Point-to-Point Protocol (PPP) Automaton Events

Option Negotiation Automaton generally provides finite-state automaton. Events, actions, and state transitions, as with most finite state machines are various attributes of this finite-state automaton. One of these attributes i.e. Event generally causes Point-to-Point Protocol (PPP) connection to transition from one state to another. This is known as state transitions.

Event is basically one of external occurrences or any command that initiates or triggers state machine to change state from one to another or remains in its present or current state. Actions are also triggered due to events.

So, we can say that both state transitions and actions are caused or initiated due to events infinite automaton.

There are total of thirteen events that result in one of different PPP transition states. These events are given below in table :

Event Description
Up This event label simply means that lower layer is Up. This event only occurs when it gets signals from lower layer that it is ready to transmit data frames. This event also indicates to LCP (Link Control Protocol) that connection or link is going to enter link establishment phase i.e. establishment of connection will take place through exchange of data frames or packets.
Down This event label simply means that lower layer is Down. This event only occurs when it gets signals from lower layer that it is now ready to transmit data frames. This event also indicates to LCP (Link Control Protocol) that connection or link is going to enter link dead phase i.e. termination of connection or link will take place.
Open This event label simply means administrative open. This event indicates that connection or link is allowed to be Opened for exchanging data frames.
Close This event label simply means administrative open. This event indicates that connection or link is not allowed to be Opened, instead, it will remain closed for exchanging data frames.
TO+ This event label simply means timeout with counter is greater than 0. It indicates that restart timer is expired along with restart counter remains greater than zero. It will initiate retransmission of configure-request or terminate-request packets.
TO- This event label simply means timeout with counter expired. It indicates that restart timer is expired along with restart counter no longer greater than zero. It will not initiate retransmission of configure-request or terminate-request packets.
RCR+ This event label simply means receive configure requests is acceptable. It indicates that configure-request packet that is received from peer or client for wanting to open connection is good and acceptable. Therefore, it initiates transmission of corresponding configure-ack.
RCR- This event label simply means receive configure request is unacceptable. It indicates that configure-request packet that is received from peer or client for wanting to open connection is not good and is unacceptable. Therefore, it initiate transmission of corresponding configure-nak or configure-reject.
RCA This event label simply means receive configure acknowledgment. This event mainly occurs when a valid positive response i.e. configure-ack packet to configure-request packet is received from the client or peer.
RCN This event label simply means receive configure nak/rej. This event mainly occurs when a valid negative response i.e. configure-nak or configure-reject packet to configure-request packet is received from the client or peer.
RTR This event label simply means receive terminate request: This event occurs when terminate-request packet is received. This terminate-request packet indicates that the peer or client wants to close or terminate the link or connection.
RTA This event label simply means receive terminate acknowledgment. This event generally occurs peer or client sends terminate-ack packet in response to terminate-request packet.
RUC This event label simply means receive unknown code. This event generally occurs peer or client sends an un-interpretable packet i.e. Code-reject packet in response.
RXJ+ This event label simply means receive code reject permitted or receive protocol reject. This event occurs when peer or client sends code-reject or protocol reject packet that is acceptable like code-reject of an extended code or protocol rejects of NCR.
RXJ- This event label simply means receive code reject catastrophic or receive protocol reject. This event occurs when peer or client sends code-reject or protocol reject packet that is unacceptable like code-reject of configure-request or protocol reject of LCP.
RXR This event label simply means receive echo requests, receive echo reply, or receive discard requests. This event occurs when packet i.e. echo-request, echo-reply or discard request is sent by the peer or client.

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