QoS Policies
[Infrastructure Module]

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


 Attaches a buffer of opaque data that is distributed by means of Built-in Topics during discovery.
 Attaches a buffer of opaque data that is distributed by means of Built-in Topics during discovery.
 Attaches a buffer of opaque data that is distributed by means of Built-in Topics during discovery.
 This QoS policy specifies whether or not RTI Data Distribution Service will store and deliver previously published data samples to new DDS_DataReader entities that join the network later.
 Specifies how the samples representing changes to data instances are presented to a subscribing application.
 Expresses the maximum duration (deadline) within which an instance is expected to be updated.
 Provides a hint as to the maximum acceptable delay from the time the data is written to the time it is received by the subscribing applications.
 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).
 Specifies and configures the mechanism that allows DDS_DataReader entities to detect when DDS_DataWriter entities become disconnected or "dead.".
 Filter that allows a DDS_DataReader to specify that it is interested only in (potentially) a subset of the values of the data.
 Set of strings that introduces a logical partition among the topics visible by a DDS_Publisher and a DDS_Subscriber.
 Indicates the level of reliability offered/requested by RTI Data Distribution Service.
 Controls the criteria used to determine the logical order among changes made by DDS_Publisher entities to the same instance of data (i.e., matching DDS_Topic and key).
 Specifies the behavior of RTI Data Distribution Service 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.
 Various settings to configure the external RTI Persistence Service used by RTI Data Distribution Service for DataWriters with a DDS_DurabilityQosPolicy setting of DDS_PERSISTENT_DURABILITY_QOS or DDS_TRANSIENT_DURABILITY_QOS.
 Controls the amount of physical memory allocated for DDS entities, if dynamic allocations are allowed, and how they occur. Also controls memory usage among different instance values for keyed topics.
 This QoS policy allows the application to take advantage of transports that are capable of sending messages with different priorities.
 Specifies how long the data written by the DDS_DataWriter is considered valid.
 Controls how a DataWriter handles the lifecycle of the instances (keys) that it is registered to manage.
 Controls how a DataReader manages the lifecycle of the data that it has received.
 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 physical transports a DDS_DataWriter or DDS_DataReader may use to send or receive data.
 <<eXtension>> Specifies a subset of transports and a port number that can be used by an Entity to receive data.
 <<eXtension>> Specifies the multicast address on which a DDS_DataReader wants to receive its data. It can also specify a port number, as well as a subset of the available (at the DDS_DomainParticipant level) transports with which to receive the multicast data.
 <<eXtension>> Specifies a list of topic expressions and addresses that can be used by an Entity with a specific topic name to receive data.
 <<eXtension>> Specifies the attributes required to discover participants in the domain.
 <<eXtension>> Specifies which built-in transports are used.
 <<eXtension>> Specifies the wire protocol related attributes for the DDS_DomainParticipant.
 <<eXtension>> Various settings that configure how DataReaders allocate and use physical memory for internal resources.
 <<eXtension>> Various settings that configure how a DDS_DataWriter allocates and uses physical memory for internal resources.
 <<eXtension>> Specifies the DataReader-specific protocol QoS.
 <<eXtension>> Along with DDS_WireProtocolQosPolicy and DDS_DataReaderProtocolQosPolicy, this QoS policy configures the DDS on-the-network protocol (RTPS).
 <<eXtension>> Configures DomainParticipant-independent resources used by RTI Data Distribution Service.
 <<eXtension>> Various settings that configure how a DDS_DomainParticipant allocates and uses physical memory for internal resources, including the maximum sizes of various properties.
 <<eXtension>> Configures the internal thread in a DomainParticipant that handles timed events.
 <<eXtension>> Various threads and resource limits settings used by RTI Data Distribution Service to control its internal database.
 <<eXtension>> Configures threads used by RTI Data Distribution Service to receive and process data from transports (for example, UDP sockets).
 <<eXtension>> Specifies how RTI Data Distribution Service sends application data on the network. This QoS policy can be used to tell RTI Data Distribution Service to use its own thread to send data, instead of the user thread.
 <<eXtension>> Specifies the discovery configuration QoS.
 <<eXtension>> Allows you to attach application-specific values to a DataWriter or DataReader that are passed to the serialization or deserialization routine of the associated data type.
 <<eXtension>> Specifies the asynchronous publishing settings of the DDS_Publisher instances.
 <<eXtension>> Configures multi-thread concurrency and deadlock prevention capabilities.
 <<eXtension>> Batch QoS policy used to enable batching in DDS_DataWriter instances.
 <<eXtension>> The QoS policy used to report the configuration of a MultiChannel DataWriter as part of DDS_PublicationBuiltinTopicData.
 <<eXtension>> Configures the ability of a DataWriter to send data on different multicast groups (addresses) based on the value of the data.
 <<eXtension>> Stores name/value (string) pairs that can be used to configure certain parameters of RTI Data Distribution Service that are not exposed through formal QoS policies. Can also be used to store and propagate application-specific name/value pairs that can be retrieved by user code during discovery.
 Configures the availability of data.
 <<eXtension>> Assigns a name to a DDS_DomainParticipant. This name will be visible during the discovery process and in RTI tools to help you visualize and debug your system.
 <<eXtension>> Configures the way that XML documents containing QoS profiles are loaded by RTI Data Distribution Service.
 <<eXtension>> Configures the RTI Data Distribution Service logging facility.

