5G Standalone Mode Registration-Attach Call Flow

A 5G Stand Alone also know as Option 2, architecture includes 5G UE, gNB and 5G Core Network. In this post we will discuss about 5G SA Registration Call Flow for OTA messages (b/w UE and gNB) and NGAP messages (b/w gNB and 5GC AMF ). In 5G SA mode term Registration is equal to Attach in 4G LTE.

At high level, 5G SA Registration call flow includes following Steps and shown in following figure:

  • Achieving DL/UL sync via SSB decode and RACH Procedure
  • SRB0 establishment with RRC Connection Request
  • Contention Resolution and SRB1 establishment with RRC setup
  • Registration Request
  • NAS Procedures like UE Identity transfer, Authentication and Security
  • AS UE Capability transfer and AS security
  • SRB2 and DRB establishment
  • Registration Complete and PDU session Establishment

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