nghiên cứu cơ chế khôi phục trong mạng mpls-te

LI CM N

Li u tin, em xin by t n i t n u t i thy ThS. T Tr Ngha, n i th t ti t n t nh h n n h em t n u t nh n hin u h n th nh u n n

Em xin h n th nh m n th t n i h B h Kh a TP HCM, th kh a in in t t n t nh i n t u n t ki n th h em t n ut thi ian ua Em xin m n th h nhim V n Ph t quan tm gip em th h n th nh tt u n n t n h k n

C n xin m n ia nh t iu kin tt nht n th chuyn t m h t Gia nh un n un n in h a n h nht tinh thn trong ut thi ian n h t

T n u t nh m u n n, em anh/ h thu h n T u n n n n a T n B u hnh Vin thn Vit Nam VNPT-HCM t iu kin thu n i un nhn thn tin t i iu hu h Em xin t n i t n t i nhn i u u

Cui n , xin i i m n n tt n Minh t, Cn Phm, Hu N Quan , N u n Cn S n, H Quan nh, T n H N Ph, Hunh Ti n Ti, N.T Thin Thanh n DD9DV un n h, n in tinh thn ti trong ut u t nh h n th nh u n n

Do hn h ki n th nn u n n khn t nh kh i nhn thi u t, em t m n nh n nhn a th n Xin h n th nh m n!

T H Ch Minh, th n n m

NGUYN AN( QUANG [email protected]

MC LC

L) G)) T()U ......................................................................................................................... 1 C(NG ) ................................................................................................................................... 3 TNG QUAN V C(UYN MC( N(N A G)AO T(C ................................................ 3

. Gii thiu MPLS .......................................................................................................................... 3 . Cc khi nim c bn trong MPLS ........................................................................................ 5 .. Min MPLS ................................................................................................................................. 5 .. Lp chuyn tip tng ng FEC ................................................................................. 6 .. Nhn v ngn xp nhn ........................................................................................................ 8 .. (on i nhn ....................................................................................................................... 10 .. ng chuyn mch nhn LSP ...................................................................................... 11 . Mt phng iu khin v mt phng chuyn tip MPLS ............................................. 13 .. Mt phng iu khin ........................................................................................................ 14

1.. Mt phng chuyn tip ...................................................................................................... 14 . nh tuyn trong MPLS .......................................................................................................... 16 .. Giao thc nh tuyn ni min )GP .............................................................................. 16 .. Giao thc nh tuyn ngoi bin m rng MP-BGP .............................................. 16 .. Cc giao thc nh tuyn rng buc v tng minh ............................................ 17 . Cc giao thc bo hiu MPLS ................................................................................................ 19 .. Giao thc LDP ........................................................................................................................ 19 .. Giao thc CR-LDP................................................................................................................. 19 .. Giao thc RSVP-TE .............................................................................................................. 21 . u im v ng dng ca MPLS .......................................................................................... 22 .. n gin ha chc nng chuyn tip .......................................................................... 22 .. ng dng k thut lu lng ......................................................................................... 23 .. Xc nh ng dn m bo QoS ti b nh tuyn bin ................................ 23 .. Mng ring o VPN .............................................................................................................. 23 .. Phn cp ng dn ........................................................................................................... 23 .. Kh nng m rng ............................................................................................................... 23 . Kt lun chng ....................................................................................................................... 24

C(NG )) ................................................................................................................................ 25 K T(UT LU LNG V CC C C( K() P(C BO V C BN TRONG MPLS ............................................................................................................................ 25

. Tng quan v k thut lu lng ....................................................................................... 25 .. Khi nim k thut lu lng ........................................................................................ 25 .. Bi ton tc nghn v k thut lu lng ................................................................. 26 .. K thut lu lng ti lp lin kt d liu ............................................................... 27 .. K thut lu lng ti lp mng ................................................................................... 29 . K thut lu lng MPLS-TE ............................................................................................... 30

. Bo v, khi phc trong MPLS-TE ....................................................................................... 33 .. S cn thit ca bo v, khi phc trong mng MPLS ......................................... 33 .. Khi nim bo v, khi phc trong MPLS-TE .......................................................... 35 .. Pht hin, thng bo li trong MPLS ........................................................................... 37 .. Phn loi cc c ch bo v, khi phc trong MPLS-TE ..................................... 39 .. K thut thit lp ng khi phc ............................................................................. 44 . Cc m hnh khi phc trong mng MPLS ....................................................................... 44

2.4.1 M hnh Makam .................................................................................................................... 44 2.4.2 M hnh Haskin ..................................................................................................................... 45 2.4.3 M hnh Hundessa ............................................................................................................... 46 2.4.4 M hnh ti nh tuyn nhanh Fast Reroute ............................................................ 46

. Kt lun chng ....................................................................................................................... 49 C(NG ))) .............................................................................................................................. 50 NNG CAO C C( K() P(C TRONG MPLS .............................................................. 50

. M hnh khi phc thc t .................................................................................................... 50 . Nng cao c ch khi phc trong MPLS ............................................................................ 53 .. C ch ti nh tuyn nhanh tin cy RFR .................................................................. 53 .. M t gii thut RFR ........................................................................................................... 54 .. C s tnh ton c ch khi phc RFR ........................................................................ 56 . Kt lun chng ....................................................................................................................... 59

CHNG )V ............................................................................................................................... 61 M P(NG V K(O ST MT S C C( BO V, K() P(C NG TRONG MPLS-TE ..................................................................................................................... 61

. Phn mm m phng NS-2 .................................................................................................... 61 4.. Kin trc module MNS v. ............................................................................................. 62

. M phng v kho st mt s c ch bo v, khi phc ng trong k thut lu lng MPLS-TE ............................................................................................................. 66 .. Xy dng Topology m phng ....................................................................................... 66 .. M phng m hnh bo v ton cc ti nh tuyn best-effort) .................... 68 .. M phng m hnh bo v Makam ............................................................................... 69 .. M phng m hnh bo v (askin ci tin ................................................................ 70 .. M phng m hnh ti nh tuyn cc b .................................................................. 71 .. M phng m hnh ti nh tuyn nhanh one-to-one .......................................... 73 . Phn tch v nh gi kt qu m phng tng hp ...................................................... 74 . Mt s gii php la chn m hnh bo v, khi phc ng dn ......................... 78 . Kt lun chng ....................................................................................................................... 80

KT LUN .................................................................................................................................. 81 T) L)U T(AM K(O ........................................................................................................... 83 P( LC: M NGUN CC C(NG TRN( M P(NG ........................................... 85

DANH MC HNH V

Hnh 1.: MPLS v m hnh tham chiu OS) .................................................................................... 4 (nh .: So snh gia chuyn tip )P v chuyn tip MPLS .................................................... 5 (nh .: Min chuyn mch nhn MPLS .......................................................................................... 6 (nh .: Lp chuyn tip tng ng trong MPLS .................................................................. 7 Hnh 1.5 : nh ngha ca mt thc th nhn trong ngn xp nhn ...................................... 8 Hnh 1.6 : Ngn xp nhn MPLS Label Stack ................................................................................ 9 (nh .: M ha ngn xp nhn trong ch khung Frame-Mode) .................................. 9 (nh .: ng chuyn mch nhn LSP ....................................................................................... 11 (nh .: Phn cp LSP trong MPLS .................................................................................................. 12 (nh .: Kin trc chc nng ca cc b chuyn mch LER/LSR ................................... 13 (nh .: (ot ng trong mt phng chuyn tip MPLS .................................................... 15 (nh .: Giao thc nh tuyn ngoi bin BGPv................................................................... 17 (nh .: Thit lp ng rng buc CR-LSP vi giao thc CR-LDP ............................... 20 (nh .: Thit lp ng rng buc TE-LSP vi giao thc RSVP-TE ............................ 21 (nh .: M hnh xp chng................................................................................................................ 27 (nh . : K thut lu lng ti lp ............................................................................................ 28 (nh .: K thut lu lng trong MPLS ...................................................................................... 31 (nh .: Tng quan c ch hot ng ca MPLS-TE ............................................................... 32 (nh . : Sa cha ton cc ................................................................................................................ 40 (nh .: Khi phc lin kt ................................................................................................................. 40 Hnh .: Khi phc nt .......................................................................................................................... 41 (nh .: Ti nh tuyn ......................................................................................................................... 42 Hnh 2.9: M hnh Makam ..................................................................................................................... 45 Hnh 2.10: M hnh Haskin ................................................................................................................... 46 (nh .: Ti nh tuyn nhanh one-to-one ............................................................................... 47 (nh .: Ti nh tuyn nhanh one-to-one sau khi tng hp ........................................... 48 (nh .: M hnh ti nh tuyn nhanh Facility ...................................................................... 48 (nh .: ng dn lu lng ti lp li v lp tp trung d liu .................................. 51 (nh .: ng dn khi phc ti lp li v lp tp trung lu lng ............................ 52 (nh .: M hnh ti nh tuyn nhanh tin cy .......................................................................... 53 (nh .: S trng thi ca gii thut RFR ............................................................................... 55 (nh .: S tnh ton c ch RFR ............................................................................................... 57 (nh .: S thi gian khi phc .................................................................................................. 59 (nh .: Kin trc chc nng nt MPLS vi module MNSv. ........................................... 63 (nh .: Qu trnh x l dnh ring ti nguyn ti mi nt ................................................. 64 (nh .: Kin trc chc nng nt MPLS vi module MNSv. m rng ........................ 65 (nh . : Topology m phng bo v, khi phc ng ........................................................ 67 Hnh 4.5 : M hnh best-effort trong NAM ..................................................................................... 69

Hnh 4.6: M hnh Makam trong NAM ............................................................................................. 70 (nh .: M hnh (askin ci tin trong NAM .............................................................................. 71 (nh .: M hnh ti nh tuyn cc b trong NAM ................................................................. 72 (nh .: M hnh ti nh tuyn nhanh one-to-one ................................................................. 73 (nh .: Biu tng hp s lng gi tin b mt trong thi gian hi t ................... 74 (nh .: Biu tng hp thi gian ngng dch v .............................................................. 76 (nh .: Biu tng hp chim dng ti nguyn ......................................................... 77

THUT NG VIT TT AAL ATM Adaptation Layer Lp tng thch ATM AS Autonomous System ( t tr ASIC Application-Specific Integrated

Circuit Mch tch hp ng dng xc nh

ATM Asynchronous Transfer Mode Giao thc truyn ti cn ng b BGP Border Gateway Protocol Giao thc nh tuyn cng bin CPU Central Processing Unit B x l trung tm CR Constraint-based Routing nh tuyn rng buc CR-LDP Constraint-based Routing Label

Distribution Protocol Giao thc phn phi nhn h tr nh tuyn rng buc

CR-LSP Constraint-based Routing Label Switched Path

ng chuyn mch nhn c nh tuyn rng buc CSPF Constraint-based Shortest Path

First Thut ton tm ng dn ngn nht trc tin da trn nh tuyn rng buc

DiffServ Differentiated Service Phn bit dch v DLCI Data Link Connection Identifier Thnh phn nhn dng giao din lin kt d liu DSCP Differentiated Service Code

Point M phn bit dch v

EBGP External Border Gateway Protocol

Giao thc nh tuyn cng bin ngoi min EGP External Gateway Protocol Giao thc nh tuyn ngoi min ER Explicite Route ng tng minh ERO Explicite Route Object i tng ng tng minh EXP Experimetal Bit Trng thc nghim FEC Forwarding Equivalence Class Lp chuyn tip tng ng FRR Fast Reroute Ti nh tuyn nhanh FIB Forwarding Information Base C s thng tin chuyn tip FIS Fault Information Signal Tn hiu thng bo xy ra li FR Frame-Relay Cng ngh Frame-Relay

FRS Fault Recovery Signal Tn hiu thng bo khi phc li FTN FEC to NHLFE Map nh x FEC sang N(LFE GMPLS Generalized MPLS MPLS tp trung IBGP Internal Border Gateway

Protocol Giao thc nh tuyn cng bin ni min

IEEE Institute of Electrical and Electronics Engineers

Vin cc k s in v in t nghin cu tiu chun quc t

IETF Internet Engineering Task Force

Lc lng nghin cu )nternet IGP Interior Gateway Protocol Giao thc nh tuyn ni min ILM Incoming Label Map nh x nhn u vo IP Internet Protocol Giao thc )nternet IPv4, IPv6 Internet Protocol version 4, 6 Giao thc )nternet phin bn , IS-IS Intermediate System

Intermediate System Giao thc nh tuyn gia cc h thng trung gian

LC-ATM Label Controlled ATM Giao thc ATM iu khin nhn LDP Label Distribution Protocol Giao thc phn phi nhn LER Label Edge Router B chuyn mch nhn ti bin LFIB Label Forwarding Information

Base C s thng tin chuyn tip nhn

LIB Label Information Base C s thng tin nhn LSA Link-State Advertisement Bn tin qung b trng thi lin kt LSP Label Switched Path ng chuyn mch nhn LSR Label Switching Router B chuyn mch nhn MNS MPLS module for NS Module m phng MPLS cho NS MPLS Multiprotocol Label Switching Chuyn mch nhn a giao thc MPLS-TE Multiprotocol Label Switching-

