ATM_Asynchronous Transfer Mode

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a fixeed length cell format,used for sending data over a N/W

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ATM : 

ATM PRESENTED BY AMIT MUKHERJEE B-TECH (CSE) 6th sem Roll No.0928210005 PRESENTED TO Mr. Shreyaskar Gaur Asst.Professor(CSE) J.P.INSTITUTE OF ENGINEERING & TECHNOLOGY

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Asynchronous Transfer Mode What is ATM? Asynchronous Transfer Mode Switching Standards ATM device and the Network enviroment ATM Devices ATM Network Interfaces Types Point to Point Point to Multipoint ATM Architecture ATM cell Basic format ATM cell structure ATM Virtual Connections Characteristics of ATM Advantages of ATM Disadvantages of ATM Applications Recent Development Conclusion Reference CONTENTS

Asynchronous Transfer Mode : 

Asynchronous Transfer Mode Used in the field of Telecommunication ATM is another Packet Switching Mode It is regarded as the technology of the 21st century It is quite similar to PCM(pulse code modulation) [a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital code] Its history starts since the development of Broadband ISDN(1970’s-1980’s) It can even be viewed as the evolution of Pocket Switching [make use of both human mobility and local/global connectivity in order to transfer data between mobile users’ devices.] ATM –a set of internationals interface & signalling standards defined By ITU-T(formerly CCITT) Formulated in 1991 & since then played a very important role

ATM Forum [An international voluntary organisation composed of vendors,service providers,research org.,users]Purpose to accelerate the use of ATM productsATM a set of internationals interface & signalling standards defined By ITU-T(formerly CCITT) : 

ATM Forum [An international voluntary organisation composed of vendors,service providers,research org.,users]Purpose to accelerate the use of ATM productsATM a set of internationals interface & signalling standards defined By ITU-T(formerly CCITT)

A means of digital communications that is capable of very high speeds; suitable for transmission of images or voice or video as well as data. ATM is used for both LAN and WAN What is ATM? A high speed Packet based Multiplexing technique , in which information are encoded into short fixed length cells Cells are generated where there is new data to be send[allows Data compression no need to send pauses that occurs in b/w] It differs from Internet protocol or Ethernet (as they uses variable size packets) It provide services that runs over a wide range of OSI physical layers It was designed for a n/w that must handle both traditional high throughput data traffic(file transfer) real time low latency content(voice & video) It uses a Connection –Orinted model (in which a Virtual Ckt must be established b/w 2 end pts before actual data exchange begins)

Figure: A Private ATM Network and a Public ATM Network Both Can Carry Voice, Video, and Data Traffic : 

Figure: A Private ATM Network and a Public ATM Network Both Can Carry Voice, Video, and Data Traffic Asynchronous Transfer Mode (ATM) are some ITU-T standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells Asynchronous Transfer Mode Switching

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ATM was originally conceived as a high-speed transfer technology for voice, video, and data over public networks. The ATM Forum extended the ITU-T's vision of ATM for use over public and private networks. The ATM Forum has released work on the following specifications: User-to-Network Interface (UNI) 2.0 UNI 3.0 UNI 3.1 UNI 4.0 Public-Network Node Interface (P-NNI) LAN Emulation (LANE) Multiprotocol over ATM Standards

Due to asynchronous nature, ATM is more efficient than synchronous technologies, such as time-division multiplexing (TDM). [ each user is assigned to a time slot, and no other station can send in that time slot. If a station has much data to send, it can send only when its time slot comes up, even if all other time slots are empty. However, if a station has nothing to transmit when its time slot comes up, the time slot is sent empty and is wasted. Because ATM is asynchronous, time slots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell] : 

Due to asynchronous nature, ATM is more efficient than synchronous technologies, such as time-division multiplexing (TDM). [ each user is assigned to a time slot, and no other station can send in that time slot. If a station has much data to send, it can send only when its time slot comes up, even if all other time slots are empty. However, if a station has nothing to transmit when its time slot comes up, the time slot is sent empty and is wasted. Because ATM is asynchronous, time slots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell] A cell-switching and multiplexing technology combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic). It provides bandwidth from a few Mbps to many Gbps. ATM Devices and the Network Environment

