VPLS today is at
one extreme of this tradeoff. Further enhancements to VPLS are being standardised to
offer more efficient multicast forwarding at the expense of adding state to the network
core (see ???Ongoing Developments,??? later in this chapter).
Forwarding Plane Bugs VPLS has no means of detecting forwarding plane bugs except
for VCCV per-pseudowire or Ethernet OAM mechanisms applied to the service layer.
VPLS OAM mechanisms may be required to detect software or hardware failures in nodes
that implement VPLS. Efforts are ongoing in the IETF to add this capability to VPLS.
Typical Deployment Scenarios
In this section we will present examples drawn from real-world networks, showing how
carriers have deployed Ethernet over MPLS in their networks.
MPLS in the Access
In this architecture, Layer 2 capable Multi-Service Access (MSA) devices are deployed as
U-PEs and are aggregated toward Layer 3 capable Multi-Service Edge (MSE) devices acting
as N-PEs (see Figure 14.8). The MSA devices groom traffic from attachment circuits
Figure 14.8 MPLS in the access
Voice
switch
TDM
MSA TDM PW
IP PW
MSE
Ethernet
(E-line)
Ethernet
(IP-VPN access)
MPLS core network
Segmented
Ethernet PW
IP VPN
460 Chapter 14
into pseudowires, and the MSE devices perform a mixture of pseudowire switching for
point-to-point services and termination into VPLS or IP-VPN instances for multipoint
services.
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