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The SNC state is a parameter that indicates the status of a resource in a GMPLS network. A resource can be a link, a wavelength, a timeslot, or a fiber. The SNC state can have different values, such as N, n, P, p, R, r, and so on. Each value has a specific meaning and implication for the resource and the LSP that uses it. The SNC state of lower case “n” means that the resource is the nominal resource on a TE-link that is notin use. A nominal resource is the default or preferred resource that is assigned to an LSP when it is created. A TE-link is a logical link that represents a set of resources that share the same attributes and constraints. A TE-link can have multiple resources, such as wavelengths or timeslots, but only one of them can be the nominal resource. If an LSP is using a resource other than the nominal resource on a TE-link, it means that the LSP has been rerouted or switched due to a failure or a constraint violation. In this case, the SNC state of the nominal resource will be “n”, indicating that it is not in use by any LSP12. References:

• 1: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 2: Nokia Network Functions Manager for Transport User Guide | Nokia

The Soft Shutting Down state in the NFM-T is an administrative maintenance state where services stay up but no new traffic can be routed over the TE-link. This state is used to prepare a TE-link for maintenance or decommissioning without affecting the existing services. The NFM-T sets the TE-link to Soft Shutting Down state by sending a Notify message with the Administrative State Change flag to the head-end node of the TE-link. The head-end node then stops accepting new LSP requests over the TE-link and sends a PathErr message with the Administrative State Change flag to all the tail-end nodes of the LSPs in the TE-link. The tail-end nodes then stop sending new traffic over the LSPs and send a ResvErr message with the Administrative State Change flag to all the intermediate nodes of the LSPs. The intermediate nodes then update their routing tables and stop forwarding new traffic over the LSPs. The existing traffic, however, continues to flow over the LSPs until they are manually deleted or rerouted by the NFM-T. References : Nokia GMPLS-controlled Optical Networks Course | Nokia, Nokia Advanced Optical Network Management with NFM-T Course | Nokia

The SNC Nominal Route is the default or preferred route that is assigned to an LSP when it is created. The SNC Nominal Route is determined by the constraints that are specified by the user during the LSP creation process, such as cost, SRLG, color, bandwidth, protection, and regeneration. The user can modify the SNC Nominal Route in NFM-T by using the Constraint Wizard, which is a tool that allows the user to change the constraints for an existing LSP. The Constraint Wizard will then compute a new SNC Nominal Route based on the modified constraints and update the LSP accordingly34. References:

• 3: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 4: Nokia Network Functions Manager for Transport User Guide | Nokia

The SNC state with an uppercase “N” means that the resource is currently using the nominal resource assigned to it. As explained in the previous question, a nominal resource is the default or preferred resource that is assigned to an LSP when it is created. If an LSP is using the nominal resource on a TE-link, it means that the LSP has not been rerouted or switched due to any failure or constraint violation. In this case, the SNC state of the resource will be “N”, indicating that it is in use by an LSP12. References:

• 1: Nokia GMPLS-controlled Optical Networks Course | Nokia
• 2: Nokia Network Functions Manager for Transport User Guide | Nokia

RSVP-TE Notify message is a message type defined in the RSVP-TE protocol, which is an extension of the RSVP protocol for MPLS traffic engineering. RSVP-TE Notify message is used to inform non-adjacent nodes of LSP events, such as setup, modification, or teardown. This allows the nodes to update their local state information and perform actions based on the notification. For example, a Notify message can be used to trigger a fast reroute mechanism in case of a link or node failure12. References:

• 1: RFC 3473 - Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Extensions
• 2: RFC 3471 - Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description