Bai Giang Mang May Tinh
description
Transcript of Bai Giang Mang May Tinh
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TRNG I HC QUY NHN KHOA K THUT & CNG NGH B MN IN T - VIN THNG
BI GING K THUT MNG
Quy Nhn, 2014
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CHNG I
TNG QUAN V MNG MY TNH
1.1 nh ngha mng my tnh
Mng my tnh l mt tp hp nhiu my tnh in t v cc thit b u cui
c kt ni vi nhau thng qua cc phng tin truyn dn nh cp, sng in t,
tia hng ngoi...nhm trao i thng tin, chia s phn cng, phn mm v d liu
vi nhau.
Hnh 1.1 Mng my tnh
1.2 Cc thnh phn c bn cu thnh nn mng my tnh
- Cc loi my tnh: Palm, Laptop, PC, MainFrame...
- Cc thit b giao tip: Card mng (NIC hay Adapter), Hub, Switch,
Router...
- Mi trng truyn dn: cp, sng in t, sng vi ba, tia hng ngoi...
- Cc protocol: TCP/IP, NetBeui, Apple Talk, IPX/SPX...
- Cc h iu hnh mng: WinNT, Win2000, Win2003, Novell Netware,
Unix...
- Cc ti nguyn: file, th mc
- Cc thit b ngoi vi: my in, my fax, Modem, Scanner...
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- Cc ng dng mng: phn mm qun l kho bi, phn mm bn v tu...
Server (my phc v): l my tnh c ci t cc phn mm chuyn dng
lm chc nng cung cp cc dch v cho cc my tnh khc. Ty theo dch v m
cc my ny cung cp, ngi ta chia thnh cc loi server nh sau: File server (cung
cp cc dch v v file v th mc), Print server (cung cp cc dch v v in n).
Do lm chc nng phc v cho cc my tnh khc nn cu hnh my server phi
mnh, thng thng l my chuyn dng ca cc hng nh: Compaq, Intel, IBM...
Client (my trm): l my tnh s dng cc dch v m cc my server cung
cp. Do x l s cng vic khng ln nn thng thng cc my ny khng yu cu
c cu hnh mnh.
Peer: l nhng my tnh va ng vai tr l my s dng va l my cung
cp cc dch v. My peer thng s dng cc h iu hnh nh: DOS, WinNT
Workstation, Win9X, Win Me, Win2K Professional, WinXP...
Media (phng tin truyn dn): l cch thc v vt liu ni kt cc my li
vi nhau.
Shared data (d liu dng chung): l tp hp cc tp tin, th mc m cc my
tnh chia s cc my tnh khc truy cp s dng chng thng qua mng.
Resource (ti nguyn): l tp tin, th mc, my in, my Fax, Modem,
CDROM v cc thnh phn khc m ngi dng mng s dng.
User (ngi dng): l ngi s dng my trm (client) truy xut cc ti
nguyn mng. Thng thng mt user s c mt username (account) v mt
password. H thng mng s da vo username v password bit bn l ai, c
quyn vo mng hay khng v c quyn s dng nhng ti nguyn no trn mng.
Administrator: l nh qun tr h thng mng.
1.3 Li ch ca mng my tnh
1.3.1 Tit kim c ti nguyn phn cng
Khi cc my tnh ca mt phng ban c ni mng vi nhau th chng ta c
th chia s nhng thit b ngoi vi nh my in, my FAX, a CDROM... thay v
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trang b cho tng my PC th thng qua mng chng ta c th dng chung cc thit
b ny.
V d 1: Trong mt phng my thc hnh c khong 30 my, nu trang b cho
tt c cc my trm c a cng th rt ph m chng ta li khng tn dng c ht
nng sut ca cc a cng . Gii php tp trung tt c cc ng dng vo server v
dng cng ngh mng bootrom chy cc my trm s lm gim chi ph phn cng
ng thi tin dng cho cng tc qun tr phng my hn ch c tnh trng cc
hc vin v tnh lm hng cc my trm.
V d 2: Mt cng ty mun rng tt c cc phng ban u c s dng
Internet thng qua modem v ng in thoi. Nu chng ta trang b cho mi phng
ban 1 modem v 1 ng in thoi th khng kh thi v vy chng ta phi tn dng
c s h tng mng chia s 1 modem v ng in thoi cho c cng ty u c
th truy cp Internet.
1.3.2 Trao i d liu tr nn d dng hn.
Theo phng php truyn thng mun chp d liu gia hai my tnh chng
ta dng a mm hoc dng cp link ni hai my li vi nhau sau chp d liu.
Chng ta thy rng hai gii php trn s khng thc t nu mt my t ti tng trt
v mt my t ti tng 5 trong mt ta nh. Vic trao i d liu gia cc my tnh
ngy cng nhiu hn, a dng hn, khong cch gia cc phng ban trong cng ty
ngy cng xa hn nn vic trao i d liu theo phng thc truyn thng khng
cn c p dng na, thay vo l cc my tnh ny c ni vi nhau qua cng
ngh mng.
1.3.3 Chia s ng dng
Cc ng dng thay v trn tng my trm chng ta s ci trn mt my server
v cc my trm dng chung ng dng trn server. Lc ta tit kim c chi
ph bn quyn v chi ph ci t, qun tr.
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1.3.4 Tp trung d liu, bo mt v backup tt.
i vi cc cng ty ln, d liu lu tr trn cc my trm ri rc d dn n
tnh trng h hng thng tin v khng c bo mt. Nu cc d liu ny c tp
trung v server tin vic bo mt, backup v qut virus.
1.3.5 S dng cc phn mm ng dng trn mng
Nh cc cng ngh mng m cc phn mm ng dng pht trin mnh v
c p dng vo nhiu lnh vc nh hng khng (phn mm bn v my bay ti
cc chi nhnh), ng st (phn mm theo di ng k v v bn v tu), cp thot
nc (phn mm qun l cng ty cp thot nc thnh ph)...
1.3.6 S dng cc dch v Internet.
Ngy nay Internet rt pht trin, tt c mi ngi trn th gii u c th trao
i E-mail vi nhau mt cch d dng hoc c th tr chuyn vi nhau m chi ph
rt thp so vi ph vin thng. ng thi cc cng ty cng dng cng ngh Web
qung co sn phm, mua bn hng ha qua mng (thng mi in t) ...
Da trn c s h tng mng chng ta c th xy dng cc h thng ng dng
ln nh chnh ph in t, thng mi in t, in thoi Internet nhm gim chi
ph v tng kh nng phc v ngy cng tt hn cho con ngi.
1.4 Giao thc mng my tnh
Cc thc th ca mng mun trao i thng tin vi nhau phi bt tay, m
phn v mt s th tc, quy tc. cng ni chung mt ngn ng. Tp quy tc hi
thoi c gi l giao thc mng (Protocols), bao gm:
C php: nh dng d liu, phng thc m ho v cc mc tn hiu.
Ng ngha: thng tin iu khin, iu khin lu lng v x l li.
Trao i thng tin gia hai thc th c th l trc tip hoc gin tip. Trong
hai h thng kt ni im im, cc thc th c th trao di thng tin trc tip
khng c s can thip ca cc thc th trung gian. Trong cu trc qung b, hai thc
th trao i d liu vi nhau phi thng qua cc thc th trung gian. Phc tp hn
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khi cc thc th khng chia s trn cng mt mng chuyn mch, kt ni gian tip
phi qua nhiu mng con.
Chc nng ca giao thc:
- ng gi: Trong qu trnh trao i thng, cc gi d liu c thm vo mt
s thng tin iu khin, bao gm a ch ngun v a ch ch, m pht hin li,
iu khin giao thc, Vic thm thng tin iu khin vo cc gi d liu c
gi l qu trnh ng gi (Encapsulation)
- Phn on v hp li: Mng truyn thng ch chp nhn kch thc cc gi
d liu c nh. Cc giao thc cc tng thp cn phi ct d liu thnh cc gi c
kch thc quy nh. Qu trnh ny gi l phn on. Ngc vi qu trnh phn on
bn pht l qu trnh hp li bn thu.
- iu khin lin kt: Trao i thng tin gia cc thc th c th thc hin hai
phng thc: hng lin kt v khng lin kt
- Gim st: Cc gi tin PDU c th lu chuyn c lp theo cc con ng
khc nhau, khi n ch c th khng theo th t nh khi pht. Trong phng thc
hng lin kt, cc gi tin phi c yu cu gim st. Mi mt PDU c mt m tp
hp duy nht v c ng k theo tun t. Cc thc th nhn s khi phc th t
cc gi tin nh th t bn pht.
- iu khin lu lng: lin quan n kh nng tip nhn cc gi tin ca thc
th bn pht sao cho bn thu khng b trn, m bo tc cao nht.
- iu khin li: l k thut cn thit nhm bo v d liu khng b mt hoc
b hng trong qu trnh trao i thng tin.
- ng b ha: Cc thc th giao thc c cc tham s v cc bin trng thi
v nh ngha trng thi, l cc tham s v kch thc ca s, tham s lin kt v
gi tr thi gian. Hai thc th truyn thng trong giao thc cn phi ng thi trong
cng mt trng thi xc nh.
- a ch ha: Hai thc th c th truyn thng c vi nhau, cn phi nhn
dng c nhau. Trong mng qung b, cc thc th phi nhn dng nh danh ca
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n trong gi tin. Trong cc mng chuyn mch, mng cn nhn bit thc th ch
nh tuyn d liu trc khi thit lp kt ni.
1.5 Phn loi mng my tnh
1.5.1 Theo khong cch a l
Mng my tnh c th c phn b trn mt khu vc nht nh hoc c th
trong mt quc gia hay ton cu. Da vo phm vi phn b, c th chia MMT thnh
cc loi nh sau:
a. Mng ni b LAN (Loacl Area Networks)
Mng cc b LAN: kt ni cc my tnh n l thnh mng ni b, ta kh nng
trao i thng tin v chia s ti nguyn trong c quan, x nghip, C hai loi mng
LAN khc nhau: LAN c dy (s dng cc loi cp) v LAN khng dy ( s dng
sng cao tn hay tia hng ngoi).
c trng ca mng LAN:
- Quy m ca mng nh, phm vi hot ng khong vi km. Cc my trong mt
ta nh, mt c quan hay x nghip ni li vi nhau. Qun tr v bo dng
mng n gin
- Cng ngh truyn dn s dng trong mng LAN thng l qung b
(Broadcast), bao gm mt cp n ni tt c cc my. Tc truyn d liu
cao t 10 100Mbps n hng trm Gbps, thi gian tr nh (c 10s), tin
cy cao, t l li bit t 10-8 n 10-11
- Cu trc topo ca mng a dng. V d mng hnh BUS, RING, Star v cc
loi mng lin kt, lai ghp, .
Hnh 1.2 Mng LAN
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b. Mng th MAN (Metropolitan Area Networks)
Kt ni cc my tnh trong phm vi thnh ph (bn knh vi km). MAN hot ng
theo kiu qung b, LAN to LAN. Mng cung cp cc dch v thoi, phi thoi v
truyn hnh cp.
Hnh 1.3 : Mng th MAN
c. Mng din rng (Wide Area Networks)
Kt ni cc my tnh trong ni b cc quc gia hay gia cc quc gia trong cng
chu lc. Thng thng cc kt ni ny c thc hin thng qua mng vin thng.
c trng c bn ca mng WAN:
- Hot ng trn phm vi mt quc gia hoc trn ton cu.
- Tc truyn d liu thp so vi mng cc b.
- Li truyn cao
- Cp quang bin v v tinh c dng cho vic truyn d liu trong mng
WAN.
Hnh 1.4 : Mng din rng WAN
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d. Kt ni lin mng (Internet Connectivity)
Nhu cu trao i thng tin v chia s ti nguyn chung i hi cc hot ng
truyn thng, cn thit phi kt ni nhiu mng thnh mt mng ln gi l lin mng.
Lin mng (internet) l mng ca cc mng con, l mt tp cc mng LAN,
WAN, MAN c lp c kt ni li vi nhau nhm:
- Gim lu thng trn mng: Cc gi tin thng c lu chuyn trn
cc mng con v cc gi tin lu thng trn lin mng khi cc mng con lin
lc vi nhau.
- Ti u ho hiu nng: Gim lu thng trn mng l ti u hiu nng
ca mng, tuy nhin my ch (Server Load) s phi tng ti khi n c s
dng nh mt Router.
- n gin ho vic qun tr mng: C th xc nh cc s c k thut
v c lp d dng hn trong mt mng c quy m nh, thng l trong mt
mt cc b chng hn.
- Hiu qu hn so vi WAN c phm vi hot ng ln, chi ph gim, hiu
nng lin mng tng v phc tp ca vic qun l nh hn
1.5.2 Theo cu trc mng (Topology)
Topology l cu trc hnh hc khng gian ca mng. Thc cht y l cch
b tr v tr vt l cc node v cch thc kt ni chng li vi nhau.
C hai kiu cu trc mng:
- Kiu im - im (Point to Point).
- Kiu qung b (Multi Point).
a. Kiu im im (Point to Point).
ng truyn ni tng cp node li vi nhau theo mt cu trc hnh hc xc
nh. Mt knh truyn vt l s c thit lp gia 2 node c nhu cu trao i thng
tin.
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Chc nng cc node trung gian: tip nhn, lu tm thi v gi thng tin sang
node tip theo khi ng truyn ri. Cu trc im - im gi l mng lu v gi
tip (Store - and - Forward).
u im ca cu hnh ny l t kh nng ng thng tin (Collision).
