Ada Audits the Offload Break-Even
Ada keeps bytes, radio charge, setup, and tail in one ledger before deciding where the workload belongs
ADA · CALCULATION AUDIT
Ada Audits the Offload Break-Even
The chapter gives a node a 6 mA radio on a 50 kbps link and a local inference that costs 30 mA-s, then asks when it is cheaper to send data than to compute it. With no setup overhead the crossover lands near 31,250 bytes, about 30 KB; add an 8 mA-s connection setup and it drops to about 22 KB. This audit works the offload break-even to the byte, so a placement decision survives a battery review.
Companion to the chapter Compute Offloading and Placement — every number here comes from that chapter.
Offloading is not a cloud magic trick; it is an energy equation. Keep local compute, payload bytes, setup charge, and radio tail in the same ledger before deciding where the workload belongs.
1. The BLE example derives its per-byte radio charge from current and throughput
The chapter gives a 6 mA active radio and an effective 50 kbps link, so one byte costs:
2. The no-setup break-even is about 31,250 bytes
The local inference costs 15 mA for 2 seconds, or 30 mA-s. Dividing by the per-byte radio charge gives:
3. Setup overhead moves the decision boundary downward
If the link spends 8 mA-s before payload transfer, only 22 mA-s remains for bytes at the break-even point:
| Review item | Arithmetic shown | Decision signal |
| 2 KB feature vector | 2048 x 0.00096 = 1.97 mA-s | Offload can beat the 30 mA-s local run before fixed overheads dominate. |
| 80 KB raw input | 81920 x 0.00096 = 78.64 mA-s | Compute locally because radio charge alone is already more than 2.6x the local compute charge. |
| Cellular tail example | 25 + (120 x 0.4) + (40 x 8) = 393 mA-s | Setup and tail flip the payload-only estimate against offloading when local compute is 90 mA-s. |
What the audit buys you: a placement decision that survives a battery review. Payload size, throughput, and radio state timing are separate measured terms; round only after the comparison is complete.
Every number above is taken from this chapter's own worked example and re-derived step by step.