说明：  RFC1661 PPP协议 （RFC1661 The Point-to-Point Protocol (PPP)） 本备忘录状态 This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
(RFC1661 PPP (RFC1661 The Point-to-Point Protocol (PPP)) This state of this memorandum memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.)