Traffic Engineering K thut lu lng trong chuyn mch nhn a giao thc

MTU Maximum Transfer Unit n v truyn ti ti a NAM Network Animator M hnh ha mng m phng NS NGN Next-Generation Network Mng th h k tip

NHLFE Next Hop Label Forwarding Entry

Ch mc nhn chuyn tip k tip NHRP Next Hop Resolution Protocol Giao thc phn gii a ch NLRI Network Layer Reachability

Information Thng tin kh ti ti lp mng

NS Network Simulator Phn mm m phng mng OSI Open System Interconnection Kt ni h thng m OSPF Open Shortest Path First Giao thc nh tuyn m ng dn ngn nht trc tin PID Protocol Identifier Thnh phn nhn dng giao thc PHP Penultimate Hop Popping G nhn chng cui PIL Protection Ingress LSR LSR bo v u vo PML Protection Merging LSR LSR khi phc PNNI Private Network-to-Network

Interface Giao thc nh tuyn link-state s dng trong mng ATM

POR Point of Repair im sa cha PPP Point-to-Point Protocol Giao thc im-im PSL Path Switch LSR LSR chuyn mch ng PVC Permanent Virtual Circuit Kt ni o tnh RFC Request for Comment Cc khuyn ngh RFR Reliable and Fast Rerouting Ti nh tuyn nhanh tin cy RIB Routing Information Base C s thng tin nh tuyn RSVP Resource Reservation Protocol Giao thc dnh ring ti nguyn SONET Sychronous Optical Network Mng quang ng b SPF Shortest Path First Thut ton nh tuyn ng dn ngn nht trc tin TCP Transmission Control Protocol Giao thc iu khin truyn ti TE Traffic Engineering K thut lu lng TLV Type, Length, Value Loi, di, gi tr TTL Time to live Thi gian tn ti ca gi tin ToS Type of Service Loi dch v ca gi tin UDP User Datagram Protocol Giao thc d liu ngi dng

Lun vn tt nghip LI GII THIU

1 Nguyn Anh Quang, DD09DV1

LI GII THIU

Trong nhiu nm qua, vic s dng Internet ngy cng ph bin, cc dch v thi gian thc ngy cng c s dng rng ri v cn phi c ci thin, pht trin hn v tc , cht lng dch v. Trc y, mng my tnh thc hin k thut chuyn mch knh truyn lin tc chui bit qua cc ng dn vt l. K thut ny thch hp cho vic truyn d liu thoi v thi gian thc cho ngi dng u cui, nhng khi c s c xy ra trn lin kt vt l s dn n vic gin on ca tt c kt ni ang s dng lin kt li ny. Ngy nay, Internet l mng chuyn mch gi, mng ny khc phc nhc im ca mng c bng cch chia d liu thnh nhiu phn nh gi l gi tin v nh tuyn chng ring l trong mng. V vy, khi c s c xy ra, gi tin c th tip tc nh tuyn n ch. c trng ny trong mng chuyn mch gi gi l khi phc resilient bi v n che giu s c mng i vi ngi dng u cui. Ni cch khc, vic qun l lung d liu trong mng chuyn mch gi s kh hn so vi mng chuyn mch knh v mi gi tin c x l ring l.

Trong mng chuyn mch gi, giao thc IP c thit k tt trong vic nh tuyn, c th thit lp li kt ni sau khi s c xy ra trong mng. Mc d kt ni c th thit lp li nhng thi gian thc hin vic ny c th s khng t yu cu i vi cc dch v c u tin cao, khng th gin on trong vi ms nh Vo)P. Nu mng cn khi phc s c cho cc loi dch v ny, cn phi c c ch thit lp li kt ni nhanh hn so vi k thut nh tuyn c s dng hin nay trong Internet.

Vic nghin cu v vn ny i vi mng )nternet tr thnh mt xu hng tt yu hin nay. Multiprotocol Label Switching (MPLS) dng nhn thc hin vic chuyn mch gi, tch hp cng ngh chuyn mch v cng ngh nh tuyn )P xy dng mng th h mi c n nh cao hn, nhanh hn. Tuy nhin, nu khng c mt ng dn LSP d phng khi ng dn LSP chnh b li, khung MPLS khng th c chuyn tip n ch. V vy, khi phc s c tr thnh mt lnh vc nghin cu quan trng trong k thut lu lng MPLS.

Lun vn tt nghip LI GII THIU


Vic khi phc s c trong mng MPLS c rt nhiu phng php vi nhng im mnh, im yu ring trong tng trng hp khc nhau. Lun vn ny c chng vi ni dng chnh nh sau: Chng ) Chuyn mch nhn a giao thc: Gii thiu tng quan cng

ngh MPLS, cc khi nim c bn, kin trc chc nng v c ch hot ng ca MPLS, cc k thut nh tuyn c h tr bi MPLS, ch bo hiu v mt s giao thc bo hiu phn phi nhn ca MPLS. Chng )) K thut lu lng v cc c ch khi phc c bn trong MPLS. Chng ))) Nng cao c ch khi phc trong MPLS: Trnh by c ch khi

phc hin nay trong mng MPLS ca VNPT (CM v sut m rng c ch tng cht lng dch v, tp trung vo vn mt gi v th t gi trong qu trnh truyn dn gi tin. Chng )V Xy dng chng trnh m phng MPLS-TE: Trnh by kt qu

thc hin m phng MPLS trn my tnh vi phn mm NS- lm r c ch m rng khi phc ca MPLS v nh gi.

Lun vn tt nghip C(NG ): C(UYN MCH NHN A G)AO T(C


C(NG I TNG QUAN V CHUYN MCH NHN A G)AO T(C

1.1 Gii thiu MPLS Trong nh tuyn IP thng thng, mi b nh tuyn trong mng thc hin vic nh tuyn c lp vi tng gi tin. Khi mt gi tin n b nh tuyn, b nh tuyn phi tra cu bng nh tuyn tm im n tip theo ca gi tin da vo a ch ch trong phn header IP. Mi b nh tuyn phi chy cc giao thc nh tuyn nh: BGP, OSPF hoc ISIS.. xy dng bng nh tuyn. Do vic chuyn tip gi tin ch da trn a ch ch nn cc lung lu lng c cng ch n s c tng hp li. tn dng tt ti nguyn mng cn phi c c ch qun l lung )P nh kh nng tp trung lu lng vo lung c kch thc ph hp, kh nng thc hin nh tuyn tng minh cc lung ny trong mng.

Vn m giao thc nh tuyn thng thng cha gii quyt c l vic quyt nh nh tuyn cha da trn c tnh lu lng, cha c kh nng p dng iu kin rng buc cho tng lung lu lng. Tnh thng minh ca mng tp trung ti khu vc mng li, qu trnh nh tuyn xy ra trn tng thit b ring l, c ch truyn ti gi tin ch da trn a ch )P ch dn n h qu l cc thit b ti khu vc ny lun lun phi chu lng ti cao.

Phn ln k thut qun l lu lng c cc nh cung cp dch v ISP p dng cho h tng kin trc mng l s dng mng lp 2 (ATM hoc FR). Xy dng m hnh xp chng (overlay) gm nhiu mch o kt ni thnh dng li xy dng mng trc IP. Trong m hnh ny, lung d liu c th c nh tuyn ring l thng qua cu trc mng lp 2 v k thut lu lng c th c p dng. im yu ca cng ngh ny l kh nng m rng km, lin kt gp s c c th lm ngng hot ng mng, buc giao thc IP phi nh tuyn li. Mng ATM c c ch cp a ch v giao thc nh tuyn ring so vi mng IP. Khng gian a ch ATM hon ton khc bit so vi IP, v vy chng khng th c nh x trc tip ln nhau m phi thng qua mt vi giao thc phn gii a ch.

Nhiu nghin cu v cc tiu chun c IETF v ATM Forum ph chun v thc hin vic tch hp gia ATM v IP tt hn. Chng hn, vic tch hp gia IP v



ATM da theo RFC1483 [1], quy nh v phng php ng gi mang lung lu lng qua ATM AAL5. Trong gii php ny, tt c mch ATM phi c thit lp th cng v vic nh x gia a ch IP trm k tip v ATM trm cui cng phi cu hnh th cng ti mi b nh tuyn s dng ATM. Mt phng php khc l thc hin vic m phng mng LAN (LANE). LANE xy dng h thng mng, m phng nh mng Ethernet, cc phn on mng Ethernet c kt ni vi nhau thng qua mng ATM WAN trung tm nh b chuyn mch Ethernet. Tuy nhin, phng php ny khng p ng c yu cu m rng v tin cy i vi mng li ngy cng ln ca nh cung cp dch v )SP. Ngoi ra, phng php Multiprotocol over ATM (MPOA) do ATM Forum quy nh, cung cp kh nng tch hp cht ch gia IP v ATM nhng y cng l phng php phc tp nht.

Gii php cho vn ny l phi hp cng ngh mng lp 2 v mng lp 3 IP. Mng MPLS ra i kt hp cc u im hiu sut, QoS v qun l lu lng ca m hnh chuyn mch lp 2; kh nng m rng v linh hot ca chc nng nh tuyn lp ; tng kh nng tch hp gia IP v ATM.

MPLS l vit tt ca Muti-Protocol Label Switching. Thut ng Muti-Protocol nhn mnh rng cng ngh ny p dng cho c tt c cc giao thc lp mng ch khng phi ch ring cho IP. MPLS hot ng tt trn bt k cc giao thc lp lin kt no. y l mt 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 swithching) (hnh 1.1).

Hnh 1.1: MPLS v m hnh tham chi u OSI Trong MPLS, vic nh tuyn gi tin c chuyn nh th no trong min MPLS

ch c thc hin mt ln khi gi tin bt u vo min MPLS. MPLS gn nhn c chiu di c nh vo cc gi tin ti bin ca min MPLS v s dng nhn ny chuyn tip gi vo ng dn n hng LSP c thit lp trc trong mng



MPLS. Tip cc thit b trn ng dn ch cn c vo ni dung ca nhn thc hin quyt nh chuyn tip gi m khng cn phi phn tch tiu gi tin nh k thut truyn ti gi tin truyn thng. V vy, cc thit b trong khu vc mng li ca min chuyn mch MPLS khng cn tiu tn mt lng nng lc x l vo cc th tc i hi nhiu CPU v b nh nh bc tch, phn tch v x l tiu ca cc gi tin. T gim c ti cho cc thit b ny v nng cao c hiu nng x l ca chng, ci thin kh nng chuyn tip thng tin ca ton b h thng mng. Ta c th so snh qu trnh ng gi v gii ng gi trong truyn ti lu lng ca cc b nh tuyn trong min IP so vi min chuyn mch MPLS nh hnh ..

Hnh 1.2: So snh gia chuyn ti p IP v chuyn ti p MPLS

1.2 Cc khi nim c bn trong MPLS .. Min MPLS Theo c t trong ti liu RFC 3031 [2] ca IETF th min chuyn mch nhn MPLS l mt tp cc nt trong 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.

Min MPLS c chia thnh 2 phn: phn mng li (core) v phn mng bin (edge). Cc nt thuc min MPLS c gi l b nh tuyn/chuyn mch nhn LSR (Label Switch Router). Cc nt phn mng li c gi l transit-LSR hay core-LSR



(thng c gi tt l LSR). Cc nt bin c gi l cc edge-LSR hay gi tt l LER (Label Edge Router). i vi cc nh cung cp dch v mng th cc b nh tuyn/chuyn mch ny thng c gi tng ng l cc b nh tuyn li P (Provider Router) v cc b nh tuyn bin PE (Provider Edge Router). V d min chuyn mch nhn MPLS nh hnh ..

Hnh 1.3: Min chuyn mch nhn MPLS Cc LER nhn vai tr a lu lng vo v a lu lng ra khi min chuyn

mch nhn MPLS. LER ng vai tr a lung lu lng vo c gi l LER li vo (ingress-LER), v LER ng vai tr a lung lu lng ny ra c gi l LER li ra (egress-LER). Do trong min MPLS, cc lung lu lng c truyn ti trn cc ng dn n hng LSP c thit lp t qu trnh nh tuyn ti cc khu vc bin nn mt LER c th l ingress-LER i vi lung lu lng ny nhng cng ng thi c th l egress-LER i vi lung lu lng khc.

Vai tr v nhim v ca cc nt trong min chuyn mch MPLS: LSR thc hin nhim v chnh l tip nhn cc gi tin d liu c gn

nhn, thc hin quyt nh chuyn mch, gn nhn mi v chuyn tip cc gi tin ra giao din lin kt d liu ph hp. Edge-LSR hay LER thc hin nhim v gn nhn cho cc gi tin v chuyn tip

chng vo min chuyn mch MPLS hoc g b nhn cho cc gi tin v chuyn tip chng ra khi min chuyn mch MPLS.

