يشتَيپهاک ياّ ِکثؿ - staff. ٍ dle-stx :نيشف كي ياّشتکاساک...

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  • (Datalink Layer)

    1

  • IEEE

    2

  • :

    3

  • :

    DLE-STX DLE-ETX:

    : (Byte Stuffing )

    : (Bit Stuffing ) 5 6 .

    1

    7

  • (a) A frame delimited by flag bytes.

    (b) Four examples of byte sequences before and after stuffing. 8

  • Bit stuffing

    (a) The original data.

    (b) The data as they appear on the line.

    (c) The data as they are stored in receivers memory after destuffing.

    9

  • ) ) CRC Check sum

    10

  • CRC

    11

  • 12

  • . ) : )

    :timeout Acknowledge

    window size 13

  • 14

    Reliable Transmission ARQ (Automatic Repeat Request)

  • Simplest

    15

  • Simplest

    16

  • Simplest

    17

  • ( ) Stop & Wait

    18

    ( ACK)

  • Stop&Wait

    19

  • 20

  • : ;

    .

    50 : kbps 1000 500 . 20

    21

    sec 2502

    500m

    sec 27025020 m sec 520250270 m ACK

    %8.3520

    20U

  • % 4

    Stop&Wait

    . ACK

    . . : ACK

    :

    .

    22

  • : m 2 m

    .

    23

    Max Seq. Number Send Window + Receive Window

  • 2 .

    : Timeout Acknowledge

    : Go-Back-N Automatic Repeat Request

    Selective Repeat Automatic Repeat Request

    25

  • Go-Back-N

    Stop-and-Wait Ws m . ACK

    . . timeout .

    26

  • Go-Back-N ARQ

    27

  • Go-Back-N ARQ

    28

    . 1 Go-Back-N Time out

  • Selective Repeat ARQ

    GBN ARQ .

    . Timeout . NAK ACK .

    .

    .

    R .

    29

  • Selective Repeat ARQ

    1 .

    . Cumulative ACK (ACK (

    ACK ACK

    .

    30

  • Goback-N Selective Repeat

    31

    Goback-N

    Selective Repeat

  • frame

    tf time

    A

    B

    tprop tack tproc tprop

    tproc

    t0 = total time to transmit 1 frame

    R

    n

    R

    ntt

    ttttt

    af

    procprop

    ackfprocprop

    22

    220 bits/info frame

    channel transmission rate

    bits/ACK frame

    Stop-and-Wait

    32

  • S&W

    33

    .)(2

    1

    1

    00

    f

    procprop

    f

    a

    f

    oof

    eff

    n

    Rtt

    n

    n

    n

    n

    R

    t

    nn

    R

    R

    bits for header & CRC

    ,bitsn informatio edeliver th torequired timetotal

    ndestinatio todelivered bitsn informatio ofnumber

    0

    0

    t

    nnR

    of

    eff

    Effect of frame overhead

    Effect of ACK frame

    Effect of Delay-Bandwidth Product

    Effective transmission rate:

    Transmission efficiency: 0

    0 0

    Rtn

    n

    propf

    f

    20

  • :

    34

    nf=1250 bytes = 10000 bits, na=no=25 bytes = 200 bits

    2xDelayxBW

    Efficiency 1 ms

    200 km

    10 ms

    2000 km

    100 ms

    20000 km

    1 sec

    200000 km

    1 Mbps 103

    88%

    104

    49%

    105

    9%

    106

    1%

    1 Gbps 106

    1%

    107

    0.1%

    108

    0.01%

    109

    0.001%

    Stop-and-Wait .

    %9.908/10001250

    1250

    20

    Rtn

    n

    propf

    f

  • S&W

    )1()(2

    1

    11

    0

    f

    f

    procprop

    f

    a

    f

    o

    f

    of

    eff

    SW P

    n

    Rtt

    n

    n

    n

    n

    R

    Pt

    nn

    R

    R

    35

    1 Pf ; 1) /1 Pf ) . 10 10

    . t0/(1 Pf) .

