What could be issue of low TCP throughput in DL 5G SA?

5G NR
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22

Transmission you need a tcp dump from gNB to Upf.

23

Working scenario and non working scenario?

24

For non working scenario.

25

Then after collecting it?

26

Check seq numbers and window sizes in wireshark for gtp.

27

What to check here?

And why on cell1 all is fine. Although both are identical in terms of configurations.

28

But cell 1 and cell 2 has a common transmission to Core?

Both qci data.

29

No, each one has its own Core.

30

So different TX backhauls.

And both test udm hss profiles are same.

You just need to check tx perf with gtp tracing.

31

Yes, but same Cores are on with same vendor.

I will take tcp dump, after taking tcpdump to look on sequence number.

So what to check or what do I check here with sequence number?

32

Keep all setting same, just swap the TX bachaul of both Cores.

When you move the TX problem appears again or not?

Sequence numbers are consecutive.

Need to see after tcpsyn it is increasing and receiving ack or not, and for the UE side same the packets sent received ack.

I think your problem is related with Core backhaul.

33

But it’s on another subnets so can’t do that.

Or it’s more complex to go on this suggestion…

By the way the ping on both cell1 cell2 is fine.

From UPF to UE.

Almost same RTT.

34

Yes, but this is only latency.

35

But as said to cell it arrives from upf like 700 Mbps not more.

So cell actually transmit all what it is receiving.

But somehow backhaul has limit to 700 Mbps.

Although udp is fine arrive 950 Mbps.

36

I think backhaul is limited to 1 Gbps and you get 700 only.

37

But it’s fiber. So can be 10G transmit.

Maybe SFP damaged?

38

Could be, not enough data coming from core is typical excuse :slight_smile: in general.

If you have packet losses on tcp no data will come :smiley:

Because your resources will be wasted for retransmission.

Swap the cells sfps if you can’t swap TX backhaul and check problem still exists on the same cell.

Easy.

39

But if there is packet loss, why on udp all is fine?

40

udp is not guaranteed, you don’t send ack.

You don’t know if packet lost or not.

41

So here you are saying to see the ratio of Harq retx on probalamtic cell compared to working cell?