.. Lp chuyn tip tng ng FEC Theo c t trong ti liu RFC 3031 [2], lp chuyn tip tng ng FEC (Forwarding Equitvalence Class) l mt nhm cc gi tin c chuyn tip trn cng mt ng dn n hng LSP, c x l vi cng mt chnh sch nh

Label Switching

Router(core LSR)

Label Edge

Router (LER)



tuyn/chuyn mch xuyn sut trn tt c cc nt dc ng dn LSP. Tt c cc gi tin c xp vo cng mt FEC s c cng mt nhn khi mt nt tip nhn v c khi nt chuyn tip chng ra giao din lin kt d liu. Tuy nhin cc gi tin c cng mt nhn cha chc thuc cng mt FEC, trong trng hp EXP nm trong ngn xp nhn ca chng mang gi tr khc nhau. Trong min chuyn mch MPLS, nt quyt nh gi tin thuc FEC no l Ingress-LER, chng l thit b u tin tip nhn, phn loi v gn nhn cc gi tin trc khi chuyn tip vo min MPLS. Vic tp trung lu lng s lm gim s lng nhn s dng cho vic gn gi tin, gim lu lng iu khin cho vic phn phi nhn. Hnh 1.4 cho thy cc x l ny.

Hnh 1.4: L p chuyn ti t n n t n MPLS Nhn cha cc thng tin cn thit ca gi tin nh ch n, u tin, thng tin

QoS, thm ch ton b tuyn ng cho gi tin do Ingress-LER quyt nh da trn chnh sch qun tr. i vi k thut MPLS, cc thit b khng ch ra quyt nh/chuyn mch da vo a ch ch, chng cn c th da vo mt s tiu ch khc, chng hn :

a ch ch dng Unicast a ch ch dng Multicast Gi tr IP-Precedence/DSCP trong trng ToS ca gi tin IPv4 Gi tr IP-Precedence/DSCP trong trng Traffic Class ca gi tin IPv6 Gi tr EXP trong ngn xp nhn MPLS

Gi tr VC VP)/VC) trong tiu ca t bo ATM Gi tr a ch chng k tip trong trng thng tin nh tuyn ca giao thc

BGP, MP-BGP



.. Nhn v ngn xp nhn Theo ti liu RFC 3031 [2], nh ngha nhn l mt b nhn dng c di

ngn c nh v thng nht trn ton min chuyn mch MPLS, c tnh cht cc b dng nhn bit mt FEC. Nhn s c gn vo gn tin v tr sau tiu lp lin kt d liu v trc tiu lp mng. Mt gi tin c th c gn nhiu, cc nhn s c gn trong cng mt ngn xp nhn, cu trc ca tng nhn nh hnh .

Hnh 1.5 : nh n ha a mt th c th nh n t n n n x p nhn Mt nhn c di 32 bit, bao gm trng thnh phn nh sau : Trng gi tr nhn LABEL c di 20 bit, l gi tr nhn thc s, s lng

nhn ti a l 20 nhn, tuy nhin cc nhn t 0 c dnh ring cho cc tc v iu khin v khng c s dng chuyn tip trong min MPLS. Trng Experimental EXP c di 3 bit, mang thng tin phc v cho cc ng dng yu cu QoS, trng ny thng c s dng mang thng tin tng ng v cc gi tr IPPrecedence/DSCP trong trng ToS ca gi tin

IPv4 hoc trong trng Traffic Class ca gi tin IPv6. Trng Bottom-of-Stack S c di bit, c s dng nh du nhn

v tr cui cng trong ngn xp nhn, khi ny trng S s c gi tr bng 1. Trng Time-to-live TTL c di bit, c s dng ngn nga vic gi

tin b nh tuyn/chuyn mch lp trong min MPLS, khi gi tin c gn nhn i qua mt nt mng, gi tr ca trng ny s gim i n v, khi gi tr gim xung 0 th gi tin s b loi b.

Mt trong nhng im mnh ca MPLS l ngn xp nhn, cho php to nhiu ng dn n hng LSP phn cp s dng cc ng dng ca mng MPLS, v d MPLS VPN (2 nhn), MPLS-TE (2 nhn tr ln.. Ngn xp nhn l mt tp hp gm mt hoc nhiu thc th nhn c t chc theo nguyn tc LIFO (Last In First Out). Cc nhn c gn vo cc gi tin bi cc Ingress-LER trc khi chuyn tip vo min chuyn mch nhn MPLS hoc c g ra khi cc gi tin bi cc Egress-LER trc khi a ra khi min MPLS. Ti mi nt mng, ch x l duy nht thc th nhn trn nh ngn xp, hay ni cch khc cc nt mng ch thc hin vic chuyn tip da trn nhn u tin ca ngn xp nhn.



Hnh 1.6 : N n x p nhn (MPLS Label Stack) Nu gi tin cha c nhn th ngn xp nhn l rng v su ca ngn xp nhn

bng 0. Nu ngn xp c su d th mc 1 s l y ngn xp (bit S trong thc th nhn t ln 1) v mc d s l nh ca ngn xp. Mt thc th nhn c th c t thm vo (push) hoc ly ra (pop) khi ngn xp.

K thut MPLS c th hot ng theo hai ch l Frame-Mode v Cell-Mode, ch Cell-Mode MPLS c s dng khi giao thc nn tng lp lin kt d liu l ATM, vi cc giao thc nn tng lp lin kt d liu cn li nh PPP, (DLC, Frame-Relay, Ethernet,.. MPLS hot ng theo ch Frame-Mode. i vi m ha ngn xp nhn trong ch khung, ngn xp nhn c nh km v tr sau tiu lp lin kt d liu v trc tiu lp mng, tr thnh gi tin c gn nhn. Do vy nht thit phi c c ch thng bo v nhn dng cc gi tin gn nhn ti mi nt. Thng thng mi giao thc lp lin kt d liu u c mt trng Protocol-)D P)D c s dng nhn dng giao thc ca phn ti tin m n truyn ti. nh ngn xp nm lin sau tiu lp v y ngn xp nm lin trc tiu lp 3.

H nh 7: M ha n n x p nhn trong ch khung (Frame-Mode) Gi tr P)D trong cc trng nhn dng ti tin ca mt s giao thc lin kt d liu ph bin c s dng truyn ti cc khung d liu MPLS nh trong bng 1.1



Bng 1.1: Gi tr PID nhn dng phn ti tin MPLS trong cc giao thc lin kt d liu

Giao thc lp lin kt d liu

Trng nhn dng giao thc

Gi tr P)D (hexa)

PPP PPP Protocol 0x0281

Ethernet/802.3 LLC/SNAP Ethernet 0x8847

HDLC Protocol (Cisco HDLC) 0x8847

Frame-Relay NLPID 0x80

Ch t bo (Cell-Mode c s dng dnh ring khi trin khai MPLS vi giao thc lp lin kt d liu nn tng l ATM do giao thc ny c mt s c tnh khc bit so vi cc giao thc lp lin kt d liu khc. Trong mng ATM, cc thit b chuyn mch ATM c th cu hnh chy cc giao thc nh tuyn v cc giao thc trao i thng tin VPI/VCI thay cho bo hiu ATM vi mc ch trin khai Cell-Mode MPLS. ATM s dng n v truyn ti dng t bo (53 byte c nh vi byte tiu v 48 byte ti trng), mt gi tin c th ng gi trong nhiu t bo (nu ti trng gi tin ln hn byte. Do mt t bo c kch thc c nh nn khng th gn trc tip nhn mt cch thng thng ln cc t bo v bn thn nhn s lm tng kch c ca t bo. Theo ti liu RFC 3035 [3] k thut MPLS trin khai trn mng ATM c mt s c im sau y:

Cell-Mode MPLS s dng tiu VP)/VC) nh mt nhn MPLS, cc thit b nh tuyn/chuyn mch ca mng ATM s s dng VP)/VC) chuyn tip. Ngn xp nhn thng thng vn c s dng trong ATM, c gn ngay sau trng tiu AAL nhng s ch c gn trong t bo u tin v khng c s dng trong mng ATM.

.. (on i nhn (on i nhn (Label Swapping) l phng thc dng cc th tc g b nhn ban u v tro i vo mt nhn mi truyn ti ra giao din lin kt d liu mi. LSR s kim tra nhn trn nh ngn xp, truy xut cc bng FIB/LFIB v dng nh x )LM )ncoming Label Map nh x nhn ti mt thc th chuyn tip nhn NHLFE (Next Hop Label Forwarding Entry). S dng thng tin trong NHLFE, LSR xc nh c ni dung tc v cn phi thc hin trn ngn xp nhn bao gm:



gi tr nhn mi hoc g b nhn, giao din lin kt d liu u ra tip theo dc ng dn n hng LSP Sau LSR s m ha ngn xp nhn mi cho gi tin v chuyn gi tin i.

Chuyn tip gi cha c nhn cng tng t nhng xy ra ingress-LER. LER phi phn tch tiu lp mng xc nh FEC ri s dng nh x FTN (FEC-to-N(LFE nh x FEC vo mt NHLFE. 1.2.5 ng chuyn mch nhn LSP ng chuyn mch nhn LSP (Label Switched Path) l mt ng dn t u vo Ingress-LER qua cc LSR ti u ra Egress-LER, c thit lp bi cc nt MPLS chuyn cc gi tin qua mi trng MPLS. ng dn ca mt LSP qua mng c nh ngha bi s hon i nhn cc LSR dc theo LSP (hnh 1.8).

Hnh 1.8: ng chuyn mch nhn LSP Trong min MPLS, cn thit phi c mt giao thc nh tuyn ni min dng Link-State )GP hoc Distance Vector )GP xy dng hon chnh ng dn gia tt c cc LER xuyn qua min MPLS nhm mc ch thit lp ng dn LSP t u vo Ingress-LER ti u ra Egress-LER ring i vi ng dng MPLS-TE, giao thc nh tuyn ni min MPLS bt buc l dng Link-State c th qung b y thng tin rng buc ca tt c cc lin kt trong ni min MPLS, gip cho qu trnh nh tuyn rng buc tnh ton cc ng dn LSP tha mn yu cu rng buc. Tip cn thit phi c mt giao thc phn phi nhn nh LDP/TDP qung b cc nhn gip cho qu trnh thit lp LSP v gi tr hon i nhn ti mi nt mng. Nh vic trin khai ca giao thc nh tuyn ni min )GP, mi LER/LSR xc nh c ng dn ti u nht n tt c cc LER/LSR khc trong min MPLS, kt hp vi giao thc phn phi nhn LDP/TDP, mi LER/LSR cng thit lp c



ng dn n hng LSP n tt c cc LER/LSR cn li trong min MPLS. Nh vy, mt mng li full-mesh LSP s c to thnh trong min MPLS. K thut g nhn chng cui P(P Penultimate (op Popping c th c s dng ti nt p cht trc khi gi tin n nt Egress-LER ca mt ng dn LSP nhm ti u ha hot ng nh tuyn ca Egress-LER, trnh tnh trng tra cu thng tin nh tuyn/chuyn mch 2 ln cho gi tin gm: tra cu bng chuyn tip MPLS thc hin tc v g nhn v tra cu bng nh tuyn lp chuyn tip n nt tip theo. thc hin P(P, Egress-LER yu cu nt p cht tin hnh tc v g nhn trn nh ngn xp nhn trc khi chuyn tip gi tin. Sau , Egress-LER nhn gi tin )P khng nhn v trc tip tra cu bng nh tuyn lp . Cc ng dn LSP c tnh cht n hng, lu lng truyn ti gia cc LER theo hai hng i v v s c truyn trn hai LSP khc bit nhau, mc d c th chui ng truyn vt l khng thay i nhng gi tr hon i nhn ca mi LSP ti mi nt LER/LSR khc nhau dn ti s tch bit thnh hai LSP. Ngn xp nhn ca MPLS [] cho php phn cp cc LSP tng t nh ATM s dng cc ch s nh dng VP) v VC) to cc phn cp knh o VC nm trong ng o VP, mt ng o c th cha nhiu knh o VC. Tuy nhin trong ATM ch tn ti phn cp, trong MPLS vic phn cp cc LSP l rt ln. Theo ti liu RFC 3031 [2] th s lng cc nhn trong ngn xp nhn l khng gii hn nn v mt l thuyt ta c th phn cp cc LSP khng gii hn. Tuy nhin trn thc t, s lng cc nhn trong ngn xp nhn ph thuc vo gi tr n v truyn ti d liu ti a MTU ca giao din lin kt d liu. Phn cp LSP c c t nh hnh 1.9

LSP1LSP3

L1IP L3

L2IP L3

L1IP

L2IP

L1IP

L2IPLSP2

Hnh 1.9: Phn cp LSP trong MPLS Phn cp LSP l mt c tnh quan trng trong MPLS, c tnh ny thng c s dng trong cc ng dng nh MPLS VPN v MPLS-TE. i vi MPLS VPN, ngn xp nhn thng yu cu c nhn, nhn trn nh ngn xp thng c gi l LDP Label c s dng chuyn tip trong min MPLS xuyn sut t LER ny ti LER ng xa, nhn k tip (thng c gi l VPN Label c s dng phn bit



cc mng ring o khc nhau. i vi MPLS-TE, ngn xp nhn c th yu cu c 2 nhn tr ln, nhn trn nh ngn xp thng c gi l TE Label c bo hiu bng giao thc RSVP-TE chuyn tip rng buc trong min MPLS gia cc LER, tuy nhin cc LSR hon ton c th gn thm ln trn nh ngn xp mt nhn khc trong trng hp LSP ang hot ng gp s c, nhn gn thm ny c s dng a lu lng qua mt LSP rng buc khc vng qua im gp s c nhng vn n c LER ng xa. 1.3 Mt phng iu khin v mt phng chuyn tip MPLS

