Công Nghệ MPLS Áp Dụng Trong Mạng Men (MAN-E)

NGUYN PHM CNG

C1!(6 SGH NPLSip DNG TRONG MNG MEN (MMI-EI

NH XUT BN THNG TIN V TRUYN THNG

M s: HT06 HM10

Chng 1

KHI NIM MNG INTERNET V M HNH THAM CHIU OSI

1.1 NGUN GC V QU TRNH PHT TRIN CA INTERNETInternet c pht minh t Cc Nghin cu cc d n

quc phng hin i (ARPA: Advanced Research Project Agency Network), l mt c quan ca B Quc phng M (DoD: Demrtment of Defence). Nm 1969, ARPA trin khai mt mng chuvn mch gi gm 4 nt gi l ARPANET. Trong qun s, DoD mun bo m truyn s liu tin cy ngay c khi cc phn ca mng b ph hu. Giao thc tng giao vn ban u (tng 4 ca m hnh OSI) c gi l giao thc iu khin mng NCP (Network Conol Protocol), v sau kch thc mng c m rng, cc kt ni lin mng rt kh khn nn thc y vic trin khai mt tng mi, tng mng v giao thc tng ny c gi l giao thc iu khin truyn dn TCP (Transmission Control Protocol) v giao thc Internet IP (Internet Protocol).

TCP/IP thc cht l chng giao thc cng hot ng cung cp cc phng tin truyn thng lin mng. Nm 1981, m hnh TCP/IP phin bn 4 (IPv4) c hon thnh v s dng ph bin trn my tnh s dng h iu hnh UNIX v tr thnh mt trong nhng giao thc c bn ca h iu hnh Windows ca Microsoft. Nm 1994, mt phin bn mi ca TCP/IP l IPv6 c hnh thnh trn c s ci tin nhng hn ch ca IPv4.

Cng ngh MPLS p dng trong mng MEN (MAN-E)

Mng Internet l mng my tnh kt ni ton cu vi nhau v hot ng truyn thng tun theo b cc giao thc TCP/IP. Ni cch khc, mng Internet l mng ca cc mng kt ni vi nhau v hot ng tun theo giao thc TCP/IP. Nh vy, mng Internet l mng din rng (WAN), bao gm hng triu cc mng my tnh tri rng khp th gii, gip cho hng triu ngi s dng trn tri t c th thng tin, trao i vi nhau. Ngoi ra n l nhng ngun ti nguyn v gi cho cc nh nghin cu, cc nh gio dc, cc quan chc chnh ph... Internet tr thnh mt cng c thit yu cho mi hot ng ca con ngi.

1.2 M HNH KIN TRC A TNGCc mng my tnh c thit k v ci t theo quan im

c cu trc a tng. Mi mt thnh phn ca mng c xem nh mt h thng gm nhiu tng v mi mt tng bao gm mt s chc nng truyn thng. Cc tng c chng ln nhau (chng giao thc), 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.

B giao thc gm mt tp hp cc giao thc xp chng ln nhau, tcmg thch, kt hp vi nhau thc hin mt tin trnh truyn thng hon chnh, c ci t v thc thi trn mt my tnh c th. Mi tng thc hin mt s chc nng truyn thng v cung cp mt s dch v cho cc hot ng ca tng trn k tip. Hai my tnh c th truyn thng vi nhau, hai my phi ang thc hin cc b giao thc ging nhau, hoc toTig thch vi nhau. Mi

mt tng trong b giao thc ca my ny phi tng tc vi tng tng ng ca my kia. Nu cc b giao ic trn cc my tng thch nhau, cc kiu my tnh khc nhau cng thc hin c uyn thng vi nhau.

.2.1 Cc quy tc phn tngT chc tiu chun quc t ISO (International Standard

Orgnazation) quy nh cc quy tc s dng trong qu trnh xy dng m hnh kt ni cc h thng m OSI (Open System Interconnection):

- Khng nh ngha qu nhiu tng, s lng tng, vai tr v chc nng ca cc tng trong mi mt 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 mi mt h thng, cn xc nh r mi quan h gia cc tng k nhau, gi l giao din tng (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 vi nhau thng nht v cc phng thc hot ng trong qu tnh truyn thng, gi l giao thc tng. Mi quan h l tp cc quy tc v cc tho thun trong hi thoi gia cc h thng truyn thng v cch thc thc hin truyn thng.

- 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

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________ 7 _

v t d liu c chuyn ngc ln cc tng trn. Gia cc ng tng xc nh lin kt logic, gia cc tng thp nht c lin kt vt l.

Nh vy mi mt tng c hai quan h: quan h theo chiu ngang v quan h theo chiu dc. s lng cc tng v cc giao thc tng c gi l kin trc mng (network architecture).

Quan h theo chiu ngang l phn nh s hot ng ca cc ng tng. Cc ng tng trc khi trao i thng tin vi nhau phi bt tay, hi thoi v tha thun vi nhau bng cc tham s ca cc giao thc (hay l i tc), c gi l giao thc tng.

Quan h theo chiu dc l quan h gia cc tng k nhau trong cng mt h thng. Gia chng tn ti giao din xc nh cc thao tc nguyn thy v cc dch v tng di cung cp cho tng trn. c gi l giao din tng.

Trong mi tng c mt hoc nhiu thc th (Entity) hot ng, thc hin mt s chc nng truyn thng. Cc thc th c th l tin trnh (Process) trong mt h a x l, hoc c th l mt chuofng trnh con... Chng thc hin cc chc nng ca tng N v giao thc truyn thng vi cc thc th ng tng trong cc h thng khc. K hiu N_Entity l thc th tng N.

Cc thc th ca tng truyn thng vi cc thc th tng trn n v cc thc th tng di n thng qua cc im truy cp dch v SAP (Service Access Point) trn cc giao din. Cc thc th phi xc nh c cung cp nhng dch v g cho cc hot ng ca cc thc th tng trn k n v cc hot ng truyn thng ca n. Nhng hot ng ny c s dng cho nhng dch v no ca cc thc th tng k di n c cung cp thng qua cc li gi hm v qua cc im truy cp (SAP) trn giao din cc tng.

8_____________________ Cng ngh MPLS p dng trong mng MEN (MAN-E)

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI

Khi m t hot ng ca bt k giao thc no trong m hnh OS, cn phi phn bit c cc dch v cung cp bi tng k di, cc hot ng bn trong ca tng v cc dch v m n khai thc, s dng. iu ny rt quan trng v khi mi c th nh ngha c chc nng ca mi mt tng trong mi quan h vi cc tng khc. S tch bit gia cc tng gip cho vic b sung, sa i chc nng ca giao thc tng m khng nh hng n hot ng ca cc tng khc, v vy c th ni h thng l mt h thng m.

H thng ATng N

G iao din I tng N/N-1 ;

G iao thc tng NH thng B

Tng N _ _ _

Tng N - 1

Tng 2

G iao thc tng N - 1

G iao thc tng 2

Tng N - 1

Tng 2G iao din i tng 2/1 ;

Tng 1G iao thc tng 1

ng truyn vt lTng 1

Hnh 1.1: M hnh kin trc phn tng

1.2.2 Lu chuyn thng tin trong kin trc a tngH thng A H t h n g B

(5)

(4)

MGiao thc tng 5

M

Giao thc tng 4 M

( 3 ) H 3 H 4 H 3 H 4 M 2 ................................................................ H 3 H 4 I M ,

1 r 1

i

t G i a o t h c t n g 7 .

< 2 ) H 2 H 3 I V t ^ T 2 H 4 M 2 T 2 H 2 H 3 T 2

H, M

H, H3 H,

n g t r u y n v t i

Hnh 1.2: V d v lu chuyn thng tin

Hnh 1.2 mt v d minh ha cho s lu chuyn thng tin trong mng my tnh kt ni gia 2 h thng A v B gm N = 5 tng. Gi s trn h thng A, bn pht (my ngun), mt thng ip M c to ra bi qu trnh thc hin ng dng trn tng 5 v gi xung tng 4 qua cc cc im truy cp (SAP) trn giao din 5/4 truyn. Tng 4 thm mt mo u (header) H4 vo trc thng ip nhn dng thng ip v a kt qu xung tng 3 qua cc cc im truy cp SAP trn giao din 4/3. Mo u bao gm thng tin iu khin, chng hn nh s th t, cho php tng 4 h thng B, my nhn, giao thng bo n ng ni nu cc tng thp hn khng duy tr c trnh t. i vi mt vi tng, cc mo u c th cha kch thc, thi gian v cc trmg iu khin khc. Gi s, tng 3 ch thc hin cc chc nng truyn thng ca n theo quy nh gii hn v kch c gi tin, nn trc khi chuyn thng tin xung tng 2, n phi chia thng bo t tng 4 chuyn xung thnh cc gi nh hn M| v M2 v thm mt mo u H3 ca tng 3 cho mi gi. Tng 3 s quyt nh s nh tuyn i n ch cho d liu v gi cc gi xung tng 2 qua cc cc im truy cp SAP trn giao din 3/2. Tng 2 khng ch thm header H2 vo phn u mi mt gi tin m cn thm thng tin nh du T2 ri gi kt qu xung tng 1 qua cc cc im truy cp (SAP) trn giao din 2/1 cho ng truyn vt l. Trn h thng B, bn nhn (my ch), d liu c chuyn ngc ln theo tun t t tng 1 cho n tng 5 thng qua giao din cc tng. Ti cc tng, nh giao thc tng v dch v tng di cung cp cho tng trn qua cc giao din tng, n tch b cc thng tin iu khin, khng c header ca tng di c chuyn ln tng trn. Trong tng 5 d liu M c khi phc tr li. V d trc khi chuyn cc gi tin t tng 2 ln tng 3, tng 2 phi tc b thng tin iu khin H3 v

10____________________ Cng ngh MPLS p dng trong mng MEN (MAN-E)

nhp M v g M2 thnh M, gi nguyn thng tin iu khin H4. Tng 2 chuyn gi tin H4M ln tng 3 qua cc im SAP trn giao din 3/2 .

1.2.3 Nguyn tc truyn thng ng tngPht sinh ng truyn ca mt thng ip (message) t tng

giao vn (Transport Layer). Thng ip c chuyn dc xung chng giao thc bn pht, thng qua mg truyn vt l, thng ip li c chuyn ngc ln theo chiu dc chng giao thc bn nhn. V nu tng giao vn trong h thng nhn hiu c cc giao thc giao vn trong my gi khi thng ip c bn giao gia my gi v my nhn. Nh vy truyn thng cng tng, thng ip khi chuyn dc xung qua tng tng s c b sung thm vo phn u thng ip bng thng tin iu khin ca tng (header). V khi thng ip c chuyn ln theo dc chng giao thc bn nhn, cc thng tin iu khin c g b qua cc tng. Vic thm header vo u cc thng ip khi i qua mi tng trong qu trnh truyn d liu c gi l ng gi {Encapsulation). Qu trnh nhn d liu s din ra theo chiu ngc li, khi thng tin qua cc tng, thng ip s tch thng tin iu khin thuc n trc khi chuyn d liu ln tng trn.

n v d liu c s dng trong cc tng bao 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. K hiu N PCI l thng tin iu khin giao thc ca tng N.

- n v d liu dch v SD (Service Data Unit): L n v d liu truyn thng gia cc tng k nhau. K hiu N_SDU l n

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________ J_

12 Cng ngh MPLS p dng trong mng MEN (MAN-E)

v d liu truyn t tng (N+1) xung tng N cha thm thng tin iu khin.

- n v d liu giao thc PDU (Protocol Data Unit): n v d liu giao thc: PDU = PCI+SDU, ngha l gi tin PDU bao gm thng tin iu khin PCI c thm vo u n v d liu dch v SDU.

Diu Tng ng dng Tng ng dng D liuD liu Tng trinh din Tng trnh din D liu Ha

D iu HpH^ Tng phin Tng phin D liu HpH^D liu HsHpH^ Tng giao vn Tng giao vn D liu HsHpH*

D liu Tng mng Tng mng D liu HxHsHpH^D liu HnHx H s HpH^ Tng lin kt d liu Tng lin kt d liu D liu11001110101010101 Tng vt l Tng vt l 110011101010101

1100111010101011110100110

Tng Tiu Tn d liu

ng dng Ha Tiu tng ng dng Thng ip v gi

Trnh din Hp Tiu tng trinh din Gi

Phin Hs Tiu tng phin Gi

Giao vn H t Tiu tng giao vn Datagram, on v g

Mng Hn Tiu tng mng Datagram v gi

Lin kt d liu Ho Tiu tng lin k d liu Khung v gi

Vt l Tiu tng vt l Bt

Hnh . 3: B sung phn u thng bo v tn d iu s dng

1.2.4 Giao din tng, quan h cc tng k nhau v dch vChc nng ca cc tng l cung cp dch v cho tng trn k

n. Trong mi mt tng c mt hay nhiu thc th. Thc th trn cng tng cc my khc nhau c gi l thc th ng tng. Thc

th tng N thc hin cc dch v m cc thc th tng N+1 yu cu s dng, khi tng N c gi l tng cung cp dch v, tng N+1 c gi l tng s dng dch v. Tng N s s dng dch v ca tng N-1 cung cp cc dch v cho tng N+1. Cht lng dch v c nhiu mc khc nhau, chng hn dch v nhanh, dch v chm... Cc thc th trao i dch v vi nhau qua cc im truy cp dch v SAP. Cc thc th tng N cung cp dch v cho cc thc th tng N+1 qua cc im truy cp dch v SAP trn giao din N+l/N. Mi SAP c mt tihn dng duy nht.

Hai tng trao i thng tin vi nhau phi c nhng tho thun v thit lp cc quy tc giao din. Thc th ca tng N+1 chuyn mt n v d liu giao thc PDU ti thc th tng N thng qua SAP. PDU bao gm mt n v d liu dch v SDU v thng tin iu khin PCI. SD l thng tin gi qua mng ti thc th ng tng v sau a ln tng N+1. Thng tin iu khin cn thit tng di phc v cho n. Nu di ca SDU ln hn di quy nh, trc khi chuyn xung tng di, cc thc th tng N chia SDU ra nhiu gi tin nh c di quy nh v thm vo mi mt gi thng tin iu khin giao thc PCI hay gi l header. Header ca PDU c cc thc th ng tng nhn dng PDU no cha d liu v PD no cha thng tin iu khin PCI...

