mmt- 05-1.pdf

Trng i Hc Bch Khoa Tp.HCM Khoa Khoa Hc v K Thut My Tnh

ThS. NGUYN CAO T

E-mail:[email protected]

Bi ging

Mng my tnh

Trng i Hc Bch Khoa Tp.HCM

Khoa Khoa Hc v K Thut My Tnh

2011

MNG MY TNH CN BN

Bi ging 1 - Chng 5: Tng lin kt d liu

2

Bi ging 11: Tng lin kt d liu

Tham kho:

Chng 5: Computer Networking A top-down approach

Kurose & Ross, 5th ed., Addison Wesley, 2010.



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Chng 5: Tng lin kt d liu

Mc tiu:

Hiu r cc nguyn tc ng sau cc dch v tng lin kt d liu: pht hin v sa li

chia s mt knh truyn qung b: a truy cp

nh a ch tng lin kt

truyn ti d liu tin cy, kim sot lu lng

Hin thc ca cng ngh ph bin tng lin kt d liu



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Tng lin kt d liu

5.1 Gii thiu v dch v

5.2 S pht hin v sa li

5.3 Cc giao thc a truy cp

5.4 nh a ch tng-Lin kt

5.5 Ethernet



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Gii thiu

Vi thut ng: MT v BT l cc node

cc knh lin lc m kt ni cc node lin k dc theo ng lin lc gi l cc lin kt

lin kt c dy

lin kt khng dy

LANs

gi tin tng-2 l mt khung, ng gi gi tin tng-3

tng lin kt-d liu c trch nhim truyn ti gi tin t mt node sang node lin k trn mt lin kt



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Ng cnh

gi tin c chuyn i bi nhiu giao thc khc nhau qua cc lin kt khc nhau: vd, Ethernet trn lin kt

u, tip sng khung trn lin kt trung gian, 802.11 lin kt cui

mi giao thc lin kt cung cp nhng dch v khc nhau

vd: c th hoc khng cung cp truyn ti d liu tin cy qua lin kt

vd tng ng: vn ti chuyn i t Sa Pa ti Thp

Mi

nga: t bn ti Sa Pa

t: SaPa ti H Ni

tu: H Ni ti HCM

t: HCM ti ng Thp

ghe: ng Thp ti T. Mi

ngi, hng = gi tin

on ng i = lin kt

loi vn ti = gt tng lk

c.ty du lch = gii thut nh tuyn



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Dch v tng lin kt d liu

chia khung, truy cp lin kt: ng gi gi tin vo cc khung, thm mo u, ui

truy cp knh truyn nu mi trng chia s

a ch MAC dng trong mo u ca khung xc nh ngun, ch

khc vi a ch IP!

truyn ti tin cy gia cc node cn k chng ta bit v vn ny tng truyn ti!

him khi dng trn mt lin kt t xy ra li (si quang, vi loi cp xon)

cc lin kt khng dy: tn s li cao

Hi: ti sao cn c tnh tin cy c tng-lin kt v u cui-u cui?



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Dch v tng lin kt d liu(tt)

kim sot lu lng: i tng bc gia cc node gi v nhn k nhau

pht hin li: li gy ra bi s suy gim ca tn hiu, nhiu.

bn nhn pht hin ra s tn ti ca li:

thng bo bn gi gi li hoc l b khung

sa li: bn nhn xc nh v sa cc li bit m khng yu cu s gi li

c ch mt-chiu v hai-chiu (half-, full-duplex) vi mt-chiu cc node ti hai u khng th truyn ti cng mt

lc



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Tng lin kt d liu c hin thc u?

trong mi my tnh

tng lin kt c h/thc card mng (hay network interface card NIC) card Ethernet, card PCMCI,

card 802.11

gn vo ng bus ca h thng

t hp bao gm phn cng, phn mm v firmware

b iu khin

s tr. ti vt l

cpu b nh

but my (vd, PCI)

card mng

lc my tnh

ng dng tr.ti

mng lin kt

lin kt vt l



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Giao tip gia card mng

bn gi: ng gi gi tin trong

khung d liu

thm vo cc bit kim tra li, truyn ti tin cy, kim sot l.lng, v.v..

bn nhn

kim tra li, tr.ti tin cy, kim sot l.lng, v.v..

