RTI Connext C API Version 7.3.0
DDS_WireProtocolQosPolicy Struct Reference

Specifies the wire-protocol-related attributes for the DDS_DomainParticipant. More...

Data Fields

DDS_Long participant_id
 A value used to distinguish among different participants belonging to the same domain on the same host. More...
 
DDS_UnsignedLong rtps_host_id
 The RTPS Host ID of the domain participant. More...
 
DDS_UnsignedLong rtps_app_id
 The RTPS App ID of the domain participant. More...
 
DDS_UnsignedLong rtps_instance_id
 The RTPS Instance ID of the DDS_DomainParticipant. More...
 
struct DDS_RtpsWellKnownPorts_t rtps_well_known_ports
 Configures the RTPS well-known port mappings. More...
 
DDS_RtpsReservedPortKindMask rtps_reserved_port_mask
 Specifies which well-known ports to reserve when enabling the participant. More...
 
DDS_WireProtocolQosPolicyAutoKind rtps_auto_id_kind
 Kind of auto mechanism used to calculate the GUID prefix. More...
 
DDS_Boolean compute_crc
 Adds RTPS CRC submessage to every message when this field is set to DDS_BOOLEAN_TRUE. More...
 
DDS_Boolean check_crc
 Checks if the received RTPS message is valid by comparing the computed CRC with the received RTPS CRC submessage when this field is set to DDS_BOOLEAN_TRUE. More...
 

Detailed Description

Specifies the wire-protocol-related attributes for the DDS_DomainParticipant.

Entity:
DDS_DomainParticipant
Properties:
RxO = N/A
Changeable = NO

Usage

This QoS policy configures some participant-wide properties of the DDS Real-Time Publish Subscribe (RTPS) on-the-wire protocol. (DDS_DataWriterProtocolQosPolicy and DDS_DataReaderProtocolQosPolicy configure RTPS and reliability properties on a per DDS_DataWriter or DDS_DataReader basis.)

NOTE: The default QoS policies returned by RTI Connext contain the correctly initialized wire protocol attributes. The defaults are not normally expected to be modified, but are available to the advanced user customizing the implementation behavior.

The default values should not be modified without an understanding of the underlying Real-Time Publish Subscribe (RTPS) wire protocol.

In order for the discovery process to work correctly, each DDS_DomainParticipant must have a unique identifier. This QoS policy specifies how that identifier should be generated.

RTPS defines a 96-bit prefix to this identifier; each DDS_DomainParticipant must have a unique value for this prefix relative to all other participants in its domain.

If an application dies unexpectedly and is restarted, the IDs used by the new instance of DomainParticipants should be different than the ones used by the previous instances. A change in these values allows other DomainParticipants to know that they are communicating with a new instance of an application, and not the previous instance.

For legacy reasons, RTI Connext divides the 96-bit prefix into three integers:

  • The first integer is called host ID. The original purpose of this integer was to contain the identity of the machine on which the DomainParticipant is executing.
  • The second integer is called an application ID. The original purpose of this integer was to contain a value that identifies the process or task in which the DomainParticipant is contained.
  • The third integer is called instance ID. The original purpose was to contain a value that uniquely identifies a DomainParticipant within a task or process.

The DDS_WireProtocolQosPolicy::rtps_auto_id_kind field can be used to configure the algorithm that RTI Connext uses to populate the 96-bit prefix. Then you can optionally overwrite specific parts of the 96-bit prefix by explicitly configuring the DDS_WireProtocolQosPolicy::rtps_host_id (first integer), DDS_WireProtocolQosPolicy::rtps_app_id (second integer), and DDS_WireProtocolQosPolicy::rtps_instance_id (third integer).

The DDS_WireProtocolQosPolicy::rtps_auto_id_kind field supports three different prefix generation algorithms:

  1. In the default and most common scenario, DDS_WireProtocolQosPolicy::rtps_auto_id_kind is set to DDS_RTPS_AUTO_ID_FROM_UUID. As the name suggests, this mechanism uses a unique, randomly generated UUID to fill the rtps_host_id, rtps_app_id, or rtps_instance_id fields. The first two bytes of the rtps_host_id are replaced with the RTI vendor ID (0x0101).
  2. (Legacy) When rtps_auto_id_kind is set to DDS_RTPS_AUTO_ID_FROM_IP, the 96-bit prefix is generated as follows:
    • rtps_host_id: The 32-bit value of the IPv4 of the first up and running interface of the host machine is assigned. If the host does not have an IPv4 address, the host-id will be automatically set to 0x7F000001.
    • rtps_app_id: The process (or task) ID is assigned.
    • rtps_instance_id: A counter is assigned that is incremented per new participant within a process.
    DDS_RTPS_AUTO_ID_FROM_IP is not a good algorithm to guarantee prefix uniqueness, because the process ID can be recycled by the OSs.
  3. (Legacy) When rtps_auto_id_kind is set to DDS_RTPS_AUTO_ID_FROM_MAC, the 96-bit prefix is generated as follows:

    • rtps_host_id: The first 32 bits of the MAC address of the first up and running interface of the host machine are assigned.
    • rtps_app_id: The last 32 bits of the MAC address of the first up and running interface of the host machine are assigned.
    • rtps_instance_id: This field is split into two different parts. The process (or task) ID is assigned to the first 24 bits. A counter is assigned to the last 8 bits. This counter is incremented per new participant.

