Unlike CORBA, the OMG DDS specification does not yet define a common wire protocol as it did with “IIOP”. Such a spec. is under development, is almost final, and is called RTPS. Therefore DDS implementations may presently support whatever they feel is appropriate.

OpenDDS supports "one to one" (point to point), and "one to many" (multicast) styles of publishing. In the case of transports it presently supports TCP/IP (which is inherently reliable, for point to point), and UDP.  Both Multicast and Reliable Multicast are offered over UDP.

The hallmark of many real-time publish/subscribe systems is a transport which is very particular to the problem domain. Different industries already have existing transports, such as factory automation, financial trading systems, defensive systems sensors (sonar, IR, radar), etc. Many of these domains have transports combined with a higher level protocol. These legacy systems must be accommodated.

OpenDDS separates the transport from the higher level protocols by means of an extensible transport framework (ETF). The diagram below shows the ETF aspects of the architecture.

OpenDDS’ ETF is non standard because there is presently no standard. This has minimal impact on a DDS developer as transport issues are transparent to them.  The ETF only has to support a transport once and all developers can leverage it. A similar approach is used within TAO and is called “Pluggable Protocols”.