Chapter 12: Asynchronous Transfer Mode (ATM)
The Origin of ATM
The ATM platform enables multimedia transmission via fixed-sized 53-byte packets called cells in network environments ranging from desk area networks (DANs) to global implementations. The term Asynchronous refers to ATM support of intermittent bit rates and traffic patterns in accordance with actual demand. The phrase Transfer Mode denotes ATM multiplexing capabilities in transmitting and switching multiple types of network traffic.
Bell Labs initiated work on ATM research projects in the 1960s and subsequently developed cell relay technology and cell switching architecture for handling bursty transmissions. Originally, ATM was called Asynchronous Time-Division Multiplexing (ATDM) and regarded as a successor to TDM (Time-Division Multiplexing). As with TDM, ATDM supports transmission of delay-sensitive and delay-insensitive traffic. TDM and ATDM assign each fixed-sized cell or information packet to a fixed timeslot. By contrast, ATM supports dynamic allocation of timeslots to cells ondemand. In comparison to ATM, TDM and ATDM protocols are limited in optimizing utilization of available bandwidth for effectively handling volume-intensive multimedia applications.
Bell Labs initiated work on ATM research projects in the 1960s and subsequently developed cell relay technology and cell switching architecture for handling bursty transmissions. Originally, ATM was called Asynchronous Time-Division Multiplexing (ATDM) and regarded as a successor to TDM (Time-Division Multiplexing). As with TDM, ATDM supports transmission of delay-sensitive and delay-insensitive traffic. TDM and ATDM assign each fixed-sized cell or information packet to a fixed timeslot. By contrast, ATM supports dynamic allocation of timeslots to cells ondemand. In comparison to ATM, TDM and ATDM protocols are limited in optimizing utilization of available bandwidth for effectively handling volume-intensive multimedia applications.
What is Asynchronous Transfer Mode (ATM)?
An ATM or the Asynchronous Transfer Mode is one of the fast packet-switching family called cell relay. ATM demands for its fast and dependable access to Web-based applications and real-time delivery of multimedia transmissions. ATM is a statistical time−division multiplexed(STDM) form of traffic that is designed to carry any form of traffic and enables the traffic to be delivered asynchronously to the network. The time-division multiplex is mainly the concept in functioning an ATM. ATM using STDM that enable to have a smooth traffic that the previous chapters was sighted as a problem.
The figure below is showing how ATM uses the TMD:
The purpose of ATM
ATM technology employs a priority switching technique for enabling ATM cells carrying delay-sensitive signals to access the first available timeslot. Because the ATM cell size is fixed and the buffer memory size is constant for each cell, switch queuing delays are predictable and jitter or the variation in signal delay is minimized. By contrast, signal delays degrade performance of real-time applications such as videoconferencing and interactive video-on-demand (IVOD) in networks such as Frame Relay (FR) and Ethernet that transport variable length packets.
What is ATM Cell
ATM networks employ a standard, fixed-size 53-byte cell comprised of a 5-byte header and a 48-byte payload or information field as the basic unit of transmission. The 5-byte header includes an error detection field and a Virtual Channel Identifier (VCI) or Virtual Path Indicator (VPI) for transporting a cell payload to a destination address.
Through utilization of a common cell format, ATM enables real-time services, public and private network interconnectivity, and global interoperability. ISDN employs STDM (Statistical Time-Division Multiplexing) for enabling transmission of frames via designated timeslots at specified intervals. In contrast to ISDN installations, the ATM protocol supports dynamic allocation of timeslots to cells on-demand for optimizing traffic throughput in high-performance network configurations.
ATM technology employs a priority switching technique for enabling ATM cells carrying delay-sensitive signals to access the first available timeslot. Because the ATM cell size is fixed and the buffer memory size is constant for each cell, switch queuing delays are predictable and jitter or the variation in signal delay is minimized. By contrast, signal delays degrade performance of real-time applications such as videoconferencing and interactive video-on-demand (IVOD) in networks such as Frame Relay (FR) and Ethernet that transport variable length packets.
The ATM Forum defines procedures for monitoring the effectiveness of network transmission based on cellular throughput. Cell Loss Ratio (CLR) describes the percentage of cells that are not transported to their destination addresses as a consequence of buffer overloads and network congestion. Cell Transfer Delay (CTD) refers to propagation and queuing delays experienced by cells transiting the network.
