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Cisco ONS 15310-MA SDH Reference Manual, Release 9.1 and Release 9.2
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Chapter 7 Circuits and Tunnels
Virtual Concatenated Circuits
A VCAT circuit is locked-PARTIAL when In Group member states are mixed and not all member
states are unlocked.
7.7.2 VCAT Member Routing
The automatic and manual routing selection applies to the entire VCAT circuit, that is, all members are
manually or automatically routed. Bidirectional VCAT circuits are symmetric, which means that the
same number of members travel in each direction. With automatic routing, you can specify the
constraints for individual members; with manual routing, you can select different spans for different
members.
Two types of automatic and manual routing are available for VCAT members on CE-100T-8, CE-MR-6,
and ML-100T-8 cards: common fiber routing and split fiber routing. In common fiber routing, all VCAT
members travel on the same fibers, which eliminates delay between members. Three protection options
are available for common fiber routing: Fully Protected, PCA, and Unprotected. Split fiber routing
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 or ports. Three protection options are
available for split fiber routing: Fully Protected, Unprotected, and DRI. 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 SDH network. At the terminating nodes, these
member circuits are multiplexed into a contiguous stream of data. Figure 7-3 shows an example of
common fiber routing.
Figure 7-3 VCAT Common Fiber Routing
Member 1
VCG-2
Member 2
271783
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
VC3
STS-2
STS-3
STS-4
VC3
STS-2
STS-3
STS-4
CE-100T-8 CE-100T-8