doanngoc revised

8/3/2019 DoAnNgoc Revised

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n tt nghip i hc Mc lc

MC LCMC LC .....................................................................................................................iLI NI U ............................................................................................................iii

THUT NG VIT TT ...........................................................................................vDANH MC HNH V ............................................................................................viiiDANH MC BNG BIU ..........................................................................................xCHNG 1: TNG QUAN V CNG NGH CHUYN MCH NHN AGIAO THC MPLS ....................................................................................................1

1.1. Gii thiu chung v chuyn mch nhn a giao thc MPLS ...........................................11.1.1. Khi nim MPLS .......................................................................................................... 11.1.2. L do ra i ................................................................................................................... 1

1.1.3. c im MPLS ........................................................................................................11.2. Cc thnh phn ca MPLS ...............................................................................................3

1.2.1. Cc thit b trong mng ............................................................................................. 3

1.2.2. ng chuyn mch nhn LSP .................................................................................31.2.3. Nhn v cc vn lin quan ....................................................................................4

1.3. Hot ng ca MPLS ....................................................................................................... 71.3.1 Hot ng c bn ....................................................................................................... 71.3.2. nh tuyn .................................................................................................................81.3.3. Cc ch hot ng ..............................................................................................10

1.4. Cc giao thc trong MPLS .............................................................................................121.4.1. Giao thc phn b nhn LDP ..................................................................................12Giao thc phn phi nhn c nhm nghin cu MPLS ca IETF xy dng v banhnh di tn RFC 3036. Phin bn mi nht c cng b nm 2001 a ra nhng nhngha v nguyn tc hot ng ca giao thc LDP. .........................................................12Giao thc phn phi nhn c s dng trong qu trnh gn nhn cho cc gi thng tin.V tr ca giao thc LDP v cc mi lin kt chc nng c bn ca LDP vi cc giaothc khc th hin trn hnh 1.7. Giao thc LDP l giao thc iu khin tch bit ccc LSR s dng trao i v iu phi qu trnh gn nhn/FEC. Giao thc ny l mttp hp cc th tc trao i cc bn tin cho php cc LSR s dng gi tr nhn thucFEC nht nh truyn cc gi thng tin. ......................................................................12Mt kt ni TCP c thit lp gia cc LSR ng cp m bo cc bn tin LDPc truyn mt cch trung thc theo ng th t. Cc bn tin LDP c th xut pht t

bt c mt LSR (iu khin ng chuyn mch nhn LSR c lp) hay t LSR bin lira (iu khin LSP theo lnh) v chuyn t LSR pha trc n LSR pha sau cn k.

Vic trao i cc bn tin LDP c th c khi pht bi s pht hin ca lung s liuc bit, bn tin lp d tr RSVP hay cp nhp thng tin nh tuyn. Khi mt cp LSR trao i bn tin LDP cho mt FEC nht nh th mt ng chuyn mch LSP t uvo n u ra c thit lp sau khi mi LSR ghp nhn u vo vi nhn u ra tngng trong LIB ca n. LDP c th hot ng gia cc LSR kt ni trc tip hay khngtrc tip.............................................................................................................................121.4.2. Giao thc dnh trc ti nguyn RSVP ..................................................................19

1.5 Kt lun chng 1 ...........................................................................................................24CHNG 2: CNG NGH CHUYN MCH NHN A GIAO THCKHNG DY WMPLS ............................................................................................25

2.1. Gii thiu chung v IP di ng ......................................................................................25

2.1.1. Xu hng v thch thc ..........................................................................................252.1.2. nh tuyn trong cc mng IP di ng ................................................................... 26

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n tt nghip i hc Mc lc

2.2. Chuyn mch nhn a giao thc khng dy WMPLS ...................................................292.2.1. Nhu cu pht trin ca WMPLS .............................................................................292.2.2. Cu trc gi tin WMPLS ........................................................................................ 302.2.3. Giao thc s dng trong WMPLS .......................................................................... 312.2.4. La chn ph tn cho WMPLS ...............................................................................34

2.2.5 K thut WMPLS .....................................................................................................372.2.6. Mng MPLS di ng ...............................................................................................392.3. Kt lun chng 2 ..........................................................................................................42

CHNG 3: QUN L DI NG CHO CC MNG WMPLS .........................433.1. Gii thiu ....................................................................................................................... 433.2. Mt s gii php lin quan .............................................................................................443.3. Chuyn mch nhn a giao thc MPLS di ng Micro .................................................46

3.3.1. Th tc ng k trong MPLS di ng Micro ..........................................................463.3.2. H tr chuyn giao trong MPLS di ng Micro .....................................................483.3.3. Cc c ch chuyn giao trong MPLS di ng Micro ..............................................503.3.4. Phn tch v c lng hiu sut ............................................................................55

3.4. Kt lun chng 3 ..........................................................................................................68KT LUN ...............................................................................................................69TI LIU THAM KHO .........................................................................................70

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n tt nghip i hc Li ni u

LI NI UCng vi s pht trin ca t nc, ngnh cng nghip vin thng cng pht

trin khng ngng. S ngi s dng cc dch v mng tng ng k, theo d on

con s ny ang tng theo hm m. Ngy cng c nhiu cc dch v mi v cht lng

dch v cng c yu cu cao hn. Trc tnh hnh ny, cc vn v mng bt u

bc l, cc nh cung cp mng v cc nh cung cp dch v cng c nhiu n lc

nng cp cng nh xy dng h tng mng mi. Nhiu cng ngh mng ra i

nhm p ng tt nht nhu cu ca khch hng v gii quyt cc vn ny sinh.

Trong s chng ta phi k n cng ngh chuyn mch nhn a giao thc MPLS.

Cng ngh chuyn mch nhn a giao thc MPLS l kt qu pht trin ca

nhiu cng ngh chuyn mch IP s dng c ch hon i nhn nh ca ATM tng

tc truyn gi tin m khng cn thay i cc giao thc nh tuyn ca IP. Bn cnh

tin cy, cng ngh MPLS cng h tr qun l mng d dng v n gin hn. Bng

cch gim st lu lng ti cc b nh tuyn chuyn mch nhn (LSR), nghn lu

lng s c pht hin v v tr xy ra nghn lu lng c th c xc nh nhanh

chng.

Hin nay, cng ngh mng khng dy ang c xu hng pht trin rt mnh

m. Do , vic m rng MPLS sang lnh vc khng dy l mt xu hng tt yu.

Chuyn mch nhn a giao thc khng dy WMPLS ang l vn c quan tm

nhiu hin nay. n ca em s trnh by cc vn lin quan n WMPLS trong 3

chng theo b cc sau y:

Chng 1: Tng quan v cng ngh chuyn mch nhn a giao thc MPLS

Chng 2: Cng ngh chuyn mch nhn a giao thc khng dy WMPLS

Chng 3: Qun l di ng cho cc mng WMPLS

Do cng ngh WMPLS cn tng i mi, vic tm hiu cc vn WMPLS

i hi phi c kin thc su rng v lu di. Do vy n khng trnh khi nhng sai

st. Rt mong nhn c s ph bnh, gp ca cc thy c gio v cc bn.

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n tt nghip i hc Li ni u

Xin gi li cm n chn thnh ti TS. L Nht Thng tn tnh hng dn

em trong sut qu trnh lm n.

Xin chn thnh cm n cc thy c gio trong khoa Vin thng gip em

trong thi gian qua v xin gi li cm n ti gia nh, bn b v ngi thn nhng

ngi gip ng vin em trong qu trnh hc tp.

H Ni, ngy 15 thng 10 nm 2006

Sinh vin

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n tt nghip i hc Thut ng vit tt

THUT NG VIT TT

Thut ng Tn Ting Anh Ch gii

AP Access Point im truy nhpARP Address Resolution Protocol Giao thc phn gii a ch

ATM Asynchronous Transfer Mode Truyn dn khng ng b

BGP Border Gateway Protocol Giao thc cng ng bin

BS Base Station Trm gc

CMR Call-to-Mobility Ratio T s tc gi n v tc ding

CoS Class of Service Phn lp dch v

CQR Classing-Queing-Scheduling Phn lp-Hng i v lp lch

CRC Cycle Redundant Check Kim tra d chu trnh

CR Constrained Routing nh tuyn cng bc

CR-LDP Constrained Routing - LDP nh tuyn cng bc - LDP

CTMC Continuous-Time Markov Chain Chui Markov thi gian lin tc

ER Explicit Routing nh tuyn hin

FA Foreign Agent i din ngoi tr

FCC Frequence Control Community Cc qun l tn s

FEC Fowarding Equivalent Class Lp chuyn tip tng ng

FMIP Fast-handoff Mobile IP C ch chuyn giao nhanh cho IPdi ng

FR Frame Relay Chuyn tip khung

HA Home Agent i din thng tr

ICMP Internet-Control-Message

Protocol

Giao thc bn tin iu

khin InternetID Identifier Nhn dng ID

IETF Internet Engineering Task Force Nhm tc v k thut Internet

IGMP Internet GroupManagement Protocol

Giao thc qun l nhmInternet

IP Internet Protocol Giao thc lin mng

LC-ATM Label Controlled-ATM ATM c iu khin nhn

LDP Label Distribution Protocol Giao thc phn b nhnLER Label Edge Router B chuyn mch nhn bin

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LFIB Label Forwarding InformationBase

C s thng tin chuyn tip nhn

LMDS Local Multipoint DistributionSystem H thng phn b a im cc b

LSP Label Switched Path ng dn chuyn mch nhn

LSR Label Switch Router Router chuyn mch nhn

MAC Media Access Controller B iu khin truy nhp

phng tin

MH Mobile Host Host di ng

MIP-RR Mobile IP- Regional Registration C ch cp nht ng k cho IP

di ng

MMDS Multichannel MultipointDistribution Service

Dch v phn b a im -

a knh

MPLS Multiprotocol Label Switching Chuyn mch nhn a giao thc

MSO Mobile Switching Office Trung tm chuyn mch di ng

PDU Protocol Data Unit n v d liu giao thc

PHB Per Hop Behavior B ng x trn tng chng

PNNI Pravite-Network-Network Interface

Giao din mng ring

PPP Point to Point Protocol Giao thc im - im

QoS Quality of Service Cht lng dch v

RA Routing Area Vng nh tuyn

RESV Resevation Bn tin dnh trc

RFC Request For Comment Yu cu kin

RSVP Resource Resevation Protocol Giao thc dnh trc ti nguynSONET Synchronous Optical Network Mng truyn dn quang ng b

TCP Transission Control Protocol Giao thc iu khin truyn dn

TLV Type-Length-Value Kiu m ha di-gi tr

TTL Time To Live Thi gian sng

UDP User Datagram Protocol Giao thc lc d liu

UMTS Universe-Mobile

Telecommunication System

H thng thng tin di ng ton

cuUNI User-Network Interface Giao din ngi s dng-mng

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UNII Unlicensed National InformationInfrastructure

H thng thng tin quc giakhng c cp php

VCI Virtual Circuit Identifier Nhn dng knh o

VPI Virtual Path Identifier Nhn dng ng oVPN Virtual Private Network Mng ring o

WAN Wide Area Network Mng din rng

WATM Wireless-ATM Phng thc truyn ti khngng b khng dy

WMPLS Wireless-MPLS Chuyn mch nhn a giao thckhng dy

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n tt nghip i hc Danh mc hnh v

DANH MC HNH V

Hnh 1. 1: Khun dng tiu nhn MPLS..............................................................4Hnh 1. 2: Cu trc ngn xp nhn............................................................................5

Hnh 1.3: nh tuyn hin...........................................................................................9Hnh 1. 4: Khung MPLS vi PPP/Ethernet l lp lin kt d liu.........................10Hnh 1. 5: Khung MPLS vi ATM l lp lin kt d liu.......................................11Hnh 1. 6: Khung MPLS vi FR l lp lin kt d liu...........................................11Hnh 1.7: V tr giao thc LDP trong b giao thc MPLS......................................13Hnh 1. 8: Tiu LDP..............................................................................................14Hnh 1. 9: M ho TLV.............................................................................................15Hnh 1. 10: Khun dng cc bn tin LDP................................................................15Hnh 1. 11: Th tc pht hin LSR ln cn.............................................................18Hnh 1.12: Cc thc th hot ng RSVP................................................................20

Hnh 1. 13: Cc bn tin PATH v RESV.................................................................20Hnh 1. 14: Nhn phn phi trong bng tin RESV.................................................22Hnh 2.1: Chc nng c bn mng IP di ng.........................................................27Hnh 2.2a: Tiu WMPLS khi khng c trng Control v CRC......................30.....................................................................................................................................31Hnh 2.2b: Tiu WMPLS c trng Control v CRC.......................................31Bng 2.1 v 2.2 di y ch ra ngha cc bit trong tiu WMPLS.................31Hnh 2.3a: M rng cho bn tin yu cu nhn CR-LDP........................................32Hnh 2.3b: M rng cho bn tin lin kt nhn CR-LDP.........................................32Hnh 2.4a: Khun dng ca bn tin PATH.............................................................33

