kỹ thuật lưu lượng trong mpls

K Thut Lu Lng Trong MPLS. Li ni u.

GVHD: Ths.Hong Trng Minh. - i - Phm c Ha - A10121

Li ni u -------------o0o-------------

S pht trin nhanh chng cc dch v IP v s bng b Internet dn n mt

lot s thay i trong nhn thc kinh doanh ca cc nh khai thc. Giao thc IP thng tr ton b cc giao thc lp mng, h qu l tt c cc xu hng pht trin cng ngh lp di u h tr cho IP. Nhu cu th trng cp bch cho mng tc cao vi chi ph thp l c s cho mt lot cc cng ngh mi ra i, trong c MPLS. Trong khong thi gian gn y, cng ngh MPLS chng minh c tnh ng dng thc tin cc tnh nng vt tri ca n so vi cc cng ngh chuyn mch truyn thng khc nh ATM. Chuyn mch nhn a giao thc MPLS l mt cng ngh chuyn mch nhn nh hng kt ni cung cp cc kh nng mi trong cc mng IP, trong khi kh nng iu khin lu lng c cp n bng cch cho php thc hin cc c ch iu khin lu lng mt cch tinh xo. MPLS khng thay th cho nh tuyn IP, nhng n s hot ng song song vi cc phng php nh tuyn khc nhm mc ch cung cp tc d liu cao gia cc b nh tuyn chuyn mch nhn LSP ng thi vi vic hn ch bng tn ca cc lung lu lng vi cc yu cu cht lng dich v QoS khc nhau. Mt trong nhng u im ln nht ca cng ngh MPLS l kh nng thc hin k thut lu lng. y cng l i tng tm hiu chnh ca chuyn tt nghip ny . Chuyn tt nghip c 3 chng vi cc ni dung chnh nh sau:

Chng I - Chuyn mch nhn a giao thc : Gii thiu tng qut v cng ngh MPLS, cc khi nim c bn, c ch hot ng chung ca MPLS. Xy dng mt ci nhn tng qut v m hnh MPLS.

Chng II - nh tuyn v bo hiu MPLS : Trnh by cc k thut nh tuyn c h tr bi MPLS, cc ch bo hiu v mt s giao thc phn phi nhn ca MPLS.

Chng III - K thut lu lng trong MPLS : Trnh by cc khi nim v mc tiu ca k thut lu lng, kh nng v cc c ch thc hin k thut lu lng ca MPLS. Cc vn trong bo v khi phc ng - mt trong nhng nhim v ca k thut lu lng cng c trnh by trong chng ny.

K thut lu lng l mt k thut tng i kh, vic tm hiu v cc vn

ca k thut lu lng i hi phi c kin thc su rng v lu di. Do vy,

K Thut Lu Lng Trong MPLS. Li ni u.

GVHD: Ths.Hong Trng Minh. - ii - Phm c Ha - A10121

chuyn tt nghip khng trnh khi nhng sai st. Rt mong nhn c s ph bnh, kin nh gi v gp ca thy c v cc bn.

Xin gi li cm n trn thnh ti Thy gio Hong Trng Minh, ngi tn tnh hng dn ti trong sut qu trnh lm chuyn tt nghip ny.

Xin trn thnh cm n cc thy c gio trong khoa Vin thng gip ti trong thi gian qua.

Xin cm n ti gia nh, bn b v ngi thn - nhng ngi gip , ng vin trong sut qu trnh hc tp.

H Ni, ngy thng nm 2010.

Sinh vin

Phm c Ha.

K Thut Lu Lng Trong MPLS. Mc lc.

GVHD: Ths.Hong Trng Minh. - iii - Phm c Ha - A10121

MC LC. Cc thut ng vit tt.................................................................................vii Danh mc hnh v........................................................................................ix Danh mc bng.............................................................................................x CHNG I CHUYN MCH NHN A GIAO THC....................1 1.1 TNG QUAN...................................................................................................1 1.2 CC KHI NIM C BN TRONG MPLS..............................................2

1.2.1 Min MPLS.................................................................................................2 1.2.2 ng chuyn mch nhn LSP (Label Switch Path) .................................2 1.2.3 Lp chuyn tip tng ng (FEC) ..................................................3 1.2.4 Nhn v stack nhn .............................................................................3 1.2.5 Hon i nhn (Label Swapping).........................................................4 1.2.6 Chuyn gi qua min MPLS................................................................4

1.3 M HA NHN V CC CH NG GI NHN.......................5 1.3.1 M ha stack nhn................................................................................5

1.3.2 Cc ch ng gi trong MPLS.........................................................5 1.4 CU TRC NT MPLS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 1.5 HOT NG CHUYN TIP TRONG MPLS............................8 1.5.1 Qu trnh hnh thnh c s d liu.......................................................8

1.5.2 Qu trnh hnh thnh bng nh tuyn..................................................9 1.5.3 Gn nhn Local cho desIP tng ng.................................................9 1.5.4 Thit lp bng LIB v LFIB......................................................................9 1.5.5 Qung b nhn ni b-local cho ton mng.......................................10 1.5.6 Cp nht thng tin qung b...............................................................11 1.5.7 PHP.....................................................................................................12 1.5.8 X l thng tin qung b....................................................................13 1.5.9 Hnh thnh bng LFIB trong ton mng.............................................14 1.5.10 Hi t gi tin qua mng MPLS...............................................................15

1.6 TNG KT..............................................................................................15 CHNG II : NH TUYN V BO HIU MPLS...............................17 2.1 NH TUYN TRONG MPLS...................................................................17

2.1.1 nh tuyn tng chng ( Hop - by - Hop )................................................17 2.1.2 nh tuyn rng buc (Constrain based Routing).................................17 2.1.3 nh tuyn tng minh (Explicit Routing)...............................................18

2.2 CH BO HIU MPLS......................................................................19 2.2.1 Ch phn phi nhn.............................................................................19

2.2.1.a Phn phi khng cn yu cu.....................................................19 2.2.1.b Phn phi theo yu cu................................................................19

2.2.2 Ch duy tr nhn..........................................................................19


GVHD: Ths.Hong Trng Minh. - iv - Phm c Ha - A10121

2.2.2.a Duy tr nhn t do.................................................................19 2.2.2.b Duy tr nhn bo th.............................................................20

2.2.3 Ch iu khin LSP.......................................................................20 2.2.3.a iu khin c lp (Independent Control)............................20 2.2.3.b iu khin tun t (Odered Control)....................................21

2.3 GIAO THC LDP (Label Distribution Protocol)........................................21 2.3.1 Hot ng ca LDP............................................................................22 2.3.2 Cu trc bn tin LDP....................................................................23

2.3.2.a LDP-PDU.............................................................................23 2.3.2.b nh dng bn tin LDP...................................................23

2.3.3 Cc bn tin LDP..................................................................................24 2.3.4 LDP iu khin c lp v phn phi theo yu cu...........................25

2.4 GIAO THC CR-LDP (Contrain-based Routing LDP)........................26 2.4.1 M rng cho nh tuyn rng buc.....................................................26 2.4.2 Thit lp mt CR-LSP (Constrain-based Routing LSP)......................27 2.4.3 Tin trnh d tr ti nguyn................................................................28

2.5 GIAO THC D TR TI NGUYN RSVP - TE..........................29 2.5.1 Cc bn tin thit lp d tr RSVP......................................................30 2.5.2 Cc bn tin Tear Down, Error v Hello ca RSVP - TE....................31 2.5.3 Thit lp tuyn tng minh iu khin tun t theo yu cu.............31 2.5.4 C ch Make-before-break..............................................................33 2.5.5 Gim lng overhead lm ti RSVP................................................35

2.6 GIAO THC BGP (Bored Gateway Protocol) ........................................35 2.6.1 Giao thc BGP....................................................................................35 2.6.2 Kt ni MPLS qua nhiu nh cung cp dch v.................................36

2.7 KHI NIM DCH V TCH HP V DCH V PHN BIT.....37 2.7.1 Khi nim dch v tch hp (Intserv)..................................................37 2.7.2 Khi nim dch v phn bit (Diffserv)..............................................38

2.8 TNG KT....................................................................................................39 CHNG III : K THUT LU LNG TRONG MPLS..............40 3.1 K THUT LU LNG (Traffic Engineer).........................................40

3.1.1 Cc mc tiu trin khai k thut lu lng........................................40 3.1.1.a Phn loi..............................................................................40 3.1.1.b Bi ton nghn......................................................................40

3.1.2 Hng i lu lng.............................................................................40 3.1.2.a Hng i FIFO (First - In , First - Out)..............................40 3.1.2.b Hng i PQ (Priority Queuing)..............................................41 3.1.2.c Hng i WFQ (Weighted Fair Queuing)..............................41

3.1.3 Gii thut thng r v thng Token....................................................42 3.1.3.a Gii thut thng r (Leaky Bucket)......................................42


GVHD: Ths.Hong Trng Minh. - v - Phm c Ha - A10121

3.1.3.b Gii thut thng Token (Token Bucket)...............................42 3.1.4 Gii php m hnh chng ph (Overlay Model).................................43

3.2 MPLS V K THUT LU LNG......................................................44 3.2.1 Khi nim trung k lu lng (Traffic Trunk)......................................44 3.2.2 hnh nghim suy (Induced Graph)................................................45 3.2.3 Bi ton c bn ca k thut lu lng..............................................45

3.3 TRUNG K LU LNG V CC THUC TNH.......................46 3.3.1 Cc hot ng c bn trn trung k lu lng...................................46 3.3.2 Thuc tnh tham s lu lng (Traffic Parameter)............................46 3.3.3 Thuc tnh la chn v qun l ng..............................................47

3.3.3.a ng tng minh c t qun tr.......................................47 3.3.3.b Phn cp cc lut u tin cho a ng...............................47 3.3.3.c Thuc tnh tng ng lp ti nguyn (Resource Class A f f i n i t y ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7 3.3.3.d Thuc tnh thch ng (Adaptivity)........................................47 3.3.3.e Phn phi ti qua nhiu trung k song song.........................47

3.3.4 Thuc tnh u tin / ln chim (Priority / Preemption)......................48 3.3.5 Thuc tnh n hi (Resilience)..........................................................48 3.3.6 Thuc tnh khng ch (Policing)........................................................48

3.4 CC THUC TNH TI NGUYN..................................................49 3.4.1 B nhn cp pht cc i (maximum allocation multiplier)...............49 3.4.2 Lp ti nguyn (Resource - Class).......................................................49 3.4.3 Metric TE.............................................................................................49

3.5 TNH TON NG RNG BUC.....................................................50 3.5.1 Qung b cc thuc tnh ca link.......................................................50 3.5.2 Giao thc nh tuyn Link-State........................................................50 3.5.3 Tnh ton LSP rng buc (CR-LSP)...................................................51 3.5.4 Gii thut chn ng........................................................................51 3.5.5 V d v chn ng cho trung k lu lng....................................52 3.5.6 Ti ti u ha (Re - optimization)........................................................54

3.6 BO V V KHI PHC NG...............................................55 3.6.1 Phn loi cc c ch bo v khi phc...............................................56

3.6.1.a Sa cha ton cc v sa cha cc b..................................56 3.6.1.b Ti nh tuyn v chuyn mch bo v................................56

3.6.2 M hnh Makam (Bo v ton cc)....................................................56 3.6.3 M hnh Haskin (Reverse Backup).....................................................57 3.6.4 M hnh Hundessa..............................................................................58 3.6.5 M hnh Shortest-Dynamic.................................................................58 3.6.6 M hnh Simple-Dynamic..................................................................60 3.6.7 M hnh Simple-Static........................................................................60


GVHD: Ths.Hong Trng Minh. - vi - Phm c Ha - A10121

3.7 TNG KT............................................................................................61 TNG KT......................................................................................62 TI LIU THAM KHO.......................................................................63

K Thut Lu Lng Trong MPLS. Cc thut ng vit tt

GVHD: Ths.Hong Trng Minh. - vii - Phm c Ha - A10121

Cc thut ng vit tt. T vit tt Gii ngha ting Anh Gii ngha ting Vit AS Autonomous System H t tr ATM Asynchronous Transfer

Mode Phng thc truyn dn khng ng b

BGP Border Gateway Protocol Giao thc cng bin CR Constrain-based Routing nh tuyn cng bc ER Explicit Route nh tuyn hin ERB Explicit Route-information

Base Bng thng tin c s nh tuyn hin

ERO Explicit Route Object i tng nh tuyn hin FEC Forwarding Equivalence

Class Lp chuyn tip tng ng

FIB Forwarding Information Base

Bng thng tin c s chuyn tip

FIFO First In First Out Kiu vo trc ra trc FIS Fault Information Signal Tn hiu thng bo li FR Frame Relay Phng thc chuyn mch

khung FRS Fault Recovery Signal Tn hiu thng bo khi phc IGP Interior Gateway Protocol Giao thc cng ni ILM Incoming Label Map nh x nhn u vo IP Internet Protocol Giao thc Internet IS-IS Intermediate System -to-

Intermediate System Giao thc nh tuyn ni vng

ISP Internet Service Provider Nh cung cp dch v LDP Label Distribution Protocol Giao thc phn phi nhn LER Label Edge Router B nh tuyn nhn LFIB Label Forwarding

Information Base C s thng tin chuyn tip nhn

LIB Label Information Base C s thng tin nhn LSP Label Switched Path Tuyn chuyn mch nhn LSR Label switching Router B nh tuyn chuyn mch

nhn MAC Medium Access Control iu khin truy cp trung tm MPLS Multi-Protocol Label

Switching Chuyn mch nhn a giao thc

K Thut Lu Lng Trong MPLS. Cc thut ng vit tt

GVHD: Ths.Hong Trng Minh. - viii - Phm c Ha - A10121

NHLFE Next Hop Label Forwarding Entry

Li i chuyn tip nhn n hop k tip.

