Reason why CSPF is used on ASON networks


Constraint Shortest Path First (CSPF) is a routing algorithm that calculates the optimal route for a service, ensuring that the service is quickly restored after rerouting.

Other related questions:
Differences between an ASON network and a common SDH network
Differences between an ASON network and a common SDH network: In an ASON network, services are classified into several protection levels including diamond, gold, silver, copper and iron. The protection level can be enhanced and the service rerouting function is added in an ASON network. As a result, the actual bandwidth utilization of an ASON network is higher than 50%. A common network does not have the rerouting function.

Gold service protection on ASON networks
1. Principles of gold services Gold services use MS link resources. When a fiber cut occurs for the first time, MSP switching is triggered. If the MS protection switching fails, rerouting restoration protection will be triggered. Establishing a service will fail if no sufficient MS link is available. In addition, service establishment complies with the timeslot consistency principle. During MSP switching upon the first fiber cut, signals do not follow the actual path of a gold service. An MSP switching failure will trigger rerouting. During rerouting, MS links are preferentially used. If no such resource is available or MS links are insufficient, an unprotected link will be used to ensure that the service is not interrupted. In this case, the service is in degraded state. If the MSP link recovers, the service will not be automatically switched back to the MS link. The MS link will be used for the next rerouting if possible. 2. Features of gold services MS links are used for establishing services, and service establishment complies with the timeslot consistency principle. Static services that completely use MS links can be upgraded to gold services. Static services that partially use MS links can be upgraded to gold services. After the upgrade, however, the protection status of the services is "Degrade". Gold services can be downgraded to static services. MSP switching is triggered upon the first fiber cut. Rerouting restoration protection is triggered if MSP switching fails. During rerouting, if links with consistent timeslots are unavailable, links with inconsistent timeslots are used; or if MSP links are unavailable, links without protection are used. Lockout of rerouting is supported. Service path optimization is supported. Service names can be modified. 3. MSP types supported by gold services 1:1 linear MSP Two-fiber bidirectional MSP ring Four-fiber bidirectional MSP ring 4. Restrictions and limitations During service creation, only loose cross-ring nodes can be specified. If a non-cross-ring node needs to be specified, the timeslot must be specified. Gold services cannot be associated. Failure nodes or links of the original trails cannot be excluded during rerouting.

Restrictions on a network for which both optical-layer ASON and electrical-layer ASON are configured
Optical-layer ASON and electrical-layer ASON can be configured on the same network but they cannot be configured on the same NE.

Reason why the recommended usage status of ASON overhead bytes is set to "Disabled" for tributary boards when electrical-layer ASON features are enabled on an ASON network
For electrical-layer ASON, tributary boards cannot transmit ASON management bytes. Therefore, you are advised to set the usage status of ASON overhead bytes to "Disabled" for the tributary boards.

Method used to select routing policies on an ASON network
Various rerouting policies are provided on an ASON network and are selected based on the available system resources. When the resources are sufficient, diamond services can be used. As resources are continuously consumed, a user may have to select copper services to ensure that sufficient resources are provided for diamond services. Copper services are rarely used. Generally, only temporary services are configured as copper services.

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