Trong kin trc MPLS, hai thnh phn c bn nht ca h thng mng l cc b nh tuyn/chuyn mch trong mng li LSR v cc b nh tuyn/chuyn mch ti khu vc mng bin LER. Kin trc chc nng ca cc b nh tuyn/chuyn mch ny tng i ging nhau v bao gm 2 phn l:

Mt phng iu khin (Control Plane) Mt phng chuyn tip (Forwarding Plane)

Ta xt kin trc chc nng chung ca b nh tuyn/chuyn mch LER v LSR trong min chuyn mch MPLS nh hnh 1.10

Hnh 1.10: Ki n trc ch n n a cc b chuyn mch LER/LSR



1.3.1 Mt phng iu khin Mt phng iu khin c 3 nhim v c bn l: Thu nhp thng tin: S dng giao thc nh tuyn IGP dng Link-State (OSPF,

ISIS) hoc dng Distance-Vector R)P, E)GRP/)GRP xy dng bng nh tuyn RIB (Routing Information Base), t thu nhp thng tin v ton b mng trong min MPLS. Cc thng tin ny v cng quan trng cho vic tnh ton cc ng dn ti u nht ti cc mng trong min MPLS phc v cho vic thit lp ng dn n hng LSP xuyn sut t LER ny xuyn qua mng li ti LER kia. (n na, cc giao thc dng Link-State (OSPF, ISIS) cn c m rng RFC 3630, RFC 3784 [5][6] mang thm thng tin ti nguyn ca cc lin kt trong mng, t c th p dng k thut lu lng trong min MPLS. La chn ng dn: S dng nh tuyn tng chng (hop-by-hop) hoc nh

tuyn tng minh la chn ng dn ti u nht ti cc mng trong min MPLS. nh tuyn tng chng cho php mi nt xc nh FEC v chn chng k tip cho tng FEC mt cch c lp, ging nh nh tuyn trong mng IP. nh tuyn tng minh xc nh mt danh sch vn tt cc nt m mt ng dn n hng LSP phi i qua, do Ingress-LER quyt nh da trn cc tiu ch hoc chnh sch ca ngi qun tr. Thit lp ng dn: S dng mt giao thc bo hiu (LDP, CR-LDP hoc RSVP thng bo cho tt c cc b nh tuyn dc theo ng dn n hng la chn. Giao thc bo hiu chu trch nhim gn/phn phi nhn cng nh tha thun nhn gia cc LSR/LER lin k v cc mng trong min MPLS cu hnh bng FIB v LFIB trong mt phng chuyn tip; cc giao

thc phn phi nhn trn mi LSR/LER xy dng bng thng tin nhn LIB (Label Information Base)

.. Mt phng chuyn tip Mt phng chuyn tip c 2 nhim v c bn l: Tng hp thng tin t cc bng RIB xy dng nn bng chuyn tip FIB Forwarding )nformation Base c dng chuyn tip nhanh cc gi tin

lp mng m khng cn phi s dng CPU ca b nh tuyn, thng thng bng FIB ch xut hin ti cc LER hoc cc b nh tuyn/chuyn mch thun IP, cc LER cn c bng F)B c th chuyn pht gi tin vo/ra min MPLS hoc chuyn pht gi tin theo phng thc truyn thng.



Tng hp thng tin t bng R)B, L)B xy dng nn bng chuyn tip LFIB Label Forwarding )nformation Base c dng chuyn tip nhanh cc gi tin c gn nhn m khng cn phi s dng CPU ca b nh tuyn, thng thng bng LFIB xut hin ti LER ln LSR. Theo ti liu RFC 3031 [2], bng LFIB l thnh phn ch cht ca cc LER v

LSR, bao gm hai loi thc th )LM v FTN, trong N(LFE l thc th con cha cc trng nh a ch chng k tip, cc tc v lin quan n ngn xp nhn (gn nhn, g nhn, hon i nhn), giao din u ra v thng tin tiu lp 2. ILM nh x mt nhn n mt hoc nhiu NHLFE. Nhn trong gi n s dng chn ra mt thc th ILM c th nhm xc nh NHLFE. Cn FTN nh x mi FEC vo mt hoc nhiu NHLFE. Nh cc thc th FTN, gi cha c nhn c chuyn thnh gi c nhn. Nh vy, khi mt gi khng nhn thuc mt FEC i vo min MPLS, Ingress-LER s s dng mt thc th LFIB loi FTN chuyn gi khng nhn thnh gi c nhn, cc LSR trong mng li s s dng mt thc th LFIB loi )LM thc hin vic hon i nhn. Cui cng, ti Egress-LER s dng mt thc th LFIB loi )LM g b nhn n v chuyn tip gi khng nhn n b nh tuyn k tip nm ngoi min MPLS. Vic ILM hoc FTN c th nh x ti nhiu NHLFE c th dng trong cn bng ti, h tr tnh nng cn bng ti trn nhiu ng c metric bng nhau hoc thm ch khng bng nhau ca cc giao thc nh tuyn ni min IGP. V d v hot ng trong mt phng chuyn tip MPLS nh hnh .

Hnh 1.11: Hot ng trong mt phng chuyn ti p MPLS



Cng theo ti liu RFC 3031 [2], cc nt MPLS s dng gi tr nhn trong cc gi n lm ch mc tra bng LFIB. Khi tm thy thc th tng ng vi nhn n, nt MPLS s thay th nhn trong gi bng nhn ra v gi n vo giao din u ra n nt k tip c c t trong thc th con NHLFE. Vi ng dng MPLS QoS thc th con c th c ch nh hng i u ra, nt MPLS s t gi trn hng i ch nh. Trong trng hp nt MPLS duy tr mt LFIB ring cho mi giao din, n s dng LFIB ca giao din u vo ca gi tin n tra cu tham s u ra v chuyn tip gi. Nt MPLS c th ly nh v c cc thng tin chuyn tip cn thit trong LFIB ch trong mt ln truy xut b nh m khng cn s dng n CPU ca LER/LSR, tc thc thi c y cao nh cc chip chuyn dng ASIC gn trc tip ti cc giao din lin kt d liu ca LER/LSR.

1.4 nh tuyn trong MPLS Tnh nng nh tuyn l mt thnh phn khng th thiu trong kin trc chc nng ca MPLS, nh tuyn nm trong mt phng iu khin vi nhim v c bn l thu nhp v phn phi thng tin cn thit v cc tuyn ng ni min MPLS cng nh tha thun gn nhn cc tuyn ng ny cho mi LSR/LER xy dng cc ng dn LSP xuyn sut gia cc LER hay trao i thng tin nh tuyn vi cc min bn ngoi MPLS. 1.4.1 Giao thc nh tuyn ni min )GP i vi k thut MPLS, yu cu nht thit phi c mt giao thc nh tuyn ni min c th trin khai dng Distance Vector nh R)P, )GRP/EIGRP hoc dng Link-State nh OSPF, )S-IS cc b nh tuyn/chuyn mch LER/LSR c th xy dng cc ng dn n hng LSP gia cc LER vi nhau.

Theo ti liu RFC 3031 [2] th giao thc nh tuyn ni min MPLS i vi k thut MPLS c bn khng bt buc l dng Distance Vector hay Link-State, tuy nhin vi ng dng nng cao MPLS-TE th giao thc nh tuyn ni min IGP bt buc phi l dng Link-State (OSPF, IS-)S tt c cc LER/LSR c th trao i v nm c cc thng tin rng buc v ti nguyn ca ton b min MPLS. .. Giao thc nh tuyn ngoi bin m rng MP-BGP

Cc giao thc nh tuyn lin min hay cn c gi l giao thc nh tuyn ngoi bin c s dng ph bin trong cc mng thun IP nhm mc ch trao i thng tin nh tuyn v kt ni cc vng t tr AS c nh ngha l mt tp



hp cc b nh tuyn thc hin cng mt chnh sch nh tuyn thng nht). Cc nh cung cp dch v thng trin khai giao thc nh tuyn ngoi bin kt ni vi cc nh cung cp dch v mng ln cn v cc nh cung cp dch v mng cp cao hn nhm thit lp cc kt ni ra mng quc t v mng Internet.

Hnh 1.12: Giao th nh tuy n ngoi bin BGPv4 Ti liu RFC3107 [7] m rng giao thc nh tuyn BGP h tr phn phi nhn MPLS c th thit lp cc ng dn n hng LSP lin mng. Bn tin cp

nht trong BGP- dng phn phi cc ng dn BGP c th mang thm cc nhn MPLS nh x vi tng ng dn BGP tng ng. Thng tin nhn ny s c cc b nh tuyn ni min AS s dng trong ngn xp nhn chuyn lu lng ti vng AS khc mong mun. Giao thc ny cc k quan trng trong ng dng mng ring o MPLS VPN, c s dng lan truyn khi lng ln cc Prefix ca khch hng qua mng li m vn m bo s ring t. Ngoi ra, giao thc BGP gip cc LER c th phn bit c cc gi tin gn nhn n t cng mt LSP nhng thuc v cc khch hng khc nhau da vo vic s dng ngn xp nhn. 1.4.3 Cc giao thc nh tuyn rng buc v tng minh 1.4.3. nh tuyn rng buc

Trong mng thun IP, cc giao thc nh tuyn ni min )GP c s dng tnh ton cc ng dn ti u nht n tt c cc mng da trn thng tin v cu trc mng, tt c cc lu lng n mt mng nht nh t mt nt c nh tuyn



theo tng chng (hop-by-hop v u c truyn theo cng mt ng dn n ch, iu ny dn n nhc im i vi cc mng s dng nh tuyn truyn thng thng thng l mt vi ng dn ti u trong mng lun lun phi chu lng ti rt cao c th vt kh nng truyn ti ca chng v khi y cn phi trin khai mt lot cc k thut hng i v cc k thut QoS phc tp khc nhm gim t l mt gi v m bo cht lng dch v cho cc lu lng truyn ti; trong khi y cc ng truyn khng ti u cn li th ch c s dng rt t, thm ch khng s dng, iu ny gy lng ph ti nguyn ca h thng mng, ng thi gy ra tc nghn trong mng. Nhc im trn vn xy ra i vi k thut chuyn mch nhn MPLS c bn s dng k thut nh tuyn tng chng nh giao thc nh tuyn ni min IGP thng thng. Mt ng dng nng cao ca k thut MPLS l k thut lu lng MPLS-TE xut mt phng php nh tuyn ti u hn nh tuyn thng thng, l phng phc nh tuyn rng buc CBR (Constraint-Based Routed. CBR cng l phng thc nh tuyn ng nh nh tuyn thng thng nhng khc phc nhc im lng ph ti nguyn mng ca giao thc nh tuyn truyn thng. CBR s dng thut ton CSPF (Constraint-Based Shortest Path First) hay cn gi l PCALC (Path Calculation). Thut ton CSPF xc nh cc ng dn truyn lu lng khng ch da trn cu trc mng nh thut ton SPF thng thng thc hin m cn da vo cc tham s c trng khc ca tng lin kt nh bng thng ti a da trn Cost, bng thng kh dng hin thi (Available-BW), s chng (Hop-Count, tr (Delay), bin ng tr (Jitter).. Tiu ch chn ng c bn cho mt lung lu lng ca thut ton CSPF l chn ng ti u nht (t Hop nht, bng thng ti a cao nht) trong s tt c cc ng c bng thng kh dng hin thi tha mn yu cu ca lung lu lng . 1.4.3.2 nh tuyn tng minh nh tuyn tng minh ER (explicit routing) l mt tp con ca nh tuyn rng buc CBR, trong vic tnh ton rng buc c thc hin vi cc i tng ng dn tng minh ER. ng dn tng minh ER l mt danh sch vn tt cc nt tru tng abstract node m mt ng dn n hng rng buc CR-LSP phi i qua. Nt tru tng c th l mt nt hoc mt nhm nt trong min MPLS. Nu ER ch quy nh CR-LSP ch i qua mt nhm trong s cc nt th n c gi l ng dn tng minh lng lo. Ngc li, nu ER quy nh CR-LSP phi i qua ton b cc nt trong tp cc nt cu hnh th c gi l tuyn tng minh nghim ngt.



nh tuyn tng minh ER m ha v thit lp cc CR-LSP theo mt chui cc ER-NextHop cha trong cc bn tin ph tr TLV (Type-Length-Value) rng buc. CR-LSP s c thit lp i ti nhm cc nt theo th t ER-NextHop c xc nh trc.

