Cisco ONS 15454 SDH Manual page 26

11.16 Virtual Concatenated Circuits
11.16 Virtual Concatenated Circuits
Virtual concatenated (VCAT) circuits, also called VCAT groups (VCGs), transport traffic using
noncontiguous time division multiplexing (TDM) time slots, avoiding the bandwidth fragmentation
problem that exists with contiguous concatenated circuits. The cards that support VCAT circuits are the
CE-Series, FC_MR-4 (both enhanced and line rate mode), and ML-Series cards.
In a VCAT circuit, circuit bandwidth is divided into smaller circuits called VCAT members. The
individual members act as independent TDM circuits. All VCAT members should be the same size and
must originate/terminate at the same end points. For two-fiber MS-SPRing configurations, some
members can be routed on protected time slots and others on PCA time slots.
11.16.1 VCAT Circuit States
The state of a VCAT circuit is an aggregate of its member circuits. You can view whether a VCAT
member is In Group or Out of Group in the VCAT State column on the Edit Circuits window.
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11.16.2 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: common fiber routing and
split routing. CE-Series, FC_MR-4 (both line rate and enhanced mode), and ML-Series cards support
common 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. Each member can use a different protection scheme; however,
CTC checks the combination to make sure a valid route exists and if it does not, the user must modify
the protection type.
Cisco ONS 15454 SDH Reference Manual, R8.5
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If all member circuits are Unlocked, the VCAT circuit is Unlocked.
If all In Group member circuits are Locked, the VCAT circuit state is Locked.
If no member circuits exist or are all Out of Group, the state of a VCAT circuit is Locked.
A VCAT circuit is Locked-partial when In Group member states are mixed and all members are not
in the Unlocked state.
Figure 11-11 shows an example of common fiber routing.
Chapter 11 Circuits and Tunnels
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