1

6. (Link Layer)

6. : , ,

(error detection, correction)

: (multiple access)

(LAN): , VLAN

2

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

3

6.5 : MPLS

6.6

6.7 :

6. : , ,

(Link Layer): (1)

(node)

(link)

LAN

(frame)

4

6. : , ,

: (2)

,

, , 802.11 (WiFi)

,

5

: JFK : JFK :

= (, , )

=

= =

6. : , ,

(1)

(framing), (link access)

, MAC(medium access control)

(reliable delivery) (, UTP)

(error rate)

(flow control)

6

6. : , ,

(2)

(error detection)

(error correction) ,

(half-duplex) (full-duplex)

7

6. : , ,

(NIC: Network Interface Card) - (network adaptor) - , 802.11 ,

,

, ,

8

6. : , ,

, rdt,

9

, rdt,

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

10

6.5 : MPLS

6.6

6.7 :

6. : , ,

(Error Detection and Correction)

EDC = ( )

D = ,

100%

,

EDC

11

6. : , ,

(Parity Checking)

12

2

6. : , ,

(Internet Checksum) -

( )

13

: 16

(1 )

UDP

:

6. : , ,

(CRC: Cyclic Redundancy Check)

D

r+1 (generator) G

8, 12, 16, 32

GCRC-32 = 100000100110000010001110110110111

r CRC R

G (-2 )

G 0 !

r+1 (burst error)

r

(, 802.11 WiFi, ATM)

14

6. : , ,

CRC

CRC -2 XOR(exclusive OR)

D.2r XOR R

R R

R D.2r XOR R = nG

D.2r = nG XOR R

XOR

G R

15

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

16

6.5 : MPLS

6.6

6.7 :

6. : , ,

(Multiple Access Link and Protocols)

(point-to-point) PPP

(broadcast)

(old-fashioned Ethernet)

802.11 LAN

17

6. : , ,

(Multiple Access Protocol, MAC Protocol)

: (interference) (collision)

(multiple access protocol)

(out-of-band)

18

6. : , ,

(Ideal Multiple Access Protocol)

R bps

1. R bps

2. M R/M bps

3. (decentralized)

,

4.

19

6. : , ,

(channel partition protocol) ( , , )

(random access protocol)

(taking-turns protocol)

20

6. : , ,

- TDMA

TDMA (Time Division Multiple Access) (time slot)

(idle)

: 6 LAN

1,3,4 , 2,5,6,

21

6. : , ,

- FDMA

FDMA (Frequency Division Multiple Access) (frequency band)

(idle)

: 6 LAN

1,3,4 , 2,5,6,

22

6. : , ,

(Random Access Protocol)

R bps

=> (collision)

e.g.,

(slotted ALOHA)

(ALOHA)

CSMA, CSMA/CD, CSMA/CA

23

6. : , ,

(Slotted ALOHA) (1)

(L )

(L/R )

p

24

6. : , ,

(Slotted ALOHA) (2)

R

25

6. : , ,

N p

= p(1-p)N-1

N-1 , (1-p)N-1

= Np(1-p)N-1

Np(1-p)N-1 p*

N Np*(1-p*)N-1 = 1/e = .37

37%

0.37R bps

26

6. : , ,

(ALOHA)

,

t0 [t0-1,t0+1]

27

6. : , ,

p( ) = p( ) .

p([t0-1,t0] ) .

p([t0,t0+1] )

= p . (1-p)N-1 . (1-p)N-1

= p . (1-p)2(N-1)

p N

= 1/(2e) = .18

28

6. : , ,

CSMA (Carrier Sense Multiple Access)

CSMA (Carrier Sense Multiple Access) ( , carrier sensing)

(, back off)

,

29

6. : , ,

CSMA

4 A,B,C,D t0 B

t1(t0

6. : , ,

CSMA/CD (Collision Detection)

CSMA/CD (Carrier Sense Multiple Access/Collision Detection)

(collision detection) LAN

,

31

6. : , ,

CSMA/CD (1)

1. (NIC)

2. (idle) , (busy)

3.

