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Cisco ONS 15454 Reference Manual, R7.0
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Chapter 11 Circuits and Tunnels
11.17 11.17 Virtual Concatenated Circuits
11.17 Virtual Concatenated Circuits
Virtual concatenated (VCAT) circuits, also called VCAT groups (VCGs), transport traffic using
noncontiguous TDM time slots, avoiding the bandwidth fragmentation problem that exists with
contiguous concatenated (CCAT) circuits. The cards that support VCAT circuits are the CE-Series,
FC_MR-4 (both line rate and enhanced 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 and terminate at the same end points. For two-fiber BLSR configurations, some members
can be routed on protected time slots and others on PCA time slots.
To enable end-to-end connectivity in a VCAT circuit that traverses through a third-party network, you
must create a server trail between the ports. For more details, refer to the "Create Circuits and VT
Tunnels" chapter in the Cisco ONS 15454 Procedure Guide.

11.17.1 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 in the Edit Circuits window.
• If all member circuits are in the IS state, the VCAT circuit state is IS.
• If all In Group member circuits are in the OOS state, the VCAT circuit state is OOS.
• If no member circuits exist or if all member circuits are Out of Group, the VCAT circuit state is
OOS.
• A VCAT circuit is in OOS-PARTIAL state when In Group member states are mixed and not all are
in the IS state.

11.17.2 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. Figure 11-14 shows an example of common fiber routing.