View HARQ re-transmitted packets on packet capture

[praghur]

Hello.

Is there is a way to obtain a packet capture that shows me the original and re-transmitted packets using HARQ? I enabled the MAC layer packet capture using:

  mac_filename: /tmp/gnb_mac.pcap       # Optional TEXT (/tmp/gnb_mac.pcap). Path for MAC PCAPs.
  mac_type: udp                         # Optional TEXT (udp). Sets the MAC PCAP pcap type. Supported: [DLT or UDP].
  mac_enable: false                     # Optional BOOLEAN (false). Enable/disable MAC packet capture. Supported: [false, true].

But, the packet capture so recorded does not show which packets are original packets and which ones are the re-transmitted ones. Please see attached MAC layer pcap files. I am using UM in RLC but re-transmissions are enabled in the MAC layer.

Please let me know if there is a way to obtain this. Thanks in advance.
gnb1_mac.zip

[Nuradioconcepts]

I don't think you can get this information from the PCAP, though if you have debugging turned on in the logs you can associated the scheduler information to a message that is being re-transmitted when the nrtx flag is incremented

2023-12-20T13:31:00.723738 [SCHED ] [D] [ 416.10] Slot decisions cell=0 t=10us (1 PDSCH, 0 PUSCHs):

• DL PDCCH: rnti=0x4601 type=c-rnti cs_id=1 ss_id=2 format=1_1 cce=0 al=4 dci: h_id=0 ndi=0 rv=2 mcs=28 dai=0
• UE PDSCH: ue=0 c-rnti=0x4601 h_id=0 rb=[0..1) symb=[2..14) tbs=92 mcs=28 rv=2 nrtx=1 k1=7

2023-12-20T13:31:00.733629 [SCHED ] [D] [ 417.10] Slot decisions cell=0 t=7us (1 PDSCH, 0 PUSCHs):

• DL PDCCH: rnti=0x4601 type=c-rnti cs_id=1 ss_id=2 format=1_1 cce=0 al=4 dci: h_id=0 ndi=0 rv=3 mcs=28 dai=0
• UE PDSCH: ue=0 c-rnti=0x4601 h_id=0 rb=[0..1) symb=[2..14) tbs=92 mcs=28 rv=3 nrtx=2 k1=7

I use the Transport Block Size (TBS) and time to correlate that to the PCAP by checking the size of the MAC packet (where if you select the MAC header it will show the size in bytes in the bottom left)