Hnh 1.4 minh ha giao din v dch v trong cc tng k nhau. Thc th tng N t h thng A khng th truyn d liu trc tip sang tng N ca h thng B m phi chuyn tun t xung cc tng di n, cho ti tng thp nht, tng vt l. Bng phng tin truyn vt l, d liu l nhng chui bit 0 v 1 c truyn sang tng vt l ca h thng B. T y d liu c chuyn ln cc tng trn.

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI____________


Hnh 1.4: Khi nim giao din v dch v trong mi trng OSI

Trong h thng A, d liu c chuyn xung tng N, N_SDU c xem nh l mt cm v d liu dch v ca tng N. Thng tin iu khin N_PCI c thm vo u N_SDU, bin i N_SDU thnh N_PDU = (N_PCI) + (N_SDU). Trng hp N_SDU qu di ieo quy nh ca mt n v d liu, n c chia nh thnh nhiu on v trong phn u ca mi on, ing tin iu khin N_PC c thm vo to nhiu N_PDU mi. N_PD c cc thc th tng N chuyn xung tng (N-1) qua cc im truy cp SAP trn giao din tng N/N-1. Trong tng (N-1) d liu c xem nh l cc on v d liu dch v tng th (N-1)_SDU. Qu trnh c tip tc din ra cho n khi n xung n tng vt l. Bn h thng nhn B qu trnh bin i s xy ra ngc li, tc l qua mi tng d liu N_PDU c phn tch v phn thng tin iu

khin N_PCI s c g b. N_SDU s c chuyn ln tng (N+1). y N_SDU s c xem nh l mt (N+1)_PDU.

1.3 M HNH KT NI CC H THNG M OSIM hnh kt ni cc h thng m OSI (Open System

Interconnection) l m hnh c 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 ca mt mi trng truyn thng c th. Cc tng c xp ln nhau thnh chng giao thc (Protocol stack) c kh nng gii quyt trn vn mt cuc lin lc gia cc thnh phn ca mng. Ni cch khc, chng giao thc l mt tp cc giao thc c xp chng ln nhau, cc giao thc c th tng thch vi nhau c ci t trn mt my c th v cng thc hin mt tin trnh truyn thng hon chnh. Cc hot ng ca tng di cung cp cc dch v cho cc hot ng ca tng trn. Nh vy giao thc nm di y ca chng giao thc phi l giao thc vt l truyn tin gia cc my vi nhau. Hai thc th c th truyn thng vi nhau nu c ci t cng mt chng giao thc hoc cc chng giao thc tng thch vi nhau.

1.3.1 Nguyn tc nh ngha cc tng h thng mM hnh OSI tun theo cc nguyn tc phn tng nh sau;- M hnh gm N = 7 tng.- OSI l h thng m, phi c kh nng kt ni vi cc h

thng khc nhau, tng thch vi cc chun OSI. Cc thc th h

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________


thng c th l cc my ch, nt mng, trm lm vic hay cc thit b u cui...

- 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 thc hin vic trao i thng tin gia cc nt.

Host A Host B

ng ng

Trinh din

Phin

Giao vn

Mng

Lin kt d liu

Vt l\

-*

*-B nh tuyn

Mng

Lin kt d liu

Vt l

ng dng

Trinh din

Phin

Giao vn

Mng

Lin kt d liu

I VtlDng truyn vt l

Hnh 1.5: M hnh tham chiu OS

.3.2 Cc giao thc trong m hnh OSIKhi m t hot ng giao thc trong m hnh OSI, cn nh

ngha vai tr v chc nng ca cc tng trong mi quan h gia chng vi nhau, cn phi phn bit cc khi nim cung cp dch v, cc dch v c cung cp v cc hot ng ca thc th ng tng. Nh vy khi xem xt chc nng ca giao thc, khng ch xem xt vai tr v chc nng ca n m cn phi xem xt n c s dng nhng dch v g m tng k di cung cp cho n v n

cung cp nhng dch v no cho cc hot ng ca tng k trn. Khi nim dch v bao gm c im v cc dch v ca tng di cung cp cho cc tng trn thng qua cc hm dch v nguyn thu, mi mt hm ng vi mt tp cc tham s dch v cc tng k trn c th giao tip vi ng tng ca mt h thng khc.

Trong m hnh OSI c hai loi giao thc c s dng: giao thc hng lin kt v giao thc khng lin kt.

Gi Un giao hc: Gi tin (packet) l mt ofn v ing tin c s dng trong qu trnh trao i thng tin. Nhng thng ip (message) trao i gia cc thc th trong mng, c chuyn i thnh cc gi tin nt ngun. Nhng gi tin ny khi n ch s c khi phc li thnh thng bo ban u. Mt gi tin c th bao gm cc thng tin v cc yu cu dch v, thng tin iu khin v thng tin d liu.

Trn quan im m hnh mng phn tng, mi tng ch thc hin mt chc nng l nhn d liu t tng k trn chuyn giao xung cho tng k di v ngc li. Chc nng ny thc cht l gn thm v g b phn header i vi mi mt gi tin trc khi chuyn n i. Ni cch khc, mi mt gi tin bao gm header v phn d liu. Khi i n mt tng mi gi tin s c ng thm mt phn mo u khc v c xem nh l gi tin ca tng mi, tip tc cho ti khi gi tin c truyn ln ng truyn vt l sang bn nhn. Bn nhn, cc gi tin c g b header tng ng tng.

1.3.3 Truyn d liu trong m hnh OSIQu trnh truyn v nhn d liu trong mi trng OSI din

ra nh sau: Tng ng dng tip nhn d liu bi cc giao thc ng dng nt ngun. Tng ny s chn thm thng tin iu khin

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________ V7_

header Ha (c th c hoc khng) vo u thng bo ri gi kt qu xung tng 6 . Tng 6 c th chuyn i d liu theo cc cch khc nhau sao cho ph hp vi ngn ng x l ca mng v c th chn thm header Hp ca n vo u bn tin, ri gi kt qu xung tng di - tng Phin. Tng ny khng phn bit header ca cc tng trn vi d liu trong thng ip m n nhn c. Qu trnh ny tip tc thc hin cho n khi d liu c truyn xung tng vt l v c bin i thnh chui bit khng cu trc truyn n nt ch. Ti nt ch, cc header tng ng c ln lt loi b khi thng ip c chuyn t tng thp nht (tng vt l) ln tng cao nht v chuyn i v ngn ng ngi s dng. Ti cc tng, nu pht hin li, n yu cu pht li.

.3.4 Cc tham s dch v v tng tc gia cc tngLin kt vi hm dch v nguyn thu l tp cc tham s dch

v. Thng qua cc tham s cc tng k nhau ong mt h thng c th trao i thng tin vi nhau v cc ng tng trong cc h thng trao i cc n v d liu PDU. *

V d: TCONNECT.Request (calling address, calledaddress,..., user data). Cc tham s called address v calling address l nhng tham s ca cc a ch cn thit lp kt ni logic. Thng thng, trmg user data (d liu ngi dng) thc cht l con tr a ch tr ti b nh m cha cc n v giao thc d liu PD c to ra bi i tng giao thc tng trn yu cu cung cp dch v. Cc gi tin PDU ny c chuyn ti cho cc i tng giao thc tng ng trong tng ca h thng t xa. Thut ng data" bao gm d liu v thng tin iu khin giao thc c to ra trao i gia cc ng tng trong cc h thng.


Chng 1: Khi nim mng Internet v m hnh tham chiu OSI 19

Hnh 1.6: Trng thi hot ng cc hm dch v

Cc tham s d liu kt hp vi mt hm dch v c hiu nh l mt n v d liu dch v SDU. SDU cha PDU v c lin quan n tng k trn, (N+1) PDU tng ng nh (N) SDU, ngha l n v d liu giao thc tng (N+1) chnh l n v d liu dch v tng N. Khi nhn c mt hm dch v, giao thc tng c cc tham s hm dch v v kt hp vi cc thng tin iu khin giao thc PCI to ra mt PDU cho tng v PDU c chuyn xung tng k di.

1.3.5 Trng thi hot ng cc hm dch v trong m hnh OSIMi tng c mt lp cc hm cung cp dch v nh thit lp

lin kt, truyn d liu v gii phng lin kt. Khi nhn c hm dch v giao din tng, thc th giao thc tng cn phi bit hm c ng theo th t hay khng. V d nh hm request khng th xut hin trc khi lin kt c thit lp. Th t chun c minh ha trong hnh 1.6 chuvn i trng thi cc hm dch v. Trong hnh 1.6 , cc dch v h tr cho php ngi s dng thit lp lin kt, truyn d liu v gii phng lin kt, tc l xem xt cc hm h tr cho vic thit lp lin kt v truyn d liu. Khi nhn c mt hm khng theo trnh t, ngha l giao thc b xm phm v lin kt b hu b.

1.4 VAI TR V CHC NNG CH YU CC TNG

.4.1 Tng ng dngTng ng dng (Application Layer) l tng cao nht ca m

hnh kt ni cc h thng m (OSI), n xc nh giao din gia ngi s dng v mi trng kt ni cc h thng m (OSI). Bao gm nhiu giao thc ng dng khc nhau cung cp cc phng tin cho ngi s dng truy cp vo mi tmng mng v cung cp cc dch v phn tn. Khi cc thc th ng dng AE (Application Entity) c thit lp, n s gi n cc phn t dch v ng dng ASE (Application Service Element). Mi thc th ng dng c th gm mt hoc nhiu cc phn t dch v ng dng. Cc phn t dch v ng dng c phi hp trong mi trng ca thc th ng dng thng qua cc lin kt gi l i tng lin kt n SAO (Single Association Object). SAO iu khin vic truyn thng v cho php tun t ha cc giao tc truyn thng.

Mt phn mm c th s dng trn nhiu thit b u cui (Terminal) c cc c tnh phn cng khc nhau, bng cch nh ngha mt thit b u cui mng o, mt nh x cc chc nng ca thit b u cui mng o ln cc chc nng ca thit b u cui thc. Tng 7 thc hin chc nng gii quyt s khng tng thch gia 2 thc th truyn thng cho nhau v cch t tn tp, cch th hin mt dng ca mt vn bn... Tng ny cng c chc nng cho php truy cp v qun l chuyn giao tp FTAM (File Transfer Access And Management), th in t (E-mail)...

1.4.2 Tng trnh dinTng trnh din (Presentation Layer) gii quyt cc vn

lin quan n c php v ng ngha ca thng tin c truyn. Biu din thng tin ngi s dng ph hp vi thng tin lm vic ca


mng v ngc li. Thng thng biu din thng tin cc ng dng ngun v ng dng ch c th khc nhau bi cc ng dng c chy trn cc h thng c th khc nhau. Tng trnh din phi chu trch nhim chuyn i d iiu gi i trn mng t mt loi biu din ny sang mt loi khc, 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.

V d in hnh chc nng ca tng ny l m ho (Encoding) d liu theo nhng chun c hai thc th truyn thng tho thun trc. cho cc thc th khc nhau s dng cc biu din d liu khc nhau c th truyn thng c vi nhau, d liu trao i c th c nh ngha mt cch tru tng km theo cc tiu chun m ho s dng. Qun l cu trc d liu tru tng v bin i (Convert) d liu. Tng ny cng thc hin cc dch v nh nn d liu gim s lng bit phi truyn, cng nh vic thc hin quyn truy cp hp php (Authentication).

1.4.3 Tng phinTng phin (Session Layer) 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. Ni cch khc tng phin thit lp "cc giao dch" gia cc thc th u cui trn mng. Tn ca mi giao dch l nht qun cho mi thnh phn i thoi vi nhau v thit lp nh x gia cc tn vi a ch ca chng. Mt giao dch phi c thit lp trc khi d liu c truyn trn mng, tng phin m bo cho cc giao dch c thit lp v duy tr theo ng qui nh.

Tng phin cho php s giao vn d liu thng thng nh tng giao vn, nhng n cng cn cung cp nhng dch v nng cao trong mt s ng dng. Tng ny c th cho php ngi s

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI____________ ^

dng ng nhp (Log Into) vo nhng h thng chia s thi gian t xa hoc truyn tp tin gia cc my tnh. Mt trong nhng dch v phin l qun l iu khin i thoi. Nu cc phin cho php truyn song cng (Full Duplex), ngha l hai bn ng thi gi d liu i th khng i hi phi c nhim v qun tr tng tc c bit no. Nu truyn bn song cng (n cng) (Half Duplex), cc thc th phin duy tr tng tc lun phin s dng quyn c truyn d liu khi n lt. Phng thc ny ph hp vi cc ng dng hi-p. Trng hp hi thoi mt chiu (Simplex), chun OSI khng xt n trng hp ny.

Dch v phin nhm mc ch cung cp mt lin kt gia 2 u cui s dng dch v phin sao cho trao i d liu mt cch ng b v khi kt thc th gii phng lin kt. S dng th bi (Token) thc hin truyn d liu, ng b ha v hy b lin kt trong cc phng thc truyn ng thi hay lun phin. Thit lp cc im ng b ha trong hi thoi. Khi xy ra s c c th khi phc hi thoi bt u t mt im ng b ha tha thun.

1.4.4 Tng giao vnTng giao vn (Transport Layer) cung cp cc chc nng cn

thit gia tng mng v cc tng trn. 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 ton trnh. Th tc trong 3 tng di (tng vt l, tng lin kt d liu v tng mng) ch phc v vic truyn d liu gia cc tng k nhau ong tng h thng. Cc th tc trong cc tng tr 4 n 7 c chc nng kim sot ton trnh. Cc thc th ng tng hi thoi, thng lng vi nhau trong qu trnh truyn tin.

Tng giao vn gn cc thc th u cui bng mt a ch duy nht v qun l s kt ni gia cc thc th. Tng giao vn


thc hin vic chia cc gi tin ln thnh cc gi tin nh hn trc khi gi i v thng thng tng giao vn 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 giao vn ph thuc nhiu vo bn cht ca tng mng.

Tng giao vn thc hin vic ghp knh v phn knh. Thng thng cc thc th ca tng to ra mt lin kt cho mi yu cu lin kt ca tng trn n, tuy nhin trong tnrofng hp tng n i hi vic giao vn thng lng cao thi tng ny c th to ra nhiu lin kt mng v truyn thng d liu i ng thi trn nhiu ng. Tng giao vn c th thc hin vic ghp knh (multiplex) mt vi lin kt vo cng mt lin kt ni gim gi inh.

