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PPP协议是哪一层协议?PPP协议是数据层的协议。
PPP协议是什么
PPP协议即点到点协议,为在同等单元之间传输数据包这样的简单链路设计的链路层协议。这种链路提供全双工操作,并按照顺序传递数据包。设计目的主要是用来通过拨号或专线方式建立点对点连接发送数据,使其成为各种主机、网桥和路由器之间简单连接的一种共通的解决方案。
PPP协议的功能
(1)PPP具有动态分配IP地址的能力,允许在连接时刻协商IP地址;
(2)PPP支持多种网络协议,比如TCP/IP、NetBEUI、NWLINK等;
(3)PPP具有错误检测能力,但不具备纠错能力,所以ppp是不可靠传输协议;
(4)无重传的机制,网络开销小,速度快。
(5)PPP具有身份验证功能。
(6) PPP可以用于多种类型的物理介质上,包括串口线、电话线、移动电话和光纤(例如SDH),PPP也用于Internet接入。
PPP协议的工作流程
当用户拨号接入 ISP 时,路由器的调制解调器对拨号做出确认,并建立一条物理连接(底层up)。PC 机向路由器发送一系列的 LCP 分组(封装成多个
PPP 帧)。
这些分组及其响应选择一些 PPP 参数,和进行网络层配置(此前如有PAP或CHAP验证先要通过验证),NCP 给新接入的 PC机分配一个临时的 IP
地址,使 PC 机成为因特网上的一个主机。
通信完毕时,NCP 释放网络层连接,收回原来分配出去的 IP 地址。接着,LCP 释放数据链路层连接。最后释放的是物理层的连接。
PPP协议的特点
PPP协议是一种点——点串行通信协议。PPP具有处理错误检测、支持多个协议、允许在连接时刻协商IP地址、允许身份认证等功能,还有其他。PPP提供了3类功能:成帧;链路控制协议LCP;网络控制协议NCP。PPP是面向字符类型的协议。