What the different transaction options ?

What the different transaction options ?
We can specify transaction in 3 ways in WCF:- 

TransactionFlowOption.NotAllowed 
This is a default option. Using this option no transaction will be propagated across the binding. If any client attempts to call the WCF service in a transaction it will be ignored for this option. 

TRANSACTIONFLOWOPTION.ALLOWED 
This option specifies that client can call this WCF service in a transaction. It’s not compulsory that the service needs to be called in a transaction. You can call without the transaction also.

TransactionFlowOption.Mandatory 
This option specifies that client must call the WCF service in a transaction mode. If the WCF service is called without transaction, ‘FaultException’ will be raised.