Giao thc tng giao vn bao gm:Giao thc lp 0 (Simple Class): Cung cp kh nng om gin

thit lp lin kt, truyn d liu v hy b lin kt trn mng "hng lin kt" loi A c t sut li v s c c bo hiu chp nhn, cc gi tin c gi thit l khng b mt. Giao thc lp 0 c kh nng pht hin v bo hiu cc li nhng khng c kh nng phc hi.

Giao hc lp (Basic Error Recovery Class): Cc giao thc lp ny s dng cc loi mng B, c t sut li chp nhn c nhng t sut s c c bo hiu li khng chp nhn c. Tng giao vn phi c kh nng phc hi li khi xy ra s c. Cc gi tin (TPDU) c nh s. Ngoi ra giao thc cn c kh nng bo nhn cho ni gi v truyn d liu khn. So vi giao thc lp 0, giao thc lp 1 c thm kh nng phc hi li.

Giao thc lp 2 (Multiplexing Class): Cc giao thc lp ny c ci tin ca cc giao thc lp 0 , cho php dn mt s lin kt

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________ ^

giao vn vo mt lin kt mng duy nht, ng thi c th kim sot lung d liu trnh tc nghn. Giao thc lp 2 khng c kh nng pht hin v phc hi li. V vy cc giao thc ny ch ph hp vi mng loi A.

Giao thc lp 3 (Error Recovery and Multiplexing Class) l s m rng giao thc lp 2 vi kh nng pht hin v phc hi li, ph hp vi mng loi B.

Giao thc lp 4 (Error Detection and Recovery Class) l cc giao thc c hu ht cc chc nng ca cc giao thc lp trc v cn b sung thm mt s kh nng khc kim sot vic truyn d liu.

1.4.5 Tng mng

Tng mng (Network Layer) thc hin chc nng nh tuyn (Routing), chn fng i cho cc gi tin t ngun ti ch. a ch ngun v a ch ch c th ong cng mt mng hoc khc mng nhau. ng i c th c c nh, t thay i, cng c th c nh ngha khi bt u hi thoi, v c th ng i l ng (Dynamic), ngha l c th thay i vi tng gi tin tu theo trng thi ti tc thi ca mng. Trong mng qung b (Broadcast Network), vic nh tuyn rt n gin.

Tng mng cung cp cc phoTig tin truyn cc gi tin qua mng. V vy cn phi p ng vi nhiu kiu mng v nhiu kiu dch v cung cp bi cc mng khc nhau. Hai chc nng ch yu ca tng mng l nh tuyn (Routing) v chuyn tip (Forward). Khi kt ni cc loi mng khc nhau, cn phi c mt b nh tuyn (quy nh bi tng mng) chuyn cc gi tin t mng ny sang mng khc v ngc li. i vi mt mng chuyn


mch gi cc gi d liu c truyn t mt h thng ti mt h thng khc trn mng phi c chuyn qua mt chui cc nt. Mi nt nhn gi d liu t mt ng vo (Incoming Link) ri chuyn tip n ti mt ng ra (Outgoing Link) hng n ch ca d liu. Nh vy mi nt trung gian phi thc hin cc chc nng nh tuyn v chuyn tip.

K thut nh tuyn phi thc hin hai chc nng chnh sau y:

- Quyt nh nh tuyn ti u da trn cc thng tin c v mng ti thi im thng qua nhng tiu chun ti u nht nh.

- Cp nht cc thng tin v mng, s dng cho vic nh tuyn. Trn mng lun c s thay i nn vic cp nht l cn thit.

Thng tin c s dng cho vic nh tuyn bao gm: trng thi ca Tig truyn, thi gian tr khi truyn trn rng dn, mc lu thng trn mi Tig v cc ti nguyn ca mng. Khi c s thay i trn mng (v d thay i v cu trc mng do c s c ti mt vi nt, phc hi ca mt nt mng, thm nt md... hoc thay i v mc lu thng...) cc thng tin ny cn c cp nht vo cc c s d liu trng thi ca mng.

Hin nay khi nhu cu truyn thng a phng tin, tch hp cc loi d liu vn bn, ha, hnh nh, m thanh ngy cng pht trin, th i hi cc cng ngh truyn dn tc cng cao nn vic pht trin cc h thng nh tuyn tc cao ang rt c quan tm.

Mt chc nng quan trng khc ca tng mng l chc nng iu khin tc nghn (Congesion control). Nu c qu nhiu gi tin cng lu chuyn trn cng mt ng th c th xy ra tnh trng tc nghn, tng mng phi gii quyt vn ny. Thc hin


chc nng giao tip gia cc mng khi cc gi tin i t mng ny sang mng khc ti ch, c nhiu vn c th xy ra:

- Cc mng c th s dng cch nh a ch khc nhau.- Cc mng c th chp nhn kch thc cc gi khc nhau.- Cc mng c th s dng cc giao thc khc nhau...

1.4.6 Tng lin kt d liuTng lin kt d liu (Data link Layer) l tng 2 trong m

hnh OSI, nm trn tng vt l v di tng mng. Tng lin kt d liu s dng cc dch v ca tng vt l v cung cp cc dch v cho tng mng thc hin ng b, kim sot lung d liu v kim sot li nhm bo m qu trnh truyn thng c tin cy cao.

Chc nng ch yu ca tng lin kt d liu l thc hin vic chuyn i thng tin mc mng thnh tng on thng tin gi l khung (Frame). m bo truyn lin tip cc khung ti tng vt l, ng thi x l cc thng bo t my thu gi tr li. Ni tm li, nhim v chnh ca tng ny l khi to v t chc cc khung cng nh x l cc thng tin lin quan ti n. Tng lin kt d liu quy nh khun dng, kch thc ca khung thng tin. Xc nh c ch truy cp phng tin truyn cho cc gi tin sao cho n ch c tin cy cao. Tng lin kt d liu c hai phng thc lin kt: phng thc im - im v phng thc a im.

Theo quy c, tng lin kt d liu c chia thnh 2 tng con: tng con iu khin lin kt logic LLC (Logical Link Control Sublayer) c nh ngha trong chun 802.2 bao gm mt s chc nng nh phn khung d liu, iu khin lung d liu v qun l li. Tng con iu khin tmy cp phcmg tin truyn MAC (Media Access Control sublayer) cung cp cc giao thc qun l truy cp ng truyn khi cc nt s dng chung mt mi trng truyn trao i thng tin.


Mt s dch v cung cp cho tng mng, bao gm:- iu khin truy cp ng truyn.- Cung cp cc lin kt gia cc thc th ca tng mng.- To khung v m bo truyn khung qua cc lin kt theo

th t.- Tnh gi tr FCS (Frame Check Sequence: Tun t kim tra

khung) khung trc khi truyn v kim tra sau khi nhn.- iu khin lu lng iu chnh s lng khung c

truyn.- La chn cc tham s cht lng dch v.Giao thc iu khin d liu mc cao HDLC (High - Level

Data Link Control) l giao thc c pht trin bi ISO 3309 v ISO 4335 s dng trong cc mng im - im v a im, song cng (Full-Duplex), cu trc khung nh hnh 1.7.

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________ 27_

8 bit 8/16 bit 8/16 bit 46-1.500 byte 16/32 bit 8 bit

Flag Address Control Information FCS Flag

01111110 Frame Header

FrameCheck

Sequence 01111110

Hnh 1.7: cu trc khung HDLC

Trong ;Flag field (Trng c): Mi mt khung d liu c bt u

v kt thc bng 1 byte gi l c c gi tr l 01111110 phn bit cc khung vi nhau. trnh s nhm ln gi tr byte c vi gi tr ca cc byte d liu, ngi ta quy nh nu xut hin 5 bit 1 lin nhau trong chui d liu th h thng s t ng in thm mt bit 0 trc khi truyn v sau khi nhn nu pht hin c bit 0 sau 5 bit 1 lin tip th h thng t ng loi b bit 0 .

Address field (Trng a ch): Trfng ny xc nh khung i khung lnh (Command) hay l khung phc p (Response). Nu l khung lnh, trng a ch s l a ch ca thit b ch. Nu l khung phc p, trng a ch s l a ch ca thit b ngun. Trng a ch c th c di l 1 byte (chun) hoc 2 byte (m rng).

Control field (Trng iu khin) cha cc ch thao tc lnh (Command) hay ch thao tc phc p (Response), ph thuc khung lnh hay l khung phc p. di chun ca trng ny l 1 byte. Nu m rng t-ng iu khin c di 2 byte phi thit lp lnh Mode gia iit b truyn v thit b nhn. C 3 loi khung: thng tin, gim st v khng nh s.

- 1 - Frame (Information Frame): l khung dng truyn cc gi d liu cho cc thc th tng 3. N cng cha thng tin v vic s gi N(R) v s th t N(S) cc gi trong trng iu khin, cu trc khung tin bao gm cc trng Flag, Address, Control, Infomation, FCS, Flag.

- s - Frame (Supervisory Frame): Khung gim st dng iu khin li d liu v kim sot lung d liu. C 3 loi s - Frame khc nhau, l cc khung mng thng tin v nt ch sn sng nhn, khng sn sng nhn v t chi nhn. Khung gim st c cc trng; Flag, Adds, Add, Control, FCS, Flag.

- u - Frame (Unnumbered Frame): Khung khng nh s v n khng cha cc tham s N(R) v N(S). Loi khung ny s dng thit lp v hu b cc lin kt d liu theo cc phcmg thc hot ng khc nhau. C 5 loi khung khng nh s loi U:

+ Phng thc tr li chun SNRM (Set Normal Response Mode): Client ch c truyn khi Server cho php.

28_____________________Cng ngh MPLS p dng trong mng MEN (MAN-E)

+ Phuofng thc tr li d b SARM (Set Asynchronous Response Mode): Client c th tmyn khng cn i s cho php ca Server.

+ Phng thc d b cn bng SABM (Set Asynchronous Balanced Mode): S dng trong trng hp im - im, 2 chiu, khng c Server/Client. Giao thc X.25 (CCITT) c xy dng theo giao thc ny ca HDLC.

+ Gii phng lin kt DISC (Disconnect).+ Tr li cho cc khung loi u khc UA (Unnumbered

Acknowledgement).Information Field (Trng thng tin): Trng ny ch dnh

cho khung loi I. di thay i ph thuc vo kin trc mng. V d mng Ethernet, di trng thng tin c th t 46 bit n1.500 bit.

FCS Field (khung Check Sequence): Trng kim sot li c th xy ra trong khung truyn. FCS c tnh ton da trn ni dung ca trng a ch, trng iu khin v trng thng tin. FCS xc nh bng phorng php m vng c d CRC (Cyclic Redundancy Code). Khi s dng phng php ny, bn pht v bn thu cng s dng mt a thc sinh G(X) (Generator Polynomial) c quc t chun ho.

Mt s giao thc dn xut t HDLC- LAP (Link Access Procedure); Tng ng vi phng thc

tr li d b ARM ca HDLC dng trong bi cnh khng cn bng (c trm iu khin).

- LAP-B (Link Access Procedure - Balanced): Tng ng vi phng thc tr li d b cn bng ABM ca HDLC cho bi cnh

Chng 1: Khi nim mng Internet v m hnh tham chiu OSI___________ 29^

30 Cng ngh MPLS p dng trong mng MEN (MAN-E)4

cn bng. c dng trong hu ht cc mng truyn d liu cng cng X.25 (CCITT X.25.2).

- LAP-D (Link Access Procedure - D channel): Cng l mt tp con ca HDLC, mc d c mt vi m rng thm, c xy dng t LAP-B v c dng nh giao thc lin kt d liu cho cc mng dch v tch hp s ISDN cho php cc DTE truyn thng vi nhau qua knh D ca n.

- SDLC (Synchronous Data Link Control): L giao thc tng ng vi phng thc tr li chun NRM v c m rng vi kh nng ty chn. Cc khung ca SDLC c cng khun dng nh khung HDLC.

- ADCCP (Advanced Data Communication Control Procedure) c pht trin bi Vin Tiu chun quc gia M ANSI. N cng tomg t nh HDLC, vi cht t thay i, c ban hnh nh mt chun quc gia (ANSI X3.66).

Cu trc khung IEEE 802.3Phn nh ranh gii

{ byte) di d liu

(2 bte) m (Pad)

(n byte)

Phn m u (7 byte)

a ch ch {6 byte)

a ch ngun (6 byte)

D lu (46 byte n .500 byte)

TP FCS (4 byte)

Phn m u

a ch ch (Destination Address): 48 bit, l a ch vt l ca trm nhn.

a chi ngun (Source Address): 48 bit, l a ch vt l ca trm pht.

di d liu (Length Count): 2 byte. di ca trng d liu, ngay sau trng ny: 46 byte n

1.500 byte.m (Pad): Cha d liu gi, sao cho phn d liu c di

nh nht l 46 byteTrng kim tra (Frame Check Sequence): CRC 4 byte, m

pht hin li. di ca ca khung IEEE 802.3, tr phn m u s l t

64 byte n 1.518 byte.1.4.7 Tng vt l

Tng vt l (Physical layer) l tng thp nht trong m hnh 7 lp OSI. Khc vi cc thc th ng tng ca cc tng trn, cc thc th tng giao tip vi nhau qua mt knh logic cn cc thc th tng vt l giao tip vi nhau qua mt cmg truyn vt l. Tng 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. Cung cp cc c ch v in, c hm, th tc... nhm thc hin vic kt ni cc phn t ca mng thnh mt h thng bng cc phng php vt l. m bo cho cc yu cu v chuyn mch hot ng nhm to ra cc ng truyn thc cho cc chui bit thng tin. Cc th tc trong tng vt l l cc th tc xc nh giao din gia ngi s dng vi mi trng mng.

Cc giao thc c xy dng cho tng vt l c phn chia thnh hai loi giao thc s dng phoTig thc truyn thng d b (Asynchronous) v phng thc truyn thng ng b (Synchronous).



Phng thc truyn d b: khng c mt tn hiu quy nh cho s ng b gia cc bit gia my gi v my nhn, trong qu trnh gi tn hiu my gi s dng cc bit c bit START v STOP c dng tch cc xu bit biu din cc k t trong dng d iu cn truyn i. N cho php mt k t c truyn i m khng quan tm n cc tn hiu ng b trc .

