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Cisco ONS 15454 Reference Manual, R8.5.x
78-18106-01
Chapter 11 Circuits and Tunnels
11.15.1 Bandwidth Allocation and Routing
• Circuit routing does not use links that are down. If you want all links to be considered for routing,
do not create circuits when a link is down.
• Circuit routing computes the shortest path when you add a new drop to an existing circuit. It tries to
find the shortest path from the new drop to any nodes on the existing circuit.
• If the network has a mixture of VT-capable nodes and VT-incapable nodes, CTC can automatically
create a VT tunnel. Otherwise, CTC asks you whethe r a VT tunnel is needed.
• To create protected circuits between topologies, install an XCVT, XC10G, or XC-VX C-10G
cross-connect card on the shared node.
• For STS circuits, you can use portless transmux interfaces if a DS3XM-12 card is installed in the
network. CTC automatically routes the circuit over the portless transmux interfaces on the specified
node creating an end-to-end STS circuit.
Note Automatic routing and its associated subfields are not available if both the Automatic Circuit Routing
NE default and the Network Circuit Automatic Routing Overridable NE default are set to FALSE. For a
full description of these defaults see Appendix C, “Network Element Defaults.”
11.15.1 Bandwidth Allocation and Routing
Within a given network, CTC routes circuits on the shortest possible path between source and destinat ion
based on the circuit attributes, such as protection and type. CTC considers using a link for the circuit
only if the link meets the following requirements:
• The link has sufficient bandwidth to support the circuit.
• The link does not change the protection characteristics of the path.
• The link has the required time slots to enforce the same time slot restrictions for BLSRs.
If CTC cannot find a link that meets these requirements, an error appe ars.
The same logic applies to VT circuits on VT tunnels. Circuit routing typically favors VT tunnels because
VT tunnels are shortcuts between a given source and destination. If the VT tunnel in the route is full (no
more bandwidth), CTC asks whether you want to create an additional VT tunnel.
11.15.2 Secondary Sources and Destinations
CTC supports secondary circuit sources and destinations (drops). Secondary sources and destinations
typically interconnect two third-party networks, as shown in Figure 11-9. Traffic is protected while it
goes through a network of ONS 15454s.