chuong 3 - nghi thuc lk dl

7/29/2019 Chuong 3 - Nghi Thuc LK DL

1/92

CC NGHI THC LPLIN KT D LIU

Kim sot li (Errror Control) Kim sot lung (Flow Control)

Qun l kt ni (Connection

management) Cc nghi thc lp lin kt d liu

8/10/2013 1Khoa in in t -HBK TP.HCM


2/92

CC NGHI THC LP LINKT D LIU

Nghi thc l qui nh c thng nht giabn pht v bn nhn.

Mc ch : Hiu cc thnh phn c bn ca mt nghi thcbao gm: Kim sot li (Errror Control).

Kim sot lung (Flow Control). Qun l kt ni (Connection management).

Tm hiu cc nghi thc lp lin kt d liu



3/92

CC NGHI THC LP LINKT D LIU

Mt s k hiu :

P : Primary (pha s cp) l pha gi i cc frame d liu. S : Secondary (pha th cp) l pha thu cc frame d liu t P. I-frame (information frame): khung thng tincha d liu pha

pht truyn cho pha thu.

I(N) : S tun t ca khung thng tin ACK frame (Acknowledge frame) : S truyn ti P bo l

nhn d liu tt (khng b li). NAK frame (Negative Acknowledge frame: S truyn ti P bo

l nhn d liu sai (b li).

P SI -frame

ACK frame or NAK frame



4/92

KIM SOT LI(ERROR CONTROL)

Pha nhn khi nhn c frame s kim tra c li hay khng,sau c 2 kh nng Gi li pha pht bn tin iu khin xc nhn l khung tin khng li. Gi li pha pht bn tin iu khin yu cu pht li khung tin nu

khung tin li.

Qu trnh ny din ra t ng nn gi l Automatic Repeat Request(ARQ) Cc phng php kim sot li:

Idle RQ (Stop and Wait) Implicit (Hiu ngm ) Explicit (Tng minh )

Continuous RQ - Selective Repeat Implicit (Hiu ngm ) Explicit (Tng minh )

Continuous RQ - Go back N



5/92

Idle RQ ( Stop and Wait )

ng dng: S dng trong kiu truyn s liu nh hng k t

(character-oriented).

Hot ng theo ch bn song cng.

nh dng ca cc frame trong Idle RQ nh sau: C 3 lol frame : I-frame, ACK-frame, NAK-frame.

Cc frame ny gi l PDU (Protocol Data Unit) trongIdle RQ



6/92


PDUs Protocol Data Units

N(S) Send Sequence Number

N(R) Receive Sequence Number

SOH Start of Header

STX Start of Text

ETX End of Text

BCC Block (sum) Check Character

ACKAcknowledge

NAK Negative Acknowledge

SOH

N(S)

STX

.

ETX

BCC

ACK

N(R)

BCC

ACK- frame format

NAK

N(R)

BCC

NAK- frame format



7/92


c im : P ch c mt I frame ang ch ACK ti mt thi im Khi nhn mt I frame khng b li, S truyn li P mt ACK frame, Khi P nhn c ACK ca frame N, P s tip tc truyn I frame k tip

(N+1).

Khi P bt u truyn I frame, n s khi ng b nh thi (Timerstart), nu qu khong thi gian gii hn (time expires/restarts) mkhng nhn c frame tr li t S th P s truyn li frame .

Nu S nhn c cng 1 frame 2 ln th s loi b bn copy. iu nythc hin c do trong mi I-frame P u truyn km theo s tun tca frame.

Khng tn nhiu b nh m Hiu sut s dng ng truyn thp



8/92


Idle RQ - Implicit (Hiu ngm) Khi S nhn c mt frame b li, S s b qua v khng gi ACK.



9/92


Idle RQ - Explicit (Tng minh) Khi S nhn c mt frame b li, S truyn li P mt NAK frame, khi

P nhn c NAK ca frame N, P s truyn li I(N).



