If there is no free B channel in all the trunks, this is signalized to the user by a second acknowledgment tone, so that he can then insert the call into the ON-hook queue. This way a B channel is reserved for the user. If a B channel is available, this is assigned to the highest priority inserted call/unit.

If a direction (AMO LDAT) is assigned the parameter LATTR with the parameter value ONKQ, the call is inserted into the ON-hook queue.