Phng thc truyn ng b ngha l cn c ng b gia my gi v my nhn, bng cch chn cc k t c bit nh SYN (Synchronization), EOT (End Of Transmission) hay c (flag) gia cc d liu ca my gi bo hiu cho my nhn bit c d liu ang n hoc n.

1.4.8 Tm tt chc nng cc tng

Tng Chc nng ch yu Giao thc

7. ng dng Cung cp cc dch v ng dng trn mng cho ngi s dng qua mj trng OSI.Giao thc ng dng

6. Trnh din Chuyn i c php d u p ng yu cu truyn thng ca cc ng dng.Giao thc bin i m

5. Phin

Qun l cc cuc lin c gia cc thc th bng c^ch thit lp, duy tr, ng b ho v hu b cc phin truyn thng gia cc ng dng

Giao thc phin

4. Giao vn Giao vn thng tin gia cc my ch (End to End). Kim sot li v lung d liu.Giao thc giao vn

3. MngThc hin vic chn ng v m bo trao i thng tin gia cc mng con trong mng ln vi cng ngh chuyn mch thch hp.

Giao thc mng

2. Lin kt d liu

Chuyn i khung thng tin (Frame) thnh cc chui bit truyn v kin to li cc khung t cc bit nhn c

Th tc kim sot truyn

1. Vt lm bo cc yu cu truyn/nhn cc chui bit qua cc phng tin vt l.

Giao din DTE - DCE

1.4.9 Mt s nhn xt v kin trc m hnh OSIM hnh OSI t chc cc giao thc truyn thng thnh 7

tng, c bt u nghin cu trong nhng nm thp k 70 ca th k XX v c hon thnh sau khi cc giao thc TCP/IP c s dng rng ri, tr thnh chun cho cng ngh mng my tnh. V vy, trn thc t, m hnh OSI khng c s dng, n tr thnh m hnh tham kho tng qut v c bn cho vic nghin cu kin trc mng tin tin hcm. Cc giao thc ca OSI cha c hon iin, phc tp. Vai tr v chc nng ca tng phin khng c s dng nhiu trong cc cc ng dng, tng trnh din gn nh khng c g, trong di tng lin kt d liu v tng mng li qu phc tp n mc phi chia thnh cc tng con vi cc chc nng khc nhau.

M hnh OSI ch quan tm n truyn thng (Communication), m khng quan tm nhiu n mi quan h gia Computing (in ton) v Communication.


Chng 2

MNG RING o

2.1 GII THIU CHUNG

2.1. Khi nim

Mt mng ring o VPN (Virtual Private Network) l s m rng ca mt mng ring bao hm cc lin kt thng qua cc mng cng cng, v d nh mng Internet. Mt VPN cho php ngi ta gi d liu gia hai my tnh qua mt mng cng cng hoc mt mng chia s theo phng thc c th m phng li cc tnh cht ca mt lin kt ring. Hnh 2.1 a ra ci nhn khi qut v ba loi hnh mng.

duy tr c tnh ring t trn c s h tng vin thng cng cng, mt VPN phi s dng cc giao thc to ng hm v cc bin php m bo an ninh. Mt VPN c th i chiu vi mt h thng knh xy dng ring hoc knh thu ring cho mt cng ty. Mc ch chnh ca VPN l cung cp cho mt ngi s dng tt c cc tnh nng m mt knh thu ring c th mang li, nhng vi mt gi thnh r hn rt nhiu thng qua vic s dng h thng h tng c s cng cng. Hn thp k qua, cc cng ty vin thng cung cp cc ti nguyn ring c chia s cho mc ch m thoi. Vi VPN, vic chia s cc ti nguyn cng cng cho d liu mt cch an ton tr thnh hin thc. Cc doanh nghip ngy nay ang quan tm ti vic s dng VPN cho mng ngoi bin v mng ni b din rng.

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Mng ring o

2.1.2 Phn loai

Phn ny a ra mt s nh ngha v cc loi VPN v cc tiu ch phn bit chng. Khi la chn cc tiu ch ngi ta phi chp nhn mt s tha hip no v kh c th s dng mt tiu ch c th a ra mt loi VPN hon ton khc bit vi cc loi khc. Khi thc hin phn loi chng ta s thy, phn loi VPN theo mt tiu ch ny li c th bao hm cc VPN c phn loi theo mt tiu ch khc.

2.1.2.1 Phn loai theo m hnh kt ni

- Mng ring o truy cp t xa (Remote Access VPN): Trong m hnh ny ngi s dng thay v quay s trc tip vo mng ca doanh nghip s s dng kt ni Internet to ra mt kt ni VPN vo mng ca doanh nghip. Hai im cui ca ng hm (turniel) s chnh l my tnh v thit b truy cp mng ring o t ti mng doanh nghip. y l m hnh c p dng cho ngi i cng tc xa, cng tc vin, V.V....

- Mng ring o t v tr n v tr (Site-to-Ste VPN)'. Trong m hnh ny mi mt v tr u c cc thit b truy cp mng ring o, cc thit b ny thng c cc kt ni TC tip vo Internet. Hai im cui ca ng hm chnh l hai thit b truy cp mng ring o. M hnh ny c p dng kt ni mng doanh nghip vi mng ti cc chi nhnh hoc mng doanh nghip vi mng ca i tc.

2. .2.2 Phn loi theo quyn truy nhp

- Mng ring o trong (Intranet VPN): L khi nim ch mt mng ring o c to ra ch dnh ring cho ngi s dng ca


doanh nghip, n hon ton khng lin quan n m hnh hay cng ngh c p dng.

- Mng ring o ngoi (Extranet VPN): Cng nh mng ring o trong, loi mng ny khng lin quan n m hnh kt ni hay cng ngh c p dng, m chi l mt khi nim ch mt mng ring o trong c m rng quyn truy nhp cho ngi s dng bn ngoi doanh nghip, v d khch hng hay nh cung cp, V .V ....

2.1.2.3 Phn loi theo nguyn tc hot ng

- Mng ring o an ton (Secure VFN): Mng ring o an ton bao gm tt c cc loi mng ring o m trong tnh ring t c m bo nh vo cc k thut an ninh, m ha. Thuc v phn loi ny bao gm cc mng ring o s dng cc giao thc GRE, L2TP, PPTP, IPSec, V . V . . . .

- Mng ring o tin cv (Trusted VPN): Mng ring o tin cy bao gm tt c cc mng ring o m trong tnh ring t c m bo thng qua vic duy tr s ton vn ca knh thng tin. Thuc v phn loi ny bao gm tt c cc mng ring o s dng FR, ATM, MPLS L2, MPLS L3, V .V ....

2.1.2.4 Phn loi theo cng ngh p dng

Cch thc phn loi ny da vo mt cng ngh hay mt giao thc c th c p dng to ra ng hm. Hai ci tn c trng nht trong cc loi cng ngh mng ring o c lit k di y.

- Mng ring o da trn giao thc an ton mng IPSec (IPSec VPN)

Chng 2: Mng ring o _____________________ ^

- Mng ring o da trn chuyn mch nhn a giao thc MPLS (MPLS VPN)

2.1.2.5 Phn loai theo m hnh OSI

- Mng ring o lp 2 (L2 VPN): L tt c cc mng ring o c to ra da vo cc cng ngh, cc giao thc hot ng lp 2 ong m hnh OSI. Mt s loi mng ring o ph bin ieo cch phn loi ny l cc mng ring o da trn ATM, L2TP, PPTP.

- Mng ring o lp 3 (L3 VPN): L tt c cc mng ring o c to ra da vo cc cng ngh, cc giao thc hot ng lp 3 trong m hnh OSI. Mt s cc loi mng ring o ph bin theo cch phn loi ny l cc mng ring o da trn giao thc cng bin/chuyn mch nhn a giao thc (BGP/MPLS), giao thc an ton mng (IPSec).

2.1.2.6 Phn loi theo m hnh qun lt khai thc

- Mng ring o khch hng khai thc (customer-provisioned VPN): i vi cc mng ring o ny khch hng phi t qun l v khai thc mng ring o ca mnh bao gm c vic qun l v cu hnh cc thit b u cui. Nh cung cp y ch ng vai tr l nh cung cp kt ni.

- Mng ring o nh cung cp khai thc (provider-provisioned VPN): i vi cc mng ring o loi ny, nh cung cp s qun l v khai thc ton b mng bao gm c vic cu hnh cc thit b u cui. Mng ring o y c coi nh l mt dch v c nh cung cp mang n cho khch hng. Hnh 2.2 a ra s phn loi mng ring o theo tiu ch ny. Ngi ta c th thy ngay rng cc tiu ch phn loi khc nh m t cc phn trc li c trn ln trong tiu ch phn loi ny.


Chng 2: Mng ring o 39

VPWS: Vitual Private Wire Service: Dch v cp ring o

VPLS: Vltual Private LAN Service: Dch v LAH ring o IPLS: IP ony ^N - like Service: Dch v IP-^N tng thch

BGP/MPLS: Border Gateway Protocx)l/Multi Protocol Label Switch Internet

Protocol: Giao thc cng bin/ chuyn mch nhn a giao thc Vltual Router: B nh tuyn o

!P See: IP Security: Giao thc mng an ton

Hnh 2.2: Phn loi mng ring o nh cung cp khai thc

2.2 NGUYN TC HOAT NG# Nh chng ta bit, mt mng ring o l s m rng ca

mt mng ring bao gm cc iin kt kt ni vi cc mng chia s hoc mng cng cng. R rng l khch hng s dng mng ring o i hi phi c mt phng thc no m bo tnh ring t khi d liu ca khch hng di chuyn qua mt mng cng cng. Ngoi vic m bo tnh ring t cho thng tin, cc k thut mng ring ang tn ti c xy dng trn cc cng ngh lp 1 hay lp 2 u c ch nng m bo cht lng dch v. Cc ng thu ring hoc cc ng quay s u m bo bng thng v tr, trong khi cc cng ngh kt ni nh FR (Frame Relay) hay ATM


(ASynchronouns Transfer Mode) cn c cc c ch rng ri m bo cht lng dch v.

c th thc hin c iu cc mng ring o phi c trin khai nh vo mt hnh thc no ca k thut to ng hm, cc khun dng gi v/hoc a ch s dng cho mng ring o khng lin quan n ci c s dng nh tuvn cc gi xuyn qua ng hm qua mt mng xng sng. Cc ng hm nh vy c th mang li mt mc an ninh thc t no , mng chung c s drig nh mng ring.

_ im cui ng hm ___

Thit bj mng ring o

Mng trung gian Thit b

.......... ^7) ng hm

Hnh 2.3: Khi nim ng hm

Mt ng hm kt ni hai im cui mng ring o chnh l thnh phn c bn nht m t ngi ta c th xy dng nn cc loi mng ring o khc nhau. Mt ng hm IP hot ng chng ln qua mt mng xng sng IP v lu lng c gi qua mt ng hm l hon ton m i vi mng xng sng pha di. Nh th mng xng sng IP c s dng nh l cng ngh lp 2 v Tig hm to ra mt lin kt im ti im nh l mt lin kt ring. C nhiu k thut to Tig hm khc nhau nh IP/IP (IP ng gi trong IP), GRE (Generic Routing Encapsulation: ng gi nh tuyn chung), PPTP (Point to Point Tunneling Protocol: giao thc ng hm im - im, L2TP (Layer 2 Tunneling

Protocol: giao thc ng hm lp 2), IPSec v MPLS [6]. Cun sch ny cp n k thut s dng MPLS to ra cc mng ring o.

2.3 SO SNH MT s M HNH MPLS

2.3.1 So snh mng ring v mng ring o

Khi nim mng ring o (VPN) ni ln c UXI im ca n. Hin nay vi tc pht trin v cng mnh m ca Internet, cc mng vin thng tc cao v li ch to ln do vic p dng cng ngh thng tin vo mi lnh vc, c bit l trong lnh vc vn phng, qun l, v.v..., th mng ring o dng nh yu cu bt buc cho cc doanh nghip. T nhu cu tniy nhp t xa vo mng ca doanh nghip, n vic to mi quan h vi khch hng, gip h c th khai thc mt phn ngun ti nguyn ca mnh m vn m bo tnh bo mt cn thit cho thng tin.

Mc ch ca VPN l cung cp cho khch hng kt ni thng qua mt c s h tng chia s vi tt c cc thun li ca mt mng ring. Mt gii php VPN phi chng li c s xm nhp tri php v s xo trn; Cung cp d liu quan trng ng lc, tin cy, v phi c kh nng qun tr c. Di y l mt s cc u im v nhc im ca VPN.

2J.1.1 u im

- Chi ph thp: Nu nhn t mi gc v chi ph, t chi ph thit lp h thng n chi ph vn hnh th r rng rng vic s dng mng ring o s c chi ph thp hn nhiu so vi chi ph phi b ra cho mt mng ring.

- n gin trong Irin khai: Vic trin khai mt mng ring cho doanh nghip ca mnh khng phi lc no cQng c th thc

Chng 2: Mng ring o____________________________ 41_

hin c, nht l i vi cc doanh nghip khng hot ng trong lnh vc vin thng.

- n gin trong vn hnh v khai thc: iu ny c bit ng i vi cc mng ring o an ton. Ch vi mt my tnh s dng Windows 2000 Server c kt ni Internet v mt my tnh c nhn thng thng c kt ni Internet ngi ta c th xy dng ngay cho mnh mt mng ring o.

- Kh nng m rng: R rng khi s dng mt h tng chia s ngd ta gn nh c th xy dng mt mng ring o bt k mt quy m no. c bit i vi cc mng ring o s dng Internet l h tng chia s.

2.3J .2 Nhc im

- Bo mt: Mng ring o c coi l c tnh bo mt thp do phi chuyn cc thng tin c tnh ring t v quan ng qua mt mng dng chung c bo mt km, nht l i vi cc mng ring o s dng Internet i h tng chia s. ng c dn n vic cc mng ring o b tn cng c th l: s cnh tranh gia cc doanh nghip, s tham lam mun chim ngun thng tin, s tr th, cm gic mnh, V .V .... Ngun tn cng c th t bn ngoi, m cng c th ngay bn trong.

