Cisco ONS 15454 SDH Manual page 21

Chapter 11 Circuits and Tunnels
Several rules apply to secondary sources and destinations:
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For bidirectional circuits, CTC creates an SNCP connection at the source node that allows traffic to be
selected from one of the two sources on the ONS 15454 SDH network. If you check the Fully Path
Protected option during circuit creation, traffic is protected within the ONS 15454 SDH network. At the
destination, another SNCP connection is created to bridge traffic from the ONS 15454 SDH network to
the two destinations. A similar but opposite path exists for the reverse traffic flowing from the
destinations to the sources. For unidirectional circuits, an SNCP drop-and-continue connection is created
at the source node.
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
11.14 Manual Circuit Routing
Routing circuits manually allows you to:
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CTC imposes the following rules on manual routes:
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CTC does not allow a secondary destination for unidirectional circuits, because you can always
specify additional destinations after you create the circuit.
Primary and secondary sources should be on the same node.
Primary and secondary destinations should be on the same node.
DRI and open-ended SNCP nodes allow primary and secondary sources and destinations on
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different nodes.
Secondary sources and destinations are permitted only for regular high-order or low-order
connections (not for low-order tunnels and multicard EtherSwitch circuits).
For point-to-point (straight) Ethernet circuits, only VC endpoints can be specified as multiple
sources or drops.
Choose a specific path, not necessarily the shortest path.
Choose a specific VC4/VC3/TUG3/TUG2/VC12/VC11 on each link along the route.
Create a shared packet ring for multicard EtherSwitch circuits.
Choose a protected path for multicard EtherSwitch circuits, allowing virtual SNCP segments.
All circuits, except multicard EtherSwitch circuits in a shared packet ring, should have links with a
direction that flows from source to destination. This is true for multicard EtherSwitch circuits that
are not in a shared packet ring.
If you enabled Fully Path Protected, choose a diverse protect (alternate) path for every unprotected
segment (Figure 11-7).
Appendix C, "Network Element Defaults."
Cisco ONS 15454 SDH Reference Manual, R8.5
11.14 Manual Circuit Routing
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