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2 Bridged Ethernet
Introduction
Features
Bridged Ethernet vs.
connection service
Bridged Ethernet vs.
protocol occupancy
E-DOC-CTC-20051017-0167 v1.0
Bridged Ethernet is by far the most simple packet service supported by the
SpeedTouch™. The Bridging entity of the Digital Subscriber Line (DSL) modem
joins the local Ethernet segment(s) connected to the local hosts, and the "virtual"
Ethernet segment on the DSL line into one common Ethernet network. In this way it
is as if the hosts are directly connected to the Service Provider (SP) access machine
(remark the term "Transparent" Bridging).
PC with fixed
SpeedTouch
Public IP address,
operating as
received by DHCP
Transparent Bridge
or statically
configured
Bridged Ethernet has the following features:
Platform and Operating System independent
Simple to configure and easy to use
Complete layer 3 and upwards protocol transparency
Concurrent access to multiple remote destinations
The Bridged Ethernet Packet Service relies on the AAL5/RFC2684/Bridged
Connection Service to achieve end-to-end connectivity.
For the SpeedTouch™, this amounts to using the ETHoA (Ethernet over ATM)
Connection Service type. This connection service type implies the encapsulation of
Ethernet frames (often referred to as IEEE802.3, MAC frames or Bridging frames) in
AAL5/ATM.
All SpeedTouch™ products are compliant with RFC2684 "Multi-protocol
Encapsulation over ATM Adaptation Layer 5" and support both the LLC/SNAP and
VC-MUX encapsulation method for Bridged Ethernet V2.0/IEEE802.3 Protocol Data
Units (PDUs). The default encapsulation method is set to LLC/SNAP.
Bridged Ethernet operates below the network layer and is transparent to any Layer 3
protocol. It does not impose any specific requirements to the local node's protocol
layers. Make sure that these protocol layers are properly installed and supported by
the remote node.
In most cases (and in all the examples) Transmission Control Protocol/Internet
Protocol (TCP/IP) will be used.
DSLAM
Connection Service Name: Virtual Ethernet
Connection Service Type: ETHoA
Virtual Channel with:
ATM Encapsulation Type: LLC/SNAP
Chapter 2
Bridged Ethernet
BRAS
Internet
11
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