Isolating service instances
from network topology enables the network to scale to an immense number of
service instances.
In the OAM-based approach, each circuit has its own end-to-end OAM flow, and failures
are only detected when a number of consecutive OAM packets are dropped. In this
approach, speed of convergence is always in tension with scalability, since increasing
the frequency with which OAM packets are sent on a circuit reduces the total number
of circuits that can be supported without overwhelming the edge devices (and the network
links) with OAM traffic.
Notwithstanding the above, MPLS also supports OAM-based approaches to fault
detection, and these may be used either in conjunction with, or instead of, the IP/MPLS
control plane.
Ability to Offer Ethernet Services over Existing IP Networks MPLS is a cost-effective way
to offer multiple services over a packet-switched network. EoMPLS is a small addition
458 Chapter 14
to an existing IP/MPLS network and enables carriers to add new revenue streams from
Ethernet services. Although some customers are willing to buy Layer 3 services, others
prefer to buy Layer 2 services??”often because they prefer to manage and maintain their
own routing infrastructure.
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