System designHardsd-g694

Subject Voip sip signaling protocolLevel Senior–Staff~45 minCommon in Networking & APIs interviewsIndustries Telecom, Technology

Question

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.