DDS::TransportMulticastQosPolicy Class Reference

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. More...

#include <managed_infrastructure.h>

Static Public Member Functions
static System::String ^	get_transportmulticast_qos_policy_name ()
	Stringified human-readable name for DDS::TransportMulticastQosPolicy. More...

Public Attributes
TransportMulticastSettingsSeq ^	value
	A sequence of multicast communications settings. More...
TransportMulticastQosPolicyKind	kind
	A value that specifies a way to determine how to obtain the multicast address. More...

Detailed Description

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.

By default, a DDS::DataWriter will send individually addressed packets for each DDS::DataReader that subscribes to the topic of the DataWriter – this is known as unicast delivery. Thus, as many copies of the data will be sent over the network as there are DataReaders for the data. The network bandwidth used by a DataWriter will thus increase linearly with the number of DataReaders.

Multicast addressing (on UDP/IP transports) allows multiple DataReaders to receive the same network packet. By using multicast, a DDS::DataWriter can send a single network packet that is received by all subscribing applications. Thus the network bandwidth usage will be constant, independent of the number of DataReaders.

Coordinating the multicast address specified by DataReaders can help optimize network bandwidth usage in systems where there are multiple DataReaders for the same DDS::Topic.

Entity:

DDS::DataReader

Properties:

RxO = N/A
Changeable = NO

Member Data Documentation

value

TransportMulticastSettingsSeq ^ DDS::TransportMulticastQosPolicy::value

A sequence of multicast communications settings.

An empty sequence means that multicast is not used by the entity.

The RTPS wire protocol currently limits the maximum number of multicast locators to 16. Note that this is a hard limit that cannot be increased. However, this limit can be decreased by configuring the 'dds.domain_participant.max_announced_locator_list_size' property in the DDS::PropertyQosPolicy associated with the DDS::DomainParticipantQos.

[default] Empty sequence.

kind

TransportMulticastQosPolicyKind DDS::TransportMulticastQosPolicy::kind

A value that specifies a way to determine how to obtain the multicast address.

This field can be set to one of the following two values: DDS::TransportMulticastQosPolicyKind::AUTOMATIC_TRANSPORT_MULTICAST_QOS or DDS::TransportMulticastQosPolicyKind::UNICAST_ONLY_TRANSPORT_MULTICAST_QOS.

• If it is set to DDS::TransportMulticastQosPolicyKind::AUTOMATIC_TRANSPORT_MULTICAST_QOS, the behavior will depend on the DDS::TransportMulticastQosPolicy::value:

  • If DDS::TransportMulticastQosPolicy::value does not have any elements, then multicast will not be used.

  • If DDS::TransportMulticastQosPolicy::value first element has an empty address, then the address will be obtained from DDS::TransportMulticastMappingQosPolicy.

  • If none of the elements in DDS::TransportMulticastQosPolicy::value is empty, and at least one element has a valid address, then that address will be used.
• If it is set to DDS::TransportMulticastQosPolicyKind::UNICAST_ONLY_TRANSPORT_MULTICAST_QOS, then multicast will not be used.

[default] DDS::TransportMulticastQosPolicyKind::AUTOMATIC_TRANSPORT_MULTICAST_QOS