Nhc im ca n l hiu sut s dng ng truyn thp, chim dng nhiu
ti nguyn, tr ln, tiu tn nhiu thi gian thit lp ng truyn v x l ti
cc node. V vy tc trao i thng tin thp.
b. Kiu qung b (Multi Point).
Tt c cc node cng truy nhp mt ng truyn vt l. Mt thng ip
truyn t mt node no s c tt c cc node cn li tip nhn v kim tra a
ch ch c phi ca n hay khng.
Cn thit phi c c ch gii quyt vn ng thng tin (Collision)
hay tc nghn (Congestion) thng tin trn ng truyn trong cc mng hnh BUS
v hnh RING.
Cc mng c cu trc qung b c phn chia thnh hai loi: qung b tnh
v qung b ng ph thuc vo vic cp pht ng truyn cho cc node. Trong
qung b ng c qung b ng tp trung v qung b ng phn tn.
Qung b tnh: Chia thi gian thnh nhiu khong ri rc v dng c ch quay
vng (Round Robin) cp pht ng truyn. Cc node c quyn c truy nhp
khi n ca thi gian ca n.
Qung b ng tp trung: Mt thit b trung gian c chc nng tip nhn yu
cu lin lc v cp pht ng truyn cho cc node. Kiu cp pht ny gim c
ti a thi gian cht ca ng truyn, hiu sut knh truyn cao, nhng thit k
phc tp v kh khn.
Qung b ng phn tn: Khng c b trung gian, cc node t quyt nh c
nn hay khng nn truy nhp ng truyn, ph thuc vo trng thi ca mng.
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1.5.3 Theo phng php chuyn mch
a. Chuyn mch knh (Circuit Switched Network)
Trc khi trao i thng tin, h thng s thit lp kt ni gia 2 thc th bng
mt ng truyn vt l. Nu thc th bn th kt ni s b hy
- Duy tr kt ni trong sut qu trnh 2 thc th trao i thng tin.
- Gii phng kt ni. Sau khi truyn xong d liu, kt ni s c hy b, gii
phng cc ti nguyn b chim dng sn sng phc v cho yu cu kt ni
khc.
Nhc im: cn nhiu thi gian thit lp knh truyn, v vy thi gian
thit lp knh chm v xc sut kt ni khng thnh cng cao.
b. Chuyn mch gi (Packet Swiched Networks)
Nguyn l chuyn mch gi: Thng ip (Message) ngi s dng c chia
thnh nhiu gi nh (Packet) c di quy nh. di gi tin cc i (Maximum
Transfer Unit - MTU) trong cc mng khc nhau l khc nhau. Cc gi tin c th
truyn c lp trn nhiu tuyn hng n ch v cc gi tin ca nhiu thng ip
khc nhau c th cng truyn trn mt tuyn lin mng. Ti mi node, cc gi tin
c tip nhn, lu tr, x l ti b nh, khng cn phi lu tr tm thi trn b
nh ngoi (nh a cng) v c chuyn tip n node k tip. nh tuyn cc gi
tin qua mng nhanh hn v hiu qu hn.
K thut chuyn mch gi c nhiu u im hn chuyn mch knh:
- Cc gi tin lu chuyn hng ch c lp, trn mt ng c th chia s cho
nhiu gi tin. V vy hiu sut ng truyn cao hn.
- Cc gi tin c xp hng v truyn qua tuyn kt ni.
- Hai thc th c tc d liu khc nhau c th trao i cc gi vi tc ph
hp.
- Trong mng chuyn mch knh, khi lu lng tng th mng t chi thm cc
yu cu kt ni (do nghn) cho n khi gim xung. Trong mng chuyn mch
gi vn c chp nhn nhng tr phn pht gi tin c th tng ln.
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1.6 Kin trc phn tng v chun ha mng
1.6.1 C s xut hin kin trc phn tng
S khc bit v kin trc mng gy tr ngi cho ngi s dng khi kt ni
lin mng, nh hng n sn xut v s dng sn phm mng.
Cn xy dng m hnh chun lm c s cho cc nh nghin cu v thit k
mng to ra cc sn phm m v mng v to iu kin cho vic pht trin v s
dng mng.
V vy cc t chc tiu chun quc t ra i. Cc nh sn xut c ting
ni chung cho cc sn phm ca h, l cc chun, cc khuyn ngh quy nh thit
k v sn xut sn phm mng
1.6.2 M hnh kin trc phn tng
Cc mng my tnh c thit k v ci t theo quan im c cu trc a
tng. Mi thnh phn ca mng c xem nh mt h thng gm nhiu tng v mi
tng bao gm mt s chc nng truyn thng. Cc tng c chng ln nhau, s
lng v chc nng ca cc tng ph thuc vo cc nh sn xut v thit k. Tuy
nhin quan im chung l trong mi tng c nhiu thc th (cc tin trnh) thc hin
mt s chc nng nhm cung cp mt s dch v, th tc cho cc thc th tng trn
hot ng.
1.6.2.1 Cc quy tc phn tng
- Khng nh ngha qu nhiu tng, s lng tng, vai tr v chc nng ca
cc tng trong mi h thng ca mng l nh nhau, khng qu phc tp khi xc nh
v ghp ni cc tng. Chc nng cc tng c lp vi nhau v c tnh m.
- Trong h thng, cn xc nh r mi quan h gia cc tng k nhau (gi l
giao din - Interface). Mi quan h ny quy nh nhng thao tc v dch v c bn
m tng k di cung cp cho tng k trn v s cc tng tc qua li gia hai tng
k nhau l nh nht.
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- Xc nh mi quan h gia cc ng tng thng nht v cc phng thc
hot ng trong qu trnh truyn thng, mi quan h l tp cc quy tc v cc
tho thun trong hi thoi gia cc h thng, gi l giao thc (protocol).
- D liu khng c truyn trc tip t tng th i ca h thng pht sang
tng th i ca h thng nhn (tr tng thp nht- tng vt l) m c chuyn t tng
cao xung tng thp nht bn h thng pht v qua ng truyn vt l, d liu l
chui bit khng cu trc c truyn sang tng thp nht ca h thng nhn v c
chuyn ngc ln cc tng trn. Gia cc ng tng c xc nh lin kt logic,
gia cc tng vt l c lin kt vt l.
- Trong mi mt tng c mt hoc nhiu thc th (Entity) hot ng. Cc thc
th c th l mt tin trnh (Process) trong mt h a x l, hoc c th l mt chng
trnh con.
- Cc thc th truyn thng vi cc thc th tng trn v tng di n thng
qua cc im truy nhp dch v trn cc giao din SAP (Service Access Point). Cc
thc th phi bit n cung cp nhng dch v g cho cc hot ng tng trn k n
v cc hot ng truyn thng ca n c s dng nhng dch v g do tng trn
cung cp thng qua cc li gi hm qua cc im truy nhp SAP trn cc giao din
tng.
Hnh 1.5: M hnh kin trc phn tng
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1.6.2.2 Nguyn tc truyn thng ng tng
truyn thng ng tng, gi tin khi chuyn xung qua cc tng s c b
sung thm vo phn u bng thng tin iu khin ca tng (gi l Header) gi l
qu trnh ng gi (Encapsulation). Bn nhn s din ra qu trnh ngc li: khi i
qua cc tng, gi tin s tch thng tin iu khin thuc n trc khi chuyn d liu
ln tng trn gi l qu trnh gii ng gi Decapsulation
n v d liu c s dng trong cc tng gm:
- Thng tin iu khin giao thc PCI (Protocol Control Information): Thng
tin c thm vo u cc gi tin trong qu trnh hot ng truyn thng ca cc
thc th.
- n v d liu dch v SDU (Service Data Unit): l n v d liu truyn
thng gia cc tng k nhau
- n v d liu giao thc PDU (Protocol Data Unit): PDU = PCI + SDU,
ngha l n v d liu giao thc bao gm thng tin iu khin PCI c thm vo
u n v d liu dch v SDU.
1.6.2.3 Dch v v cht lng dch v
Dch v l tp cc thao tc s cp hay l cc hm nguyn thy m mt tng
cung cp cho tng trn n. Dch v lin quan n 2 tng k nhau.
Qu trnh cung cp dch v thng qua cc im truy nhp SAP trn cc giao
din tng. C hai loi dch v: dch v hng lin kt (Connection Oriented) v dch
v khng lin kt (Connectionless).
a. Dch v hng lin kt
L dch v theo m hnh in thoi. Cc dch v v giao thc trong cc m hnh OSI
thc hin truyn thng 3 giai on:
- Thit lp lin kt: Mt knh logic c thit lp gia cc thc th ng tng
ca hai h thng khc nhau. Chng s m phn, thng lng vi nhau v
tp cc tham s v s dng cc tham s ny nh th no trong qu trnh truyn
s liu.
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- Truyn d liu: D liu c truyn gia hai tng ng tng theo c ch kim
sot v qun l qu trnh truyn d liu, thc hin vic ghp knh, ct hp d
liu, bo m c th t truyn, pht hin li, kim sot li, kim sot
lung d liu, pht hin tc nghn thng tin, nhm tng cng tin cy
cao v hiu sut truyn.
- Gii phng lin kt: Sau khi kt thc qu trnh truyn d liu, cc ti nguyn
ca h thng c cp pht cho qu trnh thit lp lin kt v truyn d liu
s c gii phng, sn sng cp cho lin kt tip theo
b. Dch v khng lin kt
Dch v khng lin kt khng cn tiu tn thi gian thit lp lin kt v
gii phng lin kt gia cc thc th ng tng khng yu cu kim sot lung d
liu, d liu c truyn vi tc cao nhng tin cy thp. Khng truyn li
trong trng hp xy ra li ng truyn. Cc dch v khng lin kt ph hp vi
cc yu cu truyn dung lng khng ln, cc cuc trao i thng tin ri rc v c
lp.
1.6.3 M hnh kt ni cc h thng m OSI (Open System Interconnection)
M hnh OSI l m hnh cn bn v cc tin trnh truyn thng, thit lp cc
tiu chun kin trc mng mc Quc t, l c s chung cc h thng khc nhau
c th lin kt v truyn thng c vi nhau.
M hnh OSI t chc cc giao thc truyn thng thnh 7 tng, mi mt tng
gii quyt mt phn hp ca tin trnh truyn thng, chia tin trnh truyn thng
thnh nhiu tng v trong mi tng c th c nhiu giao thc khc nhau thc hin
cc nhu cu truyn thng c th.
1.6.3.1 Nguyn tc nh ngha cc tng h thng m
M hnh OSI tun theo cc nguyn tc phn tng nh sau:
- M hnh gm 7 tng l h thng m, phi c kh nng kt ni vi cc h thng
khc nhau, tng thch vi cc chun OSI.
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- Qu trnh x l cc ng dng c thc hin trong cc h thng m, trong khi
vn duy tr c cc hot ng kt ni gia cc h thng.
- Thit lp knh logic nhm thc hin vic trao i thng tin gia cc thc th.
Hnh 1.6: M hnh kt ni cc h thng m OSI
1.6.3.2 Cc giao thc trong m hnh OSI
Trong m hnh OSI c hai loi giao thc c s dng: giao thc hng lin
kt (Connection Oriented) v giao thc khng lin kt (Connectionless).
Giao thc hng lin kt: Trc khi truyn d liu, cc thc th ng tng
trong hai h thng cn phi thit lp mt lin kt logic. Chng thng lng vi
nhau v tp cc tham s s s dng trong giai on truyn d liu. D liu c
truyn vi cc c ch kim sot li, kim sot lung d liu, ct/hp d liu nhm
nng cao tin cy v hiu qu ca qu trnh truyn d liu.
Giao thc khng lin kt: D liu c truyn c lp trn cc tuyn khc
nhau. Vi cc giao thc khng lin kt ch c giai on duy nht truyn d liu.
1.6.3.3 Vai tr v chc nng ca cc tng
-
1.6.3.3.1 Lp ng dng (Application Layer)
Cho php ngi dng (user), l ngi hay phn mm, truy cp vo mng.
Lp ny cung cp giao din cho ngi dng v h tr dch v nh th in t, remote
file access and transfer, shared database management, v cc dng dch v phn phi
d liu khc.
Hnh minh ha quan h gia lp ng dng vi user v lp trnh by. Trong s
cc dch v c c, th hnh v ch trnh by 3 dng: X.400 (message handle
services); X.500 (directory services); v chuyn file access, and management
(FTAM). User trong hnh dng X.400 v gi mt email. Ch l khng c thm
header hay trailer trong lp ny.
Application
layer X.500 X.400FTAM
L7 data
To presentation layer
User
Application
layer X.500 X.400FTAM
L7 data
From presentation layer
User
Hnh 1.7 Lp ng dng
1.6.3.3.2 Lp trnh by (Presentation Layer)
Lp trnh by gii quyt cc vn lin quan n c php (syntax) v ng
ngha (sematic) ca thng tin c truyn gia hai h thng.
Lp trnh by chu trch nhim chuyn i d liu gi i trn mng t mt
loi biu din ny sang mt loi khc. t c iu n cung cp mt dng
biu din truyn thng chung cho php chuyn i t dng biu din cc b sang
biu din chung v ngc li.
Hnh cho thy quan h gia lp trnh by vi lp ng dng v lp kim sot.
-
L7 data
From application layer
L6 data
To session layer
Presentation
layer Encoded, encrypted, and
compressed dataH6
L7 data
To application layer
L6 data
From session layer
Presentation
layer Decoded, decrypted, and
decompressed dataH6
Hnh 1.8: Lp trnh by
1.6.3.3.3 Lp phin (Session Layer)
Lp phin cho php ngi s dng trn cc my khc nhau thit lp, duy tr,
hu b v ng b phin truyn thng gia h vi nhau.
