Root ID in CFRA Rach process

5G NR
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1

In CFRA, a dedicated Preamble ID is allocated to the UE as part of the RRC ReConfiguration message.

My confusion is how/where does the UE acquire info about the root ID, especially in NSA.

As I understand it, for a UE to generate the preamble, it would actually need root ID and Ncs. I did refer to TS 38.331 to understand the Rach-ConfigDedicated structure (?).

I could locate the ZcZ element and Preamble ID message… but not the root ID!

Indeed I may be missing something.
It would be really helpful if someone kindly clear my confusion.

2

In the serving cell config common, network includes the RACH config common. UE gets all RACH related parameters from here and uses it along with the preamble id and derives final RACH sequence.

3

It’s clear now. Thanks Pradeep