This read-write integer (0..0xffffff) is a bitmap of which DS0 timeslots on a line are combined to form this logical port, with bit 0 representing DS0-1; it is not used on unchannelized FRSM-VHS or FRSM12 cards, which always report the value 0xffffff for this field instead. An administrator sets specific bits to select exactly which DS0 timeslots on a channelized T1/E1 line are bundled into this fractional logical port. For example, on a channelized card, setting only bits 0 and 1 in portDs0ConfigBitMap would bundle just DS0-1 and DS0-2 into this logical port, whereas an unchannelized FRSM-VHS card would ignore any such setting and always show 0xffffff.