Dch v phin cung cp lin kt gia 2 u cui s dng dch v phin sao
cho d liu c trao i mt cch ng b v khi kt thc s gii phng lin kt.
L6 data
From presentation layer
L5 data
To transport layer
syn syn syn
Session
layer
L6 data
To presentation layer
115
L5 data
From transport layer
syn syn syn
Session
layerH5
Hnh 1.9: Lp Phin
1.6.3.3.4 Lp vn chuyn (Transport Layer)
L tng cao nht c lin quan n cc giao thc trao i d liu gia cc h
thng m, kim sot vic truyn d liu t u cui n u cui (end to end)
Lp vn chuyn thc hin vic chia cc gi tin ln thnh cc gi tin nh hn
trc khi gi i v nh s cc gi tin v m bo chng chuyn theo ng th t.
-
L tng cui cng chu trch nhim v mc an ton trong truyn d liu
nn giao thc tng ny ph thuc nhiu vo bn cht ca tng mng. Lp vn chuyn
c th thc hin vic ghp knh (multiplex) gim gi thnh
L5 data
H4H4H4
Transport
layer
L4 data
L4 data
L4 data
From session layer
To network layer
L5 data
H4H4H4
Transport
layer
L4 data
L4 data
L4 data
To session layer
From network layer
Hnh 9
Hnh 1.10: Lp vn chuyn
1.6.3.3.5 Lp mng (Netwwork Layer)
Thc hin cc chc nng chn ng m bo truyn tin thng sut gia
hai node u cui trong mng.
Mt chc nng quan trng khc ca lp mng l chc nng iu khin tc
nghn (Congestion Control) da trn bn qu trnh c bn:
- nh a ch (Addressing).
- ng gi (Encapsulation).
- nh tuyn (Routing).
- Gii ng gi (Decapsulation).
L3 data
H3
L4 data
L3 data
H3
L4 data
From Transport layer To transport layer
To data link layer From data link layer
Network
layer
Network
layer
PacketPacket
Hnh 7
-
Hnh 1.11: Lp mng
1.6.3.3.6 Lp lin kt d liu (Data link Layer)
Chc nng ch yu ca lp lin kt d liu l thc hin thit lp cc lin kt,
duy tr v hy b cc lin kt d liu. Kim sot li v kim sot lu lng.
10101000000010
H2T2
L3 data
10101000000010
H2T2
L3 data
From network layer To network layer
Frame FrameData
link
layer
Data
link
layer
From physical layerTo physical layer
Hnh 1.12: Lp lin kt d liu
Lp lin kt d liu gm:
- Lp con LLC: nh ngha cc tin trnh phn mm cung cp cc dch v cho
cc giao thc lp mng.
- Lp con MAC: nh ngha cc tin trnh truy nhp phng tin c thc
hin bng phn cng.
1.6.3.3.7 Lp vt l (Physical layer)
-
L lp thp nht trong m hnh 7 lp OSI. Cc thc th tng giao tip vi
nhau qua mt ng truyn vt l. Lp vt l xc nh cc chc nng, th tc v
in, c, quang kch hot, duy tr v gii phng cc kt ni vt l gia cc h
thng mng. Cc chun trong lp vt l l cc chun xc nh giao din ngi s
dng v mi trng mng.
From data link layer To data link layer
Physical
layer
Physical
layer
L2 data
10101000000010
L2 data
10101000000010
Transmission medium
Hnh 1.13: Lp vt l
1.7 Cc m hnh x l d liu
1.7.1 M hnh Client Server
M hnh Client Server m t cc dch v mng v cc ng dng c s
dng truy nhp cc dch v. L m hnh phn chia cc thao tc thnh hai phn:
pha Client cung cp cho ngi s dng mt giao din yu cu dch v t mng
v pha Server tip nhn cc yu cu t pha Client v cung cp cc dch v mt cch
thng sut cho ngi dng.
-
Hnh 1.14: M hnh Client Server
1.7.2 M hnh ngang hng (Peer to Peer)
Trong m hnh ngang hng tt c cc my u l my ch ng thi cng l
my khch. Cc my trn mng chia s ti nguyn khng ph thuc vo nhau. Mng
ngang hng thng c t chc thnh cc lm vic Workgroup.
Hnh 1.15: M hnh ngang hng (Peer to Peer)
M hnh lai (Hybrid): l s kt hp gia Client/Server v Peer-to-Peer. Phn
ln cc mng my tnh trn thc t thuc m hnh ny.
CHNG II
PHNG TIN TRUYN DN V CC THIT B
LIN KT MNG
2.1 Phng tin truyn dn
Phng tin truyn vt l l vt truyn ti cc tn hiu in t gia cc thnh
mng vi nhau, bao gm cc loi cp v cc phng tin v tuyn.
2.1.1 Cc c trng c bn ca ng truyn
Bng thng (Bandwidth).
-
Bng thng ca mt ng truyn l min tn s gii hn thp v tn s gii
hn cao, tc l min tn s m ng truyn c th p ng c.
- Bng thng l hu hn.
- Bng thng khng phi min ph.
- Bng thng l yu t chnh phn tch nh gi hiu sut ca mng, thit
k mng mi v kt ni Internet.
Bng thng thc t ca mng c xc nh da trn nhiu yu t: thuc tnh
ca phng tin vt l v cng ngh c chn thc hin qu trnh bo hiu v
truyn tn hiu mng.
Thng lng (Throughput).
Thng lng ca ng truyn l s lng cc bit (chui bit) c truyn i
trong mt giy, hay ni cch khc l tc ca ng truyn. Thng thng, v
nhiu l do m thng lng c gi tr nh hn so vi bng thng s cc i ca
phng tin truyn dn c s dng trong mng.
Vi mt knh truyn dn c bng tn nht nh, ch c th truyn dn c
mt dng thng tin s c tc gii hn bi cng thc Nyquist (ch tnh trong
trng hp khng c nhiu).
Cng thc Shannon Hartley (c nhiu):
Cc yu t nh hng n bng thng:
- Cc thit b lin mng.
- Loi d liu c truyn, topo mng, s lng ngi dng trn mng.
- Tc ca ng truyn ph thuc vo bng thng v di ca n. Mt
mng LAN Ethernet tc truyn 10 Mbps v c bng thng l 10 Mbps.
Goodput
]/[log2 2 sbitMWC
]/[)1(log2 2 sbitN
SWC
-
L i lng xc nh d liu c ch c truyn trn mng trong mt khong
thi gian cho trc v y chnh l thng s ng ch nht i vi ngi s dng
mng.
Goodput = throughput - (overhead cho vic thit lp phin, ACK v ng gi)
- BW: Bng thng l thuyt ti a ca lin kt chm nht gia trm ngun v
trm ch (bits/s)
- P: thng lng thc t (bits/s)
- T: Thi gian truyn file (s)
- S: kch thc file trong chui bit
Suy hao (Attenuation).
L i lng o s suy yu ca cc tn hiu trn ng truyn. Suy hao c
xc nh bng n v decibel (dB) theo biu thc sau:
A ph thuc vo di ca cp, cp cng di th suy hao cng cao.
H s khuch i (Gain).
H s khuch i c xc nh bng n v decibel (dB) theo biu thc sau:
Nhiu (Noise): C nhiu dng nhiu nh nhiu nhit, nhiu cm ng (induced
noise), crosstalk (xuyn knh), v nhiu xung u c kh nng lm xu tn
hiu i. Nhiu nhit l cc chuyn ng ngu nhin ca electron trong dy
dn to ra thm cc tin hiu khng do my pht chuyn i. Induced noise n
t cc ng c hay thit b in, khi cc thit b ny hot ng nh mt
anten v mi trng ng vai tr b thu sng. Crosstalk l nh hng ca
out
in
out
in
P
Plog10
V
Vlog20A
in
out
in
out
P
Plog10
V
Vlog20G
P
SThay
BW
ST
-
mt dy dn ln dy khc. Mt dy ng vai tr anten v dy cn li l b thu
sng. Nhiu xung n t cc thit b cng sut, tia chp, v.v
2.1.2 Cc loi cp mng
Vi cc loi cp mng, kh nng truyn c th hiu theo ngha tc d liu
hoc bng thng, ph thuc ch yu vo khong cch v mi trng truyn thng
trong kiu kt ni l im - im hay a im, nh trong mng LAN.
2.1.2.1 Cp xon i (Twisted pair cable)
Cp xon i c dng trong cc mng LAN cc b, gi thnh r, c v bc
trnh nhit , m. Cp c hai dy ng xon vo nhau, gim nhy ca cp
vi EMI, gim bc x m nhiu tn s radio gy nhiu.
Cp xon i c hai loi:
- Cp c v bc (STP Shield Twisted Pair): gm nhiu cp xon c ph
bn ngoi mt lp v lm bng dy ng bn. Lp v bc c tc dng chng
nhiu EMI, RFI. Vi chiu di 100m, tc t 155Mbps (thng c tc
truyn vo khong 16Mbps trong mng Token Ring). Chi ph cao, kh lp t.
Hnh 2.1 Cp STP
- Cp khng c v bc (UTP- Unshield Twisted Pair): Khng c v bc chng nhiu
nhng n c tnh linh hot v bn cao. Tc truyn khong 100Mbps, di
cp ti a 100m. Do khng c v bc nn rt nhy cm vi EMI, khng ph hp vi
mi trng cc nh my. c dng ph bin cho cc loi mng cc b, gi thnh
thp, d lp t.
-
Hnh 2.2: Cp UTP
2.1.2.2 Cp ng trc (Coaxial cable)
L phng tin truyn cc tn hiu c ph rng v tc cao. Bng thng ca
cc ng trc t 2,5 Mbps (ARCnet) n 10Mbps (Ethernet). Thng s dng
lp t mng hnh BUS (cc loi mng LAN cc b Thick Ethernet, Thin Ethernet)
v mng hnh sao (mng ARCnet).
Cp ng trc gm mt dy dn trung tm, mt dy dn ngoi, to nn ng
ng bao quanh trc, tng cch in gia hai dy dn v cp v bc ngoi
Hnh 2.3: Cp ng trc
Cc loi cp ng trc:
- Cp RC-8 v RCA-11: 50 Ohm dng mng Thick Ethernet.
- Cp RC-58, 50 Ohm dng cho mng Thin Ethernet (185m).
- Cp RG-59: 75 Ohm dng cho truyn hnh cp.
- Cp RC-62: 93 Ohm dng cho mng ARCnet
ng dng:
-
- Cp ng trc c l l phng tin truyn thng a nng nht v c s dng
rng ri
- trong nhiu ng dng khc nhau. Cc ng dng quan trng nht l:
- Phn phi tn hiu truyn hnh
- Truyn tn hiu in thoi ng di
- Kt ni cc h thng my tnh khong cch gn
- Mng ni b
2.1.2.3 Cp si quang (Fiber Optic cable)
Cp quang l mt phng tin mm do, ng knh nh c kh nng truyn
tia sng. Cc cht liu thy tinh hoc cht do c th c s dng lm nn cp
quang. Cp quang c ch to bi silic yoxit nng chy tinh khit c kh nng
truyn tt nht nhng rt kh ch to. Cp quang ch to bng si thy tinh nhiu
thnh phn khng tt bng nhng kinh t hn v vn cho kt qu chp nhn c.
Si cht do c gi r nht v c th s dng cho cc ng truyn ngn v chp
nhn mt mt cao.
Cp si quang c dng hnh tr v bao gm ba thnh phn ng tm: li, lp
sn ph v v bc. Li l thnh phn trong cng v bao gm mt hoc nhiu si rt
mnh lm bng thy tinh hoc nha. Li c ng knh khong 8 n 100 m. Mi
si c bc mt loi v c bit lm bng thy tinh hoc cht do c c tnh quang
hc khc vi li. B mt gia li v lp v bc c bit c tc dng to s khc x
nh sng ton phn trong li. Lp ngoi cng bc ly mt hoc mt vi si cp ph
sn l v bc. V bc oc lm bng cht liu nha tng hp v cc cht liu khc
nhm bo v li chng li hi m, s n mn, va p v cc nguy hi t mi trng
bn ngoi.
-
Hnh 2.4: Cp quang
ng dng:
Mt trong cc cng ngh c ngha nht trong truyn d liu l s pht trin
ca cc h thng truyn thng bng cp quang. Cp quang cn c s dng trong
truyn thng ng di v cc ng dng ca n trong lnh vc qun s ang pht
trin mnh. S ci thin lin tc trong hiu sut v gi thnh ngy cng gim cng
vi cc u im vn c ca cp quang khin n c dng ngy cng nhiu
kt ni mng ni b. Cc c tnh sau ca cp quang phn bit n vi cp xon i
v cp ng trc:
Dung lng ln hn: Tim nng v bng thng ca cp quang rt ln, v vy
tc truyn d liu ca cp quang rt cao, ln ti hng trm Gbps trn qung ng
hng chc km. Ta c th so snh vi tc thc t cc i hng trm Mbps trn
qung ng 1 km ca cp ng trc v ch vi Mbps trn 1 km hay t 100Mbps
n 1 Gbps trn vi chc mt ca cp xon i.
Kch thc nh hn v nh hn: Mt si cp quang nh hn mt dy cp
ng trc v mt b cp xon i. chy trong cc ta nh hay di lng t, u
im v kch thc rt c li v kch thc nh hn cng gim cc yu cu v cu
trc cng trnh.
t suy gim hn: S suy gim trong cp quang nh hn nhiu so vi cp ng
trc v cp xon i, v l mt hng s trn mt min rng.
