第 6 讲 数据链路层( 2 )
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Transcript of 第 6 讲 数据链路层( 2 )
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6 2
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CRC
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CRC
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PPP HDLC
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InternetSLIP Serial Line IP ;PPP Point-to-Point Protocol -SLIPPPPISPInternet
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PPP PPP (Point-to-Point Protocol) PPP PPP;PPPISP
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ISP PPP
IP ISPPPP
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PPP
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Maximum Transmission UnitMTU IPMTU1500IP1500IP64KBIPIP
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PPP
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PPP 1992 PPP 1993 1994 PPP [RFC 1661] PPP IP LCP (Link Control Protocol) NCP (Network Control Protocol)
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PPP () F = 0x7E 0x 7E 01111110 A 0xFF C 0x03PPP PPP
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PPP PPP 2 0x0021 PPP IP 0xC021, PPP 0x8021 IP 121112 1500 PPP 7EFF03FACFCSF7E
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PPP PPP PPP 0x7E 2 (0x7D, 0x5E) 0x7D , 2 (0x7D, 0x5D) ASCII 0x20 0x7D PPP SONET/SDH PPP
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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
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PPP PPP PPP IP FCS
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PPP ISP PC LCP PPP PPP NCP PC IP PC NCP IP LCP
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LCP LCP LCP NCP LCP NCP LCP LCP
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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 ()
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HDLC F (Flag) 6 1 0 8 bit 888168 Info F F A C FCSFCS
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HDLC01111110511010
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HDLC F 6 1 5 1 0 F 5 1 0
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A BAP2AP1
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cont. 1 2 2
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A B
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()
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cont.
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ABDATADATADATADATA B B B BABDATA BDATA B
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ABACKACK(a)
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A(timeout timer) tout B A
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1 B B B A ACK B A ACK
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0 1
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N(S) 0 1
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ARQ ARQ ARQ
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(slide)--1n0~2n-1sending windowreceiving window
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WWWll+WWj
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ll+WiW
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30~73012345670123456701234567012345670123456701234567012345670123456701234567012345670123456701234567
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-10~11010101010101010101010101
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piggybacking
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go-back-n11112n-1(n)
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selective repeat112n-11/2
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PPPPPP
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P105,3-09,3-11,3-13,3-14,3-19ARQARQ