Which of the following can cause call routing failures?

• A. CSS/partition mismatch, missing route patterns, or trunk/gateway down.
• B. Too many calls concurrently.
• C. User misdial of digits.
• D. Endpoints not registered.

Answer: (A)

Call routing failures happen when the system can’t map the dialed number to a reachable route. The first limiter is access to the route patterns through the Calling Search Space and partitions: if the CSS or partition assignment blocks the route pattern that would lead to the destination, the system can’t even select a path, and the call fails at the routing stage. If a route pattern exists but isn’t accessible because of the CSS/partition setup, there is no valid route to take. Even with a valid route, the destination won’t be reached if the transport path is down—trunk or gateway outages prevent the call from being carried to the next hop or endpoint.

Other factors can cause call failures but aren’t the direct routing-resolution problem described above. Too many concurrent calls can lead to congestion or resource limits, not a misrouting decision. If digits are misdialed, the system might select an incorrect route or fail to route properly, and if the target endpoint isn’t registered, the call setup may fail due to endpoint availability rather than the route resolution itself.