Khng b nh hng bi in t: Cc h thng cp quang khng b nh hng
bi cc trng in t bn ngoi. V vy h thng khng b nh hng bi s nhiu
giao thoa, nhiu xung v nhiu xuyn m. Si quang khng pht ra nng lng do
-
t nh hng n cc thit b khc v c mc bo mt cao hn, trnh b nghe trm
v kh b r r.
Khong cch cn lp tn hiu ln hn: S b lp cn s dng t hn lm gim
gi thnh v t cc ngun gy li. Hiu sut ca cc h thng cp quang theo quan
im ny c s pht trin vng chc. Khong cch thng thng gia cc b lp vo
khong 10 km v c cc ghi nhn khong cch ln ti hng trm km. Cc h thng
cp ng trc v cp xon i thng phi dng b lp sau khong vi km.
C nm loi ng dng chnh ca cp quang tr nn quan trng:
- Cc cp trc ng di
- Cc cp trc trong thnh ph
- Cc cp trc gia cc vng
- ng ni gia khch hng v tng i
- Cc mng ni b
2.1.3 Cc phng tin v tuyn
i vi cc phng tin truyn khng dy, vic truyn v nhn c thc
hin bi mt ng ten. Khi truyn i, ng ten pht ra nng lng sng in t vo
trong mi trng (thng l khng kh) v khi thu, ng ten thu sng t mi trng
xung quanh. C hai loi hnh c bn trong h thng truyn dn khng dy: truyn
dn c nh hng v truyn theo mi hng.
Vi loi truyn c nh hng, ng ten s pht ra mt chm in t hi t, v
th ng ten pht v ng ten nhn phi c chnh sao cho hng thng vo nhau.
Khi truyn theo mi hng, tn hiu truyn pht ra theo mi hng v c th thu bi
nhiu ng ten. Nhn chung, tn s ca tn hiu cng ln th kh nng tp trung chng
vo mt tia c nh hng cng cao.
C 3 loi tn s chnh c quan tm. Tn s trong khong 2GHz n 40GHz
c gi l sng viba. tn s ny, c th to ra tia c nh hng tt v sng viba
ph hp vi vic truyn im - im. Sng viba cng c s dng trong truyn
thng v tinh. Tn s trong khong 30MHz n 1GHz ph hp vi truyn thng theo
-
mi hng. Ta c th thy tn s ny ging nh tn s ca i pht thanh. Bng 2.3
tm tt cc c tnh ca truyn dn khng dy ti nhiu di tn. Sng viba l 1 phn
ca di UHF v ton b di SHF, sng pht thanh gm di tn VHF v mt phn ca
di UHF. Mt loi tn s quan trng khc, dnh cho cc ng dng cc b , l tia
hng ngoi ca quang ph. Loi ny bao gm cc tn s xp x t 3.1011 ti 2.1014.
Tia hng ngoi c s dng trong vic truyn thng im im v a im trong
mt phm vi hp nh mt phng n.
2.1.3.1 Sng Radio:
S khc nhau c bn gia sng v tuyn qung b v sng ngn l sng v
tuyn qung b s truyn theo mi hng cn truyn sng ngn th c nh hng.
V vy sng v tuyn qung b khng yu cu phi s dng anten cho v anten
cng khng cn phi quay theo mt hng chnh xc.
Cc ng dng:
Sng v tuyn l thut ng chung c s dng, bao gm cc tn s trong
khong t 3 kHz n 300 GHz. Thut ng sng v tuyn qung b c s dng
bao gm c bng tn VHF v mt phn ca UHF: 30 MHz n 1 GHz. Min tn s
ny bao gm c bng tn FM ca radio v bng tn UHF v VHF ca tivi. Min tn
s ny cng c s dng cho mt vi ng dng mng truyn d liu.
-
Cc c tnh truyn dn:
Min tn s trong khong t 30 MHz n 1 GHz ph hp cho vic sng v
tuyn qung b. Khng ging nh trng hp ca cc sng in t tn s thp, tng
in ly khng phn x cc sng v tuyn c tn s trn 30 MHz. V vy vic truyn
b gii hn trong phm vi tm nhn v cc cc my pht s khng b cn tr bi cc
my pht khc do s phn x t tng kh quyn nh khi truyn sng ngn. Khng
ging nh cc tn s cao ca sng ngn, sng truyn qung b t b hng do nhiu
t cc cn ma hn.
Bc sng cng di th sng v tuyn cng t chu nh hng ca s suy gim.
Nguyn nhn chnh gy h hi cho sng v tuyn qung b l s giao thoa
ca nhiu tn hiu. S phn x t mt t, nc, t t nhin hoc t cc i tng
do con ngi to ra c th gy nn nhiu loi tn hiu gia cc anten. Mt v d l
TV s thu v pht nhiu hnh nh khc nhau lc c my bay bay qua
2.1.3.2 Sng vi ba mt t
Hu ht nhng loi ng ten pht sng viba l parabol (hay ng ten cho). Cc
ng ten nay thng c ng knh khong 3m. ng ten c lp c nh v tp trung
cc tia li trong khong hp truyn chng ti ng ten nhn. ng ten pht sng
viba thng t ti im cao trn mt t c th m rng khong cch gia cc
ng ten v c th truyn qua nhng vt cn gia. Nu nh khng c chng ngai
vt no th khong cch ln nht gia hai ng ten:
h: chiu cao ca anten
k: hng s hiu chnh gp khc ca sng (k=4/3)
truyn c vi khong cch xa, cn s dng mt lot cc trm chuyn
tip v cc kt ni im im l mt chui cc trm lin tip c th vt qua c
gii hn khong cch..
ng dng:
khd 14.7
-
Cc h thng s dng sng viba mt t u tin l cc dch v vin thng
ng di bn cnh vic s dng cc cp ng trc hay cp quang. Sng viba yu
cu cc b khuych i v b lp c t gn nhau hn cp ng trc vi cng mt
ng truyn v i hi nm trong tm nhn. Sng viba s dng ph bin trong pht
thanh v truyn hnh.
Mt ng dng ph bin khc ca sng viba l kt ni im im vi khong
cch ngn gia cc to nh. N cn c s dng trong cc mch nh ca ti vi hoc
trong vic trao i d liu ca mt mng cc b. Sng viba khong cch ngn cng
c th c s dng cho nhng ng dng ng vng.Mt doanh nghip cng c
th s dng sng viba trong vic kt ni vi tng i xa trong cng thnh ph t
tng i cc b ca cng ty.
2.1.3.2 Sng vi ba v tinh
Trong thc t, v tinh truyn thng l mt trm chuyn tip sng vi ba. N c s
dng kt ni hai hay nhiu hn cc trm pht v thu sng mt t. V tinh thu
sng trn mt bng tn (uplink), khuch i hoc lp li tn hiu, sau truyn chng
trn mt tn s khc (downlink). Mt v tinh trn qu o s iu khin mt s loi
di tn v c gi l b tip v tch sng.
Satellite
Footprint
Earth
Earth ground
station
Up
link down
link
point-to-point
Satellite
Hub station
point-to-multipoint
Up
link
down
link
down
link
VSAT VSAT
VSAT : very smal aperture terminal
Equato
rial O
rbit
22,3
00 m
iles
-
Hnh 2.5 Thng tin v tinh
vic truyn thng c hiu qu th v tinh phi gi c v tr tnh so vi
mt t. Tuy nhin s di chuyn ca v tinh s khin n khng nm trong tm nhn
ca cc trm trn mt t ti mi thi im. gi c v tr tnh so vi mt t
th v tinh phi quay cng qu o vi tri t v cn gi cao khong 35.784 km
so vi mt t.
Hai v tinh s dng cng mt di tn s, nu qu gn nhau th s gy ra
nhiu. trnh s nh hng ln nhau, cc chun hin nay yu cu khong cch l
40 (gc gia hai v tinh c o t mt t) i vi di tn 4/6 GHz v khong cch
l 30 i vi di tn 12/14 GHz. V th, s v tinh l c gii hn.
ng dng:
V tinh truyn thng l mt cuc cch mng cng ngh c tm quan trng nh
cp quang. Mt s ng dng quan trng ca v tinh:
Truyn hnh
in thoi ng di
Mng thng mi ring
2.2.3.3 Sng hng ngoi
Truyn thng bng tia hng ngoi s dng cc my thu pht c th iu chnh
cc nh sng hng ngoi. Hai my thu pht phi nm trong tm nhn ca nhau trc
tip hoc thng qua phn x t cc b mt c mu sng nh trn nh.
Hnh 2.6: Sng hng ngoi
-
2.2 Cc thit b lin kt mng
2.2.1 Card giao tip mng (Network Card Interface)
Card NIC l thit b kt ni gia my tnh vi cp mng, c cu to l bn
mch cung cp kh nng truyn thng cho my tnh. Card mng c th c tch
hp ngay trn bn mch ch (main board) hay gn trn cc khe m rng ca my
tnh. Tc d liu: 10/100/1000Mbps
Hnh 2.7: Card NIC
Chc nng chnh ca card mng l:
- Nhn gi d liu t my tnh ri hon thin khung thng tin.
- iu khin truy nhp phng tin vt l.
- M ha (gii m) tn hiu truyn (nhn) khung thng tin.
- ng b bit.
- Kim sot li (CRC, Runt, Giant (Jabber), Range, Alignment, Ghost ).
Phn loi NIC
Theo cch kt ni vi my tnh.
- On-board.
- Cardbus slot (ISA, PCI, PCI Express).
- USB port.
Theo phng tin truyn dn.
- Cp ng: Thinnet (BNC port), Thicknet (AUI port), TP (RJ45 port).
- Cp quang: ST hoc SC interface.
-
- V tuyn
Theo giao thc.
- Fast Ethernet 10Mbps, 100 Mbps, hoc 10/100Mbps.
- Ge 1000 hoc 10/100/1000/10000 Mbps.
- Token Ring (IEEE 802.5) 4/16/100 Mbps.
- WLAN (WiFi) IEEE 802.11 a/b/g, MIMO.
- Token Bus (IEEE 802.4) v FDDI.
2.2.2 B lp (Repeater)
Repeater l loi thit b phn cng n gin nht trong cc thit b lin kt mng,
n c hot ng trong tng vt l ca m hnh h thng m OSI. Repeater dng
ni 2 mng ging nhau hoc cc phn mt mng cng c mt nghi thc v mt
cu hnh. Khi Repeater nhn c mt tn hiu t mt pha ca mng th n s pht
tip vo pha kia ca mng.
Hnh 2.7: Repeater
Repeater khng c x l tn hiu m n ch loi b cc tn hiu mo, nhiu,
khuch i tn hiu b suy hao (v c pht vi khong cch xa) v khi phc
li tn hiu ban u. Vic s dng Repeater lm tng thm chiu di ca mng.
Repeater ti to tn hiu theo cc hng sau:
Ti to tn hiu.
- Chuyn tip bit gia hai hoc nhiu transceivers (lp PHY).
- Ti to tn hiu baseband (LAN) hoc broadband (WLAN, WAN).
- Duy tr hot ng cng mt tc .
Ti to khung tin.
Hin nay c hai loi Repeater ang c s dng l Repeater in v Repeater
in quang.
-
Repeater in ni vi ng dy in c hai pha ca n, n nhn tn hiu
in t mt pha v pht li v pha kia. Khi mt mng s dng Repeater in ni
cc phn ca mng li th c th lm tng khong cch ca mng, nhng khong
cch lun b hn ch bi mt khong cch ti a do tr ca tn hiu. V d vi
mng s dng cp ng trc 50 th khong cch ti a l 2.8 km, khong cch
khng th ko thm cho d s dng thm Repeater.
Repeater in quang lin kt vi mt u cp quang v mt u l cp in,
n chuyn mt tn hiu in t cp in ra tn hiu quang pht trn cp quang v
ngc li. Vic s dng Repeater in quang cng lm tng thm chiu di ca
mng.
Vic s dng Repeater khng thay i ni dung cc tn hin i qua nn n ch
c dng ni hai mng c cng giao thc truyn thng (nh hai mng Ethernet
hay hai mng Token ring) nhng khng th ni hai mng c giao thc truyn thng
khc nhau (nh mt mng Ethernet v mt mng Token ring). Thm na Repeater
khng lm thay i khi lng chuyn vn trn mng nn vic s dng khng tnh
ton n trn mng ln s hn ch hiu nng ca mng. Khi la chn s dng Repeater
cn ch la chn loi c tc chuyn vn ph hp vi tc ca mng.
2.2.3 Hub
Hub thc cht l Repeater nhiu cng. S khc bit gia Hub v Repeater th
hin s lng cng m thit b cung cp. Hub cn c gi l b tp trung dy
dn, cung cp mt im kt ni tp trung cho cc cp ca mng.
Hub b ng (HUB Passive): khng cha cc linh kin in t v cc b x
l tn hiu, ch c chc nng t hp cc tn hiu t mt s cc on mng.
khong cch ln nht gia mt my tnh vi Hub khng th ln hn mt na
khong cch cho php gia 2 my tnh.
Hub ch ng (HUB Active): c cc linh kin in t c th khuch i v
x l tn hiu. cho php khong cch gia cc thit b tng ln.
Hub thng minh (c chc nng qun l Hub v Hub chuyn mch) : l Hub
ch ng nhng c thm cc chc mi sau:
-
Qun tr hub: c b sung giao thc qun tr mng, cho php hub gi
cc thng tin v trm iu khin mng trung tm. V cho php trm
trung tm qun l hub
Chuyn mch: cha cc vi mch cho php chn ng nhanh cho cc
tn hiu gia cc cng trn hub. Thay v chuyn gi tin cho ton b cc
cng hub, chng ang thay th dn cho cc router v bridge.
