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12_how_to_configure_by_pcap_file.md

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12 Configure rs_driver by PCAP file

12.1 Overview

By PCAP files, we can learn what the MSOP/DIFOP packet is like, so as to learn how to configure rs_driver and get point cloud.

Here we use the 3rd party tool WireShark.

About how to capture a PCAP file, please refer to How to pcap PCAP file.

12.2 Format of MSOP/DIFOP

12.2.1 Protocol Layer

MSOP/DIFOP Packet is based on UDP protocol. It includes:

  • Ethernet
  • VLAN（Optional）
  • IP
  • UDP
  • User Layer（Prefix part, Optional）
  • MSOP/DIFOP Packet（Real data）
  • Tail Layer（Suffix part, Optional）

VLAN Layer is optional. It is up to:

  • Whether the LiDAR is on VLAN
  • Capture MOSP/DIFOP packets on phisical NIC or virtual NIC

User Layer is added by the user. User determines its length.

Tail Layer is from the user too. One Example is that Domain Controller of Intelligent Car appends its 4 bytes.

12.2.2 Packet ID

WireShark can parse Ethernet layer,IP layer,UDP layer, etc.

To parse MSOP/DIFOP Packet and User Layer，first locate the ID of MSOP/DIFOP Packet.

To parse MSOP/DIFOP Packet与Tail Layer，first find out the length of MSOP/DIFOP Packet (excludes User Layer and Tail Layer).

The ID and the length of LiDARs is fixed as below.

LiDAR Type Packet Type ID Packet Length
RS16/RS32/RSBP MSOP 55 aa 05 0a 5a a5 50 a0 1248
DIFOP a5 ff 00 5a 11 11 55 55 1248
RS128/RS80/RS48/RSP128/RSP80/RSP48/RSHELIOS/RSHELIOS_16P MSOP 55 aa 05 5a 1248
DIFOP a5 ff 00 5a 11 11 55 55 1248
RSM1/RSM2/RSE1 MSOP 55 aa 5a a5 1210
DIFOP a5 ff 00 5a 11 11 55 55 256

Note: MSOP and DIFOP packets have different IDs, so we can determine which packet is MSOP or DIFOP.

12.3 Steps

Below are the steps to analysis PCAP file.

  • Find out the destination IP address of MSOP/DIFOP Packet。In design of RoboSense LiDAR, MSOP and DIFOP packets always have the same destination IPs.

​ Also find out what address is it? broadcast/multicast/unicast address? If it is multicast, groud_address and host_address are required.

  • Find out the destination port of MSOP/DIFOP packets.

​ Here show a specified type of packet with filter criteria.

​ Here exclude a specified type with filter criteria.

​ Just set filter criteria on msop_port and difop_port.

  • Is there VLAN layer? If Yes,

    • create virtual NIC in case of online LiDAR.

    • set use_vlan=true, in case of PCAP file.

  • Find out the ID bytes first. Is there User Layer? How long is it?

​ If Yes, set user_layer_bytes.

  • Is there Tail Layer ? How long is it?

​ If Yes, set tail_layer_bytes.

12.4 Examples

12.4.1 RS32 - MSOP Packet

Below is a example of RS32 MSOP packet.

  • Destination IP is 192.168.1.102 (labeled by red 1)
  • Destination port is 6699 (labeled by red 2)
  • Length of MSOP Packet is 1248`(labeled by red 3)
  • ID bytes of RS32 MSOP Packet is 55 aa 05 0a 5a a5 50 a0. It is at the beginning (labeled by red 4), so no User Layer here.

12.4.2 RS32 - DIFOP Packet

Below is an example of RS32 DIFOP Packet.

  • Destination IP is 192.168.1.102 (labeled by red 1)
  • Destination port is 7788 (labeled by red 2)
  • Length of MSOP Packet is 1248`(labeled by red 3)
  • ID bytes of DIFOP Packet is a5 ff 00 5a 11 11 55 55. It is at the begining(labeled by red 4), so no User Layer here.

12.4.3 VLAN Layer

Below is an example of VLAN layer. This is a MSOP packet of RSM1.

VLAN Layer is between Ethernet Layer and IP Layer. vlan id is 69.

12.4.4 User Layer

Below is an example of User Layer. This is a MSOP Packet of RSM1.

ID bytes of MSOP Packet is 55 aa 5a a5. There are 16 bytes before it。This is just User Layer.

12.4.5 Tail Layer

Below is an example of User Layer. This is a MSOP Packet of RSM1. The length of MSOP Packet is 1210 bytes, plus bytes of lower laytes 14 + 20 + 8 = 42, and then it should be 1252 bytes. Actually WireShark captures 1256 bytes. These extra 4 bytes are at the tail of MSOP packet(c9 77 8e c3 in the picture). This is Tail Layer.

12.4.6 Unsupported Case

Below is unsupported case with Linux cooked capture(labeled line). It is captured on any NICs, such as tcpdump -i any.

It is not Ethernetprotocol, rs_driverdoesn't accept it.