virtual path (ATM) (VP)
The ATM layer provides the ability to transmit over virtual paths (VP), each of which can include many virtual channels.
Each ATM cell contains an identification field in its header that includes a virtual path identifier( VPI) and virtual channel identifier( VCI). This identification is used to associate each cell with a single connection.
A virtual path is formed at a specific reference point from a group of virtual channels( VC) that contain the same path identifier. Such a reference point could be an ATM switching unit.
Between two reference points of a virtual path, only VPIs are processed by the ATM network nodes; the VCIs remain unprocessed. At the physical layer, each multiplex layer can support multiple virtual paths. In addition, each transmission medium can in turn contain several physical layers.