    DDS_RTPS_AUTO_ID_FROM_IP is not a good algorithm to guarantee prefix uniqueness, because the process ID can be recycled by the OSs.

Some examples are provided to clarify the behavior of this QoSPolicy in case you want to change the default behavior with DDS_RTPS_AUTO_ID_FROM_MAC.

First, get the participant QoS from the DomainParticipantFactory:

&participant_qos);
DDS_DomainParticipantFactory * DDS_DomainParticipantFactory_get_instance(void)
Gets the singleton instance of this class.
DDS_ReturnCode_t DDS_DomainParticipantFactory_get_default_participant_qos(DDS_DomainParticipantFactory *self, struct DDS_DomainParticipantQos *qos)
Initializes the DDS_DomainParticipantQos instance with default values.

Second, change the DDS_WireProtocolQosPolicy using one of the options shown below.

Third, create the DDS_DomainParticipant as usual, using the modified QoS structure instead of the default one.

Option 1: Use DDS_RTPS_AUTO_ID_FROM_MAC to explicitly set just the application/task identifier portion of the rtps_instance_id field.

participant_qos.wire_protocol.rtps_auto_id_kind = DDS_RTPS_AUTO_ID_FROM_MAC;
participant_qos.wire_protocol.rtps_host_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_app_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_instance_id = (/* App ID */ (12 << 8) |
/* Instance ID*/ (DDS_RTPS_AUTO_ID));
@ DDS_RTPS_AUTO_ID
Indicates that RTI Connext should choose an appropriate host, app, instance or object ID automaticall...
Definition: infrastructure.ifc:4749
@ DDS_RTPS_AUTO_ID_FROM_MAC
Builds the GUID prefix using the MAC address and process ID.
Definition: infrastructure.ifc:4693

Option 2: Handle only the per participant counter and let RTI Connext handle the application/task identifier:

participant_qos.wire_protocol.rtps_auto_id_kind = DDS_RTPS_AUTO_ID_FROM_MAC;
participant_qos.wire_protocol.rtps_host_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_app_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_instance_id = (/* App ID */ (DDS_RTPS_AUTO_ID) |
/* Instance ID*/ (12));

Option 3: Handle the entire rtps_instance_id field yourself:

participant_qos.wire_protocol.rtps_auto_id_kind = DDS_RTPS_AUTO_ID_FROM_MAC;
participant_qos.wire_protocol.rtps_host_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_app_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_instance_id = ( /* App ID */ (12 << 8)) |
/* Instance ID */ (9) )

NOTE: If you are using DDS_RTPS_AUTO_ID_FROM_MAC as rtps_auto_id_kind and you decide to manually handle the rtps_instance_id field, you must ensure that both parts are non-zero (otherwise RTI Connext will take responsibility for them). RTI recommends that you always specify the two parts separately in order to avoid errors.

Option 4: Let RTI Connext handle the entire rtps_instance_id field:

participant_qos.wire_protocol.rtps_auto_id_kind = DDS_RTPS_AUTO_ID_FROM_MAC;
participant_qos.wire_protocol.rtps_host_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_app_id = DDS_RTPS_AUTO_ID;
participant_qos.wire_protocol.rtps_instance_id = DDS_RTPS_AUTO_ID;

NOTE: If you are using DDS_RTPS_AUTO_ID_FROM_MAC as rtps_auto_id_kind and you decide to manually handle the rtps_instance_id field, you must ensure that both parts are non-zero (otherwise RTI Connext will take responsibility for them). RTI recommends that you always specify the two parts separately in order to clearly show the difference.

Field Documentation

◆ participant_id

DDS_Long DDS_WireProtocolQosPolicy::participant_id

A value used to distinguish among different participants belonging to the same domain on the same host.

Determines the unicast port on which meta-traffic is received. Also defines the default unicast port for receiving user-traffic for DataReaders and DataWriters (can be overridden by the DDS_DataReaderQos::unicast or DDS_DataWriterQos::unicast).

For more information on port mapping, please refer to DDS_RtpsWellKnownPorts_t.

Each DDS_DomainParticipant in the same domain and running on the same host, must have a unique participant_id. The participants may be in the same address space or in distinct address spaces.

A negative number (-1) means that RTI Connext will automatically resolve the participant ID as follows.

  • RTI Connext will pick the smallest participant ID based on the unicast ports available on the transports enabled for discovery.
  • RTI Connext will attempt to resolve an automatic port index either when a DomainPartcipant is enabled, or when a DataReader or DataWriter is created. Therefore, all the transports enabled for discovery must have been registered by this time. Otherwise, the discovery transports registered after resolving the automatic port index may produce port conflicts when the DomainPartcipant is enabled.

