This read-only SSMQualityLevel is the quality-level threshold used when the port's squelch control is set to squelch-ql: if the system's current quality level drops below this configured value, the Time-of-Day output is squelched. An administrator sets this to control exactly how much clock degradation is tolerated before the TOD output is muted rather than passed downstream as unreliable. For example, setting this to a mid-range SSM quality level means a chain failure that drags the system below that grade will silence the TOD output automatically.