1 asynchronous transfer mode (atm) Presentation Transcript
Asynchronous Transfer Mode (ATM)
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Agenda Definition Basic characteristics Why asynchronous How to access the network Service Categories Connections Protocol Architecture pros & cons Troubleshooting
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".
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
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
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).
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
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
Virtual PathsPhysical Link Virtual Channels
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
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
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
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