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2. MC LCLI NI U..........................................................................................................................5CHONG 1: GII THIU........................................................................................131.1. CC YU T DN N VIC NGHIN CtJ CHUYN MCH NHN 141.1.1. S pht trin ca Internet.............................................................................................141.1.2. Gi c v hiu qu.........................................................................................................15. 1.3. S tch hp IP trn ATM...............................................................................................161.1.4. M rng cc chc nng nh tuyn...........................................................................191.2. TM TT LCH S........................................................................................................201.2.1. B nh tuyn chuyn mch t bo CSR ca Toshiba..............................................201.2.2. Chuyn mch IP [4]......................................................................................................211.2.3. Chuyn mch th...........................................................................................................211.2.4. ARIS ca IBM.................................................................................................................211.2.5. Chuyn mch nhn a giao thc MPLS....................................................................221.3. KT LUN.................................................................................:.............,........22CHNG 2: L THUYT c BN CA CHUYN MCH NHN..................232.1. TNG QUAN.......................................................................................................232.2. KHI NIM V HOT NG c BN TRONG MPLS..............................252.2. . Mt phng d liu v mt phng ii khin.............................................................252.2.2. Mtphng d liu v mt phng iu khin trong IP.............................................262.2.3. Mt phng d liu v mt phng iu khin trong MPLS.......................................262.2.4. Nhng lp chuyn tip tng ng FEC.......................................................... 272.2.5. nh tuyn nht qun....................................................................................................282.3. THNH PHN NH TUYN....................................................................................282.3.1. Nhn l g?.....................................................................................................................282.3.2. Bng chuyn mch nhn..............................................................................................292.3.3. Kh nng mang nhn trong gi....................................................................................312.3.4. Thut ton nh tuyn chuyn mch nhn..................................................................312.3.5. Thut ton nh tuyn n...........................................................................................32 3. Chuyn mch nhn a giao thc MPLS2,3.6. a giao thc: trn v di.........................................................................................332.4. THNH PHN IU KHIN.....................................................................................342.4J. Kt hp trong v kt hp ngoi..................................................................................352.4.2. Kt hp ngc dng v kt hp xui dng................................................................352.4.3. Nhn t do.....................................................................................................................362.4.4. Kt hp nhn luyn iu khin v tuyn d liu.......................................................362.4.5. Phn b thng tin kt hp nhn...................................................................................412.4.6. iu khin nh tuyn tc thi...............................................................................452.5. THIT B RA..............................................................................................462.6. QUAN H GIA CHUYN MCH NHN V VIC NH TUYN,NH A CH LP MNG..............................................................................................462.7. CHUYN MCH IP.......................................................................................................472.7. . Tng quan v chuyn mch IP....................................................................................472.7.2. Cc thnh phn c bn ca chuyn mch IP............................................................512.7.3. Giao thc qun l lung Ipsilon IFMP.......................................................................532.7.4. Giao thc qun l chuyn mch chung GSMP.........................................................572.7.5. Thc t............................................................................................................................592.8. TM TT..............................................;...........................................................................60CHNG 3: CHUYN MCH NHN A GIAO THC MPLS......................613.1. TNG QUAN CHUYN MCH TH.......................................................................613.1.1. H tr cho nh tuyn da vo a chi ch..............................................................613.1.2. nh tuyn phn cp.....................................................................................................663.1.3. Multicast........................................................................................................................693.1.4. Chuyn mch th trn ATM........................................................................................723.1.5. Kim sot'lp vng trong nh (uyn tc thi............................................................743.2. CHUYN MCH NHN A GIAO THC MPLS...............................................753.2. . Nhng im quan trng ca k thut chuyn mch nhn a giao thc MPLS... 763.2.2. Cc thnh phn ca mng MPL.................................................................................763.2.3. iu khin LSP th t v iu khin LSP c p....................................................783.2.4. ng gi d liu...........................................................................................................803.2.5. Giao thc phn phi nhn LDP...................................................................................813.2.6. Cc kiu phn phi nhn.............................................................................................843.2.7. ATM..............................................................................................................................853.3. TM TT.........................................................................................................87 4. CHNG 4: CHT LNG DCH v.................................................................884.1. CC M HNH CHT LNG DCH v...................................................894.1.1. Cc khi nim v thut ton.......................................................................................894.L2. Dch v tch hp...........................................................................................................934.1.3, Dch v phn bit.............................................................................................................:...........984.2. KNH THU RING o..............................................................................1084.2.1. Dch v m bo bng thng....................................................................................1084.2.2. Cc c nh ca mphng iu khin....................................................................1084.2.3. Cc c tnh ca mt phang chuyn tip.................................................................094.2.4. Cc bc thc hin m bo cht lng dch v trong mng li...................1104.2.5. Cc dch v hng thng m ho vi MPLS...........................................................1114.3. TM TT.........................................................................................................................112CHNG 5: NH TUYN....................................................................................1145.1. TNG QUAN GIAO THC NH TUYN..........................................................1145.2. CC GIAO THC NH TUYN.........................................................................1145.2.1. Giao thc thng tin nh tuyn RIP..........................................................................1145.2.2. Giao thc nh tuyn cng ni IGRP.......................................................................1155.2.3. Giao thc nh tuyn ni cao cp EIGRP................................................................1155.2.4. Giao thc ng i ngn nht u tin m OSPF.................................................1165.2.5. Giao thc cng bin BGP...........................................................................................1225.2.6. Cu hnh RIP, OSPF v BGP...................................................................................1285.3. KIN TRC NH TUYN INTERNET.......................................................; 1315.3.1. nh tuyn chinh sch................................................................................................1355.3.2. Tinh n nh.................................................................................................................1365.4. NH TUYN RNG BUC..................................................................................1395.4.1. nh tuyn rng buc l g?......................................................................................1395.4.2. Nhng yu cu k thut ca chc nng nh tuyn rng buc..............................140 5.4.3. CSPK ..............................................................................'.........................................1415.5.MPLS. .............................................................................................................1435.5.1. Giao thc RSVP m rng...........................................................................................1435.5.2. CR-LDP........................................................................................................................1495.5.3. So snh gia CR-LDP v RSVP................................................................................1545.5.4. Giao thc ginh trc ti nguyn h tr phn phi nhn RSVP-TE....................1555.5.5. ng dng chc nng nh tuyn rng buc vo vn qun l lu lng.....1625.5.6. Cht lng dch v oS..........................................................................................170Mc lc 9 5. 