Cisco ONS 15454 SDH Manual page 20

11.13.1 Bandwidth Allocation and Routing
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11.13.1 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:
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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.
11.13.2 Secondary Sources and Destinations
CTC supports secondary sources and destinations (drops). Secondary sources and destinations typically
interconnect two "foreign" networks
of ONS 15454 SDH nodes.
Figure 11-6
Cisco ONS 15454 SDH Reference Manual, R8.5
11-20
If you do not choose Fully Path Protected during circuit creation, circuits can still contain protected
segments. Because circuit routing always selects the shortest path, one or more links and/or
segments can have some protection. CTC does not look at link protection while computing a path
for unprotected circuits.
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 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.
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.
Secondary Sources and Destinations
Primary source
Vendor A
network
Secondary source
(Figure 11-6). Traffic is protected while it goes through a network
ONS network
Chapter 11 Circuits and Tunnels
Primary destination
Vendor B
network
Secondary destination
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