2.2.4 Bridge
Bridge l thit b hot ng lp con MAC ca lp Data Link trong m hnh
OSI. Bridge c th c s dng m rng kch thc ti a ca mt mng v linh
hot hn nhiu so vi Repeater.
Chc nng ca Bridge:
- M rng khong cch ca phn on mng, tng s lng my tnh trn mng.
- Lc nhng gi d liu gi i (hay khng gi) cho on ni, hoc gi tr
li ni xut pht.
- Phn chia mt mng ln thnh hai mng nh nhm c lp lu lng, tng tc
mng. Nu lu lng t mt nhm my tnh tr nn qu ti v lm gim
hiu sut ton mng th cu ni c th c lp my tnh hoc b phn ny.
- Lm gim hin tng nghn tc, do s lng my tnh ni vo mng qu ln.
Bridge c th tip nhn mt mng qu ti v chia n thnh hai mng ring
bit, nhm gim bt lu lng truyn trn mi on mng v do mi mng
s hot ng hiu qu hn.
- Kt ni cc phng tin truyn dn khc nhau.
- Kt ni cc on mng s dng phng thc truy cp ng truyn khc nhau,
chng hn CSMA/CD v chuyn th bi.
Nguyn l hot ng ca Bridge
- Bridge khng phn bit gia giao thc ny vi giao thc khc, ch c nhim
v chuyn lu lng ca tt c cc giao thc dc theo mng. V giao thc no
cng di chuyn ngang qua bridge, nn ty thuc vo tng my tnh quyt nh
chng c th nhn c giao thc no.
-
- Bridge hot ng trn nguyn tc mi nt mng c mt a ch ring. Bridge
chuyn gi d liu da trn a ch ca nt giao dch (a ch MAC). Khi d
liu truyn qua bridge, thng tin a ch ca my tnh c lu trong RAM
ca bridge dng xy dng bng a ch da trn a ch ngun ca gi tin.
2.2.5 Switch
Switch hot ng lp 2 ca m hnh OSI v l thit b ging bridge v hub
cng li nhng thng minh hn. Swich c kh nng chuyn d liu n ng kt ni
thc s cn d liu ny lm gim ng trn mng. Switch dng phn on
mng trong cc mng cc b ln (VLAN).
Switch c cu to gm hai thnh phn c bn:
- B nh lm b m v Bng a ch (BAT- Buffer and Address Table).
- Gin hon chuyn (Switching Fabric) to ni kt cho ng thi gia cc
cng.
Vic chuyn tip khung t segment ny segment khc ca switch c th c
thc hin theo mt trong ba phng php: Store and forward, Cut-through,
Adaptive Switching.
Store and forward
Khi khung n mt cng ca Switch, ton b khung s c lu vo trong b
nh m v c kim tra li.
- Khung s b b i nu nh c li.
- Nu khung khng li, switch s xc nh a ch MAC ch, d tm trong
bng a ch xc nh port ch v chuyn tip khung ra cng tng ng.
Gii thut ny c thi gian tr hon ln do phi kim tra khung. Tuy nhin
n cho php giao tip gia hai knh truyn khc tc .
Cut-through
Switch c 6 bytes u tin theo sau phn mo u xc nh a ch MAC
ch.
-Switch tm MAC ch trong bng switching ca n, xc nh port ch v
chuyn frame i.
-
-Switch khng i cho n khi frame vo b m hon ton v cng khng
kim tra li nn:
Thi gian tr hon ca phng php cut-through ngn hn phng php
store-and-forward.
tin cy thp hn store-and-forward v c th chuyn cc frame li, gy
lng ph ti nguyn.
Adaptive Switching
Tn dng ti a u im ca hai phng php store-and-forward v cut-
through. Ngi ta nh ngha mt ngng li cho php. u tin, Switch s hot
ng theo phng php cut-through.
- Nu t l khung li ln hn ngng cho php, switch s chuyn sang ch
hot ng theo phng php store-and-forward.
- Ngc li khi t l khung li h xung nh hn ngng, Switch li hot
ng theo phng php cut-through.
-
CHNG III
M HNH TCP/IP
3.1 M hnh TCP/IP
Cui nm 1960 v u 1970, Trung tm nghin cu cao cp (ARPA
Advanced Research Projects Agency) B quc phng M (DoD) c giao trch
nhim pht trin mng ARPANET.
u nhng nm 1980, h giao thc TCP/IP ra i v c a lm giao thc
chun cho mng ARPANET v cc mng ca DoD mang tn DARPA Internet
Protocol suit, thng c gi l TCP/IP.
Thut ng Internet xut hin vo khong nm 1974. Nm 1987, NFSnet
lin kt cc trung tm siu tnh ca ton lin bang ra i vi tc 1.5Mbit/s thay
v 56Kbit/s ca ARPANET.
3.1.1 M hnh kin trc TCP/IP
TCP/IP (Transmission Control Proctocol/ Internet Protocol) l chng giao
thc cng hot ng nhm cung cp cc phng tin truyn thng lin mng.
TCP/IP l giao thc ch yu c s dng trn Internet vi tc truyn d
liu gia 2 my tnh bt k bng tc nh sng.
-
TCP l giao thc thuc tng vn chuyn v IP l giao thc thuc tng mng
ca m hnh OSI.
M hnh TCP/IP c phn lm 4 tng:
Hnh 3.1: M hnh TCP/IP
3.1.2 Vai tr kin trc cc tng trong m hnh TCP/IP
Lp ng dng (Application layer) : h tr cc ng dng cho cc giao din
tng Host-to-Host. Cung cp giao din cho ngi s dng m hnh TCP/IP. Cc giao
thc ng dng gm HTTP, TELNET, FTP, SMTP,
Lp vn chuyn (Transport layer): thc hin nhng kt ni gia hai my
ch trn mng bng hai giao thc TCP (Transmission Control Protocol) v UDP
(User Datagram Protocol). TCP l giao thc kt ni hng lin kt chu trch nhim
m bo tnh chnh xc v tin cy cao trong vic trao i d liu gia cc thnh
phn trong mng, tnh ng thi v kt ni song cng (Full Duplex). UDP c s
dng cho nhng ng dng khng i hi tin cy cao.
Lp mng (Internet layer): cung cp mt a ch logic cho giao din vt l
mng. Giao thc thc hin ca tng mng l giao thc IP kt ni khng lin kt.
Giao thc IP cng vi cc giao thc nh tuyn RIP, OSPF, BGP, lp mng IP cho
php mt cch mm do v linh hot cc loi mng vt l khc nhau nh Ethernet,
Token Ring, X.25, ngoi ra lp mng cn h tr nh x gia a ch vt l (MAC-
IP) vi a ch logic bng giao thc phn gii a ch ARP (Address Resolution
Protocol) v phn gii a ch o (RARP (Reverse Address Resolution Protocol).
-
Cc vn lin quan n chun on li v cc tnh hung bt thng lin quan
n IP c giao thc ICMP (Internet Control Message Protocol) thng k v bo
co.
Lp truy nhp mng (Network Access Layer): cung cp cc phng tin
kt ni vt l cp, b chuyn i, card mng, giao thc kt ni, giao thc truy nhp
ng truyn nh CSMA/CD, Token Ring, Token Bus, Cung cp cc dch v
cho lp mng phn on d liu thnh cc khung.
Hnh 3.2: M hnh kin trc TCP/IP
3.1.3 Qu trnh ng gi d liu
Ngi dng thng qua lp Application a cc thng tin vo my tnh. Cc
thng tin ny c nhiu dng khc nhau nh: hnh nh, m thanh, vn bn
D liu c chuyn xung lp transport theo cc cng port. Khi truyn d
liu , lp Transport ly d liu t lp Application v chia chng ra thnh nhiu gi
( Packet ) d liu. Khi d liu nhn, giao thc TCP ly nhng gi c gi t lp
Internet v t chng theo th t ca n . Trong lp transport c 2 giao thc
UDP(User Datagram Protocol ) v TCP(Transmission Control Protocol ) .C hai
UDP v TCP s ly d liu t lp Application v thm Header vo n khi truyn d
liu. Khi nhn d liu, Header s b g trc khi gi d liu ti cng thch hp.
Lp Internet c nhim v thm Header ti gi d liu c nhn t lp
Transport , l mt loi d liu iu khin khc , n s thm a ch IP ngun v a
ch IP ch c ngha l a ch IP ca my tnh ang gi d liu v a ch IP ca
my tnh m s nhn d liu . Trong lp ny d liu c gi l Datagram .
-
Datagram c to t lp Internet s c gi xung ti lp Network
Interface , nu chng ta ang truyn d liu, hoc lp Network Interface s ly d
liu t mng v gi n ti lp Internet , nu chng ta ang nhn d liu. Lp ny
vch r mng vt l kiu no m my tnh ca bn kt ni ti. Hin nay hu ht my
tnh ca chng ta dng kt ni mng Ethernet. Trong giao thc Ethernet th c nhng
lp LLC v MAC s thm nhng header ca chng chng ti Datagram m nhn
c t lp Internet . Nhng gi truyn trn mng c gi l nhng Frame .
Hnh 3.3: Qu trnh ng gi d liu trong TCP/IP
3.1.4 Qu trnh phn mnh d liu Fragment
D liu c th c truyn qua nhiu mng khc nhau, kch thc cho php
cng khc nhau. Kch thc ln nht ca gi d liu trong mng gi l n v truyn
cc i MTU (Maximum Transmission Unit). Trong qu trnh ng gi
Encapsulation, nu kch thc ca mt gi ln hn kch thc cho php, t ng
chia thnh nhiu gi nh v thm thng tin iu khin vo mi gi. Nu mt mng
nhn d liu t mt mng khc, kch thc gi d liu ln hn MTU ca n, d liu
s c phn mnh ra thnh gi nh hn chuyn tip c gi l phn mnh d
liu (Fragment)
-
Qu trnh phn mnh lm tng thi gin x l, lm gim tnh nng ca mng
v nh hng n tc trao i d liu trong mng. Hu qu ca n l cc gi b
phn mnh s n ch chm hn so vi cc gi khng b phn mnh. Mt khc, v
IP l giao thc khng lin kt, tin cy khng cao, khi mt gi d liu b phn
mnh b mt th tt c cc mnh s phi truyn li. v vy phn ln cc ng dng
trnh khng s dng k thut phn mnh v gi cc gi d liu ln nht m khng
b phn mnh, gi tr ny l Path MTU.
3.2 Giao thc TCP
3.2.1 Gii thiu
TCP l mt giao thc hng lin kt (connection oriented). TCP nhn thng
tin t lp trn, chia d liu thnh nhiu gi theo di quy nh v chuyn cc gi
tin xung cho cc giao thc lp mng nh tuyn.
TCP cung cp kh nng truyn d liu mt cch an ton gia cc my trm
trong h thng. Cung cp cc chc nng kim tra tnh chnh xc ca d liu khi n
ch v truyefn li d liu khi c li xy ra. TCP cung cp cc chc nng chnh sau:
Thit lp, duy tr v gii phng lin kt gia hai qu trnh.
Phn pht gi tin mt cch tin cy.
nh s th t cc gi d liu nhm truyn d liu mt cch tin cy.
Cho php iu khin li.
Cung cp kh nng a kt ni vi cc qu trnh khc nhau gia trm ngun v
trm ch nht nh thng qua vic s dng cc cng.
Truyn d liu s dng c ch song cng
3.2.2 Cu trc gi tin TCP
n v d liu trong giao thc TCP c gi l segment ( on d liu). Mi
segment ca giao thc TCP bao gm phn tiu (header) v phn d liu (data).
-
Hnh 3.4 : Cu trc gi tin TCP (TCP Sgment)
Source port (16 bit) v Destination port (16 bit): s hiu cng ca host ngun
v ch.
Sequence Number (32 bit): s hiu xc nh v tr byte u tin ca segment
khi bit SYN khng c thit lp. Nu bit SYN c thit lp th y l s
hiu tun t khi u ca d liu.
Ackknowledgment Number (32 bit): k hiu l ACK, l s hiu ca segment
k tip trong dng d liu m bn nhn ang ch. Data Offset (4 bit): ch kch
thc ca phn header TCP tnh theo n v t 32 bit. Trng ny ng thi
cng xc nh v tr bt u ca phn d liu.
Reserved (6 bit): trng ny hin vn d phng v lun bng 0.
Flags (6 bit): l cc bit c c ngha nh sau:
-URG: bng 1 nu c d liu khn. D liu khn s c ch ra trong
trng Urgent Pointer. Ngc li th bng 0.
-ACK: bng 0 nu l segment khi u v khi trng ACK Number
mi c hiu lc.
-PSH: thng bo d liu cn chuyn i ngay.
-RST: xc nh li, ng thi khi ng li kt ni.
-SYN:bng 1 khi thit lp kt ni.
-FIN: bng 1 khi trm ngun ht thng tin.
Window (16 bit): y l s lng cc byte d liu, bt u t byte c ch
ra trong trng ACK Number m trm ngun sn sng nhn.
-
Checksum (16bit): m kim sot li theo phng php CRC ca ton b
segment.
Urgent Pointer (16 bit): y l con tr ti s hiu tun t ca byte i sau d
liu khn, cho php bn nhn bit c di ca d liu khn. Trng ny
c hiu lc khi bit URG c thit lp 1.
Padding ( di thay i): Phn mm chn thm vo header m bo header
lun kt thc mt mc 32 bit. Phn chn thm ny lun = 0.
