Chapter 42 All QosPolicies

Connext’s behavior is controlled by the Quality of Service (QoS) policies of the data communication Entities (DomainParticipant, Topic, Publisher, Subscriber, DataWriter, and DataReader) used in your applications. This section summarizes each of the QosPolicies that you can set for the various Entities.

The QosPolicy class is the abstract base class for all the QosPolicies. It provides the basic mechanism for an application to specify quality of service parameters. Table 42.1 QosPolicies lists each supported QosPolicy (in alphabetical order), provides a summary, and points to a section in the manual that provides further details.

The detailed description of a QosPolicy that applies to multiple Entities is provided in the first chapter that discusses an Entity whose behavior the QoS affects. Otherwise, the discussion of a QosPolicy can be found in the chapter of the particular Entity to which the policy applies. As you will see in the detailed description sections, all QosPolicies have one or more parameters that are used to configure the policy. The how’s and why’s of tuning the parameters are also discussed in those sections.

As first discussed in Chapter 11 Quality of Service (QoS), QosPolicies may interact with each other, and certain values of QosPolicies can be incompatible with the values set for other policies.

The set_qos() operation will fail if you attempt to specify a set of values that would result in an inconsistent set of policies. To indicate a failure, set_qos() will return INCONSISTENT_POLICY. 42.1 QoS Requested vs. Offered Compatibility—the RxO Property provides further information on QoS compatibility within an Entity as well as across matching Entities, as does the discussion/reference section for each QosPolicy listed in Table 42.1 QosPolicies.

The values of some QosPolicies cannot be changed after the Entity is created or after the Entity is enabled. Others may be changed at any time. The detailed section on each QosPolicy states when each policy can be changed. If you attempt to change a QosPolicy after it becomes immutable (because the associated Entity has been created or enabled, depending on the policy), set_qos() will fail with a return code of IMMUTABLE_POLICY.

Besides the QoS Policies, there are additional properties that you can configure through the 47.19 PROPERTY QosPolicy (DDS Extension) . These are not exposed through the formal QoS policies and are described in the Property Reference Guide.

