Hierarchical VPLS (H-VPLS) introduces a two-tiered architecture to address the scaling challenges inherent in a flat, full-mesh VPLS. This model significantly enhances scalability by reducing the number of Service Distribution Paths (SDPs) and signaling sessions required in the network core. Management is simplified as the access and core networks are decoupled, meaning the addition of a new customer site only requires local configuration without altering the core mesh. Furthermore, H-VPLS optimizes bandwidth utilization by centralizing the replication of Broadcast, Unknown Unicast, and Multicast (BUM) traffic. An access device sends a BUM frame once to the core, which then handles replication to all other relevant nodes, thus reducing the load on access links.

B. Reduces the FDB size within a VPLS instance: This is misleading. While access nodes have smaller FDBs, the core nodes must still learn all customer MAC addresses, so the total FDB size for the service is not reduced.

E. Reduces the routing table size: This is incorrect because VPLS is a Layer 2 technology that operates using MAC address tables (FDBs), not Layer 3 IP routing tables.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1, Part: VPLS Services, Section: "Hierarchical VPLS": This document states, "H-VPLS provides a scalable solution for VPLS services... The H-VPLS architecture provides a mechanism to scale VPLS services by segmenting the VPLS network into a core (S-PE) and access (MTU-s) layer." This directly supports option A. The guide further explains how split-horizon groups on core PEs optimize BUM traffic handling, which supports option C. The simplified provisioning model described supports option D.

2. M. L. F. de Mello, L. H. M. K. Costa, L. F. R. C. Carmo and O. C. M. B. Duarte, "An analysis of VPLS scalability and a proposal of a hierarchical model," 2008 IEEE Network Operations and Management Symposium - NOMS 2008, Salvador, 2008, pp. 319-326, doi: 10.1109/NOMS.2008.4575149: This academic paper analyzes the scalability limitations of flat VPLS, particularly the quadratic growth of signaling sessions, and identifies the hierarchical model as the solution. Section IV, "Hierarchical VPLS," details how the architecture reduces signaling overhead (supporting option A) and optimizes BUM traffic replication (supporting option C), which are primary benefits.