Asynchronous Transfer Mode (ATM)
Various network applications are requiring increasingly higher bandwidth and generating a heterogeneous mix of network traffic. Existing networks cannot provide the transport facilities to efficiently support a diversity of traffic with various service requirements. ATM was designed to be potentially capable of supporting heterogeneous traffic (e.g., voice, video, data) in one transmission and switching fabric technology. It promised to provide greater integration of capabilities and services, more flexible access to the network, and more efficient and economical service.
Overview of ATM
Internet applications have been written in the context of an IP-based network, and do not take advantage at all of the ATM network capabilities since they are hidden by this connectionless IP layer. The provision of Internet applications directly on top of ATM, described here, removes the overhead and the functional redundancies of a protocol layer, and makes it possible to take advantage of the various service categories offered by ATM networks, while maintaining the interworking with the IP-based network.
Asynchronous Transfer Mode (ATM) has emerged as the most promising technology in supporting future broadband multimedia communication services. To accelerate the deployment of ATM technology, the ATM Forum, which is a consortium of service providers and equipment vendors in the communication industries, has been created to develop implementation and specification agreements.ATM was intended to provide a single unified networking standard that could support both synchronous and asynchronous technologies and services while offering multiple levels of quality of service for packet traffic.
ATM allows the user to select the required level of service, provides guaranteed service quality, and makes reservations and preplans routes so those transmissions needing the most attention are given the best service.
Asynchronous Transfer Mode (ATM), sometimes called cell relay, is a widely deployed, high-speed, connection-oriented backbone technology that is easily integrated with technologies such as SDH, Frame Relay, and DSL. ATM uses short, fixed-length packets called cells to carry data, and combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic). ATM is more efficient than synchronous technologies such as time-division multiplexing (TDM), in which each user is assigned a specific time slot that no other station can use. Because ATM is asynchronous, time slots are available on demand. An ATM network is made up of ATM switches and ATM end systems (e.g. workstations, switches, and routers). An ATM switch is responsible for cell transit through an ATM network. It accepts an incoming call from an ATM end system (or another ATM switch), reads and updates the cell header information, and switches the cell to the appropriate output interface.
Characteristics of ATM
Asynchronous transfer mode (ATM) is a cell-oriented switching and multiplexing technology that uses fixed-length. ATM is a connection-oriented technology, in which a connection is established between the two endpoints before the actual data exchange begins. Asynchronous Transfer Mode (ATM) is a transfer protocol with the following characteristics:
- It is scalable and flexible. It can support megabit-to-gigabit transfer speeds and is not tied to a specific physical medium.
- It efficiently transmits video, audio, and data through the implementation of several adaptation layers.
- Bandwidth can be allocated as needed, lessening the impact on and by high-bandwidth users.
- It transmits data in fixed-length packets, called cells, each of which is 53 bytes long, containing 48 bytes of payload and 5 bytes of header.
- It is asynchronous in the sense that although cells are relayed synchronously, particular users need not send data at regular intervals.
- It is connection-oriented, using a virtual circuit to transmit cells that share the same source and destination over the same route.
Benefits of ATM
The high-level benefits delivered through ATM services deployed on ATM technology using international ATM standards can be summarized as follows:
- Dynamic bandwidth for bursty traffic meeting application needs and delivering a high utilization of networking resources; most applications are or can be viewed as inherently bursty, for example, voice is bursty, as both parties are neither speaking at once nor all the time; video is bursty, as the amount of motion and required resolution varies over time.
- Smaller header with respect to the data to make the efficient use of bandwidth.
- Can handle mixed network traffic very efficiently: Variety of packet sizes makes traffic unpredictable. All network equipments should incorporate elaborate software systems to manage the various sizes of packets. ATM handles these problems efficiently with the fixed size cell.
- Cell network: All data is loaded into identical cells that can be transmitted with complete predictability and uniformity.
- Class-of-service support for multimedia traffic allowing applications with varying throughput and latency requirements to be met on a single network.
- Scalability in speed and network size supporting link speeds of T1/E1 to OC–12 (622 Mbps).
- Common LAN/WAN architecture allowing ATM to be used consistently from one desktop to another; traditionally, LAN and WAN technologies have been very different, with implications for performance and interoperability. But ATM technology can be used either as a LAN technology or a WAN technology.
- International standards compliance in central-office and customer-premises environments allowing for multivendor operation.
 Siu, Kai-Yeung, and Raj Jain. “A brief overview of ATM: protocol layers, LAN emulation, and traffic management.” ACM SIGCOMM Computer Communication Review 25, no. 2 (1995): 6-20.
 Durresi, Arjan, and Raj Jain. “Asynchronous Transfer Mode (ATM).” Handbook of Computer Networks: LANs, MANs, WANs, the Internet, and Global, Cellular, and Wireless Networks, Volume 2: 183-199.
 “Archived: What is Asynchronous Transfer Mode (ATM)?” available online at: https://kb.iu.edu/d/aequ
 “Asynchronous Transfer Mode (ATM)”, available online at: https://www.technologyuk.net/telecommunications/communication-technologies/asynchronous-transfer-mode.shtml
 “Lesson 6: Asynchronous Transfer Mode Switching (ATM)”, Version 2 CSE IIT, Kharagpur, available online at: http://nptel.ac.in/courses/106105080/pdf/M4L6.pdf