Hello 5G Experts.
In IAB feature in 5G, why don’t we cascade DU component?
We are like just cascade (partitioning CU to distributed another CU units)
Any idea why we not do same for DU?
Purpose of IAB is to be used where traditional backhaul isn’t possible.
He wanted to say that IAB is used where fiber to sites is not available!
Yes… so why not also partitioning DU components in IAB feature?
We just deal with CU components to distribute them, but not distribute DU components. Why not?
As we can always use fiber, don’t we?
I mean why there would be sites without availability of using fiber if we always can use fiber cables? Irrelative to site area.
No! There are places that do NOT have fiber available, due to several reasons… So you can not use!
Why? We always have fiber cables, don’t we?
I mean fiber cables found at any place/site.
Not every place. Think of Mount Everest. It may be easier to do IAB rather than installing Fibre on Mount Everest! 
Thanks dear, now I understand.
But another query: why are we cascading and distributing just DU units (DU components) in the IAB node and not also the CU components?
I mean, we are like just having CU+DU in the donor (regular gNB) and its childs (IAB nodes) are having DU component distributed and not CU. Why not also CU distributed?
See please image below for more illustration:
I am not an Expert on IAB but one could think of having centralised CU for better management of CU’s either with or without Cloud.
There also could space restriction in remote sites where traditional backhaul is not possible so IAB is considered.
I’m with you. But why not centralized DU and distributed CU units?
Why do we prefer to centralize CU and distribute DU components? An not opposite?
What trade-off I’m gaining from?
We are like spliting DUs components but CUs not… here is my confusion. 
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Because there can be 1 CU connected to multiple DU , but you don’t have many CU connected to 1 DU.
CU processes higher layer protocols - RRC and PDCP , that are not realtime hence can be centralized. DU process lower layers example , MAC that is realtime , hence transmission delay cannot be above a limit due to HARQ. Therefore cannot be arbitrarily centralized.
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