## System Design Prompt Design a **911 emergency calling service** (or emergency call routing platform) that allows users to place emergency calls from mobile/landline/VoIP devices and routes them to the correct emergency response center. ### What to cover - End-to-end call flow (caller → network → emergency service → dispatcher) - How you determine and validate caller location - How you route to the correct PSAP/dispatch center - Reliability and availability targets (e.g., "five nines") - Handling spikes (regional disasters), partial outages, and degraded modes - Data retention, audit, security, and compliance - Observability and operational runbooks ### Assumptions You can focus on the backend/platform design and interop boundaries (telephony providers, SIP gateways, PSAP interfaces), not the physical radio systems for first responders.