4.4. Actions

Actions in the automaton are caused by events and typically indicate the transmission of packets and/or the starting or stopping of the Restart timer.

Illegal-Event (-)

This indicates an event that cannot occur in a properly implemented automaton. The implementation has an internal error, which should be reported and logged. No transition is taken, and the implementation SHOULD NOT reset or freeze.

This-Layer-Up (tlu)

This action indicates to the upper layers that the automaton is entering the Opened state.

Typically, this action is used by the LCP to signal the Up event to a NCP, Authentication Protocol, or Link Quality Protocol, or MAY be used by a NCP to indicate that the link is available for its network layer traffic.

This-Layer-Down (tld)

This action indicates to the upper layers that the automaton is leaving the Opened state.

Typically, this action is used by the LCP to signal the Down event to a NCP, Authentication Protocol, or Link Quality Protocol, or MAY be used by a NCP to indicate that the link is no longer available for its network layer traffic.

This-Layer-Started (tls)

This action indicates to the lower layers that the automaton is entering the Starting state, and the lower layer is needed for the link. The lower layer SHOULD respond with an Up event when the lower layer is available.

This results of this action are highly implementation dependent.

This-Layer-Finished (tlf)

This action indicates to the lower layers that the automaton is entering the Initial, Closed or Stopped states, and the lower layer is no longer needed for the link. The lower layer SHOULD respond with a Down event when the lower layer has terminated. Typically, this action MAY be used by the LCP to advance to the Link Dead phase, or MAY be used by a NCP to indicate to the LCP that the link may terminate when there are no other NCPs open.

This results of this action are highly implementation dependent.

Initialize-Restart-Count (irc)

This action sets the Restart counter to the appropriate value (Max-Terminate or Max-Configure). The counter is decremented for each transmission, including the first.

Implementation Note:

In addition to setting the Restart counter, the implementation MUST set the timeout period to the initial value when Restart timer backoff is used.

Zero-Restart-Count (zrc)

This action sets the Restart counter to zero.

Implementation Note:

This action enables the FSA to pause before proceeding to the desired final state, allowing traffic to be processed by the peer. In addition to zeroing the Restart counter, the implementation MUST set the timeout period to an appropriate value.

Send-Configure-Request (scr)

A Configure-Request packet is transmitted. This indicates the desire to open a connection with a specified set of Configuration Options. The Restart timer is started when the Configure-Request packet is transmitted, to guard against packet loss. The Restart counter is decremented each time a Configure-Request is sent.

Send-Configure-Ack (sca)

A Configure-Ack packet is transmitted. This acknowledges the reception of a Configure-Request packet with an acceptable set of Configuration Options.

Send-Configure-Nak (scn)

A Configure-Nak or Configure-Reject packet is transmitted, as appropriate. This negative response reports the reception of a Configure-Request packet with an unacceptable set of Configuration Options.

Configure-Nak packets are used to refuse a Configuration Option value, and to suggest a new, acceptable value. Configure-Reject packets are used to refuse all negotiation about a Configuration Option, typically because it is not recognized or implemented. The use of Configure-Nak versus Configure-Reject is more fully described in the chapter on LCP Packet Formats.

Send-Terminate-Request (str)

A Terminate-Request packet is transmitted. This indicates the desire to close a connection. The Restart timer is started when the Terminate-Request packet is transmitted, to guard against packet loss. The Restart counter is decremented each time a Terminate-Request is sent.

Send-Terminate-Ack (sta)

A Terminate-Ack packet is transmitted. This acknowledges the reception of a Terminate-Request packet or otherwise serves to synchronize the automatons.

Send-Code-Reject (scj)

A Code-Reject packet is transmitted. This indicates the reception of an unknown type of packet.

Send-Echo-Reply (ser)

An Echo-Reply packet is transmitted. This acknowledges the reception of an Echo-Request packet.