The layer of the ATM protocol stack that handles most of the processing and routing activities. These include building the ATM header, cell multiplexing/demultiplexing, cell reception and header validation, cell routing using VPIs/VCIs, payload-type identification, quality of service specification, a nd flow control and prioritization.

The middle layer of the ATM model that sits between the physical layerand the ATM adaptation layer. The ATM layer roughly corresponds to the data-linklayer of the OSI model. Standards at the ATM layer specify how to establish,clear, and maintain ATM virtual circuits.

The layer that performs four main functions: multiplexing and demultiplexing of cells of different connections; translation at ATM switches and cross-connects; cell header extraction or addition before or after cell is delivered to or from the adaptation layer; and flow control.

The layer in the ATM protocol stack for routing and processing activities. For example: building the ATM header; payload identification; header validation and cell reception; cell routing using VPIs/VCIs; cell multiplexing/demultiplexing; quality of service specification; prioritization and flow control.

The layer in the ATM model above the physical layer, responsible for cell multiplexing, virtual path identifier (VPI) and virtual channel identifier (VCI) translation, cell header generation/extraction, and generic flow control in customer networks.