Table 42.1 QosPolicies
QosPolicy	Summary
Asynchronous- Publisher	Configures the mechanism that sends user data in an external middleware thread. See 46.1 ASYNCHRONOUS_PUBLISHER QosPolicy (DDS Extension).
Availability	This QoS policy is used in the context of two features: For a Collaborative DataWriter, specifies the group of DataWriters expected to collaboratively provide data and the timeouts that control when to allow data to be available that may skip DDS samples. For a Durable Subscription, configures a set of Durable Subscriptions on a DataWriter. See 47.1 AVAILABILITY QosPolicy (DDS Extension).
Batch	Specifies and configures the mechanism that allows Connext to collect multiple DDS data samples to be sent in a single network packet, to take advantage of the efficiency of sending larger packets and thus increase effective throughput. See 47.2 BATCH QosPolicy (DDS Extension).
Database	Various settings and resource limits used by Connext to control its internal database. See 44.1 DATABASE QosPolicy (DDS Extension).
DataReaderProtocol	This QosPolicy configures the Connext on-the-network protocol, RTPS. See 48.1 DATA_READER_PROTOCOL QosPolicy (DDS Extension).
DataReaderResourceLimits	Various settings that configure how DataReaders allocate and use physical memory for internal resources. See 48.2 DATA_READER_RESOURCE_LIMITS QosPolicy (DDS Extension).
DataRepresentation	Specifies which versions of the Extended Common Data Representation (CDR) (version 1 or version 2) and which data compression setting algorithms are offered and requested for your data. See 47.3 DATA_REPRESENTATION QosPolicy.
DataTag	This QosPolicy can be used to associate a set of tags in the form of (name, value) pairs with a DataReader or DataWriter. The Access Control plugin may use these tags to determine publish and subscribe permissions. See 47.4 DATATAG QosPolicy.
DataWriterProtocol	This QosPolicy configures the Connext on-the-network protocol, RTPS. See 47.5 DATA_WRITER_PROTOCOL QosPolicy (DDS Extension).
DataWriterResourceLimits	Controls how many threads can concurrently block on a write() call of this DataWriter. Also controls the number of batches managed by the DataWriter and the instance-replacement kind used by the DataWriter. See 47.6 DATA_WRITER_RESOURCE_LIMITS QosPolicy (DDS Extension).
Deadline	For a DataReader, specifies the maximum expected elapsed time between arriving DDS data samples. For a DataWriter, specifies a commitment to publish DDS samples with no greater elapsed time between them. See 47.7 DEADLINE QosPolicy.
DestinationOrder	Controls how Connext will deal with data sent by multiple DataWriters for the same topic. Can be set to "by reception timestamp" or to "by source timestamp." See 47.8 DESTINATION_ORDER QosPolicy.
Discovery	Configures the mechanism used by Connext to automatically discover and connect with new remote applications. See 44.2 DISCOVERY QosPolicy (DDS Extension).
DiscoveryConfig	Controls the amount of delay in discovering Entities in the system and the amount of discovery traffic in the network. See 44.3 DISCOVERY_CONFIG QosPolicy (DDS Extension).
DomainParticipantResource-Limits	Various settings that configure how DomainParticipants allocate and use physical memory for internal resources, including the maximum sizes of various properties. See 44.4 DOMAIN_PARTICIPANT_RESOURCE_LIMITS QosPolicy (DDS Extension).
Durability	Specifies whether or not Connext will store and deliver data that were previously published to new DataReaders. See 47.9 DURABILITY QosPolicy.
DurabilityService	Various settings to configure the external Persistence Service used by Connext for DataWriters with a Durability QoS setting of Persistent Durability. See 47.10 DURABILITY SERVICE QosPolicy.
EntityFactory	Controls whether or not child Entities are created in the enabled state. See 46.2 ENTITYFACTORY QosPolicy.
EntityName	Assigns a name and role_name to an Entity. See 47.11 ENTITY_NAME QosPolicy (DDS Extension).
Event	Configures the DomainParticipant’s internal thread that handles timed events. See 44.5 EVENT QosPolicy (DDS Extension).
GroupData	Along with 45.1 TOPIC_DATA QosPolicy and 47.30 USER_DATA QosPolicy, this QosPolicy is used to attach a buffer of bytes to Connext's discovery meta-data. See 46.3 GROUP_DATA QosPolicy.
History	Specifies how much data must be stored by Connext for the DataWriter or DataReader. This QosPolicy affects the 47.21 RELIABILITY QosPolicy as well as the 47.9 DURABILITY QosPolicy. See 47.12 HISTORY QosPolicy.
LatencyBudget	Suggestion to Connext on how much time is allowed to deliver data. See 47.13 LATENCYBUDGET QoS Policy.
Lifespan	Specifies how long Connext should consider data sent by an user application to be valid. See 47.14 LIFESPAN QoS Policy.
Liveliness	Specifies and configures the mechanism that allows DataReaders to detect when DataWriters become disconnected or "dead." See 47.15 LIVELINESS QosPolicy.
Logging	Configures the properties associated with Connext logging. See 43.1 LOGGING QosPolicy (DDS Extension).
Monitoring	Configures RTI Monitoring Library 2.0 to collect and distribute telemetry data (metrics and logs) associated with a Connext application, for use by the RTI Observability Framework. See 43.4 MONITORING QosPolicy (DDS Extension).
MultiChannel	Configures a DataWriter’s ability to send data on different multicast groups (addresses) based on the value of the data. See 47.16 MULTI_CHANNEL QosPolicy (DDS Extension).
