$Id: end-to-end-principle.html,v 1.5 2007/07/19 15:55:07 itojun Exp $"End-to-end principle" is, in the other words, "Functionalities should be implemented in the communication endpoints, intermediate routers should concentrate on moving packets from left to right". Because of this principle, new applications can be deployed without changing intermediate routers - we just need to implement new applications/protocols support onto the end points.
This is one of the most important design rule of the Internet. Without it, World Wide Web (WWW) would not be made available. World Wide Web was deployed by installing web servers (httpd) and web clients (Mosaic in the old days, Netscape Mozilla afterwords), and nothing more. Intermediate routers needed no changes at all.