The value of tmnxNatGrpCfgSessionWatermarkHi specifies
the high watermark of the number of sessions for each MDA
in this ISA group.
The value of this object must be set together with the value of
tmnxNatGrpCfgSessionWatermarkLo.
The value of this object must be higher than the value of
tmnxNatGrpCfgSessionWatermarkLo, unless both are equal to zero.