5.6. TM TT........................................................................................................171CHNG 6: MNG RING o.............................................................................1736.1. NH TH NO L MNG RING o - VPN?........................................1736.2. M HNH CHNG LP..............................................................................1746.3. M HNH NGANG CP.........................................................................................1766.4. PHN B RNG BUC THNG TIN NH TUYN...................................1786.5. BNG A CHUYN TIP.......................................................................................1806.6. ACHVPN-IP.............................................................................................1816.7.MPL S...........................................................................................................1826.7.1. Bo mt.........................................................................................................................1846.7.2. H tr cht lng dch v..........................................................................................1846.7.3. Kh nng m rng......................................................................................................1876.8.TMT T...............................................................................................................................'......:...........CHNG 7: XY DNG MNG NG TRC MPLS................................1897.1. MNG MPLS TRN GI............................................................................................1897.2. MNG MPLS TRN ATM..........................................................................................1907.3. MNG MPLS TRN HN HP GIA ATM V GI......................................1917.4. TCH HP MPLS VO MNG ATM.............................................................1927.4.1. Nhng vn cn quan tm khi chn thit b LSR ATM ra.............................1947.4.2. Nhng yu cu trong la chn LSR ATM................................................................1947.5. XY DNG MNG MPLS.........................................................................................1957.5.1. Thit k im truy cp PoP.......................................................................................1957.5.2. Thit k PoP ca mt LSR ATM n ra..............................................................1957.5.3. Thit k PoP cho cc LSR ra v LSR ATM........................................................1957.5.4. Thit k b tp trung, LSR ra v mt LSR ATM.................................................1967.5.5. Thit kPoP ca mt LSR.........................................................................................1977.6. NH HNH LIN KT NG TRC MPLS...................................................1977.6.1. Thit k im truy cp................................................................................................1987.6.2. c tnh lu lng t mi PoP................................................................................1987.6.3. c tnh ma trn u lng n hng..................................................................1997.6.4. c tnh ma trn lim lng song hng............................................................... 1997.6.5. Thit k cu hnh rung k ng trc.....................................................................2007.6. . c tnh bng thng kt ni.....................................................................................20110 . Chuyn mch nhn a giao thc MPLS 6. 7.6.7. Gn dung lng kt ni.............................................................................................2027.6.8. iu chnh d phng.................................................................................................2027.6.9. La chn thit b thch hp........................................................................................2027.7. THIT K NH TUYN LP 3............................................................................2027.8. NH HNH LVCMPLS.............;..............................................................2047.8.1. Tin t a chi ch.....................................................................................................2047.8.2. LVC v dn vc...........................................................................................................2057.8.3. Thit k tinh ton cho LSR ra [3]........................................................................2067.8.4. Thit k tinh to.n cho LSR ATM vi dn vc....................................................2077.8.5. Thit k tinh ton cho LSRATMm khng dn vc..............................................207CHNG 8: MNG QUANG, GMPLS V MPXS.............................................2098.1. WDM V MNG QUANG........................................................................................2098.2. CHUYN MCH LAMBDA A GIAO THC...................................................2108.2.1. nh x gia chuyn mch nhn a giao thc v bc sng quang....................2108.2.2. Loi ca cc kt noi quang.........................................................................................2128.2.3. Tng thch iu khin...............................................................................................2138.3. GMPLS V DNG GMPLS CHO MNG QUANG...........................................2138.3.1. Xem xt lin mng gia tng 1 Lambda v tng 2 nhn.......................................2148.3.2. Cc hot ng ca GMPLS.............................................................................. 214CHNG 9: M PHNG HOT NG MNG MPLS V DIFFSERV ..2229.1. CU TRC NS...............................................................................................................2229.2.DIFFSER V..................................................................................................................2269.3. CHNG TRNH M PHNG HOT NG MNG MPLS; MNS....2309.3.1. Gii thiu......................................................................................................................2309.3.2. MNS h tr cc chc nng sau cho MPLS..............................................................2309.3.3. Minh ho mt s hoi ng c bn trong mng MPLS.........................................233PH LC A: NG DNG CA MPLS.......................................................................239A.l. CC NG DNG CA MPLS.................................................................................239A.I.l. K thut lu lng.....................................................................................................239A.1.2. Mng ring o VPN...................................................................................................239A.2.MPLSVATM...............................................................................................................241A.2.1. Tng quan ATM...........................................................................................................241A.2.2. Cc dng pht trin v tich hp ca IP trn ATM.................................................242Mc lc 11 7. A.2.3. c im thch hp ca ATM cho MPLS................................................................244A.2.4. Lin mng gia MPLS v ATM................................................................................248A.3. MPLS V FRAME RELAY.......................................................................................252c im thch hp ca Frame Relay cho MPLS.............................................................252PH LC B: CC BI LAB CU HNH OSPF V BGP.....................................254Labl:.......................................................................................................................................254Lab2........................................................................................................................................256Lab3........................................................................................................................................258Lai 4.............................................................................................................................................261Labs........................................................................................................................................263PH LC C: KNH THU RING o LP 2 V LP 3..................................65Cu hnh cho mng li...,......................................................................................................265Knh thu ring o IP...................................................................................................267Knh thu ring lp 2......................................................................................................267PH LC D: HIN THC MPLS TRN LINUX...............................................270Gii thiu................................................................................................................................270MPLS trn Linux....................................................................................................................270 tng c bn ca MPLS Linux Project...........................................................................270PH LC E: DERIVEIT - CHNG TRNH GI LP CHO MNG GMPLS/MPLS...........................................................................................................276MC CH V I TNG s DNG..................................................................276YU CU H THNG........................................................................................................276C IM CHNH...............................................................................................................277HOT NG...........................................................................................................................277Router chuyn mch nhn (LSR).........................................................................................277Con ng chuyn mch nhn (LSP)..................................................................................278Kin trc phn tng LSP......................................................................................................279Cc lin kt TE.......................................................................................................................280KT LUN..................................................................................................................286THUT NG VIT TT..................................................................................................287TI LIU THAM KHO.........................................................................................29312 Chuyn mch nhn a giao thc MPLS 8. CIIIG 1: GII TIlIrInternet l mt mi trng kh l tng cho nhTig pht minh v k thut mi. Khi nhng k thut v mng mi ra i th c mt vi tng hp dn i vi cc nh nghin cai v u t. K thut chuyn mch nhn a giao thc MPLS (Multiprotocol Label Switching) l mt trong nhng k thut . Chng ta s kho st s lc v k thut MPLS v tr li mt s cu hi v k thut ny, nh l, MPLS l g? n hot ng nh th no? v n s mang li nhng li ch g?MPLS irc pht trin t nhng k thut tng t c ngliin cu gia thp nin 90 ca th k 20. Trong , k thut c bit n nhiu nht l chuyn mch IP (IP Switching) do cc k s ca cng ty Ipsilon nghin cm, nhng trc Toshiba m t mt cch thc tng r t nghin cu b nh tuyn chuyn mch t bo CSR (Cell Switching Router) ca h v nhiu nghin cru khc c cng b, ng ch l chuyn mch th (Tag Switching) ca Cisco v chuyn mch IP da trn nh tuyn tng hp ARIS (Aggregate Route-based IP Switching) ca IBM. Tt c cc nghin cu trn c vi c im chung l h u s dng k thut trao i nhn nh hng d liu, dng nhmg mu iu khin ca b giao thc Internet. Ngha l, h s dng a chi IP v cc giao thc chuan nh hng d liu dng trong Internet nh OSPF v BGP. Tuy nhin, nhng nghin cii khc nhau ch yu mc ch