1.5 Cc giao thc bo hiu MPLS Bo hiu l cch thc cc b nh tuyn trao i thng tin vi nhau. Trong

mng MPLS, loi thng tin trao i ph thuc vo giao thc bo hiu c s dng, chng hn i vi mng MPLS c bn nht, nhn phi c phn phi cho tt c b nh tuyn LER/LSR c th chuyn tip d liu ca mt lp FEC c th v thit lp cc ng dn n hng LSP. 1.5.1 Giao thc LDP

LDP (label distribution protocol) l mt chun giao thc ca )ETF v c c t trong RFC 3036 [8]. Nguyn tc hot ng c bn ca LDP l mi LER/LSR ban u thc hin vic gn nhn ni b (Local Binding) cho tt c cc mng trong bng R)B, sau thit lp phin lm vic LDP vi cc LER/LSR ln cn v qung b cc nhn ni b ti cc LER/LSR xc lp phin. Mi LER/LSR lu tr cc nhn ni b v cc nhn nhn c vo bng c s d liu nhn LIB. Nhn ni b Local Binding ca LER/LSR qung b i s l nhn t xa Remote Binding i vi LER/LSR nhn c. Mt LER/LSR c th nhn c nhiu nhn Remote Binding, nhng n s chn ra nhn Remote Binding no c qung b bi LER/LSR thuc ng xung ca LSP gn vi FEC c ch ra trong bng RIB.

LDP phn phi nhn da vo c ch nh tuyn tng chng (hop-by-hop) ca cc giao thc IGP nn khng h tr k thut lu lng. Vic la chn ng dn vt l cng tng t nh giao thc nh tuyn IP truyn thng thc hin, khng khc phc c nhc im ca mng IP. Ngy nay, do s pht trin nhanh chng ca cc cng ngh nh tuyn i hi phi s dng ti nguyn mng tt hn nn LDP khng cn c s dng trong vic phn phi nhn. Tuy nhin, mt phin bn m rng t giao thc LDP h tr thm chc nng mi l giao thc CR-LDP c s dng trong MPLS.

1.5.2 Giao thc CR-LDP CR-LDP (constrain-based routing LDP) [9] l giao thc m rng t LDP nhm

h tr c bit cho nh tuyn rng buc, k thut lu lng v cc hot ng d tr



ti nguyn. Cc hot ng chnh ca CR-LDP bao gm tha thun cc tham s lu lng nh cp pht bng thng, thit lp v nm gi quyn u tin. Cc th tc mi ca CR-LDP bao gm bo hiu ng; nh ngha cc tham s lu lng; qun l LSP vi quyn u tin v cc tha thun qun tr

Nguyn tc hot ng ca CR-LDP s dng c ch gn nhn theo yu cu v iu khin tun t. Mt LSP thng thng c thit lp khi mt chui cc bn tin CR-LDP-Label-Request lan truyn t Ingress-LSR n Egress-LSR, nu LSP 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 CR-LDP-Label-Mapping lan truyn ngc v Ingress-LSR. Vic thit lp mt ng dn CR-LSP c th tht bi, li v chi tit li s c bo hiu bng bn tin CR-LDP-Notification. thit lp mt CR-LSP theo mt ng dn gm tp cc nt LER/LSR xc nh trc, CR-LDP s dng i tng tuyn tng minh ER cha ng cc bn tin CR-LDP-Label-Request nh hnh .13 . Khi mt nt nhn LER/LSR nhn c bn tin CR-LDP-Label-Request, n thc hin th tc kim sot truy nhp (Admission Control) trong CR-LDP kim tra xem n c m bo c cc ti nguyn c yu cu bi trung k lu lng hay khng. Nu m bo, th tc kim sot truy nhp s d tr n bng cch cp nht bng ti nguyn (Resource Table) v bn tin CR-LDP-Label-Request c chuyn tip n nt tip sau trong danh sch ER.

Hnh 1.13: Thi t l ng rng buc CR-LSP v i giao th c CR-LDP Khi mt nt LER/LSR nhn c mt bn tin CR-LDP-Label-Mapping, n s

thc hin mt lot cc th tc sau: Lu thng tin nhn mi v giao din nhn c vo bng LIB.

Lu thng tin CR-LDP c yu cu vo bng c s thng tin tuyn tng minh ERB (Explicit RIB).



S dng th tc kim sot ti nguyn (Resource Control/Manager) trong CR-LDP khi to mt hng i phc v cho CR-LSP va yu cu thit lp ng thi lu Service-ID ca CR-LSP vo bng ERB. Chuyn tip bn tin CR-LDP-Label-Mapping ti nt MPLS tip sau trong danh

sch ER theo chiu ngc li. 1.5. Giao thc RSVP-TE

RSVP-TE [10] l phin bn m rng ca giao thc d tr ti nguyn RSVP [11] nhm h tr cc phng thc nh tuyn rng buc, k thut lu lng v cc hot ng cp pht ti nguyn dnh cho min chuyn mch MPLS thc hin k thut lu lng MPLS-TE. RSVP-TE l mt giao thc soft state, vic d tr ti nguyn s t ng gii phng sau mt khong thi gian xc nh nu cc nt MPLS khng nhn c cc bn tin cp nht nh k t cc nt khc trong mng MPLS. Cc hot ng c bn ca RSVP-TE l:

Gn nhn cho LSP rng buc. nh tuyn tng chng hoc nh tuyn tng minh.

Bo hiu dnh ring ti nguyn cho LSP rng buc. Ti nh tuyn LSP rng buc sau s c. iu khin chng ca LSP.

Cc c ch ln chim. Nguyn tc hot ng c bn ca RSVP-TE h tr nh tuyn rng buc c c t nh trn hnh . 14

Hnh 1.14: Thi t l ng rng buc TE-LSP v i giao th c RSVP-TE



Headend-LER gi bn tin RSVP-PATH c cha cc trng Label_Request, Explicit_Route, Record_Route, Session_Attribute dc theo ng dn LSP rng buc tnh ton trc ti Tailend-LER. Mi nt trung gian trn ng dn TE-LSP gia Headend-LSR v Tailend-LSR tip nhn bn tin RSVP-PATH v thc hin th tc kim sot truy nhp Admission Control kim tra thuc tnh rng buc yu cu ca TE-LSP v so snh vi ti nguyn ca bn thn n, lng ti nguyn ny chnh l cc thuc tnh rng buc ca cc lin kt. Nu kt qu th tc ny chp nhn, nt trung gian s cho php TE-LSP c thit lp v dnh ring phn ti nguyn yu cu ca TE-LSP . Tip , nt trung gian s tip tc gi bn tin RSVP-PATH ti nt trung gian kt tip cho ti khi gi tin ny n Tailend-LSR.

Tailend-LSR tip nhn bn tin RSVP-PAT( v cng thc hin th tc kim sot truy nhp nh cc nt trung gian. Khi nhn ra rng mnh l nt cui cng trong chui Explicit_Route, Tailend-LSR gi tr v bn tin RSVP-RESV cha trng Label v Record_Route, ng i ca bn tin ny theo danh sch Explicit_Route vi chiu ngc li. Trng Label cha gi tr nhn mi dnh cho TE-LSP m cc nt trung gian v Headend-LSR c th s dng truyn lu lng ca trung k lu lng. Khi mt nt trung gian nhn c bn tin RSVP-RESV, nu c yu cu ln chim, cc nt ny s thc hin hy cc TE-LSP c u tin thp nhng ti nguyn cho cc TE-LSP c u tin cao hn. Trong trng hp c li xy ra trong hot ng thit lp v bo hiu TE-LSP, bn tin RSVP-PATHERR s ra thng bo li v chi tip li tng ng. Trong trng hp TE-LSP khng cn ti nguyn ca mng hay TE-LSP b ln chim bi mt TE-LSP khc c u tin cao hn th bn tin RSVP-PATHERR s ra thng bo hy phin lm vic ca TE-LSP v l do chi tit tng ng.

1.6 u im v ng dng ca MPLS 1.6. n gin ha chc nng chuyn tip

MPLS s dng c ch chuyn tip gi tin da vo nhn, quyt nh chuyn tip c th xc nh ngay ch vi mt ln tra cu ch mc trong bng LF)B. C ch ny n gin v nhanh hn nhiu so vi gii thut longest prefix match dng trong chuyn tip gi IP thng thng.



1.6.2 ng dng k thut lu lng u im ln nht ca MPLS l kh nng thc hin k thut lu lng TE, m bo lu lng c nh tuyn qua mng li mt cch tin cy v hiu qu nht. K thut lu lng TE cho php cc nh cung cp dch v )SP nh tuyn lu lng theo nhng phng php khc nhau c th cung cp dch v tt nht cho khch hng m bo cc tiu ch v thng lng, tr MPLS-TE cho php lu lng c phn b hp l qua ton b h tng mng, ti u ha hiu sut s dng mng. y cng l i tng nghin cu chnh ca ti ny v s c trnh by k cc chng tip theo. 1.6. Xc nh ng dn m bo QoS ti b nh tuyn bin

K thut MPLS thc hin vic xc nh cc ng dn n hng LSP da trn ti nguyn kh dng trong mng v cc yu cu QoS ca lung lu lng ti cc b nh tuyn bin Ingress-LER thay v m bo QoS ti cc b nh tuyn trong ton b mng li. Tiu ch chn ng ti b nh tuyn bin Ingress-LER c m rng bao gm thm cc tham s QoS nh bng thng kh dng, tr, bin ng tr chn ra ng dn ti u nht cho lung lu lng. 1.6. Mng ring o VPN

VPN l ng dng cho php khch hng thit lp mng ring ging nh knh thu ring nhng vi chi ph thp hn bng cch s dng h tng mng cng cng. K thut MPLS p ng c tt c cc yu cu cn thit h tr VPN bng cch thit lp ng dn LSP gia cc mng ca khch hng s dng ngn xp nhn. 1.6.5 Phn cp ng dn

Vic phn cp ng dn trong mng MPLS cho php ng gi mt ng dn n hng LSP vo trong mt ng dn LSP khc bng cch s dng ngn xp nhn. Thc ra, phn cp ng dn khng phi l k thut mi, ATM cung cp c ch phn cp 2 mc da vo khi nim ng o (VP) v knh o (VC). Tuy nhin, MPLS cho php lng nhiu ng dn LSP vo nhau mt cch ty , t trin khai cc ng dng nh MPLS VPN v MPLS-TE. 1.6. Kh nng m rng

Trong k thut chuyn mch nhn, nh tuyn lin min (inter-domain) tch bit hon ton i vi nh tuyn ni min (intra-domain, iu ny ci thin ng k kh nng m rng mng MPLS. (n na, kh nng m rng ca MPLS cn da vo qu trnh xc nh FEC tp trung d liu; v s dng ngn xp nhn tng hp



hoc lng cc ng dn LSP vi nhau. Do , nhiu ng dn LSP thuc cc FEC khc nhau c th c tng hp vo mt ng dn LSP duy nht, tng kh nng m rng ca MPLS.

1.7 Kt lun chng Chng ) thc hin tm hiu mt s ni dung v kin trc c bn ca k thut chuyn mch nhn MPLS nh sau:

Cc khi nim c bn trong MPLS. Kin trc v chc nng ca cc thnh phn trong mt nt chuyn mch nhn

LSR/LER.

Cc vn trng tm trong nguyn l hot ng ca MPLS. o Cc giao thc nh tuyn v vai tr ca chng trong MPLS. o Cc giao thc phn phi nhn v trao i nhn trong MPLS.

Vi kin trc ca k thut MPLS, chc nng iu khin v chc nng chuyn tip c tch bit, iu ny cho php nng cao hiu nng chuyn tip lu lng ca cc b nh tuyn/chuyn mch LSR trong khu vc mng li ca min MPLS, ng thi cho php h tr cc dch v t u cui ti u cui. K thut chuyn mch MPLS c bn cho php m rng trin khai nhiu loi ng dng nng cao v tin ch nh MPLS-VPN, MPLS-TE, MPLS-QoS, MPLS-AToM Cng nh s tch bit gia chc nng iu khin v chc nng chuyn tip m min MPLS c kh nng m rng rt tt. Cc loi dch v, cc loi lu lng, cc loi giao thc mng c th thay i dn ti s thay i cc thnh phn ca mt phng iu khin, tuy nhin nn tng mt phng chuyn tip vn c gi nguyn. Do cc thnh phn trong min chuyn mch MPLS khng cn thit phi nng cp hay thay th khi c s thay i trn mt phng iu khin. Chng ) ca lun vn tp trung nghin cu l thuyt v cc khi nim v cc thnh phn c bn cng nh kin trc v nguyn l hot ng ca k thut chuyn mch nhn MPLS, to c s v kin trc nn tng cho vic i su nghin cu v thuc tnh khi phc ca k thut lu lng trong MPLS (MPLS-TE) chng )).

Lun vn tt nghip C(NG )): K THUT LU LNG MPLS-TE


C(NG II K THUT LU LNG V CC C C( KHI PHC BO V C

BN TRONG MPLS

2.1 Tng quan v k thut lu lng .. Khi nim k thut lu lng gii quyt bi ton ti u hot ng ca mng v ti u ha vn s dng cc ngun ti nguyn trong mng, thng thng c hai k thut c th c p dng v trin khai, l:

K thut mng (Network Engineering): l dng k thut iu chnh h tng kin trc mng nh Topology, loi thit b, loi lin kt trong mng nhm ti u ha hot ng ca mng. K thut lu lng (Traffic Engineering): l dng k thut iu chnh cch

thc truyn ti lu lng ca mng nhm ti u hot ng mng. K thut lu lng l qu trnh iu khin cch thc cc lung lu lng i qua

mng nhm ti u ha vic s dng ti nguyn v hiu nng ca cc lin kt trong mng. K thut lu lng tin hnh o c, m hnh ha, c trng ha cc tham s c th ca cc ngun ti nguyn trong mng t iu khin lu lng nhm s dng mt cch ti u nht cc ngun ti nguyn ny.