- m bo cht lng dch v (QoS): Ta bit rng cc mng ring o ngy nay ch yu l da trn nn h tng mng IP. M c th ca mng IP l mng c cu trc n gin, lu lng ing tin ln, kh d on cng chnh v th m vic qun l cht lng cho tng dch v l rt kh khn.

- Kh nng qun l: Cng vi l do l mng ring o phi i qua mt h tng mng cng cng c th c cu thnh t mng


ca nhiu nh cung cp khc nhau nn vic qun l kt ni im cui-n-im cui cng kh thc hin.

2.3.2 So snh mt s m hnh MPLS

Phn ny chng ta a ra mt s so snh, nh gi mt s cng ngh VPN

2.3.2.1 Vai tr v th mnh ca MPLS VPN

Chuyn mch nhn a giao thc (MPLS) hp nht s thng minh ca nh tuyn (routing) vi tc ca chuyn mch (switching). N mang li nhiu thun li ng k so vi cc mng ch c kin trc thun IP, nh l cc mng kt hp IP vi ch truyn khng ng b (ATM) v cc mng vi mt s pha trn gia cc cng ngh lp hai (L2). Cng ngh MPLS chnh l cha kha cho cc VPN c kh nng m rng v gip cc nh cung cp dch v d dng s dng h thng mng ang tn ti mt cch hiu qu p ng s tng trng trong tng lai. Cht ing dch v im - ti - im ca n cho php sa li lin kt nhanh chng. MPLS cn gip mang li cc dch v IP im - ti - im c kh nng m rng cao vi s ofn gin trong cu hnh, qun l v cung cp. Sau y l cc th mnh c bn ca MPLS VPN.

- Kh nng m rng: Mt s trin khai MPLS VPN tt c th h tr hng nghn mng ring o. Kh nng m rng l vn c ca MPLS VPN bi trong MPLS VPN khng c yu cu v kt hp v tr - n - v tr (site-to-site peering).

- An ninh: MPLS gi lu lng ring bit thng qua vic s dng s phn bit tuyn (RD - Route Distingsisher) duy nht. c gn t ng khi VPN c cung cp, s phn bit tuyn c t

Chng 2: Mng rng o____________________________ 4 ^

vo u gi nh l mt cch phn tch lui lng, s phn tuyn ny l trong sut i vi ngi s dng trong cng mt VP^.

- K thut lu lng (Traffic Engineering): Traffic Engineering c thc hin trong cc c cu MPLS v cho php lu lng c chuyn i thng qua mt ng ring bit (khng nht thit phi l ng r nht). Thng qua vic s dng k thut lu lng trn mng li, cc chuyn vin mng c th thc hin cc chnh sch nhm m bo vic phn chia lu lng ti u v tng cng c hiu qu s dng mng.

- Lp dch v (CoS): Cc c tnh ca CoS trong MPLS cho php cc nh cung cp dch v a ra nhiu loi hnh dch v khc nhau trn mng MPLS, bng cch n gin l nh du cc gi vi cc im m dch v phn bit (DSCP - Distinguisher Service Code Point) v x l chng mt cch tng ng. Cc k thut s dng h tr cc dch v phn bit bao gm phn loi gi, trnh nghn v qun tr.

- H tr tha thun v dch v (SLA): Mt s trin khai MPLS VPN tt s h tr SLA v cam oan v tho thun dch v thng qua cc k thut v cht lng dch v, cam oan v bng thng v cc tnh nng v k thut lu lng (TE).

23.2.2 Vai tr v th manh ca IPSec

Da trn cc tiu chun c IETF pht trin, IPSec m bo c tnh tin cy, tnh ton vn v xc thc i vi cc vic trao i d liu thng qua mng cng cng. IPSec ng gp mt thnh phn thit yu cho mt gii php mm do, da trn tiu chun c th trin khai mt chnh sch an ninh trn ton mng. IPSec c bit hu ch cho cc kt ni mng ring o t xa vo mng ca doanh nghip. Sau y l cc th mnh ca IPSec VPN:


- An ninh: IPSec m bo tnh ring t ca d liu vi mt tp hp cc c cu to ng hm v m ha mm do, bo v cc gi khi chng di chuyn trn mng. Ngi s dng c xc thc bng chng ch s (digital certificate) hoc cc kha c chia s t trc. Cc gi khng tun th eo chnh sch an ninh s b loi b.

- Trin khai n gin: IPSec c th a ra th trng nhanh chng. N c th c trin khai trn bt k mt mng IP ang tn ti no.

2.3.3 So snh CE-based VPN v PE-based VPN

Khi nim CE-based VPN (mng ring o da trn CE) l cch tip cn m trong cc thit b bin nh cung cp (PE) khng h bit v cc nh tuyn hay nh a ch ca mng khch hng. Cc thit b PE ch n thun cung cp dch v IP v ch i s nhn cc gi IP vi phn mo u (header) cha cc a ch IP duy nht ton cc. Trong cc CE-based VPN, xomg sng ca mng khch hng l tp cc mg hm m cc im cui chnh l cc thit b bin khch hng. Mt yu cu chung l vic gi mt gi qua ng hm cn phi ng gi n vi mt a ch mo u IP mi m c a ch l duy nht.

i vi cc CE-based VPN c khai thc bi khch hng, vic khai thc v qun l cc ng hm l trch nhim ca b phn qun l mng khch hng. Thng th cc ng hm ny c cu hnh th cng. Trong trng hp ny vic nh tuyn gia cc thit b bin chch hng cng l nhim v ca khch hng.

i vi cc CE-based VPN c khai thc bi nh cung cp, vic khai thc v qun l cc ng hm l trch nhim ca nh cung cp. Trong trng hp ny nh cung cp c th cu hnh cc

Chng 2: Mng ring o_____ 45

giao'thc nh tuyn ti cc thit b bin khch hng. iu c ngha l vic nh tuyn trong mng ring ca khch hng c kim sot bi khch hng v mt phn c kim sot bri nh cung cp.

i vi cc CE-based VPN (do khch hng hay nh cung cp khai thc) vic nh tuyn trong mng khch hng c x l bi cc Tig hm nh l cc lin kt lp 2 .

Trong mt PE-based VPN (mng ring o da trn PE) cc gi ca khch hng c mang qua cc mng nh cung cp thng qua cc ng hm, cng ging ht nh l trong CE-based VPN, tuy nhin trong PE-based VPN cc im cui ca ng hm li l cc thit b PE v cc thit b PE phi bit cch nh tuyn cc gi ca khch hng da trn cc a ch IP m chng mang theo. Trong trng hp ny bn thn cc thit b CE khng c bt k mt tnh nng VPN no v cng ding cn phi bit l chng l mt phn ca mng VPN.

Ngi ta a ra mt khi nim na gi l thit b bin VPN (VPN Edge Device) ni n thit b c g vo mng khch hng v mng xng sng VPN v n thc hin cc chc nng c trng VPN. Trong trng hp ca cc CE-based VPN th thit b bin chnh l CE device, cn trong trng hp PE-based VPN ti thit b VPN bin chnh l PE device.


Chng 3

CHUYN MCH NHN A GIAO THC

3.1 SHNH THNH V PHT TRIN CA CNG NGH* Trong mt vi thp k qua, mng ton cu Internet vi thnh

phn chnh trong cu trc l giao thc Internet (IP - Internet Protocol) pht trin v cng mnh m. Ko theo s pht trin chnh l s pht trin ca cc mng my tnh, mng vin thng nh hng theo cng ngh IP. Ngy nay cc mng my tnh ln u s dng IP, cc ng dng khc nh hi thoi, truyn thanh, truyn hnh, v.v..., cng ang dn c IP ha. L do, IP l giao thc chuyn mch gi c tin cy v kh nng m rng cao. Tuy nhin, do IP s dng phng php nh tuyn theo tng chng nn vic iu khin lu lng rt kh thc hin. ng thi, IP cng khng h tr m bo cht lng dch v.

Ch truyn khng ng b (ATM - Asynchronous Transfer Mode) c nhn nhn l mt trong nhng nn tng mang li dch v tc cao lp lin kt d liu c kh nng m bo cht lng dch v (QoS) vi giao din ngi s dimg - mng (NI). i khi ngi ta cng ni rng mng ATM mang li mt mng lin kt ln lp lin kt d liu m khng c s tham gia ca cc b nh tuyn (router). Tuy nhin vi s pht trin ca mng IP, ngi ta cng vn phi cn c router u . Cho d ATM tr thnh mt nn tng mng lp lin kt d liu quan trng th cc phn

mng, tc l cc mng IP con, cn phi lin kt vi nhau thng qua router, c ngha l cc thit b hot ng lp mng.

Nm 1994, Toshiba trnh ln IETF tng v b nh tuyn chuyn mch t bo (CSR - Cell Switch Router) mt trong nhng nim u tin cho chuyn mch nhn. Nm 1996, cc cng ty nh: Ipsilon Networks, Cisco Systems v IBM a ra k hoch v pht trin cc c ch chuyn mch nhn cho ring mnh, ln lt l IP Switch, Tag Switch v ARIS (Aggregated Route-Based IP Switch). n nm 1997, IETF thnh lp nhm lm vic MPLS. Mc tiu l pht trin v chun ha mt cng ngh c c nhng u im trong nh tuyn IP v c c tc nh trong chuyn tip ATM.

3.2 NGUYN TC HOT NG

Trong phn ny chng ta tm hiu mt s cc khi nim v MPLS v m t cch thc tip cn c th s dng.

3.2.1 Mt s khi nim 3.2.1.1 Nhn

Mt nhn (label) l mt nh danh ngn, chiu di c nh, c ngha cc b, c s dng nh danh mt lp chuyn tip tng ng (FEC - Forwarding Equivalence Class). Mt nhn, khi c dn vo mt gi c th, s biu din FEC m gi c gn cho.

Nhn chnh l cc mc (entiy) trong ngn xp nhn (iabel stack). Mt nhn c biu din bi 32 bit (4 byte) v c cu trc nh hnh 3.1.


Chng 3: Chuyn mch nhn a giao thx: 49

Tiu Gi tr nhn Tiu Lp lin kt d liu Chuyn mch nhn a giao thc

' ........'sH Lp mng

' ' \ 2 3 4 5 1 5 7 3 ' J O 1 2 i 4 f . 6 7 S ' i O I 2 3 4 5 6 7 8 9 ~I I I I I I T ' I I I I I I I I IL a b e l

... L....1_LL-LLE X p T T L

Label:Exp:S:TTL:

Gi tr nhn (Label Value), di 20 bitS dng khc (Experimental Use), v d cho lp dch v (CoS), di 3 bit y ngn xp {Bottom of stack), 1 bit Thi gian sng (Time to Live), 8 bit

Hnh 3.1: cu trc mt nhn MPLS

Nhn lun xut hin ngay sau mo u lp lin kt d liu (data link) v trc bt k mt mo u lp mng no [3]. nh ca ngn xp nhn xut hin sm nht v y xut hin mun nht trong gi tun theo c ch vo sau ra trc (LIFO - Last In First Out). Gi lp mng theo sau ngay nhn c bit s c t bng 1. Cc trng trong mt nhn c nh ngha nh sau:

1. s (Stack: y ngn xp)

Bit ny c t bng 1 i vi nhn cui ca ngn xp, ngha l nhn y ca ngn xp v 0 i vi tt c cc nhn khc.

2 TTL (Time To Live: Thi gian sng)

Trng di 8 bit ny c s dng m ha gi tr thi gian sng.

3. Experimental Use (S dng khc)

TrTig di 3 bit ny c dnh cho s dng khc, trong mt s cc ti liu trng ny cn c gi l CoS (Class of Service) v n c s dng cho vic phn lp dch v.

4. Label Value (Gi tr nhn)

Trng di 20 bit ny mang gi tr tic ca nhn.

Khi nhn c mt nhn, gi tr nhn nh ca ngn xp c tra. Nu tra thnh cng ngi ta s bit:

a) Chng tip theo m gi phi c chuyn tip

b) Php ton cn c thc hin ti ngn xp trc khi chuyn tip, php ton ny c th l thay th nhn trn cng v y thm mt hoc nhiu nhn na vo ngn xp.

Thng thng, mt gi c gn cho mt FEC da trn (mt phn hoc ton b) a ch ch lp mng ca gi . Tuy nhin nhn khng bao gi l mt m ca a ch .

Nu Ru v Rd l cc b nh tuyn chuyn mch nhn (LSR - Label Switching Router), chng c th tiia thun rng khi Ru truyn mt gi ti Rd, Ru s dn nhn cho gi vi gi tr L, khi v ch khi gi l thnh vin ca mt FEC c th F. iu c ngha, chng c th tha thun v mt s gn kt gia nhn L v FEC F cho s di chuyn ca gi t Ru n Rd. Kt qu ca mt tha thun nh vy, L s tr thnh nhn i (outgoing label) ca Ru v biu din FEC F v L tr thnh nhn n (incoming label) ca Rd v biu din FEC F.

Cn lu rng L khng cn thit phi biu din FEC F i vi cc gi khc vi cc gi c chuyn t Ru ti Rd. L l mt gi tr tiy bin v s gn kt n vi FEC F ch l cc b i vi Ru v Rd.

Khi ni rng cc gi c gi t Ru n Rd, khng h m chi rng gi c bt ngun t Ru hay l ch ca n l Rd. ng ra,


ngi ta ch mun bao hm nhng gi l nhng gi qu giang (transit) qua mt hoc c hai LSR.

i khi, c th s kh khn hoc thm ch l khng th cho mt Rd ni c rng khi mt gi n mang theo nhn L th nhn L c t bi Ru hay l bi mt LSR no khc. y l trng hp c th khi m Rd v Ru khng phi l ln cn trc tip. Trong cc trng hp nh vy Rd cn phi chc chn rng s rng buc nhn n mt FEC l mt-mt (one-to-one). iu c ngha l Rd khng phi tha thun vi Rul rng buc L vo FEC Fl, trong khi li tha thun vi mt LSR Ru2 rng buc L vi mt FEC F2 khc. Tr khi Rd lun lun c th ni rng, khi n nhn mt gi vi nhn n l L, L c a vo gi bi Rul hoc bi Ru2. Trch nhim ca mi LSR l phi m bo c rng n c th xc nh cc nhn n.

a) Phm vi v tnh duy nht ca nhn

Mt LSR Rd cho trc c th rng buc nhn LI vo FEC F v phn b s rng buc ny cho ng ng phn b nhn (label disibution peer) Rul. Rd c th cng s rng buc nhn L2 vi FEC F v phn b s rng buc ny cho ng ng phn b nhn Ru2. Vic LI c trng vi L2 kling c xc nh bi cu trc ny. chi l vn cc b.