4. (jam signal)

5. (binary exponential backoff) m {0,1,2,,2m-1} K

m = min(m, 10)

K512 32

6. : , ,

CSMA/CD (2)

(jam signal) , 48

(bit time) 1

10 Mbps 0.1 usec, K=1023 50 msec

(binary exponential backoff)

(heavy load):

K 512

K {0,1}

K {0,1,2,3}

K {0,1,2,3,4,,1023}

33

6. : , ,

CSMA/CD

tprop = LAN

ttrans =

1 tprop 0

ttrans

ALOHA ,

34

transprop /ttefficiency

511

6. : , ,

(Taking-Turns Protocol)

1/N

(taking-turns protocol)

,

35

6. : , ,

- (Polling Protocol)

( ) ()

(overhead)

(latency)

36

6. : , ,

- (Token-Passing Protocol)

(token)

,

37

6. : , ,

,

TDMA(Time Division Multiple Access), FDMA(Frequency Division Multiple Access), CDMA(Code Division Multiple Access)

ALOHA, S-ALOHA, CSMA, CSMA/CD

,

CSMA/CD

802.11 CSMA/CA

,

, FDDI(Fiber Distributed Data Interface)

38

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

39

6.5 : MPLS

6.6

6.7 :

6. : , ,

MAC (Media Access Control)

IP

3( )

MAC (LAN, , ) LAN , ,

48 MAC ( LAN)

NIC ROM

e.g.: 1A-2F-BB-76-09-AD

40

6. : , ,

LAN (1)

LAN LAN

41

6. : , ,

LAN (2)

MAC IEEE MAC

MAC 24 , 24

MAC (flat address)

IP IP

MAC : ,

IP : , 42

6. : , ,

ARP (Address Resolution Protocol)

IP MAC ? (IP ) (MAC )

LAN IP (, ) ARP IP/MAC

TTL(Time to Live): ( 20)

43

6. : , ,

ARP - LAN

A B

A ARP B MAC

1. A ARP (query packet)

B IP

MAC = FF-FF-FF-FF-FF-FF

LAN ARP

2. B ARP , (response packet) A

B MAC

A MAC

3. A B IP/MAC ARP

ARP (plug-and-play)

ARP

44

6. : , ,

ARP - LAN (1)

A R B A B IP

A IP (?)

A R MAC (?)

45

6. : , ,

ARP - LAN (2)

A A, B IP

A R MAC

A B IP

46

6. : , ,

ARP - LAN (3)

A R

R NIC

R IP IP

47

6. : , ,

ARP - LAN (4)

R A B (forward)

R A B IP , B MAC

48

6. : , ,

ARP - LAN (5)

R B

49

6. : , ,

6-1: ARP,Wireshark

ARP

ARP (caching)

Explore -> ->

Wireshark

Wireshark ,

ARP

50

6. : , ,

6-1: ARP,

ARP MS-DOS arp

Q1: arp a ARP

51

6. : , ,

6-1: ARP, Wireshark (1)

arp d * ARP

,

IP Analyze->Enabled Protocols IPv4, IPv6

ARP ARP

ARP , Ethernet II Address Resolution Protocol

Q2: ARP , 16 ?

Q3: 2 16 ?

Q4: ARP opcode ?

Q5: ARP opcode ?

52

6. : , ,

6-1: ARP, Wireshark (2)

Q6: ARP sender IP ? IP ?

Q7: ARP IP ? IP ?

ARP ARP , Ethernet II Address Resolution Protocol

Q8: ARP , 16 ?

Q9: ARP opcode ?

Q10: ARP opcode ?

Q11: ARP ? IP ?

