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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.
-
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
3
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
-
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
4
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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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
5
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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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
6
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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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
7
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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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
8
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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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
9
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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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
10
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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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
11
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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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
12
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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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
13
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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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
14
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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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
15
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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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
16
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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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
17
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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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
18
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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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
19
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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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
20
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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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
21
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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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
22
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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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
23
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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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
24
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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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
25
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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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
26
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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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
27
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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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
28
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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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
29
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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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
30
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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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
31
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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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
32
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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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
33
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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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
34
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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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
35
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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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
36
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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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
37
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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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
38
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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Trng i Hc Bch Khoa Tp.HCM
Khoa Khoa Hc v K Thut My Tnh
2011
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Bi ging 1 - Chng 5: Tng lin kt d liu
39
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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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
40
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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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!