10/92


Hiu sut s dng ng truyn



11/92


Thi im gi xong gi 0, t = L / RThi im gi gi 0, t = 0

sender receiver

RTTGi 0 n

ACK n, v gi gi tip

theo, t = RTT + L / R

Gi 0 n xong



12/92

Trng hp truyn khng c li, th thi gian tng hon thnh vic truyn v x l mt I frame:

Tt= Tix+ 2Tp + Tap + Tip+ Tax

Thng thng Tap, Tip va Tax rt nh so vi Tp v Tix do :Tt Tix+ 2Tp Hiu sut lin kt c nh ngha l t s ca thi gian P pht

mt frame Tix trn thi gian tng hon thnh vic truyn mtframe Tt

Vi




13/92

Trng hp c li, cc frame b li phi thc hin vic truyn li.Gi s truyn thnh cng 1 frame th trung bnh c Nr frametruyn li, do xc sut mt frame khng li l 1/Nr v thi giantruyn tng cng :

Hiu sut:

Gi P l xc sut mt bit b li, khi xc sut mt frame (chiu di Ni) b li l:

Pf = 1 (1 P)Ni NiP , nu NiP


14/92


V d:

Mt chui cc khung d liu L=1000 bit ctruyn theo nghi thc RQ rnh. Bit tc lan

truyn sng trn lin kt l V=2.108m/s. Hy xcnh hiu sut lin kt vi cc tuyn lin kt sau:a. Tuyn lin kt c chiu di S=10km, t l li bit l

BER=10-4 v tc truyn d liu l R=9600bps

b. Tuyn lin kt c chiu di S=100km, t l li bit lBER=10-4 v tc truyn d liu l R=10Mbps



15/92


S=10km, BER=10-4, R=9600bps

Thi gian lan truyn sng:

Thi gian pht mt khung d liu:

Xc sut truyn ng mi khung:

Hiu sut lin kt:

S=100km, BER=10-4, R=10Mbps

35

p 8

S 10 *10T 5 *10 (s)

V 2 *10

ix

L 1000T 0.1(s)

R 9600

1000L 4

fP 1 BER 1 10 0.905

ix f

1 5

ix p

T * P 0.1* 0.905U

T 2 * T 0.1 2* 5*10

0.905

4

ix f2 14 5

ix r

T * P 10 * 0.905U U

T 2 * T 10 2 *50 *10

0.0905

8/10/2013 15Khoa in in t

-HBK TP.HCM


16/92

Continuous RQ

c im: P truyn cc I frame ti S mt cch lin tc m khng dng li ch ACK

frame truyn v t S. Khi c nhiu hn 1 I-frame ch ACK, P gi li bn sao ca cc I-frame trong b

m truyn li (retransmission list) hot ng theo nguyn tc FIFO S tr v ACK frame cho mi I frame nhn ng. Mi I frame cha s th t c tr v trong ACK Khi P nhn c ACK th s loai b I frame tng ng ra khi danh sch. Cc I frame nhn c khng li c S cha trong b m thu (link receive list)

ch x ly. S lun ch cc I frame k tip theo th t x l. Trong trng hp frame

nhn c khng ng th t (gi s trc nhn frame N, k n nhn frameN+2 ) th S s gi li tt c cc I frame trong b m thu cho n khi nhn li

c frame theo ng th t (frame N+1). Ngoi tr nghi thc Go Back N, bm thu bn S lun lun ch gi li ng 1 I- frame va nhn c.



17/92

Continuous RQ

Trong trng hp c li xy ra trong qu trnh truyndn, c 2 cch truyn li c p dng nh sau: S pht hin v yu cu P truyn li chnhng frame b li. Kieu

truyn li nay c goi la truyn li co la chon (selective repeat).

S pht hin v yu cu P truyn li nhng frame cha c trli ACK, ngha l tt c cc frame k t frame cui cng nhnng. Kiu truyn ny c gi l lp li N (go-back-N).

Hiu sut s dng ng truyn cao.

Cn b m ln.



