The Oracle and MS DTC two-phase commit mechanisms are similar in operation. In the first phase of a SQL Server two-phase commit, the transaction manager requests each enlisted resource manager to prepare to commit. If any resource manager cannot prepare, the transaction manager broadcasts an abort decision to everyone involved in the transaction.
If all resource managers can successfully prepare, the transaction manager broadcasts the commit decision. This is the second phase of the commit process. While a resource manager is prepared, it is in doubt about whether the transaction is committed or aborted. MS DTC keeps a sequential log so that its commit or abort decisions are durable. If a resource manager or transaction manager fails, they reconcile in-doubt transactions when they reconnect.