Constrained Protocols
MQTT, CoAP and their kin, chosen for power, packet size and intermittent links.
5 to work through
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beginner Multiple choice
A metered NB-IoT fleet must not record a reading twice, because readings drive a customer's bill. The team proposes QoS 2 so the broker delivers each publish exactly once. Which choice fits better?
2 min answer -
intermediate Multiple choice
A battery-powered sensor on a cellular network holds an MQTT session. After quiet periods the server's messages stop arriving, though the device's socket is still open and sending works. Which change fixes it at the lowest energy cost?
2 min answer -
intermediate
A soil-moisture sensor runs on two AA cells, about 2,000 mAh usable. It wakes every 15 minutes, sends roughly 60 bytes, and sleeps. Sleep draw is about 10 uA. Each transmission cycle takes roughly 2 seconds at an average 30 mA while the radio is active. Estimate the battery life, and say which assumption you would attack first.
3 min answer -
intermediate
Devices are battery-powered with intermittent low-bandwidth connectivity. What protocol properties matter, and what is usually chosen wrongly?
1 min answer -
advanced
An MQTT 5 broker cluster serving 120,000 sensors starts alerting on disk at 03:00 every night, and the oldest of those alerts is three weeks old. Publish rate is flat at roughly 900 messages per second, connected clients sit at 118,000, and the broker reports 340,000 sessions and rising. No messages are being dropped yet. What failed, and which design decision made it possible?
3 min answer
4 terms in this topic
Backhaul Cost per Device-Day
The bytes a single device sends and receives in a day multiplied by the price of the link - the figure that converts a sampling decision into a line …
protocolConstrained Protocol
Messaging protocols designed for devices and networks where power, bandwidth and packet size are hard limits rather than considerations.
conceptMessage Overhead Budget
The proportion of each transmission spent on protocol rather than payload, which on a metered or battery-powered link determines the running cost.
metricRadio Wake Budget
The number of radio wakes a device can afford per day at its target battery life - the planning number that decides protocol and batching choices, be…
Neighbouring topics
Edge, Mobile & IoT
General material on architecture beyond the data centre boundary.
Mobile App Architecture
Layering, navigation, background execution, and the platform rules you do not set.
Offline-First
Treating connectivity as an optimisation, with a local store as the source of truth.
Sync & Conflict Resolution
Two devices that both changed the same record while neither could see the other.
CRDTs
Data types that converge without coordination, and the semantics you must accept.
Mobile Release Strategy
Store review, staged rollout, and supporting versions you can never force off.
Push & Background Work
Delivery that is best-effort, and an operating system that will kill your process.
Device Identity
Identifying a thing rather than a person, and rotating a credential you cannot type.
Edge Compute Topologies
Regional, metro, on-premises and on-device, and what each tier is genuinely for.
Edge Functions
Short-lived compute at the CDN, its runtime limits, and what must stay at origin.
Edge Data Consistency
Replicated read state at hundreds of locations, and writes that still go to one.
IoT Ingest Architecture
Millions of small, unreliable, frequently duplicated messages arriving continuously.
Device Provisioning
Getting identity and configuration onto hardware at manufacture or first boot.
Fleet Management
Inventory, health, configuration and grouping across devices you will never see.
OTA Updates
Updating firmware over a flaky link, with rollback, and without bricking the device.
Device Telemetry at Scale
Deciding what a device sends, how often, and what is aggregated before it leaves.
Digital Twin
A server-side model of a physical thing's reported and desired state.
Edge Security & Attestation
Secure boot, hardware roots of trust, and proving what is running on a device.
Physical-World Failure Modes
Power loss, tampering, clock drift, thermal limits, and a truck through the fibre.