Connections in ATM are known virtual circuits or virtual channels These are known virtual, since connections are created in ATM by starting values in memory locations (tables) in ATM switches as opposed to creating actual electrical connections. The VC is shown by a 24-bit value created from the VPI or Virtual Path Indicator, which denotes a particular way through the network and the Virtual Channel Indicator or VCI (16-bits), which shows the channel in the virtual path being needed by the connection.
Most usually, the 24-bit pair is acted as just a single connection identifier by device.