Hnh 2.4b: Khun dng ca bn tin RESV..............................................................33Hnh 2.5: Khun dng ca LABEL_REQUEST.....................................................33

Hnh 2.6a: Thc th SESSION trong ng hm LSP_IPv4.........................34Hnh 2.6b: Thc th SESSION trong ng hm LSP_IPv6........................34

Hnh 2.7: Cu trc mng MMDS vi mt anten bao ph mt vng......................35Hnh 2.8: Cu trc mng LMDS vi nhiu anten bao ph mt vng ...................36(c hn mt ct thu pht)..........................................................................................36Hnh 2.9: Kin trc lp WMPLS.............................................................................36Hnh 2.10: Thit lp ng vi th tc chuyn giao WMPLS...............................38Hnh 2.11: Mng di ng MPLS...............................................................................39Hnh 2.12: Thit lp ng chuyn mch nhn trong mt mng di ng.............40Hnh 3.1: Kin trc ca mt mng truy nhp khng dy MPLS di ng Micro. .46Hnh 3.2: ng k nt di ng trong MPLS Micro di ng...................................47Hnh 3.3: Th tc chuyn giao ngoi LER trong MPLS Micro di ng................50Hnh 3.4a: Hot ng ca FH-Micro trc chuyn giao........................................52Hnh 3.4b: FH-Micro trong qu trnh chuyn giao.................................................52Hnh 3.5: Hot ng ca FC-Micro..........................................................................54Hnh 3.6: Cy nh phn y su ca mt mng truy nhp........................56Hnh 3.8: Chi ph s dng lin kt............................................................................64Hnh 3.9: Chi ph cp nht ng k theo ti mi chuyn giao lp 3....................65Hnh 3.10: nh hng ca Lth n chi ph cp nht ng k trong FC-Micro...66Hnh 3.11: nh hng ca CMR n chi ph cp nht ng k............................66

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n tt nghip i hc Danh mc hnh v

Hnh 3.12: Tng cc gi tin b mt trong mt phin lin lc theo thi gian c trti FA..........................................................................................................................68

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n tt nghip i hc Danh mc bng biu

DANH MC BNG BIUBng 2.1: Gi tr cc bit c trong tiu gi tin WMPLS......................................31Bng 2.2: Cc bit iu khin bo nhn li v iu khin lung trong tiu

WMPLS......................................................................................................................31Bng 3.1: Bng nhn ca LERG sau ng k.........................................................47Bng 3.2: Bng nhn ca mt LER/FA sau khi chuyn giao trong LER..............49Bng 3.3: Bng nhn ca LERG sau khi chuyn giao ngoi LER.........................50Bng 3.4: Thit lp cc tham s................................................................................63Bng 3.5: Thi gian chuyn giao trung bnh ca cc c ch tnh theo ms.............67

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n tt nghip i hc Chng 1: Tng quan v cng ngh ...

CHNG 1: TNG QUAN V CNG NGH CHUYN MCH

NHN A GIAO THC MPLS

1.1. Gii thiu chung v chuyn mch nhn a giao thc MPLS1.1.1. Khi nim MPLS

MPLS l mt gii php chuyn mch IP v c chun ho bi IETF.

MPLS l vit tt ca cm t: chuyn mch nhn a giao thc (Multiprotocol

Label Switching).

Gi l chuyn mch nhn v n s dng c ch hon i nhn lm k

thut chuyn tip lp bn di (lp 2). Gi l a giao thc v MPLS c th h tr nhiu giao thc lp mng

(lp 3), khng ch ring IP.

1.1.2. L do ra i

Vi mc tiu kt hp hai k thut IP v ATM vi nhau, c th l kt hp u

im ca IP (v d c cu nh tuyn) v ca ATM (nh phng thc chuyn mch),

MPLS gm hai chc nng quan trng sau:

Chc nng chuyn tip gi tin: s dng c ch hon i nhn. Bn cht

l: tm chng k tip ca gi tin trong mt bng chuyn tip nhn, sau

thay th gi tr nhn ca gi, ri chuyn ra cng ra ca b nh tuyn.

Chc nng iu khin: gm (a) cc giao thc nh tuyn lp mng c

nhim v phn phi thng tin gia cc LSR v (b) th tc gn nhn

chuyn thng tin nh tuyn thnh bng nh tuyn chuyn mch nhn.

1.1.3. c im MPLS

Tc v tr: Vi mng chuyn mch gi, cc tham s hiu nng c bn

l tc , t l mt gi, tr v bin thin tr ca lu lng ngi s

dng. C ch chuyn tip IP truyn thng l qu chm x l ti lu

lng ln trn mng Internet ton cu hay trong cc lin mng. Ngc

li vi chuyn tip IP, chuyn mch nhn t c tc cao v gi tr

nhn nh c t tiu ca gi v c s dng truy nhp bng

chuyn tip ti b nh tuyn, ngha l nhn c s dng tm kimtrong bng nh tuyn. Vic tm kim ny ch yu cu mt ln truy nhp

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ti bng, khc vi truy nhp bng nh tuyn truyn thng, khi m vic

tm kim c th cn n hng ngn ln truy nhp. Kt qu ca hot ng

ny l lu lng ngi s dng trong gi s c chuyn qua mng

nhanh hn nhiu, ng thi s tch ly tr cng gim c mt cch

ng k so vi trong mng IP truyn thng.

Jitter: L s thay i tr ca lu lng ngi s dng do vic chuyn

gi tin qua nhiu node trong mng chuyn ti ch ca n. Ti tng

node, a ch ch trong gi phi c kim tra v so snh vi danh sch

a ch ch kh dng trong bng nh tuyn ca node, do tr v bin

thin tr ph thuc vo s lng gi v khong thi gian m bng tm

kim phi x l trong khong thi gian xc nh. Kt qu l ti node cui

cng, Jitter l tng cng tt c cc bin thin tr ti mi node gia bngi v bn thu. Vi gi l thoi th do Jitter cuc thoi b mt i tnh lin

tc. Do chuyn mch nhn hiu qu hn, lu lng ngi dng c gi

qua mng nhanh hn v t Jitter hn so vi nh tuyn IP truyn thng.

Kh nng m rng mng: Chuyn mch nhn khng ch cung cp cc

dch v tc cao m n cn c th h tr kh nng m rng tng i

mm do cho mng. Kh nng m rng lin quan n nng lc iu

chnh ca h thng ph hp vi s tng nhanh ca s ngi s dngmng. Chuyn mch nhn cung cp gii php cho s pht trin nhanh

chng v xy dng cc mng ln bng vic cho php mt lng ln cc

a ch IP c kt hp vi mt hay vi nhn. Gii php ny gim ng

k kch c bng a ch v cho php b nh tuyn h tr nhiu ngi s

dng hn.

Tnh n gin: Chuyn mch nhn l giao thc chuyn tip c bn,

chuyn tip gi ch da vo nhn. Do tch bit gia iu khin vchuyn tip nn k thut iu khin d phc tp cng khng nh hng

n hiu qu ca dng lu lng ngi s dng. C th l, sau khi rng

buc nhn c thc hin, cc hot ng chuyn mch nhn chuyn

tip lu lng l n gin, c th c thc hin bng phn mm, bng

mch tch hp chuyn dng hay bng cc b x l c bit.

S dng ti nguyn: Cc mng chuyn mch nhn khng cn nhiu ti

nguyn mng thc hin cc cng c iu khin trong vic thit lpcc ng i chuyn mch nhn cho lu lng ngi s dng.



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iu khin ng i: Chuyn mch nhn cho php cc ng i qua

mt lin mng c iu khin tt hn. N cung cp mt cng c b

tr cc node v lin kt lu lng ph hp hn, thun li hn, cng nh

a ra chnh xc cc phn lp lu lng (da trn cc yu cu v QoS)khc nhau ca dch v.

1.2. Cc thnh phn ca MPLS

1.2.1. Cc thit b trong mng

LSR l mt thit b nh tuyn tc cao trong li ca mt mng MPLS, n

tham gia vo vic thit lp cc ng dn chuyn mch nhn (LSP) bng cch s dng

giao thc bo hiu nhn thch ng v thc hin chuyn mch tc cao lu lng s

liu da trn cc ng dn c thit lp.LERl mt thit b hot ng ti bin ca mng truy nhp v mng li MPLS.

Cc LER h tr a cng c kt ni ti cc mng khc nhau (chng hn FR, ATM v

Ethernet). LER ng vai tr quan trng trong vic ch nh v hu b nhn khi lu

lng vo trong hay i ra khi mng MPLS. Sau , ti li vo n thc hin vic

chuyn tip lu lng vo mng MPLS sau khi thit lp LSP nh cc giao thc bo

hiu nhn v phn b lu lng tr li mng truy nhp ti li ra.

1.2.2. ng chuyn mch nhn LSPLSP: l mt ng i gi tin qua mng chuyn mch nhn trn vn t im

bt u dn nhn n im nhn b loi b khi gi tin. Cc LSP c thit lp trc

khi truyn d liu

ng hm LSP: LSP t u ti cui c gi l ng hm LSP, n l chui

lin tip cc on LSP gia hai node k nhau. Cc c trng ca ng hm LSP,

chng hn nh phn b bng tn, c xc nh bi s tho thun gia cc node,

nhng sau khi tho thun, node li vo (bt u ca LSP) xc nh dng lu lngbng vic chn la nhn ca n. Khi lu lng c gi qua ng hm, cc node

trung gian khng kim tra ni dung ca tiu m ch kim tra nhn. Do , phn lu

lng cn li c xuyn hm qua LSP m khng phi kim tra. Ti cui ng hm

LSP, node li ra loi b nhn v chuyn lu lng IP ti node IP.

C th s dng cc ng hm LSP thc hin cc chnh sch k thut lu

lng lin quan ti vic ti u hiu nng mng. Chng hn, cc ng hm LSP c th

c di chuyn t ng hay th cng ra khi vng mng b li, tc nghn, hay l node

mng b nghn c chai. Ngoi ra, nhiu ng hm LSP song song c th c thit



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lp gia hai node, v lu lng gia hai node c th c chuyn vo trong cc

ng hm ny theo cc chnh sch cc b.

Trong mng MPLS cc LSP c thit lp bng mt trong ba cch l: nh

tuyn tng chng, nh tuyn hin (ER) v nh tuyn cng bc (CR).Mt s khi nim lin quan ti ng chuyn mch nhn l ng ln v

ng xung.

ng ln (Upstream): Hng i dc theo ng dn t ch n ngun. Mt

router ng ln c tnh cht tng i so vi mt router khc, ngha l n gn ngun

hn router c ni n dc theo ng dn chuyn mch nhn.

ng xung (Downstream): Hng i dc theo ng dn t ngun n

ch. Mt router ng xung c tnh cht tng i so vi mt router khc, ngha ln gn ch hn router c ni n dc theo ng dn chuyn mch nhn.

1.2.3. Nhn v cc vn lin quan

1.2.3.1. Nhn, ngn xp nhn, khng gian nhn

Tiu MPLS: MPLS nh ngha mt tiu c di 32 bit, c t ngay

sau tiu lp 2 v trc mt tiu lp 3.

Cu trc tiu MPLS

Hnh 1.1: Khun dng tiu nhn MPLS

ngha cc trng

Nhn: l mt thc th c chiu di c nh (20 bit) dng lm c s cho

vic chuyn tip.



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Exp (Experimental): Cc bit Exp c d tr v mt k thut cho s

dng thc t. Chng hn s dng nhng bit ny ch th QoS - thng

l mt bn sao trc tip ca cc bit ch th u tin trong gi IP. Khi

cc gi MPLS b xp hng, c th s dng cc bit Exp nh cch s dngcc bit ch th u tin IP.

BS (Bottom of stack): Bit ny dng ch th cho nhn cui ngn xp

nhn. Nhn y ca ngn xp nhn c gi tr BS bng 1. Cc nhn

khc c gi tr bit BS bng 0.

TTL (Time To Live): Thng thng cc bit TTL l mt bn sao trc tip

ca cc bit TTL trong tiu gi IP. Chng gim gi tr i mt n v

khi gi i qua mi chng trnh lp vng v hn. TTL cng c thc s dng khi cc nh iu hnh mng mun giu cu hnh mng

nm bn di.

Ngn xp nhn l mt tp cc nhn c th t c ch nh cho gi. Vic x l

cc nhn ny cng tun theo mt th t .

T iu M PL S G i IP

Nhn MPL S(20bit) E XP S T T L

Gi IPN h n#1N h n#2N h n#m

Hnh 1. 2: Cu trc ngn xp nhn

Nu ngn xp nhn ca gi c su m, nhn ti y ca ngn xp c xem

nh l nhn mc 1, nhn trn n l nhn mc 2, v nhn trn cng l nhn mc m.