Mt LSR Rd cho trc c th rng buc nhn L vi FEC F1 v phn b s rng buc ny cho ng ng phn b nhn R ul. Rd c th cng rng buc nhn L vi FEC F2 v phn b s rng buc ny cho ng ng phn b nhn Ru2.

Khi (v ch khi) Rd c th cho bit, khi n nhn mt gi vi nhn n cng l L, cho d l nhn c t vo bi Rul hay

Chng 3: Chuyn mch nhn a giao thc____________________________51

Ru2, th cu trc ny cng khng i hi l F1 trng vi F2. Trong cc trng hp nh vy, chng ta c th ni rng Rd s dng mt khong nhn (label space) khc cho cc nhn m n phn b cho Rul so vi khong nhn m n phn b cho Ru2.

Thng thng, Rd ch c th cho bit Rul hay Ru2 t nhn c th L vo u ca ngn xp nu nh cc iu kin sau y tha mn:

- Rul v Ru2 ch l cc ng ng phn b nhn m Rd phn b s rng buc ca nhn L ti

- Rul v Ru2 u trc tip kt ni vi Rd thng qua giao din im-im (point-to-point)

Nu cc iu kin ny c tha mn, mt LSR c th s dng cc nhn c phm vi theo giao din, v d ch l giao din duy nht. Chng ta c th ni rng LSR ang s dng khong rin theo giao din. Khi cc iu kin khng tha mn, cc nhn cn phi duy nht i vi LSR gn chng v chng ta c th ni rng LSR s dng khong nhn theo nn.

Nu mt LSR Rd c th c gn vi mt LSR Ru c ti qua hai giao din im ti im th Rd c th phn b cho Ru mt rng buc ca nhn L vi FEC Fl, cng nh l mt rng buc ca nhn L vi FEC F2, F1 khc F2, khi v ch khi mi rng buc ch c gi tr ch i vi cc gi m Ru gi cho Rd qua mt giao din c th. Trong tt c cc trng hp, Rd khng phi phn b cho Ru cc rng buc c cng mt gi tr nhn vi hai FEC khc nhau.

S cm ny c gi k c l cc rng buc c coi l cc mc khc nhau ca h thng phn cp (hierarchy). Trong MPLS,

52____________________ Cng ngh MPLS p dng trong mng MEN (IMAN-E)

khng c mt khi nim v vic c mt khong nhn khc nhau i vi cc mc khc nhau trong th bc, khi phn tch mt nhn th mc ca nhn khng cn thit.

Nh .vy, liu mt LSR c th s dng nhiu khong nhn theo n'i (per platform label space), hoc c th s dng nhiu khong nhn theo giao din (per interface label space) cho cng mt giao din khng. Trong kin trc m t y th iu ny b cm. Tuy nhin, trong cc trng hp nh vy LSR phi c phng tin no , khng c c t bi kin trc, xc nh i vi mi mt nhn n, th nhn thuc v khong nhn no. V d, trong [3] nu rng mt khong nhn khc c s dng cho cc gi om hng (unicast) so vi khong nhn c s dng cho a hng (multicast) v s dng im m (codepoint) ca lp lin kt d liu phn bit gia hai khong nhn.

b) Mc chuyn tip nhn chng tip theo

Mc chuyn tip nhn chng tip theo (Next Hop Label Forwarding Entry) c s dng khi chuyn tip mt gi c dn nhn. N cha cc thng tin sau:

1. Chng tip theo (next hop)

2. Php ton (operation) cn thc hin ti ngn xp nhn, c thl mt trong cc php ton sau:

Thay th nhn ti nh ca ngn xp nhn vi mt nhn mi,

a) y ngn xp nhn ra (pop),

b) Thay th nhn ti nh ca ngn xp nhn vi mt nhn miv sau y mt hoc nhiu nhn mi vo ngn xp nhn.

Chng 3: Chuyn mch nhn a giao thc____________________________5^

N C th cng cha:

c) ng gi d liu lin kt s dng khi truyn gi,

d) Phng thc m ha ngn xp nhn khi truyn gi,

e) Thng tin cn thit khc c th sp xp gi mt cch ng n.

Ch :

Ti mt LSR cho trc chng tip ieo (next hop) ca gi c th l chnh LSR . Trong trng hp ny, LSR cn phi y nhn trn cng ra v sau chuyn gi thu c n chnh n. C th n li phi thc hin mt quyt nh chuyn tip khc da vo kt qu thu c sau khi y ngn xp nhn ra. c th vn mt gi dn nhn hoc l mt gi iun IP. iu th hin rng trong mt s trng hp LSR c th cn phi da vo mo u IP chuyn tip gi.

Nu chng tip theo ca gi li chnh l LSR hin ti th php ton (operation) cn ic hin chnh l y ngn xp nhn ra.

c) Bn sp nhn n

Bn sp nhn n (ILM - In Label Menu) sp mi nhn n vo mt tp u vo chuyn tip nhn chng tip theo (NHLFE - Next Hop Label Forwarding Entry - u vo chuyn tip nhn chng tip theo). N c s dng khi chuyn tip cc gi c dn nhn.

Nu ILM sp mt nhn c th vo mt tp cc NHLFE c cha nhiu horn mt phn t, ng mt phn t ca tp phi c la chn trc khi gi c chuyn tip. Th tc la chn mt

54___________________ Cng ngh MPLS p dng trong mng MEN (MAN-E)

Chng 3: Chuyn mch nhn a giao thc 55

phn t t tp khng c phn tch chi tit trong cun sch ny. Vic ILM sp mt nhn n mt tp c cha nhiu hcm mt NHLFE c th s rt hu ch, nu nh n c yu cu phi thc hin vic cn bng ti gia cc tuyn c chi ph bng nhau.

Hnh 3.2: Mi quan h gia FEC, FTN, LM v NHLFE

d) Bn sp FEC vo NHLFE

Bn sp FEC vo NHLFE (FEC-to-NHLFE Map hay FTN) sp mi FEC vo mt tp cc NHLFE. N c s dng khi chuyn tip cc gi khng c dn nhn v cn c dn nhn trc khi c chuyn tip i.

Nu FTN Sp mt nhn c th vo mt tp ca NHLFE c cha nhiu hn mt phn t, th ng mt phn t phi c chn trc khi gi c chuyn tip. Th tc la chn mt phn t t tp khng c phn tch chi tit trong cun sch ny. Vic FTN sp mt nhn n mt tp c cha nhiu hn mt NHLFE c th s rt hu ch, nu nh n c yu cu phi thc hin vic cn bng ti gia cc tuyn c chi ph bng nhau.

e) Tro nhn

Tro nhn (label swapping) l vic s dng th tc sau y chuyn tip mt gi.

c th chuyn tip mt gi c dn nhn, mt LSR s kim tra nhn u ca ngn xp nhn. N s dng ILM xp nhn ny vo mt NHLFE. S dng thng tin NHLFE, n xc nh c phi chuyn tip gi i u v thc hin mt php ton ngn xp nhn ca gi. Sau , n s m ha ngn xp nhn mi ca gi v chuyn tip kt qu i.

c th chuyn tip mt gi khng dn nhn, mt LSR phn tch mo u lp mng xc nh FEC ca gi. Sau n s dng FTN xp FEC vo mt NHLFE. S dng thng tin NHLFE, n xc nh ni gi c chuyn tip n v thc hin mt php tnh (operation) ngn xp nhn ca gi. Sau n s m ha ngn xp mi vo gi v chuyn tip kt qu i.

Cn lu rng, nu tro nhn c s dng, chng tip theo s lun c ly t u vo chuyn tip nhn chng tip ieo NHLFE, trong mt s trng hp khc so vi chng tip theo nu nh MPLS khng c s dng.

56_____________________Cng ngh MPLS p dng trong mng MEN (MAN-E)

3.2.1.2 Gn v phn b nhn

Trong kin trc MPLS, s quyt nh rng buc mt nhn c th L vo mt FEC c th F c thc hin bi mt LSR v chnh l ng xung LSR i vi s rng buc ny. ng xung LSR sau s thng bo cho ng ln LSR v s rng buc ny. Nh vy nhn c gn ng xung v s rng buc c phn b theo hng ng xung ti ng ln.

Nu mt LSR c thit k sao cho n ch c th tm kim c cc nhn m cc nhn nm trong mt khong ch s, lc n ch n thun cn bo m rng n ch rng buc cc nhn thuc phm vi .

Mt giao thc phn b nhn (label disibution protocol) l mt tp cc th tc (procedure) trong mt LSR thng bo cho cc LSR khc v cc rng buc Iabel/FEC (nhn/lp chuyn tip tng ng) m n thc hin. Hai LSR s dng giao thc phn b nhn trao i thng tin v rng buc label/FEC c gi l ng ng phn b nhn (label distribution peers) i vi cc thng tin rng buc m chng trao i. Nu hai LSR l ng ng phn b nhn, ngi ta cn ni l mt s gn k phn b nhn (label distribution adjacency) gia chng.

Lu : Hai LSR c th l ng ng phn b nhn i vi mt s tp ca rng buc, nhng li khng l g ca nhau i vi mt s cc tp khc ca rng buc.

Giao thc phn b nhn cng hm cha bt k cc tha thun no m trong hai ng ng phn b nhn cn phi dn xp c th hc c kh nng MPLS ln ca nhau.

Kin trc MPLS m t y khng cho rng ch c mt giao thc phn b nhn duy nht. Thc t, nhiu cc giao thc phn b

Chng 3. Chuyn mch nhn a giao thc____________________________ ^


nhn khc nhau c chun ha. Cc giao thc ang tn ti c m rng, cho vic phn b nhn c th c s dng trn chng. V d BGP - Border Gateway Protocol (c m t trong [15]X RSVP-TUNNEL (c m t trong [11]). Cc giao thc mi cng c nh ngha ring cho mc ch phn b nhn nh LDP (c m t trong [10], CR-LDP (c m t trong [16]).

3.2.1.3 Ngn xp nhn

Chng ta ni v mt gi c dn nhn ch mang mt nhn. Chng ta thy rng s hu ch hn khi c mt m hnh tng qut hom trong mt gi c dn nhn mang mt s nhn, c t chc theo m hnh ngn xp L1F0 (Last In First Out). Chng ta gi l mt ngn xp nhn.

Data Link Layer MPLS Network LayerHeader Label stack Header

Nhn cp m (nh ngn xp)

Nhn cp m-1 Nhn cp 2Nhn cp 1

(y ngn xp)

Hnh 3J: Ngn xp nhn c su m cp

Ta c th thy rng MPLS h tr mt h thng phn cp (hierarchy), vic x l mt gi c dn nhn hon ton khng ph thuc vo cp ca h thng phn cp. Vic x l lun lun da vo nhn trn cng (top label) m khng cn quan tm n kh nng c mt s cc nhn tng trn n trong qu kh, hoc c mt s cc nhn khc hin ti ang bn di n.

Mt gi khng c dn nhn c th c xem nh l mt gi c ngn xp nhn rng, coi nh l ngn xp nhn c su 0.

Nu mt gi vi ngn xp nhn c su m, chng ta gi nhn di cng ca ngn l nhn mc 1, i vi nhn xp trn nhn (nu nh tn ti) s c gi l nhn mc 2 v nhn trn cng ca ngn xp s l nhn cp m.

Tnh hu dng ca ngn xp nhn s r rng hn khi chng ta ni v khi nim ca mg hm LSP v h thng phn cp MPLS.

3.2.L4 B nh tuyn chuyn mch nhn

B nh tuyn chuyn mch nhn l mt nt MPLS c kh nng chuyn tip cc gi IP gc. Ngi ta phn bit hai loi LSR l LSR dng ln (upstream LSR) v LSR lung xung (downstream LSR).

Gi s, hai LSR Ru v Rd thng nht rng buc nhn L vo FEC F i vi cc gi c gi t Ru ti Rd. Nh vy i vi rng buc ny, Ru l upstream LSR v Rd l downstream LSR.

ni mt nt l lung ln v nt kia l lung xung i vi mt rng buc cho trc ch c ngha l mt nhn c th biu din mt FEC c th trong cc gi di chuyn t nt lung in ti nt ung xung. iu khng m ch rng cc gi thuc FEC ny

c nh tuyn t nt lung ln ti nt lung xung.

3.2.1.5. ng chuyn mch nhn

ng chuyn mch nhn l mt ng qua mt hoc nhiu LSR ti mt mc ca h thng cp bc m cc gi ca mt FEC c th i qua.

Chng 3: Chuyn mch nhn a giao thc____________________________^

Mt cmg chuyn nhn (LSP) cp m (level m) i vi gi c i p chnh l chui cc router, , vi cc c im sau:

1. Rl, u vo ca LSP (LSP ingress), l mt LSR m y mt nhn vo ngn xp nhn ca p, kt qu l ngn xp nhn c su m;

2. i vi mi i, l

1. Bt u vi mt LSR u vo (LSP ingress) y nhn cp m vo;

2. Tt c cc LSR trung gian thc hin quyt nh chuyn tip bng chuyn mch nhn nhn cp m;

3. Kt thc ti mt LSR u ra (LSP egress) khi mt quyt nh chuyn tip c thc hin bng chuyn mch nhn nhn cp m-k, trong k>0, hoc l quyt nh chuyn tip c thc hin thng thng, khng theo th tc chuyn tip ca MPLS.

H qu ca iu ny l, mi khi mt LSR y mt nhn vo mt gi c dn nhn, n cn phi m bo rng nhn mi ph hp vi mt FEC m LSP u ra ca n l LSR gn nhn m by gi l nhn th hai trong ngn xp.

Gi mt chui cc LSR l LSP cho mt FEC F c th nu n # l mt LSP cp m cho mt gi p c th khi nhn cp m ca p l mt nhn tng ng vi FEC F.

