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RFC1661 - часть 7


It is the

responsibility of each protocol to distinguish padding octets from

real information.

Simpson [Page 5]

RFC 1661 Point-to-Point Protocol July 1994

3. PPP Link Operation

3.1. Overview

In order to establish communications over a point-to-point link, each

end of the PPP link MUST first send LCP packets to configure and test

the data link. After the link has been established, the peer MAY be

authenticated.

Then, PPP MUST send NCP packets to choose and configure one or more

network-layer protocols. Once each of the chosen network-layer

protocols has been configured, datagrams from each network-layer

protocol can be sent over the link.

The link will remain configured for communications until explicit LCP

or NCP packets close the link down, or until some external event

occurs (an inactivity timer expires or network administrator

intervention).

3.2. Phase Diagram

In the process of configuring, maintaining and terminating the

point-to-point link, the PPP link goes through several distinct

phases which are specified in the following simplified state diagram:

+------+ +-----------+ +--------------+

| | UP | | OPENED | | SUCCESS/NONE

| Dead |------->| Establish |---------->| Authenticate |--+

| | | | | | |

+------+ +-----------+ +--------------+ |

^ | | |

| FAIL | FAIL | |

+<--------------+ +----------+ |

| | |

| +-----------+ | +---------+ |

| DOWN | | | CLOSING | | |

+------------| Terminate |<---+<----------| Network |<-+

| | | |

+-----------+ +---------+

Not all transitions are specified in this diagram. The following

semantics MUST be followed.

Simpson [Page 6]

RFC 1661 Point-to-Point Protocol July 1994

3.3. Link Dead (physical-layer not ready)

The link necessarily begins and ends with this phase. When an

external event (such as carrier detection or network administrator

configuration) indicates that the physical-layer is ready to be used,

PPP will proceed to the Link Establishment phase.

During this phase, the LCP automaton (described later) will be in the




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