VPI
virtual path identifier
The VPI is an 8-bit field in the ATM cell header, which indicates the virtual path over which the cell should be routed.
The VPI is assigned on a connection set up by the devices at the two ends of a hop. Multihop VPC paths use multiple VPIs to go from source to destination. Each switch that the VPC traverses cross-connects the VPC from one port and VPI to another port and VPI.