Cisco Systems ONS 15600 Constraint-Based Circuit Routing, One-way, Head end, Drop and continue

Chapter 7 Circuits and Tunnels

7.12 Constraint-Based Circuit Routing

Table 7-8	Unidirectional STS Circuits
No. of Inbound Links		No. of Outbound Links	No. of Sources	No. of Drops	Connection Type
1		1	—	—	One-way
1		2	—	—	path protection
					head end
—		2	1	—	path protection
					head end
2		—	—	1+	path protection
					drop and continue

7.12 Constraint-Based Circuit Routing

When you create circuits, you can choose Fully Protected Path to protect the circuit from source to destination. The protection mechanism used depends on the path that CTC calculates for the circuit. If the network is comprised entirely of BLSR or 1+1 links, or the path between source and destination can be entirely protected using 1+1 or BLSR links, no path-protected mesh network (PPMN), or virtual path protection, protection is used.

If PPMN protection is needed to protect the path, set the level of node diversity for the PPMN portions of the complete path on the Circuit Routing Preferences area of the Circuit Creation dialog box:

•Nodal Diversity Required—Ensures that the primary and alternate paths of each PPMN domain in the complete path have a diverse set of nodes.

•Nodal Diversity Desired—CTC looks for a node-diverse path; if a node-diverse path is not available, CTC finds a link-diverse path for each PPMN domain in the complete path.

•Link Diversity Only—Creates only a link diverse path for each PPMN domain.

When you choose automatic circuit routing during circuit creation, you have the option to require or exclude nodes and links in the calculated route. You can use this option to achieve the following results:

•Simplify manual routing, especially if the network is large and selecting every span is tedious. You can select a general route from source to destination and allow CTC to fill in the route details.

•Balance network traffic; by default CTC chooses the shortest path, which can load traffic on certain links while other links are either free or use less bandwidth. By selecting a required node and/or a link, you force CTC to use (or not use) an element, resulting in more efficient use of network resources.

CTC considers required nodes and links to be an ordered set of elements. CTC treats the source nodes of every required link as required nodes. When CTC calculates the path, it makes sure the computed path traverses the required set of nodes and links and does not traverse excluded nodes and links.

The required nodes and links constraint is used only during the primary path computation and only for PPMN domains/segments. The alternate path is computed normally; CTC uses excluded nodes/links when finding all primary and alternate paths on PPMNs.

Cisco ONS 15600 Reference Manual, R7.2

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