Why is H-VPLS considered more scalable than flat VPLS?

H-VPLS creates two distinct signaling layers - a spoke layer between U-PEs and their associated N-PEs, and a hub layer consisting of a full mesh only among N-PEs - reducing total pseudowire count compared to a flat single-tier full mesh.

By limiting the full pseudowire mesh to only N-PEs, H-VPLS ensures that mesh pseudowire count grows with the number of core devices rather than the total number of all PE routers, significantly lowering signaling overhead as the network scales.

H-VPLS does not eliminate signaling overhead on core devices - N-PEs still maintain a full mesh of pseudowires and participate in LDP or BGP signaling among themselves.

H-VPLS does not eliminate signaling between N-PE and U-PE - spoke pseudowires or Ethernet aggregation connections between them still require control plane signaling.