Multi-service Transparent Transmission over PWs on a MAN
In many carrier-class services, carriers use digital subscriber line access multiplexers (DSLAMs) or Ethernet switches, to provide connections for ADSL, VDSL, or Ethernet lines. The carriers need to control certain services, including PPPoE access request termination, IP address assignment, user authentication, authorization, and accounting. Broadband remote access servers (BRASs) are responsible for controlling these services.
Large-capacity, high-performance BRASs (for example the Huawei ME60) are being developed and are moving closer to the MAN egress, where they have more responsibility in directing outbound traffic. This means that DSLAMs are connected to the MAN, and that integrated BRASs are deployed at the MAN egress to control services.
BRASs usually exchange information with users through Layer 2 links. For example, a BRAS obtains user names and passwords through PPPoE sessions. However, a MAN is a Layer 3 IP/MPLS network. If Layer 2 user information is terminated on the user-end provider edge (UPE) devices connected to DSLAMs, BRASs cannot obtain required information through Layer 2 connections, and therefore they cannot control services. To solve this problem, VLLs can be set up on the MAN to transmit Layer 2 packets exchanged between BRASs and users over PWs.
