Cisco Systems 15454 - page 370

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Cisco ONS 15454 Reference Manual, R7.0
78-17191-01
Chapter 11 Circuits and Tunnels
11.17 11.17.2 VCAT Member Routing
Figure 11-14 VCAT Common Fiber Routing
CE-Series cards also support split fiber routing, which allows the individual members to be routed on
different fibers or each member to have different routing constraints. This mode offers the greatest
bandwidth efficiency and also the possibility of differential delay, which is handled by the buffers on the
terminating cards. Four protection options are available for split fiber routing: Fully Protected, PCA,
Unprotected, and DRI. Figure 11-15 shows an example of split fiber routing.
Figure 11-15 VCAT Split Fiber Routing
In both common fiber and split fiber routing, each member can use a different protection scheme;
however, for common fiber routing, CTC checks the combination to make sure that a valid route exists.
If it does not, the user must modify the protection type. In both common fiber and split fiber routing,
intermediate nodes treat the VCAT members as normal circuits that are independently routed and
protected by the SONET network. At the terminating nodes, these member circuits are multiplexed into
a contiguous stream of data.
The switch time for split fiber routing depends on the type of circuits traversing the path.
• CCAT circuits will carry traffic after the SONET defects are cleared.
• VCAT circuits will carry traffic after the SONET defects are cleared and VCAT framers are in frame
for ALL the time slots that are part of the group. Hence the switchover takes extra time.
• LCAS circuits will carry traffic after the SONET defects are cleared, the VCAT framers are in frame,
for ALL the time slots that are part of the group, and the LCAS protocol has fed back MST=OK
(MST=Member Status) to the far end so the far end can enable the time slot to carry traffic. The MST
frame takes 64ms for high-order and 128ms for low-order VCAT. Hence VCAT LCAS circuit
switchover takes longer time.
Member 1
VCG-2
Member 2
102170
Intermediate
NE
Member 1
VCG-1
Member 2
Member 1
VCG-2
Member 2
Member 1
VCG-1
Member 2
VCAT
Function
VCAT
Function
VCAT
Function
VCAT
Function
STS-1
STS-2
STS-3
STS-4
STS-1
STS-2
STS-3
STS-4
CE-100T-8 CE-100T-8
124065
VCAT
Function
Source VCAT at NE
Traffic Traffic
Virtually
Concatenated
Group Member #1
Member #2
Member #3
Intermediate
NE
VCAT
Function
with
Differential
Delay Buffer
Destination VCAT at NE
Intermediate
NE
Intermediate
NE