DDS_DataWriterProtocolQosPolicy Struct Reference

Protocol that applies only to DDSDataWriter instances. More...

Public Attributes
struct DDS_GUID_t	virtual_guid
	The virtual GUID (Global Unique Identifier).
DDS_UnsignedLong	rtps_object_id
	The RTPS Object ID.
DDS_Boolean	push_on_write
	Whether to push sample out when write is called.
DDS_Boolean	disable_positive_acks
	Controls whether or not the writer expects positive acknowledgements from matching readers.
DDS_Boolean	disable_inline_keyhash
	Controls whether or not a keyhash is propagated on the wire with each sample.
DDS_Boolean	serialize_key_with_dispose
	Controls whether or not the serialized key is propagated on the wire with dispose samples.
DDS_Boolean	propagate_app_ack_with_no_response
	Controls whether or not a DDSDataWriter receives DDSDataWriterListener::on_application_acknowledgment notifications with an empty or invalid response.
struct DDS_RtpsReliableWriterProtocol_t	rtps_reliable_writer
	RTPS protocol-related configuration settings for the RTPS reliable writer associated to a DDSDataWriter. This parameter only has effect if both the writer and the matching reader are configured with DDS_RELIABLE_RELIABILITY_QOS DDS_ReliabilityQosPolicyKind.
struct DDS_SequenceNumber_t	initial_virtual_sequence_number
	Determines, the initial virtual sequence number for this DataWriter.

Detailed Description

Protocol that applies only to DDSDataWriter instances.

DDS has a standard protocol for packet (user and meta data) exchange between applications using DDS for communications. This QoS policy and DDS_DataWriterProtocolQosPolicy 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 DDSDataWriter and DDSDataReader 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:

DDSDataWriter

Properties:

RxO = N/A
Changeable = NO

Member Data Documentation

struct DDS_GUID_t DDS_DataWriterProtocolQosPolicy::virtual_guid

The virtual GUID (Global Unique Identifier).

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

RTI Connext uses the virtual GUID to associate a persisted writer history to a specific DDSDataWriter.

The RTI Connext Persistence Service uses the virtual GUID to send samples on behalf of the original DDSDataWriter.

[default] DDS_GUID_AUTO

DDS_UnsignedLong DDS_DataWriterProtocolQosPolicy::rtps_object_id

The RTPS Object ID.

This value is used to determine the RTPS object ID of a data writer 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 writer.

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_DataWriterProtocolQosPolicy::push_on_write

Whether to push sample out when write is called.

If set to DDS_BOOLEAN_TRUE (the default), the writer will send a sample every time write is called. Otherwise, the sample is put into the queue waiting for a NACK from remote reader(s) to be sent out.

[default] DDS_BOOLEAN_TRUE

DDS_Boolean DDS_DataWriterProtocolQosPolicy::disable_positive_acks

Controls whether or not the writer expects positive acknowledgements from matching readers.

If set to DDS_BOOLEAN_TRUE, the writer does not expect readers to send send positive acknowledgments to the writer. Consequently, instead of keeping a sample queued until all readers have positively acknowledged it, the writer will keep a sample for at least DDS_RtpsReliableWriterProtocol_t::disable_positive_acks_min_sample_keep_duration, after which the sample is logically considered as positively acknowledged.

If set to DDS_BOOLEAN_FALSE (the default), the writer expects to receive positive acknowledgements from its acknowledging readers (DDS_DataReaderProtocolQosPolicy::disable_positive_acks = DDS_BOOLEAN_FALSE) and it applies the keep-duration to its non-acknowledging readers (DDS_DataReaderProtocolQosPolicy::disable_positive_acks = DDS_BOOLEAN_TRUE).

A writer with both acknowledging and non-acknowledging readers keeps a sample queued until acknowledgements have been received from all acknowledging readers and the keep-duration has elapsed for non-acknowledging readers.

[default] DDS_BOOLEAN_FALSE

DDS_Boolean DDS_DataWriterProtocolQosPolicy::disable_inline_keyhash

Controls whether or not a keyhash is propagated on the wire with each sample.

This field only applies to keyed writers.

With each key, RTI Connext associates an internal 16-byte representation, called a keyhash.

When this field is DDS_BOOLEAN_FALSE, the keyhash is sent on the wire with every data instance.

When this field is DDS_BOOLEAN_TRUE, the keyhash is not sent on the wire and the readers must compute the value using the received data.

If the reader is CPU bound, sending the keyhash on the wire may increase performance, because the reader does not have to get the keyhash from the data.