tho gi tin ra, y ln tng trn ca bn nhn

b .khin b .khin

my gi my nhn

gi tin gi tin

gi tin

khung



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Tng lin kt d liu





5.5 Ethernet



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C ch pht hin li

EDC= cc bit dng cho pht hin v sa li (phn tha) D = D liu c bo v bng cch kim tra li, c th bao gm cc trng mo u C ch pht hin li khng ng tin cy 100%!

giao thc c th b st vi li, nhng rt him khi trng EDC cng ln th kh nng pht hin v sa li cng cao



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Kim tra tnh chn l

Mt bit chn l: Pht hin cc li 1 bit

bit chn l hai chiu: Pht hin v sa cc li 1 bit

0 0



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Tng kim tra Internet

Ng. gi: xem mt khc d liu (segment)

nh l mt chui cc s nguyn 16-bit

tng k/tra: tng b 1 (1s complement sum) ca khc d liu

ng/gi t gi tr tng k/tra vo trng tng k/tra ca mo u UDP

Ng. nhn:

tnh ton tng k/tra ca khc nhn c

kim tra xem tkt tnh c c bng gi tr trong trng tkt khng:

KHNG c li

C khng pht hin ra li. Nhng vn c kh nng c li?

Mc ch: pht hin cc li (vd: o bit) trong gi tin c truyn ti(ch : ch s dng tng tr.ti)



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Tnh tng kim tra: CRC (Cyclic Redundancy Check)

xem cc bit d liu, D, nh l s nh phn

chn r+1 bit mu (my pht), G

mc ch: chn r bit CRC , R, sao cho

chnh xc chia ht cho G (m-un 2)

ng/nhn bit G, chia cho G. nu s d khc 0: c li!

c th pht hin tt c cc li chm ngn hn r+1 bit

c s dng rng ri trong thc t (Ethernet, 802.11 WiFi, ATM)



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V d CRC

Cn:

D.2r XOR R = nG

tng ng:

D.2r = nG XOR R

tng ng:

nu chng ta chia D.2r cho G, cn c s d l R

R = s d [ ] D.2r

G



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Tng lin kt d liu





5.5 Ethernet



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Cc giao thc v lin kt a truy cp

Hai loi lin kt:

im-im (PPP) PPP dng cho truy cp quay s

lin kt PPP gia b chuyn mch Ethernet v my

qung b (ng dy/mi trng truyn chia s) Ethernet c in

ng ti ln HFC

LAN khng dy 802.11

ng y chia s(vd: Ethernet i cp)

tn s radio chia s (vd: 802.11 WiFi)

tn s radio chia s (v tinh)

mi ngi ti mt bui tic ng

(m thanh chia s)



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Cc giao thc a Truy Cp

mt knh qung b chia s chung

c nhiu s truyn ti ng ti ti cc node: giao thoa, nhiu ng nu node nhn c hn 1 tn hiu ti mt thi im

giao thc a truy cp

l gii thut phn tn m xc nh cch thc cc node chia s knh, nh l, xc nh khi no node c th truyn ti

s lin lc v chia s phi s dng chnh knh ! khng c knh ring dnh cho s iu phi



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Giao thc a Truy Cp L Tng

Knh qung b vi tc R bps

1. khi mt node mun truyn, n c th truyn vi vn tc R.

2. khi M node mun truyn, mi node c th truyn vi vn tc trung bnh l R/M

3. phn tn mt cch hon ton: khng c node ring dnh cho vic iu phi truyn ti

khng c s ng b ha ng h, thi gian

4. n gin !!!



