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Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 10 Circuits and Tunnels
10.11.1 Bandwidth Allocation and Routing
• If the network has a mixture of low-order-capable nodes and low-order-incapable nodes, CTC might
automatically create a low-order tunnel. Otherwise, CTC asks you whether or not a low-order tunnel
is needed.
10.11.1 Bandwidth Allocation and Routing
Within a given network, CTC routes circuits on the shortest possible path between source and destination
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 MS-SPRing.
If CTC cannot find a link that meets these requirements, an error appears.
The same logic applies to low-order circuits on low-order tunnels. Circuit routing typically favors
low-order tunnels because low-order tunnels are shortcuts between a given source and destination. If the
low-order tunnel in the route is full (no more bandwidth), CTC asks whether you want to create an
additional low-order tunnel.
10.11.2 Secondary Sources and Destinations
CTC supports secondary sources and destinations (drops). Secondary sources and destinations typically
interconnect two “foreign” networks (Figure 10-6). Traffic is protected while it goes through a network
of ONS 15454 SDHs.
Figure 10-6 Secondary Sources and Destinations
Several rules apply to secondary sources and destinations:
• 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.
• Secondary sources and destinations are permitted only for regular high-order or low-order
connections (not for low-order tunnels and multicard EtherSwitch circuits).
83948
Primary source
Secondary source
Primary destination
Secondary destination
Vendor A
network
Vendor B
network
ONS network