This read-only counter reports how many ports on the optical device support port-level variable optical attenuation (VOA). An admin uses it to know how many rows to expect in the nbsSigCondVoaPortTable before walking per-port attenuation settings, since not every interface on a DWDM shelf has VOA hardware. For example, a value of 8 tells the monitoring station that only 8 of the chassis's optical ports are attenuation-capable and worth polling for rx/tx attenuation values.