5.7. FastDDS tuning

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

5.7.1. Adjusting system parameters

5.7.1.1. 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
```

5.7.1.2. 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
```

5.7.1.3. 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.

5.7.2. 2. FastDDS configuration

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

5.7.2.1. 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>

5.7.2.2. Environment variables

Set the following environment variables to use the custom FastDDS 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.