18/92

Continuous RQ



19/92

Continuous RQ

Go back N Gi s I(N+1) b li S nhn I(N+2) khng ng th t (cha nhn c frame N+1) S gi NAK (N+1) cho P bo P bt u truyn li t frame N+1 v bt

u khi ng timer ch nhn I(N+1), nu qua mt khong thi gian

xc nh m khng nhn c I(N+1) th S truyn li NAK(N+1) (phng trng hp NAK(N+1) b li). S vo trng thi truyn li (Retransmission), tm thi khng tr li ACK

cho bt k frame no nhn c v ch I(N+1). Khi nhn c frame N+1, S tr li ACK (N+1) v ra khi trng thi

truyn li. Bn S khi gi mt Iframe th cng khi ng timer. Sau khong thi

gian Time Expires m khng nhn c tn hiu tr li ca frame nyth s truyn li frame .

B m thu khng cn dung lng ln.



20/92

Continuous RQ



21/92

Continuous RQ



22/92


23/92

Continuous RQ

Selective repeat - Implicit Retransmission: Gi s I-frame N+1 b li :

S tr v ACK frame cho nhg I-frame ng (N, N+2,N+3,..).

Khi nhn c ACK ca I-frame N+2, P nhn thay ACK(N+1) cha nhn c -> b li -> P xa I-frame N+2 rakhi b m v truyn li frame N+1.

Gi s ACK(N) b li : Khi nhn c ACK ca frame N+1, P pht hin ACK(N)

cha nhn c, c ngha l frame N b li do P truynli frame N.

Khi nhn frame N ln th 2, S xc nh c s trng lpva do b qua, tuy nhin S vn truyn tr v ACK(N) m bo P xa I-frame N ra khi b m.



24/92

Continuous RQ



25/92

Continuous RQ



26/92


27/92


28/92

Continuous RQ



29/92


30/92


31/92

KIM SOT LUNG(FLOW CONTROL)

Mc ch : iu khin vic truyn d liu gia bn pht v bn thu sao cho

m bo bn thu lun lun c th nhn c d liu vo b mtrc khi x l.

Theo cc c ch iu khin li trn, c nhng thi im b mbn thu b qu ti do lng ln d liu truyn n nhng chac x l. Do vic mt d liu c th xy ra. V vy phi bobn pht bit ngng pht v ch pht li khi bn thu snsng nhn.

C 2 phng php iu khin lung : X-ON/X-OFF

Sliding Window



32/92


33/92


Sliding Window

Trong kiu truyn continuous RQ, P truyn lin tip cc framekhng phi ch nhn ACK ging nh trong idle RQ.

Nu tc x l ti S chm -> S s truyn chm (hoc ngng)

truyn v ccACK frame, danh sch ch truyn li ti P tng lintuc. Hoc bn P gi lin tcc cac I-frame trong khi bn S chakp x l s lm b m thu qu ti.

Phng php ca s trt c thc hin bng cch quan stcc I frame ch truyn li ti P (v d K frame ). Gii hn ny

c xem l ca s truyn (send window). Nu n gii hn nyP s ngng truyn i n khi nhn c tn hiu ACK t bnthu.



34/92


C ch : Cc I frame pht i v ang i ACK c t trong ca s gi send

Widown.

Gii hn s lng I frame c pht trc khi nhn ACK l K (K l kchthc Send Windown).

Mi khi pht mt I Frame, cnh trn ca s UWE tng ln 1. Mi khi nhn mt ACK, cnh di ca s LWE tng ln 1. Bn pht s ngng truyn nu UWE LWE = K Bn thu cng thc hin tng t, cc frame trong b m thu c

quan st bi ca s nhn gi l Receive Widown Nguyn tc chon K m bo rng S s nhn c tt c cc I-

frame truyn ti. Cc thng s nh hng ti vic chn K l: Kch thc frame Dung lng b m Thi gian tr do lan truyn song. Tc pht



