The ATM layer is the second layer of the ATM layer model and provides the media-independent ATM cell transport. The ATM layer is divided into two sublayers, the virtual path layer( VP) for the virtual path and the virtual channel layer( VC) for the virtual channels. Both sublayers represent logically separate multiplex layers and can be handled separately in the network. A virtual path can comprise several virtual channels.
Functions of the ATM layer
At the ATM layer, the information is packetized or depacketized, placed in the information field, and the header and identifiers are determined. Cells are demarcated from each other and added to or removed from the cell stream for multiplexing or switching. Transparent transport of ATM cells between network nodes communicating at a higher level takes place.
Before this can happen, it is necessary to establish connections and negotiate quality of service( QoS) parameters for that connection. After connection establishment, the ATM cells of the different connection channels and paths( VCC, VPC) are multiplexed into a continuous stream of cells.
When the user information is passed from the ATM adaptation layer( AAL) to the ATM layer, the ATM header must be generated and prepended. At the destination, the ATM layer separates the header again before passing the information to the ATM adaptation layer (AAL). Monitoring and control mechanisms run continuously during the connection duration.