1D. When a segment of the Ethernet network fails, a new spanning tree
is calculated. If a redundant path around the failure is available, the network uses it
instead of the failed segment. This protection scheme is robust from an interoperation
point of view and has been implemented in the LAN environment for some time.
Figure 10.9 Using circuit bonding to extend Ethernet to an off-net client
SONET
NE
End-to-end transmission
layer management
SONET network
Ethernet client
Ethernet
client
SONET
NE
Transparent Ethernet connectivity
Circuit-
bonded
system
Circuit-
bonded
system
Leased
network circuits
276 Chapter 10
However, this simple method has several drawbacks, all of which are magnified in the
MAN environment:
?– Segment protection Ethernet segments are not protected within the segment.
For example, if a hub fails, all workstations on the hub can no longer communicate.
?– Protection availability There is no guarantee that a protection path is available.
Ethernet reconfigures and uses an alternate path only if the alternate path is
available.
?– Protection size There is no guarantee that a protection path will be the same
size as the failed link.
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