Coupon Delivery — Mobile/POS Sync
The scenario. An edge interaction issues a Free Ice Cream Cone coupon to a user. The coupon appears immediately on the user's mobile phone (Inter-page latency). The Point-of-Sale terminal at the redemption location updates its accepted-coupons list every 30 minutes (Inter-session latency).
The architectural problem. The same logical activation has two delivery paths with different latency budgets and different data freshness. If a user walks to the store immediately after seeing the coupon on their phone, the POS may reject it.
Three resolutions, all valid.
- Tighten POS latency — push POS into Inter-page tier; ~10× cost increase per the rule of thumb (source.real-time-clarity-md).
- Loosen mobile latency — delay the mobile coupon until POS has caught up; harms perceived experience.
- Add reconciliation — let POS query a real-time service for active coupons at scan time; introduces a hard runtime dependency.
Lesson. Cross-modality activations require explicit latency-tier reconciliation at design time. The choice depends on the cost ceiling, the brand's tolerance for at-counter friction, and the technical posture of the POS system.