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Cc giao thc MAC: phn loi

Ba lp ln:

Phn chia knh chia knh thnh nhng ming nh hn ( thi gian, tn s, m)

phn phi cc ming cho cc node c nhu cu s dng ring bit

Truy cp ngu nhin khng chia knh, cho php xy ra ng

khi phc li t ng

Theo lt cc node truyn theo lt, nhng node no c nhiu d liu hn c

th c lt di hn



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G/Thc MAC phn chia knh: TDMA

TDMA: a truy cp phn chia thi gian (time division multiple access)

truy cp knh theo vng"

mi trm c mt thi gian c di xc nh ( di = t/g gi 1 gi) trong mi vng

nhng khng dng s ri

v d: LAN 6-trm, 1,3,4 c gi tin, 2,5,6 ri

1 3 4 1 3 4

khung 6-



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G/Thc MAC phn chia knh: FDMA

FDMA: a truy cp phn chia tn s (frequency division multiple access)

ph ca knh c chia thnh nhng bng tn

mi trm c gn mt bng tnc nh

cc bng tn khng s dng s b ri

v d: LAN 6-trm, 1,3,4 c gi tin, cc bng 2,5,6 ri

cc b

ng t

n s

cp FDM



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Giao thc Truy cp Ngu nhin

Khi node c gi tin gi gi vn tc cao nht ca knh R.

khng c s iu phi u tin no gia cc node

nhiu hn 1 node cng truyn ti ng ,

giao thc MAC truy cp ngu nhin ch r: cch pht hin ng

cch phc hi li t ng (vd, thng qua truyn li tr)

V d ca cc g/thc MAC truy cp ngu nhin: ALOHA chia

ALOHA

CSMA, CSMA/CD, CSMA/CA



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a truy cp kim tra ng truyn - CSMA (Carrier Sense Multiple Access)

CSMA: lng nghe trc khi truyn:

Nu thy knh ri: gi ton vn khung

Nu knh bn, hon vic truyn ti li

v d tng ng con ngi: ng chen ngang ngi khc!



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ng trong CSMA

ng vn c th xy ra tr lan truyn ngha l hai node c th khng nghe c s truyn ti ca nhau

ng : ton b thi gian truyn ti gi tin b lng ph

s b tr cc node trong khng gian

ch : vai tr ca khong cch v tr lan truyn trong vic xc nh xc sut ng



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CSMA/CD

CSMA/CD: kim tra ng truyn, tr hon nh trong CSMA pht hin ng trong khong t/g ngn

cc truyn ti ng s b b qua, gim s hoang ph knh

pht hin ng : tng i d trong LAN i dy: o cng ca tn hiu, so snh

tn hiu gi i v nhn c.

kh trong LAN khng dy: cng tn hiu nhn c b b p o bi cng truyn ti cc b

tng ng: ngi ni chuyn lch s



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G/thc MAC Theo lt

g/thc MAC phn chia knh: chia s knh hiu qu v cng bng khi ti cao

khng hiu qu khi ti thp: tr khi truy cp knh, c s dng 1/N bng thng nu thm ch ch c 1 node lm vic!

g/thc MAC truy cp ngu nhin hiu qu khi ti thp: mt node c th s dng hon ton bng

thng

ti cao: ng b qu ti

g/thc theo lt s dng mt cch tt nht u im ca c 2!



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G/thc MAC Theo lt

Ch nh:

node ch tr mi cc node thnh vin truyn ti theo lt

thng thng c dng vi nhng t/b thnh vin cm

vn : tr do ch nh

hng ti mt im (ch tr)

ch tr

thnh vin

ch nh

d liu

d liu



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G/thc MAC Theo lt

Truyn th:

th iu khin c truyn t node ny sang node khc theo th t.

thng ip th

vn : tr do truyn th

hng ti mt im (gi th)

T

d liu

(khng c d liu)

T



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Tng kt v cc g/t MAC

phn chia knh, theo t/gian, tn s hoc m Phn chia Thi Gian, Phn chia Tn S

truy cp ngu nhin (ng), ALOHA, S-ALOHA, CSMA, CSMA/CD

kim tra ng truyn: d trong dy dn, kh trong m/trng khng dy

CSMA/CD c dng trong Ethernet

CSMA/CA c dng trong 802.11

theo lt s ch nh t node ch tr, s truyn th

Bluetooth, FDDI, IBM Token Ring



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Tng lin kt d liu





5.5 Ethernet



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a ch MAC v ARP

a ch IP 32-bit: a ch tng-mng

dng gi gi tin ti mng IP ch

a ch MAC (hay LAN hay vt l hay Ethernet): vai tr: chuyn khung t giao din ny ti giao din kt ni-vt l

khc (trong cng mng)

a ch MAC 48 bit (cho hu ht LANs)

c gn cng vo NIC ROM, i khi c th thay i c bng phn mm



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a ch LAN v ARP

Mi card mng LAN c mt a ch LAN c nht

a ch qung b = FF-FF-FF-FF-FF-FF

= card mng

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN (i dy hoc khng dy)