Khi trin khai k thut lu lng trong mng, c hai phng thc trin khai tp trung vo hai mc tiu nh sau:

K thut lu lng hng lu lng (Traffic-Oriented) K thut lu lng hng ti nguyn (Resource-Oriented)

K thut lu lng hng lu lng bao gm mt lot cc phng thc gii quyt nhng vn ny sinh t yu cu p ng cht lng dch v QoS cho tng loi lu lng c th nh bng thng, tr, bin ng tr, t l mt gi, v hai m hnh QoS ph bin l IntServ (Integrated Service) v DiffServ (Differentiate Service). Trong m hnh )ntServ p dng cho cc gi tin theo tng lung, trin khai bo hiu t u cui n u cui, cn m hnh DiffServ ch yu p dng cho tng loi dch v v c kh nng m rng cao hn rt nhiu so vi IntServ, dn dn thay th



)ntServ. M hnh ny c trin khai ng thi ti cc nt trong mng nhm h tr v b sung cho nhau. K thut lu lng hng lu lng ch yu ti u ha hot ng ca mng trong iu kin c xy ra tc nghn cc b v tm thi trong mng hoc ni cch khc l x l trong qu trnh bng n lu lng v tc nghn vi thi gian ngn. K thut ny c trin khai v pht trin mnh m trong cc mng IP truyn thng thng c gi l cc k thut IP QoS.

K thut lu lng hng ti nguyn thc hin o lng, m hnh ha, c trng ha cc ngun ti nguyn trong mng, t a ra phng thc iu khin cch thc truyn ti lung lu lng ti thi im c th nhm ti u ha hot ng ca mng. Cc ngun ti nguyn ca mng bao gm: bng thng ti a, bng thng kh dng hin thi, tr ng truyn, bin ng tr, suy hoa ng truyn, nng lc chuyn mch ca thit b, t l mt gi trung bnh Trong bng thng l mt ti nguyn ct yu ca mng, do chc nng trng tm ca k thut lu lng hng ti nguyn l qun l v a ra cc phng thc iu khin lu lng s dng hiu qu ti nguyn ny. .. Bi ton tc nghn v k thut lu lng

Tc nghn l tnh hung xy ra trong mng khi kh nng truyn ti lu lng ca mng khng p ng c nhu cu truyn ti lu lng i qua mng . Tc nghn c th xy ra do cc nguyn nhn mang tnh vt l nh lin kt, nt v cng c th xy ra do cc nguyn nhn mang tnh logic, iu khin:

Tc nghn xy ra trn mt lin kt khi tc truyn ti vt l ca lin kt khng p ng c dung lng d liu truyn ti yu cu trn lin kt . Tc nghn cng c th xy ra trong ni b mt thit b khi nng lc chuyn mch ca thit b khng p ng c yu cu. Nng lc chuyn mch ca thit b ph thuc vo trng chuyn mch ca thit b , khi nhiu u vo cng yu cu chung mt u ra tng ng th trng chuyn mch s b tc nghn. Tc nghn xy ra khi cc dng lu lng c nh x khng hiu qu ln cc

ti nguyn lm cho mt s tp con cc ti nguyn lun lun phi hot ng vi cng ti cao trong khi s khc hot ng rt t hoc thm ch khng hot ng. Tc nghn loi ny thng xy ra do s hot ng khng ti u ca cc giao thc iu khin nh cc giao thc nh tuyn, bo hiu. gii quyt bi ton tc nghn, ta c th gii quyt theo hai hng sau:



Tng cng dung lng, tc vt l ca cc lin kt, m rng nng lc x l ca cc nt trn mng, hoc ng dng cc phng thc ca k thut lu lng hng lu lng (Traffic-Oriented). S dng k thut lu lng hng ti nguyn (Resource-Oriented iu

chnh cc nh x gia lu lng v ti nguyn trong mng t cp pht cc ti nguyn sao cho ti u v hiu qu cao.

Vi iu kin bng n lu lng tm thi, k thut lu lng hng lu lng hon ton c th tr thnh mt gii php hp l cho mng, tuy nhin trong iu kin bng n lu lng xy ra thng xuyn th k thut ny khng th gii quyt trit vn tc nghn. K thut lu lng hng ti nguyn l gii php cho vn tc nghn ko di hay thng xuyn xy ra ti mt khu vc no trong mng trong khi cc khu vc khc hot ng di hiu nng kh dng. .. K thut lu lng ti lp lin kt d liu

K thut lu lng ti lp lin kt d liu (lp trong m hnh OS) c trin khai t lu, ch yu trong cc mng s dng cc kt ni o PVC v SVC nh Frame-Relay hay ATM. Trong m hnh chuyn tip lp lin kt d liu, cc thit b nh tuyn hay cc thit b hot ng lp c t trn cu trc lin kt ca lp 2. Cc thit b nh tuyn hot ng lp 3 s khng c kin thc v cu trc u ni vt l c th v bng thng kh dng hin thi trn mi lin kt. Cc giao thc nh tuyn s nhn din cc PVC v SVC nh cc ng dn im-im v a ra cc quyt nh nh tuyn/chuyn mch tng ng. Nu mng lin kt d liu cung cp full-mesh cc kt ni dng logic PVC/SVC gia cc thit b trong mng, cc giao thc nh tuyn ti lp 3 s nhn din cc kt ni ny nh cc kt ni trc tip gia cc nt v s s dng cc lin kt ny truyn ti lu lng, m t trong hnh 2.1

L2 L2

L2 L2

L2 L2

L3

L3

L3

L3

L3

L3

L3

L3

L3

L3

L3

L3

Hnh 2.1: M hnh x p chng



K thut lu lng c trin khai hon ton lp , lu lng s c truyn trn cc PVC v SVC, hng i ca chng c thit k cn thn v c nh tuyn ngun ti lp cho php nh iu hnh mng iu khin mt cch chnh xc khng ch ng truyn, lng nt m lu lng s c truyn qua, m cn l dung lng m lung lu lng s s dng. Cc PVC v SVC c qun l bi mt h thng qun l ngoi bng, c thit lp t ng hoc tnh bng cc giao thc bo hiu v thit lp ng tch hp lp nh PNN).

Trong cc mng Frame-Relay, vn thit lp cc PVC thng c s dng bi cc cng c qun l cho php nh qun tr tnh ton ng dn ti u nht ti lp 2 da trn bng thng kh dng hin thi v mt s tham s rng buc khc ca tng lin kt. Trong mng ATM, c th thit lp cc PVC nh Frame-Relay nhng ATM cn cho php s dng cc giao thc bo hiu v thit lp ng t ng nh PNN) xy dng cc ng SVC ng. K thut lu lng trong mng lin kt d liu s dng cng ngh ATM hoc Frame-Relay c m t trong hnh 2.2. Nh qun tr mng c th s dng cc phng thc thit lp PVC v SVC iu chnh sao cho lu lng t R n R6 s i qua PVC/SVC c hng R1-R2-R5-R ng dn ti u nht t R n R6; cn lu lng t R n R6 s i qua PVC/SVC c hng R7-R2-R3-R4-R. Qua lm gim tc nghn trong ng dn (2, 5, 6) v s dng hiu qu ng dn (2, 3, 4, 6), trnh lng ph bng thng nhn ri trn cc lin kt ny trong iu kin nh tuyn/chuyn mch bnh thng.

R4

R6

R5

R3

R2

R7

R1PVC

R1R2R5R6

PVC R7R2R3R4

R6

ATM/Frame-RelayNetwork

Hnh 2.2 : K thu t u ng ti l p 2



K thut lu lng c th c trin khai ti lp 2 v ti u c ng truyn ca lu lng trong mng, tuy nhin n vn mang nhiu nhc im:

Cn nhiu thit b lp 2, cc thit b trong mng lc ny s khng c u ni trc tip vi nhau m cn thit phi c nhiu cc thit b chuyn mch lp 2 nh cc b chuyn mch ATM/Frame-Relay. Cn mt c ch qun l mng phc tp, lc ny ngoi vic phi qun l cc

thit b mng hot ng vi cc giao thc nh tuyn lp 3, cn thit phi xy dng mt h thng qun l ngoi bng cho cc thit b hot ng ti lp 2. Pht sinh nhiu vn m rng i vi cc giao thc nh tuyn do s lng

qu ln cc phin thit lp quan h lin k khi mng lin kt d liu c trin khai dng full-mesh. Tn km bng thng cho lng tiu ca ATM v Frame-Relay.

Khng h tr m hnh cht lng dch v DiffServ QoS do mi dch v c phn bit lp 3 da vo cc gi tr DSCP/IP-Precedence ca trng ToS trong tiu gi tin )P u c a xung chung qua lp tng thch AAL ca ATM. Cc vn kh nng m rng O(N2) v O(N3 i vi cc mng ATM/Frame-

Relay trong m hnh full-mesh PVC/SVC. Vi mt mng N nt, khi mt lin kt im-im gp s c, hai nt trn lin kt cn thng bo cho tt c cc nt cn li bng cc bn tin iu khin/bo hiu, t gy ra ON2). Khi mt nt gp s c, (N-1) nt cn li u tin hnh thng bo cho tt c cc nt cn li bng cc bn tin iu khin/bo hiu, t gy ra ON3).

.. K thut lu lng ti lp mng i vi cc giao thc nh tuyn truyn thng ti lp mng (lp 3 trong m hnh OS), c ch nh tuyn ch yu da trn a ch ch, tiu ch nh tuyn ch da trn gi tr chi ph (Cost) cho mi ng truyn trong mng hoc tnh ton s chng (Hop Count) cn phi truyn t ngun n ch. Cc gi tr ny c gn tnh vi tng giao din lin kt vt l m khng th hin c bng thng kh dng hin thi ca lin kt, do khng th gii quyt c bi ton tc nghn ti mt khu vc trong mng trong khi cc khu vc khc th hot ng t hoc khng hot ng.

K thut lu lng c th c trin khai ti lp 3 bi mt s k thut nh nh tuyn ngun, nh tuyn tnh hay nh tuyn theo chnh sch, tuy nhin tt c nhng k thut u mang nhiu nhc im:



nh tuyn ngun c th c s dng thay th cc tuyn ng c tnh ton bi cc giao thc nh tuyn trong mng truyn ti tuy nhin yu cu cn thit b ngun phi gi cc bn tin yu cu, k thut ny rt t c trin khai. nh tuyn tnh c th c s dng dn lu lng i theo hng khc so

vi hng c tnh ton bi cc giao thc nh tuyn truyn thng, tuy vy hai nhc im ln nht ca nh tuyn tnh l khng phn bit c cc loi lu lng khc nhau n t cng mt ngun v khng tng thch c trong trng hp cc lin kt gp s c. nh tuyn theo chnh sch PBR (Policy-Based Routing) cho php phn bit c cc loi lu lng khc nhau n t cng mt ngun nhng kh nng

m rng khng kh thi do PBR yu cu lng cu hnh v thit lp cc nt rt nhiu, tuy nhin PBR vn mang nhc im khng tng thch c trong trng hp cc lin kt gp s c.

2.2 K thut lu lng MPLS-TE K thut lu lng MPLS-TE (MPLS Traffic Engineering) l mt trong nhng ng dng nng cao ca chuyn mch nhn MPLS, mang nhiu u im vt tri so

vi k thut lu lng truyn thng ti lp lin kt d liu hay ti lp mng. Trong min chuyn mch MPLS c trin khai k thut lu lng MPLS-TE, cc LER/LSR nh tuyn/chuyn mch theo chuyn mch nhn MPLS vi ng dng k thut lu lng MPLS-TE vi mc tiu iu khin ng dn lu lng ph hp vi thuc tnh ca lung lu lng.

MPLS-TE s dng cc ng hm (Tunnels) hay cn gi l cc trung k lu lng (CR-LSP/TE-LSP iu khin ng dn lu lng, mt ng hm MPLS-TE l mt tp hp cc lung lu lng c cng chung cc thuc tnh v c cng mt Ingress-LER v mt u ra Egress-LER. Mt ng hm MPLS-TE c gn vo mt ng dn n hng LSP bng cch so snh cc thuc tnh yu cu ca ng hm ny vi cc thuc tnh ca cc ng dn LSP kh dng, c thc hin bi cc thut ton tnh ton v thit lp ng rng buc. Nh trn hnh .3, cc b nh tuyn trong min MPLS-TE trao i thng tin rng buc v lin kt, sau PE ty vo thuc tnh rng buc yu cu ca lu lng t CE1 v CE2 m xy dng CR-LSP1 v CR-LSP2 l cc LSP rng buc, sau chn la ng i ph hp nht cho cc lung lu lng.



