Missing data when recording with tcpdump

Hardware
,
1

Hi all,

I have been trying to record the raw packets of an OS1 sensor using tcpdump. This is the command I use, it’s supposed to capture all the UDP packets with destination port 7502 if even they are fragmented across multiple TCP packets, as seems to be the case:

tcpdump -i ether0 -s 0 -w ‘a.pcap’ -C 500 -W 999999 ‘udp dst port 7502 or (ip[6:2] & 0x1fff !=0)’

But when I try replaying the content in Ouster Studio it shows many vertical sections of missing data in the point cloud, as in the screenshot below.

Screenshot 2025-06-30 at 09.49.33
Screenshot 2025-06-30 at 09.49.333064×1934 917 KB

Some context:

  • This tcpdump recording is being made on a NVIDIA Jetson computer
  • If I record using Ouster Studio on a different computer (Macbook) the problem doesn’t happen. It also doesn’t happen if I see the data from the sensor live on Ouster Studio
  • The json file I use has been extracted with Ouster Studio
  • Hardware: OS1 Rev3.7.1
  • Firmware: 3.1.0

“sensor_info”: {
“prod_line”: “OS-1-128”,
“prod_pn”: “OS1-071-128U-AX”,
“prod_sn”: “122512000511”,
“image_rev”: “ousteros-image-prod-bootes-v3.1.0+20240426041747”,
“build_rev”: “v3.1.0”,
“build_date”: “2024-04-26T02:34:31Z”,
“status”: “RUNNING”,
“initialization_id”: 390073
},

I appreciate any suggestions of what might solve the problem.

2

This seems to be related to packet drop

Check out this post:

3

Yes, it was the packet drop issue.
That issue was able to be greatly improved by increasing the receive buffer of the Ethernet Interface Card, but can hardly be eliminated completely.
The issue, I think, was closely related to the NIC. Because if I used a RJ45-to-USB3.0 converter, no packet drop was observed with the same software.

Best regards