Asynchronous Transfer Mode (ATM) | What Is ATM?

One of the most notable technological advancements in the world of telecommunications is ATM, or asynchronous transfer mode. Though it's since become more of an outdated technology, ATM still integrates voice, video, and data traffic into one high-speed communications system. In this article, explore what asynchronous transfer mode is, how it works, and why its improvements upon data transfer were and are so significant.

What is asynchronous transfer mode?

Asynchronous transfer mode (ATM) is a high-speed networking method used for data communications. It supports voice transmissions for calls and radio broadcasts, video transmissions for streaming, and general data communications. ATM is a core protocol - meaning an essential component - of many Internet service providers' networks, the public switched telephone network (PSTN), and the Integrated Services Digital Network (ISDN). In other words, it works for long-distance communications of every form.

How does asynchronous transfer mode work?

Asynchronous transfer mode works by relying on fixed-sized packets, called cells, to perform its functions and transfer data across a network.

Data divides up into sections called ATM cells. These fixed-size cells are 53 bytes in length, containing 48 bytes of actual data called a payload and five bytes of information called a header.

The header describes what that data is to the other device. It also contains the virtual path identifier and virtual channel identifier to direct the cell down the right path through the network.

Once the data segments, two endpoints must establish a connection. Asynchronous transfer mode uses a signaling protocol, such as ITU-T Q.2931, to trade information and resources. The virtual path identifier and virtual channel identifier values help cement the endpoints' connection and ensure that data properly transfers between them.

Using those same VPI and VCI values, cells travel through the network. Network switches read the values and move the cells along their correct path.

On the other end, cells reassemble into their original format. The endpoint checks for errors and ensures correct sequencing of the cells; then, the connection ends via a signaling protocol.

Note that throughout the process, each of these cells processes individually. None of the cells transfer at the same time, which is what makes the process asynchronous.

What are the advantages of asynchronous data transfer?

ATM networks are different from other network connections in several ways. Unlike Ethernet and Internet Protocol, asynchronous transfer mode doesn’t use routing. These other networks transfer data in segments called packets.

Data is split up into different sized sections – depending on which network connection you’re using- and sent to another device. The packets are then reorganized at the other device, the data reassembles, and the message is received.

With ATM services, dedicated hardware devices called ATM switches are used to establish a direct connection between endpoints. Data sending requires no other devices or routers; it sends straight from the source to destination. This provides massive security benefits, as it doesn’t give hackers a chance to alter or steal any data. It also means that the sender and receiver don’t need synchronization in order to transmit data.

Because the transmission is point-to-point using the ATM switches, the transmission request doesn’t have to target a particular server, and a server doesn’t have to be available for connection to occur. A connectionless protocol can also use ATM transmission.

Plus, asynchronous transfer mode is fast. It can operate at speeds of either 155 or 622Mbps. Since ATM uses cells instead of routing or data packets, networks can achieve a higher bandwidth using it over Ethernet or Internet Protocol.

What is the purpose of asynchronous transfer mode?

Ultimately, ATM protocols are designed to offer data transfer with a guaranteed quality of service. Since ATM can be used for sending so many types of data, this service quality is essential to the people using ATM protocols to transmit data.

As discussed earlier, ATM in a computer network sends data in the form of cells. The simple structure of these cells allows the ATM switches to work faster and improve the overall efficiency of data transfer. This, in turn, increases the speed of transmission.

What is the main difference between synchronous and asynchronous data transfer?

First, it's important to understand what synchronous data transfer is and how it works. Synchronous transmission is data transfer that sends data as blocks often referred to as packets. Unlike asynchronous transmission that sends cells one at a time, synchronous transmission sends packets at the same time, generally without any space between them.

Due to this key difference, synchronous data transfer works better for transmissions of large amounts of data. It sends data in packet form, whereas asynchronous sends it in the form of bits and bytes.
But, while synchronous data transfer can be faster, it can be much more costly. Asynchronous transmission is cheaper. It doesn’t rely on both devices and routers being synchronized in order to transmit data.

Also note that synchronous data transfer relies on clocks found on each communicating device. The devices divide or generate data based on a designated period of time on each of these clocks. The transmitting device must send a clock signal to the receiving device. Both of their clock periods must synchronize for the data transmission to successfully occur.

Asynchronous transfer mode does away with period clocks by sending information in one cell at a time at an unspecified bit rate. It uses predetermined ATM cell sizes, so the process always sends the same amount of data.

Is asynchronous transfer achievable through a modem?

A modem converts data into a signal to easily send it over networks. Modems are classified in several different ways. One is the mode in which they operate, and another is their type of synchronization.

One of these modes is known as half duplex mode. Half-duplex mode modems can pass data and signals through in one direction or the other, but not both directions simultaneously. Asynchronous data transfer itself is half duplex, giving these modems access to ATM technology.

Other modems operate in asynchronous transfer mode by design. Most of these have slow to moderate rates of transmission, and use two frequencies for transmitting signals and two for receiving signals. They can use a two or four wire interface, switched or leased lines, or interface when dialing up if the modem is also a dial-up modem.