53

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

54

6.5 : MPLS

6.6

6.7 :

6. : , ,

(Ethernet)

LAN 1973 Xerox Robert Mecalfe

1976 Robert Metcalfe David Boggs

, 20$

LAN ATM

: 10 Mbps 10 Gbps

55

Robert Metcalfe and David Boggs

6. : , ,

- (Physical Topology)

1990 ( )

(switch)

56

6. : , ,

(1)(Ethernet Frame Structure)

IP 46~1500

(preamble) 8

7 10101010, 10101011

,

57

6. : , ,

(2)

, 6

IP Novell IPX, AppleTalk

CRC

58

6. : , ,

: (Unreliable, Connectionless Service)

(connectionless service)

(unreliable service) NIC ACK, NACK NIC

TCP

TCP

CSMA/CD

59

6. : , ,

(Ethernet Standards)

IEEE 802.3

(MAC)

: 2 Mbps, 10 Mbps, 100 Mbps, 1Gbps, 10G bps

: ,

60

10 BASE 2

10 Mbps

200 M

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

61

6.5 : MPLS

6.6

6.7 :

6. : , ,

(Hub)

62

(dumb) (repeater)

CSMA/CD

6. : , ,

(Ethernet Switch)

(forward)

MAC

CSMA/CD

(transparent)

(self-learning),

63

6. : , ,

-

(full duplex)

A-to-A B-to-B

64

6. : , ,

(Switch Table)

Q: 4 A , 5 B ?

A: .

( MAC , , )

TTL

Q: ?

65

6. : , ,

- (Self-Learning)

66

(incoming LAN segment)

/

6. : , ,

- /(Frame Filtering/Forwarding)

:

1. MAC

2. MAC

3. if then {

if then else

}else (broadcast, flood)

67

6. : , ,

,

A'

A'

68

A

A

B

B

C

C

1 2 345

6

A A

Source: A

Dest: A

MAC addr interface TTLSwitch table

(initially empty)A 1 60

A AA AA AA AA A

A A

A 4 60

6. : , ,

(Interconnecting Switches)

Q: A G S1 S4 S3 G ?

A: ( )

69

6. : , ,

(Institutional Network)

70

6. : , ,

(Switch vs. Router)

71

(store-and-forward) :

( )

: ( )

, IP

, MAC

6. : , ,

(VALN,Virtual LAN)

CS EE CS ?

-2

(ARP DHCP ) LAN

/(security/privacy)

Wireshark

72

6. : , ,

VLANs

VLAN LAN LAN

Virtual Local Area Network

(port-based) VLAN

()

6. : , ,

VLAN (Port-based VLAN)

74

(traffic isolation) 1-8 1-8

MAC VLAN

(dynamic membership) VLAN

VLAN (forwarding)

6. : , ,

VLAN

(trunk port) VLAN

IEEE VLAN 802.1Q

75

6. : , ,

802.1Q VLAN

76

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

77

6.5 : MPLS

6.6

6.7 :

6. : , ,

(MPLS: Multiprotocol Label Switching)

(IP ) IP

IP

(VC) IP

78

6. : , ,

MPLS (MPLS Capable Router)

(label-switched router)

IP MPLS (IP )

(flexibility) MPLS IP

IP ( )

VoIP

79

6. : , ,

MPLS IP (1)

IP

80

6. : , ,

MPLS IP (2)

IP

MPLS

81

6. : , ,

MPLS (MPLS Signaling)

(e.g. OSPF) MPLS (flooding)

MPLS RSVP-TE (Resource Reservation Protocol Traffic Engineering) MPLS

82

6. : , ,

MPLS

83

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

84

6.5 : MPLS

6.6

6.7 :

6. : , ,

e- (e.g. Amazon)

(e.g., YouTube, Akamai, Apple, Microsoft)

, (e.g., Google)

85

, , (load balancing)

6. : , ,

(load balancer) -

86

6. : , ,

(Interconnection)

(fully connected topology) ( )

(redundancy) (reliability)

87

6. : , ,

6. : , ,

6.1 :

6.2

6.3

6.4 (LAN) , ARP

(VLAN)

88

6.5 : MPLS

6.6

6.7 :

6. : , ,

, , ,

(www.google.com)

89

6. : , ,

-

90

6. : , ,

(1)

IP , , DNS . => DHCP

DHCP UDP/IP/802.3 .