Cell Delay Variation (CDV) measures variations in transmission delay between adjacent cells. Minimum Cell Rate (MCR) refers to the lowest cell rate supported by ABR (Available Bit Rate) service. In addition, metrics for Cell Delay Variation Tolerance (CDVT) and parameters for Maximum Cell Transfer Delay (MCTD) are also defined. The effectiveness of QoS delivery in ATM networks depends on such variables as Cell Transfer Delay (CDT) and Cell Delay Variation (CDV).
Through utilization of a common cell format, ATM enables real-time services, public and private network interconnectivity, and global interoperability. ISDN employs STDM (Statistical Time-Division Multiplexing) for enabling transmission of frames via designated timeslots at specified intervals. In contrast to ISDN installations, the ATM protocol supports dynamic allocation of timeslots to cells on-demand for optimizing traffic throughput in high-performance network configurations.
ATM technology employs a priority switching technique for enabling ATM cells carrying delay-sensitive signals to access the first available timeslot. Because the ATM cell size is fixed and the buffer memory size is constant for each cell, switch queuing delays are predictable and jitter or the variation in signal delay is minimized. By contrast, signal delays degrade performance of real-time applications such as videoconferencing and interactive video-on-demand (IVOD) in networks such as Frame Relay (FR) and Ethernet that transport variable length packets.
The ATM Forum defines procedures for monitoring the effectiveness of network transmission based on cellular throughput. Cell Loss Ratio (CLR) describes the percentage of cells that are not transported to their destination addresses as a consequence of buffer overloads and network congestion. Cell Transfer Delay (CTD) refers to propagation and queuing delays experienced by cells transiting the network.
Cell Delay Variation (CDV) measures variations in transmission delay between adjacent cells. Minimum Cell Rate (MCR) refers to the lowest cell rate supported by ABR (Available Bit Rate) service. In addition, metrics for Cell Delay Variation Tolerance (CDVT) and parameters for Maximum Cell Transfer Delay (MCTD) are also defined. The effectiveness of QoS delivery in ATM networks depends on such variables as Cell Transfer Delay (CDT) and Cell Delay Variation (CDV).
ATM Protocols
ATM is a complex cell multiplexing and switching technology. This chapter provides a high-level introduction to ATM technical attributes, features, and functions. Representative ATM implementations that support a diverse and powerful mix of applications are examined. Wireless ATM (WATM) configurations are described, and the capabilities of next-generation ATM networks are explored.
The ATM layer is responsible for relaying cells from the Architectural Area Lighting (AAL) to the physical layer for transmission and from the physical layer to the AAL for use at the end systems, it determines where the incoming cells should be forwarded to, resets the corresponding connection identifiers and forwards the cells to the next link, as well as buffers cells, and handles various traffic management functions such as cell loss priority marking, congestion indication, and generic flow control access. It also monitors the transmission rate and conformance to the service contract (traffic policing).
The physical layer of ATM defines the bit timing and other characteristics for encoding and decoding the data into suitable electrical/optical waveforms for transmission and reception on the specific physical media used. In addition, it also provides frame adaptation function, which includes cell delineation, header error check (HEC) generation and processing, performance monitoring, and payload rate matching of the different transport formats used at this layer. SONET , DS3, Fiber, twisted-pair are few media often used at the physical layer.
The ATM layer is responsible for relaying cells from the Architectural Area Lighting (AAL) to the physical layer for transmission and from the physical layer to the AAL for use at the end systems, it determines where the incoming cells should be forwarded to, resets the corresponding connection identifiers and forwards the cells to the next link, as well as buffers cells, and handles various traffic management functions such as cell loss priority marking, congestion indication, and generic flow control access. It also monitors the transmission rate and conformance to the service contract (traffic policing).
The physical layer of ATM defines the bit timing and other characteristics for encoding and decoding the data into suitable electrical/optical waveforms for transmission and reception on the specific physical media used. In addition, it also provides frame adaptation function, which includes cell delineation, header error check (HEC) generation and processing, performance monitoring, and payload rate matching of the different transport formats used at this layer. SONET , DS3, Fiber, twisted-pair are few media often used at the physical layer.
ATM cell size is fixed and the buffer memory size is constant for each cell..
TumugonBurahinnice post fred ..keep it up ;)
ATM is very useful on the modern days for it have given us more fast and reliable ways of communication.
TumugonBurahinATM creates a fixed channel, or route, between two points whenever data transfer begins.and also differ on TCP/IP, which will send to packet.
TumugonBurahinATM also provides high performance via hardware switching and dynamic bandwidth for bursty traffic ... Great job!!
TumugonBurahin