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QoS Policies

Quality of Service (QoS) policies. More...


 <<eXtension>> Specifies the attributes required to discover participants in the domain.
 Expresses the maximum duration (deadline) within which an instance is expected to be updated.
 Specifies whether it is allowed for multiple DDS_DataWriter (s) to write the same instance of the data and if so, how these modifications should be arbitrated.
 Specifies the value of the strength used to arbitrate among multiple DDS_DataWriter objects that attempt to modify the same instance of a data type (identified by DDS_Topic + key).
 Determines the mechanism and parameters used by the application to determine whether a DDS_Entity is alive.
 Indicates the level of reliability offered/requested by RTI Connext Micro.
 Specifies the behavior of RTI Connext Micro in the case where the value of an instance changes (one or more times) before it can be successfully communicated to one or more existing subscribers.
 <<eXtension>> Specifies the Durability properties used by a DDS_DataWriter and/or DDS_DataReader.
 Specifies the resources that RTI Connext Micro can consume in order to meet the requested QoS.
 <<eXtension>> Specifies the DestinationOrder policy.
 A QoS policy for all DDS_Entity types that can act as factories for one or more other DDS_Entity types.
 Extended Qos Support
 <<eXtension>> Types and defines used in extended QoS policies.
 <<eXtension>> Specifies the system-specific resources that RTI Connext Micro can use.
 <<eXtension>> Specifies the wire protocol related attributes for the DDS_DomainParticipant.
 <<eXtension>> Specifies the DataReader-specific protocol QoS.
 <<eXtension>> Specifies the DataWriter-specific protocol QoS.
 <<eXtension>> <<cert>> Specify transport settings
 <<eXtension>> Specifies the DomainParticipant-specific resources that RTI Connext Micro can use.
 <<eXtension>> Name of the entity.


enum  DDS_QosPolicyId_t {
 Type to identify QosPolicies. More...

Detailed Description

Quality of Service (QoS) policies.

Data Distribution Service (DDS) relies on the use of QoS. A QoS is a set of characteristics that controls some aspect of the behavior of DDS. A QoS is comprised of individual QoS policies (objects conceptually deriving from an abstract QosPolicy class). RTI Connext Micro supports a subset of these QoS.

"DDS QoS policies"

The QosPolicy provides the basic mechanism for an application to specify quality of service parameters. It has an attribute name that is used to uniquely identify each QosPolicy. QosPolicy implementation is comprised of a name, an ID, and a type. The type of a QosPolicy value may be atomic, such as an integer or float, or compound (a structure). Compound types are used whenever multiple parameters must be set coherently to define a consistent value for a QosPolicy. QoS (i.e., a list of QosPolicy objects) may be associated with all DDS_Entity objects in the system such as DDS_Topic, DDS_DataWriter, DDS_DataReader, DDS_Publisher, DDS_Subscriber, and DDS_DomainParticipant.

Specifying QoS on entities

QosPolicies can be set programmatically when an DDS_Entity is created, or modified with the DDS_Entity's set_qos (abstract) function . To customize a DDS_Entity's QoS before creating the entity, the correct pattern is:

QoS compatibility

In several cases, for communications to occur properly (or efficiently), a QosPolicy on the publisher side must be compatible with a corresponding policy on the subscriber side. For example, if a DDS_Subscriber requests to receive data reliably while the corresponding DDS_Publisher defines a best-effort policy, communication will not happen as requested. To address this issue and maintain the desirable decoupling of publication and subscription as much as possible, the QosPolicy specification follows the subscriber-requested, publisher-offered pattern. In this pattern, the subscriber side can specify a "requested" value for a particular QosPolicy. The publisher side specifes an "offered" value for that QosPolicy. RTI Connext Micro will then determine whether the value requested by the subscriber side is compatible with what is offered by the publisher side. If the two policies are compatible, then communication will be established. If the two policies are not compatible, RTI Connext Micro will not establish communications between the two DDS_Entity objects and will record this fact by means of the DDS_OFFERED_INCOMPATIBLE_QOS_STATUS on the publisher end and DDS_REQUESTED_INCOMPATIBLE_QOS_STATUS on the subscriber end. The application can detect this fact by means of a DDS_Listener. The following properties are defined on a QosPolicy.

Enumeration Type Documentation

Type to identify QosPolicies.

Note that the value of these constants disagree with the values of the corresponding parameter IDs in the RTPS protocol. This conflict is unavoidable since these values are given in the DDS specification, which is not tied to RTPS.


Identifier for an invalid QoS policy.


Identifier for DDS_DeadlineQosPolicy.


Identifier for DDS_OwnershipQosPolicy.


Identifier for DDS_OwnershipStrengthQosPolicy.


Identifier for DDS_LivelinessQosPolicy.


Identifier for DDS_ReliabilityQosPolicy.


Identifier for DDS_HistoryQosPolicy.


Identifier for DDS_EntityFactoryQosPolicy.

RTI Connext DDS Micro Version 2.4.10 Copyright © Fri Jun 30 2017 Real-Time Innovations, Inc