Abstract
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
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