PPPoA architectures Deployment Methods

How the Service Destination is Reached

In PPPoA architectures, the service destination can be reached in different ways. Some of the most commonly deployed methods are:
  • Terminating PPP sessions at the service provider
  • L2TP Tunneling
  • Using SSG
In all three methods there is a fixed set of PVCs defined from the CPE to the DSLAM that is switched to a fixed set of PVCs on the aggregation router. The PVCs are mapped from the DSLAM to the aggregation router through an ATM cloud.
The service destination can also be reached using other methods such PPPoA with SVCs, or Multiprotocol Label Switching/Virtual Private Network. These methods are beyond the scope of this document and will be discussed in separate papers.

Terminating PPP at Aggregation

The PPP sessions initiated by the subscriber are terminated at the service provider which authenticates users using either a local database on the router or through RADIUS servers. After the user is authenticated, IPCP negotiation takes place and the IP address is assigned to the CPE. After the IP address has been assigned, there is a host route established both on the CPE and on the aggregation router. The IP addresses allocated to the subscriber, if legal, are advertised to the edge router. The edge router is the gateway through which the subscriber can access the Internet. If the IP addresses are private, the service provider translates them before advertising them to the edge router.
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