6.7. Fast DDS Tuning

When operating with the default configuration, Fast DDS exhibits suboptimal transmission efficiency, resulting in significant image transmission delays when used with the Orbbec camera in ROS2. This document provides guidance on optimizing Fast DDS to enhance image transfer efficiency.

6.7.1. Adjusting System Parameters

6.7.1.1. IP Fragmentation Time

Path: /proc/sys/net/ipv4/ipfrag_time (default: 30 seconds)
Purpose: Defines the duration that IP fragments are kept in memory.
Adjustment: Decrease this value to reduce the time window where no fragments are received, which can help reduce delays. Consider the specific needs of your environment as this setting affects all incoming fragments.

Example: Set to 3 seconds.
```
sudo sysctl net.ipv4.ipfrag_time=3
```

6.7.1.2. IP Fragmentation Memory Threshold

Path: /proc/sys/net/ipv4/ipfrag_high_thresh (default: 262144 bytes)
Purpose: Sets the maximum memory used to reassemble IP fragments.
Adjustment: Increase this value to allow more memory for fragment reassembly, which can improve handling of larger data packets.

Example: Increase to 128 MB.
```
sudo sysctl net.ipv4.ipfrag_high_thresh=134217728
```

6.7.1.3. Maximum Buffer Sizes

Purpose: Configures the maximum buffer sizes for receiving and sending data, which is critical for high-throughput data transmission.

Adjustment: Set the maximum buffer sizes for both receiving and sending operations.

Commands:

sudo sysctl -w net.core.rmem_max=2147483647
sudo sysctl -w net.core.rmem_default=2147483647
sudo sysctl -w net.core.wmem_max=2147483647
sudo sysctl -w net.core.wmem_default=2147483647

Alternatively, make these settings permanent by adding them to the /etc/sysctl.d/10-fastrtps-max.conf file.

sudo gedit /etc/sysctl.d/10-fastrtps-max.conf

add blow lines to the file:

net.core.rmem_max=2147483647
net.core.rmem_default=2147483647
net.core.wmem_max=2147483647
net.core.wmem_default=2147483647

then save and exit the file. run sudo sysctl -p to apply the changes.

For detailed guidance, refer to ROS 2 DDS Tuning Documentation.

6.7.2. 2. Fast DDS Configuration

Below is an example of a Fast DDS configuration file optimized for ROS2 usage with the Orbbec camera. This configuration enhances the overall data transmission by adjusting buffer sizes and transport settings.

6.7.2.1. Configuration File: `shm_fastdds.xml`

Place this file in the $HOME directory.

<?xml version="1.0" encoding="UTF-8"?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <transport_descriptors>
        <transport_descriptor>
            <transport_id>UDP_transport</transport_id>
            <type>UDPv4</type>
            <maxInitialPeersRange>10</maxInitialPeersRange>
            <maxMessageSize>65000</maxMessageSize>
            <sendBufferSize>1048576</sendBufferSize>
            <receiveBufferSize>1048576</receiveBufferSize>
        </transport_descriptor>
    </transport_descriptors>
    <participant profile_name="participant_profile_ros2" is_default_profile="true">
        <rtps>
            <name>profile_for_ros2_context</name>
            <userTransports>
                <transport_id>UDP_transport</transport_id>
            </userTransports>
            <useBuiltinTransports>false</useBuiltinTransports>
            <sendSocketBufferSize>1048576</sendSocketBufferSize>
            <listenSocketBufferSize>1048576</listenSocketBufferSize>
            <builtin>
                <initialPeersList>
                    <locator>
                        <udpv4>
                            <address>127.0.0.1</address>
                        </udpv4>
                    </locator>
                </initialPeersList>
            </builtin>
        </rtps>
    </participant>
    <data_writer profile_name="default publisher profile" is_default_profile="true">
        <qos>
            <publishMode>
                <kind>ASYNCHRONOUS</kind>
            </publishMode>
            <latencyBudget>
                <duration>
                    <sec>0</sec>
                    <nanosec>1000000</nanosec>
                </duration>
            </latencyBudget>
        </qos>
        <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
    </data_writer>
    <data_reader profile_name="default subscription profile" is_default_profile="true">
        <qos>
            <data_sharing>
                <kind>AUTOMATIC</kind>
            </data_sharing>
            <latencyBudget>
                <duration>
                    <sec>0</sec>
                    <nanosec>1000000</nanosec>
                </duration>
            </latencyBudget>
        </qos>
        <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
    </data_reader>
</profiles>

6.7.2.2. Environment Variables

Set the following environment variables to use the custom Fast DDS profile:

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export FASTRTPS_DEFAULT_PROFILES_FILE=$HOME/shm_fastdds.xml
export RMW_FASTRTPS_USE_QOS_FROM_XML=1

This configuration aims to optimize the data flow and reduce transmission delays, improving the responsiveness and reliability of the Orbbec camera system in a ROS2 environment.

###DDS Tuning

The default DDS settings (Galactic) may not be optimal for data transmission. Different DDS settings can have varying performance. In this example, we use CycloneDDS. For more detailed information, please refer to the ROS DDS Tuning。

● Edit cyclonedds configuration file

sudo gedit /etc/cyclonedds/config.xml

Add

<?xml version="1.0" encoding="UTF-8"?>
<CycloneDDS xmlns="https://cdds.io/config" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="https://cdds.io/confighttps://raw.githubusercontent.com/eclipse-cyclonedds/cyclonedds/master/etc/cyclonedds.xsd">
    <Domain id="any">
        <General>
            <NetworkInterfaceAddress>lo</NetworkInterfaceAddress>
            <AllowMulticast>false</AllowMulticast>
        </General>
        <Internal>
            <MinimumSocketReceiveBufferSize>16MB</MinimumSocketReceiveBufferSize>
        </Internal>
        <Discovery>
            <ParticipantIndex>auto</ParticipantIndex>
            <MaxAutoParticipantIndex>30</MaxAutoParticipantIndex>
            <Peers>
                <Peer address="localhost"/>
            </Peers>
        </Discovery>
    </Domain>
</CycloneDDS>

● Set the environment variables, add to .zshrc or .bashrc

export ROS_DOMAIN_ID=42 # Numbers from 0 to 232
export ROS_LOCALHOST_ONLY=1
export CYCLONEDDS_URI=file:///etc/cyclonedds/config.xml

Tip：to understand why the maximum ROS_DOMAIN_ID is 232, please visit The ROS DOMAIN ID ● Increase UDP receive buffer size Edit

/etc/sysctl.d/10-cyclone-max.conf

Add

net.core.rmem_max=2147483647
net.core.rmem_default=2147483647

If you use Fast DDS, you can refer to the Fast DDS Configuration file.