This object provides a small disambiguating index used to tell apart multiple modem calls that began at the exact same system time-tick, populated only for internal-modem sessions. Administrators rarely interpret its value directly but rely on it, together with the call start time, to uniquely identify a specific call record when many calls start in quick succession. For example, on a busy modem pool where several calls connect within the same tick, this index is what keeps their session records from being confused with one another.