Quan st tp cc nt m c th l cc nt LSP u vo cho FEC F. S c mt LSP cho FEC F m bt u vi mt nt trong tp. Nu mt s thuc cc LSP c cng mt LSP u ra, th mi LSP c th xem tp ca cc LSP nh vy l mt cy, r ca cy l LSP u ra (bi v d liu di chuyn dc theo cy ti r, cy c th c gi l cy a im-im (multipoint-to-point tree). Bi vy chng ta c th ni v cy LSP cho mt FEC F c th.

3.2.1.6 Lp chuyn tip tng ng

Lp chuyn tip tng ng l mt nhm cc gi IP c chuyn tip theo mt phng thc ging nhau, v d chuyn trn cng mt mg i v cch x l khi chuyn tip.

Chng 3: Chuyn mch nhn a giao thc___________________________ ^

3.2.1.7 ng hm v h thng phn cp

i khi mt b nh tuyn ng ln (router Ru) thc hin mt hnh ng lm cho mt gi c th c chuyn n mt b nh tuyn ng xung (router Rd) khc, mc d Ru v Rd khng phi l cc b nh tuyn lin k nhau (consecutive) n mt ng theo tng chng (hop-by-hop) i vi gi v Rd khng phi l ch n cui cng ca gi. V d, iu ny c th thc hin c bng cch ng gi mt gi vo trong mt gi lp mng m a ch mng li chnh l a ch ca Rd. iu s to ra mt ng hm (tunnel) t Ru n Rd. Gi c x l nh vy c gi l gi xuyn hm (tunneled packet).

a) Hm nh tuyn tng chng

Nu mt gi xuyn hm i theo mt ng ieo tmg chng t Ru n Rd, chng ta ni rng l mt hm nh tuyn tng chng (hop-by-hop routed tunnel) ong u pht l Ru v u thu l Rd.

b) Hm nh tuyn hin

Nu mt gi xuyn hm di chuyn t Ru n Rd qua mt ng khc vi ng theo tng chng, ngi ta ni n trong mt ng hm nh tuyn c hin (Explicitly Routed Tunnel) vi im pht l Ru v im thu l Rd. V d, ngi ta c ti gi mt gi qua hm nh tuyn trc hin bng cch ng gi n vo mt gi c ngun c nh tuyn (source routed).

c) ng hm LSP

C th ic hin mt ng hm (tunnel) nh l mt LSP v s dng chuyn mch nhn thay v ng gi lp mng khin gi phi di chuyn qua ng hm. ng hm co th l mt LSP


(Rl,..., Rn), trong RI l im pht ca ng hm v Rn l im thu ca ng hm.

Mt tp cc gi cn c chuyn qua mt ng hm LSP to thnh mt FEC v mi LSR trong Tig hm phi gn mt nhn cho FEC , ngha l phi gn mt nhn cho ng hm. Tiu ch gn mt gi c th cho mt ng hm LSP l vn cc b ti im pht ca ng hm. y mt gi vo ng hm LSP, im pht y mt nhn cho fng hm vo ngn xp nhn v gi gi c dn nhn ti chng tip theo trong ng hm.

u thu ca ng hm khng cn thit phi c kh nng xc nh l gi no c nhn qua ng hm, ngn xp nhn c i c y ra ti LSR p cht trong ng hm.

Mt ng hm LSP nh tuyn theo chng (hop-by-hop routed LSP tunnel) l mt hm c thc thi nh l mt hm LSP nh tuyn theo chng gia im pht v im thu.

Mt ng hm LSP nh tuyn trc hin l mt LSP tunnel m cng ng thi l mt LSP nh tuyn trc hin.

d) H thng cp bc

Xem xt mt LSP (Rl, R2, R3, R4). Gi s rng RI nhn mt gi khng dn nhn p v y mt nhn vo ngn xp nhn ca n khin n i theo ng ny v thc t l mt ng theo tng chng. Tuy nhin, gi s tip l R2 v R3 khng kt ni trc tip vi nhau, nhng l hng xm bi chng l cc im cui ca mt ng hm LSP. Nh vy chui thc t ca cc LSR m p i qua l (R1, R2, R21, R22, R23, R3, R4).

Khi p di chuyn t RI n R2, n s c su cia ngn xp l 1. R2 xc nh l p phi i vo ng hm. R2 trc ht thay th

Chng 3: Chuyn mch nhn a giao thc____________________________ 6 ^

theo ng i trn mng, mi LSR khi nhn c mt gi uc dn nhn s g b nhn n v gn nhn i tng ng vo gi (tro nhn) v chuyn tip gi ti LSR tip theo trong mng.

Tuyn ng m d liu i qua trong mng c nh ngha bng vic truyn cc gi tr nhn, nh l cc nhn c hon chuyn ti mi b nh tuyn LSR. Vic nh x gia cc nhn l khng i ti mi LSR, cho nn ng i c xc nh bi gi tr nhn ban u. ng i nh vy gi l mt ng chuyn mch nhn.

MPLS cng c p dng cho cc cng ngh chuyn mch d liu khng phi l gi. ng i d liu vn c nh ngha bi vic truyn cc nhn chuyn mch v do vn gi l LSP, tuy nhin, cc nhn khng dng gi (v d nhn din bc sng hay khe thi gian trong mng quang) chi c s dng thit lp cc kt ni cho (crossconnect) ti cc LSR. Mi khi kt ni cho c thit lp, d liu c i c nh tuyn m khng cn phi xem xt n, do khng cn phi t gi tr nhn vo mi gi. Ni cch khc, bc sng hay khe thi gian cng chnh l nhn. Ti u vo ca mng MPLS, mi gi c xem xt xc nh LSP no c dng v nhn no c gn cho n. Vic quyt nh ny l vn cc b, nhng cng ging nh vic da vo cc yu t nh a ch ch, cc yu cu v cht lng dch v v trng thi hin ti ca mng. im linh hot ny l mt yu t c bn lm MPLS tr nn hu ch.

#

S khc nhau chnh gia mng MPLS v mng P truyn thng l cc LSR c s dng trong min MPLS. Cc giao thc MPLS c s dng lin lc gia cc LSR. Cc b nh tuyn bin MPLS c thit k thch ng vi cng ngh IP uyn thng ti bin ca vng MPLS.

66____________________ Cng ngh MPLS p ng trong mng MEN (MAN-E)


Do MPLS s dng nhn quyt nh chng k tip, nn b nh tuyn lm vic t hn v hot ng gn ging nh b chuyn mch. V cc nhn th hin cc tuyn ng trong mng nn ta c th iu khin chnh xc qu trnh x l lu lng bng cch dng cc chnh sch gn nhn.

LER: Label Edge Router or Edge LSR; B nh tuyn nhn bin hay LSR bin LSR: Label Switch Router: B nh tuyn chuyn mch nhn LDP: Label Distribution Protocol: Giao thc phn phi nhn

Hnh 3.5: Nguyn tc hot ng ca MPLS

Nguyn tc hot ng ca MPLS c th c m t ngn gn thng qua mt s cc bc sau:

1. Cc giao thc nh tuyn truyn thng OSPF (Open Shorstest Path First: u tin ng ngn nht m), IS-IS (Intermedia System: H thng trung gian - h thng trung gian), v.v... thit lp kh nng kt ni n mng ch

2. Giao thc phn b nhn LDP thit lp bn sp nhn vo mng ch.

3. B nh tuyn bin u vo (Ingress LER) xc nh nhn, t xc nh LSP, gn nhn cho gi v chuyn gi i tip ti giao

theo ng i trn mng, mi LSR khi nhn c mt gi c dn nhn s g b nhn n v gn nhn i tng ng vo gi (tro nhn) v chuyn tip gi ti LSR tip theo trong mng.

Tuyn ng m d liu i qua trong mng c nh ngha bng vic truyn cc gi tr nhn, nh l cc nhn c hon chuyn ti mi b nh tuyn LSR. Vic nh x gia cc nhn l khng i ti mi LSR, cho nn ng i c xc nh bi gi tr nhn ban u. ng i nh vy gi l mt fng chuyn mach nhn.

MPLS cng c p dng cho cc cng ngh chuyn mch d liu khng phi l gi. ng i d liu vn c nh ngha bi vic truyn cc nhn chuyn mch v do vn gi l LSP, tuy nhin, cc nhn khng dng gi (v d nhn din bc sng hay khe thi gian trong mng quang) ch c s dng thit lp cc kt ni cho (crossconnect) ti cc LSR. Mi khi kt ni cho c thit lp, d liu c th c nh tuyn m khng cn phi xem xt n, do khng cn phi t gi tr nhn vo mi gi. Ni cch khc, bc sng hay khe thi gian cng chnh l nhn. Ti u vo ca mng MPLS, mi gi c xem xt xc nh LSP no c dng v nhn no c gn cho n. Vic quyt nh ny l vn cc b, nhng cng ging nh vic da vo cc yu t nh a ch ch, cc yu cu v cht lng dch v v trng thi hin ti ca mng. im linh hot ny l mt yu t c bn lm MPLS tr nn hu ch.

#

S khc nhau chnh gia mng MPLS v mng IP uyn thng l cc LSR c s dng trong min MPLS. Cc giao thc MPLS c s dng lin lc gia cc LSR. Cc b nh tuyn bin MPLS c thit k thch ng vi cng ngh IP truyn ting ti bin ca vng MPLS.

66____________________ Cng ngh MPLS p dng tmng mng MEN (MAN-E)


Do MPLS s dng nhn quyt nh chng k tip, nn b nh tuyn lm vic t hn v hot ng gn ging nh b chuyn mch. V cc nhn th hin cc tuyn ng trong mng nn ta c th iu khin chnh xc qu trnh x l lu lng bng cch dng cc chnh sch gn nhn.

LER: Label Edge Router or Edge LSR: B nh tuyn nhn bin hay LSR bin LSR: Label Switch Router: B nh tuyn chuyn mch nhn LDP: Label Distribution Protoc!: Giao thc phn phi nhn

Hnh 3.5: Nguyn tc hot ng ca MPLS

Nguyn tc hot ng ca MPLS c th c m t ngn gn thng qua mt s cc bc sau:

1. Cc giao thc nh tuyn truyn thng OSPF (Open Shorstest Path First: u tin ng ngn nht m), S-IS (Intermedia System: H thng trung gian - h thng trung gian), v.v... thit lp kh nng kt ni n mng ch

2. Giao thc phn b nhn LDP thit lp bn sp nhn vo mng ch.

3. B nh tuyn bin u vo (Ingress LER) xc nh nhn, t xc nh LSP, gn nhn cho gi v chuyn gi i tip ti giao

68 Cng ngh MPLS p dng trong mng MEM (MAN-E)

din ph hp. Vic xc nh nhn da vo nhiu i lng iu khin u tin ca lu lng, v d a ch ch, lp dch v (CoS: Class of Service).

4. Ti cc nt MPLS k tip, cc LSR bn trong mng l cc LSRtrung gian, chng khng thc hin cc th tc lp 3 m ch dng gi tr nhn ca mi gi xc nh nt tip theo cn chuyn gi, gn nhn mi ri chuyn gi i tip ti nt tcmg ng. Th tc ny thng c thc hin phn cng, ng thi hon i nhn v chuyn tip gi, do cho php cc mng MPLS c xy dng trn cc phn cng chuyn mch nhn c sn nh ATM v Frame Relay; cch chuyn tip gi mc ny ing nhanh hom nhiu so vi vic phi tm kim ton b mo u ca gi quyt nh nt tip theo.

5. B nh tuyn bin u ra (Egress LER) s g b nhn v chuyn gi n ch cui cng. Vic chuyn tip ny s dng nh tuyn lp 3.

LSP

IP#1 |E j f>#1 L-5 E |p#1 L-9 E

LER

IP#1 L-2

LSR LSR LER

IPAddr Nhn i Nhn n Nhn i IPAr Nhn i Nhn n Chng tio theo192.1/16 5 5 9 9 2 2 192.1/16

Lp 2 Giao vn

Dnnhn Tro nhn

Tro nhn BnhnLp 2

Giao vn

Hnh 3.6: V d v hot ng ca MPLS

Vi MPLS, vic gn gi lin quan ti mt FEC c thc hin ch mt ln ti LER u vo, l b nh tuyn u tin x l gi bt u vo mng. FEC c gn cho mi gi c m ha thnh mt nhn. Khi mt gi c chuyn tip ti chng tip theo ca n, nhn cng c gi km theo, do vy thit b tip theo trn tuyn ng i ca gi c th chuyn tip n da trn nhn mang theo thay v phi phn tch cc thng tin trong mo u lp 3.

V gi c gn vo mt FEC ngay khi n vo min MPLS, nn LER dng thc vic gn nhn ny c th dng bt k thng tin no c lin quan ti gi, v d nh bit th t ca IP, ngun/ch hoc loi ng dng, v.v..., ngay c nhng thng tin khng lin quan g ti mo u. V d, cc gi n tr cc cng khc nhau c th c gn vo cc FEC khc nhau. Trong khi kiu chuyn tip truyn thng ch quan tm n nhng thng tin no c ong mo u ca gi. iu ny mang li kh nng phn loi dch v, vi cng mt nhn khng ch nh ngha ch n ca gi m cn nh ngha u tin chuyn tip ca gi .

Ti tt c cc nt MPLS tip theo, nhn MPLS (MPLS label) ch khng phi mo u IP c s dng quyt nh chuyn tip ti nt tip theo. Ti im cui ca min MPLS, LER u ra s g b nhn v chuyn gi IP gc n thit b ca khch hng. T pha ngi dng, vic gn v g b nhn hon ton trong sut v khng cn phi thay i bt k cu hnh no trn cc b nh tuyn ca khch hng.

3.3 NH GI

Trong mt mng phi kt ni, khi mt gi (packet) ca giao thc lp mng di chuyn t mt b nh tuyn ny n mt b nh

Chng 3: Chuyn mch nhn a giao thc____________________________^

tuyn khc, mi mt b nh tuyn thc hin mt quyt (nh c ip chuyn tip gi. iu c ngha l mi b nh tuyn phn tch mo u ca gi v thc hin mt thut ton nh tiuyn lp mng. Mi mt b nh tuyn la chn chng tip theo (niext hop) cho gi mt cch c lp da vo s phn tch mo u ca gi v kt qu ca vic thc hin thut ton nh tuyn. Mo u cha nhiu ng tin hn l thng tin cn thit la chn chng tip theo. La chn chng tip theo c th c xem nh mt s tng hp ca hai chc nng. Chc nng u tin l phn chia tp hp ton b cc gi thnh cc tp hp cc FEC. Chc nng th hai l gn tng FEC cho mt chng tip theo. Nh vy, nu xt tieo phng din ca vic quyt nh chuyn tip th cc gi khc nhau khi c gn cho cng mt FEC s khng th phn bit c. Tt c cc gi thuc v mt FEC c th v di chuyn t mt nt c th s i theo cng mt tuyn, hoc nu nh s dng mt s phng thc nh tuyn a tuyn, th cc gi s i theo mt tp cc tuyn gn kt vi FEC ny.

