the airport takes control of ALL handling agents that supply deicing and they put everybody in a queue based on your CTOT.
The airport have proved themselves to be no better than the handling agents at managing the process, and why the airport believes that they are more capable than the people who's job de-icing actualy is eludes me. Although, it has been noted on several occasions that certain airline(s) (Those operating the Airbus double deck variety) do tend to get preferential treatment when the airport assumes control of de-icing .