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Building for Intermittent Connectivity: Lessons from USSD

By Sente Team19 Oct 2026
engineeringussdconnectivity

USSD remains the most accessible digital channel across Africa — it works on every phone, requires no internet, and imposes no app-install friction. But it also runs on networks where round-trips can exceed 100 ms and sessions drop mid-transaction.


Our approach


We model each USSD session as a **Redis-backed finite state machine (FSM)**, not a synchronous database write. The user navigates menus entirely in memory, and the FSM only commits a transaction when the user confirms their intent.


  • **No synchronous relational writes during navigation** — the menu feels instant.
  • **Idempotency keys** protect against double-charges when sessions reconnect.
  • **Sub-100 ms round-trip** is achievable even on 2G when the FSM is co-located with the mobile network operator's USSD gateway.

    • The result: a menu that feels as responsive as a native app, on a $15 feature phone.