35/92


0

1

234

5

6

7

Window size = 7

0

1

2

34

5

6

7 0

1

2

34

5

6

7

0

12

34

5

6

7 0

1

2

34

5

6

7 0

1

2

34

5

6

7

tx 1 frame

lowerwindow

edgeupper

window

edge

tx 1 frame

tx 1 frame

receive ACK0

max window size

cant transmit

tx 1 frame

max window size

cant transmit8/10/2013 35Khoa in in t -HBK TP.HCM


36/92


Nguyn tc nh s : nhn dng cc frame vi nhau mi frame

c gan mt s th t (Sequence number), theo

nguyn tc th co the gan en v cung. Tuy nhin han ch, ket hp vi ca s trt,

so tuan t c gii hn theo nguyn tc anhxoay vong.

S lng cc s nhn dang c han ch vaquyt nh bi kch thc ca s va nghi thc.



37/92


Vi Idle RQ s frame cn nh s l 2

Vi Go-Back-N, s frame cn nh s l

K+1 VD: k=7. nh s 0,1,2,3,4,5,6,7,0,1.

Vi Selective Repeat, s frame cn nh

s l 2K+1 VD: k=7. nh s

0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,0,1.



38/92


39/92


40/92

QUN L KT NI(CONNECTION MANAGEMENT)

Mc ch: Khi ng v kt thc cuc kt ni

user Source LinkLayer

L_Connect

request

Destination

Link Layer

Correspon

dent user

V(S)=0

Setup

frame V(R)=0

L_Connect

indicationUA

frameL_Connect

Confirm

L_Data Request I

frameACK

frame

L_Data indication

L_Disconnect

requestDISC

frameUA

frame

L_Disconnect

indicationL_Disconnect

Confirm



41/92

NGHI THC LP LIN KT D LIU(DATA LINK PROTOCOL)

Chc nng : Lp iu khin lin kt d liu (data link control layer)

lin quan n vic truyn d liu qua mt tuyn d

liu ni tip Gm cc nghi thc truyn trong cu hnh im

im, hoc a im vi cc thnh phn quan trngnh nh dng khung, kim sot li, kim sot lungv qun l kt ni.

Ty thuc vo ng dng m cung cp 2 loi hnh dchv chnh connectionless (kt ni khng nh hng )v connection-oriented (kt ni c nh hng) .



42/92


43/92


44/92


DTEDTE DTE DTE

DTE Master

DLP

DTEDTE DTE DTE

DT

E

DT

E

DT

E

DLPShare

bus



45/92




46/92


47/92

BSC

Nghi thc iu khin li l Idle RQ

Thuc nghi thc ng b, nh hng kt ni(connection Oriented).

D liu c truyn theo kiu bn song cng(Half-Duplex )

ng dng trong cu hnh imim hoc aim.

Trong cu hnh a im, c mt Master iukhin vic truyn v nhn d liu t nhiu trmSlave.



48/92

BSC

DTEDCE DTE

Mode

m

BP

DTE

DTE

DCE

Mode

m

BP: Branching Point

4 wires (2

pairs)

Master

(Supervisor)Slave

Slave

Slave



49/92

BSC

DTE

DTE

LD/R

LD/R Line termination

LD/R: Line Driver/Receiver

DTE

LD/R

DTE

LD/RMaster(Supervisor)

SlaveSlave Slave

Twisted pair



50/92

BSC

Cu trc khung (Xem hnh): c 2 loi Khung d liu (Data)

n khi (Single Block Message)

a khi (Multiblock Message): s dng [SOH,IBT] phn bit cc khung a khung: khi 1 khung qu di s c ct ra thnh

nhiu khung. Khung cui cng kt thc bng ETB(End of Transmission Block)

Khung iu khin (supervisory) Thit lp kt ni v iu khin li,lung



51/92

BSCSYN STX Data (128bytes) BCC

Cu trc mt

khung d liun gin

Cu trc mtkhung d liun gin viHeader

SYN

SYN SYN SOH Header

ETX

Data (128bytes) BCCETX

Cu trc mtkhung a khi

SYN SYN SOH Header Data BCC ETXSTX IBT Data BCCSTX ETX

Data block

Cu trc mtkhung akhung

SYN SYN SOH Header DataSTX ETB BCC

SYN SYN SOH Header DataSTX BCCETX

Khung utin

Khung cuicng

SOH Start of Header STX Start of Text ETX End of Text

BCC Block (sum) Check Character ETB End of Tranmission Block51


52/92

BSC



53/92

BSC



54/92

BSC

Hot ng ca nghi thc



55/92


56/92

Poll

- X c d liu th gi, nukhng th tr v EOT

-ACK(0) : Xc nhnkhung d liu chn nhntt.

