Ethernet Bridging 413
The MPLS world offers an excellent means for providing a point-to-point service
that can carry many different kinds of payloads, including Ethernet frames. Not only
the data movement parts of the network are available, but the important ancillary and
infrastructure components, such as network maintenance, EVC creation, and billing,
have been developed around the MPLS architecture.
The Ethernet-over-MPLS story is weaker when it comes to E-LAN EVCs or fewprivileged-
points-to-many-unprivileged-points EVCs. This is because MPLS does not
have multipoint-to-multipoint paths, but only point-to-point paths. Thus, an E-LAN
requires a full mesh of point-to-point paths; a 10-UNI EVC requires 45 point-to-point
paths. Such a mesh of connections is slow and expensive to create and maintain. It
requires that every multicast, broadcast, or flooded unicast must be replicated and
transmitted (n ??“ 1) times in an n-UNI network, potentially wasting enormous amounts
of bandwidth. To cut the bandwidth requirement, a full mesh of point-to-multipoint
paths, on top of the full mesh of point-to-point paths, is required, thus greatly increasing
the path creation and maintenance load.
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