Chapter 18 Troubleshooting : Technical Support Organization Overview : Support priority levels : Priority 1
  
Priority 1
This Critical priority is assigned to support cases in which:
The network or system is down causing customers to experience a total loss of service.
There are continuous or frequent instabilities affecting traffic-handling capability on a significant portion of the network.
There is a loss of connectivity or isolation to a significant portion of the network.
This issue has created a hazard or an emergency.