DL F1-U Packet Loss Rate

5G NR
1

Hi Experts,
as per 3gpp 28.552, V15.3

5.1.3.1.3 DL F1-U Packet Loss Rate
a) This measurement provides the fraction of PDCP SDU packets which are not successfully received at the gNB-DU). It is a measure of the DL packet loss on the F1-U interface. The measurement is optionally split into subcounters per QoS level (mapped 5QI or QCI in NR option 3).
b) SI
c) This measurement is obtained as: 1000000* Number of missing DL GTP sequence numbers (TS 29.281), representing packets that are not delivered to lower layers, of a data radio bearer, divided by Total number of UL GTP sequence numbers (also including missing sequence numbers) of a bearer, starting from the sequence number of the first packet delivered by gNB-CU-UP to gNB-DU until the GTP sequence number of the last packet. Separate counters are optionally maintained for mapped 5QI (or QCI for NR option 3).

Question:

  1. why is division by “total number of UL GTP Seq number” is mentioned while it is DL packet loss rate?
  2. When NRUP loss is already being detected and reported in DL data delivery status and same can be used as F1-U Packet Loss Rate, why 3GPP is adding another measurement w.r.t GTP Seq. Number.

Thanks,