NLRI Network Layer Reachability Information

Thng tin hin hnh tng mng

OSI Open System Interconnection

M hnh tham chiu kt ni cc h thng m

OSPF Open Shortest Path First Giao thc tm ng ngn nht

PDU Protocol Data Unit n v d liu giao thc PHP Penultimate Hop Poping Th tc g nhn hop p cui PML Protection Mergin LSR LSR khi phc POR Point Of Repair im sa cha PQ Priority Queuing Hng i u tin QoS Quality of Service Cht lng dch v RIB Routing Information Base C s thng tin nh tuyn RSVP Resource reSerVation

Protocol Giao thc dnh trc ti nguyn

TCP Transmission Control Protocol

Giao thc iu khin truyn vn

TE Traffic Engineering K thut lu lng UDP User Datagram Protocol Giao thc d liu ngi dng VC Virtual Circuit Mch o VCI Virtual Circuit Identifier Nhn din mch o VPN Virtual Private Network Mng ring o WAN Wide Area Network Mng din rng WFQ Weighted Fair Queuing Hng i c trng s

K Thut Lu Lng Trong MPLS. Dnh mc hnh v.

GVHD: Ths.Hong Trng Minh. - ix - Phm c Ha - A10121

Danh mc hnh v. Hnh 1.1: MPLS v m hnh tham chiu OSI. Hnh 1.2: Min MPLS. Hnh 1.3: Stack nhn. Hnh 1.4: Gi IP i qua mng MPLS. Hnh 1.5: nh dng mt entry trong stack nhn. Hnh 1.6: Shim header c thm vo. Hnh 1.7: Nhn trong ch cell. Hnh 1.8: Kin trc c bn mt nt MPLS. Hnh 1.9: Xy dng bng nh tuyn. Hnh 1.10: Thit lp bng LIB v LFIB. Hnh 1.11: Phn phi nhn local. Hnh 1.12: Cp nhp thng tin qung b. Hnh 1.13: Qu trnh qung b nhn xy ra tt c Router trong mng. Hnh 1.14: X l thng tin qung b. Hnh 1.15: Hnh thnh bng LFIB trong ton mng. Hnh 1.16: Hi t trong mng MPLS. Hnh 2.1: Cu trc mng hnh con c. Hnh 2.2: Phn phi nhn theo yu cu. Hnh 2.3: Duy tr nhn t do. Hnh 2.4: Duy tr nhn bo th Hnh 2.5: iu khin c lp. Hnh 2.6: iu khin tun t. Hnh 2.7: Trao i bn tin UDP. Hnh 2.8: LDP header. Hnh 2.9: Khun dng bn tin LDP. Hnh 2.10: LDP iu khin c lp v phn phi theo yu cu. Hnh 2.11: Thit lp LSP vi CR-LDP. Hnh 2.12: Tin trnh d tr ti nguyn. Hnh 2.13: M t lung ca bn tin RSVP trong vic thit lp 1 LSP. Hnh 2.14: Thit lp LSP vi RSVP-TE. Hnh 2.15: S v d cho Make-before-break. Hnh 2.16: BGP phn phi qua nhiu Autonomous System ( AS ). Hnh 3.1: Nhiu lung cho mi lp lu lng. Hnh 3.2: Gii thut thng r. Hnh 3.3: Gii thut thng Token.

K Thut Lu Lng Trong MPLS. Dnh mc hnh v.

GVHD: Ths.Hong Trng Minh. - x - Phm c Ha - A10121

Hnh 3.4: M hnh chng ph (overlay model). Hnh 3.5: Minh ha cch dng bit Affinity v Resource-Class. Hnh 3.6: Bng thng kh dng ng vi tng mc u tin. Hnh 3.7: M hnh v d v chn ng cho trung k lu lng. Hnh 3.8: Xem xt cc rng buc khng ch. Hnh 3.9: Xem xt ti nguyn kh dng. Hnh 3.10: ng tt nht c chn. Hnh 3.11: M hnh Makam. Hnh 3.12: M hnh Haskin. Hnh 3.13: M hnh Shortest-Dynamic (khi phc link). Hnh 3.14: M hnh Shortest-Dynamic (khi phc nt). Hnh 3.15: M hnh Simple-Dynamic (khi phc link).

Danh mc bng. Bng 2.1: Cc loi bn tin LDP.

K Thut Lu Lng Trong MPLS. ChngI:Chuyn mch nhn a giao thc.

GVHD: Ths.Hong Trng Minh. - 1 - Phm c Ha - A10121

Chng I :CHUYN MCH NHN A GIAO THC.

1.1 TNG QUAN. MPLS l vit tt ca Multi Protocol Label Switching . Thut ng Multi- protocol nhn mnh rng cng ngh ny c th c p dng cho nhiu cc giao thc lp mng ch khng ring IP. MPLS cng hot ng tt trn bt k cc giao thc lp lin kt. y l cng ngh lai kt hp nhng c tnh tt nht ca nh tuyn lp 3 (Layer 3 routing) v chuyn mch lp 2 (Layer 2 switching).

Trong mng chuyn mch knh, tnh thng minh ch yu tp trung mng li (core). Tt c cc thit b thng minh u t trong mng li nh cc tng i, toll, transit, MSC... Cc thit b km thng minh hn th t mng bin (edge), v d nh cc tng i ni ht, truy cp... Quan im ca MPLS l tnh thng minh cng a ra bin th mng cng hot ng tt. L do l nhng thnh phn mng li phi chu ti rt cao. Thnh phn mng li nn c thng minh thp v nng lc chuyn ti cao. MPLS phn tch hai chc nng nh tuyn v chuyn mch: Cc router bin thc hin nh tuyn v gn nhn (label) cho gi, cc router mng li ch tp trung lm nhim v chuyn tip gi tc cao da vo nhn. Tnh thng minh c y ra ngoi bin l mt trong nhng u im ln nht ca MPLS. M hnh tham chiu ca MPLS trn m hnh OSI :

Hnh 1.1: MPLS v m hnh tham chiu OSI.

MPLS c xem nh mt cng ngh lp m (shim layer), n nm trn lp 2

nhng di lp 3, v vy i khi ngi ta vn gi l lp 2,5. Nguyn l ca MPLS l tt c cc gi IP s c gn nhn (label) v chuyn tip theo mt ng dn LSP (Label Switching Path). Cc router trn ng dn ch cn c vo ni dung ca nhn thc hin quyt nh chuyn tip gi m khng cn phi kim tra header IP.



1.2 CC KHI NIM C BN TRONG MPLS.

1.2.1 Min MPLS.

Min MPLS (MPLS domain) l mt tp hp cc nt mng thc hin hot ng nh tuyn v chuyn tip MPLS. Mt min MPLS thng c qun l v iu khin bi mt nh qun tr.

Hnh 1.2 : Min MPLS.

Min MPLS c chia thnh 2 phn: phn mng li (core) v phn mng bin

(edge). Cc nt thuc min MPLS c gi l router chuyn mch nhn LSR (Label Switch Router). Cc nt phn mng li c gi l transit-LSR hay core-LSR (thng gi tt l LSR). Cc nt phn mng bin c gi l router bin nhn LER ( Label Edge Router). Nu mt LER l nt u tin trn ng i ca gi tin xuyn qua min MPLS th n c gi l LER li vo (ingress-LER), cn nu l nt cui cng th n c gi l LER li ra (egress-LER). Cc thut ng ny c p dng cn ty theo hng i vo ca lung lu lng trong mng, do mt LER c th va l ingres-LER va l egress-LER ty theo cc lung lu lng ang xt. Cc thut ng upstream-LSR v downstream-LSR l cc khi nim then cht hiu hot ng ca s phn phi nhn v chuyn pht d liu trong MPLS. D liu m Router nh gi i cho mt mng xc nh gi l downstream, cn vic cp nhp thng tin (giao thc nh tuyn hoc phn phi nhn, LDP/TDP) gn lin vi mt tin t gi l upstream. C th hiu l thng tin v nhn ca mt Router c chnh n gi i cho cc LSR k cn c gi l downstream. Cn thng tin nh tuyn th gi l upstream.

1.2.2 ng chuyn mch nhn LSP (Label Switch Path).

ng chuyn mch nhn LSP l mt ng ni gia router ng vo v router ng ra, c thit lp bi cc nt MPLS chuyn gi tin qua mng. ng dn



ca mt LSP qua mng c nh ngha bi s chuyn i cc gi tr nhn cc LSR dc theo LSP bng cc th tc hon i nhn. Khi nim LSP tng t nh khi nim mch o (VC) trong ATM.

1.2.3 Lp chuyn tip tng ng (FEC).

Lp chuyn tip tng ng FEC (Forwarding Equivalence Class) l mt tp hp cc gi c i x nh nhau bi mt LSR. Nh vy, FEC l mt nhm cc gi IP c chuyn tip trn cng mt ng chuyn mch nhn LSP, c i x theo cng mt cch thc v c th nh x vo mt nhn bi mt LSR cho d chng c th khc nhau v thng tin header lp mng.

1.2.4 Nhn v stack nhn.

Nhn c RFC 3031 nh ngha l: mt b nhn dng c di ngn v c nh, mang ngha cc b dng nhn bit mt FEC. Nhn c dn ln mt gi bo cho LSR bit gi ny cn i u. Nhn khng trc tip m ho thng tin ca mo u lp mng nh a ch lp mng. Nhn c gn vo mt gi tin c th s i din cho mt FEC m gi tin c n nh. Thng th mt gi tin c n nh cho mt FEC (hon ton hoc mt phn) da trn a ch ch lp mng ca n. Tuy nhin nhn khng bao gi l m ho ca a ch . Phn ni dung nhn c di 20 bit, nh vy s gi tr nhn c th c l 220 gi tr. Gi tr nhn nh ngha ch mc dng trong bng chuyn tip.

Mi gi li c th dn chng nhiu nhn, cc nhn ny cha trong mt ni gi l stack nhn. Stack nhn l mt tp hp gm mt hay nhiu entry nhn c t chc theo nguyn tc LIFO. Ti mi hop trong mng ch x l nhn hin hnh nm trn nh stack. Chnh nhn ny c LSR s dng chuyn tip gi.

Hnh 1.3: Stack nhn.

Nu gi tin cha c nhn th stack nhn l rng. Nu chiu su stack nhn l d th mc 1 (bit S) y nhn t ln 1 v mc d l nh stack nhn. Mt entry nhn c th c t thm vo (push) hoc c th ly ra (pop) khi stack.



1.2.5 Hon i nhn (Label Swapping).

Hon i nhn l cch dng cc th tc chuyn tip gi. chuyn tip gi c nhn, LSR kim tra nhn trn nh stack v dng nh x ILM (Income Label Map) nh x nhn ny ti mt entry chuyn tip nhn NHLFE (Next Hop Label Forwarding Entry). S dng thng tin trong NHLFE, LSR xc nh ni chuyn tip gi v thc hin mt tc v trn stack nhn. Ri n m ha stack mi vo gi v chuyn i.

Chuyn tip gi tin cha c nhn cng tng t nhng ch xy ra ingress-LER. LER ch phn tch header lp mng xc nh FEC ri dng nh x FTN (FEC-To-NHLFE) nh x mt FEC vo NHLFE.

1.2.6 Chuyn gi qua min MPLS.

Sau y l v d n gin minh ha qu trnh chuyn gi IP i qua min MPLS. Gi tin IP i t ngoi mng vo trong min MPLS c router R4 l ingress-LER v router R1 l egress-LER, hai router li R3, R2.

Hnh 1.4: Gi IP i qua mng MPLS.

R4 nhn gi c tin t a ch ch IP l 172.16.10.0/24 v gi gi tin qua min MPLS. R4 nhn bit ng i ca gi trong mng bng 1 bng nh tuyn theo nhn. R4 gn nhn L3 nhn t downstream R3 vo gi IP, chuyn gi n next hop R3. R3 nhn gi, hon i nhn L3 bng nhn L2 nhn c t router R2 v chuyn n next hop R2. R2 nhn gi tin, tip tc thay th nhn L2 bng nhn L1 v gi gi n R1. R1 l router bin, kt ni gia min IP v min MPLS. R1 bc tt c cc nhn MPLS c gn vo gi tin, tr li a ch IP nguyn thy v gi n mng 172.16.10.0/24.



Nh chuyn mch da trn nhn mng li, MPLS s c tc x l gi nhanh hn so vi mng IP. Thay v d tm trong mt bng nh tuyn di, gi tin trong MPLS ch so snh nhn vi bng chuyn mch nhn m n hc c. C th lin tng qu trnh chuyn mch trong mng li vi vic gn tag trong mng lp hai gia cc Vlan. l l do ngi ta ni rng MPLS l cng ngh kt hp cc c im tt nht gia chuyn mch lp hai v nh tuyn lp ba.

1.3 M HA NHN V CC CH NG GI NHN.

1.3.1 M ha stack nhn.

Khi nhn c dn ln gi tin, bn thn gi tr nhn 20 bit s c m ha cng vi mt s thng tin cng thm ph tr qu trnh chuyn tip gi tin to nn mt entry.