Mc ch ngn xp nhn: tng cng cc dch v (VPN, CoS), cho m rng

mng (phn cp)

Khng gian nhn: Thut ng khng gian nhn dng ch ra cch thc m

mt nhn c kt hp vi mt LSR. C hai phng php phn nhn gia cc LSR,



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tng ng vi hai dng khng gian nhn, l: khng gian nhn theo tng giao din

v khng gian nhn theo tng node.

Khng gian nhn theo tng giao din: Nhn c kt hp vi mt giao din

no trn mt LSR, v d nh DS3 hoc giao din SONET. Khng gian nhn loiny thng c s dng vi cc mng ATM v FR, trong cc nhn nhn dng

knh o c kt hp vi mt giao din. Nu LSR s dng mt gi tr giao din gi

mt bn ghi cc nhn trn mi giao din th mt gi tr nhn c th c ti dng ti

mi giao din, min l tho mn iu kin mt nhn l duy nht trong khng gian

nhn. Theo mt ngha no , b nhn dng giao din ny tr thnh mt nhn bn

trong ti LSR, khc vi nhn bn ngoi c gi gia cc LSR.

Khng gian nhn theo tng node (theo tt c cc giao din): y, nhn n

c dng chung cho tt c cc giao din trn node. iu ny c ngha l node (host

hay router) phi n nh nhn trn tt c cc giao din.

1.2.3.2. Lin kt nhn vi FEC

Khi nim FEC: FEC l mt nhm cc gi chia s cng yu cu chuyn tip

qua mng. Tt c cc gi trong mt nhm nh vy c cung cp cng cch chn

ng ti ch. Da trn FEC, nhn c tho thun gia cc LSR ln cn t li vo

ti li ra trong mt vng nh tuyn, sau c s dng chuyn tip lu lng

qua mng.

Mi LSR xy dng mt bng xc nh xem mt gi phi c chuyn tip

nh th no. Bng ny c gi l c s thng tin nhn (LIB: Label Information

Base), n l t hp cc lin kt nhn vi FEC.

FEC ph thuc vo mt s yu t, t nht l l a ch IP v c th l c kiu lu

lng trong gi (thoi, d liu, fax...)

L do dng FEC: Th nht, n cho php nhm cc gi vo cc lp. T vic

nhm ny, gi tr FEC trong mt gi c th c dng thit lp u tin cho vic

x l cc gi. Th hai, FEC c th c dng h tr hiu qu hot ng QoS.

Vic kt hp mt FEC vi mt gi c thc hin bng cch s dng mt nhn

nh danh mt FEC c trng. Vi cc lp dch v khc nhau, phi dng cc FEC

khc nhau v cc nhn lin kt khc nhau. Trong mt vi h thng, ch a ch ch IP

mi c s dng nh danh FEC c trng.

Cc phng php lin kt nhn: Hot ng lin kt nhn xy ra ti LSR, trong

mt nhn c kt hp vi mt FEC. Cc phng php lin kt nhn bao gm:



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Lin kt ti ch v lin kt xa: Lin kt ti ch l trng hp khi chnh b nh

tuyn thit lp quan h gia nhn vi mt FEC. B nh tuyn c th thit lp quan h

ny khi n nhn lu lng hay thng tin iu khin t mt node ln cn. Lin kt xa l

hot ng trong mt node ln cn ch nh mt lin kt nhn ti node cc b.

Lin kt ng ln v lin kt ng xung: Lin kt nhn ng xung lin

quan ti phng php trong lin kt nhn c thc hin bi LSR ng xung,

cn i vi lin kt nhn ng ln th c thc hin bi LSR ng ln. Thut ng

ng xung ch hng t ngun n ch, cn ng ln l t ch n ngun.

1.3. Hot ng ca MPLS

1.3.1 Hot ng c bn

C ch chuyn tip ca MPLS c thc hin bng cch tra cu trong mtbng LIB nh trc (l nh x gia gi tr nhn v cc a ch ca bc tip theo).

Mt PHB (Per Hop Behavior) c th c xc nh mi LSR cho mt FEC no .

PHB xc nh mc u tin khi xp hng gi tng ng vi FEC v xc nh chnh

sch hy gi (khi nghn mch).

Cc gi tin c th c cng LER li vo v ra nhng FEC khc nhau. Khi ,

chng c nh nhn khc nhau, c s l theo PHB khc nhau cc LSR, v c

th c vn chuyn qua mng theo cc LSP khc nhau.

V c bn MPLS phn lu lng vo cc loi FEC. Lu lng thuc mt FECs c chuyn qua min MPLS theo mt ng LSP. Tng gi d liu s c xem

nh thuc mt FEC bng cch s dng cc nhn cc b

MPLS thc hin bn bc sau y chuyn gi tin qua mt min MPLS:

Bc 1-Bo hiu

Vi bt k loi lu lng no vo mng MPLS, cc b nh tuyn s xc nh

mt lin kt gia nhn vi lp chuyn tip FEC ca lu lng . Sau khi thc hin

th tc lin kt nhn, mi b nh tuyn s to cc mc trong bng c s thng tin

nhn LIB. Tip , MPLS thit lp mt ng chuyn mch nhn LSP v cc tham s

QoS ca n.

thc hin c bc 1 cn phi c hai giao thc cho php trao i thng tin

gia cc b nh tuyn l:

- Giao thc nh tuyn bn trong mt min trao i thng

tin gia cc b nh tuyn.

Giao thc phn b nhn.

Giao thc nh tuyn cho php xc nh cu trc cng nh tnh trng hot nghin thi ca mng. Da vo cc thng tin , mt LSP c th c gn cho mt FEC.



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Nh vy giao thc nh tuyn phi c kh nng thu thp v s dng thng tin h tr

cc yu cu QoS ca FEC.

Cc nhn c gn cho cc gi ng vi FEC ca n. V gi tr ca nhn ch

mang tnh cc b gia hai b nh tuyn k nhau nn cn phi c c ch m bo tnh

xuyn sut gia cc b nh tuyn trn cng LSP nhm thng nht v vic lin kt gi

tr nhn vi FEC. Nh vy cn c mt giao thc phn b nhn gia cc LSR.

Bc 2- Dn nhn

Khi mt gi n b nh tuyn LER u vo, LER sau khi xc nh cc tham s

QoS s phn gi ny vo mt loi FEC, tng ng vi mt LSP no . Sau , LER

gn cho gi ny mt nhn ph hp v chuyn tip gi d liu vo trong mng. Nu

LSP cha c sn th MPLS phi thit lp mt LSP mi nh bc 1.

Bc 3- Vn chuyn gi d liuSau khi vo trong mng MPLS, ti mi LSR gi d liu s c x l nh

sau:

B nhn cc gi n v gn cho chng mt nhn mi u ra (i nhn).

- Chuyn tip gi d liu n LSR k tip dc theo LSP.

Bc 4- Tch nhn

B nh tuyn bin LER u ra ca min MPLS s ct b nhn, phn tch tiu

IP (hoc x l nhn tip theo trong ngn xp) v chuyn tip gi d liu n

ch.

1.3.2. nh tuyn

Khi nim nh tuyn trong mng MPLS cp n vic chn LSP cho mt

FEC no . Ni chung cc LSP c th c thit lp bng mt trong ba cch: nh

tuyn tng chng (hop-by-hop), nh tuyn hin (ER-Explicit Routing) hoc nh

tuyn rng buc (CR-Constrained Routing). Di y s gii thiu v cc phng

php nh tuyn ny.

1.3.2.1. nh tuyn tng chng

Phng php ny l tng ng vi phng php c s dng hin naytrong cc mng IP truyn thng. Cc giao thc nh tuyn truyn thng chng hn nhOSPF, BGP hay PNNI c s dng thm d a ch IP. Trong phng php nymi LSR la chn mt cch c lp tuyn k tip vi mt FEC cho trc. Mi nodeMPLS xc nh ni dung ca LIB bng vic tham chiu ti bng nh tuyn IP ca n.Vi mi li vo trong bng nh tuyn, mi node s thng bo mt rng buc (cha 1a ch mng v 1 nhn) ti cc node ln cn.



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Phng php nh tuyn ny h tr vi u im ca MPLS nh chuyn mchnhn nhanh, c th dng ngn xp nhn v cc x l khc nhau vi cc FEC trn cngmt tuyn. Tuy nhin, do c hn ch v cc tham s trong giao thc nh tuyn nnnh tuyn tng chng khng h tr tt x l lu lng v cc chnh sch qun tr.

1.3.2.2. nh tuyn hin (ER)

nh tuyn hin tng t vi nh tuyn ngun. Trong phng php ny khngmt node no c cho php la chn chng k tip. Thay vo mt LSR c lachn trc, thng l LSR li vo hay LSR li ra, s xc nh danh sch cc node mER-LSP i qua. ng dn c xc nh c th l khng ti u. Song do cctuyn c th chn trc nn nh tuyn hin cho php n gin ha cng vic qun tr.Dc ng dn cc ti nguyn c th c t trc m bo QoS cho lu lngd liu. iu ny lm cho k thut lu lng thc hin d dng hn, cc dch v c

phn bit c th c cung cp bng cch s dng cc lung da trn cc chnh schhay cc phng php qun l mng.

A

B

C

ER = LSR B LSR D LSR F

F

G

D

E

Hnh 1.3: nh tuyn hin

Hnh 1.3 th hin v d v nh tuyn hin. Cc ng i c xc nh bt u

ti b nh tuyn li vo A, sau ti B v D ri ra ti F. Trong trng hp ny nh

tuyn hin khng cho php ng i qua cc LSR C v E. Cc ng i trong nh

tuyn hin c m ha trong bn tin yu cu nhn v c th c thit lp bng vics dng cc bn tin LDP.

Cng nh cc chc nng khc ca MPLS, chc nng nh tuyn hin c chia

lm hai phn l iu khin v chuyn tip. Thnh phn iu khin chu trch nhim

thit lp trng thi chuyn tip dc theo tuyn hin. Thnh phn chuyn tip s dng

trng thi chuyn tip c thit lp bi thnh phn iu khin cng nh thng tin c

trong cc gi tin truyn chng dc theo tuyn hin.

1.3.2.3. nh tuyn rng buc (CR)



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Mt thut ton nh tuyn c tnh n cc yu cu v lu lng ca nhiu lungv ti nguyn hin c ti cc node trong mng c xem nh nh tuyn c rng buc.Khi s dng nh tuyn ny, mng c th bit c mc s dng mng hin ti, dunglng cn li ca mng v cc dch v c cam kt.

Cc tham s c tnh n trong nh tuyn rng buc c th l c tnh lin kt(bng tn, tr,vv), hop count hay QoS. Cc LSP c thit lp c th l cc CR-LSP,trong cc thng tin rng buc c th l cc chng nh tuyn hin hay cc yu cuQoS. Cc chng nh tuyn hin ch ra ng i no c dng. Cn cc yu cu QoSch ra cc tuyn v cc c ch xp hng hay lp lch no c s dng cho lung lulng.

Khi s dng nh tuyn rng buc, c th mt ng i c cost tng cng lnhn nhng chu ti t hn s c la chn. Tuy nhin, trong khi nh tuyn rng bucgia tng hiu nng mng th n cng b sung thm phc tp trong vic tnh tonnh tuyn v ng dn c la chn phi tho mn cc yu cu QoS ca LSP.

nh tuyn rng buc c th c s dng cng vi MPLS thit lp ccLSP. IETF nh ngha thnh phn CR-LDP lm cho vic thit lp ng i datrn cc rng buc tr nn thun tin hn. Giao thc ny s c trnh by c th trong

phn 1.4.

1.3.3. Cc ch hot ng

MPLS c th hot ng tng ng vi hai ch l:

Ch khung

Ch t bo

1.3.3.1. Ch khung

Ch khung l thut ng c s dng khi thc hin chuyn tip gi vi mttiu c b sung vo gia tiu lp 3 v lp 2 ca gi tin (hnh 1.4)

PPP header ShimHeader Layer 3 Header

MAC header ShimHeader Layer 3 Header

Label

PPP Header(Packet overSONET/SDH)

LAN MAC HeaderTo nhn

Hnh 1. 4: Khung MPLS vi PPP/Ethernet l lp lin kt d liu



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Do nhn MPLS c chn thm vo gi tin nh vy nn b nh tuyn githng tin phi c phng tin g thng bo cho b nh tuyn nhn bit rng giang c gi khng phi l gi IP thun m l gi c nhn (gi MPLS). thc hinchc nng ny, mt s dng giao thc mi c nh ngha trn lp 2.

1.3.3.2. Ch t bo

Ch t bo l thut ng c s dng khi chng ta c mt mng cc chuynmch ATM hay mng FR s dng MPLS trong mt phng iu khin hon ithng tin VCI/VPI thay cho vic s dng bo hiu ATM hay bo hiu FR.

