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UDP Transport

UDP is a connectionless transport, where the receiving :ref:`dds_layer_domainParticipant` must open a UDP port listening for incoming messages, and the sending DomainParticipant sends messages to this port.

Warning

This documentation assumes the reader has basic knowledge of UDP/IP concepts, since terms like Time To Live (TTL), socket buffers, and port numbering are not explained in detail. However, it is possible to configure a basic UDP transport on Fast DDS without this knowledge.

UDPTransportDescriptor

eProsima Fast DDS implements UDP transport for both UDPv4 and UDPv6. Each of these transports is independent from the other, and has its own |TransportDescriptorInterface-api|. However, all their |TransportDescriptorInterface-api| data members are common.

The following table describes the common data members for both UDPv4 and UDPv6.

Member Data type Default Description
|SocketTransportDescriptor::sendBufferSize-api| uint32_t 0 Size of the sending buffer of the socket (octets).
|SocketTransportDescriptor::receiveBufferSize-api| uint32_t 0 Size of the receiving buffer of the socket (octets).
|SocketTransportDescriptor::interfaceWhiteList-api| vector<string> Empty vector List of allowed interfaces. See |InterfaceWhitelist|.
|SocketTransportDescriptor::TTL-api| uint8_t 1 Time to live, in number of hops.
|UDPTransportDescriptor::m_output_udp_socket-api| uint16_t 0 Port number for the outgoing messages.
|UDPTransportDescriptor::non_blocking_send-api| bool false Do not block on send operations (*).

Note

When |UDPTransportDescriptor::non_blocking_send-api| is set to true, send operations will return immediately if the buffer is full, but no error will be returned to the upper layer. This means that the application will behave as if the datagram is sent and lost. This value is specially useful on high-frequency best-effort writers.

When set to false, send operations will block until the network buffer has space for the datagram. This may hinder performance on high-frequency writers.

UDPv4TransportDescriptor

|UDPv4TransportDescriptor-api| has no additional data members from the common ones described in :ref:`transport_udp_transportDescriptor`.

UDPv6TransportDescriptor

|UDPv6TransportDescriptor-api| has no additional data members from the common ones described in :ref:`transport_udp_transportDescriptor`.

Enabling UDP Transport

Fast DDS enables a UDPv4 transport by default. Nevertheless, the application can enable other UDP transports if needed. To enable a new UDP transport in a :ref:`dds_layer_domainParticipant`, first create an instance of :ref:`transport_udp_v4transportDescriptor` (for UDPv4) or :ref:`transport_udp_v6transportDescriptor` (for UDPv6), and add it to the user transport list of the :ref:`dds_layer_domainParticipant`.

The examples below show this procedure in both C++ code and XML file.

.. tabs::

   .. tab:: C++

      .. literalinclude:: /../code/DDSCodeTester.cpp
         :language: c++
         :start-after: //CONF-UDP-TRANSPORT-SETTING
         :end-before: //!--
         :dedent: 8

   .. tab:: XML

      .. literalinclude:: /../code/XMLTester.xml
         :language: xml
         :start-after: <!-->CONF-UDP-TRANSPORT-SETTING
         :end-before: <!--><-->
         :lines: 2-3,5-
         :append: </profiles>