52.10.1 Transport Locators
This section provides information about the format of the locators associated with the Real-Time WAN Transport. For general information about RTPS locators, see Chapter 26 Discovered RTPS Locators and Changes with IP Mobility.
An RTPS locator is an address at which a DDS endpoint (DataWriter or DataReader) can be reached. Default locators for discovery endpoints and user data endpoints are exchanged with the Participant Announcement (PA).
An RTPS locator consists of a transport Class ID, an address of 128 bits, and a logical port called the RTPS port, as shown in Figure 52.16: RTPS Locator.
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DDS_Long class_id |
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DDS_UnsignedLong rtps_port |
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DDS_Octet address[16] |
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The locators for Real-Time WAN Transport use the following mapping:
Figure 52.17: RTPS WAN Locator
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DDS_Long class_id |
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DDS_UnsignedLong rtps_port |
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Flags |
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DDS_Octet UUID[9] |
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public_port |
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DDS_Octet public_ip_address[4] |
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Flags has the following format: x|x|x|x|x|B|P|U
The B flag indicates whether the locator is unidirectional or bidirectional. Bidirectional locators can send/receive RTPS traffic. Unidirectional locators can only receive RTPS traffic. If the B flag is set, the P flag must be set, too. Locators with the B flag set are called BIDIRECTIONAL locators.
The P flag indicates that the locator contains a public IP address and public port where a DDS endpoint can be reached. public_ip_address contains the public IP address, and public_port contains the public UDP port. The public UDP port is always used to receive data, and, if the B flag is set, it is also used to send data. Locators with the P flag set are called PUBLIC locators.
The U flag indicates whether the locator contains a UUID. While this identifier by itself cannot be directly used to reach a DDS endpoint in a DomainParticipant DP1, the UUID can be mapped to a public address by Cloud Discovery Service and other DomainParticipants. Also, a locator can have both the U flag and the P flag, enabled simultaneously. Locators with the U flag set are called UUID locators.
A PUBLIC+UUID locator is a locator in which both the U flag and P flag are set.
Initial peers locators will have the B and P flags set and the U flag unset.
The U flag will be set for locators generated automatically by a DomainParticipant.
The P flag will be automatically set for locators generated for a transport that is configured using the property dds.transport.UDPv4_WAN.builtin.public_address. The flag will be also be set by Cloud Discovery Service when generating locators that contain the service reflexive address for a UUID locator.