What is the use of SRB 4 in NR?

Question

We have 3 SRB bearers which is for common and AS and NAS, then why do we need an extra 4th bearer in NR? What is the priority and purpose for this bearer.

Answer 1

In EN-DC, SRB3 can be used for measurement configuration and reporting, to (re-)configure MAC, RLC, physical
layer and RLF timers and constants of the SCG configuration, and to reconfigure PDCP for DRBs associated with the
S-KgNB or SRB3, provided that the (re-)configuration does not require any MeNB involvement.