Reports the number of ISDN dial-in ports currently in use, counted without separating single-B from bonded 2B channels since bonded calls are already captured by the MP count, for this specific access domain or realm (the table is indexed by the domain string itself, e.g. the realm portion of a username@domain login). An admin polls this counter alongside its sibling userStatisticsAccDomain* objects to see how the mix of dial-up service types is distributed for this particular accdomain; it lets an admin break down session counts by the ISP/realm a subscriber authenticated against.