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Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter10 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 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 MS-SPRing.
If CTC cannot find a link that meets these requirements, an error appe ars.
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 t ypically
interconnect two “foreign” networks (Figure 10-6). Traffic is protected while it goes through a network
of ONS 15454 SDHs.
Figure10-6 Secondary Sources and Destinations
Several rules apply to secondary sources and destinations:
•CTC does not allow a secondary destination for unidirectional circ uits, 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 EtherSwi tch circuits).
83948
Primary source
Secondary source
Primary destination
Secondary destination
Vendor A
network
Vendor B
network
ONS network