S4-260018 - AI Summary

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

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LS Reply on IMS Voice over NB-IoT NTN Connected to EPC

Document Information

  • Source: SA1
  • To: SA2
  • CC: RAN2, SA4, CT1, SA3, RAN1
  • Response to: S2-2507636
  • Meeting: SA1 #112 (17-21 Nov 2025, Dallas, USA)
  • Document Number: S1-254508

Overall Description

This is a reply LS from SA1 responding to SA2's inquiry regarding requirements for IMS voice over NB-IoT NTN connected to EPC.

SA2's Question

SA2 asked SA1 to confirm whether the following are required for IMS voice over NB-IoT NTN:
1. Support for more than one IMS voice call
2. Support for DTMF (Dual-Tone Multi-Frequency)

SA1's Response

SA1 provides the following clarifications:

Multiple Simultaneous IMS Voice Calls

  • Not required in this Release
  • Support for more than one simultaneous IMS voice call is explicitly excluded from the requirements

DTMF Support

  • Required for IMS voice over NB-IoT NTN
  • Dual-Tone Multi-Frequency (DTMF) support must be included

Technical Contribution

The technical contribution consists of:
- A clarification CR to TS 22.261 (CR 0852) that captures these requirements
- The CR is attached to formalize these decisions in the specifications

Action to SA2

SA2 is requested to take the above clarifications into account in their work on IMS voice over NB-IoT NTN connected to EPC.

Document Information
TDoc:
S4-260018
Source:
SA1
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
Original LS: S1-254508
Cc: RAN2, SA4, CT1, SA3, RAN1
To: SA2
Contact: Andrijana Brekalo
Uploaded: 2026-01-21T09:41:08.520000
Contact ID: 91743
TDoc Status: noted
Reservation date: 21/01/2026 09:33:55
Agenda item sort order: 7