S4-260023 - AI Summary

Reply LS on issues related to support of IMS voice over NB-IoT NTN connected to EPC

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3GPP Technical Document Summary: Reply LS on IMS Voice over NB-IoT NTN Security

Document Identification

  • Document Number: S3-253797
  • Meeting: SA3#124, Wuhan, China (13-17 October 2025)
  • Release: Rel-20
  • Work Item: FS_5GSAT_Ph4_SEC
  • Type: Reply Liaison Statement

Context

This document is SA3's response to a Liaison Statement from SA2 (S3-253118/S2-2507636) regarding security considerations for IMS voice over NB-IoT NTN (Non-Terrestrial Network) connected to EPC.

Main Technical Contribution

Security Overhead for Voice Media Packets over NAS

Question from SA2 (Question 7):

SA2 asked whether SA3 would accept eliminating the 5 bytes of NAS layer security overhead for voice media packets in the context of:
- Alternative solutions documented in TR 23.700-19
- Support of IMS voice over NB-IoT NTN connected to EPC
- Use of a specific SRB via dedicated EPS bearer for Data over NAS
- Transfer limited to voice media packets only

SA3 Decision:

SA3 rejected the proposal to eliminate the NAS layer security overhead with the following rationale:

  • The majority of companies in SA3 opposed allowing non-integrity protected voice packets to be sent over NAS to the MME
  • No consensus was reached in SA3 to eliminate the 5 bytes of NAS layer security overhead
  • This maintains the integrity protection requirement for voice packets transmitted over NAS

Implications

The decision preserves the existing NAS layer security mechanisms for voice traffic, prioritizing security over the potential bandwidth savings that would result from removing the 5-byte overhead. This is particularly relevant for NB-IoT NTN scenarios where bandwidth efficiency is typically a concern, but SA3 determined that security requirements take precedence.

Action to SA2

SA3 requests SA2 to take this security position into account when finalizing the solutions for IMS voice over NB-IoT NTN connected to EPC.

Document Information
TDoc:
S4-260023
Source:
SA3
Type:
LS in
For:
Information
Original Document:
View on 3GPP
Title: Reply LS on issues related to support of IMS voice over NB-IoT NTN connected to EPC
Agenda item: 5.2
Agenda item description: Other 3GPP groups
Doc type: LS in
For action: Information
Release: Rel-20
Original LS: S3-253797
Cc: RAN2, SA4, CT1, SA1, RAN1
To: SA2
Contact: Andrijana Brekalo
Uploaded: 2026-01-21T14:41:08.737000
Contact ID: 91743
TDoc Status: noted
Reservation date: 21/01/2026 14:31:48
Agenda item sort order: 7