Cancel behaviour: *) If has got final response, skip cancel because there is nothing to cancel. *) If transaction has got provisional response, send cancel and raise Canceled, terminate transaction. *) If transaction hasn't got provisional response, queue cancel request. If provisional response received, send cancel and raise Canceled, terminate transaction. If final response received, skip cancel because there is nothing to cancel. NOTE: Cancel completes asynchronpusly when transaction haven't got any response !