Data ( di thay i): cha d liu cn gi i ca lp trn TCP.
Options ( di thay i): khai bo cc tu chn ca TCP, trong c di
ti a ca vng TCP data trong mt segment.
3.2.3 Qu trnh thit lp v hy b kt ni trong TCP
3.2.3.1 Thit lp kt ni: c thc hin trn c s phng thc bt tay ba bc.
Mc ch ca phng php ny l thit lp kt ni gia bn gi v bn nhn trnh
mt d liu.
Hnh 3.5: Phng thc bt tay 3 bc
Bc 1: Yu cu lin kt lun c A khi to tin trnh bng cch gi mt
gi TCP vi c SYN=1 v Sequence number ca n.
Bc 2 : Khi B nhn c thng ip SYN, n gi li gi SYN cha Sequence
number ca n v ACK = Sequence number B+1
-
Bc 3: Khi A nhn c s tr li li mt ACK Segment cha Sequence
number A = ACK (B) v ACK (A) = Sequence number B+1
Sau bc 3, kt ni c thit lp v sn sng truyn d liu.
3.2.3.2 Gii phng kt ni
Hnh 3.6: Gii phng kt ni
Khi c nhu cu kt thc lin kt TCP, A gi yu cu kt thc lin kt vi
FIN=1. V lin kt TCP l song cng nn mc d nhn c yu cu kt thc lin
kt ca A, B vn c th tip tc truyn cho n khi B khng cn d liu gi v
thng bo cho A bng yu cu kt thc lin kt vi FIN=1. Khi A nhn c thng
dip FIN, sau khi gi ACK ca mnh, lin kt TCP thc s kt thc. Nh vy c
hai trm phi ng gii phng lin kt TCP bng cch gi c FIN trc khi chm
dt lin kt xy ra, vic ny m bo d liu khng b tht lc do mt bn t ngt
chm dt lin lc.
3.2.4 iu khin lu lng trong TCP
-
C ch ca s ng.
- ln ca ca s bng s lng cc gi d liu c gi lin tc m khng
cn ch ACK cho tng gi d liu .
- ln ca s quyt nh hiu sut trao i d liu trong mng.
- Giao thc TCP cho php thay i ln ca s mt cch ng, ph thuc
vo ln b m thu ca thc th TCP nhn.
C ch pht li thch nghi.
- m bo kim tra v khc phc li trong trao i d liu, TCP phi c
c ch ng h kim tra pht (Time Out - Tout) v c ch pht li (Retransmission)
mm do, ph thuc vo thi gian tr thc ca mi trng truyn dn c th.
- Thi gian tr ton phn RTT (Round Trip Time) tnh t lc pht n khi
nhn c gi d liu, l yu t quyt nh Tout. Do , Tout RTT.
3.2.5 Giao thc UDP
Giao thc UDP l giao thc kt ni khng nh hng (connectionless) c
s dng trn lp IP theo yu cu ca ng dng. Khc vi TCP, UDP khng c qu
trnh thit lp v gii phng kt ni. UDP cng khng h tr chc nng bo nhn
(acknowledgement), khng sp xp tun t cc n v d liu (packet) n v c th
dn n tnh trng mt hoc trng d liu (packet) m khng h c thng bo li cho
ng dng s dng UDP. C th ni UDP khng cung cp cc dch v truyn tin tin
cy nh TCP.
Ging nh TCP, UDP cng hot ng da trn ch s dng cc s hiu cng
(port number) nh danh duy nht mt ng dng chy trn mt my tnh ni mng.
Do c it chc nng phc tp nn UDP c tc truyn v nhn nhanh hn TCP
trong cc mng c tin cy cao nh LAN. UDP thng dng cho cc ng dng
n gin.
nh dng d liu ca UDP
-
Hnh 3.7: nh dng d liu ca UDP
- Source port (16 bit) v Destination port (16 bit): s hiu cng ca host ngun
v ch gi v nhn Datagram
- Length (16bit) : ch di ca gi tin UDP bao gm phn header v data.
- Checksum (16bit): s dng kim tra li cho phn header. Nu pht hin li th
UDP datagram s b loi b m khng c thng bo no tr li cho trm gi.
3.3 Giao thc IP
3.3.1 Gii thiu chung
IP l giao thc khng lin kt. Chc nng ch yu ca IP l cung cp cc dch
v Datagram v cc kh nng kt ni cc mng con thnh lin mng truyn d
liu vi phng thc chuyn mch gi IP Datagram, thc hin tin trnh nh i ch
v chn ng.
IP Header c thm vo u cc gi tin v c giao thc tng thp truyn
theo dng khung d liu. IP nh tuyn cc gi tin thng qua lin mng bng cch
s dng cc bng nh tuyn ng tham chiu ti mi bc nhy.
Xc nh tuyn c tin hnh bng cch tham kho thng tin thit b mng
vt l v logic nh ARP giao thc phn gii a ch. IP thc hin vic tho ri v
khi phc cc gi tin theo yu cu kch thc c nh ngha cho cc tng vt l
v lin kt d liu thc hin. IP kim tra li thng tin iu khin, phn u IP bng
gi tr tng CheckSum.
3.3.2 Cu trc gi d liu IP
Cc gi d liu IP c gi l cc Datagram. Mi Datagram c phn tiu
cha cc thng tin iu khin. Nu a ch IP ch cng mng vi trm ngun th cc
-
gi d liu s c chuyn thng n ch, nu a ch IP ch khng cng mng vi
my ngun th cc gi d liu s c chuyn n mt my trung chuyn IP Gateway
chuyn tip. IP Gateway l mt thit b mng Ip m nhn vic lu chuyn cc
gi d liu IP gia hai mng IP khc nhau.
Hnh 3.7: Cu trc gi d liu IP
Vers(4bit): ch version hin hnh ca giao thc IP thc hin ci t
Hlen(4bit): ch di ca phn u ca gi tin datagram. Trng ny buc
phi c v phn u IP c di thay i ty .
Service type: c t cc tham s v dch v nhm thng bo cho mng bit
dch v no m gi tin mun c s dng, chng hn u tin, thi gian chm tr,
nng sut truyn v tin cy.
Total length: ch di ton b gi tin, k c phn u tnh theo n v byte
vi chiu di ti a l 65535 bytes.
Identification(ID) : cng vi cc tham s khc( nh source address v
destination address) tham s ny dung ch nh danh duy nht cho mt datagram
trong khong thi gian n vn cn trn lin mng.
Flags: Lin quan n s phn on (fragment) cc datagram. Trng flags
c dng iu khin phn on v ti lp ghp b d liu.
-
Fragment offset ( 13bit): ch v tr ca on (fragment) trong datagram tnh
theo n v 8 bytes, c ngha l phn d liu ca gi tin phi cha mt vng d liu
c di l bi s ca 8bytes.
Time to live(8bits): qui nh thi gian tn ti( tnh theo giy) ca gi tin trong
mng trnh tnh trng mt gi tin b qun trn mng.
Protocol (8bits): ch giao thc tng k tip s nhn vng d liu trm ch.
Header chechsum(16bit): kim sot li s dng phng php CRC (Cyclic
Redundancy Check) dng m bo thng tin v gi d liu c truyn i mt
cch chnh xc nht.
Source Address(32bits): a ch trm ngun
Destination Address(32bits): a ch trm ch.
Options(c di thay i): s dng trong mt s trng hp. Trng option
s dng trong mt s chc nng nh tuyn c bit.
Padding( di thay i): vng m, c dng m bo cho phn header
lun kt thc mt mc 32bits.
Data( di thay i): vng d liu c di li bi ca 8bits, ti a 65535
bytes.
3.3.3 a ch IP
Hin nay, mng Internet dng h thng a ch IPv4 (32 bit) a ch ho
logic cc nt mng. Mi trm (Host) bt k trn lin mng c gn mt a ch
nh danh duy nht gi l a ch IP. Mi a ch IP c di 32 bit c tch thnh
4 vng (mi vng 1 byte hoc octet), c th c biu din di dng thp phn, bt
phn, thp lc phn hoc nh phn.
V d:
172.16.30.56
10101100 00010000 00011110 00111000.
AC 10 1E 38
a ch IP gm 2 thnh phn NetID (Network Address) v HostID (Node
Address)
-
Hnh 3.8: a ch IP
NetID l s duy nht dng xc nh 1 mng. Mi my tnh trong mt mng
bao gi cng c cng mt a ch mng
HostID l s duy nht c gn cho mt my tnh trong mng
Phn loi a ch IP
- a ch host l a ch IP c th dng t cho cc interface ca cc host.
Hai host nm cng mt mng s c network_id ging nhau v host_id khc
nhau.
- a ch mng (network address): l a ch IP dng t cho cc mng. Phn
host_id ca a ch ch cha cc bit 0. V d: 172.29.0.0
- a ch Broadcast: l a ch IP c dng i din cho tt c cc host trong
mng. Phn host_id ch cha cc bit 1. V d: 172.29.255.255.
3.3.4 Cc lp a ch IP
a ch IP c chia thnh 5 lp k hiu l A, B, C, D, E vi cu trc mi lp
c xc nh. Cc bit u tin ca byte u tin c dng nh danh lp a
ch (0-lp A, 10 lp B, 110 lp C, 1110 lp D, 11110 lp E)
Hnh 3.9: Phn lp a ch Ipv4
-
Lp Bit c
trng
S lng mng S lng
Host
Biu din bng s thp phn
A 0 127 16.777.214 0.1.0.0 126.255.255.255
B 10 16.383 65.534 128.1.0.0 -191.255.255.255
C 110 2.097.151 234 192.1.0.0 223.255.255.255
D 1110 223.0.0.0 239. 255.255.255
E 11110 240.0.0.0 247.255.255.255
Bng cc lp a ch
Cu trc cc lp a ch IP
- Lp A cho php nh danh ti a 126 mng (byte u tin), vi ti a 16 triu
Host (3 byte cn li). Lp ny c dng cho mng c s trm cc ln.
- Lp B cho php nh danh n 16384 mng con, vi ti a 65535 Host trn
mi mng. Lp a ch ny ph hp vi vi nhiu yu cu nn c cp pht
nhiu nn hin nay tr nn khan him.
- Lp C cho php nh danh n 2.097.150 mng con v ti a 254 Host cho
mi mng. Lp ny c dng cho cc mng c t trm.
- Lp D dng gi IP Datagram ti mt nhm cc Host trn mt mng (cn
c gi l a ch multicast).
-
- Lp E c dng d phng
Ngoi ra cn c mt s a ch c quy nh quy nh ring (private address).
Cc a ch ch c ngha trong mng ca tng t chc nht nh m khng cn phi
xin php
a ch mng con
i vi cc a ch lp A, B s trm trong mt mng l qu ln v trong thc
t thng khng c mt s lng trm ln nh vy kt ni vo mt mng n l.
a ch mng con cho php chia mt mng ln thnh cc mng con nh hn. Ngi
qun tr mng c th dng mt s bit u tin ca trng hostid trong a ch IP
t a ch mng con. Chng hn i vi mt a ch thuc lp A, vic chia a ch
mng con c th c thc hin nh sau:
Vic chia a ch mng con l hon ton trong sut i vi cc router nm bn
ngoi mng, nhng n l khng trong sut i vi cc router nm bn trong mng.
Hnh 3.10: Minh ha cu hnh Subnet
Mt n a ch mng con
-
Bn cnh a ch IP, mt trm cng cn c bit vic nh dng a ch mng
con: bao nhiu bit trong trng hostid c dng cho phn a ch mng con
(subnetid). Thng tin ny c ch ra trong mt n a ch mng con (subnet mask).
Subnet mask cng l mt s 32 bit vi cc bit tng ng vi phn netid v
subnetid c dt bng 1 cn cc bit cn li c t bng 0.
Nh vy, a ch thc ca mt trm s l hp ca a ch IP v subnet mask.
V d vi a ch lp C: 203.162.7.92, trong :
203.162.7 a ch mng
92 a ch IP ca trm
Nu dng 3 bit u ca trng hostid nh subnet subnet mask s l:
11111111.11111111.11111111.11100000 = 255.255.255.224
a ch ca subnet:
11001011.10100010.00000111.01011100
11111111.11111111.11111111.111- - - - -
---------------------------------------------------------- AND Logic
11001011.10100010.00000111.010- - - - - = 203.162.7.64
(Subnet address)
a ch trm: trm th 28 trong Subnet 203.162.7.64
Trong thc t subnet mask thng c vit km vi a ch IP theo dng thu
gn sau: 203.162.7.92/27; trong 27 chnh l s bit c t gi tr l 1 (gm cc
bit thuc a ch mng v cc bit dng cho Subnet). Nh vy y ta c th hiu
ngay c vi subnet mask l 27 th tng ng vi
11111111.11111111.11111111.111
3.3.5 Mt s giao thc iu khin
-
3.3.5.1 Giao thc thng bo iu khin mng ICMP (Internet Control Message
Protocol)
ICMP l giao thc iu khin ca tng IP, s dng trao i cc thng tin
iu khin dng d liu, thng bo li v cc thng tin trng thi khc ca b giao
thc TCP/IP.
- iu khin lu lng (Flow Control): khi cc gi d liu n qu nhanh,
thit b ch hoc thit b nh tuyn gia s gi mt thng ip ICMP tr li thit
b gi, yu cu thit b gi tm thi ngng vic gi d liu.
- Thng bo li: Trong trng hp khng ti c a ch ch th h thng
s gi mt thng bo li Destination Unreachable.
