Design a 911 emergency calling service
Company: Salesforce
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
## 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.
Quick Answer: This question evaluates a candidate's ability to design a highly available, scalable emergency-calling platform covering real-time call flow, accurate caller location validation, PSAP routing, interoperability with telephony/SIP providers, and regulatory/security considerations.