Hello Brahim
The pvc command is used to enter into ATM virtual circuit configuration mode. In order to do so, you must specify the Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI) in the format of VPI/VCI. These values together provide what is known as a connection identifier.
ATM is a connection-orientated protocol and as such, there is a connection identifier in every cell header which explicitly associates a cell with a given virtual channel on a physical link. The connection identifier is used in multiplexing, demultiplexing and switching a cell through the network. VCIs and VPIs are not addresses. They are explicitly assigned at each segment (link between ATM nodes) of a connection when a connection is established, and remain for the duration of the connection. Using the VCI/VPI the ATM layer can asynchronously interleave (multiplex) cells from multiple connections.
The choice of these values is up to the ISP and are typically configured within the DSLAM. The values used in the lesson were chosen randomly. More information on the specific command in Cisco devices can be found here:
I hope this has been helpful!
Laz