erous private networks in sequence. NSPs have adopted Point-to-Point Protocol (PPP) over ATM because it is easy to integrate with existing protocols and operating methods. They use RADIUS (remote authentication of dial-in user services) servers for authentication, authorization, accounting (AAA) services that are dependent on PPP session establishment to end- users. By adopting the same service access protocol that dial-up users use, NSPs facilitate service convergence and leverage a mature service platform. In lieu of an end-to-end ATM network (or of IPv6), Layer 2 Tunneling Protocol (L2TP) Access Concentrators (LAC) map multiple PPP sessions within individual PVCs from the access network to PPP sessions within an L2TP tunnel. Multiple tunnels may exist between the LAC and an NSP where the tunnel used to convey a packet depends upon the priority assigned to the packet. The NSP-gateway concept can also be deployed via a shared Broadband Access Server (BAS) with PPP Terminated Aggregation (PTA). The same BAS that a NSP would use to terminate PPP can be operated within the ADSL access network. Each AAA server manages sessions to the BAS through a RADIUS proxy interface to the BAS and thereby permits service autonomy. The BAS strips PPP encapsulation from the user packets before forwarding the packet to a NSP. The BAS serves as an IP router and participates in the IP domain of each NSP when IP is the L3 protocol. SVCs or the NSP gateway (LAC or BAS) permit users to alternate between service providers sequentially, and permit the network access provider and Internet service provider to efficiently provision service to large numbers of customers. ADSL accommodates ATM transport with variable rates and compensation for ATM overhead. The ATM Forum recognizes ASDL as a physical layer transmission protocol. ADSL modems use forward error correction to reduce errors caused by impulse noise, and isolate POTS channels from digital channels to protect them from interruption because of a digital services failure. Virtually all 