VoIP SIP signaling system
Design a VoIP signaling system (the control plane for placing and tearing down calls) for a cloud telephony provider handling 2M registered endpoints and a peak of 5,000 call setups/sec. Signaling uses SIP. You need <250 ms post-dial delay, correct call state through network blips, and the ability to survive a signaling-node failure mid-call. Media (RTP) flows separately — focus on signaling, registration, and call-state management.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.