Hnh 1. 5: Khung MPLS vi ATM l lp lin kt d liu

Trong ch t bo, nhn c m ho trong cc trng VPI/VCI hay DLCI(xem hnh 1.5 v hnh 1.6). Sau khi qu trnh trao i thng tin nhn c thc hintrong mt phng iu khin, trong mt phng chuyn tip, b nh tuyn li vo phnchia cc gi vo trong cc t bo ATM, dn nhn cho chng v thc hin truyn. CcATM LSR trung gian x l cc gi nh mt chuyn mch ATM thng thngchngchuyn tip t bo da trn gi tr VPI/VCI v thng tin cng vo. Cui cng, b nhtuyn li ra tng hp cc t bo tr li thnh gi.

Hnh 1. 6: Khung MPLS vi FR l lp lin kt d liu

Ch t bo cn c gi l ATM c iu khin nhn (LC-ATM).

o Th Minh Ngc D04VT2

Ip headerData

DLCIData

Shim header Ip headerData

DLCIData

Gi IP

Tonhn

Cc khungFR

Ip headerData

VPI/VCIData

Shim header Ip headerData

VPI/VCIData

Gi IP

Tonhn

T boATM

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1.4. Cc giao thc trong MPLS

Tham gia vo qu trnh truyn thng tin trong mng MPLS c mt s giao thc

nh LDP, RSVP, CR-LDP, MPLS-BGP. Trong phn ny ch cp n hai giao thc

c bn c s dng trong MPLS l CR-LDP v RSVP.

1.4.1. Giao thc phn b nhn LDP

1.4.1.1. Gii thiu chung

Giao thc phn phi nhn c nhm nghin cu MPLS ca IETF xy dng v

ban hnh di tn RFC 3036. Phin bn mi nht c cng b nm 2001 a ra

nhng nh ngha v nguyn tc hot ng ca giao thc LDP.

Giao thc phn phi nhn c s dng trong qu trnh gn nhn cho cc githng tin. V tr ca giao thc LDP v cc mi lin kt chc nng c bn ca LDP vi

cc giao thc khc th hin trn hnh 1.7. Giao thc LDP l giao thc iu khin tch

bit c cc LSR s dng trao i v iu phi qu trnh gn nhn/FEC. Giao thc

ny l mt tp hp cc th tc trao i cc bn tin cho php cc LSR s dng gi tr

nhn thuc FEC nht nh truyn cc gi thng tin.

Mt kt ni TCP c thit lp gia cc LSR ng cp m bo cc bn tinLDP c truyn mt cch trung thc theo ng th t. Cc bn tin LDP c th xut

pht t bt c mt LSR (iu khin ng chuyn mch nhn LSR c lp) hay t

LSR bin li ra (iu khin LSP theo lnh) v chuyn t LSR pha trc n LSR pha

sau cn k. Vic trao i cc bn tin LDP c th c khi pht bi s pht hin ca

lung s liu c bit, bn tin lp d tr RSVP hay cp nhp thng tin nh tuyn. Khi

mt cp LSR trao i bn tin LDP cho mt FEC nht nh th mt ng chuyn

mch LSP t u vo n u ra c thit lp sau khi mi LSR ghp nhn u vovi nhn u ra tng ng trong LIB ca n. LDP c th hot ng gia cc LSR kt

ni trc tip hay khng trc tip.



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T h n h p h n g i a o t h c M P L S

T h n h p h n g i a o t h c n o n - M P L S

M g r Q u n l L DD s c y B n t i n p hS e s s B n t i n q u A d v t P h t h n hN o t f B n t i n x c

Hnh 1.7: V tr giao thc LDP trong b giao thc MPLS

LDP nh ngha 4 loi bn tin: Bn tin thm d, Bn tin phin, Bn tin pht

hnh, Bn tin thng bo. Bn loi bn tin ny cng ni ln chc nng m n thc hin.

Bn tin thm d (Discovery): Dng thng bo v duy tr s c mt ca

mt LSR trong mng. Theo nh k, LSR gi bn tin Hello qua cng UDP

vi a ch multicast ti tt c cc b nh tuyn trn mng con. Bn tin phin (Session): thit lp, duy tr v xo cc phin gia cc

LSR. Hot ng ny yu cu gi cc bn tin Initialization trn TCP. Sau khi

hot ng ny hon thnh cc LSR tr thnh cc i tng ngang cp LDP.

Bn tin pht hnh (Advertisement): Dng to, thay i v xo cc rng

buc nhn vi cc FEC. Nhng bn tin ny cng c mang trn TCP. Mt

LSR c th yu cu mt lin kt nhn t LSR ln cn bt k khi no n cn.

N cng pht hnh cc lin kt nhn bt c khi no n mun ti mt i

tng ngang cp LDP no s dng lin kt nhn.

Bn tin xc nhn (Notification): Dng cung cp cc thng bo li, thng

tin chn on, v thng tin trng thi. Nhng bn tin ny cng mang trn TCP.

a s cc bn tin LDP chy trn giao thc TCP m bo tin cy ca cc

bn tin (ngoi tr bn tin thm d).

1.4.1.2. Cc bn tin LDP

a) Tiu LDP



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Mi mt bn tin LDP c gi l n v d liu giao thc PDU, c bt u

bng tiu bn tin v sau l cc bn tin LDP nh c trnh by trn. Hnh

1.8 ch ra cc trng chc nng ca tiu LDP v cc trng ny thc hin cc chc

nng sau:

Phin bn: Ch s phin bn ca giao thc, phin bn ang s dng hin ti

l phin bn 1.

di PDU: Tng di ca PDU tnh theo byte, ngoi tr trng phin

bn v trng di.

Nhn dng LDP: Nhn dng khng gian nhn ca LSR gi bn tin ny.

Bn byte u tin cha a ch IP c gn cho LSR nhn dng b nh

tuyn. Hai byte cui nhn dng khng gian nhn bn trong LSR.Vi LSR ckhng gian nhn ln, trng chc nng ny t v gi tr 0.

.

0 1 5 3 1

P h i n b n d i P D U

N h n d n g L D P

N h n d n g L D P

Hnh 1. 8: Tiu LDP

b) M ha TLV

LDP s dng lc m ho kiu- di-gi tr TLV (Type-Length-Value)

m ho cc thng tin mang trong bn tin LDP. Nh ch ra trn hnh 1.9, TVL c m

ho thnh mt trng 2 byte trong s dng 14 bt c trng cho kiu, v 2 bit

(U, F) cho trng hp LSR khng nhn ra c kiu, 2 byte tip theo l trng di

v trng gi tr c di thay i.

Bit U (Unknown TLV): TLV khng bit;

Bit F (Forward Unknown TLV): chuyn tip TLV khng bit;

Trng kiu: qui nh cc trng m gi tr c dch;

Trng di: xc nh di ca trng gi tr;

Trng gi tr: c th cha cc TLV khc.



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0 1 5 3 1

K i u d i

G i t r

U F

Hnh 1. 9: M ho TLV

Da trn bn tin nhn c, khi bit U c gi tr 0, LSR s gi thng bo ngc

li ti ni pht v ton b bn tin s c b qua. Nu U c gi tr 1 th mc d khng

nhn ra kiu, LSR khng cn gi thng bo phn hi li pha pht v vn x l phn

cn li ca bn tin nh th l bn tin cha bit kiu ny khng tn ti.

Bit F ch c s dng khi bit U = 1 v bn tin LDP cha bn tin cha bit kiu

ny c truyn i. Nu bt F bng 0 th bn tin cha bit kiu s khng chuyn i

cng bn tin LDP cha n v nu bit F=1 th bn tin cha bit kiu s chuyn i cng

bn tin LDP cha n.

c) Khun dng chung

Khun dng bn tin LDP

Hnh 1. 10: Khun dng cc bn tin LDP

Bit U: bit bn tin cha bit, lin quan n bn tin cha bit kiu. Nu U=0th mt thng bo s c phn hi li cho pha gi, cn nu U=1 th bn tin

khng th c thng dch bi pha nhn, lc bn tin b b qua m khng

c phn hi.

Kiu bn tin: Ch ra kiu bn tin l g.

di bn tin: Ch ra chiu di ca cc phn nhn dng bn tin, cc thng

s bt buc v cc thng s tu chn.

Nhn dng bn tin: l mt s nhn dng duy nht bn tin. Trng ny cth c s dng kt hp cc bn tin Thng bo vi mt bn tin khc.


ID bn tin

Thng s bt buc

Thng s tu chn

U Kiu bn tin di bn tin

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Thng s bt buc,v Thng s tu chn tu thuc vo tng bn tin LDP.

V mt nguyn l, mi th xut hin trong bn tin LDP c th c m ho

theo TLV, nhng cc c t LDP khng phi lun lun s dng lc TLV. N

khng c s dng khi n khng cn thit v s s dng n khi s gy lng phkhng gian. Chng hn khng cn thit phi s dng khun dng TLV nu chiu di

ca gi tr l c nh hay kiu ca gi tr c bit v khng phi ch nh mt nhn

dng kiu.

d) Mt s bn tin LDP

Bn tin Hello

Bn tin Hello (Cho hi) c trao i gia hai LSR ngang cp trong mt phin

pht hin LDP. Mt LSR lu gi bn ghi ca cc bn tin Hello c gi t cc LSRngang cp khc. Cc cp LSR thng lng thi gian lu gi dng cho bn tin Hello.

Mi cp ngh mt thi gian lu gi v thi gian lu gi c dng l s l gi tr

nh nht c ngh trong cc bn tin.

Bn tin Initialization (Khi to)

Cc bn tin thuc loi ny c gi khi bt u mt phin LDP gia hai LSR

trao i cc tham s, cc i lng tu chn cho phin. Cc tham s ny bao gm:

Ch phn b nhn

Cc gi tr nh thi

Phm vi cc nhn s dng trong knh gia hai LSR .

Bn tin Label Mapping v Label Withdraw

Cc bn tin Label Mapping (Lin kt nhn) c s dng qung b lin kt

gia FEC (tin t i ch) v nhn. Bn tin Label Withdraw (Thu hi nhn) thc hin

qu trnh ngc li: n c s dng xo b lin kt va thc hin. Bn tin nyc s dng khi c s thay i trong bng nh tuyn (thay i tin t a ch) hay

thay i trong cu hnh LSR lm tm dng vic chuyn nhn cc gi trong FEC .

Bn tin Label Request (Yu cu nhn)

Trong ch hot ng gn nhn theo yu cu, LSR ng ln s yu cu

LSR ng xung gn v qung b nhn bng cch s dng bn tin Label Request.

Bn tin Label Request Abord



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Nu bn tin Label Request cn phi hy b trc khi c chp nhn (do nt k

tip trong FEC yu cu thay i) th LSR yu cu s hy b yu cu vi bn tin

Label Request Abord (Hy b yu cu nhn).

Bn tin Label Release:Bn tin ny c LSR s dng khi n nhn c lin kt nhn khng cn cn

thit na. iu ny thng xy ra khi LSR nhn thy nt tip theo cho FEC khng

phi l LSR qung b lin kt nhn tng ng.

1.4.1.3. Th tc thm d LSR ln cn

Th tc pht hin LSR ln cn ca LDP chy trn UDP thc hin nh sau

(hnh 1.11):

Mt LSR nh k gi bn tin Hello ti cc cng UDP bit trong tt c cc

b nh tuyn trong mng con ca nhm multicast.

Tt c cc LSR tip nhn bn tin Hello ny trn cng UDP. Nh vy, ti mt

thi im no LSR s bit c tt c cc LSR khc m n c kt ni trc

tip.

Khi LSR nhn bit c a ch ca LSR khc bng c ch ny th n s

thit lp kt ni TCP n LSR .

Khi phin LDP c thit lp gia hai LSR. Phin LDP l phin hai chiu c

ngha l mi LSR hai u kt ni u c th yu cu v gi rng buc nhn.

Trong trng hp cc LSR khng kt ni trc tip trong mt mng con, ngi

ta s dng mt c ch b sung nh sau:

LSR nh k gi bn tin Hello trn UDP n a ch IP c khai bo khi lp

cu hnh. Pha nhn bn tin ny c th tr li li bng bn tin HELLO khc truyn mt

chiu ngc li n LSR gi v vic thit lp cc phin LDP c thc hin nh trn.Thng thng trng hp ny hay c p dng khi gia hai LSR c mt

ng LSP cho iu khin lu lng v n yu cu phi gi cc gi c nhn qua

ng LSP .



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UDP Hello

UDP Hello

TCP Open

Initialization

Label Request

Label Mapping

IP

Hnh 1. 11: Th tc pht hin LSR ln cn

1.4.1.4. Giao thc CR-LDP

Giao thc CR-LDP c s dng iu khin cng bc LDP. Giao thc ny

l phn m rng ca LDP cho qu trnh nh tuyn cng bc ca LSP. Cng ging

nh LDP, n s dng cc phin TCP gia cc LSR ng cp gi cc bn tin phn

phi nhn.

