ATM adaptation layer (AAL) refers to the service provided by the ATM protocol for adapting different types of user traffic into cells that can be transmitted over an Asynchronous Transfer Mode (ATM) network. It acts as an interface layer between the upper-layer protocols and the underlying ATM network.
AAL is responsible for segmenting and reassembling higher-layer protocol data units (PDUs) into ATM cells, and vice versa for receiving data from the ATM network. It provides the necessary mechanisms to ensure the reliable and efficient transfer of various types of traffic, including voice, video, and data, over an ATM network.
The main purpose of AAL is to overcome the differences in format, timing, delay, and bandwidth requirements between the source data and the ATM network. It achieves this by providing different adaptation techniques to suit the characteristics of different traffic types. AAL performs functions such as segmentation, reassembly, multiplexing/de-multiplexing, and error control.
AAL also includes important features like flow control to match the different data rates between the source and destination, while ensuring that congestion is avoided or minimized within the network. It can also handle the mapping of user-specific functions, like quality of service (QoS) parameters and traffic priorities.
In summary, the ATM adaptation layer is a crucial component of the ATM protocol that enables the efficient and reliable transmission of various types of user traffic over an ATM network.
