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计算机网络技术 PowerPoint PPT Presentation


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计算机网络技术. 第 4 章 数据链路层. 4.1 数据链路层的基本概念 4.2 数据链路控制协议 4.3 流量控制 4.4 高级数据链路控制协议 HDLC 4.5 因特网的点对点链路协议 PPP. 第 4 章 数据链路层. 物理层的问题: 物理链路是 有差错和不可靠 的。 物理设备之间可能存在 传输速度不匹配 的问题。 数据链路层的作用: 通过一些 数据链路控制 协议,在 不太可靠 的物理链路上实现 可靠 的数据传输。. 4.1 数据链路层的基本概念. 物理链路

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计算机网络技术

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4


4.1

4.2

4.3

4.4 HDLC

4.5 PPP

4


4.1


MODEM

MODEM


(PDU)


  • ASCIIIBM BSCHDLC



OSI




FTP message

Data

Data

Segment

Segment

Header

Data

(Bytes)

Packet

Network

Header

Segment

Header

Data

Frame

Frame

Header

Network

Header

Segment

Header

Data

Frame

Trailer

(medium dependent)

Bits

0111111010101100010101101010110001


10101010 10101010|10101011

  • 10101010

  • SOF10101011B11SOF




4.2

B

A

AP1

AP2


(ACK)

(NAK)

1. --


N(S) 1

B A ACK


DATA0

DATA0

DATA0

tout

tout

A

B

A

B

A

B

A

B

DATA0

DATA0

DATA1

DATA0

NAK

DATA0

ACK

ACK

ACK

ACK

ACK

ACK

(b)

(d)

(c)

(a)



2. ARQ


0

0

1

1

2

2

2

3

3

3

4

4

4

5

5

5

6

6

6

7

7

7

D

D

D

D

D

ACK2

ACK3

ACK0

ACK1

ARQ

A

B


3. ARQ


0

1

2

3

4

5

2

3

4

5

6

0

1

2

3

4

5

2

3

4

5

6

ACK1

ACK3

ACK0

NAK

ACK2

(a)

0

1

2

3

4

5

2

6

7

8

9

0

1

2

3

4

5

2

6

7

8

9

ACK1

ACK3

ACK5

ACK6

ACK0

NAK

ACK4

ACK2

(b)

ARQ

(a)

(b)


4.3


ARQ

ARQ


WT


WT

WT

(a)

0

1

2

3

4

5

6

7

0

1

2

5

(b)

2

4

0

1

3

5

6

7

0

1

2

4

WT

(c)

0

1

2

3

4

5

6

7

0

1

2

WT

0

1

2

3

4

5

6

7

0

1

2

(d)

3


ARQ WR = 1


WR

(a)

0

1

2

3

4

5

6

7

0

1

2

WR

0

(b)

0

1

2

3

4

5

6

7

0

1

2

1

WR

(c)

0

1

2

3

4

5

6

7

0

1

2

4


1


n 1 WT 2n 1 ARQ

3 bit 7 8


ARQ

ARQ

ARQ n WR2n-1

WT= WR= 2n-1

ARQ


4.4.1 HDLC

HDLC(High-Level Data Link Control)ISO ISO 3309

IBMSDLC(Synchronous Data Link Control)

01111110(7EH)

4.4 HDLC


Primary Station

Secondary Station

Combined Station

HDLC


HDLC


/

/

HDLC


NRM

ARM

ABM

HDLC


4.4.2 HDLC

8b 8nb 8b/16b 16b 8b

HDLC

  • F(01111110B7EH)

    • 0


HDLC F 6 1

5 1 0

F 5 1 0


5 1

0

0 1 0 0 1 1 1 1 1 0 1 0 0 0 1 0 1 0

0

5 1

0

0 1 0 0 1 1 1 1 1 0 1 0 0 0 1 0 1 0

0

F

0 1 0 0 1 1 1 1 1 1 0 0 0 1 0 1 0

F


F


8b 8nb 8b /16b 16b 8b

HDLC

  • A

    • 10

    • 1


8b 8nb 8b /16b 16b 8b

HDLC

  • C

  • I

    • 16CRCg(x)=x16+x12+x5+1

    • 0


HDLC

HDLC

8b 8nb 8b /16b 16b 8b

(I)

