With ISDN30 (DASS) each channel can individually be assigned a single number or a DDI range in multiples of 10. The maximum allowed is dependant on exchange capacity.
Similarly, a group of several channels can be assigned a single number or a DDI range.
You can stack up to 5 DDI ranges on any channel or group of channels as long as the group is the same (i.e. you can’t have 1 range over 5 channels and another layer over 10 channels). Each group of channels is treated like a totally separate circuit and what you do to one channel in the group has to apply to them all.
Please note: You cannot 'stack' single numbers.