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Understanding ATM: Architecture, Cells, and Signaling in Asynchronous Transfer Mode Networks

This chapter delves into the fundamentals of Asynchronous Transfer Mode (ATM), a crucial technology in networking. It covers key concepts such as ATM cells, architecture, and the significance of addressing and signaling. ATM employs fixed-size cells for efficient data transmission, particularly for voice and video applications. It establishes virtual circuits before communication and utilizes a unique three-dimensional model composed of layers and planes. The chapter emphasizes the importance of the ATM Adaptation Layer (AAL) for data encapsulation and segmentation, along with various connection types supported by ATM.

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Understanding ATM: Architecture, Cells, and Signaling in Asynchronous Transfer Mode Networks

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  1. CHAPTER #6 • Introduction to ATM

  2. Contents • Introduction • ATM Cells • ATM Architecture • ATM Connections • Addressing and Signaling • IP over ATM

  3. 6.1. Introduction • ATM-Asynchronous Transfer Mode • A transfer mode in which the information is organized into cells • It is asynchronous in the sense that the recurrence of cells containing information from a particular user is not necessarily periodic

  4. Asynchronous transfer mode (= Statistical multiplexing) – Sources packetize data. Packets are sent only if there is data

  5. ATM requires connections to be established before any communication takes place • A connection is called a virtual circuit (VC) which could be permanent or switched

  6. Information to be transmitted is divided into cells consisting of: 5 bytes header and 48 bytes user data. • Fixed sized cells enable HW switching • Typical speeds of ATM are 155 and 622 Mbps

  7. 6.2.ATM’s Key Concepts • ATM uses Virtual-Circuit Packet Switching(VCPS) • ATM can reserve capacity for a VC • This is useful for voice and video, which require a minimum level of service • Overhead for setting up a connection is expensive if data transmission is short (e.g., web browsing)

  8. 6.2. (Follow) • ATM packets are small and have a fixed size – Packets in ATM are called cells – Small packets are good for voice and video transmissions

  9. 6.3.ATM Cells • Why 53 Bytes? • Advantages • Disadvantages

  10. 6.3.1.Why 53 Bytes? • A 48 byte payload was the result of a compromise between a 32 byte payload and a 64 byte payload •

  11. 6.3.2.Advantages – Low packetization delay for continuous bit rate applic- ations (video, audio) – Processing at switches is easier

  12. 6.3.3.Disadvantages – High overhead (5 Bytes per 48) – Poor utilization at lower line rates links

  13. 6.3.4. UNI Cells

  14. 6.3.5. NNI Cells

  15. 6.4.ATM Architecture • The ATM Reference Model: ATM technology has its own protocol architecture

  16. 6.5.ATM Reference Model

  17. 6.6.ATM Layers and Planes • ATM is a three dimensional model consisting of layers and planes • Physical layer deals with physical media issues,further divided into: (1) PMD and (2) TC sub layers

  18. ATM layer defines cell format and connection setup

  19. 6.6.(Follow) • ATM Adaptation Layer (AAL) segments and reassembles upper layer into and from cells,divided into : • SAR and • CS sub layers

  20. User planes deals with data transport,flow and error control

  21. Control plane deals with connection management

  22. The Layer and Plane management deals with resource management and interlayer coordination

  23. 6.7.ATM Adaptation Layer (AAL) • AAL encapsulates user-level data • Performs segmentation and reassembly of user-level messages

  24. 6.8.Layers of ATM

  25. 6.8.1..Functions of Layers

  26. 6.9.ATM Layer • The ATM Layer is responsible for the transport of 53 byte cells across an ATM network

  27. Multiplex logical channels within a physical channel

  28. The ATM Layer can provide a variety of services for cells from an ATM virtual connection: -Constant Bit Rate (CBR) -Variable Bit Rate(VBR) - Available Bit Rate(ABR) -Unspecified Bit Rate(UBR) -Guarantees Frame Rate(GFR)

  29. 6.10. Correspondence between ATM and OSI Reference Models

  30. 6.11.ATM Connections • A Packet Switch

  31. 6.12.Forwarding with VCs

  32. 6.13.Addressing and Signaling ATM End system Addresses (AESA) • ALL ATM addresses are 20 bytes long

  33. Source and destination address are supplied when setting up a connection

  34. ATM endpoints use the NSAP (Network Service Access Point) format from ISO OSI

  35. Three different types of addresses : • NSAP encoding for E.164: ISDN telephone numbers (e.g., 001-434-9822200) -

  36. 2.DCC format: for public networks, 3.ICD format: for private networks

  37. 6.14.ATM End system Addresses (AESA)

  38. 6.15.Formats of an ATM address

  39. 6.16.ATM UNI Signaling • Significant Signaling Protocols

  40. ATM Forum: • UNI 3.0. UNI signaling protocol for point-to- point connections. -

  41. 2.UNI 3.1. Supports point-to-multipoint connections.

  42. 3.UNI 4.0. Supports Leaf initiated join multipoint connections

  43. 4. -PNNI. for network node signaling

  44. 6.17.Which Address Format To Use? • Currently each service provider makes its own choice – This introduces problems (SVC compatibility)

  45. Most ATM switches support multiple formats

  46. ATM Forum prepares standards to translate addresses at network boundaries (NNI interfaces) –

  47. Interworking of ATM Networks (IAN)

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