10.7. Transport descriptors

This section defines the XML elements available for configuring the transport layer parameters in Fast DDS. These elements are defined within the XML tag <transports_descriptors>. The <transport_descriptors> can contain one or more <transport_descriptor> XML elements. Each <transport_descriptor> element defines a configuration for a specific type of transport protocol. Each of these <transport_descriptor> elements are uniquely identified by a transport ID with the <transport_id> XML tag. Once the user defines a valid <transports_descriptor>, i.e. defines the transport layer parameters, these can be loaded into the XML profile of the DomainParticipant using the <transport_id> XML tag. An example of how to load the <transport_descriptor> into the XML profile of the DomainParticipant is found in DomainParticipant profiles.

The following table lists all the available XML elements that can be defined within the <transport_descriptor> element for the configuration of the transport layer. A more detailed explanation of each of these elements can be found in Transport Layer.

Name	Description	Values	Default
<transport_id>	Unique name to identify each transport descriptor.	string
<type>	Type of the transport descriptor.	UDPv4	UDPv4
		UDPv6
		TCPv4
		TCPv6
		SHM
<sendBufferSize>	Size in bytes of the send socket buffer. If the value is zero then Fast DDS will use the system default socket size.	uint32_t	0
<receiveBufferSize>	Size in bytes of the reception socket buffer. If the value is zero then Fast DDS will use the system default socket size.	uint32_t	0
<maxMessageSize>	The maximum size in bytes of the transport’s message buffer.	uint32_t	65500
<maxInitialPeersRange>	Number of channels opened with each initial remote peer.	uint32_t	4
<netmask_filter>	Transport’s Netmask filtering configuration.	OFF	AUTO
		AUTO
		ON
<interfaces>	Allows defining an Interfaces configuration.	Interfaces configuration
<interfaceWhiteList>	Allows defining an interfaces Whitelist.	Whitelist
<TTL>	Time To Live (UDP only). See UDP Transport.	uint8_t	1
<non_blocking_send>	Whether to set the non-blocking send mode on the socket (NOT available for SHM type). See UDPTransportDescriptor and TCPTransportDescriptor.	bool	false
<output_port>	Port used for output bound. If this field isn’t defined, the output port will be random (UDP only).	uint16_t	0
<wan_addr>	Public WAN address when using TCPv4 transports. This field is optional if the transport doesn’t need to define a WAN address (TCPv4 only).	IPv4 formatted string: XXX.XXX.XXX.XXX
<keep_alive_frequency_ms>	Frequency in milliseconds for sending RTCP keep-alive requests (TCP only).	uint32_t	50000
<keep_alive_timeout_ms>	Time in milliseconds since the last keep-alive request was sent to consider a connection as broken (TCP only).	uint32_t	10000
<max_logical_port>	The maximum number of logical ports to try during RTCP negotiations (TCP only).	uint16_t	100
<logical_port_range>	The maximum number of logical ports per request to try during RTCP negotiations (TCP only).	uint16_t	20
<logical_port_increment>	Increment between logical ports to try during RTCP negotiation (TCP only).	uint16_t	2
<listening_ports>	Local port to work as TCP acceptor for input connections. If not set, the transport will work as TCP client only. If set to 0, an available port will be automatically assigned (TCP only).	List <uint16_t>
<tls>	Allows to define TLS related parameters and options (TCP only).	TLS Configuration
<calculate_crc>	Calculates the Cyclic Redundancy Code (CRC) for error control (TCP only).	bool	true
<check_crc>	Check the CRC for error control (TCP only).	bool	true
<enable_tcp_nodelay>	Socket option for disabling the Nagle algorithm. (TCP only).	bool	false
<tcp_negotiation_timeout>	Time to wait for logical port negotiation (in ms) (TCP only).	uint32_t	0
<segment_size>	Size (in bytes) of the shared-memory segment. (Optional, SHM only).	uint32_t	262144
<port_queue_capacity>	Capacity (in number of messages) available to every Listener (Optional, SHM only).	uint32_t	512
<healthy_check_timeout_ms>	Maximum time-out (in milliseconds) used when checking whether a Listener is alive (Optional, SHM only).	uint32_t	1000
<rtps_dump_file>	Complete path (including file) where RTPS messages will be stored for debugging purposes. An empty string indicates no trace will be performed (Optional, SHM only).	string	Empty

The following XML code shows an example of transport protocol configuration using all configurable parameters. More examples of transports descriptors can be found in the Transport Layer section.