-ACK(1) : Xc nhnkhung d liu l nhn tt.

- NAK(0) : Xc nhnkhung d liu chn b li

- NAK(1) : Xc nhn

khung d liu l b li.- EOT : Kt thc truynd liu



57/92

Select /Poll



58/92


59/92

HDLC

8/10/2013 Khoa in in t -HBK TP.HCM 59

Secondary

Command

Response

Primary Secondary

Command Response

ResponseCommand

Primary

Secondary

Command / Response

Command / Response

Primary Secondary

Command

Response

Primary

Response

Secondary

/ Secondary / Primary


60/92

HDLC

Cc ch truyn HDLC Ch p ng thng (NRM Normal

Response Mode)

C cu hnh khng cn bng Trm s cp khi to qu trnh truyn ti trm th cp

Trm th cp c th ch pht d liu p ng lnht trm s cp

c s dng trn ng truyn c nhiu im r My ch l trm s cp

Cc u cui l trm th cp



61/92

HDLC

Cc ch truyn HDLC Ch p ng bt ng b (ARM

Asynchronuos Response Mode)

C cu hnh khng cn bng Trm th cp c th khi to qu trnh truyn m

khng cn s cho php ca trm s cp

Trm s cp chu trch nhim c ng truyn

t c s dng



62/92

HDLC

Cc ch truyn HDLC Ch cn bng bt ng b (ABM

Asynchronous Balanced Mode)

C cu hnh cn bng C hai trm c th khi to qu trnh truyn m khng

cn nhn lnh cho php

c s dng rng ri nht

Khng cn hi vng



63/92

HDLC

Cu trc khung Truyn ng b

Tt c truyn dn dng khung

Dng khung n cho trao i d liu v iu khin



64/92

HDLC

Trng c Xc nh v tr bt u v kt thc ca khung 01111110

C th ng 1 khung v m khung tip theo

My thu tm chui c ng b K thut chn bit c s dng trnh s nhm ln vi

d liu cha chui 01111110 0 c chn sau mi chui 5 bit 1 Nu my thu pht hin 5 bit 1 th kim tra bit tip theo

Nu bit tip theo l 0 th n c xo b Nu bit tip theo l 1 v bit th 7 l 0 th l c Nu bit tip theo l 1 v bit th 7 l 1, th n tip tc m s bt 1

Nu s bt 1 < 15 : my pht ch s kt thc Nu s bt 1 15 : My pht ch knh ri.



65/92

HDLC



66/92


67/92

HDLC

Trng iu khin C cu trc khc nhau ng vi nhng loi

khung khc nhau, c 3 loi khung trong HDLC Thng tin (I-frame) : Mang d liu cn gi Gim st (S-frame) : iu khin li v lung, cha

s th t khung gi v nhn

Khng nh s (U-frame) :Thit lp v kt thckt ni.

di c th 1 hay 2 byte



68/92

HDLC



69/92

HDLC

Trng iu khin 1 hay 2 bit u tin ca trng iu khin ch ra loi

khung

N(S) : S th t frame gi

N(R) : S th t frame nhn P/F : C 2 chc nng Poll hoc Final ph thuc hon

cnh s dng Khung lnh

Bit P

1 yu cu p ng t i phng Khung p ng

Bit F

1 ch rng y l tr li cho lnh



70/92

HDLC

S gm 2 bit xc nh loi khung gim st. C 4 loi khung gim st

S Lenh

00 RR : Receive Ready ->Dung 4 cach

ACK RR: dung nh mot xac nhan dng cua 1 khung thong tin a nhan khi bo thu khong co d lieu etruyen (tc khong the dung piggyback).

