PDF | The purpose of this paper is to summarize the Asynchronous Transfer Mode (ATM) technology and determine where it is in its evolutionary development. Asynchronous Transfer Mode (ATM) is an International Telecommunication Union- switching, ATM is designed for high-performance multimedia networking. ATM is a form of packet switching technology. That is, ATM networks transmit their information in small, fixed length packets called “cell” each of which contains .
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Vast majority of ATM networks will run on optical fiber networks with extremely low error rates. 4. ATM must supports low cost attachments. • This decision lead to. Virtual channels and virtual paths. • Virtual channel connections (VCC): logical connections in ATM. – a VCC is analogous to a virtual circuit in X – VCCs are . Asynchronous transfer mode (ATM) is a high-performance, cell-oriented switching and multiplexing technology that utilizes fixed-length packets.
The function of the VCI is similar to that of the data link connection identifier DLCI in frame relay and the logical channel number and logical channel group number in X. The VPI is useful for reducing the switching table of some virtual circuits which have common paths. When an ATM circuit is set up each switch on the circuit is informed of the traffic class of the connection.
ATM traffic contracts form part of the mechanism by which " quality of service " QoS is ensured. There are four basic types and several variants which each have a set of parameters describing the connection.
ABR - Available bit rate: a minimum guaranteed rate is specified. UBR - Unspecified bit rate: traffic is allocated to all remaining transmission capacity. VBR has real-time and non-real-time variants, and serves for "bursty" traffic.
Non-real-time is sometimes abbreviated to vbr-nrt. Most traffic classes also introduce the concept of Cell-delay variation tolerance CDVT , which defines the "clumping" of cells in time.
Traffic policing[ edit ] To maintain network performance, networks may apply traffic policing to virtual circuits to limit them to their traffic contracts at the entry points to the network, i. If the traffic on a virtual circuit is exceeding its traffic contract, as determined by the GCRA, the network can either drop the cells or mark the Cell Loss Priority CLP bit to identify a cell as potentially redundant.
Basic policing works on a cell by cell basis, but this is sub-optimal for encapsulated packet traffic as discarding a single cell will invalidate the whole packet.
As a result, schemes such as partial packet discard PPD and early packet discard EPD have been created that will discard a whole series of cells until the next packet starts.
This reduces the number of useless cells in the network, saving bandwidth for full packets. Traffic shaping[ edit ] Traffic shaping usually takes place in the network interface card NIC in user equipment, and attempts to ensure that the cell flow on a VC will meet its traffic contract, i.
Since the reference model given for traffic policing in the network is the GCRA, this algorithm is normally used for shaping as well, and single and dual leaky bucket implementations may be used as appropriate. Types of virtual circuits and paths[ edit ] ATM can build virtual circuits and virtual paths either statically or dynamically. Static circuits permanent virtual circuits or PVCs or paths permanent virtual paths or PVPs require that the circuit is composed of a series of segments, one for each pair of interfaces through which it passes.
They also do not support the re-routing of service in the event of a failure.
ATM networks create and remove switched virtual circuits SVCs on demand when requested by an end piece of equipment. One application for SVCs is to carry individual telephone calls when a network of telephone switches are inter-connected using ATM.
Each packet is passed through the network from node to node along some path leading from source to destination.
At each node, the entire packet is received, stored briefly, and then transmitted to the next node. Packet-switching networks are commonly used for terminal-to-computer and computer-to-computer communications.
Frame Relay Packet switching was developed at a time when digital longdistance transmission facilities exhibited a relatively high error rate compared to todays facilities. As a result, there is a considerable amount of overhead built into packet-switching schemes to compensate for errors.
The overhead includes additional bits added to each packet to introduce redundancy and additional processing at the end stations and the intermediate switching nodes to detect and recover from errors.
With modern high-speed telecommunications systems, this overhead is unnecessary and counterproductive. It is unnecessary because the rate of errors has been dramatically lowered and any remaining errors can easily be caught in the end systems by logic that operates above the level of the packet-switching logic.
It is counterproductive because the overhead involved soaks up a significant fraction of the high capacity provided by the network. Frame relay was developed to take advantage of these high data rates and low error rates.
Whereas the original packet-switching networks were designed with a data rate to the end user of about 64 kbps, frame relay networks are designed to operate efficiently at user data rates of up to 2 Mbps. The key to achieving these high data rates is to strip out most of the overhead involved with error control.
ATM Asynchronous transfer mode ATM , sometimes referred to as cell relay, is a culmination of developments in circuit switching and packet switching. ATM can be viewed as an evolution from frame relay. The most obvious difference between frame relay and ATM is that frame relay uses variable-length packets, called frames, and ATM uses fixed-length packets, called cells.
By using a fixed packet length, the processing overhead is reduced even further for ATM compared to frame relay. The result is that ATM is designed to work in the range of 10s and s of Mbps, and in the Gbps range. ATM can also be viewed as an evolution from circuit switching. With circuit switching, only fixed-data-rate circuits are available to the end system.
ATM allows the definition of multiple virtual channels with data rates that are dynamically defined at the time the virtual channel is created. By using small, fixed-size cells, ATM is so efficient that it can offer a constant-data-rate channel even though it is using a packet-switching technique.
Asynchronous transfer mode
Thus, ATM extends circuit switching to allow multiple channels with the data rate on each channel dynamically set on demand. Local Area Networks As with WANs, a LAN is a communications network that interconnects a variety of devices and provides a means for information exchange among those devices.
The scope of the LAN is small, typically a single building or a cluster of buildings.In this respect, ATM really has the edge. Additionally, It was designed for networks that must handle both traditional high-throughput data traffic e.
An ATM cell consists of a 5-byte header and a byte payload. The increased link speeds by themselves do not alleviate jitter due to queuing.
This has two implications. Synchronization is also maintained at AAL1.
Traffic shaping usually takes place in the network interface card NIC in user equipment, and attempts to ensure that the cell flow on a VC will meet its traffic contract, i.
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