Protocol States

In STP, a process may execute many concurrent transactions. Each transaction is in one of the following states:

null

A transaction is in the null state until the initialization exchange is completed. In our model, this is the starting state for all transactions.

sending, receiving

A transaction which has been successfully initialized and is currently active (its processes are currently exchanging messages) will be either in the sending or receiving states.

ready

When a process wishes to commit a transaction, the transaction enters the ready state. This signifies that data transfer is over. Note that only one process (the one that tries to commit the transaction) will enter this state.

committed

If both processes agree to end the transaction successfully, the transaction will enter the committed state, a terminal state.

aborted

The other terminal state for a transaction is the aborted state. This signifies that a transaction failed for some reason.