Trong chuyn tip IP thng thng, mt b nh tuyn c th s thng xem hai gi cng mt FEC nu nh trong bng nh tuyn (routing table) ca b nh tuyn c mt tin t a ch (address prefix) X, m X ph hp nht (longest match) i vi a ch ch ca mi gi. Khi gi i qua mng, mi im ln lt kim tra li gi v gn n cho mt FEC.

Trong MPLS, vic gn mt gi c th cho mt FEC c th ch c thc hin mt ln khi gi i vo mng. Sau khi cc gi c gn, FEC c m bng mt nhn. Khi gi c chuyn tip n im tip theo, nhn c gi cng vd n, c ngha l cc gi c dn nhn trc khi c chuyn tip i. Ti cc im


sau , s khng c vic phn tch mo u lp mng ca gi na. Nhn c s dng l mt ch s (index) trong mt bng, bng nh r chng tip theo v mt nhn mi. Nhn c c thay th bng nhn mi v gi c chuyn tip n im tip theo.

Trong m hnh chuyn tip MPLS, khi mt gi c gn cho mt FEC, vic phn tch mo u cc b nh tuyn tip theo khng cn phi thc hin na, tt c vic chuyn tip c iu khin bi cc nhn. iu mang li rt nhiu li th so vi chuyn tip lp mng thng thng.

- Chuyn tip MPLS c th c thc hin thng qua cc b chuyn mch m c kh nng thc hin vic tra cu v thay th nhn, tuy nhin chng khng c kh nng phn tch mo u ca lp mng hoc khng c kh nng phn tch mo u lp mng vi tc thch hp.

- Bi v mt gi c gn cho mt FEC khi n i vo mng, b nh tuyn u vo c th s dng bt k thng tin no v gi , cho d l nu thng tin ny khng th thu lm c t mo u lp mng. V d, cc gi n cc cng khc nhau c th c gn cho cc FEC khc nhau. Ngc li, chuyn tip thng thng ch c th xem xt thng tin i cng vi gi ong mo u ca gi.

- Mt gi i vo mng mt b nh tuyn c th c th c dn nhn khc so vi gi nu nh i vo mng mt b nh tuyn khc. Kt qu l, quyt nh chuyn tip m ph thuc vo b nh tuyn u vo c th d dng thc hin. iu ny khng th lm c i vi chuyn tip thng thng bi v nh danh ca b nh tuyn u vo ni gi i vo khng i cng vi gi.

Chng 3: Chuyn mch nhn a giao thc___________________________ ^

- S xem xt xc nh mt gi c gn chocnt FEC nh th no c th tr nn rt phc tp, nu nh khg c bt k nh hng no n cc b nh tuyn m chi oti hun chuyn tip cc gi dn nhn.

- i khi l cn thit buc mt gi phi tto mt tuyn c bit c chn ring ti hoc trc thi im gi i vo mng thay cho vic la chn thng qua thu ton nh tuyn ng thng thng khi gi di chuyn qua mi|. iu c th thc hin nh l mt ni dung ca chnh schioc l h k thut liru lng. Trong chuyn tip thngthng, iu i hi gi phi mang theo cng n m ca tyn ng (nh tuyn ngun). Trong MPLS, mt nhn c th lc s dng biu din tuyn ng, nh vy nh danh cuyn khng cn phi c mang theo cng vi gi.

Mt s b nh tuyn phn tch mo u lpnng khng ch la chn chng tip theo, m cn xc nh uyn u tin hay lp dch v. Chng c i c p t cc ngfn|loi b hoc cc quy tc thd gian khc nhau cho cc gi khc hau. MPLS cho php (nhng khng yu cu) quyn u tin hay lp dch v c th suy ra t nhn. Trong trng hp ny, ngd I c th ni rng nhn th hin mt s kt hp ca mt FEC v )t quyn u tin hay lp dch v.

Trn thc t, ngi ta khng so snh MPLS i IP nh l cc thc ti ring bit bi v MPLS hot ng kt hrp vi IP v cc giao thc nh tuyn ni vng khc. MPLS mangi cho cc mng IP k tKut lu lng (TE), kh nng chuyn tilP VPN vi cc khong a chi xp chng (overlay) v h tr taly dn (pseudo wire) lp 2.

72____________________ Cng ngh MPLS p dng trong nng MEN (MAN-E)

Trong khi cc giao thc v cng ngh lp di l khc nhau, c MPLS v ATM u cung cp cc dch v hng kt ni chuyn ti d liu q ua mt mng. Cc kt ni ca c hai loi cng ngh u c bo hiu t cc im cui, trng thi kt ni c duy tr ti mi nt tirn ton tuyn fng v cc k thut ng gi c s dng mang d liu i dc theo kt ni. Ngoi nhng khc bit v cc giao thc bo hiu (RSVP/LDP cho MPLS v PNNI cho ATM) cn c nhng khc bit c bn khc trong hot ng ca hai cng ngh.

Khc bit quan trng nht l cc phng thc vn chuyn v ng gi. MPLS c kh nng lm vic vi cc gi c di khc nhau trong khi ATM ch c kh nng vn chuyn cc t bo c di c nh l 53 byte. Cc gi phi c chia nh, vn chuyn v ghp ni li khi truyn qua mng ATM s dng lp ich ng (adaption layer), ci m s to nn s phc tp v ph ti (overhead) cho dng d liu. Trong khi MPLS ch n thun thm mt nhn vo mo u ca mi gi v truyn n qua mng.

Mt kt ni MPLS l n hng v cho php d liu ch i theo mt hng gia hai im cui. Khi to mt kt ni hai chiu gia hai im cui cn phi thit lp mt cp LSP. Bi v hai LSP c i hi cho kt ni do vy d liu truyn theo chiu xui s s dng mt ng khc vi d liu truyn theo chiu ngc li. Trong khi, cc kt ni im - im ca ATM (VC), l song hTig v cho php d liu truyn theo c hai hng trn cng mt ng. Lu l cc kt ni ATM svc l song hng cn cc kt ni ATM PVC l n hng.

C ATM v MPLS u h tr cc kt ni xuyn hm ni trong kt ni. MPLS s dng chng nhn thc hin iu trong khi

Chng 3: Chuyn mah nhn a giao thc____________________________ 7 ^


ATM li s dng cc ng o (Virtual Path). MPLS c th xp chng nhiu nhn to ra cc ng hm trong ng hm. C ATM VPI v VCI c mang cng nhau trong mo u ca t bo v do vy hn ch ch mt cp cmg hm.

Li th ln nht ca MPLS so vi ATM l n c tiit k ngay t u b tr cho IP. Cc b nh tuyn hin i u h tr c MPLS v IP trn cng mt giao din v nh vy cho php cc nh khai thc mt s mm do trong thit k v vn hnh mng. Do ATM khng hon ton tomg thch vi IP do i hi phi c s thch ng phc tp v lm cho ATM khng thc s thch hp vri cc mng IP ang c u th hn.

3.4 M HNH KT NI VT L MPLS TRN NN METRO

ETHERNET

3.4. S tng qut

Hnh 3.7; M hnh vt l mng MEN

Hnh 3.7 m t mt m hnh vt l tiu biu ca mng MEN (Metropolitan Ethernet Network). Cc b nh tuyn nm li ca MEN c gi l cc b nh tuyn p kt ni vi nhau ng vai

mng li. Cc b nh tuyn pha ngoi ca mng gi l cc b nh tuyn bin NPE (Network Provide Edge: Bin mng cung cp) l cc thit b trung gian kt ni cc v tr ca khch hng vi mng li. Cc NPE ny kt ni ti cc CE ca khch hng thng qua cc b nh tuyn UPE (User Provider Edge: Bin nh cung cp ngi s dng). Thng thng, cc b nh tuyn p c kt ni vi nhau qua cc ng vt l c tc cao nht, thng l Gigabit Ethernet hoc 10 Gigabit Ethernet. Cc b nh tuyn p ny cng c kt ni vi nhau thnh mch vng, c th l vng Ethernet hoc vng RPR ty theo yu cu thc t v cu hnh c la chn. Cc b nh tuyn p ny cng chy chung cc giao thc nh tuyn do nh cung cp quy nh v chy MPLS trn cc giao din kt ni trc tip nu chng ng thi l cc thit b li MPLS. Giao din kt ni t b nh tuyn p ti cc NPE cng thng l cc ng Gigabit Ethernet. Cc NPE cng s dng cc ng Gigabit Ethernet kt ni ti PE. Cc UPE th dng Gigabit Ethernet v Fast Ethernet kt ni xung cc CE ti cc v tr ca khch hng.

3.4.2 Cc thnh phn c bn v chc nng

3.4.2.1 p Router (Provider Router)

p Router (a nh tuyn nh cung cp) l thit b trong mng li ca nh cutg cp dch v (ISP - Internet Service Provider) thc hin chuyn mch nhn MPLS. Mng i ca nh cung cp dch v bao gEi nhiu b nh tuyn p v NPE kt ni cung cp kt ni MPLS >uyn sut. Chc nng chnh ca b nh tuyn P;

- Cung c cc kt ni xng sng tin cy kt ni cc NPE.- Cung c) khng gian iu khin c kh nng m rng cho cc

dch v mng ring o lp 2 (L2 VPN) v mng ring o chuyn mch nhn

- Cho php qun l lu lng.

Cn bng ti qua nhiu ng MPLS.

3.4.2.2. NPE Router

NPE (Network Provider Edge - mng cung cp bin) l thit b nm gia h thng lp 3 trong li v h thng truy xut lp 2. B nh tuyn NPE thc hin cc nhim v sau:

Cng cung cp cc dch v MPLS v IP

nh ngha cc dch v EoMPLS (Eiemet of MPLS).

Lp cung cp dch v VPN lp 3.

Chuyn mch ni b cho cc dch v Eiemet.

Qun l nghn v lu lng.

s.4.2.3. UPE

UPE (User Provider Edge - Bin nh cung cp ngi s dng) l thit b nm gia h ing mng ca nh cung cp dch v v khch hng. UPE thng thcmg l mt iit b lp 2 t khch hng nhng thuc quyn s hu v qun l ca nh cung cp dch v. Chc nng chnh ca UPE l:

Cung cp nhiu UNI (User to Network Interface - s dng giao din mng) kt ni n cc CE (Customer Equipment - thit b khch hng) khch hng.

Xc nh cc dch v Eiemet bng cch s dimg 802. Iq tunneling hay 802. Iq tagging.

iu khin cc chnh sch qun l dch v.

Cho php iu Idiin lu lng v nghn.

76_____________________ Cng ngh MPLS p dng trong mng MEN (MAN-E)

3.4.3 EoMPLS3.4.3.1 To ng hm lp 2

To ng hm lp 2 (L2 Tunneling) cho php nh x cc VLAN n mt ng hm (tunnel) trong min MPLS. Mt dch v L2 khng yu cu khch hng s dng IP, thay vo lu lng khch hng c nh x n 1 v c da trn 802.Iq VLAN. Nh vy khi qua mng li MPLS, lu lng khch hng c ng gi v vn chuyn da trn k thut to ng hm lp 2.3.4.5.2 ng gi EoMPLS

Vic ng gi EoMPLS c da trn Martini hoc Vkompella IETF EoMPLS draft, thc hin kt ni P2P, PE ng gi VLAN v nh tuyn n qua mng li MPLS.

Ngn xp nhn 2 mc (8 bytes) cho mi L2 Frame c mang qua mng MPLS

Nhn Tunnel, outer label, chuyn tip gi tin qua mng

Nhn vc, inner label, kt ni giao din L2 ti gi tin c chuyn tip vc, b nhn dng 32 bit ch lin quan n nhn dng v c cho tng timel, cn gi l LSP tunnel. C 2 loi VC:

v c type 5 dng vi EoMPLS chuyn tip lu lng da n port (ong sut)

v c type 4 dng vi EoMPLS chuyn tip lu lng da frn VLAN (Trong sut VLAN)

Chng 3: Chuyn mch nhn a giao thc____________________________ 77^

12 Header Tunnel Label VC Label Orignal EthFrame

Hnh 3.8: ng gi EoMPLS

3.4.S.3 c im

c im chc nng: Khng tm kim a ch MAC ch lp2, khng hc a ch lp 2 m cc VLAN ring bit hoc gi tin Ethernet c nh x n cc EoMPLS v c v nh ng hm qua mng MPLS.

c im dch v: Cc port vt l chuyn dng cho mi khch hang, c th cu hri nhiu EoMPLS VCs ttn mt port vt l

- Da trn draft Martini, EoMPLS l kt ni P2P- Da n draft Vkompella, EoMPLS l kt ni P2MPMi EoMPLS v c i qua cng LSP. Ti u vo LER xc nh

FEC v vy cc router khc khc khng cn bit v cc v c vn chuyn lp 2. i vi cc router ong mng li thi 12 VPN l hon ton ong sut.

EoMPLS m rng tng cho kt ni L2 dng Ethernet tc ng ti khch hng v nh cung cp dch v. EoMPLS tc ng mnh n mng ng trc trin khai MPLS cung cp nhiu dch v vn chuyn qua MPLS core, ch yi l cc yu cu cho mng Metro nh:

Cc dch v LAN ong sut (Transpareit LAN Service -TLS) hoc cu ni gia cc v tr ca mt doanh nghip

Cc dch v IP cho truy nhp Internet tc cao hoc n cc v t ca doanh nghip dira trn Meo

Vi MPLS, cc nh cung cp dch v CC i eimg ep MPLS L2 VPN cho khch hng. Cc VPN ny c th h cc giao tic ng hm L2 Tunnel bao gm: FR, ATM, HDLC, ppp, Ethernet v 802. Iq VLAN nhng vi Metro y ch tp ung vo 2

Documents

Công Nghệ MPLS Áp Dụng Trong Mạng Men (MAN-E)