Reply LS on the RAN simulation assumptions for ULBC
This document is SA2's reply to SA4's liaison statement requesting clarification on RAN simulation assumptions for Ultra-Low Bandwidth Communication (ULBC), specifically regarding protocol overhead considerations for IMS voice over NB-IoT NTN via GEO satellite.
SA4 requested SA2 and RAN2 to comment on different protocol stack options and their respective packet overhead, including:
- User Plane (UP) vs Control Plane (CP) options
- IP vs Non-IP PDN types
- Overall packet overhead including RTP/UDP/IP with RoHC, PDCP, RLC, and MAC headers
- Potential AS layer optimizations
SA2 Response:
- SA2 has documented multiple alternative solutions in TR 23.700-19 for "Key Issue #1: Support of IMS voice call over NB-IoT NTN via GEO satellite connecting to EPC"
- These solutions cover various options for:
- CIoT EPS Optimisation (User Plane or Control Plane)
- PDN type selection (IP or non-IP)
- No conclusion has been reached yet on the solutions for Key Issue #1
- Final protocol overhead depends on the selected solutions
- Conclusions and estimated overhead will be provided later
- Expected completion: December 2025 (SA#110) per FS_5GSAT_Ph4_ARC SID
SA4 specifically questioned whether a 1-byte MAC header overhead assumption is realistic.
SA2 Response:
- SA2 defers this question to RAN2 for proper assessment
- SA2 requests RAN2 to provide feedback on expected overhead for:
- PDCP
- RLC
- MAC
SA2 requests SA4 to take the provided answers into account for their ongoing work on ULBC RAN simulation assumptions.