Best-effort delivery with manual liveliness

Rule 5 · applies to publishers and subscribers · Back to all rules

Breaks a guarantee. Liveliness assertions can be lost, so the reader may report the writer as lost even though it is alive.

If you set Reliability = BEST_EFFORT together with Liveliness = MANUAL_BY_TOPIC

Breaks a guarantee

• Settings involved: Reliability and Liveliness
• What QoS Guard checks: [LIVENS = MANUAL] ∧ [RELIAB = BEST_EFFORT]

Example

A heartbeat publisher asserts liveliness manually over best-effort. Under packet loss the subscriber sees false liveliness-lost events.

How to fix it

Use RELIABLE when liveliness is asserted manually, so the assertions are retransmitted instead of dropped.

Why this rule is flagged

What the DDS specification says

The DDS specification does not settle this case on its own, so the rule rests on direct measurement.

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What the engine source code shows

The behavior here does not depend on a specific engine's implementation, so the rule follows from the measurements.

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What the measurements show

Item	Value
Dataset	Download CSV
Fixed QoS setting	None
Tested variable	RELIAB.kind, LIVENS.kind, LIVENS.lease_duration
Tested values	RELIAB ∈ {BEST_EFFORT, RELIABLE}, LIVENS ∈ {AUTOMATIC, MANUAL_BY_TOPIC}, lease_duration ∈ {150 ms, 300 ms}
Rule-relevant case	RELIAB = BEST_EFFORT, LIVENS = MANUAL_BY_TOPIC
Tested engines / versions	Fast DDS 2.6.11 (Humble), Fast DDS 2.14.6 (Jazzy), Cyclone DDS 0.10.5
Network setting	RTT = 1 ms, loss = 0%, PP = 50 ms, message size = 1024 B

Engine	Tested setting	Observed behavior
Fast DDS 2.6.11 (Humble)	RELIAB = BEST_EFFORT, LIVENS = MANUAL_BY_TOPIC	Profile accepted, matched, and delivered.
Fast DDS 2.14.6 (Jazzy)	RELIAB = BEST_EFFORT, LIVENS = MANUAL_BY_TOPIC	Profile accepted, matched, and delivered; liveliness_lost = 2, reader_not_alive = 2
Cyclone DDS 0.10.5	RELIAB = BEST_EFFORT, LIVENS = MANUAL_BY_TOPIC	Profile creation/matching failed; reader_not_alive = 1