[default] -1 [automatic], i.e. RTI Connext will automatically pick the participant_id, as described above.

[range] [>= 0], or -1, and does not violate guidelines stated in DDS_RtpsWellKnownPorts_t.

See also
DDS_Entity_enable()
NDDS_Transport_Support_register_transport()

◆ rtps_host_id

DDS_UnsignedLong DDS_WireProtocolQosPolicy::rtps_host_id

The RTPS Host ID of the domain participant.

A specific host ID that is unique in the domain.

[default] DDS_RTPS_AUTO_ID. The default value is interpreted as follows:
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_IP, the value will be interpreted as the IPv4 address of the first up and running interface of the host machine.
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_MAC, the value will be interpreted as the first 32 bits of the MAC address assigned to the first up and running interface of the host machine.
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_UUID, the value will be the first 32 bits of the GUID prefix assigned by the UUID algorithm.

[range] [0,0xffffffff]

◆ rtps_app_id

DDS_UnsignedLong DDS_WireProtocolQosPolicy::rtps_app_id

The RTPS App ID of the domain participant.

A participant specific ID that, together with the rtps_instance_id, is unique within the scope of the rtps_host_id.

If a participant dies and is restarted, it is recommended that it be given an app ID that is distinct from the previous one so that other participants in the domain can distinguish between them.

[default] DDS_RTPS_AUTO_ID. The default value is interpreted as follows:
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_IP the value will be the process (or task) ID.
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_MAC the value will be the last 32 bits of the MAC address assigned to the first up and running interface of the host machine.
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_UUID, the value will be the middle 32 bits of the GUID prefix assigned by the UUID algorithm.

[range] [0,0xffffffff]

◆ rtps_instance_id

DDS_UnsignedLong DDS_WireProtocolQosPolicy::rtps_instance_id

The RTPS Instance ID of the DDS_DomainParticipant.

This is an instance-specific ID of a participant that, together with the rtps_app_id, is unique within the scope of the rtps_host_id.

If a participant dies and is restarted, it is recommended that it be given an instance ID that is distinct from the previous one so that other participants in the domain can distinguish between them.

[default] DDS_RTPS_AUTO_ID. The default value is interpreted as follows:
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_IP, a counter is assigned that is incremented per new participant. For VxWorks-653, the first 8 bits are assigned to the partition id for the application.
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_MAC, the first 24 bits are assigned to the application/task identifier and the last 8 bits are assigned to a counter that is incremented per new paricipant.
If DDS_WireProtocolQosPolicy::rtps_auto_id_kind is equal to DDS_RTPS_AUTO_ID_FROM_UUID, the value will be the last 32 bits of the GUID prefix assigned by the UUID algorithm.

[range] [0,0xffffffff] NOTE: If you use DDS_RTPS_AUTO_ID_FROM_MAC as rtps_auto_id_kind and you decide to manually handle the rtps_instance_id field, you must ensure that both the two parts are non-zero, otherwise the middleware will take responsibility for them. We recommend that you always specify the two parts separately in order to avoid errors. (examples)

◆ rtps_well_known_ports

struct DDS_RtpsWellKnownPorts_t DDS_WireProtocolQosPolicy::rtps_well_known_ports

Configures the RTPS well-known port mappings.

Determines the well-known multicast and unicast port mappings for discovery (meta) traffic and user traffic.

[default] DDS_INTEROPERABLE_RTPS_WELL_KNOWN_PORTS

◆ rtps_reserved_port_mask

DDS_RtpsReservedPortKindMask DDS_WireProtocolQosPolicy::rtps_reserved_port_mask

Specifies which well-known ports to reserve when enabling the participant.

Specifies which of the well-known multicast and unicast ports will be reserved when the DomainParticipant is enabled. Failure to allocate a port that is computed based on the DDS_RtpsWellKnownPorts_t will be detected at this time, and the enable operation will fail.

[default] DDS_RTPS_RESERVED_PORT_MASK_DEFAULT

◆ rtps_auto_id_kind

DDS_WireProtocolQosPolicyAutoKind DDS_WireProtocolQosPolicy::rtps_auto_id_kind

Kind of auto mechanism used to calculate the GUID prefix.

[default] DDS_RTPS_AUTO_ID_FROM_UUID

◆ compute_crc

DDS_Boolean DDS_WireProtocolQosPolicy::compute_crc

Adds RTPS CRC submessage to every message when this field is set to DDS_BOOLEAN_TRUE.

The computed CRC covers the entire RTPS message excluding the RTPS header.

[default] DDS_BOOLEAN_FALSE

◆ check_crc

DDS_Boolean DDS_WireProtocolQosPolicy::check_crc

Checks if the received RTPS message is valid by comparing the computed CRC with the received RTPS CRC submessage when this field is set to DDS_BOOLEAN_TRUE.

DDS_WireProtocolQosPolicy::compute_crc must be enabled at the publishing application for validating the message at the subscribing application.

[default] DDS_BOOLEAN_FALSE