- nh hng li cc tuyn (Redirect Router): Mt Router gi mt thng ip
ICMP cho mt trm thng bo nn s dng Router khc. Thng ip ny c th ch
c dng khi trm ngun trn cng mt mng vi hai thit b nh tuyn.
- Kim tra cc trm xa: Mt trm xa c th gi mt thng ip ICMP
Echo kim tra trm c hot ng hay khng.
Cc loi thng ip ICMP: Cc thng ip ICMP c chia thnh hai nhm:
Cc thng ip truy vn v cc thng ip thng bo li.
-Cc thng ip truy vn: Gip cho ngi qun tr mng nhn cc thng tin
xc nh t mt node mng khc.
- Cc thng ip thng bo li: Lin quan n cc vn m b nh tuyn
hay trm pht hin ra khi x l gi IP. ICMP s dng a ch IP ngun gi thng
ip thng bo li cho node ngun ca gi IP.
3.3.5.2 Giao thc phn gii a ch ARP (Address Resolution Protocol)
Giao thc TCP/IP s dng ARP dng tm a ch vt l (MAC) ca trm
ch. Trc khi trao i thng tin vi nhau, node ngun cn phi xc nh a ch
vt l MAC ca node ch bng cch tm kim trong bng a ch IP. Nu khng tm
thy, node ngun gi qung b (Broadcast) mt gi yu cu ARP c cha a ch IP
ngun, a ch IP ch cho tt c cc my trn mng. Cc my nhn, c, phn tch
v so snh ddaiacj ch IP ca n vi a ch IP ca gi. Nu cng a ch IP, ngha
-
l node ch tm trong bng thch ng a ch IP-MAC ca n v tr li bng mt
gi ARP Rely c cha a ch MAC cho node ngun. Nu khng cng a ch IP, n
chuyn tip gi yu cu nhn c di dng qung co cho tt c cc trm trn
mng.
Tin trnh ca ARP gm cc bc nh sau:
- IP yu cu a ch MAC.
- Tm kim trong bng ARP.
- Nu tm thy s tr li a ch MAC.
- Nu khng tm thy, to gi ARP yu cu v gi ti tt c cc trm.
- Tu theo gi tin tr li, ARP cp nht vo bng ARP v gi a ch MAC.
Hnh 3.11 Giao thc phn gii a ch ARP
3.3.5.3 Giao thc phn gii a ch ngc RARP (Reverse Address Resolution
Protocol)
RARP l giao thc phn gii a ch ngc. Qu trnh ny ngc li vi qu
trnh ARP. Nh vy, RARP c s dng xc nh a ch IP khi bit a ch vt
l MAC.
S I E M E N S N I X D O R F
S I E M E N S N I X D O R F
Host A
Host B IP Address: 128.0.10.4 HW Address: 080020021545
ARP Reply
ARP Request - Broadcast to all hosts
What is the hardware address for IP address 128.0.10.4?
S I E M E N S N I X D O R F
-
My A cn bit a ch IP ca n, n gi qung b gi tin RARP Request cha
a ch MAC ca n trong ton mng. Mi my trong mng u c th nhn gi tin
ny nhng ch c Server mi tr li RARP Reply cha a ch IP ca my A.
Hnh 3.12 Giao thc phn gii a ch ngc RARP
3.4 K thut phn chia mng con
thun tin cho vic qun l v nh hng d liu trn mng, ngi ta
thng t chc mng IP theo c ch a ch phn cp: mi mng c chia nh thnh
nhiu mng con. S phn cp ny cho php gim khi lng cng vic chn ng
cho cc goi tin trong ton lin mng.
Mi mng con chu trch nhim nh tuyn cho cc gi IP trong mng ca
mnh. Trong cc mng loi A, B, C th phn a ch my c di c nh. linh
hot trong vic phn chia mng con th a ch mng c th m rng sang cc bit a
ch my. l k thut phn chia mng con.
V d mt mng loi B c a ch mng l 203.160.9.0 v mt n mng l 255.
255. 255.0 (a ch di 24 bit). Ngi ta cn chia mng ny thnh 4 mng cc b
ring, do s ly thm 2 bit cho a ch amnjg (26 bit). Vy ta c a ch cc mng
con l:
-
3.5 a ch IPv6
Giao thc IPng (Next General Internet Protocol) l phin bn mi ca giao
thc IP c IETF (Internet Engineering Task Force) xng v nm 1994, IESG
(Internet Engineering Steering Group) ph chun vi tn chnh thc l IPv6. IPv6 l
phin bn k tha pht trin t IPv4.
3.5.1 Nguyn nhn ra i ca IPv6
- Internet pht trin mnh, nhu cu s dng a ch IP tng dn n khng gian
a ch ngy cng b thu hp v tnh trng thiu ht a ch tt yu s xy ra trong vi
nm ti.
- Vic pht trin qu nhanh ca mng Internet dn n kch thc cc bng nh
tuyn trn mng ngy cng ln.
- Ci t IPv4 bng th cng hoc bng giao thc cu hnh a ch trng thi
DHCP (Dynamic Host Configuration Protocol), khi m nhiu my tnh v cc thit
b kt ni vo mng th cn thit phi c mt phng thc cu hnh a ch t ng
v n gin hn.
- Trong qu trnh hot ng IPv4 pht sinh mt s vn v bo mt v
QoS. Khi kt ni thnh mng Intranet cn nhiu a ch khc nhau v truyn thng
qua mi trng cng cng. V vy i hi phi c cc dch v bo mt bo v d
liu mc IP.
-
- Mc d c cc chun m bo cht lng dch v QoS trong IPv4 trng IPv4
TOS (Type of Service), nhng hn ch v mt chc nng, cn thit h tr tt hn
cho cc ng dng thi gian thc.
V vy vic cn thit phi thay th giao thc IPv4 l tt yu. Thit k IPv6 nhm
mc ch ti thiu ha nh hng qua li gia cc giao thc lp trn v lp di
bng cch trnh vic b sung mt cch ngu nhin cc chc nng mi.
3.5.2 Cc c trng ca IPv6
IPv6 c chn thay th cho giao thc IPv4 khng ch do IPv4 khng cn ph
hp vi yu cu pht trin hin ti ca mng Internet m cn v nhng u im ca
giao thc IPv6:
- n gin ho Header: Mt s trng trong Header ca IPv4 b b hoc chuyn
thnh cc trng tu chn. Gim thi gian x l v tng thi gian truyn.
- Khng gian a ch ln: di a ch IPv6 l 128 bit, gp 4 ln di a
ch IPv4. gian a ch IPv6 khng b thiu ht trong tng lai.
- Kh nng a ch ho v chn ng linh hot: IPv6 cho php nhiu lp a
ch vi s lng cc node. Cho php cc mng a mc v phn chia a ch thnh
cc mng con ring l. C kh nng t ng trong vic nh a ch. M rng kh
nng chn ng bng cch thm trng Scop vo a ch qung b (Multicast).
- T ng cu hnh a ch: Kh nng t cu hnh ca IPv6 c gi l kh nng
cm v chy (Plug and Play). Tnh nng ny cho php t cu hnh a ch cho giao
din m khng cn s dng cc giao thc DHCP.
- Kh nng bo mt: IPsec bo v v xc nhn cc gi tin IP:
+ M ha d liu: Pha gi s tin hnh m ha gi tin trc khi gi.
+ Ton vn d liu: Pha nhn c th xc nhn gi tin nhn c m
bo rng d liu khng b thay i trong qu trnh truyn.
+ Xc nhn ngun gc d liu: Pha nhn c th bit c pha gi gi tin.
Dch v ny ph thuc vo dch v ton vn d liu.
+ Antireplay: Pha nhn c th pht hin v t chi gi tin gi li.
-
- Cht lng dch v QoS (Quanlity Of Service): Cht lng dch v QoS trong
IPv4 khng cao.Trong Header IPv4 cha a ch ngun v a ch ch, truyn c
tin cy khng cao. IPv6 Header c thm mt s trng mi x l v xc nh lu
lng trn mng. Do c ch xc nhn gi tin ngay trong Header nn vic h tr QoS
c th thc hin c ngay c khi gi tin c m ha qua IPsec.
- Giao thc pht hin ln cn NDP (Neighbor Discovery Protocol) ca IPv6 l
mt dy cc thng bo ICMPv6 cho php qun l tng tc gia cc node ln cn,
thay th ARP trong IPv4. Cc thng bo ICMPv4 Router Discovery v ICMPv4
Redirect c thay bi cc thng bo Multicast, Unicast Neighbor Discovery.
- Kh nng m rng: Thm vo trng Header m rng tip ngay sau Header,
IPv6 c th c m rng thm cc tnh nng mi mt cch d dng.
- Tnh di ng: IPv4 khng h tr cho tnh di ng, IPv6 cho php nhiu thit
b di ng kt ni vo Internet theo chun ca PCMCIA (Personal Computer
Memory Card International Association) qua mng cng cng nh sng v tuyn.
3.5.3 Cc lp a ch IPv6
3.5.3.1 Phng php biu din a ch IPv6
a ch IPv6 c biu din bng chui s Hexa c chia thnh cc nhm 16
bit tng ng vi bn ch s Hexa, ngn cch nhau bi du :. V d mt a ch
IPv6 : 4021 : 0000 : 240E : 0000 : 0000 : 0AC0 : 3428 : 121C. C th thu gn bng
cch thay cc nhm 0 lin tip bng k hiu ::.
V d 12AB : 0000 : 0000 : CD30 : 0000 : 0000 : 0000 : 0000 /60 c th vit l
12AB : 0 : 0 : CD30 : 0 : 0 : 0 : 0 /60 hoc 12AB :: CD30 : 0 : 0 : 0 : 0 /60 hoc
12AB : 0 : 0 : CD30 :: /60 . Khng c vit 12AB :: CD30 /60 hay 12AB :: CD30
:: /60
3.5.3.2 Phn loi a ch IPv6
- a ch Unicast: L a ch ca mt giao din. Mt gi tin c chuyn n
a ch Unicast s ch c nh tuyn n giao din gn vi a ch
-
- a ch Anycast: L a ch ca mt tp giao din thuc ca nhiu node khc
nhau. Mi gi tin ti a ch Anycast c chuyn ti ch mt trong tp giao din
gn vi a ch (l giao din gn node gi nht v c Metrics nh nht).
- a ch Multicast: a ch ca tp cc giao din thuc v nhiu node khc nhau.
Mt gi tin gi ti a ch Multicast s c gi tt c cc giao din trong nhm.
CHNG 4
K THUT MNG CC B
-
4.1. Cc phng thc truy nhp ng truyn
4.1.1 Phng thc a truy nhp s dng sng mang (Carrier Sense Multiple
Access)
Cn c gi l phng php nghe trc khi truyn LBT (Listen Before
Transmitting). Khi mt trm truyn d liu, trc ht n s phi nghe xem ng
truyn bn hay ri. Nu ri n s truyn d liu i (theo khun dng chun),
nu ng truyn ang bn th n s thc hin 1 trong 3 gii thut sau:
Gii thut non-persitent : Trm tm rt lui ch i trong mt thi gian
ngu nhin, sau li bt u nghe ng truyn. Gii thut ny c hiu qu
trnh xung t nhng c thi gian cht.
Gii thut 1-persitent : Trm tip tc nghe n khi ng truyn ri th
truyn d liu i vi xc sut p = 1. Gii thut ny khc phc nhc im c
thi gian cht bng cch cho php mt trm c th truyn ngay sau khi mt
cuc truyn kt thc, song nu c nhiu trm cng ch v tin hnh pht d
liu cng lc th s gy ra xung t.
Gii thut p-persitent : Trm tip tc nghe n khi ng truyn ri th
truyn d liu i vi xc sut p xc nh trc (mi trm c gn mt h s u
tin). Ngc li trm rt lui trong mt thi gian c nh ri truyn vi xc
sut p hoc tip tc ch i vi xc sut 1 p. Gii thut ny gim c ti
a xung t v thi gian cht.
-
Hnh 4.1 : Cc gii thut ca phng php CSMA
u, nhc im ca tng gii thut trn: Gii thut 1 c hiu qu trong vic
trnh xung t. Tuy nhin, c th c thi gian cht ca ng truyn v c hai
cng i. Gii thut 2 ngc li, c gng gim c thi gian cht ca ng
truyn nhng nu c hn mt trm cng truyn th kh nng xy ra xung t s cao
v gii thut 3 vi gi tr p chn mt cch hp l c th ti thiu ho c kh nng
xung t cng nh gim c thi gian cht ca ng truyn.
Phng php CSMA ch : nghe trc khi ni khng c kh nng pht hin
xung t trong qu trnh truyn, dn n lng ph ng truyn.
4.2.2. Phng thc a truy nhp s dng sng mang c pht hin xung t
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
Phng php ny c ngun gc t h thng radio pht trin ti trng i hc
Hawai vo khong nm 1970 gi l ALOHANET. Cn gi l phng php LWT
(Listen While Transmitting - nghe trong khi truyn). Cc va chm lun xy ra ti
mt cp no trn mng vi s lng tng t l thun khi cc phin truyn tng.
-
Gii php CSMA/CD (hay cn gi l LWT - Listen while talk) c th pht hin
xung t nh sau:
- Khi mt trm ang truyn, vn tip tc nghe ng truyn.
- Nu pht hin thy xung t th n ngng ngay vic truyn nhng vn tip tc
gi sng mang i thm mt thi gian m bo rng cc trm trn mng u c
th nghe c xung t .
- Sau , trm ch i trong mt thi on ngu nhin, n tip tc th truyn
li theo nguyn tc cc gii thut ca CSMA.