Hnh 1.5: nh dng mt entry trong stack nhn.

- Label: gm 20 bits, thnh phn nhn tht s dng ring cho hot ng thit yu ca mt mng MPLS.

- EXP (Experimental): dng cho mc ch CoS (cost of service ) tng t nh trong mng IP truyn thng.

- S: ty kch thc cng nh dch v m MPLS c th s dng mt hay nhiu nhn. Nu s dng nhiu nhn th cc nhn s c lu tr trong mt ngn xp. Bit ny s c set ln 1 khi nhn cn x l l cui cng trong ngn xp router trong MPLS bit kt thc quy trnh x l nhn.

- TTL( time to live ): c chc nng chng lp vng bng cch nh thi gian tn ti ca gi tin trong mng MPLS tng t nh thnh phn TTL trong header gi tin IP.

1.3.2 Cc ch ng gi trong MPLS.

MPLS c to ra nhm khc phc nhng yu km ca nhng m hnh WAN nh ATM hay Frame Relay nhng cng i hi phi k tha, pht trin MPLS trn nn h thng mng c. Do cc cu trc ca frame hay cell dng trong cc h thng mng c cn c gi nguyn, MPLS ch ng gi cc gi ny cng vi



nhng phn cn thit cho hot ng ca MPLS. Chnh v l do trn, trong cu trc nhn ca MPLS chia lm hai loi: ch dng cho Frame v dng cho cell.

Nu MPLS pht trin t h thng mng dng Frame nh Frame Relay th cu trc nhn n gin ch l thm vo 32 bit gia header ca layer 2 v layer 3 trong gi tin. Trong mng ATM, lin lc gia u-cui thng qua cc thng s l VPI/VCI, nhng thng s ny c xem nh nhng ch s c trng cho mt mch o. Cc gi d liu k tip (ti cng mt ch) sau khi mch o c thit lp s c gn thng s ny truyn qua mch o duy nht, khc vi Frame Relay khi cc gi tin c th theo nhiu ng khc nhau. c tnh ny ca ATM ging vi MPLS, do nu s dng MPLS da trn ATM th MPLS s s dng li cc thng s VPI/VCI lm nhn cho mnh.

Nhn trong ch Frame:

Hnh 1.6: Shim header c thm vo. Nhn trong ch cell: Ch ny dng khi c mt mng gm cc ATM-LSR dng MPLS trong mt phng iu khin trao i thng tin VPI/VCI thay v dng bo hiu ATM. Trong ch ny nhn chnh l VPI/VCI. Sau khi trao i nhn trong mt phng iu khin, mt phng chuyn tip tc l ti Ingress LER s phn tch gi tin tr thnh li kiu t bo trong ATM v dng gi tr VPI/VCI chuyn gi tin i qua mng li theo ng mch o ( y l LSP) chuyn gi tin i.

Hnh 1.7:Nhn trong ch cell.



GFC (Generic Flow Control): iu khin lung chung. VPI (Virtual Path Identifier): Nhn dng ng o. VCI (Virtual Cicuit Identifier): Nhn dng knh o. PT (Payload Type): Ch th kiu trng tin. CLP (Cell Loss Priority): Ch th u tin hu b t bo. HEC (Header Error Check): Khi bit dng kim tra li tiu .

1.4 CU TRC MT NT MPLS. Mt nt ca MPLS c hai mt phng: mt phng chuyn tip v mt phng iu khin MPLS. Nt MPLS c th thc hin nh tuyn lp ba hoc chuyn mch lp hai.

Hnh 1.8: Kin trc c bn mt nt MPLS. Mt phng iu khin c chc nng nh tuyn IP dng giao tip vi cc LSR, LER khc hoc cc router IP thng thng bng cc giao thc nh tuyn IP. Kt qu l mt c s thng tin nh tuyn RIB (Router Infomation Base) c to lp thnh cc thng tin miu t cc router kh thi tm ra prefix a ch IP. LER s dng cc thng tin ny xy dng c s thng tin chuyn tip FIB (Forward - ing Infomation Base) trong mt phng chuyn tip. Mt phng iu khin cn c chc nng bo hiu MPLS dng giao tip vi cc LSR khc bng mt giao thc phn phi nhn. Kt qu l mt c s thng tin nhn LIB (Label Infomation Base) gm cc thng tin lin quan n cc gn kt nhn c thng lng vi cc router MPLS khc. Thnh phn bo hiu MPLS nhn thng tin t chc nng nh tuyn IP v LIB xy dng c s thng tin chuyn tip nhn LFIB (Lable Forwarding Infomation Base) trong mt phng chuyn tip. Mt LER c th



chuyn tip cc gi IP, gn nhn vo gi, hoc g nhn ra khi gi, trong khi mt transit-LSR ch c kh nng chuyn tip gi c nhn, thm hoc b bt nhn. Nhim v ca cc giao thc trong mt phng iu khin l phn phi thng tin cn thit cho cc LSR v LER cu hnh bng FIB v LFIB. Mt s giao thc nh tuyn s dng trong bng thng tin nh tuyn RIB hot ng kt hp vi mt giao thc bo hiu MPLS s dng bng thng tin nhn LIB phn phi cc nhn. Vic phn tch mt phng iu khin v mt phng chuyn tip cho php ci t mt giao thc iu khin trn mt ATM switch. Trong MPLS c s dng giao thc bo hiu MPLS kt hp vi mt giao thc nh tuyn (khc vi router c in ch cn nh tuyn IP) l phc v vic thc hin nh tuyn rng buc ca ng chuyn mch nhn MPLS.

1.5 HOT NG CHUYN TIP CA MPLS. Ni dung phn ny s miu t c ch thc hin vic thnh lp cc bng FIB, LFIB trong thnh phn d liu (data plane) cc quy tc gn nhn, trao i nhn bng giao thc LDP. Ni dung cng phn tch vic ti sao mt gi IP nhn c li c tham chiu n cc bng d liu tng ng (FIB hoc LFIB), cng nh ngha ca vic chuyn gi tin qua MPLS m khng qua nhn (dng nh tuyn IP thng thng). Do cu trc c th ca gi tin c gn nhn trong mng MPLS ch dng frame phc tp hn so vi ch dng cell (MPLS da trn ATM), s khng lm mt i tnh tng qut nu ta phn tch vic x l nhn ch dng Frame.

1.5.1 Qu trnh hnh thnh c s d liu.

Qu trnh xc nh, thit lp, phn phi v gn nhn trong mng MPLS c th chia lm cc bc sau:

Bc 1: Cc router trao i thng tin nh tuyn vi nhau thng qua giao thc IGP nh OSPF, IS-IS, EIGRP.

Bc 2: Ti mi LSR tng ng vi mi a ch ch nhn c s pht sinh mt nhn local, v nhn ny c lu tr trong LIB (label information base). Bng LIB dng lm c s d liu trong phng thc phn phi nhn, do bng LIB thuc thnh phn iu khin (control plane) trong s chc nng ca mt LSR.

Bc 3: Cc nhn local c qung b n cc router ln cn, ti y cc nhn s c i km vi a ch IP cn n trong bng FIB v bng LFIB. Da vo cc bng ny, gi tin s c chuyn i da vo nhn.

Bc 4: Mi LSR (label switch router) xy dng bng LIB, FIB, LFIB da trn nhn m n nhn c t cc router k cn.



1.5.2 Qu trnh hnh thnh bng nh tuyn.

M hnh sau m t cc router hnh thnh bng nh tuyn thng qua cc giao thc nh tuyn IP nh: OSPF, EIGRP, IS-IS, BGP v.v

Hnh 1.9: Xy dng bng nh tuyn.

Trong qu trnh hnh thnh bng nh tuyn, vic xc nh bng nh tuyn l bc u tin. Khi bng nh tuyn hnh thnh, ti mi router, mt desIP s tng ng vi mt interface m qua n s ti c hop k. Nu gi tin IP i vo mng MPLS ti thi im ny, th gi tin s c chuyn i da vo bng nh tuyn nh trong m hnh nh tuyn IP.

1.5.3. Gn nhn Local cho desIP tng ng.

Sau khi thit lp xong bng nh tuyn, cc LSR s gn nhn local cho cc desIP tng ng. Vic gn nhn gia cc LSR l hon ton c lp nhau. Mc d c th c nhiu LSR cng pht sinh nhn local cng lc nhng vic ny xy ra c lp, tc l c th c nhiu LSR cng ghp chung mt desIP vi mt nhn local. Tuy nhin trong cng mt LSR th s rng buc ny l duy nht tc mt desIP ch tng ng vi mt nhn local.

1.5.4 Thit lp bng LIB v LFIB.

Khi mt nhn c gn km vi mt desIP th mi quan h rng buc ny c lu tr trong 2 bng: LIB v LFIB.

Bng LIB dng gn tng ng mt desIP (a ch mng cn n) vi mt nhn local do LSR pht sinh trong v d ny l nhn 25.

Bng LFIB cha nhn local, nhn remote nhn t pha router k trn ng ti ch (upstream) km theo l hnh ng x l gi tin khi n i ra khi interface. Trong trng hp ny hnh ng l khng gn (untagged) nhn cho gi tin khi n ti hop k do LSR vn cha nhn c nhn local t LSR (hop) ny cho vo nhn remote trong LFIB.



Hnh 1.10: Thit lp bng LIB v LFIB.

1.5.5 Qung b nhn ni b-local cho ton mng.

Ni dung phn ny s miu t lm th no cc nhn MPLS c phn phi v qung b thng tin trong mng MPLS. Sau khi bng nh tuyn c thit lp trong ton b router trong mng MPLS v mi desIP ti LSR c gn mt nhn local tng ng, tc l bng LIB c thnh lp. Vn t ra l lm th no qung b cc nhn local ny n cc router k cn. Ngi ta a ra hai kh nng gii quyt vn ny: hoc m rng kh nng ca cc giao thc nh tuyn hin ti, hoc thm vo mt giao thc mi iu khin qu trnh phn phi nhn.

Hnh 1.11: Phn phi nhn local.

phng n u s gp kh khn do c nhiu giao thc nh tuyn khc nhau nh OSPF, EIGRP, IS-IS, BGP cng tn ti trong mng vin thng, nn vic thc hin m rng chc nng c th gy ra kh khn khi m hnh mng lin min s



dng a giao thc c trin khai. Hn na vic mt s router c m rng chc nng trong khi mt s router khc vn gi nguyn c th gy ra nhiu sai st khi hot ng. Gp phn ch yu gy ra nhng kh khn trn l vic c s d liu m y l bng nh tuyn c s dng li khi m rng chc nng phn phi nhn cho LSR. iu ny c gii quyt khi ta s dng phng php th hai l s dng giao thc mi LDP, s dng mt c s d liu mi c tham chiu t bng nh tuyn l bng LIB thc hin vic phn phi nhn trong MPLS. LDP c s dng ch yu do u im hi t nhanh v c kh nng m rng cao.

1.5.6 Cp nht thng tin qung b.

Ty theo thng tin cp nht t gi tin LDP nhn t B m cc LSR A, C, E s cp nht vo cc bng FIB, LFIB ca mnh. Ti LSR B nhn 25 c gn vi desIP (network X) v c lu tr trong bng LIB. Ti LSR A, nhn 25 nhn c t B v lu tr trong bng FIB ca mnh. Sau khi cp nhp nhn cho cc LSR k cn, qu trnh qung b thng tin ra ton mng din ra nh trong v d sau:

Bc 1: gi tin IP vi ch n l mng X cha c gn nhn i vo mng MPLS ti LER A (label edge router A).

Bc 2: da vo bng FIB ca mnh LSR A s xc nh c mun ti c mng X gi tin ny phi c gn nhn 25 v c chuyn ra interface tng ng. Lu l nhn 25 l nhn remote c A nhn t B thng qua LDP.

Bc 3: Gi tin c gn nhn 25 v ng gi Frame chuyn ti B Bc 4: Ti B, gi tin c g b nhn v c chuyn ti hop k l C

di dng gi tin IP thng thng do B cha nhn c nhn remote do C gi thng qua LDP (hnh ng trong bng LFIB vi gi tin c nhn 25 l khng gn nhn untagged).



Hnh 1.12: Cp nhp thng tin qung b.

Ti LER A din ra qu trnh x l desIP, trong khi ti B l hnh ng x l nhn. Ti B gi tin c b nhn v chuyn i di dng gi tin IP thng thng. iu ny gip cho mng MPLS vn chuyn gi tin i ti ch d cho qu trnh phn phi nhn (LDP) cha c hon thnh trong ton mng MPLS. V cc qu trnh xy ra trong cc LSR din ra mt cch bt ng b, nhng g xy ra vi LSR A, B cng xy ra tng t nh C, D. Do sau mt thi gian ngn ng dn chuyn mch t A ti D c hon thnh.

Hnh 1.13: Qu trnh qung b nhn xy ra tt c Router trong mng.

V LSR D c ni trc tip vi mng X, LSR C bit c iu ny nn trong bng LFIB ca n hnh ng i vi gi tin vi nhn local 47 l g b nhn (pop). Gi tin i n D di dng gi tin IP thng thng. K thut trn gi l PHP Penultimate Hop Poping (G nhn hop p cui).

1.5.7 PHP (Penultimate Hop Poping).

Nh trong v d trn ti cc LER (label edge router) cc gi tin c th n di dng khng nhn. Ti y din ra 2 qu trnh:

Da vo bng LFIB nhn bit hnh ng g b nhn cho gi tin khi ra mng ngoi.