P

CE1

CE2

MPLS-TECE3

Lu lng 20Mbps ti CE3

Lu lng 40Mbps ti CE3

CR-LSP 1

CR-LSP 2

P

P

PE1 PE2

40Mbps

55Mbps 55Mbps

40Mbps 40Mbps

Min MPLS

Hnh 2.3: K thu t u ng trong MPLS Trung k lu lng phn bit vi cc ng dn n hng LSP, cc LSP s l ng cho trung k lu lng i xuyn qua. Ti nhng thi im khc nhau, mt

trung k lu lng c th i qua cc ng dn LSP khc nhau. Ty tng thi im m LSP no bao gm tp cc lin kt c cc thuc tnh rng buc tha mn cc thuc tnh rng buc ca trung k lu lng th LSP s c la chn v s dng. Ngoi ra khi mt LSP thit lp v c s dng bi mt trung k lu lng m vn cn d ti nguyn th LSP hon ton c th c mt trung k lu lng khc thit lp v s dng. Trung k lu lng truyn ti trn cc ng dn n hng LSP nn chng cng c tnh cht n hng, do truyn ti c lu lng theo hai chiu gia mt cp LER th cn thit phi c t nht hai trung k lu lng ti mi LER c th m bo c k thut lu lng ha cho lu lng gia hai nt ny.

K thut chuyn mch MPLS cn c trin khai trong mng trc khi ng dng k thut lu lng MPLS-TE. Trong h thng mng s dng k thut MPLS, mt LER xy dng cc ng dn n hng LSP ti cc LER cn li, cc LSR trong khu vc mng li ch thc hin qu trnh chuyn mch nhn MPLS.

K thut lu lng MPLS-TE cho php thc hin k thut lu lng ti LSR u ngun ca mt ng dn LSP, nt ny tnh ton ng dn hiu qu nht qua mng truyn lu lng ti LSR u xa ca ng dn LSP . thc hin c iu ny LSR u ngun cn phi nm c cu trc lin kt ca ton b mng cng nh thuc tnh v bng thng kh dng hin thi v cc thuc tnh khc ca tng lin kt trong mng. Do giao thc nh tuyn c s dng gia cc u cui MPLS-TE hay gia LSR u ngun v LSR u cui ca mt LSP bt buc phi l



giao thc nh tuyn dng Link-State. K thut chuyn mch MPLS cho php nh tuyn theo ngun SBR, LSR ti u ngun ca LSP s c quyn s dng LSP no ti c LSR ti u ra. LSP ny c gi l LSP c lu lng ha hay cn gi l trung k lu lng hoc ng hm TE. Cc lu lng c chung cc c tnh c ghp vo trong mt trung k lu lng c iu khin bi nh qun tr mng. Cc lu lng ny s c truyn ti t Headend-LSR ti Tailend-LSR theo mt LSP ph hp ti mi thi im.

Ba vn c bn trong vn thc hin k thut lu lng ca k thut lu lng MPLS-TE l: nh x loi lu lng ln cc lp chuyn tip tng ng FEC

nh x cc FEC ln cc lp trung k lu lng (Traffic Trunk) nh x cc trung k lu lng ln cu trc lin kt ca mng vt l thng qua

cc LSP rng buc

P

PE1 P

P

P

PE2

MPLS-TEMPLS

OSPF-TE / ISIS-TE P PE3

PCALC/CSPFHeadend-LSR

CR-LSP 1

RSVP-PATH

RSVP-RESV

Tailend-LSR

Cc thuc tnh rng buc ca lin kt

Trung k lu lng

Hnh 2.4: Tn uan h hot ng ca MPLS-TE thc hin bi ton c bn ca MPLS-TE, cc thnh phn ca k thut lu lng MPLS-TE c trin khai trong mng bao gm: Xc lp v gn cc thuc tnh rng buc cho tng lin kt bng thng ti a, bng thng kh dng hin thi, tr, bin ng tr..) Phn phi thng tin rng buc ca lin kt bng giao thc OSPF/IS-IS m rng

cho MPLS-TE

Khi to cc trung k lu lng cng cc thuc tnh rng buc yu cu ca n



Thc hin tnh ton ng rng buc bng thut ton CSPF/PCALC ti nt Headend-LSR

Thit lp v bo hiu ng rng buc bng giao thc CR-LDP/RSVP-TE Thc hin mt loi c ch ghp lu lng ln trn ng dn lu lng va

tnh ton v thit lp, bo hiu thnh cng.

2.3 Bo v, khi phc trong MPLS-TE K thut lu lng MPLS-TE c cc c ch bo v, khi phc nhm gim thiu

ti a hu qu ca cc s c trong min chuyn mch MPLS-TE, t cung cp kh nng truyn ti lu lng tin cy. Lu lng trong min chuyn mch MPLS-TE i trn cc ng dn LSP rng buc bao gm mt tp cc lin kt i qua cc nt, khi c s c xy ra vi cc nt v lin kt tng ng ca mt LSP rng buc th LSP khng th tip tc truyn ti lu lng nh bnh thng. V nguyn tc c bn ca bo v, khi phc trong MPLS-TE l ngay lp tc chuyn lu lng ca LSP rng buc gp s c sang mt LSP rng buc khc m bo kh nng truyn ti trong mng. .. S cn thit ca bo v, khi phc trong mng MPLS Cc nh iu hnh mng phi ng u vi cc s c v lin kt v nt trong mng t khi h thng mng ra i. Cc giao thc nh tuyn ni min IGP thng thng c cc phng thc thch nghi v nhanh chng phc hi sau khi gp s c. Qu trnh t lc pht hin s c cho ti khi khc phc hon ton s c c gi l qu trnh hi t. Trong mng cn phi m bo thi gian hi t thp gim thiu thi gian xy ra vn mt gi. Tuy nhin kh nng hi t ca cc giao thc IGP c mt s nhc im nh:

Trong mt mng ln, thi gian hi t tng i ln, trong thi gian hi t mt gi xy ra, thng thng khi phc mt lin kt b flapping trong mng li c th cn ti 5-10 giy. Mt lin kt b s c c th dn ti tc nghn ti mt s khu vc trong mng,

trong khi mt s khu vc khc th khng c s dng. Nu cu hnh gim thi gian hi t xung thp th c th lm cho mng qu

nhy cm vi cc s c nh nh tnh trng lin kt b flapping.



Vi cc giao thc nh tuyn IGP dng Link-State nh OSPF/)S-IS, b nh tuyn s dng timer pht hin s c. Cc b nh tuyn trong mng s gi cc bn tin hello nh k ti cc nt ln cn. Nu nt ln cn khng nhn s lng bn tin hello trong mt khong thi gian xc nh, b nh tuyn s kt lun lin kt hoc nt gp s c, gi bn tin LSA (Link State Advertisement) thng bo cho tt c cc nt khc trong mng v thc hin thut ton SPF. Trong trng hp xu nht, lin kt b hin tng flapping up, down xy ra lin tc) th thut ton SPF s phi thi hnh nhiu ln dn n tnh trng mt n nh trong mng v tiu th nng lc x l ca nt. K thut MPLS-TE i hi s c mt ca cc giao thc nh tuyn loi ny, tnh hnh cn ti t hn, khi mt lin k xy ra s c, qu trnh hi t thng thng s din ra vi cc s kin nh sau:

1. Lin kt gp s c, cc ng dn LSP thng thng tng ng b hy, thut ton SPF thi hnh li tnh ton li cc bng nh tuyn, giao thc LDP thc hin gn nhn li cho cc LSP mi.

2. Cc LSP rng buc tng ng vi lin kt gp s c s b hy, cc Headend-LSR c cc LSP rng buc b hy phi thi hnh li thut ton CSPF tnh ton ng LSP rng buc mi.

3. CR-LDP/RSVP-TE phi thc hin thit lp v bo hiu LSP rng buc mi. 4. Headend-LSR phi thc thi phng thc ghp lu lng ca trung k lu lng ln LSP rng buc mi. Do thi gian hi t trong min MPLS-TE khi xy ra s c c th din ra vi

thi gian lu hn rt nhiu so vi nh tuyn IP truyn thng, trong thi gian pht hin s c da vo c ch hello l ln nht. gim thi gian khi phc h thng, cc nh qun tr mng c th gim thi gian pht nh k cc bn tin hello. Tuy nhin, trong trng hp nghn dn n mt nhiu gi tin hello lin tip, b nh tuyn c th nhm ln trong vic kt lun c s c xy ra. Ngay c khi h thng mng li s dng cc phng thc chuyn mch bo v t ng APS (AutoProtection Switching) nh trong mng SONET cho php chuyn i lin kt b hng sang lin kt d phng vi thi gian tr nh hn ms th thi gian hi t ca min MPLS-TE vn b nh hng do cc giao thc nh tuyn (OSPF/IS-IS) vn phi thit lp cc mi quan h ln cn mi.

Tuy cc giao thc nh tuyn c kh nng khc phc nhiu s c xy ra trong mng, nhng thi gian khi phc h thng khng c m bo. Thi gian ny ph thuc rt nhiu vo kch thc mng v giao thc nh tuyn c s dng. Ngoi ra,



hin ti cha c c ch chun thc hin vic trao i thng tin trng thi mng gia lp IP v cc lp thp hn, lp IP ch nhn bit c s tn ti ca s c da vo hin tng mt bn tin hello hoc keep alive, lp IP khng th bit i tng gp s c l lin kt hoc l nt. Tuy nhin, lp IP c th bit c loi lu lng no cn phi c khi phc nhanh v d tr trc bng thng m bo cht lng dch v.

Mt s c ch pht hin s c ti lp thp nh trnh qun l phn cng, thit b nhn bit mt kt ni in hoc quang gip thi gian pht hin s c trong mng nhanh hn so vi c ch ca cc giao thc nh tuyn. Trong trng hp khi phc cc b, nt pht hin s c c th trc tip chuyn i lung lu lng sang ng khi phc thit lp trc m khng cn phi thng bo li cho cc nt khc, vic khi phc h thng s din ra nhanh hn. Tuy nhin, cc c ch ny yu cu cc phn cng chuyn dng v tn km, mt s m hnh s dng ti nguyn khng hiu qu chng hn nh: trong m hnh mng Ring ca SONET/SDH, vic d tr bng thng c th chim hn mt na bng thng kh dng ch phc v cho vic khi phc; trong m hnh mng mesh, c rt nhiu ng dn c th phc v cho qu trnh khi phc dn n vic d tha ti nguyn hoc s dng ng dn khi phc khng ti u. Ngoi ra, c ch khi phc ti lp thp khng th phn bit cc lung lu lng c u tin khc nhau, khng th khi phc cc knh ring v m bo cht lng cho tng loi lu lng. Do nht thit phi c c ch bo v, khi phc trong MPLS-TE m bo kh nng truyn ti tin cy ca k thut ny. Mc tiu ca cc c ch bo v, khi phc trong MPLS-TE l gim thiu nhiu nht c th t l mt gi, thi gian gin on dch v, lng ti nguyn dnh ring cho ng dn trc thi im xy ra s c, m bo QoS v bng thng ca ng khi phc tng ng vi ng lm vic gc, m bo cht lng cho cc lung lu lng u tin. .. Khi nim bo v, khi phc trong MPLS-TE

Khi nim cc c ch bo v, khi phc trong MPLS-TE [12] [13] l tp cc th tc cho php p dng i vi mt hoc nhiu ngun ti nguyn ca mng mt cch c chn la nhm m bo t l mt gi thp trc s c trong mng. Ti nguyn c bo v c th l cc ti nguyn mang tnh vt l nh lin kt, nt, hoc cng c th l cc ti nguyn mang tnh logic nh cc ng dn LSP rng buc i trn mt lin kt hoc i qua mt nt. Khi mt lin kt gp s c, cc LSP rng buc i trn lin kt hoc i qua nt ny cng s gp s c, do bo v, khi phc ti nguyn vt l cng chnh l bo v ti nguyn logic. Thng thng ti nguyn c la chn bo



v, khi phc l lin kt, nt hoc ng TE-LSP. Cc khi nim c bn s dng trong khi phc MPLS:

ng TE-LSP lm vic: l ng chuyn ti trung k lu lng khi xy ra li. y l ng c bo v bi c ch khi phc. ng TE-LSP khi phc: l ng m trung k lu lng s c ti nh

tuyn sau khi xy ra li, c thit lp bo v cho ng lm vic. PSL (Path Switch LSR): l b nh tuyn LSR ng trc v tr li trn ng

lm vic chu trch nhim chuyn mch hoc ti to lu lng sang ng khi phc. PML (Path Merge LSR): l b nh tuyn LSR chu trch nhim nhn lu lng trn ng khi phc v s hp nht lu lng tr v ng lm vic

hoc chuyn lu lng ra khi min MPLS nu bn thn n l ch. POR (Point Of Repair): POR l mt b nh tuyn LSR chu trch nhim sa

cha mt ng dn LSP, n c th l PML hoc PSL ty theo c ch khi phc no c dng. FIS (Fault Indication Signal): l bn tin ch th c li xy ra trn ng,

chng c chuyn tip bi cc b nh tuyn LSR trung gian cho ti khi n n c POR. F)S c pht i theo chu k bi cc nt k cn v tr li trong khong thi gian c cu hnh trc hoc cho n khi nhn c xc nhn t cc nt ln cn ca n. FRS (Fault Recovery Signal): l bn tin ch th li trn ng lm vic c sa cha xong. FRS c chuyn tip cho n khi n n c mt LSP m nhn cng vic chuyn tr li ng lm vic gc. FRS cng c pht i theo nh k tng t nh F)S.

