This phase of the Simple Discovery Protocol is performed by the Simple Endpoint Discovery Protocol (SEDP).
During the Endpoint Discovery phase, Connext DDS matches DataWriters and DataReaders. Information (GUID, QoS, etc.) about your application’s DataReaders and DataWriters is exchanged by sending publication/subscription declarations in DATA messages that we will refer to as publication DATAs and subscription DATAs. The Endpoint Discovery phase uses reliable communication.
As described in Discovery Implementation, these declaration or DATA messages are exchanged until each DomainParticipant has a complete database of information about the participants in its peers list and their entities. Then the discovery process is complete and the system switches to a steady state. During steady state, participant DATAs are still sent periodically to maintain the liveliness status of participants. They may also be sent to communicate QoS changes or the deletion of a DomainParticipant.
When a remote DataWriter/DataReader is discovered, Connext DDS determines if the local application has a matching DataReader/DataWriter. A ‘match’ between the local and remote entities occurs only if the DataReader and DataWriter have the same Topic, same data type, and compatible QosPolicies (which includes having the same partition name string, see PARTITION QosPolicy). Furthermore, if the DomainParticipant has been set up to ignore certain DataWriters/DataReaders, those entities will not be considered during the matching process. See Ignoring Publications and Subscriptions for more on ignoring specific publications and subscriptions.
This ‘matching’ process occurs as soon as a remote entity is discovered, even if the entire database is not yet complete: that is, the application may still be discovering other remote entities.
A DataReader and DataWriter can only communicate with each other if each one’s application has hooked up its local entity with the matching remote entity. That is, both sides must agree to the connection.
Discovery Implementation describes the details about the discovery process.
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