Transport Aliases

In order to use a transport plugin instance in a Connext DDS application, it must be registered with a DomainParticipant using the register_transport() operation (Installing Additional Builtin Transport Plugins with register_transport()). register_transport() takes a pointer to the transport plugin instance, and in addition allows you to specify a sequence of "alias" strings to symbolically refer to the transport plugin. The same alias strings can be used to register more than one transport plugin.

Multiple transport plugins can be registered with a DomainParticipant. An alias symbolically refers to one or more transport plugins registered with the DomainParticipant. Pre-configured builtin transport plugin instances can be referred to using preconfigured aliases.

A transport plugin's class name is automatically used as an implicit alias. It can be used to refer to all the transport plugin instance of that class.

You can use aliases to refer to transport plugins in order to specify:

• Transport plugins to use for discovery (see enabled_transports in DISCOVERY QosPolicy (DDS Extension)), and for DataWriters and DataReaders (see TRANSPORT_SELECTION QosPolicy (DDS Extension)).
• Multicast addresses on which to receive discovery messages (see multicast_receive_addresses in DISCOVERY QosPolicy (DDS Extension)), and the multicast addresses and ports on which to receive user data (DDS_DataReaderQos::multicast).
• Unicast ports used for user data (see TRANSPORT_UNICAST QosPolicy (DDS Extension)) on both DataWriters and DataReaders.
• Transport plugins used to parse an address string in a locator.

A DomainParticipant (and its contained entities) will start using a transport plugin after the DomainParticipant is enabled (see Enabling DDS Entities). An entity will use all the transport plugins that match the specified transport QoS policy. All transport plugins are treated uniformly, regardless of how they were created or registered; there is no notion of some transports being more "special" that others.

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