5G Signalling Radio Bearers (SRBs)

As we delve deeper into the world of 5G, it’s essential to understand the different Signalling Radio Bearers (SRBs) that play a critical role in the transmission of RRC and NAS messages. Here’s a quick overview of the various SRBs and their specific functions:

1. SRB0: – Used for RRC messages via the CCCH logical channel, excluding SRB0 of L2 U2N Remote UE.
2. SRB1: – Handles RRC messages (including piggybacked NAS messages) and NAS messages before SRB2 establishment, via DCCH logical channel, excluding SRB1 of L2 U2N Remote UE.
3. SRB2: – For NAS messages and RRC messages with logged measurement info, using DCCH logical channel; lower priority than SRB1 and configured post-AS security activation, excluding SRB2 of L2 U2N Remote UE.
4. SRB3: – Dedicated to specific RRC messages when UE is in (NG)EN-DC or NR-DC, using DCCH logical channel.
5. SRB4: – For RRC messages including application layer measurement reports, using DCCH logical channel; lower priority than SRB1 and configured by the network post-AS security activation.
6. SRB5: – For RRC messages with application layer measurement reports, using DCCH logical channel; lower priority than SRB1 and SRB3, configured by the SN serving the SCG when the UE is in NR-DC, post-AS security activation.

Understanding these SRBs is crucial for telecom professionals as they enhance network efficiency and performance, ensuring seamless communication in 5G networks.