Which of the following statement about guaranteed restriction (GR) in generalized Multiprotocol label Switching (GMPLS) is correct?

Guaranteed Restoration (GR), also known as pre-planned restoration, is a GMPLS recovery mechanism where a backup Label Switched Path (LSP) is pre-calculated and pre-signaled before a failure occurs. Critically, network resources (such as bandwidth and wavelength) are reserved along this backup path during its signaling. Upon failure of the primary LSP, the head-end node is notified and activates the already established and resource-reserved backup LSP. This pre-provisioning of the path and its resources is what "guarantees" the restoration, providing a high degree of survivability with faster recovery times than dynamic restoration.

B: While GR is designed to provide 100% survivability for single failures, this is a goal, not the defining mechanism. Other schemes, like 1+1 protection, also achieve this.

C: This is incorrect. All protection and restoration mechanisms, including GR, fundamentally rely on the detection and signaling of a fault to trigger the switchover to the backup path.

D: This statement describes dynamic (or pure) restoration, where the backup path is calculated and signaled only after a failure has occurred. GR's key advantage is pre-calculating the path.

1. IETF RFC 4872: RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery.

Section 3.2, "Pre-planned Protection": "With this approach, the recovery LSP is pre-computed and can be pre-signaled before a failure occurs. Resources for the recovery LSP may or may not be pre-reserved." (Note: In the context of "Guaranteed" Restoration, resources are pre-reserved). This supports the pre-establishment and resource configuration aspect of option A.

2. Nokia 7750 SR OS MPLS Guide, Release 22.10.R1.

Section: GMPLS-UNI: The guide describes end-to-end path protection mechanisms. It explains that for pre-planned (guaranteed) restoration, a secondary LSP path is established to protect the primary LSP. This secondary path has its resources reserved, ready for activation upon a primary path failure, which aligns directly with the statement in option A.

3. IETF RFC 4427: Recovery (Protection and Restoration) Terminology for GMPLS.

Section 3.1, "Recovery Schemes": This RFC defines "Pre-planned Restoration" as a mechanism where "the recovery path(s) is (are) pre-computed... The recovery path(s) may also be pre-established." This confirms that the backup path is configured before a failure, contrasting with pure restoration (option D).