This following is a short description about the error message of PPP:

1. PPPoE server not found
    This message occurs only if the PPPoE fail in the PPPoE discovery stage.

2. LCP no response
    This message can occurs for both PPPoA and PPPoE. In the PPP Initialization
    phase, the PPP client of the CPE will keep sending out LCP Conf-Req packet.
    This message shows up if the PPP client gets no response and the LCP Conf-Req 
    is timed-out.

3. LCP fail
    This message occurs if both end of the PPP connection can not reach an 
     agreement about the option negotiation.

4. Authentication fail
    This message occurs if the user fails to be authenticated by the other end of the 
    PPP connection. 

5. IPCP fail
    The original idea is to notify user if there is anything wrong about the IPCP 
    negotiation. However, this will not  happen, since we don't insist on any 
    IPCP option.

6. Idle time expired
    This message occurs if the idle time of the connect-on-demand timer is expired.
    In other words, if there are not any outgoing packet originated from the CPE for
    pre-configured "idle time". The connection will be dropped, and this message 
    will occur.

7. Keep-alive timer expired
    If the other end of the PPP connection stop replying the LCP echo request packet 
    for 30 seconds. The PPP connection will be dropped, and this message will occur. 

8. User Abort
    This message occurs if the user hit the "Disconnect" button from the web.

9. Peer abort
    The original idea of this message is to notify the user if the PPP connection is dropped
    by the other end of the PPP connection. However, I have only taken care of the PADT 
    packet (for PPPoE). Which means, this only works for PPPoE. I will handle 
    "LCP Terminate Request" packet in the next version. Then we can take care of the 
    PPPoA too.

10.Physical Layer fail
    Honestly, the feature is not completed yet. We do have plan to add this message. (Next version)
    The idea is to notify the user if the ADSL line is dropped. Then we do not need to wait 
    for 30 seconds until the keep-alive timer expired.