There are a number of transaction protocols that support two-phase commit. Most commercial transaction systems use proprietary protocols internally, but there are also several standard protocols (for some sense of the word "standard") - these include OSI TP, OMG OTS and TIP.
Microsoft have said that their transaction monitor, MTS, will support TIP. Several existing transaction monitor products now support OTS, but Microsoft are very unlikely to.
Basic, non-transactional, interworking between Microsoft COM (aka DCOM, COM+) and CORBA is specified in the CORBA specification and implemented in several bridge products. The specification defines how the operations (methods) and their parameters are mapped from one domain to the other, allowing a client in one world to use a server in the other. However, if these operations are part of an atomic transaction, as well as communicating the application messages, the commitment messages must be passed across as well. This cannot be done straight-forwardly by the COM/CORBA bridge.
However, support for the TIP protocol in MTS opens up a way of sending the commitment messages. Our "TIPOTS" bridge interfaces between OTS and TIP, mapping the commitment signals between the two protocols. As shown in the diagram, for the application path, we interpose two proxies either side of a COM/CORBA bridge. The "client-side proxy" acts (within the COM world) as a transactional server, receiving a method invocation with an implicit transaction context. It asks the TIP implementation within MTS for the TIP URL that corresponds to the transaction and adds this as an extra parameter on a COM call with no implicit transaction context to the gateway. On the CORBA side, a "server-side proxy" removes the TIP URL and passes it to TIPOTS. TIPOTS uses the TIP protocol to link the transaction up to MTS and creates a subordinate coordinator in the OTS. This generates an OTS transaction context, which is passed back to the server, which can then invoke the target server with an implicit transaction context. Assuming the application exchange completes successfully, the client will at some stage initiate commitment, which is propagated through MTS, across the TIP connection to TIPOTS and into OTS.
TIPOTS is in fact bi-directional, and the whole diagram can be swapped round, with a CORBA/OTS client and a COM/MTS server.
Although so far we have only used TIPOTS with converted COM/CORBA calls, it could also be used with a CORBA-based implementation of some other protocol (perhaps XML-based) to support the use of TIP with that protocol.