Backoff Indicator (BI)

Technical Explanation

If the gNodeB detects heavy cell congestion during random access, it inserts a Backoff Indicator (BI) subheader in Msg2 RAR. When UEs fail contention resolution, instead of retrying immediately, they select a random delay uniformly distributed between 0 and the Backoff Value (e.g. up to 960 ms), spreading out retry attempts.

Key Functions

• Mitigates random access congestion during high-density cell events
• Randomizes retry delays between 0 and signaled Backoff Value (up to 960 ms)
• Carried in dedicated MAC PDU subheader of Msg2 RAR