RTI Connext C API  Version 5.1.0
DDS_DataWriterProtocolQosPolicy Struct Reference

Protocol that applies only to DDS_DataWriter instances. 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 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.
 The reliable protocol defined in RTPS.

Detailed Description

Protocol that applies only to DDS_DataWriter 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 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.

RxO = N/A
Changeable = NO

Field 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 DDS_DataWriter.

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

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

[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.


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.


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.


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 DDS_DataReader entities will receive incorrect data and/or encounter deserialization errors.


struct DDS_RtpsReliableWriterProtocol_t DDS_DataWriterProtocolQosPolicy::rtps_reliable_writer

The reliable protocol defined in RTPS.

[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;
max_bytes_per_nack_response 131072

RTI Connext C API Version 5.1.0 Copyright © Mon Feb 3 2014 Real-Time Innovations, Inc