Da vo bng FIB tham chiu vi a ch IP m cho ra interface tng ng, do ti LER ny nhn remote khng c gn trong khi trong cc LSR trong mng nhn ny c tc dng tham chiu trc tip n bng ARP cache bit interface tng ng vi a ch layer cn n (a ch MAC ca interface hop k).



Phng php PHP gip lc b bt yu cu thc hin cc LER bng cch gi ti cc LER ny cc gi tin khng nhn.

1.5.8 X l thng tin qung b.

Router B sau khi nhn y thng tin v nhn c th xc nh ng i ti mng X v thm nhn local (25), nhn remote (47) nhn c t LSR C vo bng LFIB. Tng t LSR E cng nhn c cc gi qung b LDP (d E khng thuc ng i ti X khi xut pht t A), E ng nhin cng s cp nhn local cho desIP X tng ng trong bng LIB, ng thi cng qung b tnh cht ny cho cc LSR k cn. iu ny c th dn n tnh trng lp vng trong MPLS. Tnh hung ny c th trnh c bng hai c ch:

Hnh 1.14: X l thng tin qung b.

Mt l s dng trng bit TTL (khc vi TTL trong gi IP) gii hn thi gian lp. Trng TTL trong nhn cng dng chng loop nh trong gi IP v c gi tr t 0 n 255. Khi qua mi LSR, gi tr TTL gim xung 1. Khi TTL c gi tr bng 0, LSR s tr v ngun thng gi ICMP cha thng tin TTL expired in transit. Vi phng php ny, cc gi tin c lp ln trong mng u b loi b. Hai l s dng cch thc tng t nh phng php plit-horizon trong mng IP. y cn lu l thnh phn nhn trong cc bng FIB, LFIB c tc dng nh con tr, tham chiu n a ch IP trong bng nh tuyn, do cc interface ti hop k trn ng i l c xc nh, cc gi tin qung b s khng nhn ngc li gi LDP t hop trc . Tuy nhin gi s tch bit gia nh tuyn



IP v LDP cng nh nhng vn phc tp ny sinh m phng php u tin thng c s dng hn.

Mt cch khc, nu s dng c ch LDP c s rng buc (odered control l phng php da trn c s bo hiu u cui dc theo ng dn) th s khng xy ra loop nhng hi t chm hn. Cc phng php trao i nhn c rng buc l phng php bt buc dng cho k thut lu lng s c trnh by chi tit trong chng sau.

1.5.9 Hnh thnh bng LFIB trong ton mng.

Giao thc nh tuyn IGP s qung b ton b bng nh tuyn ca cc LSR trong ton min MPLS. Giao thc LDP dng phn phi v hi t nhn trong mng ny. Lu rng mi LSR s t quyt nh ng i ngn nht ti ch bng cch s dng IGP. Cc LSR khi nhn c cc nhn do giao thc LDP phn phi ti s thm cc nhn cn thit vo bng FIB v LFIB. Ch c nhng nhn ti t cc LSR k trn ng ti ch mi c thm vo cc bng ny bt k LDP s dng phng php phn phi nhn c iu khin hay c lp. Ti LSR B n cng gn mt nhn local cho mng X v to mt li i (entry) trong bng LFIB. Nhn remote c chuyn t LSR k v c thm vo LFIB. Sau khi LSR C qung b nhn local ra cc LSR ln cn, ng dn hay ng hm (tunnel) c hnh thnh v gm c 2 hop. Cc bc tip theo dng hnh thnh ng dn t A n mng X din ra nh sau:

Bc 1: Ti A mng X c gn vi nhn 25 ca hop k (LSR B). Bc 2: Ti B nhn 25 c hon i vi nhn 47 (nhn remote nhn t C). Bc 3: Do LSR C khng nhn c nhn remote t LSR D do n

nhn bit c D l hop cui v s hon i nhn 47 (nhn local ca C) vi hnh ng l g b (pop).



Hnh 1.15: Hnh thnh bng LFIB trong ton mng.

1.5.10 Hi t gi tin qua mng MPLS.

Khi mt gi tin IP vo mng MPLS, n u tin s c chuyn i da vo bng LIB, v s c chuyn i trong MPLS di dng cc gi tin c hay khng nhn. Nhng khi bng LFIB c hnh thnh trong ton mng cc gi tin s hon ton c chuyn i di dng c gn nhn. Tm li nu mt LSR khng nhn c nhn remote t LSR k th gi tin s c chuyn ti LSR k di dng khng gn nhn. M hnh di y m t vic gi tin c chuyn i trong MPLS nh th no. Qu trnh din ra tun t theo cc bc sau:

Bc 1: Gi IP vi ch l X vo LSR A. Bc 2: LSR A gn nhn 25 cho gi tin. Bc 3: LSR A chuyn gi tin IP c gn nhn 25 ti LSR B. Bc 4: LSR B da vo bng LFIB tro nhn 25 thnh nhn 47. Bc 5: LSR B chuyn gi tin n LSR C. Bc 6: LSR C g b nhn (bng LFIB quy nh). Bc 7: LSR C gi gi tin n LSR D di dng khng nhn.

Hnh 1.16: Hi t trong mng MPLS.

1.6 TNG KT. Cng ngh chuyn mch nhn cho php thay th cng ngh chuyn tip gi truyn thng theo kiu hop-by-hop bng k thut hon i nhn. K thut ny da vo nhn c di ngn c nh ci thin c nng lc nh tuyn lp 3, n



gin ha vic chuyn gi, cho php d dng vic m rng v c bit l h tr k thut lu lng. Hot ng c bn ca mt mng MPLS c th tm gn nh sau: Mi LSR gn mt nhn local tng ng vi mt ch n trong bng nh tuyn. Cc nhn ny sau c qung b ti cc LSR k cn bng giao thc phn phi nhn thch hp (giao thc c bn l LDP). Khi nhn c cc nhn remote t LSR k cc LSR s b sung vo bng LIB, FIB, LFIB ca mnh ty vo thng tin n nhn c v c s d liu m n c. Khi mng MPLS hi t, cc gi tin s c chuyn i dc theo ng dn (tunnel) da vo bng LFIB thay v bng nh tuyn. PHP dng ti u ha hot ng ca MPLS bng cch gim bt yu cu hot ng ca LER.

K Thut Lu Lng Trong MPLS. ChngII: nh tuyn v bo hiu MPLS.


Chng II : NH TUYN V BO HIU MPLS.

2.1 NH TUYN TRONG MPLS. Trong MPLS h tr c hai k thut nh tuyn l : nh tuyn tng chng (hop-by-hop) v nh tuyn rng buc (constrain-based routing). nh tuyn tng chng cho php mi nt nhn dng cc FEC v chn hop k tip cho mi FEC mt cch c lp, ging nh trong mng IP truyn thng. Tuy nhin nu mun khai trin k thut lu lng vi mng MPLS, bt buc phi s dng kiu nh tuyn rng buc.

2.1.1 nh tuyn tng chng (Hop - by - Hop).

Phng php ny l tng ng vi phng php c s dng hin nay trong cc mng IP truyn thng. Cc giao thc nh tuyn truyn thng chng hn nh OSPF, BGP c s dng thm d a ch IP. Trong phng php ny mi LSR la chn mt cch c lp tuyn k tip vi mt FEC cho trc. Mi nt MPLS 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 nt s thng bo mt rng buc (cha mt a ch mng v mt nhn) ti cc nt ln cn.

2.1.2 nh tuyn rng buc (Constrain - based Routing).

nh tuyn rng buc l mt phng tin thc hin x l t ng ha k thut lu lng, khc phc c hn ch ca nh tuyn theo ch (destination-based routing). N xc nh cc tuyn khng ch da trn topo mng m cn s dng cc metric c th khc nh bng thng, ch, hay cost...

Gii thut chn ng c kh nng ti u ha theo mt hay nhiu metric ny, thng thng ngi ta chn metric da trn s lng hop v bng thng. ng c chn c s lng ngn nht v m bo bng thng kh dng trn sut cc chng lin kt, quyt nh nh sau: chn ng ngn nht trong tt c cc ng m bo bng thng kh dng tha mn yu cu. minh ha cho nh tuyn rng buc, ta xt cu trc mng con c kinh in nh hnh v 2.1. Gi s nh tuyn rng buc s dng metric l s hop v bng thng kh dng. Lu lng 600 Kbps c nh tuyn trc tin, sau l lu lng 500 Kbps v 200 Kbps. C ba lu lng ny u hng ti cng mt LER ra. Bng thng kh dng trn cc chng u bng 1 Mbps. V lu lng 600 Kbps c nh tuyn trc nn n i theo ng ngn nht l R8-R2-R3-R4-R5. Lc ny tuyn ng ny b chim 60% bng thng. Sau bng thng tuyn ng trn khng cho 500 Kbps nn lu lng 500 Kbps phi i theo tuyn ng mi qua R6-R7 mc d nhiu hn mt hop.



Hnh 2.1 : Cu trc mng hnh con c. Lu lng 200 Kbps c truyn i trn tuyn ng ngn nht do bng thng kh dng ca tuyn ng ny 400 Kbps. nh tuyn rng buc c hai kiu online v offline. Kiu online cho php cc router tnh ng cho cc LSP bt c lc no. Trong kiu offline th mt server tnh ng cho cc LSP theo nh k (thng l vi gi, hoc vi ngy). Cc ng LSP c bo hiu thit lp theo cc con ng c chn.

2.1.3 nh tuyn tng minh (Explicit Routing).

nh tuyn tng minh (hay cn gi l nh tuyn hin) l mt tp con ca nh tuyn rng buc. Trong s rng buc l i tng tng minh ER (Explicit Route). Tuyn tng minh ER l mt danh sch cc nt tru tng m mt ng chuyn mch nhn rng buc phi i qua. Nt tru tng c th l mt nt hoc mt nhm nt. Nu ER ch quy nh mt s nt trong cc nt m tuyn ng rng buc (CR-LSP) i qua th n c gi l tuyn ng tng minh th lng. Ngc li nu ER quy nh trn ton b cc nt m CR-LSP i qua th gi l tuyn ng tng minh nghim ngt. CR-LSP c m ha nh l mt chui cc ER-hop (chng tng minh) cha trong mt cu trc Type-Length-Value (TLV) rng buc. Mi ER-hop c th xc nh mt nhm cc nt. CR-LSP khi bao gm tt c cc nhm nt c xc nh theo th t xut hin trong cu trc TLV.



2.2 CH BO HIU MPLS.

2.2.1 Ch phn phi nhn.

MPLS cho php hai ch hot ng ca cc LSR phn phi cc nh x nhn. l phn phi khng cn yu cu (Downstream Unsolicited) v phn phi theo yu cu (Downstream on Demand). 2.2.1.a Phn phi khng cn yu cu. Downstream-LSR phn phi cc gn kt nhn n upstream-LSR m khng cn c yu cu thc hin gn kt nhn. V d nh R2 l downstream ca upstream-R1, R2 s thc hin vic gn kt nhn v thng bo vic gn kt cho R1 bit, nu R2 l hop k tip ca R1 th R1 c th dng kiu gn kt nhn ny chuyn tip cc gi FEC n R2. 2.2.1.b Phn phi theo yu cu. Pha upstream-LSR phi yu cu r rng mt gn kt nhn cho mt FEC c th th downstream-LSR mi phn phi. Trong phng thc ny th downstream-LSR khng nht thit l hop k tip ca nh tuyn IP cho FEC . iu ny rt quan trng vi cc LSP nh tuyn tng minh.

Hnh 2.2: Phn phi nhn theo yu cu.

2.2.2 Ch duy tr nhn.

Mt upstream-LRS c th nhn nhiu cc gn kt nhn cho cng mt FEC t nhiu pha downstream-LSR khc nhau. Do cn ch duy tr nhn cho upstream-LSR. C hai ch duy tr nhn l ch duy tr nhn t do (liberal lable retention) v duy tr nhn bo th (conservative label retention). 2.2.2.a Duy tr nhn t do. Pha upstream-LSR lu gi tt c cc gn kt nhn nhn c, bt chp vic downstream-LSR c phi l hop k tip i vi ng nh tuyn hay khng. u im ca ch ny l c th phn ng nhanh vi s thay i ca ng nh tuyn v cc gn kt nhn lun c sn. Nhc im l LSR lun phi duy tr nhiu nhn kt ni khng dng v c th gy ra loop nh tuyn tm thi khi c thay i nh tuyn.



Hnh 2.3: Duy tr nhn t do.

2.2.2.b Duy tr nhn bo th. Pha upstream-LSR hy tt c cc gn kt nhn khc, ch gi li gn kt nhn ca downstream-LSR ang l hop k tip ca ng c nh tuyn. Ch ny c u im l LSR ch cn duy tr s gn kt nhn FEC t hn, nhng p ng chm khi thay i nh tuyn v gn kt nhn mi li phi c yu cu v phn phi li. y l ch thch hp cho cc LSR ch h tr mt s lng nhn hn ch (nh cc chuyn mch ATM).

Hnh 2.4: Duy tr nhn bo th.