LAN (dest:FFFFFFFFFFFF), DHCP .

, IP , UDP , DHCP .

91

6. : , ,

(2)

DHCP IP , IP , DNS IP DHCP ACK .

DHCP , LAN ( ), .

DHCP DHCP ACK .

92

IP , DNS , IP .

6. : , ,

ARP (DNS, HTTP )

HTTP www.google.com IP . => DNS

DNS UDP/IP/Ethernet . MAC . => ARP

ARP , MAC ARP .

MAC , DNS .

93

6. : , ,

DNS

94

DNS IP LAN .

IP comcast , (RIP, OSPF, IS_IS, BGP ) DNS

DNS .

DNS www.google.comIP .

6. : , ,

HTTP TCP

95

HTTP TCP .

TCP SYN (3- 1) ( ).

TCP SYNACK (3- 2).

TCP .

6. : , ,

HTTP /

96

HTTP TCP .

HTTP IP www.google.com .

( ) HTTP .

HTTP IP .

6. : , ,

6-2: ,Wireshark

Explore -> ->

Wireshark

Wireshark ,

97

6. : , ,

6-2: , Wireshark (1)

HTTP GET HTTP

98

6. : , ,

6-2: , Wireshark (2)

IP Analyze->EnabledProtocols IPv4, IPv6

99

6. : , ,

6-2: , Wireshark (3)

HTTP GET , Ethernet II

Q1: 48 ?

Q2: 48 ?

Q3: ?, ?

Q4: 2 16 ?

Q5: GET G ?

100

6. : , ,

6-2: , Wireshark (4)

HTTP , Ethernet II

Q6: ?

Q7: ? ?

Q8: ? ?

Q9: 2 16 ?

Q10: OK O ?

101

6. : , ,

(Summary)

:

LAN, VLAN

: MPLS

-

102

6. : , ,

6-1: ARP,Wireshark

ARP

ARP (caching)

Explore -> ->

Wireshark

Wireshark ,

ARP

103

6. : , ,

6-1: ARP,

ARP MS-DOS arp

Q1: arp a ARP

104

6. : , ,

6-1: ARP, Wireshark (1)

arp d * ARP

,

IP Analyze->Enabled Protocols IPv4, IPv6

ARP ARP

ARP , Ethernet II Address Resolution Protocol

Q2: ARP , 16 ?

Q3: 2 16 ?

Q4: ARP opcode ?

Q5: ARP opcode ?

105

6. : , ,

6-1: ARP, Wireshark (2)

Q6: ARP sender IP ? IP ?

Q7: ARP IP ? IP ?

ARP ARP , Ethernet II Address Resolution Protocol

Q8: ARP , 16 ?

Q9: ARP opcode ?

Q10: ARP opcode ?

Q11: ARP ? IP ?

106

6. : , ,

6-2: ,Wireshark

Explore -> ->

Wireshark

Wireshark ,

107

6. : , ,

6-2: , Wireshark (1)

HTTP GET HTTP

108

6. : , ,

6-2: , Wireshark (2)

IP Analyze->EnabledProtocols IPv4, IPv6

109

6. : , ,

6-2: , Wireshark (3)

HTTP GET , Ethernet II

Q1: 48 ?

Q2: 48 ?

Q3: ?, ?

Q4: 2 16 ?

Q5: GET G ?

110

6. : , ,

6-2: , Wireshark (4)

HTTP , Ethernet II

Q6: ?

Q7: ? ?

Q8: ? ?

Q9: 2 16 ?

Q10: OK O ?

111