The number of calls currently in use. igCurrActiveCalls is used in conjunction with igMaxActiveCalls, the maximum number of calls available, to provide a metric for describing current utilization. Does not imply that a call has completed, but rather that the DS0 time-slot has been allocated for a call by the GR-303 interface. The DS1 frame is composed of 24 consecutively numbered (1-24) time-slots (channels or DS0s). Maximum number of currently active calls is the maximum number of DS1s assigned to the IG times the maximum number of channels or DS0s per DS1 less 2 or 4 channels for primary only EOC/TCM and primary/secondary EOC/TCM = ({1..28} * 24 - {2,4}) = {22..670} 28*24 equals maximum number of DS0's on a DS3, with 0 signaling channels. If you have one 28-T1 IG with no redundancy you can have 672 - 2 signaling DS0's , or 670, or 670 DS0's available for active calls. If you have a single-T1 IG, you have only 24 - 2 signaling DS0's, or 22, DS0's available for active calls.