com.dalsemi.tininet.ppp
Interface PPPEventListener

public interface PPPEventListener

extends EventListener

Propagates PPPEvents.

It is easiest to understand the operation of PPP as a Finite State Machine (FSM). Note that there are actually two Finite State Machines at work here. The true PPP FSM that is implemented as part of the network stack beneath the IP module and the high level state machine implemented by a PPPEventListener whose state transitions are driven by events generated by the PPP deamon thread and method invocations on a PPP object. The PPP FSM is more complex than the event listener FSM and includes several additional states. For the most part the arcane details of native implementation are hidden from the application developer by the PPP class. The purpose of the PPPEventListener interface is to provide a mechanism to drive a much simpler, higher level state machine that gives the application an opportunity to control the physical data link, user authentication and handling of error information.

After creating a new PPP object the FSM is in the INIT state. At this point there is no PPP traffic traveling across the physical link. To transition to the STARTING state the owner of the PPP object invokes the PPP.open method.

The STARTING state provides the application with a chance to intialize the physical data link, a serial port object. Intialization of the physical link can be as simple as openeing the port and setting the speed and bit counts or as complicated as initializing a modem and initiating or accepting a call. Once the physical layer has been initialized and the application is prepared to start PPP link negotiation the application invokes the PPP.up method passing a serial port object as the argument. Once the serial port reference is passed to PPP it assumes exclusive access to the serial port. At this point PPP attempts to bring up the link. If any error occurs during the link negotiation phase PPP will issue a STOPPED event at which point the user application can examine the error code associated with the STOPPED event.

Most errors are fatal with the exception of timeouts. In the event of a timeout the user application can re-envoke the ppp.UP method. Error codes and thier descriptions can be found in the PPP.event class documentation.

Once the initial negotiation has completed and if this peer has been configured to request authentication from the remote peer an AUTHENTICATION_REQUESTED event will be generated when the remote peer presents it's authentication password and username. After the application has examined the authentication infromation the application then invokes PPP.authenticate with an argument of true to signal the lower level FSM that link negotiation can continue or with and argument with false argument indicating that link negotiation should be terminated.

When link negotiation is successfuly completed an UP event is generated at which point the application should add the PPP interface to the network interface table by invoking the PPP.addInterface() method.

Figure1. PPP "client/server" FSM Diagram

                  +-----------+
                  |           |
                  |   INIT    |
                  |           |
                  +-----------+
                        |
                        | open()
                        V
                  +-----------+
          open()  |           |       up()
       +--------->|   START   |------------------OR---------------------+
       |          |           |                  |                      |
       |          +-----------+                  | "server" operation   |
       |                |                        V with authentication  |
 +-----------+          |                  +-----------+                |
 |           |          | Link             |           |                |
 |  CLOSED   |          | Negotiation      |   AUTH    |                |
 |           |          | Error            |           |                |
 +-----------+          |                  +-----------+                |
       ^                |                    |      |                   |
       |                V                    |      |     "server" or   |
       |          +-----------+              |      |      "client"     |
       |  close() |           |              |      |      operation    |
       +----------|  STOPPED  |<-------------+      |      with out     |
       |          |           | authenticate(false) |    authentication |
       |          +-----------+                     |                   |
       |                ^                           |                   |
       |                | remote termination        |                   |
       |                |                           |                   |
       |          +-----------+ authenticate(true)  |                   |
       |  close() |           |<--------------------+                   |
       +----------|    UP     |                                         |
                  |           |<----------------------------------------+
                  +-----------+
 

See Also:

PPP, PPPEvent

Method Summary

void	pppEvent(PPPEvent ev) Propagates a PPPEvent event.

Method Detail

pppEvent

public void pppEvent(PPPEvent ev)

Propagates a PPPEvent event.