Someone regard it as a extension for ppp ( point to point protocol ) . there are two causes to explain this 由于它主要的封装对象是ppp协议，因此，也有人把它看成是ppp协议的扩展。
4.
The main research works in this paper is summarized as below : 1 . the multicast security ca n ' t be ensured because ipsec is a point to point protocol 本文做的主要研究工作如下： ( 1 )由于ipsec是一种点到点的协议，所以无法保护多播通信的安全。
5.
This paper includes two parts : part one consists of four chapters . it mainly researches the technology of using mcu to connect to internet which is based on the simplified networking - protocols of tcp / ip . it describes two schemes to use mcu to connect to internet : ialing into the internet using point to point protocol ; ( 2 ) connecting to the lan directly and the mcu having its own exclusive ip address 本文共分两个部分，第一部分为第2 、 3 、 4 、 5章，主要是对以简化tcp / ip网络协议组为基础的单片机上网技术进行研究，在文中提出了两种单片机上网的方案：基于ppp的拨号上网；作为一个有单独ip地址的节点直接连入局域网。
