DDS_DataReaderProtocolQosPolicy Struct Reference

Along with DDS_WireProtocolQosPolicy and DDS_DataWriterProtocolQosPolicy, this QoS policy configures the DDS on-the-network protocol (RTPS). More...

Data Fields
struct DDS_GUID_t	virtual_guid
	The virtual GUID (Global Unique Identifier).
DDS_UnsignedLong	rtps_object_id
	The RTPS Object ID.
DDS_Boolean	expects_inline_qos
	Specifies whether this DataReader expects inline QoS with every sample.
DDS_Boolean	disable_positive_acks
	Whether the reader sends positive acknowledgements to writers.
DDS_Boolean	propagate_dispose_of_unregistered_instances
	Indicates whether or not an instance can move to the DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE state without being in the DDS_ALIVE_INSTANCE_STATE state.
struct DDS_RtpsReliableReaderProtocol_t	rtps_reliable_reader
	The reliable protocol defined in RTPS.

Detailed Description

Along with DDS_WireProtocolQosPolicy and DDS_DataWriterProtocolQosPolicy, this QoS policy configures the DDS on-the-network protocol (RTPS).

DDS has a standard protocol for packet (user and meta data) exchange between applications using DDS for communications. This QoS policy and DDS_DataReaderProtocolQosPolicy give you control over configurable portions of the protocol, including the configuration of the reliable data delivery mechanism of the protocol on a per DataWriter or DataReader basis.

These configuration parameters control timing, timeouts, and give you the ability to tradeoff between speed of data loss detection and repair versus network and CPU bandwidth used to maintain reliability.

It is important to tune the reliability protocol (on a per DDS_DataWriter and DDS_DataReader basis) to meet the requirements of the end-user application so that data can be sent between DataWriters and DataReaders in an efficient and optimal manner in the presence of data loss.

You can also use this QoS policy to control how RTI Connext responds to "slow" reliable DataReaders or ones that disconnect or are otherwise lost. See DDS_ReliabilityQosPolicy for more information on the per-DataReader/DataWriter reliability configuration. DDS_HistoryQosPolicy and DDS_ResourceLimitsQosPolicy also play an important role in the DDS reliable protocol.

This QoS policy is an extension to the DDS standard.

Entity:

DDS_DataReader

Properties:

RxO = N/A
Changeable = NO

Field Documentation

struct DDS_GUID_t DDS_DataReaderProtocolQosPolicy::virtual_guid

The virtual GUID (Global Unique Identifier).

The virtual GUID is used to uniquely identify different incarnations of the same DDS_DataReader.

The association between a DDS_DataReader and its persisted state is done using the virtual GUID.

[default] DDS_GUID_AUTO

DDS_UnsignedLong DDS_DataReaderProtocolQosPolicy::rtps_object_id

The RTPS Object ID.

This value is used to determine the RTPS object ID of a data reader according to the DDS-RTPS Interoperability Wire Protocol.

Only the last 3 bytes are used; the most significant byte is ignored.

If the default value is specified, RTI Connext will automatically assign the object ID based on a counter value (per participant) starting at 0x00800000. That value is incremented for each new data reader.

A rtps_object_id value in the interval [0x00800000,0x00ffffff] may collide with the automatic values assigned by RTI Connext. In those cases, the recomendation is not to use automatic object ID assigment.

[default] DDS_RTPS_AUTO_ID

[range] [0,0x00ffffff]

DDS_Boolean DDS_DataReaderProtocolQosPolicy::expects_inline_qos

Specifies whether this DataReader expects inline QoS with every sample.

In RTI Connext, a DDS_DataReader nominally relies on Discovery to propagate QoS on a matched DDS_DataWriter. Alternatively, a DDS_DataReader may get information on a matched DDS_DataWriter through QoS sent inline with a sample.

Asserting DDS_DataReaderProtocolQosPolicy::expects_inline_qos indicates to a matching DDS_DataWriter that this DDS_DataReader expects to receive inline QoS with every sample. The complete set of inline QoS that a DDS_DataWriter may send inline is specified by the Real-Time Publish-Subscribe (RTPS) Wire Interoperability Protocol.

Because RTI Connext DDS_DataWriter and DDS_DataReader cache Discovery information, inline QoS are largely redundant and thus unecessary. Only for other stateless implementations whose DDS_DataReader does not cache Discovery information is inline QoS necessary.

Also note that inline QoS are additional wire-payload that consume additional bandwidth and serialization and deserialization time.

[default] DDS_BOOLEAN_FALSE

DDS_Boolean DDS_DataReaderProtocolQosPolicy::disable_positive_acks

Whether the reader sends positive acknowledgements to writers.

If set to DDS_BOOLEAN_TRUE, the reader does not send positive acknowledgments (ACKs) in response to Heartbeat messages. The reader will send negative acknowledgements (NACKs) when a Heartbeat advertises samples that it has not received.

Otherwise, if set to DDS_BOOLEAN_FALSE (the default), the reader will send ACKs to writers that expect ACKs (DDS_DataWriterProtocolQosPolicy::disable_positive_acks = DDS_BOOLEAN_FALSE) and it will not send ACKs to writers that disable ACKs (DDS_DataWriterProtocolQosPolicy::disable_positive_acks = DDS_BOOLEAN_TRUE)

[default] DDS_BOOLEAN_FALSE

DDS_Boolean DDS_DataReaderProtocolQosPolicy::propagate_dispose_of_unregistered_instances

Indicates whether or not an instance can move to the DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE state without being in the DDS_ALIVE_INSTANCE_STATE state.

This field only applies to keyed readers.

When the field is set to DDS_BOOLEAN_TRUE, the DataReader will receive dispose notifications even if the instance is not alive.

To guarantee the key availability through the usage of the API FooDataReader_get_key_value, this option should be used in combination DDS_DataWriterProtocolQosPolicy::serialize_key_with_dispose on the DataWriter that should be set to DDS_BOOLEAN_TRUE.

[default] DDS_BOOLEAN_FALSE

struct DDS_RtpsReliableReaderProtocol_t DDS_DataReaderProtocolQosPolicy::rtps_reliable_reader

The reliable protocol defined in RTPS.

[default] min_heartbeat_response_delay 0 seconds; max_heartbeat_response_delay 0.5 seconds