2.2.3 Ch iu khin LSP.

Khi mt FEC ng vi mt prefix a ch c phn phi bi nh tuyn IP, vic thit lp mi quan h gia cc gn nhn ti mt LSR c th thc hin theo hai cch sau y. 2.2.3.a iu khin c lp (Independent Control). Khi mt LSR nhn dng ra mt FEC no th n quyt nh gn kt mt nhn cho FEC v cng b kt qu gn nhn cho cc i tc phn phi nhn. iu ny tng t nh nh tuyn IP thng thng, mi router quyt nh c lp v ni chuyn gi i. iu khin c lp c li th l thit lp tuyn LSP nhanh v vic gn kt nhn din ra song song gia nhiu cp LSR, dng lu lng c th bt u truyn m khng cn i cho tt c vic gn kt nhn thit lp xong.



Hnh 2.5: iu khin c lp.

2.2.3.b iu khin tun t (Odered Control). Vic thit lp LSP tun t bt u LSR li ra v din ra ni tip theo hng ngc v LSR li vo. Mt downstream-LSR thc hin gn kt nhn v thng bo gn kt nhn ch khi n l LSR li ra hoc n nhn c mt gn kt nhn cho FEC t router hng downstresam ca n. Cc LSP nh tuyn tng minh bt buc phi s dng kiu iu khin tun t v qu trnh phn phi nhn theo chui c th t s to ra thi gian tr trc khi dng lu lng i trn LSP c th bt u. Tuy nhin iu khin tun t cung cp phng tin trnh loop v t c mc thu gom chc chn hn.

Hnh 2.6: iu khin tun t.

Cc giao thc phn phi nhn trong MPLS. Giao thc phn phi nhn l mt tp cc th tc m nh n mt LSR c th thng bo cho cc LSR khc bit v cc mi gn kt nhn vi FEC m n thc hin. Trong MPLS khng ch nh mt giao thc phn phi nhn duy nht no, do c th c nhiu la chn, mi giao thc c u nhc im ring. Sau y l mt s giao thc phn phi nhn c s dng ph bin.

2.3 GIAO THC LDP (Label Distribution Protocol). LDP c chun ha trong RFC 3036, n c thit k thit lp v duy tr cc LSP nh tuyn khng rng buc. Vng hot ng ca LDP c th l gia cc LSR ln cn (LSR-neighbor) trc tip hay gin tip.



2.3.1 Hot ng ca LDP.

LDP c 4 chc nng chnh l pht hin LSR ln cn (discovery), thit lp v duy tr phin (session), qung b nhn (advertisment) v thng bo (notification). Tng ng vi 4 chc nng trn LDP c 4 lp thng ip sau:

Discovery: trao i nh k bn tin Hello nhm loan bo v thm d mt LSR kt ni gin tip v trc tip.

Session: thit lp, thng lng cc thng s cho vic khi to, duy tr v chm dt cc phin ngang hng LDP. Nhm ny bao gm bn tin Initialization v KeepAlive.

Advertisment: to ra, thay i hay xa cc nh x FEC ti nhn. Nhm ny bao gm bn tin Label Mapping, Label Withdrawal, Label Release, Label Request, Label Request Abort.

Notification: truyn t cc thng tin trng thi, li, cnh bo. Cc thng ip Discovery c trao i trn UDP. Cc kiu thng ip cn li

i hi phn pht tin cy nn dng TCP. Trng hp 2 LSR c kt ni lp hai trc tip th th tc pht hin ln cn trc tip nh sau: - Mt LSR nh k gi i bn tin Hello ti cc cng UDP vi a ch multicast (tt c cc router trong subnet). - Tt c cc LSR tip nhn bn tin Hello ny trn cng UDP. Ti mt thi im no LSR s bit c tt c cc LSR khc m n c th 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 song hng nn mi LSR hai u kt ni u c th gi yu cu v gi lin kt nhn.

Hnh 2.7: Trao i thng ip UDP.



Trong trng hp hai LSR khng c lin kt trc tip (ln cn gin tip) th LSR nh k gi bn tin Hello n cng UDP n a ch IP xc nh c khai bo khi thnh lp cu hnh. Pha nhn bn tin ny c th tr li li bng bn tin Hello khc truyn ngc li n LSR gi v thit lp cc phin LDP thc hin nh trn.

2.3.2 Cu trc bn tin LDP.

Trao i bn tin LDP thc hin bng cch gi cc LDP-PDU (LDP- Protocol Data Unit n v d liu giao thc) thng qua cc phin LDP trn kt ni TCP. Mi LDP-PDU c th mang mt hay nhiu bn tin v cc bn tin ny khng nht thit phi lin quan n nhau. 2.3.2.a LDP-PDU. Mi PDU ca LDP bao gm mt header LDP v theo l mt hay nhiu bn tin LDP. Phn header LDP c dng nh sau:

Hnh 2.8: LDP header.

- di PDU (2 octet): Tng di PDU tnh theo octet, khng tnh trng Version v trng di PDU. - Nhn dng PDU (PDU Identifier) : Nhn dng khng gian nhn ca LSR gi bn tin ny. 4 octet u tin l gi tr duy nht ton cc nhn dng LSR, nh a ch IP c gn cho LSR. 2 octet cui nhn dng khng gian nhn bn trong LSR. Vi LSR c khng gian nhn ln, trng ny c gi tr bng 0. 2.3.2.b nh dng bn tin LDP. Tt c cc bn tin LDP u c khun dng nh sau:

Hnh 2.9:Khun dng bn tin LDP.



- Bit U (Unknown): Bit bn tin cha bit. Lun l 0 v c t LDP khng c kiu bn tin Unknown. (Nu bit ny bng 1 th bn tin khng th c thng dch pha nhn, lc bn tin b b qua m khng c phn hi.) - Kiu bn tin: ch ra kiu bn tin l g. Cc loi bn tin LDP c trong bng:

Bng 2.1: Cc loi bn tin LDP.

Tn bn tin Gi tr

Thng bo 0x0001 Hello 0x0100 Khi to 0x0200 Duy tr 0x0201 a ch 0x0300 Thu hi a ch 0x0301 Hon i nhn 0x0400 Yu cu nhn 0x0401 Gii phng nhn 0x0403 Thu hi nhn 0x0402 Hy b yu cu nhn 0x0404

- di bn tin: di ca bn tin tnh theo octet, bao gm phn nhn dng bn tin v cc thng s. - ID bn tin: L nhn dng duy nht ca bn tin, gip kt hp cc bn tin, thng bo vi cc bn tin khc.

2.3.3 Cc bn tin LDP.

Hello : c trao i trong sut qu trnh hot ng ca LDP. Khi to: c gi i khi bt u mt phin LDP gia hai LSR trao i

cc tham s, cc ty chn phin. Cc tham s ny gm: o Ch phn b nhn. o Cc gi tr b nh thi. o Phm vi cc nhn s dng trong knh gia 2 LSR .

C 2 LSR u c th gi cc bn tin Khi to v LSR s tr li bng bn tin Duy tr nu cc tham s c chp nhn. Nu c mt tham s no khng c chp nhn th LSR tr li thng bo c li v phin kt thc.

Duy tr: c gi nh k khi khng cn bn tin no cn gi m bo cho mi thnh phn LDP bit rng LDP khc ang hot ng tt. Trng hp khng xut hin bn tin Duy tr hay mt s bn tin LDP khc trong



mt khong thi gian nht nh th LSR s xc nh i tc LDP c s c v phin chm dt.

Hon i nhn: c s dng qung b gn kt nhn gia FEC v nhn Thu hi nhn: Thc hin qu trnh ngc li vi bn tin Hon i nhn.

Bn tin ny s dng trong trng hp: o Khi c s thay i trong bng nh tuyn, lc LSR khng cn

nhn ra FEC na. o Thay i cu hnh LSR lm tm dng vic chuyn nhn cc gi

trong FEC . Gii phng nhn: c s dng bi LSR khi nhn c chuyn i nhn

m n khng cn thit na. iu thng xy ra khi LSR gii phng nhn thy nt tip theo cho FEC khng phi l LSR qung b lin kt nhn trn FEC .

Yu cu nhn: bn tin ny s dng trong ch hot ng gn nhn theo yu cu, LSR s yu cu gn nhn t pha LSR k cn pha downstream bng bn tin ny.

Hy b yu cu nhn: Nu bn tin Yu cu nhn cn phi hy b trc khi c chp nhn (do nt k tip trong LSP yu cu thay i), th LSR yu cu s loi b yu cu trc bng bn tin ny.

2.3.4 LDP iu khin c lp v phn phi theo yu cu.

V d di y minh ha vic s dng bn tin Yu cu nhn v bn tin Hon i nhn trong ch cng b nhn theo yu cu v iu khin LSP c lp. Trnh t thi gian trao i cc bn tin LDP gia cc i tc thit lp mt LSP t router li vo R1 qua R2 ri n router li ra R3 cho mt FEC c prefix l a.b/16. R1 khi to tin trnh bng cch yu cu mt nhn cho FEC a.b/16 t hop k ca n l R2. V s dng iu khin c lp nn R2 tr mt nhn v cho R1 trc khi R2 nhn c nh x nhn t pha downstream l R3. C R2 v R3 p ng bng bn tin Hon i nhn, kt qu l trong FIB ca R1 v LFIB ca R2, R3 c cc entry gn kt nhn hnh thnh nn ng chuyn mch nhn LSP.



Hnh 2.10: LDP iu khin c lp v phn phi theo yu cu.

LDP cn h tr cc ch phn phi nhn khc. Khi cu hnh ch cng b

khng cn yu cu, cc router khng dng bn tin Yu cu nhn. Nu iu khin tun t c cu hnh trn mi giao din, cc yu cu nhn s lm cho cc bn tin Hon i nhn c tr v theo th t t R3 n R2 ri v R1. iu ny c ngha l nh x nhn din ra u tin router li ra, sau ln lt ngc v n router li vo.

2.4 GIAO THC CR-LDP (Contrain-based Routing LDP). CR-LDP l giao thc m rng t LDP (RFC 3212) nhm h tr c bit cho nh tuyn rng buc, k thut lu lng v cc hot ng d tr ti nguyn. Cc kh nng ca CR-LDP ty chn bao gm thng lng cc tham s lu lng nh cp pht bng thng, thit lp v cm gi quyn u tin.

2.4.1 M rng cho nh tuyn rng buc.

CR-LDP b sung thm cc i tng Type-Length-Value mi sau y (RFC 3212):

Tuyn tng minh ER (Explicit Route). Chng tng mnh ER-Hop (Explicit Route Hop). Cc tham s lu lng.



S ln chim (Preemptions). Nhn din LSP (LSPID). Ghim tuyn (Route Pinning). Lp ti nguyn (Resource Class). CR-LSP FEC.

Mt s th tc mi cng c b sung h tr cc chc nng cn thit : Bo hiu ng (Path Signalling). nh ngha cc tham s lu lng. Qun l LSP (quyn u tin, cam kt qun tr...).

CR-LDP s dng c ch gn nhn theo yu cu v iu khin tun t. Mt LSP c thit lp khi mt chui cc bn tin Yu cu nhn lan truyn t LSR li vo n LSR li ra, v nu ng c yu cu tha mn cc rng buc (v d nh bng thng kh dng), th cc nhn mi c cp pht v phn phi bi mt chui cc bn tin Hon i nhn lan truyn ngc v LSR li vo. Vic thit lp mt CR-LSP c th tht bi v nhiu l do khc nhau v cc li s c bo hiu bng bn tin Thng bo.

2.4.2 Thit lp mt CR-LSP (Constrain-based Routing LSP).

thit lp mt LSP theo mt con ng nh trc, CR-LDP s dng i tng tuyn tng minh ER. ER c cha trong cc bn tin v nhn.

Hnh 2.11: Thit lp LSP vi CR-LDP.

Gi s LSR A mun thit lp mt con ng tng minh l B-C-D. thc hin vic ny, LSR A xy dng i tng ER cha tun t 3 nt tru tng l LSR B, LSR C, LSR D. Mi nt c i din bng mt a ch IP prefix. LSR A sau xy dng mt bn tin Yu cu nhn c cha i tng ER mi to. Khi bn tin c to xong, LSR A s xem xt nt tru tng u tin trong i tng ER l LSR B, tm kt ni n LSR B v gi bn tin Yu cu nhn trn kt ni . Khi LSR B nhn bn tin Yu cu nhn, LSR B nhn thy n l nt tru



tng u tin trong i tng ER. LSR B sau tm kim nt tru tng tip theo l LSR C v tm kt ni n LSR C. Sau LSR B thay i i tng ER v gi bn tin Yu cu nhn n LSR C, lc ny i tng ER ch gm LSR C v LSR D. Vic iu khin bn tin ny ti LSR C tng t nh LSR B. Khi bn tin n LSR D, LSR D nhn thy n l nt cui cng trong i tng ER. V vy, LSR to mt bn tin Hon i nhn v gi n n LSR C. Bn tin ny gm i tng nhn. Khi nhn bn tin ny, LSR C dng nhn cha trong bn tin cp nht LFIB. Sau , LSR C gi bn tin Hon i nhn n LSR B. Bn tin ny cng cha nhn m LSR C qung b. Vic iu khin bn tin Hon i nhn LSR B tng t LSR C. Cui cng LSR A nhn c bn tin v LSP c thit lp theo con ng nh tuyn tng minh cho trc mang thng tin v ti nguyn cn phi d tr.

