IP access service provision for broadband customers

Broadband Internet access architectures for residential, SOHO and small business are being developed largely in the ADSL Forum, where two architectures have been proposed for service provider access. The two architectures proposed are the PTA-PPP Termination Aggregation Architecture, and the LAA-L2TP Aggregation Architecture. These IP access architectures can also be applied to cable modem deployments. The PTA model uses BAS (Broadband Access Server) technology to terminate PPP sessions from the user and the LAA model uses the LAC (L2TP Access Server) to transport PPP sessions from the LAC to a LNS (L2TP Network Server) which performs tunnel termination and AAA proxy at the ingress to a service provider (SP). Optionally a L2TP Tunnel Switch (LTS) can be used in the transport network to perform the grooming of traffic between tunnels. Use of these architectures provides a means for an access network provider to provide open access mechanisms based on the use of the structured user name for service provider selection, and secondly to provide a transport architecture solution based on virtual private IP network technology. The transport alternatives available in these architectures are based on IP in IP encapsulation schemes from a BAS, or L2TP over UDP/IP, ATM or Frame Relay. These solutions are discussed and are briefly compared. The ADSL Forum is also looking to standardise the protocols to be used between the CPE and the ATU-R. There are a number of different proposals that are being considered seriously, and there have been over a dozen proposals in total. The paper looks at some of the options and briefly outlines optimal choices