If a provider has access to dark fibre (or wavelengths), then Ethernet interconnection
is generally the most cost-effective option; however, in some cases,
providers may only be able to obtain SONET/SDH connectivity, which is not
suitable for interconnecting Ethernet switches unless additional adaptations
such as Ethernet over SONET/SDH are deployed. MPLS enables providers to
use the cheapest available transport to interconnect PE devices because MPLS
is link-layer agnostic.
Network Convergence
Many network technologies, from ISDN to ATM, have promised to offer convergence
of multiple voice and data services over one common infrastructure, but without much
success. However, carriers are now increasingly standardising on Ethernet and on IP
for future services. Ethernet over MPLS offers a way to provide Ethernet services over
an IP core. Some carriers are now deploying multi-service PE devices that enable them
to offer Ethernet, IP, and legacy services (e.g., ATM, frame relay, and TDM) over the
same network using EoMPLS for Ethernet services, IP VPNs for IP services, and pseudowires
for legacy services.
452 Chapter 14
When Does This Solution Fit?
In this section we will look at ideal deployment scenarios for Ethernet over MPLS,
describing cases where the technology may be the optimal choice of the different options
available (many of which are described in other chapters of this book).
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