Vi CSMA/CD, thi gian chim dng v ch ng truyn gim xung ng
bng thi gian dng pht hin mt xung t. CSMA/CD cng s dng 3 gii thut
persitent ca CSMA, trong gii thut 1-persistent l c dng trong mng
Ethernet, Mitrenet v c chn c trtong chun IEEE.802. Ngoi ra mi chun
LAN cn c thm cc c ch b sung.
-
4.2.3 iu khin truy nhp bus vi th bi
cp pht quyn truy nhp ng truyn cho mt trm cn truyn d liu,
mt th bi c lu chuyn trn mt vng logic c thit lp bi cc trm c nhu
cu. Khi mt trm nhn c th bi n c quyn truy nhp ng truyn trong mt
thi gian xc nh v c th truyn mt hoc nhiu n v d liu. Khi ht d liu
hoc ht thi gian cho php, n chuyn th bi cho trm tip theo trn vng logic.
Th bi (Token) l mt n v d liu c bit, c kch thc v ni dung gm cc
thng tin iu khin c quy nh ring cho mi phng php.
Hnh 4.2 Token Bus
Thit lp vng logic: Vng logic gia cc trm c nhu cu truyn, c xc
nh theo mt chui c th t m trm cui cng lin k vi trm u tin ca vng.
Mi trm c bit a ch ca trm lin k trc v sau n. Th t ca cc trm
trn vng logic c lp vi th t vt l. Cc trm khng hoc cha c nhu cu
truyn d liu th khng a vo vng logic v chng ch c th tip nhn d liu.
Duy tr trng thi thc t ca mng
- B sung nh k cc trm nm ngoi vng logic nu c nhu cu truyn d
liu.
- Loi b mt trm khng cn nhu cu truyn d liu ra khi vng logic.
- Qun l li: Li: c th t vng hoc trng a ch.
Khi to vng logic: Khi ci t mng hoc t vng cn phi khi to li
vng. Vic khi to vng logic c thc hin khi mt hoc nhiu trm pht hin
Bus hot ng vt qua gi tr ngng thi gian (Time-out) hoc th bi b mt. C
-
nhiu nguyn nhn, chng hn mng mt ngun hoc trm gi th bi hng. Lc ,
trm pht hin s gi thng bo yu cu th bi ti mt trm c ch nh trc
c trch nhim sinh th bi mi v chuyn i theo vng logic.
4.2.4. iu khin truy nhp vng vi th bi
y l giao thc thng dng c dng trong cc mng LAN c cu trc vng
(Ring). Phng php ny da trn nguyn l dng th bi cp pht quyn truy
nhp ng truyn.
Nguyn tc ca phng php: Dng th bi lu chuyn trn ng vt l
cp pht truy nhp ng truyn. Mt trm mun truyn d liu th phi i n khi
nhn c mt th bi ri. Khi trm s i bit trng thi ca th bi sang trng
thi bn v truyn mt n v d liu cng vi th bi i theo chiu ca vng. Cc
trm khc mun truyn d liu phi i. D liu n trm ch phi c sao li,
sau cng vi th bi i tip cho n khi quay v trm ngun. Trm ngun s xo
b d liu v i bit th bi thnh ri v cho lu chuyn tip trn vng cc trm
khc c th nhn c quyn truyn d liu.
Hnh 4.3: S hot ng ca phng php Token Ring
S quay v li trm ngun ca d liu v th bi nhm to ra c ch bo nhn
t nhin: trm ch c th gi vo n v d liu (phn header) cc thng tin v kt
qu tip nhn d liu ca mnh. Chng hn, cc thng tin c th l: (1) trm ch
khng tn ti hoc khng hot ng; (2) trm ch tn ti nhng d liu khng c
sao chp ; (3) d liu c tip nhn; (4) c li.
-
Cc vn lin quan: Cn gii quyt hai vn c th dn n ph v h thng.
Mt l mt th bi. Hai l mt th bi bn lu chuyn khng dng trn vng. C
th c nhiu gii php khc nhau khc phc vn ny, sau y l mt gii php
c khuyn ngh:
i vi vn mt th bi: C th quy nh trc mt trm iu khin ch
ng (Active Monitor), pht hin mt th bi bng cch dng c ch ngng thi
gian Time-out. Sau khong thi gian , nu khng nhn li c th bi, trm s
pht hin tnh trng phc hi bng cch pht li th bi mi.
i vi vn th bi bnlu chuyn trn vng khng dng: trm Monitor
s dng mt bit trn th bi nh du (M=1) khi gp mt th bi bn i qua n. Nu
n gp li mt th bi bn vi bit nh du th c ngha l trm ngun khng
nhn li c n v d liu ca mnh v th bi bn c quay vng mi. Lc ,
trm Monitor s i bit trng thi ca th bi thnh ri v chuyn tip trn vng.
Tuy nhin, cn chn mt gii thut chn trm thay th cho trm monitor khi b
hng.
4.2.5 So snh CSMA/CD vi cc phng php dng th bi
phc tp ca phng php dng th bi ln hn nhiu so vi phng php
truy nhp ngu nhin CSMA/CD, x l n gin hn.Trong iu kin ti nh phng
php th bi khng cao do mt trm c th i kh lu mi n lt (c th bi).
Ngc li,: trong iu kin ti nng, phng php dng th bi hiu qu hn so vi
CSMA/CD.
u im ln nht ca phng php dng th bi l kh nng iu ho lu
thng trong mng bng cch cho php cc trm truyn s lng n v d liu khc
nhau khi nhn c th bi hoc bng cch lp ch u tin cp pht cho cc trm
cho trc.
4.3 Cc chun mng LAN
Cc chun LAN l cc chun cng ngh cho LAN c ph chun bi cc t
chc chun ho quc t, nhm hng dn cc nh sn xut thit b mng i n s
-
thng nht kh nng s dng chung cc sn phm ca h v li ch ca ngi s
dng v to iu kin cho cc nghin cu pht trin.
4.3.1 Chun Ethernet
4.3.1.1 Gii thiu chung v Ethernet
Ethernet l cng ngh ca mng LAN cho php truyn tn hiu gia cc my
tnh vi tc 10Mb/s n 10 Gigabit/s. Trong cc kiu Ethernet th kiu s dng
cp xon i l hay thng dng nht. Hin nay c khong 85% mng LAN s dng
cng ngh Ethernet.
Nm 1980, Xerox, tp on Intel v tp on Digital Equipment a ra tiu
chun Ethernet 10 Mbps (Tiu chun DIX).
IEEE (Institute of Electrical and Electronics Engineers, Inc- Vin cng ngh
in v in t) a ra tiu chun v Ethernet u tin vo nm 1985 vi tn gi
"IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
Access Method and Physical Layer Specifications"
Gn y, vi cc phng tin truyn dn v cng ngh mi, cng ngh
Ethernet ngy cng pht trin v t c tc trao i s liu n 10 Gigabit
trn giy.
Thnh phn mng Ethernet bao gm:
- Data terminal Equipment (DTE): Cc thit b truyn v nhn d liu DTEs
thng l PC, Workstation, File Server, Print Server ...
- Data Communication Equipment (DCE): L cc thit b kt ni mng cho
php nhn v chuyn khung trn mng. DCE c th l cc thit b c lp nh
Repeter, Switch, Router hoc cc khi giao tip thng tin nh Card mng, Modem
- Interconnecting Media: Cp xon i, cp ng (mng/dy), cp quang.
Nhng c im c bn ca Ethernet
- Cu hnh truyn thng: Bus ng thng/ Star
- Cu hnh khc Star bus
- K thut truyn: Base band
- Phng php truy nhp: CSMA/CD.
-
- Quy cch k thut: IEEE 802.3.
- Vn tc truyn 10Mbps, 100Mbps ... 10Gbps
- Loi cp: Cp ng trc mnh, cp ng trc dy, cp xon i, cp quang.
4.3.1.2 Cc tng trong IEEE 802
Hnh 4.4 Cc tng trong IEEE 802
Chun IEEE 802 bao gm chc nng tng vt l (Physical) v lin kt d liu
(Data Link) trong m hnh OSI. iu ny c ngha l U ban 802 ca IEEE nhn
mnh ti vic tiu chun ho cc cng ngh phn cng s dng ti tng vt l v
tng lin kt d liu.
-
Hnh 4.5 Chun IEEE 802
Chun IEEE chia tng lin kt d liu thnh hai tng con, tng iu khin truy
nhp MAC (Media Access Control) v iu khin lin kt logic LLC (Logical Link
Control).
Hnh 4.6 Cc lp con
Tng LLC (Logical Link Control ): Tt c mng LAN theo chun IEEE c
cng lp LLC c nh ngha bi 802.2. Dng chung tng con LLC, c ch cc
tng trn nh nhau bt k loi phn cng no c s dng. Giao din gia tng k
trn vi LLC c nh ngha bi cc im LSAP (Link Service Access Points ).
-
LSAP l cc a ch lin kt logic. a ch Ethernet c nhiu a ch LSAP, nhng
a ch ny cho php lin kt gia cc thc th trn mng. a ch MAC l duy nht.
- Nu thit b l DTE, n quy nh giao din gia gia tng MAC v tng mng.
LLC qun l lin kt d liu v nh ngha cc im truy nhp dch v (Service
Access Point - SAP). LLC Sublayer c tiu chun ho trong IEEE 802.2
- Nu thit b DCE l Bridge. Brige cung cp giao din LAN-to-LAN s dng
chung Protocol (Ethenet to Ethenet) hoc gia cc LAN s dng khc Protocol (nh
Ethernet to Token Ring). Bridge c tiu chun ho trong IEEE 802.1
- LLC Header:
+ DSAP (Destination Service Access Point): Con tr thng bo cho NIC v tr
b m lu tr thng tin nhn.
+ SSAP (Source Service Access Point) V tr b m lu tr thng tin i.
+ DSAP and SSAP cho php nhiu giao thc cng s dng chung NIC Card.
+ Cont (Control). Kiu ca LLC.
+ Data: D liu c a xung t lp Network, c chiu di ti a l 1497
bytes.
Tng con LLC cung cp cc dch v sau:
- Type 1: Dch v Datagram khng lin kt v khng c c ch bo nhn bit
(Unacknowledgement). Cung cp kt ni Point to Point, Multipoint v Broadcast.
- Type 2: Dch v mch o, kiu lin kt (Connection -Oriented ). Cung cp cc
dch v tun t, kim sot lung, khng li gia cc LSAP.
- Type 3: Dch v Datagram kiu khng lin kt v c c ch bo nhn bit
(Acknowledgement).
Tng Ethernet Mac Sublayer: Lin quan n cc phng php truy nhp v
kim sot truy nhp n ng truyn chung. Token RING v Ethernet thc hin
trong tng MAC bng cc phng php khc nhau cng chia s ng truyn.
- To Frame: Thm cc trng PRE, SFD, DE, SA, Length/Type, PAD, FCS
v d liu t LLC a xung to thnh khung d liu cung cp cho tng Vt l.
-
- Nhn khung d liu t tng Vt l, kim tra li v gi d liu cho tng LLC.
- iu khin truy nhp phng tin truyn dn.
Tng Vt l: Xc nh tc truyn, phng php m ho v phng tin
truyn dn v cch thc kt ni vt l. Tng vt l ca IEEE 802.3 c phn chia
l 2 phn:
- Phn c lp vi ng truyn c t giao din gia tng MAC v tng vt
l.
- Phn ph thuc ng truyn v c t giao din vi ng truyn ca LAN
v cc tn hiu trao i vi ng truyn. C nhiu tu chn khc nhau v kiu
ng truyn, phng thc truyn tn hiu v tc truyn, cch thc m ho.
4.3.1.3 Cu trc khung Ethernet
Hnh 4.7 Cu trc khung Ethernet
Cc trng quan trng trong phn mo u s c m t di y:
Preamable (7 bytes) l mt mu cha cc bit 1 v 0 xen k nhau, c dng
ng b trong hot ng truyn bt ng b t 10Mbps tr xung. Cc
phin bn nhanh hn ca Ethernet l ng b th thng tin nh thi ny l d
tha nhng vn c gi li nhm mc ch tng thch.
Trng Start Frame Delimiter (1 byte).
L mt file di mt octet nh du kt thc phn thng tin nh thi v cha
chui bit 10101011.
Destination MAC Address Field (6 byte).
-
Cha MAC ch, y c th l a ch unicast, multicast hoc broacast. y
l a ch lp 2 h tr cc thit b xc nh khung dnh cho n.
Source MAC Address Field (6 byte).
Trng ny cho php xc nh ngun gc ca frame. Cc switches s dng
a ch ny v t trong bng tm kim.
Length/Type Field (2 byte).
nh ngha chnh xc di ca trng d liu trong khung v s dng nh
mt phn ca FCS nhm m bo bn tin c thu nhn hon ton.
Trng Data v Pad (46 1500 byte).
Bao gm d liu c m ha t lp cao hn (l PDU lp 3 v ph bin hn
l IPv4 packet). Tt c cc frame phi c di ti thiu l 46 bytes. Nu mt
gi d liu nh hn 46 bytes, th trng Pad c s dng (b sung cc bit
0) tng kch thc ca frame n gi tr ti thiu ny.
Trng FCS (4 bytes).
Trng FCS cha 4 bytes CRC (cycle redanduncy check - pha gi s tnh
ton trng ny trc khi truyn khung. Pha nhn tnh ton li CRC ny theo
cch tng t. Nu hai kt qu trng nhau, khung c xem l nhn ng,
ngc li khung coi nh l li v b loi b.
4.3.1.4 Cu trc a ch Ethernet
a ch MAC ra i, cho php xc nh a ch