2.4.3 Tin trnh d tr ti nguyn.

Hnh 2.12 th hin tin trnh d tr ti nguyn. Khi mt nt CD-LDP nhn c mt bn tin Yu cu nhn, n gi iu khin tip nhn - AC (Admission Control) kim tra xem nt ny c cc ti nguyn c yu cu khng. Nu c ti nguyn kh dng, iu khin tip nhn AC d tr n bng cch cp nht bng ti nguyn (Resource table). Sau bn tin Yu cu nhn c chuyn tip n nt MPLS k sau. Khi nt CD-LDP nhn bn tin Hon i nhn, n lu thng tin nhn v giao din vo bng LIB, lu thng tin CR-LSP c yu cu vo c s thng tin tuyn tng minh ERB (Explicit Route infomation Base). Ri n gi qun l ti nguyn-RM (Resource Manager) to mt hng i phc v cho CR-LSP c yu cu, v lu Service ID ca n vo bng ERB. Cui cng, n chuyn tip bn tin Hon i nhn ti nt MPLS k trc.



Hnh 2.12: Tin trnh d tr ti nguyn.

2.5 GIAO THC D TR TI NGUYN RSVP-TE. Nh tn gi ca n, giao thc dnh trc ti nguyn RSVP (Resource

reSerVation Protocol ) dng dnh trc cc ti nguyn cho mt phin lm vic (dng lu lng) trong mng Internet. Kha cnh ny ca Internet l khc so vi d nh thit k h thng nm bn di ban u l ch dng h tr cc dch v n lc ti a m khng xem xt n cc yu cu c xc nh trc v cht lng dch v hay c tnh lu lng ca ngi s dng. RSVP c d tnh m bo hiu nng bng vic dnh trc cc ti nguyn cn thit ti mi nt tham gia trong vic h tr dng lu lng (chng hn nh hi ngh video hay audio). Cn nh rng IP l giao thc khng hng 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 tn cho ng i .

RSVP c mt s c ch cn thit thc hin bo hiu phn phi nhn nhm rng buc nh tuyn. IETF chun ha phn m rng k thut lu lng RSVP-TE, nh ngha cc ng dng ca RSVP-TE nh h tr phn phi nhn theo yu cu cp pht ti nguyn cho cc LSP nh tuyn tng minh. Cch dng RSVP-TE h tr ti nh tuyn make before break, theo di ng thc s c chn qua chc nng ghi tuyn cng nh h tr u tin v ln chim.



Nguyn l chc nng ca RSVP l thit lp d tr cho lung gi n hng. Cc bn tin RSVP thng i theo con ng hop-by-hop ca nh tuyn IP nu khng hin din ty chn tuyn tng minh ER. Cc router hiu RSVP dc theo ng c th chn v x l bn tin bt c lc no. RFC 2205 nh ngha 3 kiu bn tin RSVP: thit lp d tr (reservation setup), tear down v error. Ngoi ra RSVP-TE cn nh ngha thm bn tin Hello.

2.5.1 Cc bn tin thit lp d tr RSVP.

RSVP s dng khi nim d tr u nhn. Trc tin u gi pht i mt bn tin PATH nhn din mt lung v cc c tnh lu lng ca n. Bn tin PATH cha mt session-ID, sender-template, label-request, sender-Tspec v ty chn l i tng tng minh ERO (Explicit Router Object).

- Session-ID cha mt a ch ch i km mt nhn dng hm 16 bit (tunnel ID) nhn din mt ng hm LSP. Nh trnh by chng trc, ch c LSR li vo mi cn bit v mt FEC c gn vo mt ng hm LSP. Do khng ging nh LDP, FEC nh x vo ng hm LSP khng bao gm bt k bn tin RSVP no.

- i tng label-request h tr ch cng b nhn theo yu cu. - Sender-template cha a ch IP ca u gi i km vi mt LSP ID c h tr

phng thc make before break khi thay i ng i ca mt ng hm LSP. - c tnh lu lng Tspec s dng tc nh (peak rate), thng token (token

bucket) nh ngha tc v kch thc bng pht, n v khng ch ti thiu (minimum policed unit) v kch thc gi ti a. Khi bn tin i n ch, bn nhn p ng bng mt bn tin RESV nu n ng khi to vic gn kt nhn c yu cu trong bn tin PATH. Bn tin RESV c truyn v theo chiu ngc li so vi bn tin PATH bng cch dng thng tin hop k trc trong bn tin PATH. RESV cng cha cng session-ID nh bn tin PATH tng ng, i tng ghi tuyn ty chn (route record) v thng tin l thuc kiu d liu (reservation style). Kiu FF (Fixed Filter) c mt nhn v Tspec c n nh cho mi cp gi-nhn (sender-receiver). Kiu SE (Share Explicit) n nh mt nhn khc nhau cho mi sender, nhng chng cng phi p dng cho mt lung d liu r rng. i tng record-route ghi nhn tuyn ng thc t c chn bi LSP bt u t li ra dn ngc v li vo. N c th c mt route dng ghim mt tuyn tng minh th lng bng cch copy tuyn ghi c trong bn tin RESV sang i tng tng minh ERO trong mt bn tin khc c gi theo chiu ngc li.



Hnh 2.13: M t lung ca bn tin RSVP trong vic thit lp 1 LSP.

2.5.2 Cc bn tin Tear Down, Error v Hello ca RSVP-TE.

RSVP-TE nh ngha hai bn tin dnh cho vic gii ta LSP l PATH TEAR v RESV TEAR. Hai bn tin ny c gi theo chiu ngc vi bn tin PATH v RESV tng ng. Bn tin TEAR xa b bt k trng thi ci t c lin quan n bn tin PATH hay RESV. Cc bn tin TEAR cng c th dng xa cc trng thi p ng cho mi li bc u tin trong hot ng ti nh tuyn. C cc bn tin thng bo li cho bn tin PATH v RESV cng nh bn tin RESV CONFIRMATION ty chn. Cc bn tin li cho bit c vi phm chnh sch, m ha bn tin hay mt s c no khc. V d khi mt LSP thy rng khng th h tr Tspec c t trong mt bn tin RESV, n s khng chuyn tip RESV v cho pha upstream, thay vo n s to ra mt bn tin RESV ERROR gi cho pha downstream xa b n lc thit lp LSP. Tuyn tng minh v cc ty chn record-route ca RSVP-TE c mt s cc m li phc cho vic debug. Bn tin Hello ty chn cho RSVP-TE, n cho php mt LSP pht hin ra mt neighbor b li nhanh hn khi so vi RSVP lm ti tnh trng hoc pht hin li ng truyn bng mt giao thc nh tuyn IP. iu ny kh hu ch trong vic ti nh tuyn nhanh.

2.5.3 Thit lp tuyn tng minh iu khin tun t theo yu cu.

S m rng ca RSVP dng h tr MPLS trong vic thit lp cc LSP bng cch s dng hay khng s dng vic t trc ti nguyn. Nhng m rng ny cng dng ti nh tuyn LSP, cn bng ti, nh tuyn cng bc v pht hin lp vng. Nhng m rng ny ca RSVP phn nh nhiu hot ng trong LDP



nh ni trn. Cc host v cc router h tr c RSVP v MPLS c th kt hp cc nhn v cc dng lu lng RSVP. Mi ln mt LSP c thit lp, lu lng i qua ng dn ny c xc nh bi gi tr nhn c gn vo gi ti li vo ca LSP. Tp cc gi c n nh cng gi tr nhn thuc v cng mt FEC v cng ging nh tp cc gi tr nhn n nh cho dng lu lng cho RSVP. Khi cc nhn c kt hp vi cc dng lu lng, th router c th nhn ra cc trng thi dnh trc RSVP tng ng cho mi gi, da trn gi tr nhn ca gi.

Ta xt v d trong hnh sau y v vic trao i bn tin RSVP-TE s dng i tng tng minh ERO ci t mt LSP i qua mt con ng khng phi l ng ngn nht. Router R1 s n nh FEC a.b/16 cho mt ng hm LSP v n tnh ra mt tuyn tng minh l R4-R5-R3 i n hop k cho FEC . R1 khi to vic thit lp bng cch pht ra mt bn tin PATH n R4 vi mt ERO, Tspec, sender-template (cha a ch sender) v mt i tng nhn yu cu label-request. Mi bn tin PATH lin quan n ng hm ny u mang session-ID v filter-spec nguyn thy ca bn gi sender R1 gi mi tng quan vi nhau. Tip theo, R4 tip nhn yu cu v gi bn tin PATH n router k tip ghi trong ERO l R5. n lt mnh, R5 gi bn tin ny n egress-router R3. Ti ch n ca bn tin PATH, R3 xc nh rng lin kt chng R3-R5 c th h tr cho yu cu v l hop cui cng trn ng dn cho FEC a.b/16. R3 p ng bng bn tin RESV c cha ERO, Tspec ca dung lng d tr, mt filter spec tha mn bn gi, v gn mt nhn null ngm (implicit null) cho chng lin kt ny. Theo RFC 3031, nhn null l mt quy c c dng trong phn phi nhn cho php egress-LER bo hiu cho i tc upstream bit rng y l hop p cng ca LSP, do vy cn g nhn nh ca stack. Tip theo, R5 thu np bn tin RESV yu cu cho chng R5-R4, n nh nhn B v gi bn tin RESV n hop k trc trong ERO l R4. Cui cng R4 chp nhn yu cu, n nh nhn A v gi RESV v R1. n lc ny th LSP thit lp xong v cc gi c nhn cho FEC a.b/16 c chuyn tip qua ng hm. Khc vi giao thc LDP, cc bn tin RSVP-TE khng mang FEC, v ch duy nht R1 cn bit v nh x gia cc FEC v tuyn ng c nh trc .



Hnh 2.14: Thit lp LSP vi RSVP-TE.

2.5.4 C ch Make-before-break.

Make-before-break (thit lp trc khi hy) l mt c ch RSVP-TE cho php thay i mt s c tnh ca ng hm (nh l bng thng v ng i) m khng lm mt d liu v khng cn t trng lp bng thng (double-booking bandwidth).

Hnh 2.15 : S v d cho Make-before-break.

Bng thng c ch nh trc khi bt k bng thng no c dnh ring t mng. Nu router A truyn tn hiu yu cu 35Mb n mng, n s i trn ng path l A-B-F. Khi bng thng cn li c sn trn router A-B l 10Mb, trn B-F l 65Mb. iu g s xy ra khi router A mun tng kch thc bng thng dnh



ring ca n ln 80Mb (tng thm 45Mb). Lc ny ng i A-B-F khng th p ng c na. Bt buc bng thng ny phi i ng di qua router C v D, lc ny th bng thng sn c l 100Mb. Trong mt khong thi gian ngn, router A dnh ring bng thng qua c hai ng v v th dnh ring tng cng l 115Mb (35Mb ca tuyn trn v 80Mb ca tuyn di). Tuy nhin s dnh ring 35Mb sm c gii phng sau khi dnh ring 80Mb c to ra. Nguyn tc ca make-before-break l lm cho ng hm khng gii phng s dnh ring c n khi c s dnh ring mi thay th. iu ny gip lm gim ti thiu vic mt d liu.

Kiu dnh ring chia s tng minh (Share Explicit Reservation Style). Tng t nh trn, router A c gng dnh ring 80Mb qua path A-C-D-B-F

nhng khng th. V hin gi bng thng sn c trn B-F ch cn 65Mb. Router A c th ct b dnh ring trn ng A-B-F ri sau xy dng dnh ring trn ng A-C-D-B-F. Nhng khng nn lm nh vy, c cch tt hn khc phc hin tng ny. RSVP c mt kh nng c gi l chia s tng minh (SE). SE l mt kiu dnh ring cho php mt LSP ang tn ti chia s bng thng vi chnh n trnh xy ra t trng (double booking).

Hot ng SE gm hai phn: - Yu cu kiu dnh ring SE t mng. - Xc nh s dnh ring yu cu trng vi s dnh ring ang tn ti chia s

bng thng. u ng hm c yu cu dnh ring kiu SE s dng mt c (flag) trong i

tng Session-Attribute. Mi s dnh ring RSVP c xc nh duy nht bng mt b nm (Sender

Address, LSP ID, Endpoint Address, Tunnel ID v Extended Tunnel ID). Nu hai thng ip Path c cha 5 yu cu ny trng nhau th chng quan tm ti cng mt s dnh ring. a ch bn gi Sender Address l RID (Router ID) ca u ng hm. a ch kt thc Endpoint Address l RID ca cui ng hm. Extended Tunnel ID l 0 hoc a ch IP trn b nh tuyn, n c dng trong vn bo mt. Tunnel ID l ch s giao tip ng hm ti u ng hm. LSP IP nh l b m, mi ln ng hm thay i bng thng yu cu hay i ng i, LSP IP tng ln 1.

Nguyn tc dnh ring SE cho MPLS TE l nu hai s dnh ring c cc phn nm trong b nm k trn ging nhau, ch khc LSP ID (khc LSP) nhng chng vn c chia s bng thng. Theo cch ny th RESV 1 v RESV 2 c php cng tn ti n khi RESV 1 b xa khi mng. Sau khi RESV 2 c chia s bng thng vi RESV 1, th RESV 1 s khng c gng s dng bng thng cng thi im vi RESV 2 na.



