Keeping track of attendance

I need to keep track of the amount of time that attendees are on a meeting.  This is easy when they sign on at the beginning of the meeting and off at the end of the meeting.   However, it becomes more complicated if someone gets logged off for one reason or another (eg poor internet service, computer crash) and I can have difficulty knowing the amount of time an individual attended the meeting.  Is there a way to identify users that can keep track of this?