ca n cng nh chi tit xy dng to thnh.Vi cc hot ng nh vy, IETF (Internet Engineering Task Force) thnh lp mt nhm nghin cu chun ha nhng kt qu chung da trn nhng tirng trn. V khng mun trng tn vi cc sn phm ca cc cng ty, IETF t tn cho nhm l MPLS (Multiprotocol Label Switching). K thut MPLS dn ang tr thnh mt chun cng nghip.Chng ta s nghin cu tng quan v phn tch v k thut MPLS cng nh nhng vn lin quan. d dng hn trong qu trnh tim hiu, chng ta s lm r vi thut ng c s dng thng xuyn: Chuyn tip (forwarding): l hot ng chuyn (switch) v nh tuyn (route) mt gi (packet): nhn gi mt ng vo, xc nh n cn i n u bng cch xem xt trng thng tin trong n v gi n ra ng ng ra thch hp. Nhn (label): cm gin l mt khung nhn dng ngn, c chiu di c nh c dng nh tuyn cc gi. Gi t ca nhn thng c gn vi 1 lin kt n (single link).Nhn khng c cu trc, ngha l n khng bao gm nhng thnh phn phn bit. Mt thit b chuyn mch nhn s thay nhn trong mt gi bng mt gi tr mi trc khi chuyn tip n ti im tip theo, do chng ta gi thut ton nh tuyn l thut ton trao i nhn. Ngoi ra chng ta cn nh ngha mt thit b chuyn mch nhn l B nh tuyn chuyn mch nhn LSR (Label Switching Router), dng nhng giao thc iu khin IP chun (v d giao thc nh tuyn RSVP) xc nh phi chuyn tip gi i u. 9. Chng ta cng s kho st nhng k thut c trc MPLS, cc k thut ny u l k thut chuyn mch nhn, nhng mi ci c cch thc hin ring. Nhng tn khc c cc nh nghin cu t cho LSR l B nh tuyn chuyn mch t bo CSR (Cell Switching Router), chuyn mch IP (IP Switching), B nh tuyn chuyn mch th TSR (Tag Switching Router) hay chuyn mch th (Tag Switch) v B nh tuyn chuyn mch tch hp ISR (Integrated Switch Router). Ngoi ra cn c nhiu nghin cu khc m chng ta khng cp y v n khng khc bn nghin cu trn lm. Chng ta cng khng xt n cc b nh tuyn da trn chuyn mch (Switch-based Routers), c hot ng ging mt router bnh thng nhng c lm bn trong mt Switch hn hp. Nhng thit b l nhng thit b hu dng nhng dng gii quyt cc vn khc ch khng phi l LSR,Trc khi xem xt chi tit cc nghin cu trn, chng ta cn nn bit qua mt s yut sau:1.1. CC YU T DN N VIC NGHIN cu CHUYN MCH NHNC nhiu yu t dn n s pht trin ca chuyn mch nhn. Trc kia ngi ta chi quan tm n mt yu t, l yu cu c nhng b nh tuyn IP gi r, nhng tc nhanh. N c th ng cho mt hoc hai nghin cu trc MPLS, chng ta s cp phn sau, ni chung chyn mch nhn c thc y pht trin bi nhiu yu t khc hn l yu cu v tc . Trong phn sau, ta s cp n tm quan trng ca tmg yu t trong 6 pht trin ca chuyn mch nhn. Tuy nhin, s kt hp ca tt c cc yu t li s cho ta thy ti sao MPLS dng nh chc chn l mt phn ca cng ngh v mng trong hin ti v tng lai.1.1.1. S pht trin ca InternetInternet r rng ang pht trin khng ngng, v chnh s pht trin ny cho thy cc im yu ca cc k thut c. S gia tng c v s lng ngi dng lm tng yu cu v bng thng c cung cp t cc nh cung cp dch v Internet (ISP). e tha mn yu cu v bng thng, cc ISP cn c nhng sn phm chuyn mch v nh tuyn c hiu qu cao. Chng ta s tho lun v nh hng v hiu qu trong phn k tip.Khi pht trin nhanh, cc mng phi i mt vi s gia tng s lng nt mng, s lng router trong cc bng nh tuyn, s lng cc lung i qua mt nt mng,.... Nhn chung, cc nh cung cp mng cn quan tm n vn kh nng pht trin, ngha l, kh nng pht trin mi hng. Chuyn mch nhn c thc y mt phn cng do nhu cu ca vn pht trin.Nhng c l yu t quan trng nht l nhu cu a dng chc nng nh tuyn ca Internet v ca mng IP (IP Network) ni chung. S pht trin ca Internet lin tc t ra nhng yu cu mi cho cc giao thc nh tuyn. Trc kia, cc chc nng nh tuyn kh c th a dng, mt phn l do l s ging nhau gia vn nh tuyn v chuyn tip trong mng IP. V d, xem xt qu trinh x l ong vic s dng nh tuyn lin min khng phn lp CIDR (Classless Interdomain Routing). S nh hng ca CIDR l ni v tin t mng IP, trc kia l 8, 16 hay 24 bit, gi c th ly ty . S m rng ny cho php m rng a chi v thng tin nh tuyn. Tuy nhin, thc hin thay i ny cng yu cu thay i gii thut nh tuyn ca tt c cc b nh tuyn IP, bi vi tin t c th ly bt c gi14 Chuyn mch nhn a giao thc MPLS 10. tr no. Nhng gii thut ny c thc hin c phn cng ln phn mm, do vic thay i n khng phi l chuyn n gin.Mt trong nhng im th v ca chuyn mch nhn l gii tiut nh tuyn thi c nh v nhng cch iu khin mi c th s dng m khng cn phi thay i n, v chng ta s thy trong cc phn tip l cc cch iu khin khc nhau c th c s dng iu khin qu trnh chuyn mch nhn v chng hu nh s dng chung gii thut nh tuyn. Do , c th a ton b vic thc hin gii thut nh tuyn bng phn cng hay bng mt phn mm c tc cao m khng quan tm n vic phi ti u li n mi khi trin khai mt chc nng nh'tuyn mi. N ha hn hp dn trong vic pht trin v trin khai nhng chc nng mi trong mng IP. V y c th chnh l li ch ln lit ca chuyn mch nhn v kt qu l chuyn mch nhn dng nh thc hin nn mng cho th h tip theo ca kin trc nh tuyn.1.1.2. Gi c v hiu quTrong bt k mng no m da trn b giao thc ca Internet, th mt trong cc thnh phn quan trng l b nh tuyn (router). Nhim v c bn nbt ca mt router l nh tuyn cc gi IP (hoc datagram) qua mng. Ngoi ra, router cn thc hin cc chc nng khc nh l lc ra mt lung ca cc gi t nhng phn khc Iihau ca mng. Tht s, tnh cht quan trng nht ca mt router cho nhiu ng dng khng phi l tc m l s a dng v chc nng m n cung cp.Mt b phn quan trng khc ttong mng l chuyn mch (switch). Trong khi router l thit b lp 3 (n nh tuyn cc gi IP) th switch l thit b lp 2 (n nh tuyn cc gi ca giao thc lp 2). So snh vi router th switch n gin hn, n ch cung cp mt s lng rt gii hn cc giao thc v cc kiu giao tip, cn router thng cung cp mt lng ln cc giao thc, nhiu kiu giao tip v tc . Gii thut nh tuyn ca switch th n gin v t thay i, nhiu kiu chuyn mch (switch) nh chuyn mch ATM (ATM switch) hay chuyn mch Frame Relay (Frame Relay switch) s dng gii thut nh tuyn da trn vic trao i nhn.Vi s khc nhau nh vy gia switch v router, th ng nhin c s khc nhau v gi c / hiu qu gia chng. Nhumg trc ht chng ta phi xem hiu qu l g trong trng hp ny, vic ny kh phc tp v b nh hng bi nhiu yu t, tuy nhin thng thTig n c tnh l s lng gi m thit b c th nh tuyn trong 1 giy gia ng vo v ng ra trn tng dung lng bng thng ca n.Khi chng ta xem xt gi c / hiu qu ca switch v router, ta thy switch thng tri hn. Ngha l, vi mt mc hiu qu nh trc, gi ca mt router thng cao hn gi ca mt switch tng ng, ngc li, vi mt chi ph cho trc, mt switch thng cho hiu qu cao hom mt router v ta thy router phi nh tuyn gi v thc hin cc dch v khc trong khi switch chi nh tuyn gi. vn m chng ta bn n y nhm mc ch chi ra l switch thng c hiu qu cao hn router.Switch dn ra mt s yu t thc y a ra chuyn mch nhn. Chng ta c th xy dng mt thit b m c th thc hin hu ht cc cng vic ca mt router m s dng phn cng ging mt switch. Khi quy m Internet c m rng v IP l giao thc duy nht c s dng thi vic nh tuyn IP mc gi c / hiu qu ca mt switch qu l hp dn.Chng 1: Gii thiu 15 11. 16 Chuyn mch nhn a giao thc MPLS1.1.3. S tch hp IP trn ATMChng ta bit rng kin trc ca ATM rt khc vi kin trc ca IP, trong khi IP phn phi cc datagram v s dng kiu khng kt ni thi ATM da trn kiu hTig kt ni hay kt ni o. ATM v IP cng hon ton khc nhau trong cch nh a ch cc host. Nhng s khc nhau ny a ra nhiu thch thc ln, chuyn mch nhn ra i cng nhm p ng cc thch thc ny.Vi nhng UXI im ca ATM v s pht trin ngy cng ln ca Internet a ra vn lm sao a kin trc IP vo mng ATM. S khc nhau v hiu qu gia cc chuyn mch ATM v cc router hin ti lm cho vn thm phc tp. Phn ln mng hm nay c xy dng theo kiu l cc router tc chm bao xung quanh cc chuyn mch ATM (ATM switch) nh hnh 1.1.Hnh Ll: M hnh IP tch hp trn ATM[1].Router Switch Mng ATMoKiu ca mng ny thng gi l kiu xp chng, tng l mng IP nm bn trn mng ATM. Mng ATM cung cp kt ni tc cao v mng IP gm cc router c kt ni vi nhau bi cc kt ni o ca ATM.Vn nh x IP vo ATM c nghin cu bi nhiu nhm ngoi hai t chc chnh l ATM Forum v IETF nh l: 12. Nhm IP ATM (The IP over ATM) nghin cu vic gi cc IP datagram vo lp PDU ca ATM v mt giao thc phn gii a ch ATMARP nh x a ch IP vo a chi ATM. Nhm IPLPDN (IP over Large Public Data Networks) v sau l nhm ROLC (Routing over Large Clouds) a ra NHRP (Next Hop Revolution Protocol) cho php cc host v router c the to mt kt ni o trc tip thng qua mng ATM. Nhm LANE (The LAN Emulation) a ra nhng th tc lm cho mng ATM hot ng ging mng LAN a Tiy cp. Nhm MPOA (Multiprotocol over ATM) kt hp v pht trin cc kt qu cc nhm khc a ra s h tr nhiu giao thc (protocol) lp mng (trong c IP).Hu ht cc nhm trn u a ra vi kiu server (ATMAPR, MARS, NHRP, BUS,...) thc hin vic nh x ny cng nh nhng giao thc cn thit giao tip vi cc server ny. vn tip theo l phi c thm cc server khc cng vi cc giao thc ng b gi chng hot ng ng b vi nhau.Ti sao vn li phc tp nh vy, l do cc giao thc Internet v cc giao thc ATM c pht trin c lp vi nhau v hot ng trn cc im khc nhau. V c nhiu ngi t hi nu mt chuyn mch ATM (ATM switch) c th s dng cc giao thc khc ngoi nhng giao thc do ATM Forum v ITU nh l cc giao thc ph hp vi kin trc IP hn th s gim nhiu s phc tp ca vic nh x. Nhiu k thut chuyn mch nhn thc s to ra nhng giao thc nh vy, n c th iu khin mt chuyn mch ATM (ATM switch) hot ng nh l nh tuyn cc gi IP mt cch t nhin m khng cn nh n cc server nh x gia IP v ATM.Thay v c hai kin trc giao thc khc nhau vi s khc nhau v cch nh a chi, cc giao thc nh tuyn, cc k hoch nh ti nguyn,... thi chuyn mch nhn cho php nhng giao thc iu khin IP chy trc tip trn phn cng ca ATM. Nhng chuyn mch ATM (ATM switch) th vn nh tuyn cc gi nh k thut trao i nhn, nhng cch thc m n to bng nh tuyn v tnh ton ti nguyn u c iu khin bi cc giao thc iu khin ca IP. Vi cch thc iu khin nh vy, chuyn mch ATM (ATM switch) thnh cc router ca IP do loi b yu cu phi nh x gia IP v ATM.* Vn pht triny l vn t c bit n nhng li tr nn quan trng khi mt mng IP c xy dng xp chng trn mt lp 2 khc kiu, nh l Frame Relay hay ATM.Xem xt mng trong hinh 1.2, mng ATM trung tm cung cp kt ni tc cao cho tt c cc router bng cc knh o ni gia chng, nh ta thy lun c mt switch nm gia cc cp router v iu ny c th gy ra nghn ti switch ny. Tuy nhin, mt kt ni hon ton cc knh o cho php cc router c th ni trc tip n cc router cn li. Trong hnh 1.2 ch v nhng knh o cho 1 router trnh lm ri hnh, ch tht s l c n(n-l)/2 knh o, l 55 trong hnh. c th hiu r vn y, chng ta cn bit qua cch hot ng ca cc giao thc nh tuyn. Mi router thng c cu hnh c. mt ch s gn cho mi router kic kt ni trc tip vi n, ch s ny cho php router lun bit nhng router c kt ni n nChng 1: Gii thiu 17 13. 18 Chuyn mch nhn a giao thc MPLSv bit c kt ni no khng th hot ng, n cn c dng trao i thng tin nh tuyn gia cc router.Hnh 1.2: Cc knh o gia cc router trong mng IP/A TM []].RouterSwitch Mng ATM Mch o ng vt lNhiu nghin cu thc hin lm gim nh vn pht trin. Trong c cch l khng lm kt ni hon ton gia cc router, ngha l c vi kt ni gia hai router phi qua mt router trung gian khi m hiu qu ca router trung gian ny chp nhn c. Cch khc, Next Hop Resolution Protocol (NHRP) cho php router thit lp nhng knh o n nhng trm m n cn gi d liu m khng cn phi thit lp cc chi s nh tuyn qua knh o. Tuy nhin, n c nhng vn ring nh l n cn phi c cc NHRP server v phi c kh nng khng cho xy ra vic nh tuyn lp vng. NHRP chi ph hp cho cc lu lng unicast, n khng h tr cho multicast.Nhng nghin cu khc gii quyt vn ny bng chuyn mch nhn. u tin, nhc li l mt LSR s dng cc giao thc iu khin ca IP, bao gm c cc giao thc nh tuyn chy trn phn cng ca ATM. Do , vi cu trc mng nh hnh 1.2, chng ta c th gim ng k s lng chi s ca cc router s dng giao thc ca IP trn nn ATM, c th thy iu ny trn hnh 1.3.V chuyn mch ATM c th chy cc giao thc nh tuyn ca IP, nn cc m trung gian thay v l cc router th nay l cc LSR, do s lng cc ch s m cc router phi c gim ng k v s khng tng theo kch thc ca mng. Ch rng hnh 1.2 cc 14. Chng 1: Gii thiu 19router c 10 chi s th nay ch c 1 (ni vi LSR), v LSR c khng qu 5 ch s, 3 ni vi 3 router, 2 ni vi LSR khc. Ta thy n lun gi ch s khi mng c m rng, v vn pht trin c th c chp nhn.Hnh L3: Thay chuyn mch A TMbng LSR [1].RouterLSR1.1,4. M rng cc chc nng nh tuyniu quan trng chng ta phi ch y l chuyn mch nhn khng ch nhm bin mt phn cng ATM hot ng'ging mt router m n cn cung cp nhng chc nng mi m cc k thut nh tuyn IP hin ti khng cho php. y cng l mt yu t thc y s ra i ca chuyn mch nhn, phn ny chng ta s tm hiu thm v s pht trin ca vic nh tuyn ni trong phn trc.Hin nay, vic nh tuyn trong mng IP l da vo a ch ch, ngha l quyt nh phi gi gi i u l da vo a ch ch, v nguyn tc, cc tnrofng khc trong tiu IP (IP header) (a ch ngun, kiu ca dch v) u c th c s dng trong vic quyt nh cho gi tin nhng hu ht cc nghin cu thit k cho router u ch s dng a ch ch. Trong khi cc k thut mng m c s dng k thut trao i nhn nh l Frame Relay hay ATM c th cung cp nhng chc nng khc nhau.e c th hiu chuyn mch nhn h tr nhng k thut mi nh th no, ta xt mng c cu trc trong hnh 1.4. 