Mt h thng h tr nh tuyn cng bc cn m bo cc yu cu sau: th

nht, nt ngun cn bit cu hnh mng. Th hai, ngun cn bit cc thuc tnh ca

lin kt trong mng. Th ba, h thng c h tr nh tuyn hin. Th t, ging nh

tuyn c thit lp gia nt ngun v nt ch, s dnh ring ti nguyn c th xy ra

v trng thi thuc tnh ca ng lin kt phi c cp nht lin tc. Nh vy, h

tr nh tuyn cng bc ngoi mt s iu kin khng ch v bng thng, khong

cch qun l cn cn c kh nng nh tuyn hin (hoc nh tuyn ngun).

xc nhn thng tin ti nguyn dnh ring theo LSR, CR-LDP to thm i

tng mi tham s iu khin lu lng gm 6 tham s: Tc s liu nh, kch

thc s liu bng pht, tc s liu ngu nhin, kch thc ln qu hn, tn s v

trng s. Hai tham s u nh ngha v s lng ln nht ca lu lng trong LSP.

Hai tham s sau nh ngha v s lng lu lng. Tn s ch ra khong thi gian LSP

t c cung cp rng bng ca LSR v trng s c dng xc nh rng

bng trn CDR, phn chia theo LSP.



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C hai l do s dng MPLS. Trc ht MPLS cho php tch cc thng tin s

dng chuyn tip (nhn) t cc thng tin c trong mo u ca gi IP. Th hai l

vic chuyn i gia FEC v LSP ch c gii hn trong LSR ti mt u ca LSP.

Ni mt cch khc, vic quyt nh gi IP no s c nh tuyn hin ra sao honton do LSR tnh ton xc nh tuyn. V nh trnh by trn, y chnh l chc

nng cn thit h tr nh tuyn cng bc.

1.4.2. Giao thc dnh trc ti nguyn RSVP

1.4.2.1. Gii thiu chung

Giao thc dnh trc ti nguyn RSVP c m t chi tit trong cc RFC

2205/3209. Nh tn gi ca n, giao thc dnh trc ti nguyn (RSVP) dng dnhtrc cc ti nguyn cho mt phin lm vic (dng lu lng) trong mng Internet.

Kha cnh ny ca Internet l mt iu kh c bit v hi khc nhng g chng ta

c bit Internet cung cp cc dch v n lc cao nht, khng lin quan n nhng

yu cu xc nh trc cho ng dng ngi dng.

Cn nh rng IP l giao thc phi kt ni, n khng thit lp trc ng i

cho cc dng lu lng, trong khi RSVP thit lp trc nhng ng i ny v

m bo cung cp bng thng cho chng. RSVP khng cung cp cc hot ng

nh tuyn m s dng IPv4 hay IPv6 nh l c ch truyn ti ging nh cch m

cc giao thc bn tin iu khin Internet ICMP v giao thc bn tin nhm Internet

IGMP hot ng

RSVP yu cu pha thu a ra tham s QoS cho dng lu lng. Cc ng dng

pha thu phi xc nh bn ghi QoS v chuyn ti RSVP. Sau khi phn tch cc yu

cu ny, RSVP gi cc yu cu ti tt c cc nt tham gia trong vic vn chuyn dnglu lng. Nh th hin trong hnh 1.12, cht lng dch v ca mt dng lu lng

no c thc hin bng cc k thut:Phn loi gi, iu khin chp nhn kt ni,

lp lch gi v iu khin chnh sch.



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Hnh 1.12: Cc thc th hot ng RSVPB phn loi xc nh lp QoS (v c th l ng i) cho mi gi, da trn s

kim tra tiu lp vn chuyn v lp IP. Vi mi giao din u ra, b lp lch gi

hay mt c ch ph thuc lp lin kt d liu no khc s m bo t c gi tr

QoS nh cam kt. B lp lch gi thc hin cc m hnh dch v QoS c nh

ngha bi nhm lm vic dch v tch hp IntServ.

Nh ch ra trong hnh 1.12, qu trnh RSVP chuyn cc yu cu QoS ti hai

khi quyt nh ti ch liu khin chp nhn viu khin chnh sch. iu khinchp nhn xc nh xem nt c ti nguyn cung cp cho dng lu lng vi mc

QoS c yu cu hay khng. iu khin chnh sch xc nh xem mt dng lu

lng c c cho php theo cc quy tc qun l hay khng, chng hn nh a ch IP

hay nhn dng giao thc no c hay khng c php dnh trc bng thng...

Trong qu trnh thit lp vic dnh trc ti nguyn, nu xy ra trng hp mt

trong hai hot ng iu khin chp nhn v iu khin chnh sch khng thnh cng

th s dnh trc ti nguyn s b hy b v qu trnh RSVP tr li bn tin thng bo

li ti pha nhn tng ng.

1.4.2.2 Cc bn tin chnh ca RSVP

RSVP s dng hai bn tin c bn l bn tin PATH v bn tin RESV.

Hnh 1. 13: Cc bn tin PATH v RESV



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Cc hot ng RSVP c bt u bng bn tin PATH. N c s dng bi

pha gi thit lp ng i cho phin (dng lu lng). Mt phin RSVP c xc

nh bi a ch IP ch (DestAddress), nhn dng giao thc IP (ProtocolIP) v nhn

dng cng ch.

Cc bn tin RESV c gi bi pha nhn v chng cho php pha gi cng

nh cc nt trung gian bit cc yu cu ca pha nhn.

ng i ca bn tin RESV ging vi ng i ca bn tin PATH nhng theo

chiu ngc li.

Cc trng bn trong bn tin RSVP c gi l i tng. T khi ra i, nhiu

i tng lin tc c b sung. Chng ta s cp n nhng i tng trong cc

bn tin RSVP lin quan n MPLS trong phn tip theo.1.4.2.3. MPLS h tr RSVP

Mc tiu u tin ca vic h tr RSVP vo MPLS l cho php cc LSR da

vo vic phn loi gi tin theo nhn ch khng phi theo mo u IP nhn bit cc

gi tin thuc cc lung ca cng dnh ring. Ni cch khc, cn phi to v kt hp

cc lung v cc nhn cho cc lung c cc cng dnh ring RSVP. Chng ta c th

xem mt tp hp cc gi tin to ra bi cng dnh ring RSVP nh l mt trng hp

ring khc ca FEC.

iu ny tr nn kh d dng kt hp cc nhn vi cc lung dnh ring

trong RSVP, t nht l vi unicast (n hng). Chng ta nh ngha mt i tng

RSVP mi l i tng LABEL c mang trong bn tin RSVP RESV. Khi mt LSR

mun gi bn tin RESV cho mt lung RSVP mi, LSR cp pht mt nhn t trong

tp nhn ri, ti mt li vo trong LFIB ca n vi nhn li vo c t cho nhn cp

pht, v gi i bn tin RESV c cha nhn ny. Ch l cc bn tin RESV truyn t

b nhn ti b gi l di dng cp pht nhn xui.

Khi nhn c bn tin RESV cha i tng LABEL, mt LSR thit lp LFIB

ca n vi nhn ny l nhn li ra. Sau n cp pht mt nhn s dng nh l

nhn li vo v chn n vo bn tin RESV trc khi gi n i. R rng l, khi cc bn

tin RESV truyn n LSR ngc th LSP c thit lp dc theo tuyn ng. Cng

ch l, khi cc nhn c cung cp trong cc bn tin RESV, mi LSR c th d dng

kt hp cc ti nguyn QoS ph hp vi LSP. Hnh 1.14 minh ho qu trnh trao i

ny. Trong trng hp ny chng ta gi s cc my ch khng tham d vo vic phn

phi nhn. LSR-R3 cp pht nhn L cho cng dnh ring ny v thng bo n viLSR-R2. LSR-R2 cp pht nhn M cng cho cng dnh ring ny v thng bo n ti



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LSR-R1. By gi c mt LSP cho lung dnh ring t LSR-R1 ti LSR-R3. Khi

cc gi tin tng ng vi cng dnh ring ny (v d gi tin gi t H1 ti H2 vi s

cng ngun, ch thch hp v s giao thc giao vn thch hp) ti R1, R1 phn bit

n bng cc thng tin mo u IP v lp truyn ti to ra QoS thch hp cho cng

dnh ring v d nh c im v hng i cc gi tin trong hng i li ra. Ni cch

khc, n thc hin cc chc nng ca mt b nh tuyn tch hp dch v s dng

RSVP. Hn na, LSR-R1 a mo u nhn vo cc gi tin v chn gi tr nhn li ra

l M trc khi gi chuyn tip gi tin ti LSR-R2.

Khi LSR-R2 nhn gi tin mang nhn M, n tm kim nhn trong LFIB v

tm tt c cc trng thi lin quan n QoS xem kim sot lung, xp hng i gi

tin, v.v.. nh th no. iu ny tt nhin khng cn kim tra tiu lp IP hay lp

truyn ti. Sau R2 thay th nhn trn gi tin vi mt nhn li ra t LFIB ca n(mang gi tr L) v gi gi tin i.

L S R - R 3L S R - R 1 L S R - R 2P A T H

R E S VM y g i M y nN h n = M N

H 1 H 2

Hnh 1. 14: Nhn phn phi trong bng tin RESV

Lu rng, do vic to ra nhn kt hp c iu khin bi cc bn tin RSVP

v vy vic kt hp c iu khin nh trong cc mi trng khc ca MPLS. y

cng l mt v d chng t vic mang thng tin kt hp nhn trn mt giao thc c sn

khng cn mt giao thc ring nh LDP.

Mt kt qu quan trng ca vic thit lp mt LSP cho mt lung vi cng

dnh ring RSVP l ch c b nh tuyn u tin trong LSP m trong v d trn l

LSR-R1 lin quan ti vic xem xt cc gi tin thuc lung dnh ring no. iu ny

cho php RSVP c p dng trong mi trng MPLS theo cch m n khng th

thc hin c trong mng IP truyn thng. Theo qui c, cc cng dnh ring RSVP

c th ch to cho nhng lung ng dng ring l, tc l nhng lung c xc nh

nh cc trng mo u. Tuy nhin, c th t cu hnh LSR-R1 la chn cc gi

tin da trn mt s cc tiu chun. V d, LSR-R1 c th ly tt c cc gi tin c cng

mt tin t ng vi mt ch v y chng vo LSP. V vy thay v c mt LSP cho

mi lung ng dng ring, mt LSP c th cung cp QoS cho nhiu lung lu lng.Mt ng dng ca kh nng ny l c th cung cp ng ng vi bng thng m



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bo t mt im ny ti mt im khc. Kh nng ny cng hu ch cho mc ch

iu khin lu lng, y mt lu lng ln cn c gi dc theo cc LSP vi

bng thng ti lu lng.

h tr mt s cch s dng RSVP m rng, MPLS nh ngha mt itng RSVP mi c th mang trong bn tin PATH l: i tng LABEL_REQUEST.

i tng ny thc hin hai chc nng. Th nht, n c s dng thng bo cho

mt LSR ti pha cui ca LSP gi RESV tr v thit lp LSP. iu ny hu ch

cho vic thit lp cc LSP Site-to-Site. Th hai, khi LSP c thit lp cho mt tp

cc gi tin, khng ch l mt lung ng dng ring, i tng cha mt trng xc

nh giao thc lp cao hn s s dng LSP. Trng ny c s dng tng t nh

m phn knh xc nh giao thc lp cao hn (IPv4, IPX, v.v..), v vy s khng c

trng phn knh trong mo u MPLS na. Do vy, mt LSP c th cn c thitlp cho mi giao thc lp cao hn nhng y khng gii hn nhng giao thc no

c h tr. c bit, khng yu cu cc gi tin mang trong LSP c thit lp s

dng RSVP phi l cc gi tin IP.

1.4.2.4. RSVP v kh nng m rng

Mt trong nhng iu chc chn v RSVP l n c th chu tn tht v kh

nng m rng mt mc no y. Trong thc t, c tnh ny khng chnh xc hon

ton. RSVP khi u c thit k h tr d tr ti nguyn cho cc lung ng dngring v y l nhim v vi nhng thch thc v kh nng m rng vn c.

Ni chung thut ng ny c s dng ch gii hn s dng ti nguyn tng

nhanh nh th no khi mng tng trng. V d, trong mng IP quy m ln nh mng

xng sng, chng ta c th quan tm n vic liu mt bng nh tuyn s chim b

nh ca b nh tuyn ln n mc no, kh nng b x l v bng thng lin kt ra

sao. V th, bng nh tuyn tng chm hn nhiu so vi s ngi s dng kt ni vo

mng.D tr ti nguyn cho cc lung ng dng ring r rng l nh hng xu n

kh nng m rng. Chng ta c th cho rng mi ngi s dng s d tr ti nguyn

ti mt vi tc trung bnh, v th s ti nguyn d tr c to ra trn mng quy m

ln c kh nng tng nhanh bng s ngi s dng ca mng. iu ny s dn n chi

ph ln nu mi b nh tuyn phi lu tr trng thi v tin trnh mt vi bn tin cho

cho lung ng dng ring.

