1 asynchronous transfer mode (atm)


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1 asynchronous transfer mode (atm)

  1. 1. Asynchronous Transfer Mode (ATM)
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  3. 3. Agenda Definition Basic characteristics Why asynchronous How to access the network Service Categories Connections Protocol Architecture pros & cons Troubleshooting
  4. 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. 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. 6. ATM CharacteristicsA Cell network uses the cell as the basic unit of data exchange. A cell is defined as a small, fixed-sized block of informationATM 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. 7. Asynchronous Transfer Mode (ATM) MUX Wasted bandwidth 4 3 2 1 4 3 2 1 4 3 2 1
  8. 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. 9. STDUCTURE Private ATM network Private UNI X X Private NNI Public ATM X network A X X NNI Public X UNI B-ICI Public ATM network B X Public UNI X X
  10. 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. 11. Virtual PathsPhysical Link Virtual Channels
  12. 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. 13. ATM Protocol Architecture Management plane Plane managementControl plane User plane Layer managementHigher layers Higher layers ATM adaptation layer ATM layer Physical layer
  14. 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 AAL user physical layer ATM layer Physical layer
  15. 15. Pros & cons higher transmission speeds quality of service bandwidth-on-demand application-independent Cost Complexity Availability
  16. 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. 17. References:1. Asynchronous Transfer Mode (ATM) fundamentals, white paper from Internation Engineering Consortium2. ATM tutorial-fnc educational services3. Higher Layer Protocols:TCP/IP and ATM- Eytan Modiano,Massachusetts Institute of Technology4. ATM Switch Troubleshooting Guide-Cisco