SIP Trunk Failure Metrics in Performance Dashboard

Could someone explain the mapping between SIP trunk status codes and the Performance Dashboard queue metrics? Our EU-West BYOC environment shows zero abandoned calls, yet the telephony logs indicate persistent 503 Service Unavailable errors from the carrier.

trunk_config:
 timeout: 5s
 retry: 0
 channel: voice

How does the system categorize these failures in the agent performance views?