    Effect of frame loss

    )1(2

    f

    propf

    f

    sw PRtn

    n

  • :

    36

    nf=1250 bytes = 10000 bits, na=no=25 bytes = 200 bits

    Find efficiency for random bit errors with p=0, 10-6, 10-5, 10-4

    1 Pf Efficiency

    0 10-6 10-5 10-4

    1 Mbps

    & 1 ms

    1

    88%

    0.99

    86.6%

    0.905

    79.2%

    0.368

    32.2%

    pnepP fpnn

    fff small and largefor )1(1

    . 1 nfp

  • . . 4 .

    Go-Back-N ARQ

    A

    B

    fr 0

    Time fr 1

    fr 2

    fr 3

    fr 4

    fr 5

    fr 6

    fr 3

    ACK1

    out of sequence frames

    Go-Back-4: 4 frames are outstanding; so go back 4

    fr 5

    fr 6

    fr 4

    fr 7

    fr 8

    fr 9

    ACK2

    ACK3

    ACK4

    ACK5

    ACK6

    ACK7

    ACK8

    ACK9

    Rnext 0 1 2 3 3 4 5 6 7 8 9

    37

  • .

    Go Back-N

    . :nf :R :tprop

    38

    frame

    prop

    frame

    frameprop

    frame

    transfull

    optt

    t

    t

    tt

    t

    TWin 21

    2

    frameproptransfull ttT 2

    R

    nt

    f

    frame

  • Go-Back-N with Timeout

    Go-Back-N :

    . timeout :

    timeout .

    39

  • Go-Back-N Go Back-N

    ( . ( . ( .

    (

    ) ( ACK ) Psuccess

    40

    101

    f

    f

    GBNn

    nn

    o

    success

    frame

    frame

    GBN

    success

    retransmit

    oretransmitframetransfull

    TP

    t

    t

    PN

    TNtT

    11

    11

    2

    Time out

  • () Go-Back-N ( wopt .

    41

    opt

    send

    o

    success

    frame

    frame

    GBNw

    w

    TP

    t

    t

    11

    3

    Time out

  • 42

    opt

    sendsuccess

    f

    f

    SRPTw

    wP

    n

    nn

    0

    1

    1

  • GBN :

    nf=1250 bytes = 10000 bits, na=no=25 bytes = 200 bits

    : S&W GBN p = 0, 10-6, 10-5, 10-4 and R = 1 Mbps & 100 ms

    1 Mbps x 100 ms = 100000 bits = 10 frames Use Ws = 11

    Efficiency 0 10-6 10-5 10-4

    S&W 8.9% 8.8% 8.0% 3.3%

    GBN 98% 88.2% 45.4% 4.9%

    GBN S&W Delay-bandwidth product GBN . 43

  • 1000

    . : m/s 108*2

    1 ( km 1 Mbps 2

    50000 ( km 2 Mbps 127

    44

  • . 1000 : m/s 108*2

    1 ( km 1 Mbps 2

    50000 ( km 2 Mbps 127

    45

    1

    001.110

    1052121

    sec10101

    10

    sec105102

    10

    3

    6

    3

    6

    3

    6

    8

    3

    optsend

    frame

    prop

    opt

    frame

    prop

    ww

    t

    tw

    t

    t

    127.01001

    127127

    1001105

    25.02121

    sec105102

    10

    sec25.0102

    1050

    4

    4

    6

    3

    8

    6

    optsend

    frame

    prop

    opt

    frame

    prop

    ww

    t

    tw

    t

    t

  • MAC Sub-layer

    Data link layer

    802.3 CSMA-CD

    802.5 Token Ring

    802.2 Logical link control

    Physical layer

    MAC

    LLC

    802.11 Wireless LAN

    Network layer Network layer

    Physical layer

    OSI IEEE 802

    Various physical layers

    Other LANs

    46

  • IEEE IEEE 1980

    . IEEE 802.1 : LAN IEEE 802.2 : LLC IEEE 802.3 : IEEE 802.4 : Token Bus IEEE 802.5 : Token Ring IEEE 802.11 :

    47

  • IEEE 802.3 1973

    .IEEE 802.3

    10Base5 10Base2 10BaseT 10BaseF

    48

  • 500 4 10 AUI Transceiver

    .

    10Base5 implementation

    49

  • 185 4 30 . 10 T BNC .

    10Base2 implementation

    13.50

  • 100 4 10UTP . . RJ45 .

    10Base-T implementation

    51

  • 3 2 10 . ST SC .

    10Base-F implementation

    52

  • 53

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