Ethernet over
SONET/SDH could alternatively be provisioned with much larger VCAT groups connecting
adjacent ???islands,??? but in this case, spanning tree protection would have to be
used over the wide area, leading to some links being unused unless multiple spanning
trees were constructed, for example, one spanning tree per pair of ???islands???.
Ethernet Access to MPLS-based Metro Core Network
Ethernet is rapidly becoming the standard interface for handoff from service providers
to customers. Where all services are delivered over Ethernet interfaces, the cheapest
access technology is generally to deploy Ethernet switches. But in order to scale such
a deployment, carriers need to deploy a carrier-class technology into the metro core.
Because most service providers wish to offer IP services as well as Ethernet services,
they often deploy IP/MPLS routers into the metro edge and core and use them to interconnect
the access layer of Ethernet switches, offering both Layer 2 and Layer 3
services. In very large metros, carriers may deploy as many as four layers of equipment
(see Figure 14.6):
?– MPLS Core Routers provide connectivity between PE devices.
Pages:
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024