Two stages of PPP negotiations are adopted for users to access a virtual private network (VPN). The access concentrator for providing PPP connections is designed to provide the two-stage connection. In the first stage, a user is verified as an authenticated VPN user, and a first network address is assigned....http://www.google.de/patents/US6694437?utm_source=gb-gplus-sharePatent US6694437 - System and method for on-demand access concentrator for virtual private networks