P - RR : Poll ->yeu cau tram th cap xem co d lieu e gi khong ?F - RR : ap ng cho Poll ->Tram th cap tra li cho s cap la khong co d lieu gi (xac nhanam). Neu co th se ap ng bang I-frame

FRR : ap ng cho Select -> Tram th cap tra li cho s cap la co kha nang nhan d lieu (xac nhan dng)

01 REJ : Reject -> la xac nhan am (NAK) c tra ve trong he thong Go-back n khi bo thu khong co d lieugi (tc khong the truyen theo piggyback)

10 RNR : Receive not Ready Dung 3 cach

ACK RNR : Yeu cau tram gi ngng khong gi them na cho en khi 1 RR c phat

PRNR : Select -> Khi tram s cap muon truyen d lie u cho tram th cap nao o.

FRNR : ap ng cho Select -> Khi mot th cap c chon ma khong the nhan d lieu (xac nhan am).

11 SREJ : Selective Reject -> la xac nhan am (NAK) c tra ve trong he thong Selective Repeat khi bo thukhong co d lieu gi (tc khong the truyen theo piggyback)


71/92

HDLC

Trng iu khin: M gm 5 bit xc nh cc loi U-frame

M Lenh ap ng

00 001 SNRM

11 011 SNRME

11 000 SARM DM11 010 SARME

11 100 SABM

11 110 SABME

00 000 UI UI

00 110 UA

00 101 DISC RD

10 000 SIM RIM

00 100 UP

11 001 RSET

11 101 XID XID

10 001 FRMR

Unnumbered

Information (UI)

Exchange ID (XID)

Set Initilization

Mode (SIM)Unnumbered Poll

(UP)

RequestDisconnect (RD)

Request Information Mode

(RIM)


72/92

HDLC

Trng thng tin Ch c trong khung thng tin v vi khung khng

nh s

Phi c mt s nguyn ln octets Chiu di thay i c



73/92

HDLC

Trng kiem tra

Phat hien sai

16 bit CRC

Tuy chon 32 bit CRC



74/92

HDLC

Hot ng ca HDLC iu khin kt ni : Thit lp v gii phng kt ni logical

gia 2 bn pht v nhn Trao i d liu : Trao i d liu gia 2 bn. Trong qa

trnh ny iu khin li v iu khin lung c ngdng.

V du: V hot ng ca HDLC nh sau : V(S) ch s tun t truyn k tip N(S). V(R) ch s tun t ca I-frame m pha thu ang mong i

nhn. Ti pha thu nu N(S) = V( R) th xem nh thu ng v

ng th t, ngc li nu N(S) V( R) th xem nh thusai v khng ng th t.



75/92

HDLC



76/92

HDLC



77/92


78/92

HDLC



79/92

HDLC



80/92

HDLC



81/92

HDLC

Qu trnh ng khung trong HDLCPACKET Lp mang 3

Tao C vagiai C

Tao A vagiai A

Tao FCS vagiai FCS

Nhoi bit vatach bit

Gan c

Lp vat ly

PACKETC

PACKETCA

PACKETCA FCS

PACKET'C'A' FCS'

PACKET'C'A' FCS'F F

PACKET

PACKETC

PACKETCA

PACKETCA FCS

PACKET'C'A' FCS'

PACKET'C'A' FCS'F F

Ben thuBen phat



82/92

HDLC

LAPB Link Access Procedure, Balanced L 1 phn ca mng X.25 (ITU-T) L 1 tp con ca HDLC ABM S dng cho ng im im gia h thng v cc nt ca mng chuyn mch gi

LAPD Link Access Procedure, D-Channel ISDN (ITU-D)