Data Structures

struct  DDS_QosPolicyCount
 Type to hold a counter for a DDS_QosPolicyId_t. More...
struct  DDS_QosPolicyCountSeq
 Declares IDL sequence < DDS_QosPolicyCount >. More...


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).


Supported 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.

QosPolicies can also be configured from XML resources (files, strings). With this approach, you can change the QoS without recompiling the application. For more information, see Configuring QoS Profiles with XML.

To customize a DDS_Entity's QoS before creating the entity, the correct pattern is:

Each QosPolicy is treated independently from the others. This approach has the advantage of being very extensible. However, there may be cases where several policies are in conflict. Consistency checking is performed each time the policies are modified via the set_qos (abstract) operation, or when the DDS_Entity is created.

When a policy is changed after being set to a given value, it is not required that the new value be applied instantaneously; RTI Data Distribution Service is allowed to apply it after a transition phase. In addition, some QosPolicy have immutable semantics, meaning that they can only be specified either at DDS_Entity creation time or else prior to calling the DDS_Entity_enable operation on the entity.

Each DDS_Entity can be configured with a list of QosPolicy objects. However, not all QosPolicies are supported by each DDS_Entity. For instance, a DDS_DomainParticipant supports a different set of QosPolicies than a DDS_Topic or a DDS_Publisher.

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 Data Distribution Service 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 Data Distribution Service 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 or a DDS_Condition.

The following properties are defined on a QosPolicy.

Enumeration Type Documentation

Type to identify QosPolicies.

