This is the flat transmit power spectral density level, in dBm/Hz, configured for this single-carrier VDSL profile, giving a single overall power setting rather than the per-tone granularity available in the multi-carrier PSD tables. It's the simpler, single-value power control appropriate for SCM's single-carrier modulation, where the whole signal occupies one continuous band rather than many independent tones needing individual shaping. Raising this value increases reach on longer loops at the cost of higher potential crosstalk into neighboring lines sharing the same binder, the classic DSL power-versus-interference tradeoff in its simplest single-carrier form.