5G • RAN
Msg4
Contention Resolution (Msg4 / RRC Setup)
Downlink transmission on PDSCH resolving random access collisions between multiple UEs.
Technical Explanation
If multiple UEs transmitted the same preamble in Msg1, they decode the same RAR and transmit Msg3. The gNodeB resolves contention in Msg4 by echoing back the exact UE Contention Resolution Identity of the winning UE. The winning UE promotes its TC-RNTI to C-RNTI; losing UEs abort and restart random access.
Key Functions
- Resolves collision between UEs that transmitted identical preambles
- Echoes winning UE Contention Resolution Identity in MAC CE
- Promotes Temporary C-RNTI (TC-RNTI) to permanent C-RNTI
Specifications
3GPP TS 38.213, TS 38.321
Interfaces
Uu
Related 5G Concepts
Want to memorize 5G concepts like this one?
Study it with SuperMemo SM-2 spaced repetition flashcards.