Isolation of an end office occurs when

• A. The central office links are interrupted
• B. The DBMS is damaged
• C. The PSAP is destroyed
• D. An end office that feeds the 911 system has its communications links to the Tandem Switch or Selective Router broken.

Answer: (D)

Isolation of an end office happens when the path from that end office to the 911 routing infrastructure is broken. Specifically, if the communications links between the end office and the Tandem Switch or Selective Router are down, calls from that area cannot reach the 911 network, effectively isolating that end office. The Tandem Switch or Selective Router is the hub that routes 911 calls to the appropriate PSAP, so losing those links means no route for 911 calls from that location. Other problems, like a central office issue affecting multiple areas, a damaged database management system, or destruction of a PSAP, don’t capture the precise scenario of an end office being cut off from its routing path.