5.3.3. STATIC Discovery Settings

Fast DDS allows for the substitution of the SEDP protocol for the EDP phase with a static version that completely eliminates EDP meta traffic. This can become useful when dealing with limited network bandwidth and a well-known schema of DataWriters and DataReaders. If all DataWriters and DataReaders, and their Topics and data types, are known beforehand, the EDP phase can be replaced with a static configuration of peers. It is important to note that by doing this, no EDP discovery meta traffic will be generated, and only those peers defined in the configuration will be able to communicate. The STATIC discovery related settings are:

Name

Description

STATIC EDP

It activates the STATIC discovery protocol.

STATIC EDP XML Configuration Specification

Specifies an XML content with a description of the remote DataWriters and
DataReaders.

Initial Announcements

It defines the behavior of the DomainParticipant initial announcements (PDP phase).

5.3.3.1. STATIC EDP

To activate the STATIC EDP, the SEDP must be disabled on the WireProtocolConfigQos. This can be done either by code or using an XML configuration file:

C++

DomainParticipantQos pqos;

pqos.wire_protocol().builtin.discovery_config.use_SIMPLE_EndpointDiscoveryProtocol = false;
pqos.wire_protocol().builtin.discovery_config.use_STATIC_EndpointDiscoveryProtocol = true;

XML

<participant profile_name="participant_profile_static_edp">
    <rtps>
        <builtin>
            <discovery_config>
                <EDP>STATIC</EDP>
            </discovery_config>
        </builtin>
    </rtps>
</participant>

5.3.3.2. STATIC EDP XML Configuration Specification

Since activating STATIC EDP suppresses all EDP meta traffic, the information about the remote entities (DataWriters and DataReaders) must be statically specified, which is done using dedicated XML files. A DomainParticipant may load several of such configuration files so that the information about different entities can be contained in one file, or split into different files to keep it more organized. Fast DDS provides a Static Discovery example that implements this EDP discovery protocol.

The following table describes all the possible elements of a STATIC EDP XML configuration file. A full example of such file can be found in STATIC EDP XML Example.

Name

Description

Values

Default

<userId>

Mandatory.
Uniquely identifies the DataReader/DataWriter.

uint16_t

0

<entityID>

EntityId of the DataReader/DataWriter.

uint16_t

0

<expectsInlineQos>

It indicates if QOS is expected inline
(DataReader only).

bool

false

<topicName>

Mandatory.
The topic of the remote DataReader/DataWriter.
Should match with one of the topics of the local
DataReaders/DataWriters.

string_255

<topicDataType>

Mandatory.
The data type of the topic.

string_255

<topicKind>

The kind of topic.

NO_KEY

NO_KEY

WITH_KEY

<partitionQos>

The name of a partition of the remote peer.
Repeat to configure several partitions.

string

<unicastLocator>

Unicast locator of the DomainParticipant.
See Locators definition.

<multicastLocator>

Multicast locator of the DomainParticipant.
See Locators definition.

<reliabilityQos>

See the ReliabilityQosPolicy section.

BEST_EFFORT_RELIABILITY_QOS

BEST_EFFORT_RELIABILITY_QOS

RELIABLE_RELIABILITY_QOS

<durabilityQos>

See the DurabilityQosPolicy section.

VOLATILE_DURABILITY_QOS

VOLATILE_DURABILITY_QOS

TRANSIENT_LOCAL_DURABILITY_QOS

TRANSIENT_DURABILITY_QOS

<ownershipQos>

See Ownership QoS.

<livelinessQos>

Defines the liveliness of the remote peer.
See Liveliness QoS.

5.3.3.2.1. Locators definition

Locators for remote peers are configured using <unicastLocator> and <multicastLocator> tags. These take no value, and the locators are defined using tag elements. Locators defined with <unicastLocator> and <multicastLocator> are accumulative, so they can be repeated to assign several remote endpoints locators to the same peer.

  • address: a mandatory string representing the locator address.

  • port: an optional uint16_t representing a port on that address.

5.3.3.2.2. Ownership QoS

The ownership of the topic can be configured using <ownershipQos> tag. It takes no value, and the configuration is done using tag elements:

  • kind: can be one of SHARED_OWNERSHIP_QOS or EXCLUSIVE_OWNERSHIP_QOS. This element is mandatory withing the tag.

  • strength: an optional uint32_t specifying how strongly the remote DomainParticipant owns the Topic. This QoS can be set on DataWriters only. If not specified, default value is zero.

