Reply LS on issues related to support of IMS voice over NB-IoT NTN connected to EPC
This LS provides RAN1's response to SA2's question regarding the probability of consecutive packet losses in IMS voice over NB-IoT NTN scenarios.
Question 2 (To RAN1): Can RAN1 provide any data regarding the probability that such number of consecutive packets (e.g., 16 or 64) can be lost or erroneously decompressed? How often such event can occur?
Under the following conditions:
- Line-of-sight maintained for the duration of the call
- No change in large scale parameters (e.g., fixed shadowing)
- Using NTN TDL-C channel model (previously used by RAN1 and SA4 evaluations)
Finding: The probability of having 16 or 64 packets consecutively lost is negligible under typical operating conditions (e.g., up to 10% packet error rate).
When line-of-sight cannot be guaranteed for the duration of the call:
- Intermittent blockage may occur in practice (e.g., according to the land mobile satellite channel model in TR 38.811)
- In this case, the probability of having 16 or 64 packets consecutively lost may not be negligible
Note: RAN1 has not reached consensus on whether to consider this case.
ACTION: RAN1 asks SA2 to take the above information into account.