15. 20 Chuyn mch nhn a giao thc MPLSHnh L4: ng dn chuyn mch nhn.'>,Routery l mt v d in hnh v cc chc nng m kiu nh tuyn truyn thng kh th cung cp. Xem xt trng hp khi router B l mt router kiu truyn thng, nh tuyn cc gi bng cch s dng a chi IP ch. Khi mt gi n B t mt trong cc router ln cn, quyt nh nh tuyn ch da vo a ch ch m khng b nh hng bi bt c yu t khc. Nhng gi gi s ta mun nhng gi i tt router A n router F th i qua router D, cn nhng gi khc n router F th i qua router E, r rng c ch nh tuyn ch da vo a chi ch khng th thc hin c iu ny.Nhng s d dng thc hin iu ny ti router B nu B nh tuyn gi bng k thut chuyn mch nhn. Nguyn nhn chnh l A v c s dng cc nhn khc nhau, gi s A s dng nhn c gi tr l 5 cho cc gi c ch l F cn c s dng nhn 12. Do , ti B khi cc gi n n s nh tuyn gi c nhn 5 n D v gi c nhn 12 n E.Mc d v d nh ny khng i su vo chi tit nhvmg n cho ta thy chuyn mch nhn h tr nhiu chc nng nh tuyn mi m kiu nh tuyn truyn thng khng th h tr.1.2. TM TT LCH sBy gi chng ta bit nhng l do ti sao cc nh nghin cu li quan tm n k thut chuyn mch nhn, v chng ta cng nn c mt ci nhn tng quan v cc s kin dn n tnh hnh hin nay.1.2.1. B nh tuyn chuyn mch t bo CSR ca ToshibaB nh tuyn chuyn mch t bo (Cell Switching Router) ca Toshiba l nghin cu u tin v chuyn mch nhn c cng b. Kin trc ca CSR gii thiu tng l mt phn cng ATM hn hp c th c iu khin bd IP (nh l cc giao thc nh tuyn IP hay Rsyp) hn l cc giao thc bo hiu ca ATM (nh Q.2931). Theo nghin cu ny thi c th b cc bo hiu ATM v c chc nng nh x gia IP v ATM. tng CSR u tin c trnh by trc IETF vo cui nm 1994 v u 1995, vo thi im ny cng c nhiu nhm nghin cu khc ang tp trung vo pht trin tng tng t. . 16. Chng .1: Gii thiu 211.2.2. Chuyn mch IP [4]Vi nhiu nguyn do, bao gm ti u v thi gian, sn phm c cht lng, cch thc tip th hiu qu, chuyn mch IP (IP Switching) c nh ngha ban u bi cng ty Ipsilon nh hng ln ln th trng v gii k thut hcm l nghin cu CSR. Ipsilon cng b nghin cu ca h vo u nm 1996. v mt k thut thl hai nghin cu c nhiu im tng ng, tuy nhica nhng u im ca'chuyn mch IP hn cc nghin cu trc c th d dng thy c nh sau: Chuyn mch IP cho php 1 thit b vi hiu qu ca mt chuyn mch ATM m c th thc hin cng vic ca mt router. Nhng router tc cao (khng phi l chuyn mch ATM) c th thc hin bi v IP v cc giao thc ca Internet ang l nhng giao thc ch yu hin nay m cc router hin ti th qu chm. Bo hiu ATM v vic nh x IP vo ATM tr nn qu phc tp, cho mc ch nh tuyn IP chng ta cng khng cn cc giao thc iu khin ATM.Nhng ti liu ca Ipsilon c cng b trong mt s cc ti liu Internet l RFC. Mc d khng phi tt c RFC u l tiu chun, cc ti liu ca Ipsilon c coi l nghin cu m v vi giao thc c cng b c thc hin. Mt ng gp c gi na l vic lm r mt giao thc iu khin chuyn mch on gin GSMP cho php bin bt c mt chuyn mch ATM no thnh mt chuyn mch IP vi nhng chc nng mi c b sung. r rng, chng ta s s dng thut ng chuyn mch IP l ni v nghin cu ca Ipsilon, mc d n ing c s dng ch khc cp n vic m rng vn ca cc nghin cu khc. Thut ng tng qut c s dng khi cn thit th chng ta s dng thut ng chuyn mch nhn.1.2.3. Chuyn mch thVi thng sau khi Ipsilon cng b nghin cu ca h, Cisco Systems cng b mt nghin cu khc v chuyn mch nhn m h t tn l chuyn mch th (Tag Switching). Nh chng ta s thy phn sau, chuyn mch th l mt k thut xut sc xut pht t cc nghin cu chuyn mch IP v CSR. V d l n khng da trn dng lu lng d liu thit lp bng nh tuyn trong chuyn mch v n cn c lm ph hp vi nhiu k thut lrp lin kt (link layer) khc na ngoi ATM.Ging Ipsilon, Cisco dng 1 RFC m t nghin cu ca h, nhng khng ging Ipsilon, Cisco cng b pht minh ca h thuyt phc s tiu chun ha ca chuyn mch th qua IETF. V sau , mt lng ln cc bi vit v Internet c cng b, m t nhng k vng ca chuyn mch th, bao gm hot ng trn ATM, ppp, lin kt 802.3, h tr cho nh tuyn multicast, cho d tr ti nguyn s dng RSVP, S tiu chun ha nhng c gng lm vic ca Cisco a ra tr thnh chuyn mch nhn a giao thc MPLS (Multiprotocol Label Switching) v MPLS hin nay c s dng rng ri nh l mt thut ng ca chuyn mch nhn.1.2.4. ARIS ca IBMChi sau cng b ca Cisco v vic c gng tiu chun ho ca IETF mt thi gian ngn, mt lng bi vit Intenet c pht hnh bi cc tc gi t IBM, m t mt 17. nghin cu khc v chuyn mch nhn gi l chuyn mch IP da trn b nh tuyn tng hp (Aggregate Router-based IP Switching) hay ARIS. ARIS th ging vi chuyn mch th hn l cc nghin cu khc ch dng lu lng iu khin thit lp bng nh tuyn ch khng phi dng lu lng d liu, nhng ARIS khc vi chuyn mch th vi im ng k. Nhiu tng ca ARIS c trong vic tiu chun ha MPLS.1.2.5. Chuyn mch nhn a giao thc MPLSKhi Cisco cng b v chuyn mch th, h cng mong mun c tiu chun ha k thut ny. Sau mt lot bo co u tin ca chuyn mch th trn bo co Intenet, mt hi ngh BOF (Birds of a Feather), l hi ngh cn thit trc khi t chc mt nhm nghin cu, v xc nh vn no cn tiu chun ho) c t chc vo thng 12 nm 1996, vi s trnh by ca Cisco, IBM, v Toshiba (lc ny cng b nhng bo co mi v CSR).Vi mc quan tm trong BOF v vi thc t l c qu nhiu cng ty a ra nhiu gii php tng t chi cho 1 vn , th vic tiu chun ha phi ra i l chuyn phi lm. Do vic thnh lp nhm nghin cu cho vic tiu chun ha c IETF chp nhn vo u nm 1997. V cuc gp u tin ca nhm din ra vo thng 4 nm 1997.Nh ni trn, tn chuyn mch nhn a giao thc MPLS (Multiprotocol Label Switching) c chp nhn ch yu bi tn chuyn mch IP v chuyn mch th c t cho sn phm ca cc cng ty. Mc d dng tn l a giao thc (Multiprotocol) nhng ch yu chi tp trung vo cc giao thcca IP horn l cc giao thc ca lp mng khc.1.3. KT LUNChng ta kho st mt cch s lc s ra i ca k thut chuyn mch nhn.-V hiu r hn v k thut ny chng ta s xem xt cc nghin cu tiu biu cho k thut ny, l chuyn mch IP, chuyn mch th, sau cng l MPLS.22 Chuyn mch nhn a giao thc MPLS 18. CHIIVG 2: L THUYT c Bl^ CA CHHYM MCH niHN2.1. TNG QUANKhi mng Internet ngy cng i rng cng vi s pht ttin ca cc dch v gia tng cng nh cc yu cu v cht lng dch v v tnh bo mt, MPLS l mt gii php ti u. N kt hp cc u im ca IP v ATM m chi ph trin khai cng khng qu t, c th phi hp v nng cp t cc mng ATM hoc Frame Relay c sn. Ngoi ra, MPLS cn l mt gii php ti u cho dch v VPN v cc ng dng i hi v cht lng dch v v k thut lu lng.Hu ht cc mng din rng Vit Nam u c t chc vi kt ni s dng dch v thu knh ring, X25 hoc Frame Relay thng qua cc nh cung cp dch v vin ing. Hu ht chng u hot ng da trn nh tuyn IP truyn thng vi khng t nhc im, p ng chm khi c yu cu x l lung lu lng ln trn mng, lm cho vic x l ti cc router b qu ti. Hu qu l mt lu lng, mt kt ni v lm gim c tnh mng. Ngoi ra, mi nt trong mng u phi thc hin hai chc nng l nh tuyn v chuyn tip. Qu trnh chuyn tip chi da trn a ch ch ca gi m khng da trn cc tham s cht lgrng dch v.MPLS c xem l gii php cho cc vn ny. im ni bt ca cng ngh MPLS l kh nng chuyn tip lu lng nhanh, om gin, iu khin phn lung, nh tuyn linh hot v tn dng ti nguyn mng. N kt hp nhng c im tt nht ca chuyn mch knh ttong ATM v chuyn mch gi trong IP, c kh nng chuyn tip gi rt nhanh trong mng li v nh tuyn nh bnh thfng mng bin. Khi cc gi i vo min MPLS, thng l mng trc ca nh cung cp dch v, chng c chuyn mch n gin bng chuyn mch nhn. Cc nhn cn gip xc nh cht lng dch v m cG-gLnhn c. Khi chng ra khi mng th cc nhn s c ct b cc router bin mng v ^c nh tuyn nh thng thng.MPLS c mt s iru im hcm nh tuyn IP nh chuyn cc gi qua mng nhnh hn router IP. Trong IP, vic nh tyn ch da vo tiu ca gi cn MPLS c th phn bit cc giao din khc nhau, cc thng tin khc nhau xc nh chnh sch x l thch hp, i khi gi c th c nh tuyn theo mt ng bit trc khi gi i vo mng.Ta xt qua hot ng ca cc router h tr MPLS, gi l b nh tuyn chuyn mch nhn LSR (Label Switching Router): chng u tin trong mng MPLS, router chuyn tip gi da vo a chi ch (hoc bt c thng tin no phn tiu theo chnh sch cc b); sau n xc nh mt nhn thch hp - gi tr ny c xc nh cho mt lp chuyn tip tng ng FEC - gn nhn cho gi v chuyn n ti nt tip theo, chng tip theo, router dng gi tr ca nhn nh mt ch mc ca mt bng xc nh nhn mi. LSR gn 19. 24 Chuyn mch nhn a giao thc MPLSnhn mi ri chuyn gi n nt tip theo. Tuyn cmg m mt gi gn nhn i qua c gi l ng chuyin mch nhn LSP (Label Switched Path). Do MPLS s dng nhn quyt nh chng tip theo nn router t phi lm vic hn v hot ng gn ging vi switch. V cc nhn th hin cc tuyn ng i trong mng nn cc nh qun tr mng c th iu khin chnh xc hn cc qu ttnh x l lu lng ttong mng bng cch dng cc chnh sch nhn.C hai cch chnh gn v phn phi nhn l m hnh li d liu v m hnh li iu khin. M hnh li d liu nh chuyn mch IP (Ipsilon) hay b nh tuyn chuyn mch t bo (Toshiba). M hnh li iu khin nh chuyn mch th (Cisco), IP Navigator (AscencyLucent) v ARIS MPLS (BM), MPLS.Khc vi qu trnh nh tuyn v chuyn mch thng thTig ca mng IP l da trn tiu ca gi tin IP, trong mng MPLS, qu trnh chuyn mch da trn mt nhn gn thm vo gi tin. Cn qu trnh nh tuyn th khng khc bit nhiu lm, tc vn da vo a ch IP v cc giao thc nh tuyn nh tuyn. Tuy nhin router cn phi nm gi s thay i v hhn ca cc gi tin khi i cc gi ny c chuyn tip qua router. Nh vy, khc vi router thng thig, cc router trong mng MPLS phi hiu c cc giao thc phn phi nhn. (Tuy nhin, vi nh tuyn rng buc, ta c th ch nh mt con ng c lp vi cc giao thc nh tuyn). minh ho hot ng ca MPLS, ta hy xt ng i ca mt gi tin theo tng bc ong mng sau.Hnh 2.1: S mngIP 28IP 27IP 24SO/0 SO/0^^0/1 SO/^^O/1 so/PE1 P1 P2 PE2CE1CE2Thit bSerial 0/0Serial 0/1Loopback 0PE1192.168,1.10192.168.1.1P1192.168.1.9192.168.1.14192.168.1.2P2192.168.1.13192.168.1.18192.168.1.3PE2192.168.1.17192.168.1.4Bng 2.1: a chi IP cc thit bTrc ht, cc giao thc nh tuyn nh OSPF, IS-IS hot ng xy dng nhng router k cn trong bng nh tuyn ca mt router. (Router k cn l router k tip m gi tin cn c truyn n n c mt ch no ). 