System designHardsd-g707

Subject Carrier sms routing protocolLevel Senior–Staff~45 minCommon in Networking & APIs · Distributed systems interviewsIndustries Telecom, Technology

Question

Design a carrier-grade SMS routing gateway (an SMPP-based messaging hub) that routes 50,000 messages/sec between application senders and dozens of mobile carriers, each carrier with its own throughput limits, encoding rules, and delivery-receipt behavior. You need least-cost/quality routing across carriers, reliable delivery-receipt correlation, and to never exceed a carrier's bind/throughput cap. How do you bind to carriers, route, and reconcile receipts?

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

Loading whiteboard…

Run or narrate your approach, then ask the coach.