Access Nodes In Ethernet Aggregation Networks Overview; Atm-To-Ethernet Interworking Overview - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - LINK LAYER CONFIGURATION GUIDE 2010-10-13 Configuration Manual

JunosE 11.3.x Link Layer Configuration Guide

Access Nodes in Ethernet Aggregation Networks Overview

ATM-to-Ethernet Interworking Overview

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IEEE 802.1q (Virtual LANs)
RFC 2516—Method for Transmitting PPP over Ethernet (PPPoE) (February 1998)
NOTE: IETF drafts are valid for only 6 months from the date of issuance.
They must be considered as works in progress. Please refer to the IETF
Web site at http://www.ietf.org for the latest drafts.
The access node is the first aggregation point in the digital subscriber line (DSL) access
network and apart from terminating the DSL physical layer signals, it also terminates the
user ATM layer. The access node contains an Ethernet uplink to provide connectivity to
the aggregation network. When ATM is supported on the DSL line, the access node
provisions an interworking function between the ATM layer on the user side and the
Ethernet layer on the network side, encompassing protocol translation, access loop
identification, QoS, security, and OAM attributes. This functionality might require the
access node to snoop, modify, or terminate protocols in layers above the ATM Adaptation
Layer 5 (AAL5) encapsulation. The access node operates as an Ethernet switch, while
it also offers enhanced functionality for protocol interworking, multicast support, and
customization for support of access networks (such as ARP and IGMP processing, and
user identification and isolation).
The subscriber's access node indicates to the B-RAS application running on the router
whenever a PPPoE session carries interworked PPPoA or PPPoE over ATM traffic. This
indication enables the B-RAS application to modify its behavior for interworked PPPoE
sessions. To denote that a PPPoE session contains interworked traffic, the PPPoE client
or the host includes the IWF-Session DSL Forum VSA (26-254) in the unicast PPPoE
Active Discovery Request (PADR) packet that it transmits to the PPPoE access
concentrator to which it wants to connect.
In the ATM-to-Ethernet IWF topology, each ATM virtual path identifier (VPI) or virtual
circuit identifier (VCI) is mapped to a corresponding stacked Ethernet Virtual Local Area
Network (VLAN). When this feature is used, the ATM packets are translated into Ethernet
packets through mapping between an ATM link and an Ethernet link. The VPI of ATM
packets is mapped to the external stacked VLAN (S-VLAN) tag, and the VCI of ATM
packets is mapped to the internal customer VLAN (C-VLAN) tag, thereby enabling the
transmission of ATM packets over Ethernet links. VPI and VCI are mapped to double tags.
The inner and outer SVLAN tags identify ATM digital subscriber line access multiplexer
(DSLAM) device information and user information, respectively. After the PPPoE
authentication packet reaches B-RAS, B-RAS can authenticate based on user account,
device information (the outer tag), and user information (the inner tag). In this way,
account hacking can be avoided in terms of security.
The DSL Forum defined the IWF to devise the process for conversion of PPP over ATM
(PPPoA) and PPPoE over ATM sessions to PPPoE sessions at the DSLAM to the B-RAS
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