[Slightly OT] VPI & VCI for ADSL Connections
- Recently, while configuring the BSNL Broadband connection for a neighbour, I came across the necessity to enter the VPI (Virtual Path Identifier) and VCI (Virtual Circuit Identifier) values in the router administration.
From what I have gathered from a quick reading of Wikipedia  is that these values are used to help connect to an ISP and route packets either from network to network or from user to network. Can someone explain with a few more details on what these parameters are?
Why are these values constant for everyone if they are used for routing?