20. Ta c th dng lnh:PEl#show ip routeK n, giao thc phn phi nhn s hot ng gn nhn v ta s c mt s tng ng gia mt nhn v mt router k cn cng vi cng ng ra tng ng. Trong mng MPLS, b nh tuyn ngoi ra c 2 ng l ingress (ng vo) v egress (ng ra). B nh tuyn ng v^s nhn vo mt gi IP v thc hin so snh trong bng nh tuyn, sau gn nhng dch v tng ng ln gi tin , v cui cng gn nhn thch hp da trn nhng dch v . Nhng nhn khc nhau s biu th nhng mc dch v khc nhau trong mng. V khi gi tin c nhn, n c chuyn n thit b k tip v router k tip s xem trong bng chuyn tip xc nh cng ra v nhn cn dng cho gi tin.Ta c th dng lnh;PE#show mpls forwarding-tableSau khi i qua mt b chuyn mch nhn gia th nhn ca mi gi tin s thay i. Mi b chuyn mch nhn gia chi hot ng on gin l chuyn i (swapping) nhn. V hot ng tng t nh th xy ra thit b k tip cho n khi gi tin n thit b cui cng l b nh tuyn chuyn mch nhn ng ra. B nh tuyn ny bit n l thit b cui cng trong mng MPLS. N s tch nhn ra v gi gi tin IP n chng k tip tc vo mng IP ca khch hng. Qu trnh di chuyn tip theo ca gi th hon ton tng t nh trong ng hp mng IP thng thng.Nh vy y, ta thc hin chuyn cc gi tin trong mng ch da vo nhn gi tin thay v a ch. V qua y ta cng thy c mt s u im tuyt vd ca chuyn mch nhn. u tin l tc rt nhanh v tr cng nh tr rung pha (jitter) l rt thp. Do nhn dng tham chiu (index) trc tip n bng chuyn tip ca router nn ch yu cu truy cp bng ny mt ln, trong khi nh tuyn truyn thng phi yu cu truy cp bng nh tuyn hng ngn ln tm ra a ch IP ph hfp nht. Do chuyn mch nhn gim c tr v thi gian ch p ng ti mi nt ko theo lm gim bin ng tr rang pha cng dn khi gi tin i qua nhiu nt, iu ny rt c ngha i vi cc ng dng thi gian thc. Tuy nhin, l do s dng chuyn mch nhn khng ch dng y m cn do tnh n gin v d m rng ca n. Chuyn mch nhn cho php ghp nhiu a chi IP vi mt hoc mt s nhn m thi nn lm gim kch thc ca bng a ch, cho php router h nhiu ngi dng hon. V i vi cc c s h tng mng vn c sn chc nng chuyn mch, chuyn tip trong phn cng nh cc router hay cc chuyn mch ATM, Frame Relay, ta ch cn ph ln tim phn mm tng ng iu khin vic chuyn mch nhn m ii.2.2. KHI NIM V HOT NG c BN TRONG MPLS2.2.1. Mt phng d liu v mt phng iu khinMt mt phng iu khin (control plane) l mt tp hp phn mm v/hoc phn cng trong mt thit b, chng hn mt router, v c dng iu khin nhiu hot ng thit yu trong mng, nh phn phi nhn, tm tuyn mi, v khc phc li. Nhim v ca mt phang iu khin l cung cp cc dch v cho mt phng d liu. Mt phang d liu chu trch nhim chuyn tip lu lng ngi dng qua router. Cc thut ng mt phng ngi dng (user plane) hoc mt phng truyn dn (transport plane) cng c dng m t mt phang d liu.Chng 2: L thuyt c bn ca chuyn mch nhn , 25 21. 26 Chuyn mch nhn a giao thc MPLS2.2.2. Mt phng d lu v mt phng iu khin trong IP Hnh 2.2: Mt phng iu khin v d liu IP.RouterHnh 2.2 m t mi quan h gia mt phng iu khin IP v mt phng d liu IP. i vi cc giao thc Internet, cc v d ca mt phng iu khin l cc giao thc nh tuyn nh OSPF, IS-IS, BGP. N cho php IP chuyn tip lu lng mt cch chnh xc.Cc bn tin iu khin c ao i gia cc router thc hin nhiu hot ng khcnhau, bao gm: Trao i cc bn tin gia cc nt thit lp mt tuyn lin kt. Trao i cc bn tin ieo chu k (gi l bn tin hello) chc rng cc nt gn k hotng tt. Trao i cc bn tin qung co (advertisement) v a chi v tuyn xy dng cc bng nh tuyn c s dng bi IP chuyn tip lu lng.2.23. Mt phng d liu v mt phng iu khin trong MPLS Hnh 2.3: Mt phng iu khin v d liuLSR 22. MPLS cng hot ng vi cc mt phang iu khin v d liu, nh m t hnh 2.3. Nhim v chnh ca mt phng iu khin l qung co cc nhn, a ch v lin kt chng.B nh tuyn chuyn mch nhn l mt router c cu hnh h tr MPLS. N dng c s thng tin chuyn tip nhn (Label Forwarding Information Base_LFIB) xc nh cch x l cc gi MPLS n, chng hn xt xem nt k tip nhn gi l nt no.Cc bn tin iu khin c trao i gia cc LSR thc hin nhiu hot ng khc nhau, bao gm thit lp lin kt. Sau khi hot ng ny hon thnh, cc nt c gi l cc LSR ngang hng (peer), trao i cc bn tin chu k (bn tin hello) chc rng cc nt gn , k hot ng tt, ttao i cc bn tin a ch v nhn lin kt cc a ch vi nhn v xy dng bng chuyn tip cho mt phng d liu MPLS. Mt phng d liu MPLS s chuyn tip liru lng bng cch kim tra nhn trong tiu gi MPLS, a chi IP khng cn kim tra. Tiu nhn sau b b i, v a chi IP li c dng phn phi lu lng n ngi dng cui.2.2.4. Nhng lp chuyn tip tng ong FEC* Lp chuyn tip tng ng FECThut ng lp chuyn tip tcmg ng FEC (Forwarding Equivalence Classes) c s dng trong hot ng chuyn mch nhn. FEC m t s lin h gia cc gi vi a ch ch ngi nhn cui, FEC cng c th lin kt vi mt a ch ch v loi lu lng lin quan n mt cng ch no .Ti sao li s dng FEC? Trc tin, n cho php nhm cc gi vo cc lp khc nhau, c th s dng h tr cht ng dch v hiu qu. V d, FEC c th lin kt vi u tin cao, lu lng thc ...FEC c xc nh duy nht bng vic s dng mt nhn. i vi cc lp dch v khc nhau, ngi ta s dng cc FEC v cc nhn lin kt khc nhau. Vi Internet, cc gi sau c s dng thnh lp mt FEC: a ch IP ngun v/hoc ch, s cng ngun v/hoc ch, nhn din giao thc (PID), im m (codepoint) ca cc dch v khc bit IPv4, dng nhn IPv6.Chng ta c th ngh v cc th tc c s dng bi thnh phn nh tuyn nh l cch chia thnh tp tt c cc gi m router c th nh tuyn vo mt s hu hn cc subnet ri nhau. T quan im nh tuyn, nhng gi trong mi subnet c router i x nh nhau (ngha l chng u c gi n cng mt trm k tip) ngay c nu nhng gi trong subnet khc nhau v nhng thng tin cn li ong tiu (header) lp mng. Chng ta xem cc subnet nh l cc lp chuyn tip tng cmg (FEC). Nguyn nhn m router nh tuyn tt c cc gi trong 1 FEC ging nhau l v s nh x gia thng tin c mang trong tiu lp mng v nhng mc trong bng nh tuyn l nhiu - mt (m mt - mt l trng hp c bit). Ngha l nhng gi khc nhau v ni dung trong tiu lp mng c th c nh x vo cng mt mc trong bng nh tuyn khi mc c gn vi mt FEC xc nh.Mt v d ca FEC l mt tp cc gi unicast m a ch ch lp mng c cng tin t a ch IP xc nh. Mt v d khc ca FEC l mt tp cc gi multicast c cng a ch ngun v ch lp mng.Chng 2: L thuyt c bn ca chuyn mch nhn 27 23. Mt phn quan ng ca mt mc nh tuyn c duy tr bi router l a ch router k tip. Mt gi khi ri vo mt FEC m lin kt vi mt mc nh tuyn xc nh th c nh tuyn .n router k tip c ch r bi mc . Do vic xy dng bng nh tuyn bi thnh phn iu khin c th xem nh l vic xy dng mt tp FEC v m k tip cho mi FEC .Mt tnh cht quan trng ca mt FEC l tnh nh tuyn phn cp ca n. V d nh mt FEC c th bao gm nhng gi m c a chi ch lp mng gn vi cng mt tin t a ch xc nh. Kiu ny ca FEC cung cp nh tuyn th. Mc khc, mt FEC c th bao gm ch nhng gi thuc vo mt ng dng xc nh chy gia hai my tnh, ngha l n ch bao gm nhng gi c cng a ch ngun v ch lp mng (a ch hai my tnh) cng nh cng s port lp vn chuyn (nhng port ny xc nh ng dng trong my tnh). Kiu ny ca FEC cung cp nh tuyn tinh.C th thy r rng l nh tuyn th cn thit cho vic m rng ton mng. Nhng mc khc nu ch h tt nh tuyn th s lm mng hot ng khng c uyn chuyn, nh vy n khng cho php c nhiu kiu lu lng khc nhau. Nhng nhn nh trn cho thy mun xy dng mt h thng ln v c nhiu chc nng th yu cu h thng phi h tr nhiu kiu nh tuyn cng nh kh nng n ln v kt hp nhiu kiu nh tuyn khc nhau.2.2.5. nh tuyn nht qunMt h thng nh tuyn chnh xc yu cu c s nht qun qua nhiu router. S nht qun ny c thit lp bi s kt hp ca nhiu c ch.Thnh phn iu khin chu trch nhim phn b nht qun cc thng tin nh tuyn c s dng bi router cho vic xy dng bng nh tuyn ca n. Thnh phn iu khin cn chu trch nhim trong vic nht qun cc th tc m router dng xy dng bng nh tuyn. Kt hp hai yu t ny cho php c s nht qun gia cc bng nh tuyn.Thnh phn nh tuyn chu trch nhim nht qun cc th tc ong vic ly thng tin t cc gi cng nh vic s dng thng tin ny tm mt mc thch hp trong bng nh tuyn, kt qu l c s nht qun trong nh x nhng gi vo cc FEC qua nhiu router. V s nht qun ny cho php h thng c chc nng nh tuyn chnh xc.2.3, THNH PHN NH TUYNS phn tch vic nh tuyn lp mng ra lm hai phn: iu khin v nh tuyn khng ch c p dng vo kiu nh tuyn truyn thng m cn c th p dng cho k thut chuyn mch nhn. Trng phn ny chng ta m t vi l thuyt nn tng lin quan n thnh phn nh tuyn ca chuyn mch nhn.Thut ton m thnh phn nh tuyn ca chuyn mch nhn s dng a ra quyt nh nh tuyn cho mt gi tin s s dng hai ngun thng tin: thng tin th nht l bng nh tuyn c duy tr bi mt router chuyn mch nhn LSR (Label Switching Router) v th hai l mt nhn cha ong gi.23.1. Nhn lNhn l mt khung nhn dng ngn, c chiu di c nh v khng c cu trc. Mt nhn khng thc hin trc tip bt c thng tin no t tiu lp mng. Dng ca nhn s c xt phn sau.28 Chuyn mch nhn a giao thc MPLS 24. Chng 2: L thuyt c bn ca chuyn mch nhn 2923.2. Bng chuyn mch nhnLIB v LFIBHnh 2.4: LIB cho nt D192.168.20.1192.168.20,9192.168.20.7Hnh 2.4 l c s d liu thng tin nhn LIB ca nt D cho cc lin kt nhn m n to v nhn c t cc hng xm MPLS cho tin t a ch 192.168.20.0/24. Cc thc th LIB ca cc LSR khng phi k cn th khng cn lu trong LIB v khng cn thit cho vic chuyn tip gi. Theo hot ng ca cc giao thc nh tuyn, nt D c th n 192.168.20.0/24 thng q'ua nt I, E hoc J. Mt cu hi rt hp l c t ra l ti sao n phi cha tt c lin kt nhn ca tt c cc hng xm trong khi mt s ttong chng khng phi l xui dng theo a ch ch v thm ch mt s khng trong LSP. Cu tt li s c gii thch phn sau.Hnh 2.5 l bng LFIB ti nt D cho tin t a ch 192.168.20.4/24. Lu rng bng ny ch cha thng tin cn thit chuyn tip gi n chng k trong LSP, n chnh l tp con ca LIB. Nhn 40 c dng cho LSP gia nt c v D, nhn 38 gia D v E, nhn 47 gia E v F. Nhn 40 l nhn ni (local label) ca nt D v n c to bi D v phn phi n tt c cc ngang cp ca D. Cn nhn 38 c cp bi nt E. Do hai nhn ny l nhn c gn bi nt xui dng n nt ngc dng tng ng vi tin t 192.168.20.0/24. Trong bng LFIB ti D ta thy (a) nhn ni cho tin t a ch 192.168.20.0/24 l 40, (b) nhn ra l 38 vn c gn trc bi nt E, (c) giao tip vt l n chng k tc hop E l giao tip n. Hai iu quan trng cn nh l nu LSR khng nhn thng ip lin kt nhn t LSR k, gi tin s c chuyn i bnh thng m khng gn nhn. Cn nu LSR nhn c thng ip lin kt nhn t LSR k th nhn ny v nhn ni s c thm vo LFIB.Khi mt lin kt hay mt nt b pht hin l h bng giao thc phn phi nhn hay bng giao thc nh tuyn lp 3, cc s kin sau s ln lt xy ra: v d nt D pht hin lin kt n E b h. LFIB c cp nhn phn nh s h hng ny bng cch xa lin 25. 30 Chuyn mch nhn a giao thc MPLSkt t D n E. Giao tip ca lin kt b h cng c xa khi bng nh tuyn. Vic xa ny kch hot OSPF chn ra mt lin kt thay th Ichc v a vo bng nh tuyn, v d lin kt gia D v J. Vic thm mt FEC mi vo bng nh tuyn lp 3 s kch hot nt D cp nht LFIB m khng cn triu gi giao thc phn phi nhn bi v trc nt D thit lp mi quan h MPLS ngang hng vi tt c nt ln cn v ci t lin kt nhn cho nhng nt ny trong bng LIB ri. Do nt D s gn nhn 87 cho cc gi n 192.168.20.0/24 v gi chng n nt J. J lc ny l thnh vin mi ca con ng chuyn mch nhn n 192.168.20.0/24.Hnh 2.5: LFIB cho nt D 192.168.20.1192.168.20.9192.168.20.7192.168.20.3 192.168.20,47V192.168.20.61/192.168.20.2o 1Arp-yp1 QO ICQ oo rIONt cuicr1 9^. ID0.ZU.U/Z4.-'192.168.20.5 192.168.20.10192.168.20.8Vi a ch 192.168.20.0/24 Nhn ni Nhn ra Giao din4038Mt bng nh tuyn bao gm chui cc mc, mi mc bao gm mt nhn vo v mt hay nhiu mc con, mi mc con bao gm mt nhn ra, mt giao din ng ra v mt a chi trm k (hnh 2.6). Nhng mc con khc nhau trong tng mc ring c th c cng hoc khc nhn ra. y c nhiu mc con l kim sot nh tuyn multicast, khi m mt gi n t mt ng vo cn c gi n nhiu giao din ng ra.Hnh 2.6: Mc trong bng nh tuynNhn voMc con th nhtMc con th haiNhn raNhn raNhn voGiao din raGiao din raa ch trm ka ch trm kBng nh tuyn c nh ch s mc bi gi tr cha trong nhn vo. Ngha l gi tr cha trong nhn vo ca mc th N trong bng l N.Ngoi thng tin dng iu khin nh tuyn mt gi, mt mc trong bng nh tuyn c th cha thng tin lih quan n nhng ti nguyn m gi tin c th s dng, nh l mt hng i ng ra m gi tin c t vo. 26. Chng 2: L thuyt c bn ca chuyn mch nhn 31Mt LSR c th duy tr mt bng nh tuyn n hay l nhiu bng nh tuyn, mi bng cho mi giao din ca n. Vi trfng hp sau, vic x l mt gi tin c xem xt khng bi ch nhn cha trong gi m c giao din no m gi tin i ti, cn trong rrng hp u th ch cn thng tin cha trong nhn. LSR c th s dng trTig hp mt hoc hai nh l mt tu chn, hay c th kt hp c hai.2.33. Kh nng mang nhn trong giMt chc nng quan ng ca thnh phn nh tuyn chuyn mch nhn l kh nng mang nhn trong gi, c nhiu cch thc hin iu ny.Vi cc k thut lp lin kt, nh ATM v Frame Relay, c th mang nhn nh mt phn ca tiu (header) lp lin kt ca n. C th, vi ATM, nhn c th c mang trong trng VCI hay VPI ca tiu ATM. Cn vi Frame Relay, nhn c th c mang ong tTTng DLCI ca tiu Frame Relay.S dng ty chn vic mang nhn nh l mt phn ca tiu lp lin kt cho php h tr chuyn mch nhn vi mt s k thut lp lin kt ch khng phi l tt c. Bt buc chuyn mch nhn chi cho nhng k thut lp lin kt m c th mang nhn trong tiu lp lin kt s gii hn nhiu n s hu dng ca chuyn mch nhn (hn ch s s dng chuyn mch nhn n nhng mi trng khc nh Ethernet hay lin kt point-to-point).Mt cch cho php chuyn mch nhn hot ng trn nhiu k thut lp lin kt khi m nhng k thut khng th mang nhn trong tiu ca n l bng cch mang nhn trong mt tiu nhn ring. Tiu nhn ny c xen vo gia tiu lp mng v tiu lp lin kt (xem hnh 2.7), nn do c th c s lng bi bt c k thut lp lin kt no nh Ethernet, FDDI, Token Ring, point-to-point.Hnh 2.7: Mang nhn trong tiu thmTiu Tiu thmTiu D liulp lin ktcha nhnlp mngp mng2 J.4. Thut ton nh tuyn chuyn mch nhnThut ton nh tuyn m c s dng bi thnh phn nh tuyn ca chuyn mch nhn da vo s hon i nhn. Thut ton hot ng nh sau:Khi LSR nhn mt gi tin, n s ly nhn trong gi lm chi mc xc nh ong bng nh tuyn. Mt khi mc trong bng nh tuyn c tm thy (mc ny c nhn vo bng vi nhn cha trong gi tin), trong mi mc con s thay th nhn trong gi tin bng vi nhn ra ca n v gi gi tin ra giao din ng ra n trm k tip c xc nh bi mc con .Trong phn trc, chng ta gi s l mt LSR duy tr mt bng nh tuyn cm, tuy nhin, mt LSR c th duy tr 1 bng nh tuyn ring bit cho mi giao din ca n. Trong trng hp ny, sau khi LSR nhn gi tin, LSR s dng giao din m gi tin i ti la chn bng nh tuyn nh tuyn gi tin . 