<?xml version="1.0" encoding="UTF-8" ?>
<dds xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <profiles>
        <transport_descriptors>
            <transport_descriptor>
                <transport_id>my_udpv4_transport</transport_id>
                <type>UDPv4</type>
                <sendBufferSize>8192</sendBufferSize>
                <receiveBufferSize>8192</receiveBufferSize>
                <maxMessageSize>16384</maxMessageSize>
                <maxInitialPeersRange>100</maxInitialPeersRange>
                <netmask_filter>AUTO</netmask_filter>
                <interfaces>
                    <allowlist>
                        <interface name="wlp59s0" netmask_filter="ON"/>
                    </allowlist>
                    <blocklist>
                        <interface name="127.0.0.1"/>
                        <interface name="docker0"/>
                    </blocklist>
                </interfaces>
                <interfaceWhiteList>
                    <address>192.168.1.41</address>
                    <interface>lo</interface>
                </interfaceWhiteList>
                <TTL>250</TTL>
                <non_blocking_send>false</non_blocking_send>
                <output_port>5101</output_port>
                <wan_addr>80.80.55.44</wan_addr>
                <keep_alive_frequency_ms>5000</keep_alive_frequency_ms>
                <keep_alive_timeout_ms>25000</keep_alive_timeout_ms>
                <max_logical_port>9000</max_logical_port>
                <logical_port_range>100</logical_port_range>
                <logical_port_increment>2</logical_port_increment>
                <listening_ports>
                    <port>5100</port>
                    <port>5200</port>
                </listening_ports>
                <tls><!-- TLS Section --></tls>
                <calculate_crc>false</calculate_crc>
                <check_crc>false</check_crc>
                <enable_tcp_nodelay>false</enable_tcp_nodelay>
                <segment_size>262144</segment_size>
                <port_queue_capacity>512</port_queue_capacity>
                <healthy_check_timeout_ms>1000</healthy_check_timeout_ms>
                <rtps_dump_file>rtsp_messages.log</rtps_dump_file>
            </transport_descriptor>
        </transport_descriptors>
    </profiles>
</dds>

Note

The Real-time Transport Control Protocol (RTCP) is the control protocol for communications with RTPS over TCP/IP connections.

10.7.1. TLS Configuration

Fast DDS provides mechanisms to configure the Transport Layer Security (TLS) protocol parameters through the <tls> XML element of its <transport_descriptor>. Please, refer to TLS over TCP for a detailed explanation of the entire TLS configuration in Fast DDS. More information on how to set up secure communication in Fast DDS can be found in the Security section.

Warning

For the full understanding of this section, a basic knowledge of network security in terms of SSL/TLS, Certificate Authority (CA), Public Key Infrastructure (PKI), and Diffie-Hellman is required; encryption protocols are not explained in detail.

The full list of available XML elements that can be defined within the <tls> element to configure the TLS protocol are listed in the following table:

Name	Description	Values	Default
<password>	Password of the <private_key_file> or <rsa_private_key_file> if provided.	string
<private_key_file>	Path to the private key certificate file.	string
<rsa_private_key_file>	Path to the private key RSA certificate file.	string
<cert_chain_file>	Path to the public certificate chain file.	string
<tmp_dh_file>	Path to the Diffie-Hellman parameters file	string
<verify_file>	Path to the Certification Authority (CA) file.	string
<verify_mode>	Establishes the verification mode mask. Several verification options can be combined in the same <transport_descriptor>.	VERIFY_NONE
		VERIFY_PEER
		VERIFY_FAIL_IF_NO_PEER_CERT
		VERIFY_CLIENT_ONCE
<options>	Establishes the SSL Context options mask. Several options can be combined in the same <transport_descriptor>.	DEFAULT_WORKAROUNDS
		NO_COMPRESSION
		NO_SSLV2
		NO_SSLV3
		NO_TLSV1
		NO_TLSV1_1
		NO_TLSV1_2
		NO_TLSV1_3
		SINGLE_DH_USE
<verify_paths>	Paths where the system will look for verification files.	List <string>
<verify_depth>	Maximum allowed depth to verify intermediate certificates.	uint32_t
<default_verify_path>	Specifies whether the system will look on the default paths for the verification files.	bool	false
<handshake_role>	Role that the transport will take on handshaking. On default, the acceptors act as SERVER and the connectors as CLIENT.	DEFAULT	DEFAULT
		SERVER
		CLIENT
<server_name>	server name or host name required in case Server Name Indication (SNI) is used.	string

An example of TLS protocol parameter configuration is shown below.

<?xml version="1.0" encoding="UTF-8" ?>
<dds xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <profiles>
        <transport_descriptors>
            <transport_descriptor>
                <transport_id>Test</transport_id>
                <type>TCPv4</type>
                <tls>
                    <password>Password</password>
                    <private_key_file>Key_file.pem</private_key_file>
                    <rsa_private_key_file>RSA_file.pem</rsa_private_key_file>
                    <cert_chain_file>Chain.pem</cert_chain_file>
                    <tmp_dh_file>DH.pem</tmp_dh_file>
                    <verify_file>verify.pem</verify_file>
                    <verify_mode>
                        <verify>VERIFY_PEER</verify>
                    </verify_mode>
                    <options>
                        <option>NO_TLSV1</option>
                        <option>NO_TLSV1_1</option>
                    </options>
                    <verify_paths>
                        <verify_path>Path1</verify_path>
                        <verify_path>Path2</verify_path>
                        <verify_path>Path3</verify_path>
                    </verify_paths>
                    <verify_depth>55</verify_depth>
                    <default_verify_path>true</default_verify_path>
                    <handshake_role>SERVER</handshake_role>
                    <server_name>my_server.com</server_name>
                </tls>
            </transport_descriptor>
<!-->
    </profiles>