2.5.5 Gim lng overhead lm ti RSVP.

RSVP l giao thc trng thi mm (soft-state), tin trnh pht mt bn tin PATH v RESV hi p tng ng phi c nh k lm ti, thng khong 30s mt ln. Phng php lm ti phng cc bn tin b mt v trong trng hp nh tuyn tng chng t ng chuyn d liu ti nguyn sang ng mi khi c bt k thay i nh tuyn IP. Vic x l khi to cc bn tin PATH v RESV ln hn nhiu so vi vic lm ti trng thi mt bn tin nhn trc , tuy nhin vi s lng ln cc LSP th vic x l lm ti c nh hng ng k n hiu nng. Mt cch gii quyt l lm tng chu k lm ti, nhng li lm tng ch bo hiu khi mt bn tin. Mt gii php cho hn mc x l v vn tr bo hiu. C ch ny bao gm vic b gn bn tin gim ti x l, cng nh cc cch router d dng nhn dng bn tin khng thay i hn. Vic hi bo bn tin cng c b sung chuyn ti tin cy bn tin RSVP v x l trng hp mt cc bn tin PATH TEAR v RESV TEAR v hai bn tin ny khng c lm ti trong hot ng RSVP. Cui cng, gii php ny nh ngha mt bn tin tng kt (summary) lm ti trng thi m khng yu cu truyn ton b bn tin lm ti. Cc ci tin ny nhm gim lng overhead lm ti ca RSVP trong mng MPLS.

2.6 GIAO THC BGP (Bored Gateway Protocol).

2.6.1 Giao thc BGP.

BGP l mt giao thc nh tuyn gn kt tp hp cc mng cung cp dch v trn Internet. V n ch l giao thc s dng gia cc nh cung cp, RFC 2017 m rng BGP h tr phn phi nhn MPLS c th thit lp cc LSP lin mng.

Trong BGP c khi nim quan trng l s AS h t tr (Autonomous System) duy nht, c nh ngha l mt tp hp router thc hin mt chnh sch nh tuyn ngoi thng nht c th nhn thy i vi router ca AS khc. BGP khng truyn cc thng tin topo ni gia cc AS, n ch cung cp cc thng tin v cc prefix a ch m c th tm n hoc c th qu giang qua n. S dng BGP gia cc router bin (border) ni trong mt AS c gi l BGP ni (iBGP), cn s dng BGP gia cc router trong cc AS khc nhau c gi l BGP ngoi (eBGP).

BGP chy trn mt phin TCP v n cn tin cy, phn pht ng th t. N c 3 giai on hot ng: thit lp phin, trao i bn tin cp nht v chm dt phin. Trong thit lp phin, cc i tc BGP (BGP peer) trong cc AS ln cn trao i cc bn tin OPEN c cha ch s AS, mt gi tr keep-alive timeout v cc tham s ty chn. Cc BGP peer nh k trao i bn tin keep-alive, nu pht hin timeout s chm dt phin. Sau khi thit lp phin th cc BGP peer trao i cc bn tin UPDATE c cha prefix a ch c th n c hin hnh (rechability), c gi l thng tin hin hnh tng mng NLRI (Network Layer Rachability



Information). Sau khi trao i ng b khi to, cc thay i nh tuyn gia tng c lin lc bng bn tin UPDATE.

Ni dung bn tin BGP UPDATE c 3 phn: cc tuyn thu hi (withdrawn route), mt danh sch cc prefix a ch NLRI v mt danh sch ty chn cc thuc tnh lin quan. Cc i tc BGP to quyt nh chnh sch cc b khi xem cng b mt NLRI vi cc thuc tnh ng c chn hay thu hi thng bo trc . Chnh sch thng dng l chn NLRI c prefix a ch c t trng nht, chn mt s ng c hop AS t nht.

Khi bn tin UPDATE cha thng tin NLRI, mt s thuc tnh ng l bt buc, mt s l ty chn. Cc thuc tnh bt buc l: ORIGIN, AS-PATH v NEXT-HOP. ORIGIN nhn din ngun gc ca NLRI, v d n c c qua giao thc nh tuyn ni hay ngoi. AS-PATH lit k mt path-vector gm mt tp AS i qua n thi im hin ti (mt chui th t cc AS). V chiu di ca AS-PATH thng l yu t quyt nh chn mt tuyn, nn BGP c gi l giao thc nh tuyn path-vector. Cc router s dng AS-PATH trnh loop bng cch khng chuyn cc thng bo tuyn c cha s AS ca chng. NEXT-HOP nhn din a ch IP ca router bin cn dng tm n NLRI. BGP c mt s tham s ty chn c th thc hin mt dng cn bng ti : LOCALPREF v MED. LOCALPREF cho php AS u gi ch nh mt s u tin (preference) nh tuyn lu lng i ra trn nhiu lin kt n AS khc. Trong khi MED cho php mt AS pha nhn ch nh mt u tin cho lu lng n t mt AS khc.

2.6.2 Kt ni MPLS qua nhiu nh cung cp dch v.

BGP m rng phn phi nhn MPLS nm trong mt phn ca NLRI. Cc BGP peer thng lng h tr cho kh nng ty chn ny vo lc thit lp phin. Th tc c bn l k sinh vic phn phi nhn theo kiu khng cn yu cu song song vi vic phn phi tuyn BGP. BGP c th dng thit lp phn phi nhn cho cc LSP i xuyn qua cc mng ca cc nh cung cp khc nhau.



Hnh 2.16: BGP phn phi qua nhiu Autonomous System ( AS ).

Hnh trn gm 3 h t tr AS: A, B, C. AS-C cung cp cho khc hng prefix a ch (FEC) a.b/16. Router C3 qung b n nh mt NLRI cho AS-A v AS-B bng bn tin BGP UPDATE c cha NEXT-HOP v AS-PATH. Bn tin UPDATE c gi t C3 n A3 cn mang mt nh x t FEC a.b/16 sang nhn L. Router A3 trong AS A thu np tt c thng bo ny vo trong bng RIB ca n (c th lm c nh thng qua mt li cc phin iBGP). Nhm tm cch tt nht chuyn tip cc gi n prefix a.b/16, A1 c th xc nh rng ng ngn nht l qua hop k A3 s dng nhn L. Nh nh tuyn ni v giao thc phn phi ca minh, A1 cng bit rng tuyn tt nht n A3 l i qua A2 s dng nhn M. Kt qu l khi chuyn gi n prefix a.b/16, A1 thm nhn L ln gi ri thm tip nhn ln nh stack. Nh vy, mt LSP c chui vo trong mt ng hm LSP khc. LSP 1 bn ngoi ko di t A1 n A3. Trong khi , LSP 2 ko di t AS-A n AS-C v c mt on chui trong LSP 1.

2.7 KHI NIM DCH V TCH HP V DCH V PHN BIT.

2.7.1 Khi nim dch v tch hp (Intserv).

T chc IETF u nhng thp k 90 a ra cc cu trc Intserv nh mt gii php hu hiu m bo QoS trn nn mng IP. Ct li ca Intserv l m bo QoS cho tng lung IP vi m. Lung IP vi m l mt chui cc gi tin IP c chung 5 tham s ging nhau. C th, mt lung IP vi m uc xc nh bi 5 tham s: a ch IP u gi, a ch IP u nhn, s th t ca cng gi, s th t ca cng nhn, loi hnh ca giao thc uc s dng trn lp truyn ti (TCP/UDP) cho lung IP ang uc xt.



Mt mng Intserv in hnh cha cc b nh tuyn bin v cc b nh tuyn li. Trc khi bt u truyn d liu ca mt lung IP vi m, u gi thng bo mt s s liu lin quan n lu lng s c chuyn cho b nh tuyn bin. Bn cnh , bn gi cng chuyn n b nh tuyn bin yu cu QoS cho lung IP. Nhng s liu lu lng v QoS s c b nh tuyn bin s dng tnh dung lng cn thit cho lung IP c quan tm. Sau giao thc bo hiu RSVP s lm nhim v xc nh ng truyn (kt hp vi cc giao thc ci t ti cc b nh tuyn) v chim gi dung lng dc ng truyn cho lung IP. Nu s chim gi dung lng ti tt c cc b nh tuyn dc ng truyn u thnh cng, cc gi ca lung IP bt u c truyn ti t u gi n u nhn. Trong trng hp c bt k 1 lin kt dc ng truyn khng c dung lng cn thit, qu trnh chim gi s b dng v thng tin v s chim gi khng thnh cng s c chuyn n u gi bng mt thng tin ring ca RSVP. Lung IP vi m s b chn khng c phc v. Cn lu rng ngay c khi ng truyn c xy dng thnh cng, trong qu trnh truyn ti cc gi ca lung IP vi m, cn thit phi c s kim tra dung lng c chim gi mt cch nh k, u n nh giao thc bo hiu RSVP m bo trng thi c dng s dung lng cn thit dc ng truyn. thc hin qu trnh chim gi dung lng, cng nh kim tra trng thi chim gi lin quan n tng lung IP vi m, mi b nh tuyn trong c ch Intserv cn phi lu tr tt c cc d liu v c tnh cp nht ca tt c cc lung gi vi m ang tn ti trong mng. ng thi tt c cc b nh tuyn phi c chc nng hot ng c cng vi giao thc RSVP. Tuy nhin, mt b nh tuyn bnh thng trong mng IP ngy nay phi x l cng mt lc mt lng rt ln cc lung IP vi m. V th, lu tr, truyn ti v x l tng lung IP vi m to ra mt lu lng bo hiu khng l, lm gim ng k hiu sut hot ng ca b nh tuyn. Nhc im ny l nguyn nhn v sao cu trc Intserv ch c tnh kh thi trong mng c tm bao ph nh. Vi mng IP tri rng ton cu nh mng Internet hin nay, trng i s u t v a vo hot ng ph bin l khng thc t.

2.7.2 Khi nim dch v phn bit (Diffserv).

M hnh kin trc dch v phn bit DiffServ c coi l bc pht trin tip theo ca m hnh tch hp dch v IntServ. Hng tip cn ca m hnh ny l khng x l theo tng lung lu lng ring bit m ghp chng vo 1 s lng hn ch cc lp lu lng m bng thng v cc ti nguyn mng khc c ch nh trong cc lp lu lng ny. Mt khc, DiffServ hng ti x l trong tng vng dch v phn bit DS (Differential Service) thay v x l t u cui ti u cui nh trong m hnh tch hp dch v IntServ.



Trong cu trc DiffServ, b nh tuyn c chia lm 2 th loi, b nh tuyn bin v b nh tuyn li. Tuy nhin, khc vi m hnh IntServ, ch c cc b nh tuyn bin cn kh nng x l cc lung IP vi m, cc b nh tuyn li thay v x l mt lng rt ln cc lung IP vi m th n ch x l vi lung IP tng trong cu trc DiffServ. Lung IP tng cha tt c cc gi ca lung IP vi m thuc v cng mt chng loi. Ch cn nh ngha mt vi chng loi c bn, yu cu vi b nh tuyn tr nn n gin hn rt nhiu. C ch DiffServ a ra s phn loi cho 3 loi hnh dch v: Dch v u tin, dch v m bo v dch v ng bin theo kh nng ti a. Dch v cui cng chnh l dch v c cung cp bi mng Internet hin nay. ng vi mi loi hnh dch v, DiffServ nh ngha cch thc x l cc gi tin IP ti b nh tuyn li. Ni cch khc, ti cc b nh tuyn li, cc gi IP s c x l tng ng vi loi hnh dch v ca chng. Gi IP ca dch v u tin nhn c cch x l chuyn nhanh, cn gi IP ca dch v m bo nhn c cch x l chuyn m bo. Nguyn l hot ng ca kin trc DiffServ gm cc c im c bn sau. Khi bt u i vo mng DiffServ m trc tip l b nh tuyn bin, gi IP s c phn loi. B nh tuyn bin s thc hin vic phn loi bng cch kim tra m DSCP (DiffServ Code Point) cha chng loi dch v nm trong phn u gi cng vi mt s d liu khc lin quan n lung vi m ca gi tin IP (a ch u gi, a ch u nhn). Sau khi chng loi ca gi IP c xc nh, b nh tuyn bin s thc hin mt s iu chnh cho gi tun theo nhng tnh cht c nh ngha cho chng loi ca n. Ti b nh tuyn li, gi IP s c x l trn c s duy nht l chng loi ca n. B nh tuyn li ch c nhim v kim tra chng loi ca gi IP v chuyn tip gi IP theo cch m chng loi c nhn bao gm: nh tuyn cho gi, xp gi vo b m thch hp.

2.8 TNG KT. Trong chng ny gii thiu cc chc nng nh tuyn v bo hiu c bn trong mt phng iu khin ca MPLS h tr t ng ha vic cu hnh ca mt phng chuyn tip. Trnh by mt s giao thc bo hiu MPLS thc hin phn phi nhn theo cc c tnh chung nh tuyn tng minh hay tuyn tng chng, phn phi theo yu cu hay khng cn yu cu... Cnh cng trnh by khi nim dch v tch hp v dch v phn bit, l cc khi nim quan trng khi nhc ti iu khin lu lng da trn cht lng dch v QoS. Vi cc giao thc c bn trn s gip chng ta c c c s nghin cu v k thut lu lng TE (Traffic Enginneering ) da trn MPLS, mt gii php rt hiu qu trong vic iu khin cc lung d liu i qua mng sao cho ti u ha vic s dng ti nguyn v hiu nng ca mng. Chng ta s tm hiu c th vn ny trong chng sau.

K Thut Lu Lng Trong MPLS. ChngIII:K thut lu lng trong MPLS.


Chng III : K THUT LU LNG TRONG MPLS.

3.1 K THUT LU LNG (TRAFFIC ENGINEER ). K thut lu lng (TE) l qu trnh iu khin cc lung lu lng qua mng sao cho ti u ha vic s dng ti nguyn v hiu nng mng.