27. 32 Chuyn mch nhn a giao thc MPLSNhng ai quen thuc vi ATM ch rng khi LSR duy tr bng nh tuyn trn mi giao din ca n, thut ton nh tuyn trn ty thuc vo thut ton nh tuyn ca chuyn mch ATM. y l yu t quan trng ca mt s nghin cu chuyn mch nhn v chng ta s tho lun phn sau.Mt nhn lun lun mang thng tin nh tuyn v cn c th mang c thng tin ti nguyn dnh ring. Nhn mang thng tin nh tuyn l v ni dung ca n xc nh mt mc ong bng nh tuyn v mc ny cha thng tin xc nh phi nh tuyn gi tin i u. Cn nhn c th mang thng tin v vic dnh ti nguyn l v mc m c xc nh bi nhn c th, ty chn, bao gm thng tin lin quan ti ti nguyn no m gi tin c th s dng, v d nh l mt hng i xc nh m gi tin c t vo. Khi nhn c mang trong tiu ATM (header ATM) hay Frame Relay, nhn phi mang c hai thng tin nh tuyn v ti nguyn dnh ring. Cn khi nhn c mang trong mt tiu ring, th thng tin v ti nguyn m gi tin c th s dng c th b m ha nh l mt phn ca tiu , nn nHn ch mang thng tin v nh tuyn. Nhng vic m ha phn thng tin ca nhn l ty chn do mt nhn trong tiu ring c th mang c hai thng tin trn.ofn gin ha thut ton nh tuyn m c s dng bi thnh phn nh tuyn chuyn mch nhn s lm n gin vic to thut ton bng phn cng v s cho php nh tuyn nhanh hn m khng cn n cc phn cng t tin.Mt tnh cht quan trng ca thut ton nh tuyn c s dng bi chuyn mch nhn l mt LSR c th ly tt c thng tin cn thit cho vic nh tuyn mt gi tin cng nh phi quyt nh ti nguyn no m gi tin c th s dng ch trong mt ln truy cp b nh. Bi v mt mc trong bng nh tuyn c cha tt c cc thng tin cn thit v nh c nhn m ta s xc nh ng mc cn tm. Chnh c im ny lm cho chuyn mch nhn thch hp nh l mt k thut cho hiu qu nh tuyn cao.Vic trao i nhn kt hp vi kh nng mang nhn trong cc k thut lp lin kt s cho php nhiu thit b khc nhau c th c s dng lm LSR. V d, mang nhn trong trng VCI ca t bo ATM cho php bin phn cng ca chuyn mch ATM thnh LSR vi vic cung cp thm phn mm iu khin thch hp. Tng t, vic mang nhn trong tiu ring trong gi tin lm cho cc router truyn thng c th x l n bng phn mm, do , vi mt phn mm thch hp, mt router truyn thng c th tr thnh mt LSR.2.3.5. Thut ton nh tuyn nTrong kin trc nh tuyn truyn thng, nhng chc nng khc nhau c cung cp bi thnh phn iu khin (nh l nh tuyn unicast, nh tuyn multicast, nh tuyn unicast vi kiu ca dch v) yu cu nhng thut ton khc nhau trong thnh phn nh tuyn (xem hnh 2.8).Hnh 2,8: Kin trc nh tuyn truyn thong.Chc nng nh tuynnh tuyn unicastnh tuyn unicast vi Loi dch vnh tuyn multicastThut ton nh hngKt hp di nht vi a ch chKt hp di nht vi a ch ch + kt hp chnh xc vi Loi dch vKt hp di nht vi a ch ngun + kt hp chnh xc vi a ch ch v giao din ng vo 28. Chng 2: L thuyt c bn ca chuyn mch nhn 33Mt tnh cht quan trng ca chuyn mch nhn l s khng c nhiu thut ton nh tuyn khc nhau trong thnh phn nh tuyn ca n, thnh phn nh tuyn ch gm mt thut ton da trn vic trao i nhn (xem hnh 2.9). y l im phn bit quan trng gia hai kiu kin trc nh tuyn.Hnh 2.9: Kin trc chuyn mch nhn.Chc nng nh tuynnh tuyn unicastnh tuyn unicast vi Loi dch vnh tuyn multicastThut ton nh hngThut ton nh hng chung (trao i nhn)Chng ta c th ngh rng nu thnh phn nh tuyn chi c mt thut ton nh tuyn c th hn ch n cc chc nng c h tr bi chuyn mch nhn. Nhng tht s th khng phi vy, ch nng h tr nhiu chc nng nh tuyn vi ch mt thut ton nh tuyn l mt trong nhng im quan trng ca chuyn mch nhn. Thc s, nh chng ta s xem sau, th chc nng m chuyn mch nhn h tr nhiu hn so vi cc kin trc nh tuyn truyn thng.23.6. a giao thc: trn v d4T nhng m t trc v thnh phn nh tuyn chuyn mch nhn, chng ta c th thy r hai iu quan ng. iu u tin l thnh phn nh tuyn khng lm r l vi mt lp mng no c, v d, cng mt thnh phn nh tuyn c th c s dng chuyn mch nhn vi IP cng nh chuyn mch nhn vi IPX. iu ny lm cho chuyn mch nhn nh l mt gii php a giao thc (multiprotocol) tng thch vi cc giao thc lp mng (xem hnh 2.10).Hnh 2A0: a giao thc: trn v di.IPv6IPv4IPXApple TalkChuyn mch nhn (Label Switching)iUJ>%(00)E0)Q2EQH2Li., tin t a ch xc nh mt FEC xc nh v th l gi tr th m TSRs dng cho kt hp trong ca n vi FEC.Khi TSR hon tt qu nh kt hp trong ca n, phn thng tin cn thiu duy nht trong mc TFIB l th ra. TFEB ly thng tin ny t thng tin kt hp th t cc TSR khc. Khi TSR nhn thng tin kt hp th t cc TSR khc, n s x l qu ttnh nh sau. u tin, TSR kim tra s hin din ca kt hp trong ca n cho FEC mang trong thng tin kt hp ti m n nhn c. Nu kt hfp trcng c, TSR kim tra trm k trong thng tin kt hp cho FEC . Nu n c, TSR xc nh mc ong bng TFEB ca n m c cha s kt hp cho FEC v cp nht th ra trong bng bi th c mang trong thng tin kt hp m n nhn c. V lc ny, mc trong TFIB y v c th c dng nh tuyn.Nu TSR nhn thng tin kt hp th t cc TSR khc m n khng c kt hp trong cho FEC mang trong thng tin kt hp, lc ny TSR c hai ty chn. Ty chn u tin l gi thng tin ny trong trng hp TS. c th dng n sau (khi kt hp ong s c thc hin sau ) v ty chn th hai l loi b thng tin. ng nhin nu TSR chn loi b thng tin, th n s c th yu cu cc TSR khc gi li thng tin khi n cn, v iu ny s t thm yu cu cho cc c ch phn b thng tin kt hp th. V cng s c hai ty chn tcmg t khi TSR nhn thng tin kt hp th t cc TSR khc v TSR c kt hp trong cho FEC , nhng m k trong kt hp trong khc vi trm kt trong thng tin kt hp th nhn c.C ch xc nh cho phn b thng tin kt hp th ty thuc vo giao thc nh tuyn m TSR s dng to nh x gia FEC v m k. Neu nhng nh x c xy dng qua62 . Chuyn mch nhn a giao thc MPLS 58. Chooig 3: Chuyn mch nhn a giao thc MPLS 63cc giao thc nh tuyn ng thi lin kt (link-state routing protocol) (nh OSPF), s phn b thng tin kt hfp th c cung cp qua mt giao thc ring, gi l giao thc phn b th (Tag Distribution Protocol: TDP). Nguyn nhn l vi cc giao thc nh tuyn trng thi lin kt, thng tin nh tuyn bao gm cc tp router (c c cc router khng k nhau), ong khi thng tin kt hp th thng uc phn b gia cc router k nhau. iu ny lm cho cc giao thc nh tuyn trng thi lin kt khng ph hp cho vic t thng tin kt hp th vo. Cng nh vy i vi cc gio thc vector khong cch nh RIP. Thc t, ngay c vi cc giao thc nh RIP hay RIP-II, th vic phn b thng tin kt hp th vn ch nh vo TDP, l do l rt kh sa i cc giao thc ny. Tuy nhin khi nh x c to thnh nh vo BGP th thng tin kt hp th c th t vo u BGP nh l mt phn b ring ca BGP. Bi v BGP phn b thng tin v tin t a ch (FEC) v c m rng cho php mang thm thng tin v th. TSR phn b thng tin kt hp th, TSR phi bit tp cc TSR m thng tin ny c gi ti. TSR xy dng tp ny bng cc giao thc nh tuyn chy trn TSR. TSR to mt quan h nh tuyn ngang cp cho cc TSR trong mt tp . hiu r Tag Switching h tr nh tuyn da vo a ch ch, chtg ta xem xt mt v d trong hnh 3.1. Gi s l c cc a ch ch (biu din bi tin t a ch 192.6/16) c ni trc tip ti TSR E, v gi s (khi tt c cc lin kt u hot ng) c hai TSR B v TSR D dng TSR E l trm k cho FEC lin kt vi 192.6/16, TSR A dng TSR B nh l trm k cho FEC ny, v TSR c s dng TSR D l trm k cng cho FEC ny. Mi TSR c ba giao din, c ghi l IfO, Ifl, If2. Trong v d ny, chng ta gi s tt c TSR duy tr bng TFIB ca n, cng nh tp nhn t do trn mi TSR (khng phi l trn mi giao din).Hnh 3.1: nh tuyn da vo a chi ch ca Tag Switching [1 ].192.6/16TSRu tin xem xt lm th no m TSR xy dng TFIB ca n. Ngay khi TSR A xc nh TSR B l m k (TSR B) cho FEC lin kt vi 192.6/16, TSR A ly mt th t tp th t do ca n, gi s l th ny c gi tr l 100. TSR A s dng th ny nh l mt ch mc trong bng TFTB tm mt mc trong TFIB cp nht. Mt khi mc c tm thy, A thit lp th vo ca mc l 100, trm k l B, giao din ng ra l Ifl. Ngay khi B xc nh trm k (TSR E) cho FEC lin kt vi 192.6/16 n ly mt th t tp th t do ca n, gi s 59. 64 Chuyn mch nhn a giao thc MPLSl th ny c gi tr l 6. TSR B s dng th ny nh l mt chi mc trong bng TFIB tm mt mc trong TFIB cp nht. Mt khi mc c tm thy, B thit lp th vo ca mc l 6, trm k l E, giao din ng ra l Ifl. TSR c v D s dng cch thc tng t to kt hp ong ca n.Bng 3.1 cho thy trng thi ca mc trong cc TEDB lin kt vi 192.6/16. ch l mi dng l mt mc ttong TFIB ca cc TSR khc nha.Bng 3.1: Mc ban u ca TFIB [1],Th voTh raTrm kGiao din ng raTrong TSR A100TSRBIf1Trong TSR BTSREIf1Trong TSR c17TSRDIf2Trong TSR DTSREIf0Trong TSR ETSREIf0R rng ti thi im ny, khng c mc no c nhn ra, bi v chng mi ch c kt hp th trong m kt hp th trong khng c thng tin v th ra.Gi ta s xem xt qu tnh xy ra khi cc TSR phn b thng tn kt hp th ca n n cc TSR khc. TSR A gi thng tin kt hp th ca n n B v c. Tuy nhin, khi B nhn c thng tin ny, n thy rng thng tin khng n t trm k ca n cho 192.6/16. Do , n khng s dng thng tin ny cp nht th ra ca mc trong TFIB lin kt vi 192.6/16. Cng tng t nh vy khi c nhn c thng tin ny.TSR B gi thng tin v kt hp th ca n cho A, D, E. Bi v, c D ln E khng coi B l trm k ca n trong vic kt ni vi 192.6/16, do hai TSR ny khng s dng thng tin ny cp nht th ra trong bng TFIB. Tuy nhin, khi A nhn c thng tin ny, n thy rng thng tin ny n t trm k ca n n 192.6/16. Do , n dng thng tin nh l kt hp ngoi cho 192.6/16 v s dng th trong thng tin ny (th 6) cp nht th ra trong mc ca TFIB m lin kt vi 192.6/16. Ti thi im ny, A c mc y trong TFIB ca n.Thng tin kt hp th ca c gi cho A v D khng c s dng v 2 TSR ny khng coi c l trm k ca n.Thng tin kt hp th ca D gi cho B, c v E ch c s dng bi c v ch c c coi D l trm k ca n n 192.6/16 v n s cp nht th ra ca n trong mc ca TFIB vi th trong thng tin ny (th 5).Thng tin kt hp th gi tr E n B v D s c s dng bi c hai TSR ny v c hai TSR ny u coi E l trm k n 192.6/16. Ngay khi B v D nhn c thng tin ny chng s cp nht th ra trong mc TFIB bng vi th cha trong thng tin m chng nhn c (th 6).Lc ny nhng mc TFIB lin kt vi 192.6/16 y nh trong bng 3.2. 