Ownership	Along with Ownership Strength, specifies if DataReaders for a topic can receive data from multiple DataWriters at the same time. See 47.17 OWNERSHIP QosPolicy.
OwnershipStrength	Used to arbitrate among multiple DataWriters of the same instance of a Topic when Ownership QoSPolicy is EXLUSIVE. See 47.18 OWNERSHIP_STRENGTH QosPolicy.
Partition	Adds string identifiers that are used for matching DataReaders and DataWriters for the same Topic or for matching DomainParticipants with the same domain ID and domain tag. See 44.6 PARTITION QosPolicy.
Presentation	Controls how Connext presents data received by an application to the DataReaders of the data. See 46.4 PRESENTATION QosPolicy.
Profile	Configures the way that XML documents containing QoS profiles are loaded by RTI. See 43.2 PROFILE QosPolicy (DDS Extension) .
Property	Stores name/value(string) pairs that can be used to configure certain parameters of Connext that are not exposed through formal QoS policies. It can also be used to store and propagate application-specific name/value pairs, which can be retrieved by user code during discovery. See 47.19 PROPERTY QosPolicy (DDS Extension) .
PublishMode	Specifies how Connext sends application data on the network. By default, data is sent in the user thread that calls the DataWriter’s write() operation. However, this QosPolicy can be used to tell Connext to use its own thread to send the data. See 47.20 PUBLISH_MODE QosPolicy (DDS Extension).
ReaderDataLifeCycle	Controls how a DataReader manages the lifecycle of the data that it has received. See 48.3 READER_DATA_LIFECYCLE QoS Policy.
ReceiverPool	Configures threads used by Connext to receive and process data from transports (for example, UDP sockets). See 44.7 RECEIVER_POOL QosPolicy (DDS Extension).
Reliability	Specifies whether or not Connext will deliver data reliably. See 47.21 RELIABILITY QosPolicy.
ResourceLimits	Controls the amount of physical memory allocated for Entities, if dynamic allocations are allowed, and how they occur. Also controls memory usage among different instance values for keyed topics. See 47.22 RESOURCE_LIMITS QosPolicy.
Service	Intended for use by RTI infrastructure services. User applications should not modify its value. See 47.23 SERVICE QosPolicy (DDS Extension).
SystemResourceLimits	Configures DomainParticipant-independent resources used by Connext. Mainly used to change the maximum number of DomainParticipants that can be created within a single process (address space). See 43.3 SYSTEM_RESOURCE_LIMITS QoS Policy (DDS Extension).
TimeBasedFilter	Set by a DataReader to limit the number of new data values received over a period of time. See 48.4 TIME_BASED_FILTER QosPolicy.
TopicData	Along with Group Data QosPolicy and User Data QosPolicy, used to attach a buffer of bytes to Connext's discovery meta-data. See 45.1 TOPIC_DATA QosPolicy.
TopicQueryDispatch	Configures the ability of a DataWriter to publish historical samples in response to a TopicQuery. See 47.24 TOPIC_QUERY_DISPATCH_QosPolicy (DDS Extension).
TransferMode	Configures the properties of a Zero Copy DataWriter. See 47.25 TRANSFER_MODE QosPolicy.
TransportBuiltin	Specifies which built-in transport plugins are used. See 44.8 TRANSPORT_BUILTIN QosPolicy (DDS Extension).
TransportMulticast	Specifies the multicast address on which a DataReader wants to receive its data. Can specify a port number as well as a subset of the available transports with which to receive the multicast data. See 48.5 TRANSPORT_MULTICAST QosPolicy (DDS Extension).
TransportMulticastMapping	Specifies the automatic mapping between a list of topic expressions and multicast address that can be used by a DataReader to receive data for a specific topic. See 44.9 TRANSPORT_MULTICAST_MAPPING QosPolicy (DDS Extension).
TransportPriority	Set by a DataWriter or DataReader to tell Connext that the data being sent is a different "priority" than other data. See 47.26 TRANSPORT_PRIORITY QosPolicy.
TransportSelection	Allows you to select which physical transports a DataWriter or DataReader may use to send or receive its data. See 47.27 TRANSPORT_SELECTION QosPolicy (DDS Extension).
TransportUnicast	Specifies a subset of transports and port number that can be used by an Entity to receive data. See 47.28 TRANSPORT_UNICAST QosPolicy (DDS Extension).
TypeConsistencyEnforcement	Defines rules that determine whether the type used to publish a given data stream is consistent with that used to subscribe to it. See 48.6 TYPE_CONSISTENCY_ENFORCEMENT QosPolicy.
TypeSupport	Used to attach application-specific value(s) to a DataWriter or DataReader. These values are passed to the serialization or deserialization routine of the associated data type. Also controls whether padding bytes are set to 0 during serialization. See 47.29 TYPESUPPORT QosPolicy (DDS Extension).
UserData	Along with Topic Data QosPolicy and Group Data QosPolicy, used to attach a buffer of bytes to Connext's discovery meta-data. See 47.30 USER_DATA QosPolicy.
WireProtocol	Specifies IDs used by the RTPS wire protocol to create globally unique identifiers. See 44.10 WIRE_PROTOCOL QosPolicy (DDS Extension).
WriterDataLifeCycle	Controls how a DataWriter handles the lifecycle of the instances (keys) that the DataWriter is registered to manage. See 47.31 WRITER_DATA_LIFECYCLE QoS Policy.