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Understanding Asynchronous Transfer Mode (ATM): A Comprehensive Overview

Explore the basics, characteristics, and advantages of ATM technology, including connections, protocol architecture, service categories, and troubleshooting techniques. Learn about ATM's packet-switching, virtual circuits, network access, and more. Reference white papers and tutorials to deepen your knowledge.

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Understanding Asynchronous Transfer Mode (ATM): A Comprehensive Overview

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  1. Asynchronous Transfer Mode (ATM)

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  3. Agenda • Definition • Basic characteristics • Why asynchronous • How to access the network • Service Categories • Connections • Protocol Architecture • pros & cons • Troubleshooting

  4. ATM – definition "A transfer mode in which information is organized into cells; it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic".

  5. ATM Characteristics • ATM uses packet switching with fixed length packet of 53 bytes – CELLs. Each cell has a 5-byte header and 48-byte payload • ATM uses Virtual Circuits • ATM can run over any physical layer. Often runs over fiber optics using the SONET standard at speeds of 155.52 Mbps, 622 Mbps and higher

  6. ATM Characteristics A Cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-sized block of information ATM uses asynchronous TDM – to multiplex cells coming from different channels • Uses fixed slots (size of cells) • Fills a slot with a cell from any input channel that has a cell – slot is empty if none of the channels has a cell to send

  7. Asynchronous Transfer Mode (ATM) MUX Wasted bandwidth 4 3 2 1 4 3 2 1 4 3 2 1

  8. ATM Access • ATM is a cell-switched network. • The user access devices, called the endpoints, are connected through a user-to-network interface (UNI) to the switches inside the network. • The switches are connected through network-to-network interfaces (NNIs).

  9. STDUCTURE Private ATM network Private UNI X X Private NNI Public ATM network A Public UNI X X X NNI X Public UNI B-ICI Public ATM network B X Public UNI X X

  10. ATM Connections • two levels of ATM connections: virtual path connections virtual channel connections • indicated by two fields in the cell header: virtual path identifier VPI virtual channel identifier VCI

  11. Virtual Paths Physical Link Virtual Channels

  12. ATM Service Categories • Real-time services • Constant bit rate – uncompressed audio/video info • Videoconferencing, TV, pay-per-view, VOD, etc. • rt-Variable bit rate • Non-real-time services • nrt-VBR – high end system QoS, critical response time • Bank transactions, airline reservations, etc. • Unspecified bit rate – best-effort service • e.g. text/image messaging, telecommuting • Available bit rate – bursty apps requiring reliable end-to-end connection • e.g. LAN, router-to-router reliability

  13. ATM Protocol Architecture Management plane Plane management Control plane User plane Layer management Higher layers Higher layers ATM adaptation layer ATM layer Physical layer

  14. adaptation layer: only at edge of ATM network • data segmentation/reassembly • roughly analogous to Internet transport layer • ATM layer: “network” layer • cell switching, routing • physical layer AAL user ATM layer Physical layer

  15. Pros & cons • higher transmission speeds • quality of service • bandwidth-on-demand • application-independent • Cost • Complexity • Availability

  16. Troubleshooting • Performing Basic Interface Checks • Determining Network Connectivity • Performing Loopback Tests • Troubleshooting 155-Mbps and 622-Mbps Interfaces • Troubleshooting T1 and E1 Interfaces • Troubleshooting DS3 and E3 Interfaces • Troubleshooting CBR T1 and CBR E1 Interfaces • Troubleshooting 25-Mbps Interfaces

  17. References: • Asynchronous Transfer Mode (ATM) fundamentals, white paper from Internation Engineering Consortium • ATM tutorial-fnc educational services • Higher Layer Protocols:TCP/IP and ATM-Eytan Modiano,Massachusetts Institute of Technology • ATM Switch Troubleshooting Guide-Cisco

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