ABM

Lun l chui s 7 bit Trng a ch 16bit cha 2 a ch con

1 cho thit b v 1 cho ngi s dng

LLC Logical Link Control IEEE 802

Dng khung khc iu khin kt ni tch bit gia MAC (Medium Access Layer) v LLC (lp trn cng ca MAC) Khng c trm s cp v th cp cn 2 a ch: ngi gi v ngi nhn Pht hin sai lp MAC: 32 bit CRC Cc im truy xut ngun v ch (DSAP, SSAP)


Chng 3 Bi tp :


83/92

Chng 3_Bi tp :

Cc Nghi Thc LpLin Kt D Liu



84/92

Bi 1

V tin trnh trao i khung (c ghi ch thngtin cn thit) ca nghi thc Idle- RQ loitng minh gia DTE A v DTE B tho mn

cc gi s sau: bt u truyn khung th Nv khung d liu b sai mt ln, khung d liuth N+1 truyn ngay ln u tin khng b linhng hai khung xc nhn lin tip b li vkhung xc nhn ln ba l tt



85/92

Bi 2

DTE A truyn cho DTE B 7 khung d liutheo nghi thc Idle- RQ loi khng tngminh , tho mn cc gi s sau: khung d

liu th 1 b sai mt ln, khung d liu th 3truyn ngay ln u tin b li v hai khungxc nhn lin tip b li v khung xc nhnln ba l tt. V tin trnh trao i khung (cghi ch thng tin cn thit)



86/92

Bi 3

DTE A truyn DTE B 5 khung d liu dngnghi thc iu khin li Go back N, kchthc ca s k = 3. V tin trnh trao i

khung vi cc gi s sau: Khung d liu th 2 b li 1 ln



87/92

Bi 4

DTE A truyn DTE B 6 khung d liu dngnghi thc iu khin li Selective Repeatdng tng minh, kch thc ca s k = 3.

V tin trnh trao i khung vi cc gi ssau: Khung d liu th 2 b li 1 ln Khung tr li ca khung th 3 b li 1 ln. Khung th 5 v khung tr li ca khung 5 b

li 1 ln



88/92

Bi 5

DTE A truyn DTE B 6 khung d liu dngnghi thc iu khin li Selective Repeatdng khng tng minh, kch thc ca s k

= 3. V tin trnh trao i khung vi cc gis sau: Khung d liu th 2 b li 1 ln Khung tr li ca khung th 3 b li 1 ln. Khung th 5 v khung tr li ca khung 5 b

li 1 ln



89/92

Bi 6

Mt chui cc khung d liu c chiu di L =1000 bits c pht trn ng truyn c chiudi S = 4000Km, tc bit l R = 2Mbps, t l libit l BER = 10-4. Tnh hiu sut lin kt khi s

dng cc giao thc sau (b qua thi gian cagi ACK/NAK v thi gian x l, Tc truynsng l C = 3 x 108 m/s):

Stop & Wait

Selective Repeat vi kch thc ca s l N=7 Go-back-N vi kch thc ca s l N=12 Go-back-N vi kch thc ca s l N=127



90/92

Bi 8

Cho m hnh truyn s liu nh sau

Bit rng Slave A truyn cho Slave C 4 khung d liu bng nghi thcBSC, s dng nghi thc iu khin li Idle RQ (hi p c ngh) dngtng minh. V tin trnh trao i khung d liu, vi cc gi s sau :

Khi Slave A truyn Master th khung d liu th 2 b li 1 ln Khi Master truyn d liu cho Slave C khung d liu th 3 b li 1 ln .



91/92

Bi 9

Xc nh frame HDLC pht i t s cpvi gi s sau:

Data : pht ch vo theo m ASCII 7 bits,

kim tra chn S th t ca frame pht l 7, s dng Stop

and Wait ARQ.

D liu c gi n mi terminal trongmng.

B qua FCS



92/92

Bi 10

V qu trnh trao i cc frames. Bit rngs dng giao thc HDLC mode NRM vicc gi s sau:

Primary gi 3 frame n secondary v I-frame th 2 b li.

Kch thc ca s k =2, dng giao thc Go-

Back N

chuong 3 - nghi thuc lk dl

Documents