5 Asynchronous Transfer Mode

  11. ATM Cells • Fixed size • 5-octet header • 48-octet information field • Small cells reduce delay for high-priority cells • Fixed size facilitate switching in hardware Chapter 5 Asynchronous Transfer Mode

  12. Header Format • Generic flow control • Virtual path identifier (VPI) • Virtual channel identifier (VCI) • Payload type • Cell loss priority • Header error control Chapter 5 Asynchronous Transfer Mode

  13. Figure 5.4 CLP = Cell Loss Priority bit Chapter 5 Asynchronous Transfer Mode

  14. Generic Flow Control • Control traffic flow at user-network interface (UNI) to alleviate short-term overload conditions • When GFC enabled at UNI, 2 procedures used: • Uncontrolled transmission • Controlled transmission Chapter 5 Asynchronous Transfer Mode

  15. Header Error Control • 8-bit field calculated based on remaining 32 bits of header • For error detection • In some cases, error correction of single-bit errors in header Chapter 5 Asynchronous Transfer Mode

  16. 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) Chapter 5 Asynchronous Transfer Mode

  17. Figure 5.8 Chapter 5 Asynchronous Transfer Mode

  18. ATM Adaptation Layer (AAL) • Support non-ATM protocols • Maps to ATM cells • AAL Services • Handle transmission errors • Segmentation/reassembly (SAR) • Handle lost and misinserted cell conditions • Flow control and timing control Chapter 5 Asynchronous Transfer Mode

  19. Applications of AAL and ATM • Circuit emulation (e.g., E-1/T-1 synchronous TDM circuits) • VBR voice and video • General data services • IP over ATM • Multiprotocol encapsulation over ATM (MPOA) • LAN emulation (LANE) Chapter 5 Asynchronous Transfer Mode

  20. AAL Protocols • AAL layer has 2 sublayers: • Convergence Sublayer (CS) • Supports specific applications using AAL • Segmentation and Reassembly Layer (SAR) • Packages data from CS into cells and unpacks at other end Chapter 5 Asynchronous Transfer Mode

  21. Figure 5.9 Chapter 5 Asynchronous Transfer Mode

  22. Figure 5.10 (CBR source) CBR Service (connectionless or connection-oriented) VBR Service (higher-layer connection-oriented services) Connection-oriented Service Chapter 5 Asynchronous Transfer Mode

  23. AAL Type 1 • Constant-bit-rate source • SAR simply packs bits into cells and unpacks them at destination • Sequence Number (SN) used in reassembling SAR PDUs • Sequence Number Protection (SNP) provides error detection/correction • No CS PDU since CS sublayer primarily for clocking and synchronization Chapter 5 Asynchronous Transfer Mode

  24. AAL Type 3/4 • May be connectionless or connection oriented • May be message mode or streaming mode Chapter 5 Asynchronous Transfer Mode

  25. AAL Type 5 • Streamlined transport for connection oriented protocols • Reduce protocol processing overhead • Reduce transmission overhead • Ensure adaptability to existing transport protocols Chapter 5 Asynchronous Transfer Mode

  26. Figure 5.13 Chapter 5 Asynchronous Transfer Mode

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