The Path Computation Engine (PCE) is a core functional component of a Software-Defined Networking (SDN) controller. It is responsible for calculating optimal paths for traffic across the network. The PCE maintains a real-time, comprehensive view of the network topology, resource utilization, and defined policies. When a link or node failure occurs, the SDN controller is notified and invokes the PCE to compute a new, viable alternative path that avoids the point of failure while still adhering to the service's constraints (e.g., latency, bandwidth). This capability is fundamental to enabling automated network resilience and traffic engineering in transport networks.

A. Path Correlation Engine: This is not a standard term for path computation; it suggests a function for analyzing relationships or dependencies between different paths, not calculating them.

B. Alternative Route Finding: This is a generic phrase describing the process or outcome, not the specific name of the standardized functional component that performs the calculation.

C. Alternative Path Computing: Similar to option B, this describes the action being performed but is not the industry-standard term for the SDN engine itself.

1. IETF RFC 4655: A Path Computation Element (PCE)-Based Architecture. Section 1, "Introduction," defines the PCE as "an entity that is capable of computing a network path or route based on a network graph and applying computational constraints." This foundational document establishes the PCE's role in path computation, which includes finding paths for restoration.

2. Nokia Network Services Platform (NSP) Data Sheet. The official data sheet for Nokia's SDN controller platform explicitly states that the NSP includes a "powerful, multi-layer, and multi-vendor Path Computation Element (PCE) for path computation and network optimization across the IP/MPLS and optical layers." This confirms the PCE is the correct Nokia terminology for this function. (Reference: Nokia Network Services Platform Data Sheet, Document ID: SR2007046385EN, 2020).

3. Stallings, W. (2016). Foundations of Modern Networking: SDN, NFV, and Cloud Computing. In Chapter 10, "SDN: Software Defined Networking," the text discusses the architecture of SDN controllers, highlighting that a key application is Traffic Engineering, where a centralized element like a PCE calculates optimal paths based on global network state, including for rerouting during failures. (Pearson Education, Inc.).