10x Smaller Headers, Only ~8% Less Bandwidth

Ada re-derives this chapter’s own numbers step by step, at full precision

ADA · CALCULATION AUDIT

10x Smaller Headers, Only ~8% Less Bandwidth

Misconception 4 pits two numbers against each other: AMQP’s header runs up to 10x larger than MQTT’s, yet over 10,000 messages of 200-byte payload MQTT sends only about 8% less data — 2.02 MB against 2.18 MB. Both figures are correct, and reading one as the other is how a team reaches for MQTT on the wrong axis. This audit rebuilds the comparison from the payload up and asks how a header 9x smaller can move the total transfer by barely 7%.

Companion to the chapter AMQP Implementation Pitfalls — every number here comes from that chapter.

Ada: Misconception 4 sets two numbers against each other. The overhead row says AMQP’s header runs up to 10x larger than MQTT’s — 2 bytes versus 8-20 — yet the bandwidth row says MQTT sends only about 8% less data. Both are correct, and reconciling them is the whole lesson. Let me rebuild the comparison from the payload up.

The scenario is 10,000 messages of 200-byte payload. MQTT adds a 2-byte header: 10000 x (200 + 2) = 2,020,000 bytes, about 2.02 MB — matching the table. Take AMQP at the 18-byte overhead its 2.18 MB total implies: 10000 x (200 + 18) = 2,180,000 bytes, 2.18 MB. The header ratio is 18 / 2 = 9x, right beside the quoted 10x.

Now the bandwidth gap. MQTT saves 2,180,000 - 2,020,000 = 160,000 bytes, which against AMQP’s total is 160,000 / 2,180,000 = 0.0734 — about 7%, which the table rounds to 8%. A 9x smaller header shrank the transfer by only ~7%, because the payload is 200 / 218 = 0.917 of every AMQP message: trimming the ~8% that is header can never move the total by more than ~8%.

Design meaning: header overhead only dominates when the payload is tiny, so MQTT’s real advantage lives in the table’s battery, setup-RTT, and memory rows — not in steady bandwidth — and reaching for MQTT “to save bandwidth” on 200-byte telemetry optimises the one axis where the two protocols are all but tied.

Every number above is taken from the chapter’s own material and re-derived step by step.