DDS_INVALID_QOS_POLICY_ID  Identifier for an invalid QoS policy.
DDS_USERDATA_QOS_POLICY_ID  Identifier for DDS_UserDataQosPolicy.
DDS_DURABILITY_QOS_POLICY_ID  Identifier for DDS_DurabilityQosPolicy.
DDS_PRESENTATION_QOS_POLICY_ID  Identifier for DDS_PresentationQosPolicy.
DDS_DEADLINE_QOS_POLICY_ID  Identifier for DDS_DeadlineQosPolicy.
DDS_LATENCYBUDGET_QOS_POLICY_ID  Identifier for DDS_LatencyBudgetQosPolicy.
DDS_OWNERSHIP_QOS_POLICY_ID  Identifier for DDS_OwnershipQosPolicy.
DDS_OWNERSHIPSTRENGTH_QOS_POLICY_ID  Identifier for DDS_OwnershipStrengthQosPolicy.
DDS_LIVELINESS_QOS_POLICY_ID  Identifier for DDS_LivelinessQosPolicy.
DDS_TIMEBASEDFILTER_QOS_POLICY_ID  Identifier for DDS_TimeBasedFilterQosPolicy.
DDS_PARTITION_QOS_POLICY_ID  Identifier for DDS_PartitionQosPolicy.
DDS_RELIABILITY_QOS_POLICY_ID  Identifier for DDS_ReliabilityQosPolicy.
DDS_DESTINATIONORDER_QOS_POLICY_ID  Identifier for DDS_DestinationOrderQosPolicy.
DDS_HISTORY_QOS_POLICY_ID  Identifier for DDS_HistoryQosPolicy.
DDS_RESOURCELIMITS_QOS_POLICY_ID  Identifier for DDS_ResourceLimitsQosPolicy.
DDS_ENTITYFACTORY_QOS_POLICY_ID  Identifier for DDS_EntityFactoryQosPolicy.
DDS_WRITERDATALIFECYCLE_QOS_POLICY_ID  Identifier for DDS_WriterDataLifecycleQosPolicy.
DDS_READERDATALIFECYCLE_QOS_POLICY_ID  Identifier for DDS_ReaderDataLifecycleQosPolicy.
DDS_TOPICDATA_QOS_POLICY_ID  Identifier for DDS_TopicDataQosPolicy.
DDS_GROUPDATA_QOS_POLICY_ID  Identifier for DDS_GroupDataQosPolicy.
DDS_TRANSPORTPRIORITY_QOS_POLICY_ID  Identifier for DDS_TransportPriorityQosPolicy.
DDS_LIFESPAN_QOS_POLICY_ID  Identifier for DDS_LifespanQosPolicy.
DDS_DURABILITYSERVICE_QOS_POLICY_ID  Identifier for DDS_DurabilityServiceQosPolicy.
DDS_WIREPROTOCOL_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_WireProtocolQosPolicy
DDS_DISCOVERY_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DiscoveryQosPolicy
DDS_DATAREADERRESOURCELIMITS_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DataReaderResourceLimitsQosPolicy
DDS_DATAWRITERRESOURCELIMITS_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DataWriterResourceLimitsQosPolicy
DDS_DATAREADERPROTOCOL_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DataReaderProtocolQosPolicy
DDS_DATAWRITERPROTOCOL_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DataWriterProtocolQosPolicy
DDS_DOMAINPARTICIPANTRESOURCELIMITS_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DomainParticipantResourceLimitsQosPolicy
DDS_EVENT_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_EventQosPolicy
DDS_DATABASE_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DatabaseQosPolicy
DDS_RECEIVERPOOL_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_ReceiverPoolQosPolicy
DDS_DISCOVERYCONFIG_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_DiscoveryConfigQosPolicy
DDS_EXCLUSIVEAREA_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_ExclusiveAreaQosPolicy
DDS_SYSTEMRESOURCELIMITS_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_SystemResourceLimitsQosPolicy
DDS_TRANSPORTSELECTION_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_TransportSelectionQosPolicy
DDS_TRANSPORTUNICAST_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_TransportUnicastQosPolicy
DDS_TRANSPORTBUILTIN_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_TransportBuiltinQosPolicy
DDS_TYPESUPPORT_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_TypeSupportQosPolicy
DDS_PROPERTY_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_PropertyQosPolicy
DDS_PUBLISHMODE_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_PublishModeQosPolicy
DDS_ASYNCHRONOUSPUBLISHER_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_AsynchronousPublisherQosPolicy
DDS_ENTITYNAME_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_EntityNameQosPolicy
DDS_BATCH_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_BatchQosPolicy
DDS_PROFILE_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_ProfileQosPolicy
DDS_LOCATORFILTER_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_LocatorFilterQosPolicy
DDS_MULTICHANNEL_QOS_POLICY_ID  <<eXtension>> Identifier for DDS_MultiChannelQosPolicy
DDS_AVAILABILITY_QOS_POLICY_ID  Identifier for DDS_AvailabilityQosPolicy.

RTI Data Distribution Service C API Version 4.5e Copyright © 23 Oct 2011 Real-Time Innovations, Inc