Veins自定义消息扩展文件、AirFrame11p.msg作用及仿真技术问询

Hey there! Let's walk through your questions about Veins step by step—since you've already got the demo up and running, you're halfway there!

1. Which file do I need to extend for custom messages in Veins? #

To add custom messages in Veins, you typically extend the BaseFrame1609_4.msg file (or create a new .msg file that inherits from it) to align with the existing 802.11p/WAVE message structure. Here's a quick breakdown of the process:

• Create a new .msg file (e.g., MyCustomWaveMsg.msg) and import the base message type:

  import veins/modules/messages/BaseFrame1609_4.msg;
  
  message MyCustomWaveMsg extends BaseFrame1609_4 {
      // Add your custom fields here—like int sensorData; string vehicleID;
  }
  

• After compiling your project, OMNeT++ will generate a header file (MyCustomWaveMsg_m.h) that you can include in your application layer code (e.g., your custom TraCIDemo11p subclass).
• Make sure your module's NED file or omnetpp.ini references the new message type so the simulator recognizes it.

2. What's the role of AirFrame11p.msg? #

Think of AirFrame11p.msg as the "wireless envelope" for all messages sent over the 802.11p network in Veins. It defines the frame structure that the physical and MAC layers use to transmit data. Key things it handles:

• Encapsulates upper-layer messages (like WSMs or WSAs) via its encapsulatedMsg field.
• Stores critical wireless transmission parameters: transmission power, data rate, RSSI (received signal strength indicator), frame duration, and more.
• Without this structure, upper-layer messages wouldn't have the necessary metadata to travel over the wireless channel—this is the layer that bridges application-level logic with actual wireless communication.

3. Where are AirFrame11p messages populated for vehicle nodes in the demo? #

Great catch noticing that TraCIDemo11p.cc only deals with WSM/WSA messages! The AirFrame11p encapsulation happens automatically in lower-layer modules, so you don't have to handle it in the application layer. Here's the flow:
When you call sendDown(wsm) in your application code (like in TraCIDemo11p), the message travels through:

1. WaveAppToMac1609_4Interface (handles application-to-MAC layer communication)
2. Mac1609_4 (the 802.11p MAC layer)
3. Finally, the PhyLayer80211p (physical layer) wraps the WSM into an AirFrame11p, fills in all the required wireless parameters (power, rate, etc.), and sends it to the channel.

As for BaseWaveApplLayer::checkAndTrackPacket, that method is just for tracking the status of upper-layer packets (like whether they were received, lost, etc.)—it doesn't touch the AirFrame11p encapsulation process at all.

内容的提问来源于stack exchange，提问作者Ahmad Ahsan