Which of the following statements about the recovery time for protection and restoration combined (PRC) is correct?

Protection and Restoration Combined (PRC) is a resilience mechanism in GMPLS-controlled networks. It leverages a pre-computed, pre-signaled protection path to provide very fast recovery for the first network failure. This initial recovery action is a protection switchover, which is designed to be as fast as traditional protection schemes like Sub-Network Connection Protection (SNCP) or 1+1 protection, typically completing within 50 milliseconds. For subsequent or concurrent failures, PRC then relies on slower, dynamic restoration mechanisms to establish new paths. Therefore, its initial recovery speed is comparable to SNCP.

B. PRC is as fast as restoration mechanisms. This is incorrect. The primary advantage of PRC's protection component is that it is significantly faster than dynamic restoration, which involves signaling and path computation after a failure.
C. PRC has a recovery time that depends on the broken links. This is misleading. While failure detection is a prerequisite, the initial protection switchover time is largely pre-determined and not dependent on the specific link that failed, unlike dynamic restoration.
D. PRC has a typical recovery time greater than 50 ms. This is incorrect. The protection phase of PRC is specifically designed to meet the carrier-grade requirement of sub-50 ms recovery, which is a key performance indicator for protection switching.

1. Nokia 7750 SR and 7950 XRS GMPLS and ASON Guide, Release 21.10.R1, Document ID: 3HE 17489 AAAC TQZZA, Edition 01. In the "Protection and Restoration Combined (PRC)" section, it is explained that PRC provides fast protection for the first failure. The document states: "PRC provides fast protection for the first failure (within 50 ms) and restoration for subsequent failures." This directly supports that PRC's initial recovery is not greater than 50ms (refuting D) and is on par with fast protection schemes like SNCP (supporting A).

2. Martini, B., et al. (2005). "On the Integration of Protection and Restoration in GMPLS-based Networks." In Proceedings of the First International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks (QSHINE'04). This academic paper discusses hybrid approaches like PRC. It highlights that the goal is to combine the "fast recovery time of protection schemes" with the "high resource efficiency of restoration schemes." This confirms that the protection aspect of PRC is designed for speed, comparable to standalone protection mechanisms. (DOI not readily available for this specific older conference proceeding, but the concept is foundational in GMPLS literature).

3. RFC 4427, "Recovery (Protection and Restoration) Terminology for Generalized Multi-Protocol Label Switching (GMPLS)," Section 3. This RFC defines the terminology. It distinguishes "Protection" as using a pre-computed and often pre-provisioned recovery path, enabling very fast switching times (typically < 50ms). "Restoration" involves computing a path after failure detection, which is inherently slower. PRC combines these, using the fast protection mechanism first.