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a ch LAN (tt)

phn phi a ch MAC c qun l bi IEEE

cc nh sn xut mua mt phn ca khng gian a ch MAC ( m bo tnh c nht)

v d tng ng:

(a) a ch MAC: s CMND

(b) a ch IP: a ch th tn

a ch phng MAC tnh di ng c th di chuyn card mng t mt LAN sang LAN khc

a ch phn lp IP KHNG di ng a ch ph thuc vo mng con IP m nt gn vo



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ARP: Giao thc phn gii a ch (Address Resolution Protocol)

Mi nt (my, bt) trn LAN c 1 bng ARP

bng ARP: cc nh x a ch IP/MAC ca mt vi nt trong LAN

< a ch IP; a ch MAC; TTL>

thi gian sng TTL (Time To Live): thi gian tn ti ca mt nh x trong bng ARP, sau t/g ny nh x s b xa i (thng l 20 pht)

Cu hi: lm sao xc nh a ch MAC ca B nu bit a ch IP ca B?

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

137.196.7.23

137.196.7.78

137.196.7.14

137.196.7.88



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Giao thc ARP: cng LAN (mng)

A mun gi gi tin cho B, v a ch MAC ca B khng nm trong bng ARP ca A.

A qung b gi truy vn ARP, cha a ch IP ca B

a ch MAC ch = FF-FF-FF-FF-FF-FF

tt c cc my trn LAN u nhn truy vn ARP

B nhn c gi truy vn ARP, phn hi cho A vi a ch MAC ca n (B)

khung c gi ti a ch MAC ca A (gi-1-ch)

Mt bn lu cp a ch IP-sang-MAC c gi trong bng ARP ca A cho n khi t/tin tr nn c (ht gi)

trng thi mm: t/tin s b xa khi bng ARP nu khng c lm mi

ARP cm-v-chi: cc nt to ra bng ARP ca

chng m khng c s can thip t pha qun tr vin ca mng



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nh a ch: nh tuyn ti LAN khc

cc bc: gi gi tin t A sang B thng qua R

gi s A bit /c IP ca B

hai bng ARP trong bt R, mt cho mi mng IP (LAN)

R

1A-23-F9-CD-06-9B

222.222.222.220

111.111.111.110

E6-E9-00-17-BB-4B

CC-49-DE-D0-AB-7D

111.111.111.112

111.111.111.111

A 74-29-9C-E8-FF-55

222.222.222.221

88-B2-2F-54-1A-0F

B 222.222.222.222

49-BD-D2-C7-56-2A



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A to ra gi IP vi ngun A, ch B

A s dng ARP ly a ch MAC ca R vi IP l 111.111.111.110

A to khung tng-lin kt vi a ch ch l /c MAC ca R, khung cha gi tin IP A-ti-B

NIC A gi khung

NIC R nhn khung

R g b gi IP t khung Ethernet, thy n gi cho B

R s dng ARP ly a ch MAC ca B

R to ra khung cha gi tin IP A-ti-B ,gi cho B

R

1A-23-F9-CD-06-9B

222.222.222.220

111.111.111.110

E6-E9-00-17-BB-4B

CC-49-DE-D0-AB-7D

111.111.111.112

111.111.111.111

A 74-29-9C-E8-FF-55

222.222.222.221

88-B2-2F-54-1A-0F

B 222.222.222.222

49-BD-D2-C7-56-2A



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Tng lin kt d liu





5.5 Ethernet



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Ethernet

cng ngh thng tr ca LAN i dy:

r, $20 cho mi NIC

cng ngh LAN u tin c dng rng ri

n gin hn, r hn LAN dng th v ATM

theo kp nhp tng tc: 10 Mbps 10 Gbps

bn phc tho Ethernet ca Metcalfe



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S hnh Sao

s but ph bin sut nhng nm 90 tt c nt trong cng min ng (c th ng vi vi nhau)

ngy nay: s Sao chim u th b chuyn mch hot ng ti trung tm mi nan hoa chy mt giao thc Ethernet ring l (nt khng va

chm vi nhau)

b chuyn mch

but: cp ng trc hnh sao



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Cu trc khung Ethernet

Nic gi ng gi gi IP (hoc l gi tin ca giao thc tng khc) vo Khung ethernet

Phn khi u:

7 byte vi mu 10101010 theo sau bi 1 byte vi mu 10101011

s dng ng b ha tc ng h ca ngi gi vi ngi nhn.



