15.1.1. Large Data Mode

The following snippets show how to configure Fast DDS DomainParticipants to run the PDP discovery phase over UDP multicast and communicate application data over a TCP Transport or Shared Memory Transport, which is called the LARGE_DATA configuration (See Managing the Builtin Transports). With this approach, applications managing large samples can benefit from transmitting their data over TCP or SHM, while at the same time have the flexibility of automatic discovery. The LARGE_DATA mode can be set using the FASTDDS_BUILTIN_TRANSPORTS environment variable (see FASTDDS_BUILTIN_TRANSPORTS), XML profiles or via code.

Environment VariableXMLC++

export FASTDDS_BUILTIN_TRANSPORTS=LARGE_DATA

Note

LARGE_DATA configuration of the builtin transports will also create a SHM transport along the UDP and TCP transports. Shared Memory will be used whenever it is possible. Manual configuration will be required if a TCP communication is required when SHM is feasible.

C++XML

eprosima::fastdds::dds::DomainParticipantQos pqos = PARTICIPANT_QOS_DEFAULT;

/* Transports configuration */
// UDPv4 transport for PDP over multicast
auto pdp_transport = std::make_shared<eprosima::fastdds::rtps::UDPv4TransportDescriptor>();
pqos.transport().user_transports.push_back(pdp_transport);

// TCPv4 transport for EDP and application data (The listening port must to be unique for
// each participant in the same host)
constexpr uint16_t tcp_listening_port = 0;
auto data_transport = std::make_shared<eprosima::fastdds::rtps::TCPv4TransportDescriptor>();
data_transport->add_listener_port(tcp_listening_port);
pqos.transport().user_transports.push_back(data_transport);

pqos.transport().use_builtin_transports = false;

/* Locators */
// Define locator for PDP over multicast
eprosima::fastrtps::rtps::Locator_t pdp_locator;
pdp_locator.kind = LOCATOR_KIND_UDPv4;
eprosima::fastrtps::rtps::IPLocator::setIPv4(pdp_locator, "239.255.0.1");
pqos.wire_protocol().builtin.metatrafficMulticastLocatorList.push_back(pdp_locator);

// Define locator for EDP and user data
eprosima::fastrtps::rtps::Locator_t tcp_locator;
tcp_locator.kind = LOCATOR_KIND_TCPv4;
eprosima::fastrtps::rtps::IPLocator::setIPv4(tcp_locator, "0.0.0.0");
eprosima::fastrtps::rtps::IPLocator::setPhysicalPort(tcp_locator, tcp_listening_port);
eprosima::fastrtps::rtps::IPLocator::setLogicalPort(tcp_locator, tcp_listening_port);
pqos.wire_protocol().builtin.metatrafficUnicastLocatorList.push_back(tcp_locator);
pqos.wire_protocol().default_unicast_locator_list.push_back(tcp_locator);

/* Create participant as usual */
eprosima::fastdds::dds::DomainParticipant* participant =
        eprosima::fastdds::dds::DomainParticipantFactory::get_instance()->create_participant(0, pqos);