5.3.3.2.3. Liveliness QoS

The LivelinessQosPolicy of the remote peer is configured using <livelinessQos> tag. It takes no value, and the configuration is done using tag elements:

5.3.3.2.4. STATIC EDP XML Example

The following is a complete example of a configuration XML file for two remote DomainParticipant, a DataWriter and a DataReader. This configuration must agree with the configuration used to create the remote DataReader/DataWriter. Otherwise, communication between DataReaders and DataWriters may be affected. If any non-mandatory element is missing, it will take the default value. As a rule of thumb, all the elements that were specified on the remote DataReader/DataWriter creation should be configured.

XML

<staticdiscovery>
    <participant>
        <name>HelloWorldSubscriber</name>
        <reader>
            <userId>3</userId>
            <entityID>4</entityID>
            <expectsInlineQos>true</expectsInlineQos>
            <topicName>HelloWorldTopic</topicName>
            <topicDataType>HelloWorld</topicDataType>
            <topicKind>WITH_KEY</topicKind>
            <partitionQos>HelloPartition</partitionQos>
            <partitionQos>WorldPartition</partitionQos>
            <unicastLocator address="192.168.0.128" port="5000"/>
            <unicastLocator address="10.47.8.30" port="6000"/>
            <multicastLocator address="239.255.1.1" port="7000"/>
            <reliabilityQos>BEST_EFFORT_RELIABILITY_QOS</reliabilityQos>
            <durabilityQos>VOLATILE_DURABILITY_QOS</durabilityQos>
            <ownershipQos kind="SHARED_OWNERSHIP_QOS"/>
            <livelinessQos kind="AUTOMATIC_LIVELINESS_QOS" leaseDuration_ms="1000"/>
        </reader>
    </participant>
    <participant>
        <name>HelloWorldPublisher</name>
        <writer>
            <unicastLocator address="192.168.0.120" port="9000"/>
            <unicastLocator address="10.47.8.31" port="8000"/>
            <multicastLocator address="239.255.1.1" port="7000"/>
            <userId>5</userId>
            <entityID>6</entityID>
            <topicName>HelloWorldTopic</topicName>
            <topicDataType>HelloWorld</topicDataType>
            <topicKind>WITH_KEY</topicKind>
            <partitionQos>HelloPartition</partitionQos>
            <partitionQos>WorldPartition</partitionQos>
            <reliabilityQos>BEST_EFFORT_RELIABILITY_QOS</reliabilityQos>
            <durabilityQos>VOLATILE_DURABILITY_QOS</durabilityQos>
            <ownershipQos kind="SHARED_OWNERSHIP_QOS" strength="50"/>
            <livelinessQos kind="AUTOMATIC_LIVELINESS_QOS" leaseDuration_ms="1000"/>
        </writer>
    </participant>
</staticdiscovery>

5.3.3.3. Loading STATIC EDP XML Files

Statically discovered remote DataReaders/DataWriters must define a unique userID on their profile, whose value must agree with the one specified in the discovery configuration XML. This is done by setting the user ID on the DataReaderQos/DataWriterQos:

C++

// Configure the DataWriter
DataWriterQos wqos;
wqos.endpoint().user_defined_id = 1;

// Configure the DataReader
DataReaderQos rqos;
rqos.endpoint().user_defined_id = 3;

XML

<data_writer profile_name="writer_xml_conf_static_discovery">
    <userDefinedID>3</userDefinedID>
</data_writer>

<data_reader profile_name="reader_xml_conf_static_discovery">
    <userDefinedID>5</userDefinedID>
</data_reader>

On the local DomainParticipant, you can load STATIC EDP configuration content specifying the file containing it.

C++

DomainParticipantQos pqos;

pqos.wire_protocol().builtin.discovery_config.static_edp_xml_config("file://RemotePublisher.xml");
pqos.wire_protocol().builtin.discovery_config.static_edp_xml_config("file://RemoteSubscriber.xml");

XML

<participant profile_name="participant_profile_static_load_xml">
    <rtps>
        <builtin>
            <discovery_config>
                <static_edp_xml_config>file://RemotePublisher.xml</static_edp_xml_config>
                <static_edp_xml_config>file://RemoteSubscriber.xml</static_edp_xml_config>
            </discovery_config>
        </builtin>
    </rtps>
</participant>

Or you can specify the STATIC EDP configuration content directly.

C++

DomainParticipantQos pqos;

pqos.wire_protocol().builtin.discovery_config.static_edp_xml_config(
    "data://<?xml version=\"1.0\" encoding=\"utf-8\"?>" \
    "<staticdiscovery><participant><name>RTPSParticipant</name></participant></staticdiscovery>");