Ni tm li, s chnh xc hn nu ni rng mc d tr ti nguyn cho cc lung

ng dng l km hn so vi RSVP. S khc nhau ny c bit quan trng khi chng ta



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xem xt rng RSVP khng nhng cn thit cho vic d tr ti nguyn cho cc lung

ng dng ring m cn cn d tr ti nguyn cho lu lng tng hp.

1.5 Kt lun chng 1

Chng 1 a ra cc vn c bn ca chuyn mch nhn a giao thcMPLS. l: cc khi nim c bn v cc thnh phn ca MPLS, hot ng ca

MPLS v cc giao thc c s dng trong mng MPLS. y s ny l c s tm

hiu cc vn trong mng MPLS khng dy WMPLS m em s trnh by trong cc

chng tip theo.



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n tt nghip i hc Chng 2: Cng ngh chuynmch...

CHNG 2: CNG NGH CHUYN MCH NHN A GIAO

THC KHNG DY WMPLS

2.1. Gii thiu chung v IP di ng2.1.1. Xu hng v thch thc

Cc mng da trn gi ang c hon thin tr thnh mt phng thc

mc nh mang thng tin trong th gii mng c nh. Lu lng thoi v video

cng c chuyn tr bi gi tin trn cc mng. Trong khi nhng u im v tim

nng kinh doanh ca gi tin trn cc mng di ng l rt ln th tnh phc tp trong

vic thc thi cng khng phi l nh. Cc mng IP c mong i l c th h tr

nhiu hn mt chc nng nh tuyn nhng vn phi m bo c cht lng dchv nh sn.

Cc b iu khin mng khng dy di ng phi i mt vi cc yu cu ca th

trng ngy cng nghim ngt v tin cy, cht lng v chi ph dch v, bn cnh

yu cu bng thng ngy cng tng. Sc p v mt cnh tranh to ra nhu cu pht

trin cc dch v mi v to ra s khc bit trong cc th trng c tnh cnh tranh cao.

Cng ngh truy nhp a dch v cung cp cho b iu khin khng dy mt gii php

nng cp loi b chi ph cao, loi b cc chu k lp lch di hn cng nh vic thay

th cc thit b truy nhp hin c.Chun khng dy 3G v cc din n c nh hng n chun hin ang

nghin cu xem bng cch no h c th kt hp cht ch cng ngh IP vo mng

khng dy. L do h lm vic ny l ti s dng cc thit b mng hin c ca

IETF, gim chi ph s hu bng cch gim chi ph hot ng ca mng, ... Tt c

nhng iu ny b sung thm u im cho cc giao thc IP c th nh tuyn t

ng, thit lp li cu hnh...

Phn d liu gi ca UMTS c da trn cc giao thc TCP/IP. Node d liu

gi ca UMTS l mt b nh tuyn IP phm vi rng. Node ny cng c chc nng h

tr cc ngi dng khng dy di ng. L mng th h 3, UMTS h tr cc ng dng

a phng tin v lu lng thi gian thc.

Trong nhng nm va qua, Internet pht trin thnh mt mng rng khp v

c kh nng pht trin cc ng dng mi khc nhau trong kinh doanh v trong cc th

trng ngi tiu dng. Cc ng dng ny dn n yu cu m bo bng thng v

tnh trng tng bng thng trn mng ng trc. Bn cnh cc dch v d liu truyn

thng hin c cung cp trn Internet, th nhng dch v a phng tin v thoi miang ngy cng pht trin. Internet xut hin ging nh mt la chn v mng h



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tr cc dch v hi t ny. Tuy nhin, yu cu v bng thng v tc ca cc dch v

v ng dng mi ny lm cn kit ngun ti nguyn ca h tng Internet hin nay.

IP l kt ni khng c hng v c nh tuyn ti lp 3. Hin nay, khng c

m bo no v QoS trong mng IP. Vic h tr QoS s rt phc tp v IP l kt ni

khng hng, tr khi c mt iu gi s rng bng thng kh dng l khng hn ch

ti mi phn mng. t c iu ny cn phi c cc bin php iu khin lung

lu lng. Lp dch v CoS v cht lng dch v QoS cn phi c nh a ch

h tr nhng yu cu thng xuyn thay i ca cc ngi s dng mng di ng.

MPLS vi nhng u im vn c ca n ang chng t l mt gii php ti u

gii quyt cc vn ni trn. Cc phn tip theo ca chng s ch r nhn nh

ny.

2.1.2. nh tuyn trong cc mng IP di ngIP di ng l mt giao thc lin mng c thit k h tr host di ng, c

im ny khng ging vi IP hin thi v IP hin thi cn c nh a ch IP vi mng.

Mc tiu ca IP di ng l h tr kh nng kt ni lin mng cho host m khng cn

quan tm n vng mng. IP di ng c th bm theo host di ng m khng cn phi

thay i a ch IP di hn ca host di ng .

2.1.2.1. Cc thc th ca IP di ng

IP di ng bao gm cc thc th sau:a. Mobility Node (MN): L mt host hay mt b nh tuyn c th thay i im

tham gia vo mng ca n t mt mng hay mt mng con ny ti mt mng

hay mt mng con khc thng qua lin mng. Thc th ny c gn trc mt

a ch thng tr c nh trn mng thng tr ca n, a ch ny l a ch

cc host trao i khc s dng nh a ch cc gi tin ca chng m khng

quan tm n vng hin thi ca host.

b. Home Agent (HA) (i din thng tr): L mt b nh tuyn duy tr mt

danh sch cc node di ng trong mt mng thng tr. HA c s dng

chuyn tip cc gi tin c nh a n mng cc b tng ng khi node

di ng ny ra khi mng thng tr ca n. Sau khi kim tra cc rng buc di

ng hin thi cho mt node di ng c th, HA s ng gi datagram (d liu

) v gi chng n a ch tm thi ca host di ng.

c. Foreign Agent (FA) (i din ngoi tr): L mt b nh tuyn h tr mt node

di ng di chuyn t mng thng tr ca n sang mng ca FA ny. FA s

phn pht thng tin gia node di ng v HA.



37/80


d. Care-of-Address (CoA): l a ch ch th vng hin thi ca node di ng. N

cng c th c xem l phn cui ca mt ng hm hng thng ti node di

ng. N cng c th c cp pht ng hoc c kt hp vi FA ca n.

e. Correspondent Node (CN): Node ny gi cc gi tin c nh a ch ti

node di ng.

f. Home Address: a ch thng tr: L phn a ch c nh c cp pht cho

mt node di ng. N c gi khng i, khng quan tm n v tr node di

ng tham gia vo mng Internet.

g. Mobility Agent: Mt Agent h tr di ng. N c th l HA hoc FA

h. Tunnel(ng hm): L phn ng b chim bi cc gi tin ng gi. N

l phn ng dn gi tin t HA n FA.

Khi mt node di ng ri khi khu thng tr ca n, n s ng k a chCoA ca n vi HA ca n, thng qua FA m HA c th bit cn phi chuyn cc gi

tin ca node n u. Ty theo cu hnh mng, node di ng c th ng k trc

tip vi HA ca n, hoc gin tip thng qua s tr gip ca FA ca n.

2.1.2.2. Giao thc IP di ng c bn

Giao thc IP di ng c bn cho php kh nng di ng IP i vi d liu

khng dy m khng lm mt cc kt ni lp truyn ti v cc kt ni lp cao hn

trong khi di chuyn qua cc vng mng. N cho php bt k node di ng no i li

bn trong mng Internet, trong khi node vn tip tc c nhn dng thng qua a

ch IP thng tr ca n.

Hnh 2.1: Chc nng c bn mng IP di ng



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Nh ch ra trong hnh 2.1, cc node trung chuyn gi cc gi datagram n mt

node di ng bng cch s dng mt a ch IP thng tr di ng. Khi mt node di

ng nm bn trong mng thng tr th mt i din khu vc c gi l i din

thng tr HA s phc v n. Khi node ny ra khi mng thng tr ca n, th mt

i din trong mng khch hin thi c gi l i din ngoi tr FA s iu khin

cc gi datagram c nh tuyn. Thut ton nh tuyn IP thng thng c s

dng gi cc gi datagram n node di ng khi node vn nm trong mng

thng tr ca n. Giao thc IP di ng s dng c ch ng hm phn pht cc

gi tin n node di ng. i din ngoi tr FA cng phc v, ging nh mt router,

node di ng gi cc gi tin.

2.1.2.3. iu khin QoS trong cc mng IP di ng

Theo d on, lu lng IP trong mng di ng s tng nhanh theo nhng yucu khc nhau t pha khch hng, ging nh vic tng lu lng trong cc mng IP

c nh. Hin nay, dch v IP ang gp phi vn mt gi khng d on trc c

v hin tng jitter. Nu mt cng u ra tr thnh im tp trung ca hai hay nhiu

hn cc lung lu lng kt hp th cc gi tin u ra s c xp hng theo ch

vo trc ra trc FIFO. Vic xp hng ny s gy ra tr, v mt gi tin nu hng i

b trn khi c qu nhiu lu lng n. Tr do hng i gy ra thay i khng on

trc c t gi ti gi, biu hin ca chnh n l jitter.

Trong cc mng IP, mc ch ca QoS trn mi chng l cho php cc b nh

tuyn v cc chuyn mch tc nghn c kh nng d on mt gi, tr v cc c tnh

jitter i vi cc lp lu lng ca nh cung cp dch v v khch hng. Mt hng i

FIFO n khng th h tr QoS cho c lu lng khng nhy cm v nhy cm.

Trong khi mt hng i di li c t kh nng b trn gi hn trong sut qu trnh bng

n lu lng. V vy, vic gim xc sut mt gi s lm tng tr hng i cho cc gi

tin khng b rt. Mt hng i ngn s gim c tr hng i nhng li lm tng mt

gi. khc phc iu ny, ti mi im xy ra tc nghn, lu lng c phn chia

vo nhiu hng i, do vy cc lp lu lng khc nhau c gn vo cc hng i

khc nhau sao cho mi lp lu lng ny t c mt gi, tr v jitter nh mong

mun. V vy, cc b nh tuyn v cc chuyn mch c kh nng h tr QoS cn phi

phn loi cc gi tin, xp hng khc nhau cho cc gi tin trn mi lp. V khi c

th iu khin v lp lch d bo cho truyn dn gi tin t mi hng i n lin kt

u ra. y c gi l kin trc phn lp, xp hng v lp lch CQS.

Trong nh tuyn IP, ng dn ngn nht gia vng hin thi ca gi tin v

ch ca n l xc nh v cc gi tin s i theo ng dn . iu ny c th gy ralu lng qu ti trn mng khi c vng hin thi v ch n l cc im nng trn



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mng. Do , t l mt gi, tr v jitter tng khi ti trng trung bnh tng. C th khc

phc hin tng ny bng cch phn tn vic chuyn tip gi tin qua cc tuyn xen k

(nhau nh chng ta thy trong MPLS) v qua cc lin kt v cc router tc cao hn.

2.1.2.4. Cc vn chuyn tip IP

Trong chuyn tip IP, chng tip theo v cng ra ca mi gi c xc nh bi

bng chuyn tip, n thc hin vic tm kim a ch IP ch ca gi tin ging nh cha

kha. Thc hin phn loi gi tin tm c hng i cng u ra v cc quy lut lp

lch. Nu phn loi khng c thc hin th gi s c mt hng i FIFO n. Vi

iu kin ny, gi tin s c xp hng ti cng u ra tng ng. Quy lut bo

hiu IP l giao thc dnh trc ti nguyn. Nh chng ta thy trn, phng

php chuyn tip ny s dn n tr hng i, theo dn n mt gi v tng jitter.

Nh trnh by trong chng 1, MPLS c kh nng khc phc cc nhc im nynh th no.

2.2. Chuyn mch nhn a giao thc khng dy WMPLS

2.2.1. Nhu cu pht trin ca WMPLS

Chuyn mch nhn a giao thc MPLS l mt cng ngh mi, bt u c

nghin cu vo nm 1997. N l thnh phn chnh trong cc mng WAN nh ci

thin ng k hiu nng ca mng. Tuy nhin khi nhu cu s dng mng ngy cng

tng th MPLS li gp phi vn v cht lng dch v v tc truyn dn. Trongkhi , cng ngh mng khng dy ang c xu hng pht trin rt mnh m. V do

, vic m rng MPLS sang lnh vc khng dy l mt xu hng tt yu.