Thng thng, vic khi phc s c trong h thng mng gm c bc: H thng mng phi c kh nng pht hin s c. Nt pht hin s c phi thng bo s c cho cc nt khc trong mng, nt

thng bo li ph thuc vo c ch khi phc s dng. Thc hin tnh ton thit lp ng khi phc trong mng.

Thc hin chuyn i lu lng sang ng khi phc.



2.3.3 Pht hin, thng bo li trong MPLS 2.3.3.1 C ch m rng Hello RSVP-TE C ch ny do Martin Petersson xut [12] cho php b nh tuyn LSR pht hin vic mt lin lc vi cc nt k cn trong mng. C ch m rng ny thm mt bn tin Hello trong giao thc RSVP-TE cha i tng yu cu HELLO REQUEST v i tng xc nhn HELLO ACK. Thi gian pht nh k bn tin Hello ti b nh tuyn LSR c th c cu hnh ty thuc vo ngi qun tr, mc nh l 5ms. Vic pht hin li da trn vic thu nhn v lu tr gi tr instance ca nt k cn, v d: B nh tuyn A gi bn tin Hello cha i tng HELLO REQUEST vi gi tr instance A ca chnh n v gi tr instance B ca nt k cn B. Khi nt k cn nhn bn tin ny, n thc hin vic so snh gi tr instance A vi gi tr nhn c trc , ng thi n cng kim tra pha gi A c tr li ng gi tr instance B ca mnh hay khng. Nu cc gi tr ny khc nhau th nt A c phng on ang thit lp li. Nt nhn (ELLO REQUEST sau s to bn tin HELLO ACK. Nu vic kim tra chnh xc, bn tin ACK s cha gi tr instance ca c pha gi v pha nhn, nu khng th pha gi ACK s t gi tr instance ca pha nhn l ch ra kt ni tng b mt. Nu khng c bn tin Hello no c nhn trong mt khong thi gian xc nh th b nh tuyn LSR kt lun nt k cn mt lin lc, mc nh gp 3.5 ln khong thi gian pht bn tin Hello (5 * 3.5 = 17.5 ms). 2.3.3.2 RSVP-TE Softstate

Vic s dng cc bn tin cp nht PATH v RESV ca giao thc RSVP-TE c th dng pht hin s c trong mng MPLS. Nu bn tin PATH hoc RESV gp li trong qu trnh cp nht, bn tin PathErr hoc ResvErr s ra thng bo li v chi tit li tng ng gi tr v b nh tuyn Ingress-LSR. Thi gian cp nht cc bn tin ny thng c thit lp gi tr ln gim lu lng iu khin trong mng, mc nh l 30s. V vy, c ch ny khng thch hp trong vic khi phc nhanh s c trong mng MPLS. 2.3.3.3 LSP Ping/Traceroute C ch ny dng kim tra hot ng ca mt phng chuyn tip ca b nh tuyn LSR trong ng dn n hng LSP, kim tra cc gi tin thuc lp FEC c thc s chuyn tip chnh xc n b nh tuyn Egress-LSR hay khng.

Trong c ch Ping, mt gi tin c ng gi trong mt gi UDP v chuyn vo ng dn LSP nh cc gi tin khc thuc cng lp FEC. Khi gi tin n b nh tuyn Egress-LSR, n c i chiu li vi mt phng iu khin, kim tra b nh



tuyn LSR ny c phi l b nh tuyn Egress-LSR thuc lp FEC hay khng. Sau , mt gi tin phn hi cha kt qu c gi ngc li b nh tuyn yu cu. Trong c ch Traceroute, gi tin c i chiu vi mt phng iu khin ti mi b nh tuyn LSR dc theo ng dn n hng LSP kim tra b nh tuyn ny c phi l b nh tuyn tham gia chuyn tip cho lp FEC hay khng. Nu gi tin Ping gp li, c ch Traceroute c th c s dng xc nh v tr s c xy ra trong mng, kim tra s thng nht gia mt phng iu khin v mt phng chuyn tip. Tuy nhin, cc c ch ny lm tng thm nng lc tnh ton ca cc thit b nh tuyn LSR trong mng. Qu trnh trao i cc bn tin pht hin s c tn nhiu thi gian nn c ch ny khng thch hp trong vic khi phc nhanh h thng mng MPLS.

Ngoi ra, mt c ch khc do )ETF sut l Bi-directional Forwarding Detection (BFD) c th gim thi gian pht hin s c ca mt phng chuyn tip. Tuy nhin, cn phi lu khi s dng c ch BFD cng vi c ch ti nh tuyn nhanh cho lin kt hoc nt trong mng MPLS, khong thi gian pht hin s c ca c ch BFD phi ln hn thi gian chuyn mch sang ng khi phc nhm trnh vic phng on sai s c xy ra ti mt phng chuyn tip ca cc b nh tuyn LSR.

2.3.3.4 Tng kt Giao thc RSVP-TE c s dng phn phi nhn trong mng MPLS, c th

s dng thuc tnh soft-state pht hin li. Tuy nhin, khong thi gian cp nht cc bn tin trong ng dn LSP thng c t cao lm gim lu lng iu khin, v th n khng thch hp cho vic khi phc nhanh trong mng.

S c lin kt c th c pht hin nhanh da vo phn cng v thng bo cho MPLS hoc da vo c ch Hello trong RSVP-TE. Mc d vic pht hin s c da vo phn cng nhanh hn so vi c ch (ello, nhng cn thit phi c mt c ch pht hin s c ring trong MPLS c lp vi cc c ch pht hin s c trong trng hp lp di khng h tr c ch pht hin li hoc khng pht hin s c lin quan n nt.

Vic pht hin s c lin quan n mt phng d liu thng pht hin chm. pht hin cc li ny, c ch Ping v Traceroute c th c s dng nhng khng thch hp cho vic pht hin nhanh s c. Chnh v th, BFD c )ETF xut pht hin s c trong mt phng d liu nhanh hn.



2.3.4 Phn loi cc c ch bo v, khi phc trong MPLS-TE C ch khi phc MPLS chuyn tip lu lng vo ng dn mi tng t nh cc c ch ca cc lp khc. Vic quyt nh im khi phc, tnh ton v cch thc xy dng ng dn khi phc ph thuc vo c ch s dng.

Nu khng c c ch khi phc c s dng trong min MPLS th vic khi phc c thc hin mc nh bi giao thc bo hiu dng thit lp v duy tr ng dn LSP, gi l khi phc dng best-effort. Vic pht hin s c c th dng c ch Hello hoc c ch soft-state RSVP-TE v thng bo cho b nh tuyn Ingress-LSR c gng thit lp li ng dn LSP. Thi gian khi phc ca c ch ny thng ln v ch p dng cho cc lu lng dng best-effort.

Nu mun khi phc nhanh trong MPLS, cc c ch khc cn phi ti thiu thi gian thng bo li hoc thi gian tnh ton ng khi phc. C hai phng thc phn loi cc c ch bo v, khi phc trong k thut MPLS-TE, l:

Phn loi da trn v tr bo v, khi phc kt hp loi ti nguyn c la chn bo v, khi phc. Vi phng thc ny ta c cc c ch:

o Bo v, khi phc dng sa cha ton cc. o Bo v, khi phc dng sa cha ton cc. Phn loi da trn c im ca ti nguyn d phng. Vi phng thc ny ta c cc c ch:

o Bo v, khi phc dng ti nh tuyn. o Bo v, khi phc dng chuyn mch bo v.

2.3.4.1 Sa cha ton cc v sa cha cc b 2.3.4.1.1 Sa cha ton cc

Sa cha ton cc l bo v, khi phc khi c s c bt k xy ra trn ng lm vic, ngoi tr s c xy ra ti cc b nh tuyn Ingress-LSR v Egress-LSR ca ng dn LSR. im sa cha POR ( y chnh l )ngress-LSR thng cch xa v tr li v thng c thng bo bng tn hiu FIS. Vic khi phc ng c tnh cht end-to-end, trong ng lm vic v ng bo v tch bit nhau hon ton. u im ca sa cha ton cc l tt c cc lin kt v nt trong ng lm vic c bo v bng ng khi phc duy nht. Nhc im l tn hiu FIS phi lan truyn v b nh tuyn Ingress-LSR trc khi khi phc bt u.



Hnh 2.5 : Sa cha ton cc 2.3.4.1.2 Sa cha cc b

Sa cha cc b nhm bo v khi s c lin kt hoc nt nhng khi phc nhanh hn do vic sa cha c thc hin cc b ti thit b pht hin s c. Nt lin k trc tip trc v tr li s ng vai tr PSL khi to cng tc khi phc. Sa cha cc b c th c thit lp theo hai trng hp:

Khi phc lin kt: bo v lin kt trn ng lm vic. Nu mt li xy ra trn ng lin kt, khi phc s kt ni PSL v PML hai u lin kt li bng mt ng khi phc tch bit vi ng lm vic cha lin kt li.

Hnh 2.6: Khi phc lin k t Khi phc nt: bo v nt trn ng lm vic. ng khi phc phi tch

bit vi ng lm vic cha nt li v cc lin kt ni vi nt ny. Trong khi phc nt, c th c mt hoc nhiu nt gia PSL v PML.



Hnh 2.7: Khi phc nt u im ca sa cha cc b l tn hiu FIS khng cn phi lan truyn v b nh tuyn Ingress-LSR trc khi khi phc bt u. Ngay khi pht hiu s c, khi phc c th bt u, thi gian khi phc s ngn hn. Nhc im l ch c mt on ng lm vic c bo v.

2.3.4.2 Ti nh tuyn v chuyn mch bo v ng khi phc c th c tnh ton, thit lp ti thi im pht hin s c, hoc trc khi s c xy ra. iu ny dn n c c ch khi phc khc nhau: Ti nh tuyn v chuyn mch bo v. 2.3.4.2.1 Ti nh tuyn i vi khi phc bng ti nh tuyn (re-route, ng khi phc c thit lp theo yu cu sau khi xy ra s c da trn thng bo li, chnh sch nh tuyn, thng tin cu trc h thng mng. Khi pht hin s c trn ng lm vic, mt LSR ng trc v tr li c vai tr l POR bt u bo hiu mt ng khi phc i vng qua im li v ni vo mt nt sau im li ca ng lm vic. ng khi phc ny c th c b nh tuyn PSL tnh ton sn trc hoc tnh ton sau khi pht hin s c hoc sau khi nhn tn hiu FIS thng bo v s c. Khi ng khi phc c thit lp xong, PSL bt u chuyn lu lng trn ng ny.

Ti nh tuyn vi ng khi phc tnh ton sn s nhanh hn so vi ng khi phc tnh ton theo yu cu, do ng khi phc c tnh ton v la chn trc khi s c xy ra. Tuy nhin, ng khi phc c th l ng dn khng ti u ngay ti thi im xy ra s c. ci thin vn ny, mt c ch c xut [14] cho php tnh ton li ng khi phc mi khi b nh tuyn LSR nhn c cc



bn tin cp nht. V vy, b nh tuyn LSR s c ng khi phc hiu qu hn, nhng c ch ny i hi ti nguyn x l nh b nh, CPU v ch bo v cho cc s c lin quan n lin kt.

Mt c ch khc c xut [15] nhm bo v cc s c lin quan n nt. Cc nt trong mng u c thit lp l im thc hin khi phc POR v c kh nng nhn bit c tt c cc nt pha sau n b nh tuyn Egress-LSR da vo gi tr Record_Route trong bn tin RSVP-RESV trong qu trnh thit lp ng lm vic. Khi pht hin s c, b nh tuyn LSR s tnh ton ng khi phc ti cc nt pha sau v la chn mt ng khi phc ti u nht v tha mn cc yu cu rng buc tng ng vi ng lm vic gc. Ta xt mt trng hp nh hnh 2.8, khi LSR 5 gp s c, LSR 2 s c gng tm ng khi phc n LSR 8 v LSR 10. Nu la chn ng dn da trn s Hop nh nht th ng khi phc LSR 2 LSR 4 LSR 7 LSR10 s c chn.

Hnh 2.8: T i nh tuy n u im khi phc bng ti nh tuyn l khng s dng ti nguyn d tr trong mng trc khi bo hiu ng khi phc. Nhc im l ti nguyn c th s khng p ng yu cu ca lu lng ti thi im ng khi phc thit lp hoc c u tin thp hn so vi lu lng ang s dng trong ng dn ny, do ng khi phc c th thit lp khng thnh cng.



2.3.4.2.2 Chuyn mch bo v Trong chuyn mch bo v, ng khi phc c tnh ton v thit lp trc

khi s c xy ra trn ng lm vic. PLS

nghiên cứu cơ chế khôi phục trong mạng mpls-te

Documents