What type of service interruption occurs when 911 calls directed to a seven-digit number do not route through the 911 tandem switch?

The scenario described in the question refers to a specific situation in telecommunications concerning the routing of emergency calls. Central office isolation occurs when a failure prevents calls from being properly routed from a central office to the appropriate handling equipment, such as the 911 tandem switch. This situation typically arises when there is an issue within the central office's equipment or software that affects the ability to connect calls, leading to an inability to route calls effectively to emergency services.

In this case, 911 calls directed to a seven-digit number not routing through the 911 tandem switch indicates a clear disruption in the typical call flow. This aligns with the concept of central office isolation, where specific functionalities within the central office are compromised, preventing proper call processing and routing.

Choosing the correct type of service interruption is essential for understanding the nature of telecommunications failures, especially in emergency services, where reliable access to 911 is critical. It helps in diagnosing the issue and implementing the right solution to restore proper function, ensuring public safety.