Cc cng ty nh Juniper, Nortel v Cisco hin ang u t thi gian v tin ca

nghin cu v pht trin vn tch hp MPLS vi cng ngh Internet trn lnh vc

khng dy. Nguyn nhn l do: IP trong Wiless hin nay ang gp phi mt s thch

thc, nh cc giao thc nh tuyn IP khng hon ton ph hp vi cc mng khng

dy di ng khi em so snh n vi cng ngh WMPLS. Vic tch hp MPLS vi IP

di ng ang tr thnh mt cng ngh hp dn. N cho php qun l cc b, h trchuyn giao, cp pht a ch, nh tuyn v chuyn giao lu lng trong mi trng

khng dy.

C mt s cng ngh khc nh cng ngh ATM, cc cng ngh 3G cng v

ang c sa i h tr IP di ng. Tuy nhin, MPLS l cng ngh c u thch

hn c v n c th n gin ha vic iu khin lu lng trong cc mng li. Hn

na, MPLS l cng ngh khng ch cung cp tc x l nhanh ci thin hiu nng

cho IP hin nay vi chi ph thp nht m cn khng gy nh hng n cht lng

dch v khi h tng thay i.



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2.2.2. Cu trc gi tin WMPLS

WMPLS s dng hai khun dng tiu c bn c ch ra trong hnh 2.2.

Trong mng WMPLS, 2 bit u tin trong s 20 bit trng Nhn s c c ging

nh trng C (Flag). Trng ny s quyt nh trng Controlv trng CRCcc s dng hay khng, v n cng ch th di ca trng Controlc s dng l

1 hay 2 byte, tng ng vi cc bit ch s th t l 3 hay l 7.

Trong m hnh chng ln, ti giao thc lp thp hn s h tr vic iu

khin lung v li, khun dng tiu WMPLS s khng c trng Controlv trng

CRC. xc nh khun dng cho nhn khi ny th hai bit u tin ca trngNhn

c thit lp bng khng biu th rng trng Controlv trng CRCkhng c

s dng. (Hnh 2.2a)

Trong trng Control, ch ra hnh 2.2b,N(S) l s th t gi/khung ang gi

v N(R) l s th t khung yu cu pht li t ng hoc s th t khung bo nhn

iu khin lung. S bit ca N(S) v N(R) ph thuc vo gi tr ca C (bng 2.1).

Trong , i vi cc dch v tc truyn ti thp, N(R) v N(S) ch c 3 bit, v

ngc l s l 7 bit. S dng cng nhiu bit s th t s cho php ca s iu khin

lung c thit lp cng rng h tr vic truyn dn chui khung tc cao. Ty

chn ny c kh nng iu khin lung v iu khin li t u cui n u cui hoc

iu khin trn tng chng khi cn thit da trn c s gi c dn nhn. Trng

Control ca phn tiu WATM gm cc chc nng iu khin lung v li. Trong

cc ng dng ca mng ty bin di ng, cn thit phi c ty chn ca iu khin

lung v li trn tng chng. WATM khng c kh nng iu khin lung v li trn

tng chng, chc nng iu khin ny c chuyn sang cho cc ngi s dng u

cui qun l, hoc nu s dng m hnh chng ln, iu khin lung v li trn tngchng c th thc hin c nu giao thc lp thp hn c th h tr chc nng ny.

Hnh 2.2 a v 2.2b di y a ra khun dng tiu WMPLS.

C

(2 bit)

Nhn

(18 bit)

CoS

(1 bit)

S

(1 bit)

TTL

(8 bit)

Hnh 2.2a: Tiu WMPLS khi khng c trng Controlv CRC



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Hnh 2.2b: Tiu WMPLS c trng Control v CRC

Bng 2.1 v 2.2 di y ch ra ngha cc bit trong tiu WMPLS

Bng 2.1: Gi tr cc bit c trong tiu gi tin WMPLS

Cc bit c (Flag) N(S), N(R)0 0 Khng c trng Control v CRC0 1 3 bit N(R) v 3 bit N(S)1 0 7 bit N(R) v 7 bit N(S)1 1 D phng cho cc ng dng tng lai

Bng 2.2: Cc bit iu khin bo nhn li v iu khin lung trong tiu WMPLSCc bit iu khin

lung ARQ

Bo nhn cc khung iu khin li v

iu khin lung

Biu tng iu

khin00 Bo nhn tch ly cho N(R-1) RR

01 Pha thu khng sn sng iu khinlung v bo nhn tch ly cho N(R-1)

RNR

10 Tn hiu N(R) loi b ARQ Go-Back-

N v bo nhn tch ly cho N(R-1)

REJ

11 Tn hiu N(R) lp/loi b c chn lc SREJ

2.2.3. Giao thc s dng trong WMPLS

Hai giao thc c s dng trong mng MPLS l giao thc phn b nhn LDP

v giao thc ginh trc ti nguyn RSVP. Khi tin hnh m rng MPLS sang minkhng dy, ngi ta tin hnh sa i hai giao thc ny c th h tr cc dch v

WMPLS. Mng WMPLS s dng giao thc LDP rng buc lng (CR-LDP) nh

ngha ngi s dng u cui v giao thc RSVP m rng (E-RSVP) thit lp LSP.

Di y s trnh by v cc m rng cho mi giao thc ny.

2.2.3.1. M rng cho CR- LDP


C (2 bit) Nhn (18 bit) CoS (3 bit) S (1 bit) TTL (8 bit) Control (8;16) CRC(8)

N(S) (3; 7 bit) ARQ (2 bit) N(R) (3; 7 bit)

-31-


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Phn m rng cho CR-LDP cn c cc thng tin v CoS v tnh di ng c

th thc hin cc dch v WMPLS. Vic m ha bn tin Label Request cn phi c

m rng vi thng tin v nhn v CoS ca mng WMPLS. Thm vo , vic m ha

bn tin lin kt nhn CR-LDP cng cn c m rng cha thng tin knh t lin

kt khng dy.

0 Label Request (0x0401)

(15 bits)

di bn tin

(2bytes)Message ID(4bytes)

FEC TLVLSPID TLV (CR-LDP, bt buc)Traffic TLV (CR-LDP, ty chn)

Hnh 2.3a: M rng cho bn tin yu cu nhn CR-LDP

0 Label Request (0x0400)

(15 bits)

di bn tin

(2bytes)Message ID(4bytes)

FEC TLVLabel TLV

Label Request Message ID TLVTraffic TLV (CR-LDP, ty chn)

Hnh 2.3b: M rng cho bn tin lin kt nhn CR-LDP

Trong CR-LDP, h thng khng dy c th thit lp mt LSP h tr cc ngdng WMPLS thng qua trng FEC TLV hoc Traffic TLV, phn xc nh cc tham

s lu lng c cha trong bn tin bo hiu. Cc tham s ca TE cho cc dch v

LSR l CDR (Committed Data Rate), CBS (Committed Burst Size), PDR (Peak Data

Rate), v PBS (Peak Burst Size). Trong cc trng hp m FEC c s dng bo

hiu kt ni LSP cho WMPLS, th CoS s c bo nhn thay v xc nh cc tham s

v tc d liu.

2.2.3.2. M rng cho RSVPPhn m rng thm cho RSVP c a ra h tr cho vic nh tuyn hin

LSP (ER-LSP). Khi giao thc RSVP c s dng h tr vic thit lp LSP

WMPLS, th cn phi tin hnh sa i v b sung cho giao thc ny p ng c

nhng yu cu v iu khin lu lng. Nhng sa i v b sung chnh ri vo cc

vng c thm cc tnh nng iu khin lu lng v cc vng phi gii quyt cc vn

tranh chp. Giao thc RSVP sa i h tr cc LSP nh tuyn hin (ER-LSP)

cht v lng. i vi phn nh tuyn lng trong ER-LSP, c th thc hin nh tuyn



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tng chng quyt nh xem gi bn tin PATH ti u. Do , RSVP cng h tr

phng thc nh tuyn tng chng theo yu cu ng xung.

Bn tin PATH v RESV trong giao thc RSVP c ch ra trong hnh 2.4a v

hnh 2.4b.

Tiu chungSession

RSVP_HOPTIME-VALUE

LABEL_REQUESTCc trng ty chn khc

Sender Descriptor

Hnh 2.4a: Khun dng ca bn tin PATH

Tiu chungSession

RSVP_HOPTIME-VALUE

STYLEflow descriptor list

Hnh 2.4b: Khun dng ca bn tin RESV

Reserved(2 byte)

L3ID(2 byte)

Hnh 2.5: Khun dng ca LABEL_REQUEST

Phn bi en l cc trng cha thng tin m rng cho WMPLS a vo cc

c tnh mong mun. Phn Yu cu nhn (Label_Request) l mt phn ca bn tin

PATH. Nu nhng thay i thch hp c thc hin trn phn nhn ny th n c th

c s dng xc nh kt ni WMPLS c nhn ang c yu cu. Trong phnYu cu nhn ny, cc phn ca trng Reserved c th c s dng bo hiu lin

kt WMPLS v cng c th hot ng ging nh con tr a ch chuyn giao di ng

v iu khin thng tin. Cc phn Session (v phn Sender Descriptor) c th c sa

i cha cc tham s lu lng v thng tin nhn chuyn giao phn hi v trm gc

ca mng khng dy.

Hnh 2.6 dc y a ra cc thc th trong SESSION ca giao thc RSVP.

a ch con tr cui ng hm IPv4 (4 byte)Reserved (2 byte) ID ca ng hm (2 byte)



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ID ca ng hm m rng (4 byte)

Hnh 2.6a: Thc th SESSION trong ng hm LSP_IPv4

a ch con tr cui ng hm IPv6 (16 byte)Reserved (2 byte) ID ca ng hm (2 byte)

ID ca ng hm m rng (16 byte)

Hnh 2.6b: Thc th SESSION trong ng hm LSP_IPv6

2.2.4. La chn ph tn cho WMPLS

Nh ni trn, WMPLS l dng m rng ca MPLS c dy, nhng n s

dng cc bc sng v tuyn m thay v s dng cp.

Ti Hoa K, Cc qun l tn s FCC quy nh cc tn s/bc sng v

tuyn m v cp giy php truyn dn WMPLS. Cc ngi dng khng dy s s

dng cc bng tn ny v do m bo c QoS cho cc ngi dng WMPLS. Cc

bng tn hin nay tp trung ti cc tn s 2,5; 5,8; 10,5; 24; 28; 38; v 48 GHz. V cc

dch v v tinh c nh s dng cc tn s thuc bng Ku nn WMPLS s dng tn s

t 18 n 31 GHz. cc tn s cao hn th bng thng kh dng ln hn v khi ny

tc truyn dn s nhanh hn. Nhng tn s cao c rng ph hp hn v c tnh

ng hn so vi cc tn s thp. Do , iu khin truyn dn trong WMPLS cthc hin d dng hn.

WMPLS kt ni trc tip vi phn bng tn c n nh bng cch s dng

cc mt phng qun l v mt phng iu khin khng dy. Sau khi c c kt ni,

cc thit b u cui ca kt ni ny s bt u thng tin vi nhau thng qua mng

ng trc MPLS c dy/khng dy. Khi qu trnh trao i thng tin kt thc, kt ni

s b ngt v bng tn v tuyn c cp pht s c gii phng cho cc ngi

dng WMPLS kh dng. WMPLS c th h tr QoS cng mc so vi MPLS c dy.

Cc h thng ph tn cho WMPLS: Vi cc cng ngh truy nhp khng

dy bng rng tc cao th mt trong nhng vn quan tm chnh l ph

tn. C ba h thng ph tn c a ra di y:

UNII (Unlicensed National Information Infrastructure) hot ng khng c

giy php ti di tn 2,4GHz v 5,8GHz. N t tn km hn so vi cc dng

ph tn khc nhng li nhy cm vi nhiu. Nhiu s gy ra mt gi v tin

cy thp.



45/80


MMDS (Multichannel Multipoint Distribution Service) hot ng ti tn s

2,5GHz. N h tr dch v a im, trong cc ngi dng truy nhp vo

cng mt trm gc v chia s bng thng t cng mt ct thu pht nh ch ra

trong hnh 2.7. Nhc im ca MMDS l cn phi c tm nhn thng tngi dng n trm gc. Cy ci, ta nh cao tng, v a hnh s cn tr

ng lin kt trong mi trng truyn dn .

Hnh 2.7: Cu trc mng MMDS vi mt anten bao ph mt vng

LMDS (Local Multipoint Distribution System) hot ng ti di tn t 28 n

40GHz. H thng ny cho tin cy cao hn i vi cc ng dng mc cao

v bng thng rng hn, nhng thit b li t tin hn. Do vy s phi c cc

ct thu pht nm gia cc vng phc v, nh miu t trn hnh 2.8. Mt

nhc im khc ca LMDS l n nhy cm vi thi tit v hn ch v

khong cch (xp x khong 3,2 km tnh t trm gc).