If the writer is CPU bound, sending the keyhash on the wire may decrease performance, because it requires more bandwidth (16 more bytes per sample).

Note: Setting disable_inline_keyhash to DDS_BOOLEAN_TRUE is not compatible with using RTI Real-Time Connect or RTI Recorder.

[default] DDS_BOOLEAN_FALSE

DDS_Boolean DDS_DataWriterProtocolQosPolicy::serialize_key_with_dispose

Controls whether or not the serialized key is propagated on the wire with dispose samples.

This field only applies to keyed writers.

We recommend setting this field to DDS_BOOLEAN_TRUE if there are DataReaders where DDS_DataReaderProtocolQosPolicy::propagate_dispose_of_unregistered_instances is also DDS_BOOLEAN_TRUE.

Important: When this field is DDS_BOOLEAN_TRUE, batching will not be compatible with RTI Connext 4.3e, 4.4b, or 4.4c. The DDSDataReader entities will receive incorrect data and/or encounter deserialization errors.

[default] DDS_BOOLEAN_FALSE

DDS_Boolean DDS_DataWriterProtocolQosPolicy::propagate_app_ack_with_no_response

Controls whether or not a DDSDataWriter receives DDSDataWriterListener::on_application_acknowledgment notifications with an empty or invalid response.

When this field is set to DDS_BOOLEAN_FALSE, the callback DDSDataWriterListener::on_application_acknowledgment will not be invoked if the sample being acknowledged has an empty or invalid response.

[default] DDS_BOOLEAN_TRUE

struct DDS_RtpsReliableWriterProtocol_t DDS_DataWriterProtocolQosPolicy::rtps_reliable_writer

RTPS protocol-related configuration settings for the RTPS reliable writer associated to a DDSDataWriter. This parameter only has effect if both the writer and the matching reader are configured with DDS_RELIABLE_RELIABILITY_QOS DDS_ReliabilityQosPolicyKind.

For details, refer to the DDS_RtpsReliableWriterProtocol_t

[default]
low_watermark 0;
high_watermark 1;
heartbeat_period 3.0 seconds;
fast_heartbeat_period 3.0 seconds;
late_joiner_heartbeat_period 3.0 seconds;
virtual_heartbeat_period DDS_DURATION_AUTO;
samples_per_virtual_heartbeat DDS_LENGTH_UNLIMITED;
max_heartbeat_retries 10;
inactivate_nonprogressing_readers DDS_BOOLEAN_FALSE;
heartbeats_per_max_samples 8;
min_nack_response_delay 0.0 seconds;
max_nack_response_delay 0.2 seconds;
nack_suppression_duration 0.0 seconds;
max_bytes_per_nack_response 131072 bytes;
disable_positive_acks_min_sample_keep_duration 1.0 milliseconds;
disable_positive_acks_max_sample_keep_duration 1.0 seconds;
disable_positive_acks_enable_adaptive_sample_keep_duration DDS_BOOLEAN_TRUE;
disable_positive_acks_decrease_sample_keep_duration_factor 95;
disable_positive_acks_increase_sample_keep_duration_factor 150;
min_send_window_size DDS_LENGTH_UNLIMITED;
max_send_window_size DDS_LENGTH_UNLIMITED;
send_window_update_period 3s;
send_window_increase_factor 105;
send_window_decrease_factor 70;
enable_multicast_periodic_heartbeat DDS_BOOLEAN_FALSE;
multicast_resend_threshold 2 readers;

struct DDS_SequenceNumber_t DDS_DataWriterProtocolQosPolicy::initial_virtual_sequence_number

Determines, the initial virtual sequence number for this DataWriter.

By default, the virtual sequence number of the first sample published by a DataWriter will be 1 for DataWriters that do not use durable writer history. For durable writers, the default virtual sequence number will be the last sequence number they published in a previous execution, plus one. So, when a non-durable DataWriter is restarted and must continue communicating with the same DataReaders, its samples start over with sequence number 1. Durable DataWriters start over where the last sequence number left off, plus one.

This QoS setting allows overwriting the default initial virtual sequence number.

Normally, this parameter is not expected to be modified; however, in some scenarios when continuing communication after restarting, applications may require the DataWriter's virtual sequence number to start at something other than the value described above. An example would be to enable non-durable DataWriters to start at the last sequence number published, plus one, similar to the durable DataWriter. This property enables you to make such a configuration, if desired.

The virtual sequence number can be overwritten as well on a per sample basis by updating DDS_WriteParams_t::identity in the FooDataWriter::write_w_params.

[default] DDS_AUTO_SEQUENCE_NUMBER