Case 1: nCELL- Femto - TCP DL Low Throughput

Equipment: Ncell-F2240
Version: 5GNR_fa.tdd.fr1.2.3.0_397+Firmware_241.00.2_N78_20230314_v2.5.1
1.Issue Description:
TCP Downlink speed test is low as below.

2.Achieve Network Topology and NE Information

Attention: This networking is special at the beginning, the PC which connects CPE LAN by
cable also connects to AGW by Wifi as a ftp server, but the Wifi bandwidth is only 72Mbit/s
and the

3.Suggested Troubleshooting Methods:
3.1 Check the radio interface environment by pre-scheduling.
3.2 Determine if insufficient dispatch/Low MCS/ low RANK by mac-layer print watching.
3.3 Determine if transmission bandwidth is restricted by UDP testing.
3.4 Configuration parameter check by web check and xml comparation.
3.5 Gather log +User Plane +Signal plane + FAPI log analysis.

4.Troubleshooting Procedures:
4.1 Open DL pre-scheduling and observed full dispatch and good MCS, normal layers.

4.2 DL UDP iperf3 test, speed can reach maximum 400 Mbps.

4.3 Check the configuration parameter and compare, no abnormalities found.
4.4 Original protocol version is 310, upgrade to version 397, but there is no improvement.
4.5 Collect gather log + fapi3+user plane log at gNB, and found lots of TCP out of order and TCP dup. Though appoint the packet length and packet gNodeB received is still bigger than the appointed packet length.

Collect tcpdump from ftp server and User Plane log of gNB at same time, same appearance with above capture.
Collect the tcpdump from ftp server, agw and user plane log of GNB at same time, observe that the packet length of many packets sent by agw are more than 2500, need AGW check the MTU and TCP fragmentation function.

After AGＷ changed the MTU of Ethernet card and enable TCP fragmentation function, the DL TCP speed rate improved to 179Mbps in public internet .

5. Conclusion:
Core Network network card TCP Segmentation offload function were not enabled, the
packet size sent by AGW can’t be handled properly by Femto and dropped.

 Troubleshooting Methods: Download