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Cu trc khung Ethernet (tt)

a ch: 6 bytes nu NIC nhn c khung vi ng a ch MAC ca n hoc l a

ch pht tn rng (vd gi tin ARP), n s y d liu trong khung ln giao thc tng mng

ngoi ra, NIC b khung

Loi: xc nh giao thc tng cao hn (hu ht l IP nhng thnh thong c nhng g/t khc, vd, Novell IPX, AppleTalk)

CRC: kim tra ti ngi nhn, nu c li, khung s b b



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Ethernet: khng tin cy,khng kt ni

khng kt ni: khng c bt tay gia cc NIC gi v nhn

khng tin cy: NIC nhn khng gi ACK hoc l NACK cho NIC gi lung gi tin truyn ti tng mng c th c ch gin on (cc gi

tin b mt)

cc ch gin on c th c lp y nu /d dng TCP

ngoi ra, /d s thy cc ch gin on ny

Giao thc MAC ca Ethernet: CSMA/CD khng-chia-



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Gii thut CSMA/CD Ethernet

1. NIC nhn c gi tin t tng mng, to ra khung

2. Nu NIC thy knh truyn ri, bt u truyn khung. Nu NIC thy knh bn, i n khi knh ri, sau truyn

3. Nu NIC gi ton b khung i m khng pht hin ra s truyn ti no khc, NIC hon thnh vic gi khung!

4. Nu NIC pht hin s truyn ti khc trong khi ang truyn: hy b v gi tn hiu nghn

5. Sau khi hy b vic gi, NIC bc vo thoi lui hm m - exponential backhngff: sau ln ng th m, NIC chn K ngu nhin t {0,1,2,,2m-1}. NIC ch K512 t/gian bt, quay li bc 2



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CSMA/CD Ethernet (tt)

Tn hiu tc nghn: m bo rng tt c cc ngi gi khc bit v s ng ; 48 bits

T/g bt: .1 microsec cho mng Ethernet 10 Mbps; vi K=1023, thi gian ch vo khong 50 msec

thoi lui hm m:

Mc tiu: thay i thi gian ch truyn li cho ph hp vi ti hin ti

ti nng: thi gian ch ngu nhin s di hn

ng u tin: chn K t {0,1}; tr l K 512 t/g bt

ng ln 2: chn K t {0,1,2,3}

sau va chm ln 10, chn K t {0,1,2,3,4,,1023}

Xem/tng tc vi vi m Java trn Web AWL: rt khuyn khch !



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Hiu sut CSMA/CD

Tlan truyn = tr lan truyn ti a gia 2 nt LAN

ttruyn ti = thi gian truyn ti khung ln nht

Hiu sut tin ti 1 khi tlan truyn tin ti 0

ttruyn ti tin ti v cng

Hiu sut tt hn ALOHA: v n gin, r , khng tp trung!

truyentailantruyen/t+=Hieusuat

5t1

1



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Chun Ethernet 802.3: Tng Lin Kt v Vt L

nhiu chun Ethernet khc nhau giao thc MAC v nh dng khung ph bin

vn tc khc nhau: 2 Mbps, 10 Mbps, 100 Mbps, 1Gbps, 10G bps

mi trng vt l khc nhau: cp quang, cp TH

ng dng truyn ti

mng lin kt vt l

giao thc MAC v nh dng khung

100BASE-TX

100BASE-T4

100BASE-FX 100BASE-T2

100BASE-SX 100BASE-BX

tng vt l si quang tng vt l dy ng (cp xon)



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Chuyn m Manchester

s dng trong 10BaseT

mi bit c mt s chuyn i

cho php cc ng h pha nhn v gi ng b ha vi nhau khng cn ng h tp trung, tng qut cho cc nt!

Nhng, y l vn ca tng-vt l!

mmt- 05-1.pdf

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