Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the International Telecommunication Union (ITU-T) for cell relay where information is organized into small, fixed-size cells. It is designed to transport a variety of different kinds of data such as voice, video, and data, and is commonly used in both LAN (Local Area Network) and WAN (Wide Area Network) environments.

Features of ATM:

• Cell-based Transmission: In ATM, data is transmitted in fixed-size cells of 53 bytes. This fixed size is beneficial for predictable and efficient transmission of data, regardless of the type of information being transmitted.
• Asynchronous Transfer: "Asynchronous" in ATM refers to the fact that cells from different sources can be interleaved and transmitted over the network independently of each other. This allows for flexible allocation of bandwidth and efficient multiplexing of different types of traffic.
• Connection-oriented Communication: ATM establishes virtual circuits between endpoints before data transmission begins. These virtual circuits can be either Permanent Virtual Circuits (PVCs), which are pre-configured, or Switched Virtual Circuits (SVCs), which are set up dynamically as needed.
• Quality of Service (QoS): ATM supports various Quality of Service parameters, allowing for different levels of service for different types of traffic. This enables ATM networks to prioritize certain types of traffic, such as voice or video, to ensure low latency and minimal packet loss.
• Scalability: ATM networks can scale to support large numbers of users and high bandwidth requirements by utilizing various multiplexing techniques and by allowing for the dynamic allocation of bandwidth as needed.