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6G NAS: CT1 waits on SA2’s modular design

CT1’s 6G NAS study (TR 24.860) will define the protocol a device uses to register, move and set up sessions. Its shape depends on two open SA2 questions: how modular NAS signalling should be, and how NAS messages are routed.

In 60 seconds

  • Study: FS_6G_NAS_CT, one of the first four CT 6G studies approved at CT#111, Fukuoka. Rapporteur Yanchao Kang (vivo).
  • Upstream: SA2 key issue #1, “modular control signalling”, would separate mobility, session and NAS transport.
  • Open at SA#113: NAS routing is one of the architecture issues still disputed.
  • Target: September 2027, like all CT 6G studies.
CTCT1 · TR 24.860

The study

TR 24.860, “Study on NAS protocol for 6G System”, is CT1’s main 6G study. Its rapporteur is Yanchao Kang (vivo). TSG CT approved it at CT#111 in Fukuoka in March 2026, alongside CT4’s control-plane, user-plane and resilience studies. 3GPP’s report of that meeting says All TSG CT studies are targeted to finish in September 2027.

As Stage 3, CT1 designs the messages and procedures for an architecture SA2 defines. Most of the NAS design questions are therefore being settled in SA2 first.

SASA2 · TR 23.801-01

Modular NAS: the SA2 key issue

SA2’s architecture study includes a key issue on modular control signalling. Abhijeet Kumar’s summary of TR 23.801-01 v0.4.0 describes its goal as making NAS modular: introduce new functionalities with minimal or no impact to existing ones. It has two sub-issues:

  • isolate mobility management, session management and NAS transport from each other;
  • let UEs interact with network functions through generic mechanisms, instead of a dedicated message for every new feature.

In 5G, 5GMM and 5GSM are both specified in TS 24.501, and new features usually add information elements to existing messages. A modular 6G NAS would change how CT1 specifies new features in every release after Release 21.

Still open

At SA#113, NAS routing was listed among the contested architecture issues, together with the role of AI agents in connectivity. The 17-operator coalition’s principle that essential connectivity must not depend on AI agent functionality bears directly on what NAS has to carry.

CTCT1 · 5G-Advanced

What CT1 is optimising now

CT1’s current NAS work shows its priorities. In 3GPP Highlights, Qualcomm’s Amer Catovic, Osama Lotfallah and Lena Chaponniere describe two recent enhancements:

  • Control-plane CIoT overhead reduction: a new EMM_TRANSPORT message cuts overhead to 7 octets, 5 of which are security overhead. That is a 46% reduction in connected mode and 64% in idle. It had 26 supporting companies, 7 of them satellite companies. It is an EPS feature and is not supported in 5GS.
  • Faster service recovery: event triggers, such as a new cell or a 10 dB RSRP improvement, stop the fixed back-off timers (T3511 at 10 s, T3502 at 12 min) after patchy coverage. It applies to both 5GS and EPS.

Both address overhead and recovery on constrained or satellite links. The same pressures will shape 6G NAS.

Watch next

  • SA2#178 (November): the architecture decision, including modular signalling and NAS routing.
  • CT1: the first 6G NAS key issues and solutions once SA2’s direction is set.

Sources

The SA2 key-issue description is a third-party summary of TR 23.801-01 v0.4.0. SA#113 items are as reported by 6G Futures.