60. Chng 3: Chuyn mch nhn a giao thc MPLS 65Bng 3.2: Cc mc TFIB sau khi phi b th [I]Th voTh raTrm kGiao din ng raTrong TSR A100TSRBTrong TSR BTSREIf1Trong TSR c17TSR DIf2Trong TSR DTSR EIf0Trong TSR ETSR EIf0Ch l TSR E vn cha c th ra trong mc TFIB cho 192.6/16. Ngoi ra, trm cui ca mc ny l chnh n (TSR E). iu ny bi v 192.6/16 ni trc tip vi E, khi E nhn c gi c th 6 n s hnh ng nh mt TSR ra, ly th ra khi gi v gi n n 192.6/16.Lc ny cc TSR u c mc y ca n cho tin t a ch 192.6/16, chng ta s xem hot ng nh tuyn din ra nh th no.Khi TSR nhn mt gi v gi ny c mang nhn 100. A s dng th ny nh l mt ch mc tm mt mc TFIB. Khi mc ny c xc nh (th vo trong mc bng vi th mang trong gi), A thay th th mang trong gi (th 100) bng th ra trong mc tm thy ca n (th 6) v gi n n TSR B qua giao din ng ra Ifl. Khi TSR B nhn c gi ny, n s dng th mang trong gi (th 6) nh l mt ch mc tm mt mc TFIB. Khi mc ny c xc nh (th vo trong mc bang vi th mang trong gi), B thay th th mang trong gi (th 6) bng th ra trong mc tm thy ca n (th 6) v gi n n TSR E qua giao din ng ra Ifl. Khi E nhn gi ny, n ch ly th ra khi gi v gi n n ch qua giao din ng ra IfO.Khi c s thay i ca mng thy Tag Switching hot ng khi c s thay i cu hnh mng, ta xem iu g xy ra khi ung lin kt gia TSR D v E b h. Mt khi D pht hin ng lin kt ny b h, n s dng thng tin cung cp bi cc giao thc nh tuyn unicast thay i trm k ca n t TSR E thnh TSR B. Kt qu l th ra trong mc TFIB s khng cn ng. c mt th ra chnh xc, D cn phi c thng tin phn b th t trm k mi ca n, TSR B. Vic c c thng tin ny ty thuc vo cch D nhn cc thng tin phn b th t cc TSR m khng phi trm k ca n. Nu D c gi li thng tin ny, t B gi t ban u, th n s c th lp tc thit lp c th ra ca n n B. Nu n khng gi li thng tin ny th bt buc n phi gi yu cu n B B gi li thng tin kt hp th ca n.Nh ta thy, s to kt hp th c thc y bi s to nh x gia mt FEC v trm k ca n v iu ny c thc y bi cp nht thng tin nh tuyn. Do , theo nh phn trc. Tag Switching s dng kt hp tuyn iu khin. Ngoi ra ta thy rng s kt hp th gia mt th vo v mt FEC c to bi TSR (mt cch ni b), s kt hp gia mt th ra v mt FEC c to nh l mt kt qu ca vic nhn thng tin kt hp th t trm k m lin kt vi FEC . V vy, Tag Switching s dng kt hp th xui dng. 61. 3.1.2. nh tuyn phn cpCn nhc li rng mt trong s cc mc tiu ca Tag Switching l lm d dng tnh cht pht trin ca h thng nh tuyn. Tag Switching gii quyt vn ny bng vic s dng phn cp kin thc nh tuyn. c ti hiu c ci gi l nh tuyn phn cp (Hierarchy of routing), chng ta s xem li vi kha cnh ca kin trc nh tuyn.Kin trc nh tuyn c s dng ngy nay trn Internet l mt s tp trung ca cc min nh tuyn, khi nh tuyn trong tng khu vc th c cung cp bi cc giao thc nh tuyn ong min (nh OSPF, RIP, EIGRP), khi nh tuyn qua nhiu min th c cung cp bi cc giao thc a min (nh BGP). Mt li im ca vic chia nh tuyn thnh hai thnh phn ong v a min l lm gim s lng thng tin nh tuyn m c duy tr bi router, v iu ny cho php d dng pht in nh tuyn. Tuy nhin, s chia ti cp giao thc nh tuyn khng a ra mt s phn chia hon ton thng tin nh tuyn. R rng hcm, mi router trong min nh tuyn trung chuyn (l mt min m mang lu lng chi i qua n) phi duy tr trong bng nh tuyn ca n tt c cc router c cung cp bi cc giao thc a min, bt k n l cc router ong min hay l cc router ra. Duy tr tt c cc router c cung cp b nh tuyn a min trong tt c cc router ttong min l cn thit nh tuyn cc lu lng ttung chuyn qua min.Ch l cc router ttong min ttung chuyn cn bn ch chuyn cc gi t mt mt router ra ny n mt router ra khc, nhng dng nh c s lng ph cho chng khi phi duy tr mt bng nh tuyn y cho tt c cc router trn Internet. Tag Switching cung cp mt phng tin m nh cc router trong min trung chuyn c th chi lu nhng thng tin nh tuyn m chng cn, ngha l gi cc gi tin n router ra phi, l ni m cc thng tin nh tuyn y vn phi duy tr. R rng hn, cc router trong ca mt min s ch phi duy tr thng tin ca nhng router n ch ong mt min hn l phi duy tr tt c cc ch n Internet. Do chng ta c th coi y l mt bc tin ca s phn chia nh tuyn thnh phn trong v a min.B i s cn thit cho cc router trong phi duy tr thng tin nh tuyn a min l s n nh nh tuyn nhanh hn. Mt l do cho iu ny l khi mt router a min thay i, bng cch s dng s phn cp kin thc nh tuyn, ch cc router ra, ch khng phi cc router trong, phi cp nht thng tin v s thay i. V cng nhiu router cn phi cp nht th lm h thng cng lu n nh.Mt nguyn nhn khc thy ti sao b i s duy tr cc thng tin nh tuyn a min lm s nh tuyn mau n nh l khi mt router trong khi ng, vi s phn cp kin thc nh tuyn, n ch cn thit lp nhng router n cc router trong cng min ca n m khng cn phi thit lp tt c cc router trong a min, iu ny lm cho s nh tuyn lu n nh.B i s duy tr cc thng tin nh tuyn a min cn cung cp s trnh li tt hn, v cc router bn trong s hon ton b qua bt k vn no trong nh tuyn a min. Nhanh n nh v ttnh li tt s lm d dng cho vn pht trin.S xy dng TFIB h tt mt phn cp nh tuyn c da trn nhng th tc c dng h nh tuyn da a chi ch ca Tag Switching. Tt c TSR teong mt min nh tuyn cng dng chung cc giao thc nh tuyn trong min v s dng cc th tc m t phn trc xy dng TFIB ca n cho cc FEC lin kt vi nhng ch ong66 Chuyn mch nhn a giao thc MPLS 62. Chng 3: Chuyn mch nhn a giao thc MPLS 67min, l cc TSR ra ca min . Bi v mt router ra vo c th xc nh router ra ra u n c th gi gi tin, gi tin ny c th c chuyn mch nhn trn tt c cc ng n u ra ca min bi cc TSR txong.e mt TSR ra c th thc hin c chuyn mch th, tt c cc TSR ra trong cng mt min v nhng TSR ra c ni trc tip trong cc min khc nhau c th to v trao i thng tin kt hp th cho mi router (v FEC lin kt vi router ) c nhn qua protocol a min (BGP). Mt ln na, s to v trao i thng tin kt hp th ny theo cc th tc c m t phn trc, ngoi tx phn trm k TSR c to ra bao gm TSR ra tip theo. Khi mt TSR ra, TSR A, nhn thng tin kt hp th t TSR ra khc, TSR B, v TSR A c kt hptrong cho FEC mang trong thng tin kt hp th nhn c t B, TSR A kim tra xem TSR B c l TSR ra tip theo cho FEC ny (thng tin cn thit cho s kim tra ny c cung cp bi BGP). Neu ng nh th, TSR A xc nh mt mc trong TFIB ca n m cha s kt hp cho FEC v cp nht th ra trong mc bng vi th mang trong thng tin kt hp th.Kt qu ca cc th tc m t trn, TFIB ca mt TSR ra cha cc mc cho nhng FEC cho c cc router trong min v a min, ong khi TFIB ca cc TSR trong chi cha mc cho nhng FEC cho cc router trong min. h tr nh tuyn khi c s phn cp nh tuyn, Tag Switching cho php mt gi s mang nhiu hn mt th, c t chc thnh mt chng th (tag stack). Khi mt gi c nh tuyn t mt min nh tuyn ti mt min nh tuyn khc, chng th cha hai th. tm mc trong TFIB c th c nh tuyn, mt TSR lun lun s dng th trn cng ca chng th. Khi mt gi mang mt chng th, TSR, ngoi vic ao i th u chng, cn c th ly ra hay thm vo th vo chng th. Vic ly ra hay thm vo th xy ra bin gii cc min. Ti u vo min, mt th c thm vo chng th, v ti u ra, th c ly ra khi chng.Ve r rng hn v vic Tag Switching h tr nh th no v s phn cp kin thc chuyn mch nhn, ta xt mt v d trong hnh 3.2. Min nh tuyn A bao gm hai TSR ra, TSR T v TSR w, v hai TSR trong, TSR X v TSR Y. C mt tp cc ch (tin t a ch) trong min nh tuyn c c th i ti qua TSR z, TSR ra ca min c. TSR z phn b thng tin v cc ch ny ti TSR w, v TSR ny s thng bo cho TSR T, v TSR T s thng bo cho TSR V.Hnh 3.2: Chuyn mch th vi nh tuyn phn cp [1],Min nh hng BMin nh hng AMin nh hng c 63. 68 Chuyn mch nhn a giao thc MPLSBi v tt c TSR trong A u tham gia vo vic iih tuyn trong min nn chng u c thng tin ca nhau, ngha l TSR T, TSR X v TSRY u c mt nh tuyn n TSR w. Mi TSR trn to mt kt hp trong cho uh tuyn trn v phn b thng tin kt hji ny cho TSR khc. S dng s kt hp trong v ngoi, TSR T, TSR X, TvSR Y xy dng mt mc TFIB lin kt vi TSR w nh trong bng 3.3.Bng 3.3: Mc TFIB trong min nh tuyn A [1J.Th voTh raTrm kTrong TSR TKhng xt10TSRXTrong TSR X1012TSR YTrong TSR Y1217TSRWTrong TSR w17KhnxtTSRWCh l trm k trong mc TFIB ca TSR w ch vo chnh n (TSR W) chi' cho TSR w khi nhn mt gi c nhn ng bng nhn vo ca n (nhn 17) th n phi ly nhn ra khi chng nhn trong gi. Sau TSR w tm mt mc TFIB theo nhn trn cng ca chng nhn (sau khi ly nhn 17 ra) v dng mc ny quyt nh phi gi gi i u.Chng ta m t nhng TSR trong min nh tuyn A xy dng TFIB ca n vi nhiig mc lin kt vi cc tuyn trong min (l vi cc tuyn i n TSR W). V by gi chng ta xem cc TSR ra (TSR T, TSR w, TSR V, TSR Z) xy dng TFIB ca no vi cc mc lin kt vi cc tuyn a min.Gi s l TSR z to s kt hp trong cho FEC lin kt vi mt tp cc ch trong c, vi 6 nh l th trong. Tng t nhng th tc m t phn trc TSR z phn b thng tin kt hp ny n TSR w to kt hp th trong cho cng FEC trn vi 2 l th vo, v n gi thng tin ny n TSR T. Khi TSR w nhn thng tin kt hp th t z n ly gi tr th trong thng tin nhn c lm th ra ca n (th ). Tng t nh vy cho TSR T, gi s n to kt hp trong cho FEC v s dng th 5 l th vo, sau n gi thng tin kt hp th ny ti TSR V. Khi TSR T nhn thng tin kt hp th t TSR ra k ca n TSR w, TSR T s dng th trong thng tin lm th ra.Khi TSR T nhn thng tin kt hp th t TSR ra k TSR w, n pht hin l trm k lin kt lin kt vi kt hp ny (TSR W) khng trc tip ni vi TSR T.Bng 3.4: Mc TFIB ca cc tuyn a min.Th voTh raTrm kTrong TSR VKhng xt5TSRTTrong TSR T52TSRWTrong TSR w26TSRZTrong TSR z6Khng xtch 64. Do , T8R T tm trong TFIB ca n tm mc m tng ng vi a ch ca trm k (TSR W). Th ra t mc tm thy (th 10) s l th c TSR T t ln trn u chng ca mt th (l thp 5).By gi ta s xcm xt vic nh tuyn cc gi, Gi s l TSR T nhn gi t TSR V c th l 5 TSR T hy l th ra IrrV muc IFIB ca th 5 l 2. Do TSR T thay th th trong gi bng th 2 v SR T t ihe 10 ln ti chng th trong gi v gi n trm k ca n (TSR X). Khi TSR X nhn gii ih 10 n tm mc TFIB toTig ng v n tm thy th ra l 12 v trm k l TSR Y Do n ihay th th trong gi bng th 12 v gi n TSR Y. Khi TSR Y nhu gi c th 12 n thay th th ny bng th 17 v gi n TSR w. Cui cng, khi TSR w nhn c gi. c th 17, n thy rng mc TFD3 m c th vo l th 17 ch ra rng n phi ly th ny ra khi chng th. Sau khi TSR w rt th 17 ra khi chng th th th by gi l th 2 l th c thay th bi TSR T. TSR w s dng th ny nh l ch mc tm mc TFIB m c th vo l 2. S dng thng tin trong mc tm c, TSR w thay th th trong gi tin bng th 6 v gi gi tin ti TSR z. v TSR z s hot ng nh trn, thm th vo, a gi n ng a ch cn thit.Tm li, vic s dng nh tuyn phn cp cho php cch ly hon ton cc router trong mt min nh tuyn khi nh tuyn a min. V iu ny s gip d dng trong vn pht trin.3.1.3. MulticastCt li ca nh tuyn multicast l cy phn b multicast (multicast distribution tree). Nhng cy nh vy c to thnh t cc giao thc nh tuyn multicast (nh DVMRP, PIM, CBT, MOSPF) v c s dng bi thnh phn nh tuyn ca lp nh tuyn mng nh tuyn multicast cc gi tin. Trong phn ny chng ta s tm hiu Tag Switching h tr multicast klii cy phn b multicast c xy dng bi Protocol Independent Multicast (PIM). h tr multicast vi Tag Switching, mt TSR ph c th chn la mt cy phn b multicast da vo duy nht: Th c mang trong gi tin. Giao din m gi tin c nhn.Nh chng ta tho lun chng 2, iu ny yu cu mt TSR phi duy tr TFIB ca n trn mi giao din v phi chp nhn hai yu cu ca thnh phn iu khin Tag Switching: Khng c hai TSR c ni n cng mt mng con kt hp chung th trn mng con lm khc cy phn b multicast. Cc TSR m c ni n cng mng con v l mt phn chung ca cy phn bmulticast, phi ng gia chng irit th chung s c s dng bi tt c cc TSR khi gi hoc nhn nhng gi !in quan n cy trong cc giao din ni n mng con .Ch l yu cu u tin lun lun tha mn khi LSR c ni trn mt mng con im n im. e tha mn yu cu u tin khi cc TSR c ni n mng con a tray cp (nh Ethernet), Tag Switching xc nh nlrng th tc m TSR dng chia nh tp cc nhn r s dng trong multicast cc mrm con khng lin kt. Mi TSR qung b mt lot cc th thng qua ban lin PIiV HLLO rng TSR mun s dng cho kt hp trong caChng 3: Chu}.'n mch nhn a giao thc MPLS 69 65. n. Khi TSR ni n mt mng con a truy cp khi ng, n kim tra lot th m n mun s dng c ng vi cc lot th m cc TSR khc cng ni vi mng con s dng hay khng bng cch lng nghe bn tin PIM HELLO nhn c trn giao din ni n mng con . Nu n nhn t cc- TSR khc bn tin PIM HELLO vi mt lot th ttng vi lot th m n ang qung b ong bn tin PM HELLO ca n th mt trong TSR phi thay i lot th. Duy tr TFIB cho multicast trn mi giao din (hn l n mi TSR) cho php mt TSR thc hin cc th tc trn trong mi giao din. Mt lot cc th m TSR dng trn mi giao din c lp ln nhau. tho mn yu cu th 2, Tag Switching xc nh nhng th tc la chn