3.1.1 Cc mc tiu trin khai k thut lu lng.

3.1.1.a Phn loi. Cc mc tiu trin khai k thut lu lng c th phn chia thnh hai hng sau:

- Hng lu lng. - Hng ti nguyn.

Cc mc tiu hng lu lng lin quan n vic tng cng QoS cho cc lung lu lng, cc mc tiu nh: gim thiu tr v mt gi, tng ti a thng lng v tun th cc hp ng mc dch v... Cc mc tiu hng ti nguyn lin quan n vic ti u ha s dng ti nguyn. Bng thng l mt ti nguyn ct yu ca mng, do chc nng trng tm ca k thut lu lng l qun l hiu qu ti nguyn bng thng. 3.1.1.b Bi ton nghn. Nghn thng xy ra theo hai hng sau:

Khi bn thn cc ti nguyn mng khng cp cho ti yu cu. Khi cc dng lu lng c nh x khng hiu qu n cc ti nguyn,

lm cho mt s tp con ti nguyn tr nn qu ti trong khi s khc nhn. C th gii quyt tc nghn bng cch: Tng dung lng hoc ng dng cc k thut iu khin nghn c bn nh:

gii hn tc , iu khin lung, qun tr hng i, iu khin lch trnh... Dng k thut lu lng nu nghn l do cp pht ti nguyn cha hiu qu

i tng gii quyt ca k thut lu lng l nghn ko di ch khng phi l nghn nht thi do bng pht lu lng.

3.1.2 Hng i lu lng.

3.1.2.a Hng i FIFO (First-In,First-Out). Hng i vo trc, ra trc l c ch mc nh cho cc gi tin khi i vo mt nt mng khi khng c s hin din ca thut ton c bit no ti . Trong hng i FIFO cc gi tin c xp vo cng mt hng i v c chuyn i theo cng mt cch m chng c sp xp trong hng i. u im chnh ca hng i FIFO l tnh n gin ca n, khng c bt k gii thut phc tp no c thit k ring cho FIFO. Trong hng i FIFO, cc gi tin c i x nh nhau.



Do hng i ny ch dng s dng cho loi dch v n lc ti a (BE) v cng l loi dch v c h tr duy nht trong mng IP truyn thng. 3.1.2.b Hng i PQ (Priority Queuing). Hng i theo u tin l s ci tin ca FIFO. Trc khi c a vo hng i tng ng, cc gi tin phi c phn loi theo tng loi dch v. Cc hng i c thit k theo u tin ca loi gi tin m n phi cha. Cc gi tin hng i c u tin thp hn ch c x l khi v ch khi khng cn bt c cc gi tin no trong cc hng i c u tin cao hn. PQ cho php ngi qun l mng cu hnh bn thuc tnh lu lng cao (high), thng thng (normal), trung bnh (medium) v thp (low). Lu lng n c gn vo mt trong bn hng i. Trong thc t ngi ta s dng hng i PQ c iu khin tc . Vi loi hng i ny, cc gi tin trong hng i c u tin cao ch c x l nu tng s gi tin trong hng i nh hn mt lng xc nh. 3.1.2.c Hng i WFQ (Weighted Fair Queuing). Bng thng ri c chia cho cc hng i ty thuc vo trng s (weight) ca chng. Xt v d: c 12 lung lu lng A,B,C...,N v trng s ca chng c nh s nh hnh sau, trong : c bn lung (D,E,F,G) c trng s 5, c hai lung trng s 4, cn trng s khc ch c mt lung.

Hnh 3.1: Nhiu lung cho mi lp lu lng.



Tng trng s: 8 + 7 + 6 + 5*4 + 4*2 + 3 + 2 + 1 = 55. Khi mi lung c trng s 5 s nhn c 5/55 phn bng thng, lung c trng s thp nht (1) s nhn c 1/55 phn bng thng v lung c trng s cao nht (8) nhn c 8/55 phn bng thng. Tng t cho cc lung c trng s khc.

3.1.3 Gii thut thng r v thng Token.

Thng r v thng Token l c ch thc hin chc nng gim st v nn dng lu lng o tc nhn hay truyn d liu. Gim st loi b gi d tha m bo tc truyn khng vt qu tc tha thun. Nn dng xp cc gi d tha ny vo hng i, v i ra hng i tc nn dng. 3.1.3.a Gii thut thng r (Leaky Bucket). M hnh thng r c th c din t hnh tng nh sau: bt chp tc nc vo thng l bao nhiu, th tc dng chy ra l khng thay i min l trong thng cn nc. Mt khi thng y nc, lng nc c thm vo s b trn v mt. Tng t nh d liu khi ti mt router trong mng nu hng i y th gi tin s b drop. Cc thng s cn ch trong m hnh thng r l kch thc ca thng v tc dng chy ra.

Hnh 3.2 Gii thut thng r.

M hnh trn c th p dng cho gi. Bt k lu lng ti c tc bin ng nh th no, lu lng ra u c tc khng thay i. 3.1.3.b Gii thut thng Token (Token Bucket). Thng Token c kch thc B, cc gi tin chy vo thng c gi l Token. Tc Token chy vo thng khng i l p. Nu s Token trong thng vt qu B, thng s trn v b mt, do B l s lng Token ti a trong thng. Trong m hnh thng Token, mi Token cho php truyn mt bit. Mi ln truyn c mt gi, th s s dng Token t thng Token dnh quyn truyn gi. Nu gi tin c di 1000 bit th 1000 Token s c ly ra t thng Token.



Hnh 3.3: Gii thut thng Token.

Gi G l kch thc gi n, mt gi l hp l khi lng Token trong thng ln hn hay bng G, ng thi lng Token trong thng c gim i G. Ngc li khi lng Token trong thng nh hn kch thc gi, gi c xem l vt mc hay khng hp l. Tu vo cc chnh sch khc nhau m cc gi hp l hoc khng hp l c x l khc nhau. Mt iu cn lu trong gii thut thng Token l tc chy vo v tc chy ra phi bng nhau. Thng token cho php d liu bng pht mt mc nht nh (kch thc B), nhng khng cho php tc chy vo thng vt qu p trong mt khong thi gian nht nh. Gii thut thng Token c th c dng trong vic sa dng lu lng hay c ng dng trong vic thc thi khng ch. Trong vic sa dng lu lng, thut ton thng Token cho php mt t bng pht ng ra, iu ny khng c thut ton thng r v tc u ra l khng i. Nh vy thng Token cho p ng ra tt hn so vi thng r. Trong vic thc thi khng ch, thng Token c th c dng c lp hay dng phi hp.

3.1.4 Gii php m hnh chng ph (Overlay Model).

Mt cch tip cn ph bin b p cc thiu st ca cc giao thc IGP (Interior Gateway Protocol) l s dng m hnh chng ph (IP over ATM hay IP over FR). Tt c cc giao thc lp 3 c kt ni trc tip vi nhau bng mt mng li full-mesh cc mng o VC. K thut lu lng c thc hin lp 2 (ATM hay FR). Nhng ni chung cc m hnh ny c nhiu nhc im sau y:



Tn km thm nhiu thit b (i hi nhiu cc chuyn mch ATM hay FR) Qun l mng phc tp: Mng lp 2 c cng c qun l ring vi nhiu tc

v h tr k thut lu lng. ng thi cc router lp 3 vi cc giao thc IGP cng phi c qun l. Vic qun l 2 lp mng ny khng tch hp c.

Pht sinh nhiu vn m rng i vi IGP do s lng qu ln cc neighbor khi kt ni full-mesh tn dng cc tin ch cung cp bi lp 2.

Tn thm bng thng cho lng overhead ca ATM hoc FR (cell tax). Khng h tr dch v phn bit (Diffserv). Mi dch v phn bit ca IP

a xung (PPP ca Frame hoc AAL5 ca ATM) u tr thnh best-effort.

Hnh 3.4: M hnh chng ph (overlay model).

3.2 MPLS V K THUT LU LNG. MPLS c ngha chin lc i vi k thut lu lng v n cung cp hu ht cc chc nng hin c m hnh chng ph nhng theo cch thch hp vi chi ph thp hn. iu quan trng l MPLS cn xut kh nng t ng ha cc chc nng k thut lu lng.

3.2.1 Khi nim trung k lu lng (Traffic Trunk).

MPLS gii thiu khi nim trung k lu lng thc hin mc tiu TE. c tnh trong mt LSR l cho php tp hp cc c tnh ca mi lung d liu i trong mng nh tc cc i, tc trung bnh v kch c bng n (burst) cc i. Nhng c tnh ny vn c trong tt c cc lung d liu, khi i vo mng MPLS nh c trung k lu lng l mt khi thu gom (aggregate) cc lung lu lng trong mng, c t bn trong mt LSP m d liu c qun l hiu qu hn. Trung k lu lng c th thu gom cc lung d liu trn cng mt lp (n lp) hay c th trn a lp.



Trong m hnh dch v a lp, mt trung k lu lng c th ng gi ton b lu lng gia mt router li vo v mt router li ra. Trong trng hp phc tp hn, lu lng ca cc lp dch v phn bit (DiffServ) vi cc c tnh la chn QoS cho cc gi tin, s c n nh vo cc trung k lu lng ring bit.

Trung k lu lng l i tng c th nh tuyn. Trung k lu lng phn bit vi LSP l ng cho trung k i xuyn qua.

Trong bi cnh hot ng, mt trung k lu lng c th chuyn t mt LSP ny sang mt LSP mi, hay nhiu trung k lu lng c th cng i chung trn mt LSP.

Trung k lu lng l n hng.

3.2.2 hnh nghim suy (Induced Graph).

hnh nghim suy gn ging nh topo o trong m hnh chng ph. N c nh x ln mng vt l thng qua vic la chn cc ng LSP cho cc trung k lu lng. Mt hnh nghim suy gm mt nhm cc nt LSR c kt ni lun l vi nhau bng cc LSP. Khi nim ny rt quan trng v bi ton qun l bng thng c bn trong mt min MPLS t ra l lm th no nh x hiu qu hnh nghim suy ln trn mng topo mng vt l. hnh nghim suy c cng thc ha nh sau: t G = ( V, E, C ) l mt hnh m t topo vt l ca mng. Trong , V l tp hp cc nt mng, E l tp hp cc ng link, C l tp hp cc kh nng v rng buc cho E v V (nh tr, dung lng...). Ta coi G l topo c s. t H = ( U, F, D ) l hnh MPLS nghim suy. Trong , U l tp con ca V gm mt nhm cc LSR ti cc u ca LSP. F l tp hp cc LSP. Tham s D l tp hp cc yu cu v ch ti cho F. Nh vy H l mt hnh trc tip v ph thuc vo cc c tnh truyn ti ca G.

3.2.3 Bi ton c bn ca k thut lu lng.

C ba vn c bn lin quan n k thut lu lng trn MPLS l: nh x cc gi tin ln cc lp chuyn tip tng ng (FEC). nh x cc FEC ln cc trung k lu lng (traffic trunk). nh x cc trung k lu lng ln topo mng vt l thng qua cc LSP.

Cc phn sau ca chng s tp trung vo vn th ba, tc l tnh ton ng i tt nht qua mng cho cc trung k lu lng sao cho mng hot ng hiu qu v tin cy. y chnh l bi ton nh x hnh nghim suy H ln topo mng c s G.



3.3 TRUNG K LU LNG V CC THUC TNH. xy dng v duy tr trung k lu lng, ngi ta tm cch m hnh ha n bng cc tham s. Mt thuc tnh l mt tham s c gn v c nh hng n cc c trng hnh vi ca trung k lu lng. Cc thuc tnh c th c gn c th thng qua hnh ng qun tr hay gn ngm n bi cc giao thc bn di khi cc gi tin c phn loi v nh x vo FEC ti li vo min MPLS. Thc t, mt trung k lu lng c th c trng ha bi:

- LSR li vo v LSR li ra ca trung k lu lng. - Tp cc FEC c nh x vo trung k. - Mt tp cc thuc tnh nhm xc nh cc c trng hnh vi ca trung k. Hai vn c bn c ngha c bit l: Tham s ha cc trung k lu lng

v nhng quy lut sp t, duy tr ng dn cho cc trung k lu lng.

3.3.1 Cc hot ng c bn trn trung k lu lng.

y l cc tin trnh khc nhau xy ra trong thi gian tn ti ca mt trung k lu lng:

- Establish: Thit lp, to ra mt trung k lu lng bng cch quyt nh mt LSP, gn cc nhn MPLS v quan trng nht l gn ti nguyn cho trung k .

- Activate: Hot ng, lm cho trung k lu lng bt u chuyn d liu bng cch dng mt s chc nng nh tuyn a lu lng vo trung k.

- Deactivate: Ngng hot ng, trung k lu lng ngng chuyn d liu bng cch dng mt chc nng nh tuyn dng vic a lu lng vo trung k.

- Modify Attributes: Thay i c tnh, thay i cc c trng ca trung k lu lng, chng hn nh bng thng kh dng.

- Reroute: Ti nh tuyn, chn mt ng i mi cho trung k lu lng (thng l do s c trong mng hay khi khi phc xong s c trong mng).

- Destroy: Hy b, loi b hon ton mt trung k lu lng ra khi mng v thu hi ton b ti nguyn cp cho n.

3.3.2 Thuc tnh tham s lu lng (Traffic Parameter).

Thuc tn

kỹ thuật lưu lượng trong mpls

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