Question E2D08:
What type of packet frame is used to transmit APRS beacon data?  

Choices:  
A: Acknowledgement  
B: Burst  
C: Unnumbered Information  
D: Connect    

Correct Answer is  C: Unnumbered Information  

To transmit APRS beacon data, AX.25 uses an Unnumbered Information (UI) frame.

Why C (Unnumbered Information) is correct
- APRS is designed for connectionless, one-to-many distribution (beacons, position reports, weather, telemetry).
- AX.25 UI frames are unconnected U-frames that carry payload without establishing a link or requiring link-layer acknowledgements.
- APRS digipeaters repeat UI frames along the specified path (e.g., WIDE1-1,WIDE2-1).

Why the others are incorrect
- A: Acknowledgement
  - AX.25 acknowledgements are Supervisory (S) frames (e.g., RR, RNR, REJ) used in connected mode.
  - While APRS messages can include application-level acks, the link-layer frame carrying them is still a UI frame, not an AX.25 acknowledgement frame.
- B: Burst
  - “Burst” is not an AX.25 frame type; it describes a transmission style, not a protocol frame.
- D: Connect
  - AX.25 connection establishment uses U-frames like SABM/UA for connected mode.
  - APRS beacons do not establish connections; they use unconnected UI frames.

Rules of thumb
- If it’s a beacon or broadcast-like payload (APRS, telemetry, bulletins): use AX.25 UI frames.
- Connected, reliable streams use I-frames with S-frame acknowledgements; APRS beacons are not in this category.