# 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.