ATM network is made up of an ATM switch and ATM endpoints. ATM switch responsible for cell transit through an ATM network.It accepts the incoming cell from an ATM endpoint or another ATM switch. It then reads and updates the cell header information and quickly switches the cell to an output interface toward its destination. ATM endpoint (or end system) contains an ATM network interface adapter. Examples of ATM endpoints are workstations, routers, digital service units (DSUs), LAN switches, and video coder-decoders (CODECs). ATM Devices

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Figure : An ATM network containing ATM switches and End points

ATM switches support two primary types of interfaces: UNI and NNI. UNI connects ATM end systems (such as hosts and routers) to an ATM switch. NNI connects two ATM switches. ATM Network Interfaces

A private UNI connects an ATM endpoint and a private ATM switch. Its public counterpart connects an ATM endpoint or private switch to a public switch. A private NNI connects two ATM switches within the same private organization. A public one connects two ATM switches within the same public organization. the broadband intercarrier interface (B-ICI), connects two public switches from different service providers. : 

A private UNI connects an ATM endpoint and a private ATM switch. Its public counterpart connects an ATM endpoint or private switch to a public switch. A private NNI connects two ATM switches within the same private organization. A public one connects two ATM switches within the same public organization. the broadband intercarrier interface (B-ICI), connects two public switches from different service providers. Depending on whether the switch is owned and located at the customer's premises or is publicly owned and operated by the telephone company, UNI and NNI can be further subdivided into Public and Private UNIs and NNIs

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Figure: ATM Interface Specifications Differ for Private and Public Networks

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TYPES ATM NETWORK CONNECTION POINT-TO-POINT POINT-TO-MULTIPOINT

Point-to-point connects two ATM end systems and can be unidirectional (one-way communication) or bidirectional (two-way communication) : 

Point-to-point connects two ATM end systems and can be unidirectional (one-way communication) or bidirectional (two-way communication) POINT-TO-POINT SOURCE SYSTEM DESTINATION SYSTEM

Point-to-multipoint connects a single-source end system (known as the root node) to multiple destination end systems (known as leaves). Such connections are unidirectional only. : 

Point-to-multipoint connects a single-source end system (known as the root node) to multiple destination end systems (known as leaves). Such connections are unidirectional only. POINT-TO-MULTIPOINT SOURCE SYSTEM DESTINATION SYSTEM DESTINATION SYSTEM DESTINATION SYSTEM DESTINATION SYSTEM

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ATM is a combination of Hardware and Software that can provide an end-to-end network The structure of ATM and its software components comprise the ATM architecture The primary layers of ATM are the Physical layer, the ATM layer and the ATM Adaptation layer. ATM ARCHITECTURE

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Physical layer – manages the medium-dependent transmission. Cells are converted into a bitstream, the transmission and receipt of bits on the physical medium are controlled, ATM cell boundaries are tracked The ATM physical layer is divided into two parts: Physical medium-dependent (PMD) sublayer and the Transmission convergence (TC) sublayer. ATM layer – responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell. It has no sub layers

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ATM adaptation layer (AAL) – responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads. Finally, the higher layers residing above the AAL accept user data, arrange it into packets, and hand it to the AAL.

