6 2

CRC

CRC

PPP HDLC

InternetSLIP Serial Line IP ;PPP Point-to-Point Protocol -SLIPPPPISPInternet

PPP PPP (Point-to-Point Protocol) PPP PPP;PPPISP

ISP PPP

IP ISPPPP

PPP

Maximum Transmission UnitMTU IPMTU1500IP1500IP64KBIPIP

PPP

PPP 1992 PPP 1993 1994 PPP [RFC 1661] PPP IP LCP (Link Control Protocol) NCP (Network Control Protocol)

PPP () F = 0x7E 0x 7E 01111110 A 0xFF C 0x03PPP PPP

PPP PPP 2 0x0021 PPP IP 0xC021, PPP 0x8021 IP 121112 1500 PPP 7EFF03FACFCSF7E

PPP PPP PPP 0x7E 2 (0x7D, 0x5E) 0x7D , 2 (0x7D, 0x5D) ASCII 0x20 0x7D PPP SONET/SDH PPP

0 1 0 0 1 1 1 1 1 0 1 0 0 0 1 0 1 00 1 0 0 1 1 1 1 1 1 0 0 0 1 0 1 00 1 0 0 1 1 1 1 1 0 1 0 0 0 1 0 1 0 F 8 5 1 0 5 1 0 F 0 0

PPP PPP PPP IP FCS

PPP ISP PC LCP PPP PPP NCP PC IP PC NCP IP LCP

LCP LCP LCP NCP LCP NCP LCP LCP

HDLC HDLC1974IBM SDLC (Synchronous Data Link Control) ISO SDLC HDLC (High-level Data Link Control)ISO 3309CCITT HDLC LAP (Link Access Procedure)HDLC LAP LAPBB(Balanced) LAPB ()

HDLC F (Flag) 6 1 0 8 bit 888168 Info F F A C FCSFCS

HDLC01111110511010

HDLC F 6 1 5 1 0 F 5 1 0

A BAP2AP1

cont. 1 2 2

A B

()

cont.

ABDATADATADATADATA B B B BABDATA BDATA B

ABACKACK(a)

A(timeout timer) tout B A

1 B B B A ACK B A ACK

0 1

N(S) 0 1

ARQ ARQ ARQ

nlml

(slide)--1n0~2n-1sending windowreceiving window

WWWll+WWj

ll+WiW

30~73012345670123456701234567012345670123456701234567012345670123456701234567012345670123456701234567

-10~11010101010101010101010101

piggybacking

go-back-n11112n-1(n)

selective repeat112n-11/2

PPPPPP

P105,3-09,3-11,3-13,3-14,3-19ARQARQ