(S)

(U)


HDLCI

N(S)

N(R)

P/FPollFinal

P=1 F=1

81637

HDLC


HDLCS4

RRSS=00

RNRSS=10

REJSS=01N(R)

SREJSS=11N(R)

N (R)

HDLC


HDLC

WT 2n 1

WR 2n/2= 2n-1

n

RRRNR

7

7

7

7

0

0

0

0

6

6

6

6

1

1

1

1

5

5

5

5

2

2

2

2

4

4

4

4

3

3

3

3

HDLC


HDLCU

MMMMM32

15

HDLC



4.4.3 HDLC

HDLC


A

B

USNRMP=1

UUAF=1

IN(S)=0N(R)=0

IN(S)=1N(R)=0P=1

IN(S)=0N(R)=2

IN(S)=1N(R)=2

IN(S)=2N(R)=2F=1

IN(S)=2N(R)=3P=1

IN(S)=3N(R)=3

IN(S)=4N(R)=3F=1

UDISCP=1

UUAF=1


A

B

USNRMP=1

UUAF=1

IN(S)=0N(R)=0

IN(S)=1N(R)=0P=1

SREJN(R)=0

IN(S)=0N(R)=0

IN(S)=1N(R)=0P=1

IN(S)=0N(R)=2

IN(S)=1N(R)=2

IN(S)=2N(R)=2

SRRN(R)=3

IN(S)=3N(R)=2

IN(S)=4N(R)=2F=1

UDISCP=1

UUAF=1


, ()

RR

HDLC


0

HDLC


ITUHDLC

LAPBDTEDCE

DLAPD ISDND

LAPM HDLC

LAPX


4.5.1 PPP

PPPPoint-to-Point Protocol

IETF1992PPPInternetRFC 1661RFC 1662PPP

PPP

4.5 PPP


PPP

  • PPP

PSTN/ISDN

PPP


PPPSLIPSerial Line Internet Protocol

PPP

IPIPX

IP

PPP


OSI

PPP

IPIPX

IPCPIPXCPATCP

LCP

PAP/CHAP

/

PPPOSI


PPP

LCP

PPP

NCPIPCPIPXCPATCP

PAPCHAP

PPP


TCP/IP

NOVELL IPX

PPP

LCPNCP

NCPs

LCP


4.5.2 PPP

PPP0x7E HDLC

A 0xFF

C 0x03PPPRFC1663

PPP

1 1 1 2 1500 2/4 1


PPP7eHRFC1662

PPPHDLC

PPP

7eH7dH67d5eH7e7d5e

7dH7d5dH7d7d5d

20H 0d7d2d

PPP


(RFC1700)

0021HIP

C021HPPP

8021HIP

C023HPAP

C223HCHAP

CRC24

PPP


4.5.3 PPP

LCP

MRU

LCP

LCP


NCP

PPPNCPIPCP

NCP

IPCPIPXCPATCP

IPCPIP

LCP


PAP

PAP

+

/

PAP


CHAP

CHAPPAP

CHAP


MD5

MD5

+

+

/

CHAP


4.5.4 PPP

PPP

PPPLCP

PPPNCP

LCPNCP

PPP


PPP

Dead

Establish

Authenticate

up

LCPup

Terminate

Network

  • PPPDead

down


EstablishLCP

Configure Request

Configure Ack

Configure Nac

Configure RejectLCP


PAPCHAPAuthenticate

PAPCHAP

TerminateLCP

Network

PPP


NetworkPPPNCPPPP

IPIPCP

NCPOpenedPPPpackets

NCPOpenedpackets


PPP

LCPTerminatePPP

Terminate

Terminate-Request-Terminate-Ack-

Terminate-RequestTerminate-RequestRestart time


ARQ

HDLCPPP

HDLC

PPP


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