Publisher's liveliness is weaker than the subscriber requires

Rule 25 · applies to publisher and subscriber matching · Back to all rules

Won't connect. A weaker offered liveliness kind, or a longer offered lease, is incompatible with the request.

If you set a Reader that requests a strong liveliness kind or short lease together with a Writer that offers a weaker kind or a longer lease

Won't connect

• Settings involved: Liveliness and Liveliness
• What QoS Guard checks: [W.LIVENS < R.LIVENS] ∨ [W.lease > R.lease]

Example

The reader asks for MANUAL_BY_TOPIC with a 1 s lease, the writer offers AUTOMATIC with 2 s. They never match.

How to fix it

Offer a liveliness kind at least as strong, and a lease no longer than, what the reader requests.

Why this rule is flagged

What the DDS specification says

OMG DDS §	QoS policy	Standard statement
§2.2.3.11	LIVELINESS kind	The inequality "offered kind >= requested kind" evaluates to 'TRUE.' For the purposes of this inequality, the values of LIVELINESS kind are considered ordered such that AUTOMATIC < MANUAL_BY_PARTICIPANT < MANUAL_BY_TOPIC.
§2.2.3.11	LIVELINESS lease_duration	The inequality "offered lease_duration <= requested lease_duration" evaluates to TRUE.

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What the engine source code shows

Both engines reject endpoint matching when the writer offers a lower liveliness kind or a longer lease duration than the reader requests.

Fast DDS implementation evidence

// EDP::valid_matching: liveliness kind and lease duration are both checked.
if (wdata->m_qos.m_liveliness.lease_duration >
        rdata->m_qos.m_liveliness.lease_duration)
{
    incompatible_qos.set(fastdds::dds::LIVELINESS_QOS_POLICY_ID);
}
if (wdata->m_qos.m_liveliness.kind < rdata->m_qos.m_liveliness.kind)
{
    incompatible_qos.set(fastdds::dds::LIVELINESS_QOS_POLICY_ID);
}

Cyclone DDS implementation evidence

// q_qosmatch.c: writer liveliness kind and lease must satisfy reader request.
if ((mask & QP_LIVELINESS) &&
        rd_qos->liveliness.kind > wr_qos->liveliness.kind)
{
    *reason = DDS_LIVELINESS_QOS_POLICY_ID;
    return false;
}
if ((mask & QP_LIVELINESS) &&
        rd_qos->liveliness.lease_duration < wr_qos->liveliness.lease_duration)
{
    *reason = DDS_LIVELINESS_QOS_POLICY_ID;
    return false;
}

Item	Value
Dataset	Download CSV
Fixed QoS setting	None
Tested variable	writer_liveliness, reader_liveliness
Tested values	writer_liveliness ∈ {AUTOMATIC, MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC}, reader_liveliness ∈ {AUTOMATIC, MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC}
Valid / boundary cases	writer_liveliness >= reader_liveliness, including AUTOMATIC ≥ AUTOMATIC, MANUAL_BY_PARTICIPANT ≥ AUTOMATIC, MANUAL_BY_PARTICIPANT ≥ MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC ≥ AUTOMATIC, MANUAL_BY_TOPIC ≥ MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC ≥ MANUAL_BY_TOPIC
Violating cases	writer_liveliness < reader_liveliness, including AUTOMATIC < MANUAL_BY_PARTICIPANT, AUTOMATIC < MANUAL_BY_TOPIC, MANUAL_BY_PARTICIPANT < 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)	writer_liveliness, reader_liveliness ∈ {AUTOMATIC, MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC}	Matched when writer_liveliness >= reader_liveliness; match rejected when writer_liveliness < reader_liveliness
Fast DDS 2.14.6 (Jazzy)	writer_liveliness, reader_liveliness ∈ {AUTOMATIC, MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC}	Matched when writer_liveliness >= reader_liveliness; match rejected when writer_liveliness < reader_liveliness
Cyclone DDS 0.10.5	writer_liveliness, reader_liveliness ∈ {AUTOMATIC, MANUAL_BY_PARTICIPANT, MANUAL_BY_TOPIC}	Matched when writer_liveliness >= reader_liveliness; match rejected when writer_liveliness < reader_liveliness

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What you'll see when you run it

QoS Guard reports this mismatch as a structural conflict:

[STRUCTURAL] [hb_pub] Writer.LIVENS.kind <-> Reader.LIVENS.kind (Writer<Reader)

At runtime the two endpoints never connect. DDS matches a publisher and subscriber only when the offered QoS satisfies the requested QoS (the Requested-Offered, or RxO, rule). Here the reader requests the stronger MANUAL_BY_TOPIC kind while the writer offers only AUTOMATIC, so the offered liveliness is weaker than requested and discovery refuses the match. No connection forms and no samples flow, with no error printed.