TRNG I HC QUY NHN KHOA K THUT & CNG NGH B MN IN T - VIN THNG

BI GING K THUT MNG

Quy Nhn, 2014

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...

- 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

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.

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

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

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

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

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.

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.

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.

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.

- 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

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.

- 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.

- 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