trong cc TSR m cng ni n mt mng con v l mt phn trong cy phn b multicast mt TSR chu trch nhim cho vic kt hp trong cho FEC lin kt vi cy , v xc nh th tc phn b thng tin kt hp ny gia cc TSR . tham gia vo mt cy phn b lin kt, mt TSR, ging nh mt router truyn ' thng, cn phi gi mt bn tin PIM JOESi v pha gc ca cy. to kt hp trong cho cy ny, TSR ly mt th lin lin kt vi giao din m bn tin s c gi v to mt mc trong TFIB ca n vi th trong c t hng th trong bn tin PIM JOIN v gi bn tin v pha gc ca cy. Khi mt TSR l mt thnh phn ca cy nhn mt bn tin PM JOIN t mt TSR xui dng (so vi gc ca cy), TSR ny s cp nht mc trong TFIB ca n m gn vi cy bng th trong bng tin v giao din m n nhn bn tin. R rng hn, TSR s dng th thay th ra v giao din thay giao din ra trong mc.Th tc m chng ta m t ttn tha mn yu cu th hai khi cc TSR cng ni n mng con im ni im. V by gi ta xem xt khi cc TSR cng ni n mt mng con a truy cp. R rng l trong mng con a uy cp, bn tin PIM JOIN c multicast, do tt c cc TSR cng ni n mng u nhn c tt c cc bn tin PIM JOIN c gi bi cc TSR khc qua giao din ni n mng con ny. TSR u tin ong mng con quyt nh tham gia vo mt cy phn b multicast l TSR to ra s kt hp mt th v cy. Tt c cc TSR khc trong mng con u nhn thng tin v s kt hp ny trong bn tin PIM JOIN m cc TSR gi v gc ca cy. Do , bt c TSR no sau quyt nh tham gia vo cy u bit c th lin kt vi cy trong mng con . V TSR mun tham gia vo cy, n s s dng th trong bn tin PIM JOIN m n nhn c l i vo cho mc TFIB ca n gn vi cy. Nu mt TSR ni vi mt mng con xc nh mun bit l s kt hp cho mt cy multicast gia cc TSR khc trong mng c tn ti hay khng, n gi bn tin PM JOIN vi th 0. Khi cc TSR khc nhn c bn tin ny, v tn ti s kt hp cho cy, th n s gi tr li bn tin PIM J0 vi th lin kt vi cy. Bi v cc TSR duy tr TFIB ca n trn mi giao din (ch khng phi ttn mi TSR), mt TSR c th p dng cc th tc ttn ong mi kt ni, m khng cn c s phi hp gia cc th tc ca cc TSR trn mi kt ni. xem Tag Switching h tr multicast nh th no, ta kho st mt v d trong hnh 3.3 c TSR D, TSR E, TSR F c li vo mt mng con a truy cp, trong khi cc kt ni khc l mng con im ni im.Gi s l c mt cy multicast c gc ti TSR A v cy ny ch gm TSR A v TSRD. Khi TSR B mun tham gia vo cy, n phi gi mt bn tin PIM JOIN v pha TSR A, ngha l n phi gi bn tin ra giao din IfO. Trc khi gi bn tin, B ly mt th trong tp th t do gn vi giao din IfO v to mt mc TFIB vi th ny l th vo. TSR B gi bn70 Chuyn mch nhn a giao thc MPLS 66. Chng 3: Chuyn mch nhn a giao thc MPLS 71tin PM JOIN c cha th ny n D. Khi TSR D nhn bn tin ny, n tm thy trong TF1B mt mc c lin kt n cy, v n ly th va nhn c lm th ra trong mc v ly giao din m n nhn c lm giao din ra trong mc y l trng hp kt ni ca mt TSR hng v pha gc ca cy multicast thng qua mng con im ni im. V chng 'I^r xt trng hp kt ni ihiig qua mng con a truy cp.Hnh 3.3: Multicast trong chuyn mch th [1 ].LSRNu TSR E mun iam gia vo cy, th n s gi bn tin PIM JOIN v pha TSR A, ngha l n phi gi bn tin t cng giao din ifO n D. Trc khi gi bn tin, E ly mt th trong tp th t do gn vi giao din m n gi bn tin (giao din ifO) v to mt mc TFIB cho th ny nh l mt th vo. TSR E sau gi bn tin PM JOIN c cha th ny. V bn tin ny c multicast nn tt c cc TSR ni n mng con ny u nhn c, ngha l n s c nhn bi cc TSR D, E v F. Khi TSR D nhn c bn tin ny, n tm trong TFIB mc c lin kt vi cy v sau n ly th nhn c lm th ra cho mc v ly giao din bn tin c nhn lm giao din ng ra (giao din If2). Ch l ti thi im ny, TSR D c hai giao din ng ra (If 1 v If2) v tng ng vi n c hai th ra.V by gi gi s l TSR F mun tham gia vo cy multicast. Ch l ti thd im n quyt nh tham gia vo cy th n nhn c th lin kt vi cy, l th mang trong bn tin PIM JOIN do TSR D gi (multicast). Do n chi cn tm mc trong TFIB ca n lin kt vi th ny v ly th ny lm th trong. trn chng ta m t qu nh to cy multicast c gc t A. Ch l mi TSR mun c th multicast th n phi t to cy multicast cho ring n.Chng ta c th h tr multicast cho Tag Switching bng cch t thng tin kt hp th n u ca PIM s ngn cn Tag Switching trong cc mi trng m nh tuyn multicast c cung cp bi cc giao thc khc (nh MOSPF, DVMRP). Tuy nhin ngoi s dng PIM phn b thng tin chuyn mch th, Tag Switching cn cung cp mt cch phn b chuyn mch th khc l phn b thng tin kt hp th ca multicast bng cc giao thc phn b th (Tag Distribution Protocol - TDP). Bng cch ny Tag Switching c th h tr multicast vi cc giao thc nh tuyn khc ngoi PM. 67. 3.1.4. Chuyn mch th trn ATMTrong phn ny, chng ta s tm hiu cch thc hot ng ca chuyn mch th (Tag Switching) trn mt chuyn mch ATM. Khi nhng chuyn mch ATM c tn gi ATM_TSR. Bi v ATM v chuyn mch th cng s dng k thut chuyn mch th. Chuyn mch th c th hot ng trn phn cng ca mt chuyn mch ATM truyn thng. Tuy nhin mt phang iu khin ATM (ATM control plane) s c thay th bng thnh phn iu khin chuyn mch th (Tag Switching control component). Nh vy mt chuyn mch ATM s iu khin s hot ng ca n bng cch s dng cc giao thc nh OSPF (Open Shortest Path First), BGP (Border Gateway Protocol), RSVP (Resource Reservation Protocol) thay V s dng cc giao thc c IT hay ATM Forum nh ngha nh UNI v PNNI.3.1.4.1. Thng tin nhnThng tin nhn c ghi trong header ca mt t bo ATM. Nu stack nhn ch c mt mc nhn th gi tr nhn nm trong vng VCI ca header. Chiu di vng VCI l 16 bit nn s lng nhn ti a l 2' nhn. Bi v bng nh tuyn ca cc chuyn mch ATM uc xy dng da trn tng giao din nn s lng nhn ca mt ATM-LSR c th ln hn 2^. Nu stack nhn c hai mc nhn th mc nhn u tin cha trong vng VCI v mc nhn th hai s cha trong vng VPI ca ti . V chiu di l 12 bit nn s lng nhn ti a cha trong vng VPI cho mt giao din l 4096 (2') nhn.3.1.4.2. Chuyn tip da trn chCung cp chc nng nh tuyn da trn a chi ch cho nhng ATM_TSR phi iu chnh nhng th tc m Tag Switching s dng cung cp chc nng cho nhng thit b khng phi l ATM-TSR (non ATM TSR). Trong phn ny chng ta ch cp n nhng thay i ny.S thay i quan trng nht l hnh thc trao i thng tin th gia cc ATM_TSR. Mt ATM_TSR s khng thng bo gi m n s dng cho mt TSR bt k cho n khi n nhn c yu cu t TSR ny. V th c th nhn c thng tin th t mt TSR no, ATM_TSR phi gi n TSR li yu cu. Vi hnh thc ny cc chuyn mch ATM c th hn ch c s lng th lu gi. Tuy nhin li ny sinh mt vn l xen ln t bo (cell interleave). hiu v vn ny, chng ta xem xt v d sau. C hai TSR A v TSR B cng gi d liu n ATM_TSR X. Cc gi d liu ca TSR A v TSR B s c phn on thnh nhng t bo ATM. Ti ng ra ca TSR A v TSR B, cc t bo ny u c gn th bng 7 (VCI = 7). Nh vy, gi s, u tin ATM_TSR X nhn c t bo ATM do TSR B gi n, X s s dng cch thc chuyn mch truyn thng, thay nhn c VCI bng 7 bng th mi VCI bng 3 v gi t bo n nt mng k tip trn giao din If2. T bo ATM k tip m ATM_TSR X rhn c l t bo ca TSR A. Tng t, X s gn th mi VCI bng 3 cho t bo ny v chuyn n n nt mng k tip cng trn giao din If2. Gi s t bo tip theo ATM_TSR X nhn c cng do TSR A gi n. Cch thc x l t bo cng din ra tofng t.Nh vy cc t bo ATM m ATM_TSR X chuyn n nt mng k tip trn giao din EF2 bao gm nhng t bo n t TSR A v nhng t bo n nhng t TSR B. Hai t bo lin tip trn cng mt u ra (gi tr th ging nhau) nhng thuc nhng gi d liu72 Chuyn mch nhn a giao thc MPLS 68. khc nhau, dn n nt mng nhn s khng th ti hp t bo thnh gi d liu mt cch chnh xc.Gii php cho vn ny i hi cc ATM_TSR s gi cc t bo ATM ca cng mt gi d liu trong b m cho n khi nhn c t bo cui cng. Sau khi nhn c ton b t bo ca gi d liu, ATM-TSR s gi cc t bo ny cng mt lc. Nh vy s khng c s xen ln cc t bo ca nhng gi d liu khc nhau. Gii php ny c tn gi vc_merge.Tr li v d trn, vi gii php vc_merge, khi ATM_LSR X nhn c t bo vi gi tr th VCI bng 7 trn giao din If 0, X s kim tra t bo ny c phi l t bo cui cng ca mt gi d liu hay khng. Nu khng phi, t bo s c lu gi trong b m dnh cho giao din If 0. Tong t klii nhn c t bo do TSR A gi n trn giao din If1,^ X cng kim tra t bo c phi l t bo cui cng ca mt gi d liu hay khng. V nu kling phi, t bo cng s c lu gi trong b m dnh cho giao din Ifl. Ngay khi ATM_TSR X nhn c t bo cui cng vi VCI bng 7 trn giao din If 0, X s tin hnh gi tt c cc t bo trong b m cng vi t bo mi nhn n nt mng k tip trn giao din lf2 vi th mi VCI bng 3. V.th cc gi d liu s c ti hp chnh xc t cc t bo ATM.S dng gii php VC_merge yu cu cc ATM_TSR phi c kh nng phn bit t bo c phi l t bo cui cng ca gi d liu hay khng v xy dng nhng b m cho tng ng vo. Tuy nhin c hai ycu ny hoc l c cung cp hoc .l cung cp mt phn bi cc chuyn mch ATM. Yu cu th nht s c hai thut ton thc hin l Early Packet Discard (EPD)v Partial Packet Discard (PPD).Ch rng gii phpVC_merge ch c s dng cho Tag Switching h chc nng nh tuyn da vo a ch ch (destination based forwarding). Khng c s dng phng php ny cho nhng lu ltig yu cu s dnh sn ti nguyn mng. V th nh hng ca b m ln cc yu t nh Jitter s khng quan trng.Gii php th hai cho vn xen ln t bo l s dng nhiu hn mt th cho mt ng dn trong mng. Chng ta bit rng s xen ln t bo ATM ca cc ng vo khc nhau l do chng c cng gi tr nhn VCI ng ra. Do , nu cc t bo n t nhng u vo khc nhau c gn th u ra khc nhau th cc gi d liu vn s c ti hp chnh xc t cc t bo.Mt trong nhng u im ca vic s dng nhiu th khc nhau cho mt ng ra l khng yu cu s thay i no i vi phn cng ca chuyn mch ATM. Nhng s lng kt ni o vc cn xy dng s xp x vi m hnh mng overlay tch hp Ip trn ATM. Do gii php ny kh nng ng dng khng kh thi nh gii php VC_merge.3.1.4.3. ng gi d liu trn nhng lin kt non_ATMi vi nhng k thut lp lin kt d liu (data link) nh ATM, header ca tng ny c s dng mang thng tin th. V th cho php s dng li nhng chc nng chuyn mch c sn (v d nh s dng phn cng ca chuyn mch ATM). Tuy nhin vi nhng k thut lp lin kt d liu nh point-to-point, Ethernet..cu trc tiu ca lp 2 khng th mang thng tin th. V th, thng tin th c ghi trong mt th, c gi l shim label, chn vo gia tiu lp mng v lp lin kt d liu ca gi d liu.Chng 3: Chuyn mch nhn 'a giao thc MPLS 73 69. Trong mt mng con point-to-point, cc gi d liu c gn th c nhn dng bi vng giao thc ppp, vi mt gi tr chi nh unicast v gi tr cn li ch nh multicast. Trong nhng mng con a ttuy nhp, cc gi d liu nh vy cng c nhn dng bng etheitype v cng c mt gi tr xc nh unicast, gi cn li xc nh multicast.Nu nh gi d liu c nhiu mc th th chng th s bao gm mt chui cc th c cu trc (hnh 3.4).Hnh 3.4: cu trc ca mt th trong chng th [6].74 Chuyn mch nhn a giao thc MPLSTag (20 bit)Cos (3 bit)s (1 bit)TTL (8 bit)Mc th cao nht nm bn phi ngay sau tiu lp lin kt d liu v mc th thp nht nm tri trc tiu lrp mng. Cc nt mng s dng thng tin trong mc th cao nht thc hin chuyn gi i.Vng chng (Stack) s c mt bit. Nu s bng 1, th ny l th cui cng (hay mc nhn thp nht) trong chng th. Ngc li, s bng 0.Vng Time_to_Live (TTL) chiu di 8 bit hon ton tong t nh vng TTL trong tiu IP. Ch rng TSR chi x l vng TTL ca mc th cao nhtVng Class of Service (CoS) xc nh lp dch v ca gi d liu. Khi TSR ra gn th u tin cho gi d liu, chnh edge TSR ny cng s quyt nh lp dch v dnh cho gi v n nh mt gi tr tng ng cho vng CoS. Khi mt TSR trung gian gn thm vo gi mt mc th mi, gi tr CoS trong th mi ny s gi li gi tr CoS ca mc th cao nht trc y hoc TSR ny s n nh mt gi tr mi. Gi vng CoS c s dng tomg t nh gi tr vng IP Precedence trong tiu IP.Gi tt th c TSR nhn s dng tin hnh tm kim trong bng TFIB (Tag Forwarding Information Based), xc nh phng thc x l gi d liu. Vng ny c chiu di l 20 bit cho php s lng th ln n 1.048.576 th. Nh ni trn, cc gi d liu multicast v unicast c gi tr vng giao thc ppp (i v mng con point-to-point) hay vng ethertype (i vi mng con a truy nhp) khc nhau. V th, mi hnh ic unicast v multicast c s lng th ln n 1.048.576 th. Nhumg trn thc t, s lng th c s dng s b hn
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