One key to the draft-martini approach was to maximise reuse of existing hardware
and software technology. Using MPLS labels as the forwarding plane identifiers for
pseudowires and extending LDP signalling to establish pseudowires made it relatively
straightforward to implement pseudowires on the IP/MPLS router platforms available
at the time. Some minor compromises were, in fact, made to make it easier for existing
hardware to implement the technology.
Layer 2 pseudowires have been defined to carry Ethernet, ATM, Frame Relay,
HDLC, and PPP traffic. Layer 1 pseudowires have also been defined to enable service
providers to transport TDM signals and SONET/SDH frames across IP/MPLS networks.
IP pseudowires have been defined to enable interconnection of IP endpoints
running different Layer 2 protocols but using Layer 2 forwarding (the IP pseudowire
encapsulation removes all Layer 2 framing and carries only the IP payload). In the
pseudowire architecture, as in the Layer 2 and Layer 3 VPN architectures, the LER is
known as a provider edge or PE device (core LSRs are known as provider or P devices),
and the device at the far end of the attachment circuit to the LER is known as the
customer edge or CE device.
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