Point-to-Point Protocol (PPP) is specially designed for establishment of simple and easy connections or links like transmitting packets among two different peers or clients. Finite state automation is basically provided to reach Open state and enter NLP phase.
Finite station automaton consists of events, states, and actions. Event is basically class of transition states. These events cause change in state of link also known as transition in states or state transitions. The state transition is also referred to as reaction of state machine to an event.
There are basically two important events i.e. OPEN and CLOSE.
OPEN event generally causes control protocol to try to develop or establish connection whereas CLOSE event causes to terminate the connection.
This CLOSE event also makes state machine to remain in this closed state without even doing any actions. Therefore, we can say that state transition can keep machine in its current or present state. The actual details of establishing, maintaining, and handling connection or link are very much complex as on interaction with some events may result in one of total 10 different states in link. To display state of PPP link (LCP) and NCPs that are running on that particular connection, we can use command :
Different states for control protocols of PPP are given below :
|Initial||This state is Startup state. During this state, no occurring of OPEN event takes place and hardware is DOWN i.e. lower layer is unavailable. Restart timer is also not running during this state.|
|Starting||This state is generally Open Counterpart to Initial state. During this state, OPEN event usually occurs and gets initiated but hardware is still DOWN i.e. lower layer is still not available. Restart timer is also not running during this state.|
|Stopped||This state is generally Open Counterpart to Closed state During this state, hardware is generally UP i.e. link is available and even DOWN or TIMEOUT event usually occurs. Restart timer is also not running during this state.|
|Closed||During this state, hardware is generally UP i.e. link is available but no occurring of OPEN event takes place. Restart timer is also not running during this state.|
|Stopping||This state is generally Open Counterpart to Closing state During this state, link might be OPEN and remote station generally tries to CLOSE connection or link.|
|Closing||During this state, link might be UP, and occurring of CLOSE event takes place that tries to close link or connection. An attempt is also made to terminate to end connection by sending Terminate-Request but terminate request has nor has been received yet. Restart timer also starts running during this state.|
|Request-Sent||During this state, Configure-Request for configuring connection is sent usually but Configure-Ack has not been received yet nor has been sent. Restart timer also starts running during this state.|
|Ack-Sent||During this state, configure request is received usually i.e. Configure-Request and acknowledge is sent i.e. Configure-Ack.|
|Ack-RCVD||During this state, configure request is sent usually i.e. Configure-Request and acknowledge is received i.e. Configure-Ack.|
|Opened||During this state, acknowledge has been sent or transmitted and received i.e. Configure-Ack. Restart timer is also not running during this state.|