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Figure: The ATM Reference Model Relates to the Lowest Two Layers of the OSI Reference Model

Figure: An ATM Cell Consists of a Header and Payload Data : 

Figure: An ATM Cell Consists of a Header and Payload Data ATM transfers information in fixed-size units called “cells” Each cell consists of 53 bytes. The first 5 bytes contain cell-header information,the remaining 48 contain the payload (user information). ATM Cell Basic Format

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An ATM cell header can be one of two formats: UNI or NNI. The UNI header is used for communication between ATM endpoints and ATM switches in private ATM networks. The NNI header is used for communication between ATM switches Unlike the UNI, the NNI header does not include the Generic Flow Control (GFC) field. Additionally, the NNI header has a Virtual Path Identifier (VPI) field that occupies the first 12 bits, ATM CELL STRUCTURE

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Generic Flow Control (GFC)—Provides local functions, such as identifying multiple stations that share a single ATM interface. Virtual Path Identifier (VPI)—In conjunction with the VCI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination. Virtual Channel Identifier (VCI)—In conjunction with the VPI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination. ATM CELL STRUCTURE CONTD..

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Payload Type (PT)—Indicates in the first bit whether the cell contains user data or control data. If the cell contains user data, the bit is set to 0. If it contains control data, it is set to 1. Cell Loss Priority (CLP)—Indicates whether the cell should be discarded if it encounters extreme congestion as it moves through the network. If the CLP bit equals 1, the cell should be discarded in preference to cells with the CLP bit equal to 0. Header Error Control (HEC)—Calculates checksum only on the first 4 bytes of the header. HEC can correct a single bit error in these bytes, thereby preserving the cell rather than discarding it. ATM CELL STRUCTURE CONTD...

ATM networks are fundamentally connection-oriented, which means that a virtual channel (VC) must be set up across the ATM network prior to any data transfer. 2 types of ATM connections exist: virtual paths, which are identified by virtual path identifiers, virtual channels, which are identified by the combination of a VPI and a virtual channel ientifier (VCI). : 

ATM networks are fundamentally connection-oriented, which means that a virtual channel (VC) must be set up across the ATM network prior to any data transfer. 2 types of ATM connections exist: virtual paths, which are identified by virtual path identifiers, virtual channels, which are identified by the combination of a VPI and a virtual channel ientifier (VCI). Figure: VCs Concatenate to Create VPs ATM Virtual Connections

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Fragmentation into fixed size cells Statistical multiplexing Virtual Circuit Routing Support for narrow & wide bit rates Constraints on cell delay & loss Handling of cell loss priorities Designed for future unforeseen demands CHARACTERISTICS OF ATM

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Better utilization of the bandwidth Thus, in addition to general Internet use, it can also be used to transfer very large amounts of data over wide area networks and local area networks. Asynchronous transfer mode can also be used between the two types of networks as well. Allows for end-to-end flow and error control The speed of asynchronous transfer mode can reach up to 10 billion bytes per second ADVANTAGES OF ATM

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ATM has not been widely accepted. ATM switch costs much more than inexpensive LAN hardware. Assumption of Homogeneity: ATM is designed to be a single, universal networking system. DISADVANTAGES OF ATM

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ATM combines the low-delay of circuit-switched networks with the bandwidth flexibility and high-speed of packet-switched networks. It’s advanced applications such as remote sensing, 3-D (three-dimensional) interactive simulations. Tele-instruction, biological tele research, and medical tele consultations APPLICATIONS

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Interest in using native ATM for carrying live video and audio has increased recently. In these environments very high quality of service are required to handle linear audio and video streams. Towards this goal standards are being developed such as AES47 (IEC 62365). The Largest ATM Network is developed by the Eighteen major European network operators RECENT DEVELOPMENT

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ATM Technology is uniquely suited for supporting error-free multimedia transport in high-speed network configurations. ATM is regarded as a key enabler for tele-education, tele-business, E-government, and telemedicine applications. ATM networks resolve problems voice, video, and data transmission over wireline, and wireless network configurations With this qualities ATM network will dominate for the next decade or more. CONCLUSION

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Black, Uyless D. (1998). ATM—Volume III: Internetworking with ATM. Toronto: Prentice Hall. ISBN 0-13-784182-5.  McDysan, David E.; Darren L. Spohn (1999). ATM Theory and Applications.Montreal: McGraw-Hill.ISBN 0-07-0453462. www.authorstream.com REFERENCES

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THANK YOU!