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Atm
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Atm

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  • 1. ATM By Kauleshwarnath Pandey Maravar Kannan
  • 2. Asynchronous Transfer Mode • ATM is the cell relay protocol designed by ATM Forum and adopted by ITU-T. • The combination of ATM & B-ISDN will allow high-speed interconnection of all the world’s networks. • In fact, ATM can be thought of as the “highway” of the information superhighway. • ATM operates at a speed of 155 & 622 Mbps & is a connection oriented network
  • 3. Design Goals• Need for a transmission system to optimize the use of high- data-rate transmission media, in particular optical fiber.• A system that can interface with the existing systems, such as various packet networks, & to provide wide area interconnectivity between them without lowering their effectiveness or requiring their replacement.• design that can be implemented inexpensively• able to work with & support the existing telecommunications hierarchies• must be connection oriented to ensure accurate & predictable delivery.• to move as many of the functions to hardware as possible and eliminate as many software functions as possible
  • 4. Packet Networks • Data communications today are based on packet switching & packet networks. A packet is a combination of data & overhead bits that can be passed through the network as a self contained unit. The overhead bits, in the form of a header & trailer, act as an envelope that provides identification & addressing information as well as the data required for routing, flow control, error control, …
  • 5. ATM LANs Issues to be resolved • Connectionless Vs Connection-oriented • Physical Addresses Vs Virtual Connection Identifier • Multicasting & Broadcasting delivery • varying size & intricacy • To improve utilization
  • 6. Cell Networks• Many of the packet internetworking problems are solved by adopting a concept called cell networking.• A cell is a small data unit of fixed size. In a cell network, all data are loaded into identical cells that can be transmitted with complete predictability & uniformity.• As packets of different sizes & formats reach the cell network from a tributory network, they are split into multiple small data units of equal length & loaded into cells.• Because of the same size, the problems associated with multiplexing different sized packets are avoided.
  • 7. Advantages of Cells• High speed of the link coupled with the small size of the cells• A cell network can handle real time data• To a cell network, the smallest unit is a cell, not a bit.• Switching & multiplexing can be implemented in hardware rather than software
  • 8. Asynchronous TDM • ATM uses asynchronous TDM (that’s why called as ATM) to multiplex cells coming from different channels. It uses fixed size slots. • ATM mux fill a slot with a cell from any input channel that has a cell, the slot is empty if none of the channels has a cell to send. • At the first tick of the clock, the multiplexer fills the slot with a cell from each channel. When all the cells from all the channels are multiplexed. The output slots are empty.
  • 9. ATM Switching:Contentionless Time Division • Advantages • Non-blocking • Deterministic performance—probability of cell loss = 0 • Flexible port speeds – (DS-1, E-1, DS-3, E-3, 100M, 155M, 622M) • Hardware multicast without increasing fabric cell traffic • Low transit delays • Disadvantages • Limited scalability on single TDM fabric – Use time-space-time to expand
  • 10. ATM Architecture ATM is a cell switched network. The user access devices, called the end points, are connected through a user-to-network interface (UNI) to the switches inside the network. The switches are connected through network-to-network interfaces.
  • 11. ATM Protocol Stack Upper Layers ATM Adaptation Layer ATM Layer Physical Layer
  • 12. The ATM Layer header payload Fixed length packet = cell
  • 13. ATM Layers in end-pointdevices & switchesThe end points use all three layers while theswitches use only the two bottom layers.
  • 14. ATM Process Conventional Conventional ATM Telecom LAN Traffic Type Data, Voice, Video Voice Data Transmission Fixed Fixed Variable Unit Cell Frame Packet Switching Cell Circuit PacketConnection Type Connection-oriented Connection-oriented Connectionless Delivery Defined Classes Guaranteed Best Effort Access Dedicated Dedicated Shared Rate & Media Application Dependent Channel Dependent Protocol Dependent
  • 15. ATM Process Conventional Conventional ATM Telecom LAN Traffic Type Data, Voice, Video Voice Data Transmission Fixed Fixed Variable Unit Cell Frame Packet Switching Cell Circuit PacketConnection Type Connection-oriented Connection-oriented Connectionless Delivery Defined Classes Guaranteed Best Effort Access Dedicated Dedicated Shared Rate & Media Application Dependent Channel Dependent Protocol Dependent
  • 16. ATM is packet switching!• Switched or permanent connections• Traffic type independent (voice, data, interactive video)• Fixed length packet - 53 bytes (cell) header payload Fixed length packet = cell
  • 17. Anatomy of an ATM Cell 8 7 6 5 4 3 2 1Byte 1 GFC (UNI) or VPI (NNI) VPIByte 2 VPI VCIByte 3 VCI HeaderByte 4 VCI PTI CLPByte 5 HEC 48 Bytes Payload VPI: Virtual Path Identifier CLP: Cell Loss Priority VCI: Virtual Channel Identifier HEC: Header Error Check PTI: Payload Type Indicator GFC: Generic Flow Control
  • 18. Thank You

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