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Hnh 2.8: Cu trc mng LMDS vi nhiu anten bao ph mt vng

(c hn mt ct thu pht)

Lp iu khin truy nhp mi trng (MAC)

Mc d mng khng dy c nhiu u im, nhng chng ta khng th qun

rng t l li bit ca mi trng khng dy cao; do cn thc hin iu chnh li

mc cao hn c c tin cy n nh nh mong mun. gim thiu nhng

thay i ca mi trng khng dy, cn phi s dng lp MAC, v thc hin viciu chnh li bit chng ta phi s dng lp Lin kt d liu.

Hnh 2.9 miu t cc lp ca WMPLS t lp mng (Network Layer) n lp

vt l khng dy (Wireless Physical Layer). Lp lin kt v tuyn (Radio Link Layer)

v lp MAC khng dy (Wireless MAC Layer) c t gia lp mng v lp vt

l khng dy.

Hnh 2.9: Kin trc lp WMPLS



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2.2.5 K thut WMPLS

WMPLS s dng giao thc hi t truyn dn (TCP) c th thit lp v gii

phng cc kt ni, v xa b cng nh ti thit lp cc kt ni khi cc u cui di

ng di chuyn. Khi ny cn c s qun l cc b v mt kin trc mng vng chc.

c th thc hin c WMPLS th cn phi c mt vi nhng thay i v

mt k thut. Nhng thay i ny bao gm: qun l cc b, nh tuyn, chuyn giao

lu lng khng dy ng, v mt vi thay i v kin trc mng.

Qun l cc b

Mng phi c chc nng qun l cc b c th bit c ng di chuyn

ca cc u cui di ng. Do , mng s c c thng tin v v tr ca cc ngi

dng v cung cp dch v cho cc ngi dng .

nh v mt u cui di ng, mng c th xc nh vng nh tuyn RAphc v u cui thay v tm tt c cc trm gc c th phi phc v u cui .

Tt c nhng g cn thit xc nh thnh cng mt u cui di ng l cp

nht nhng thay i xy ra trc tip vi RA. Mi u cui di ng (host) s c h

tr bi mt i din thng tr HA. HA cha thng tin lin quan n v tr hin thi

ca u cui (v tr vng). bit chnh xc hn v v tr ca mnh, u cui phi cn

n s tr gip ca i din ngoi tr FA. Trn thc t FA l b nh tuyn gn vi

host nht.

Chuyn giao

gii quyt vn di chuyn ca u cui di ng, cn thc hin ba bc sau

y: 1- nh v u cui, 2- ti nh tuyn: thit lp mt kt ni bng cch xc nh

mt ng i mi n mt RA mi ti u cui ang i vo, 3- chuyn giao:

chuyn lung d liu qua ng mi va thit lp trn v thot ra khi ng c m

khng gy nh hng n kt ni .

Th tc chuyn giao trong WMPLS

Trong mt mng truyn thng di ng, cc Host di ng (MHs) tip tc dichuyn ti cc trm trm gc khc nhau (BSs). Do , mt phn ca tuyn ng

trong mng truyn thng di ng s tip tc thay i v s l phn nh tuyn hin

lng ca ton b tuyn chuyn mch nhn LSP.

Mt khi nim mi trong phn l vn phng chuyn mch nhn di ng

(MSO). MSO l mt b nh tuyn trong mng truyn thng di ng, n h tr truy

nhp im ti cc MHs. Mt MSO ti bin ca mng truyn thng di ng v mng

ng trc c gi l MSO cng (MSO GW).



48/80


Gi s rng MSO GW bit r topo mng v c kh nng thc hin xuyn

ng. c th phn pht gi tin theo chui trong qu trnh chuyn giao, WMPLS

phi lm vic vi cc giao thc bo hiu nh LDP, RSVP v RSVP-TE. Gi s mt

MH hin ang c kt ni vi mt Router chuyn mch nhn (LSR A) thng qua mt

trm gc BS1 v n cn c chuyn giao ti BS2, th tc chuyn giao mm c

thit lp nh sau. MH gi mt bn tin PATH (hoc mt bn tin yu cu nhn trong

LDP) ti BS2, yu cu kt ni ti LSR A. Khi MSO 1A l MSO kt ni trc tip vi

BS2, n s nhn bn tin PATH ny (hoc bn tin Yu cu nhn trong LDP). Khi MSO

1A pht hin ra rng MSO GW l node chung ti cc ng LSP gp nhau, th

MSO 1A ny s chn ra mt ng n c MSO GW, v d nh: MSO 1A

MSO 2AMSO 2.1AMSO 2.2AMSO GW. Do , ton b phn ng t MH

thng qua BS2 l MH BS2 MSO 1A MSO 2A MSO 2.1A MSO 2.2AMSO GW. Mt bn tin PATH (hay bn tin Yu cu nhn trong LDP) c gi bi

MH s i qua tuyn chn thng qua cc node c mt trn tuyn cho ti khi n

c MSO GW. Phn ng t MSO GW n LSR A c duy tr c nh.

Sau MSO GW s gi bn tin RESV (hay bn tin nh x nhn trong LDP)

qua tuyn ng chn ti MH.Ti tt c cc Node s din ra vic cp pht v dnh

trc ti nguyn. (Trong LDP, d tr ti nguyn din ra cng vi bn tin Yu cu

Nhn).Cc nhn cng c gn cho cc lin kt ring l trong mt LSP mi. Cng vi

bn tin RESV, MSO GW cng s gi mt bn tin PATH (hay bn tin Yu cu Nhn

trong LDP) thit lp mt ng dn t MSO GW n MH.MH gi tr li bn tin

RESV (hay bn tin nh x nhn trong LDP). Sau , LSP t MH n MSO GW s

c cp pht ti nguyn v cc lin kt ring l s c gn nhn. Khi tuyn ng

ny thit lp thnh cng, cc gi d liu s c chuyn i thng qua ng mi va

c thit lp, phn ng c t MH qua BS1 n MSO GW (MHBS1MSO 1

MSO 2MSO 2.1MSO 2.2MSO GW) ch ra trn hnh 2.10 l ng t nt.

Hnh 2.10: Thit lp ng vi th tc chuyn giao WMPLS



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2.2.6. Mng MPLS di ng

Mng MPLS di ng l mt gii php nhm h tr cc mng khng dy da

trn MPLS. Di y a ra m hnh v mt s vn c bn trong MPLS di ng

Hnh 2.10 ch ra mt m hnh n gin ca mt mng di ng vi cc nhn

c phn b gia mt node trung chuyn v node di ng ch trong mt mng ngoi

tr. Hnh ny ch ra mt v d v v tr m cc host di ng ang tham gia trc tip vo

mng chuyn mch nhn. Theo phng php hng d liu (data-driven) trong

node di ng khi to yu cu nhn da trn cc lung lu lng, vic host tham gia

vo chuyn mch nhn d hn mt cht so vi phng php hng iu khin

(control-driven), trong cn phi c cc giao thc nh tuyn.

Hnh 2.11: Mng di ng MPLS

Khi node di ng bt u qu trnh thit lp ng dn, theo phng php

hng iu khin, th mi node di ng s cn phi c mt cu hnh mng hon tt v

cn chy mt giao thc nh tuyn nh OSPF. y khng phi l gii php ti u vn yu cu ti nguyn ln cho mi node di ng v mi node di ng khng cn bit

thng tin cu hnh ca mng ti bt k ni no m chng ang hot ng. Tuy nhin,

vic s dng tt c cc u im ca cc giao thc nh tuyn l rt cn thit. Do ,

cc giao thc nh tuyn c chy ti cc trung tm chuyn mch di ng v trn cc

giao din lin mng (gia cc mng di ng v khng di ng).

Nghin cu hot ng chuyn tip IP, cc ng chuyn mch nhn c th

c thit lp gia hai node/chuyn mch bin ca mt mng di ng v c th s

dng ng dn ny to mt ng hm cho cc gi tin IP i qua. Cc gi tin IP c



50/80


th c gn vo cc ng chuyn mch nhn khc nhau da trn a ch IP ch ca

chng v tiu chun khc nh cc thuc tnh QoS.

Bt k khi no mt node di ng mun thit lp mt ng chuyn mch nhn,

th mt node chuyn mch di ng trong khu vc thng tr s cung cp thng tin

nh tuyn r rng cho node di ng , v vy m node di ng c th bt u bo

hiu vi mt tuyn ng xc nh.

Chuyn tip IP trong mt node di ng thng lin quan ti hai hot ng ring

bit, l tp hp cc gi tin IP vo mt lp chuyn tip tng ng FEC v nh x

FEC vo chng tip theo trn ng dn. Hai hot ng ny c mi node di ng

thc hin. MPLS t u cui n u cui s node di ng nh x cc gi tin vo

FEC v m ha FEC ny thnh mt nhn. Khi ng dn c thit lp, cc node di

ng trung gian (bao gm cc node thu pht gc, v cc trung tm chuyn mch ding) ch cn thc hin thao tc th hai, nh x nhn vo chng tip theo v thc hin

chuyn dch nhn thch hp.

2.2.6.1. Thit lp cuc gi MPLS trong mng di ng

Phn ny s ch ra cc phn t MPLS khc nhau c nh hng n nhau nh

th no trong sut qu trnh thit lp, sa i v sp ca mt LSP. Vn iu

khin di ng s c ni n trong phn tip theo. Chng ta xt trng hp mt node

di ng thit lp mt ng dn MPLS n mt node di ng khc trong mng. Giao

thc bo hiu c s dng c th l RSVP hoc LDP. Xt thy tnh ni tri ca

RSVP trong mi trng hin nay, chng ta s dng RSVP l giao thc bo hiu thit

lp ng.

Hnh 2.12: Thit lp ng chuyn mch nhn trong mt mng di ng

Hnh 2.12 ch ra mt mng di ng c cc LSP c thit lp t u cui n

u cui. Node di ng A gi mt yu cu bo hiu UNI n trm gc cc b ca n.

Trm gc cc b ny ghi li yu cu ny v chuyn n n chuyn mch di ng.



51/80


Chuyn mch di ng, l thit b ang chy giao thc nh tuyn, duy tr cu hnh

mng v c kh nng xc nh c ng n node ch cn c vo cc node

ch, vng thng tr, ngoi tr hin thi. Yu cu cht lng dch v, bng thng

tng cn thit v cn bng ti u c thc hin trong mng... Thng tin ny c

chuyn mch di ng s dng bo hiu cho cc node ng ln trn ng dn

thit lp nhn cho n tn node ch B.

Khi node ch p li bng bn tin RESV RSVP th mi node ng xung

trong ng dn s ghi li nhn ny v to mt thc th chuyn tip nhn. Khi node

chuyn mch di ng u tin nhn c bn tin RESV, n s thng bo cho trm gc

u tin v node A.

Trm gc u tin phi kt ni nhiu lung t trm gc khc v gi chng n

mt chuyn mch di ng. iu ny s dn n vic hnh thnh mt phn cp ngnxp nhn, vi hai lp nhn, mt gia cc node di ng v trm gc, v mt nhn khc

gia trm gc v chuyn mch di ng.

Khi ng dn t u cui n u cui c thit lp th cc node di ng c

th bt u pht cc gi tin c gn nhn, sau cc gi tin ny c nh tuyn

sn n node ch.

Phn ng b sp c th c thng bo bi node di ng ngun hay ch

hoc chnh mng . Trong hai trng hp u, mt bn tin TEAR c gi ti mi

node trn ng dn, v sau xa b cc thc th chuyn tip nhn. Trong trnghp th ba, giao thc nh tuyn c trch nhim phn b cc nhn c v do cung

cp thng tin ng dn bt u sp , c ng xung v ng ln.

2.2.6.2. iu khin di ng s dng MPLS

Trong mng di ng, c node ngun v node ch u c th di chuyn, di

chuyn t (1) mt trm thu pht ny n mt trm thu pht khc, (2) t mt trm gc

ny n mt trm gc khc, (3) t mt chuyn mch di ng ny n mt chuyn

mch di ng khc, hoc (4) t mt mng ny sang mt mng khc.Trong trng hp 1, trm gc c th vn gi li cc nhn c thit lp gia

node di ng v trm gc, v do c th c rt t gi b mt. Trong trng hp 2, khi

m ng dn c thit lp trc (vt ra khi phm vi ca chuyn mch di ng

ngun (ch)) vn khng b thay i th cn phi thit lp li cc ng dn t chuyn

mch di ng n node di ng thng qua mt trm gc mi. Trong trng hp 3,

chuyn mch di ng c c th cung cp thng tin v trng thi hin thi ca LSP,

nhng nhng thng tin ny cn c thay i v ti thit lp gia b nh tuyn k

tip v chuyn mch di ng mi, thm na cn phi thit lp ng cho node di



52/80


ng. Trng hp cui cng tng t vi trng hp trm gc c cung cp thng tin

doanngoc revised

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