ATM is a Wide Area Network (WAN) technology that support both #Packet Switching and #Circuit Switching functionalities. It operates at #Data Link Layer. The basic components in an ATM network are ATM switches#, which is responsible for moving cells through the network, and ATM endpoints, such as workstations, Router, data service units (DSU) etc.
Switches are interconnected by point-to-point ATM links, which could come in 2 forms: User-Network Interface (UNI) and Network Node Interface (NNI). The former is used to connect ATM endpoints to ATM switches, whereas the latter connect ATM switches together. Depend on the type of network (private or public) the switch reside, it could be further classified as private or public interface.
ATM supports asynchronous transmission using an optimised version of Time-Division Multiplexing (TDM)#. Since in standard TDM, an end station could not use an idle time slot owned by another end station, this could result in some inefficiency. Instead of favouring static allocation, ATM improves it letting the end stations to choose their slot based on priority. The slot that has the highest priority is the primary time slot for that end station. If the slot is not being used by its primary owner, it can be assigned to other end station temporarily to transmit data over.
The information or frame transferred by ATM will have a fixed size of 53 bytes, where 5 bytes are allocated for header and 48 bytes for information. Because of its predictable size, it eases the network management and the debugging process chore as the serialisation delay or the delay of processing cells is deterministic. This is particularly useful in voice and video traffic since they are time-sensitive (though its advantages has been chipped away as the wide adoption of Voice over IP (VoIP)). However, it does add to the network overhead. For example, suppose ATM wants to transfer 100 bytes of information, it needs to split it up to 3 frames, where 15 bytes of them are allocated to headers instead of being used to carry the information.
As a connection-based service, ATM requires that the connection must be requested, established, and confirmed before any operation on sending user information over the network. Each connection is composed of virtual channels and virtual paths. Virtual channels, which could take different physical paths through the network, are bundled into a single logical group: virtual path. Multiple virtual paths will be bundled into a larger logical grouping called transmission path.
There are two kinds of circuits primary used by ATM: Permanent Virtual Circuit (PVC)# and Switched Virtual Circuit (SVC)# . The latter is quite common among ATM installation. ATM also utilises the LAN Emulation (LANE)# technology, which offer user the ability to communicate using Local-Area Network (LAN) protocols within the ATM network.