Port Use Auditor stats heuristic:

PortUseAuditor is usually run on per building basis.

get all access devices associated with the "ns" building (eg. cssc)

iterate over devices
  check to see if there is NetWatch activity on port within specified timeframe. (max 1yr limited by netwatch data retention) if so, mark active.

  call addLinkUpPorts()
    iterate over all access devices
    operate on only ^s* devices
    get current port status for device via snmp 
    iterate over ports
      if no netwatch data, but link is up, mark as active

summary: ports on access devices with either netwatch data in the specified timeframe, or link up is counted as "in use"