In computer networking, a wire protocol refers to a way of getting data from point to point: A wire protocol is needed if more than one application has to interoperate. It generally refers to protocols higher than the physical layer
The purpose and scope of the Data-Distribution Service Interoperability (DDSI) Wire Protocol is to ensure that applications based on different vendors’ implementations of DDS can interoperate. The protocol was standardized by the OMG in 2008, https://www.omg.org/spec/DDSI-RTPS/About-DDSI-RTPS/, and was designed to meet the specific requirements of data-distribution systems.
Its full name is “The Real-time Publish-Subscribe Wire (RTPS) Protocol DDS Interoperability (DDSI) Wire Protocol Specification”. Thus you can see that the protocol used by the standard is the RTPS, while the standard itself is often called DDSI. The two are sometimes used interchangeably
The best way is to refer to them together as DDSI-RTPS.