Luan Van QoS MPLS

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CHNG 1: GII THIU MT S TH H MNG 1.1 MNG IP a. Chuyn tip IP v nhng hn ch ca n Nh ta bit, Internet l mt tp hp cc mng kt ni vi nhau dng chuyn tip gi tin gia cc host s dng IP. IP cung cp dch v ng gi v hng, khng c s m bo phn phi gi tin. Trong m hnh Internet cc h thng dng chuyn tip gi tin gi l Router dng chuyn tip gi tin n ch. thc hin iu ny router cn xc nh nexthop v interface ng ra chuyn tip gi tin. Thng tin ny c c thng qua cc thng tin nh tuyn c s dng xy dng bng chuyn tip gi tin (Forwarding Information Base FIB). Tin trnh chuyn tip gi tin gm 3 hot ng sau: + Tm a ch xc nh interface ng ra + Chuyn tip gi tin + Phn lch.

Hnh 1.1: Chuyn tip gi tin trong IP

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QoS trong MPLS

Mi router duy tr mt bng nh tuyn hc c thng qua cc giao thc nh tuyn hoc nh tuyn tnh. Bng nh tuyn ny c th c kch thc cc k ln, trong Internet n c th c n 50 ngn entry. i vi mi gi tin i vo router, a ch IP ch s c kim tra, da vo thng tin trong bng nh tuyn s xc nh hop k tip v interface ng ra chuyn tip gi tin. Quyt nh chuyn tip c thc hin c lp trn mi router trong mng. Ngoi ra, vic s dng subnet mask yu cu a ch IP ch trong mo u ca gi tin i vo phi thch hp vi mask trong bng nh tuyn, ngha l da trn quy tc "longest match" xem th entry no c mask vi s bit ng nht vi a ch gi tin s c dng lm thng tin chuyn tip. Do , chuyn tip IP c th c xem l tin trnh nh x mi a ch IP ch n hop k tip. V mi router c s lng next-hop gii hn, nn chuyn tip IP c th c xem nh l qu trnh nh x tp hp cc gi tin vo s next-hop gii hn hoc tng ng vi s lng subnet trn router. Tt c cc gi tin trong mt subnet khng c s phn bit nhau v c chuyn tip theo cng mt phng thc xc nh, chng i qua cng mt ng dn n mng. Mt nhm gi tin nh vy c gi l lp chuyn tip tng ng FEC (Forwarding Equivalence Class). Khi gi tin di chuyn n ch cui cng, mi router dc ng i s kim tra a ch ch ca gi tin v ng k n n FEC. Ta c th thy r rng chuyn tip IP yu cu hot ng tm kim a ch IP phc tp mi router dc ng i ca gi tin. Bt c s thay i no v thng tin iu khin vic chuyn tip ca gi tin s c thng bo cho tt c cc thit b trong min nh tuyn, dn n x l cho xong mt gi tin lm tn thi gian cho nhng vic sau: thi gian tm kim, thi gian cp nht, v tn b nh x l, tn CPU. Tt c tin trnh nh tuyn v chuyn tip ni trn y din ra lp Network. Cc router c th kt ni trc tip vi nhau theo m hnh im-im, hoc l c th kt ni vi nhau bng cc switch mng LAN hay mng WAN (v d mng Frame Relay, ATM).

Hnh 1.2: Mng Frame-relaySVTH: TRN VN TR 2 GVHD: ThS TRNG TN C ANH

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QoS trong MPLS

Nhng khng may, cc switch lp 2 ny khng c kh nng nm gi thng tin nh tuyn lp 3 hoc chn ng i cho gi tin bng cch phn tch a ch ch lp 3 ca gi tin. Do , cc switch lp 2 khng tham gia vo qu trnh chuyn tip gi tin trong lp 3, chng ch cha thng tin v MAC Address ca ch n. Cc ng i LAN lp 2 c thit lp kh n gin - tt c LAN switch u trong sut vi cc thit b kt ni vi chng. Nhng vic thit lp ng i trong mng WAN lp 2 li phc tp hn nhiu. ng i ca gi tin trong mng WAN lp 2 c thit lp th cng v ch c thit lp khi c yu cu. Thit b nh tuyn bin mng lp 2 (ingress router) mun chuyn d liu n thit b ng ra (egress router) cn thit lp hoc l kt ni trc tip n egress router (kt ni ny c gi l cc knh o VC) hoc l gi d liu ca n n mt thit b khc truyn dn n ch. m bo chuyn tip gi tin ti u trong mng WAN lp 2, cc knh o phi tn ti gia hai router bt k kt ni vo mng WAN . iu ny c v n gin xy dng n nhng li gp mt vn khc l kh nng m rng b hn ch. Cc vn m ta c th gp phi l: + Mi ln mt router mi kt ni vo mng WAN li, mt knh o phi c thit lp gia router ny v router khc (nu c nhu cu cn chuyn tip gi tin ti u). + Vi vic cu hnh giao thc nh tuyn, mi router gn vo mng WAN lp 2 (c xy dng vi cc ATM hay Frame Relay switch) cn c mt knh o dnh trc vi mi router khc kt ni vo mng li . t c d phng mong mun, mi router cng phi thit lp mi quan h cn k nh tuyn vi router khc. Kt qu l to ra m hnh mng fullmesh, trong bn thn mi router s nm gi mt s lng ln lng ging c mi quan h cn k v giao thc nh tuyn, t to ra lu lng nh tuyn vi s lng ln. + Kh m bit chnh xc bao nhiu lu lng chy gia trn hai router trong mng. T nhng hn ch ni trn r rng cn phi c mt c ch khc c th trao i thng tin lp mng gia cc router v WAN switch, v cho php cc switch tham gia vo tin trnh quyt nh chuyn tip gi tin tc l khng cn phi c cc knh o gia cc router bin na. t c s chuyn tip nh vy th trong bt k mi trng mng no cc thit b chuyn tip khng nn ph thuc vo thng tin c trong mo u gi tin, thit b ny ch cn chuyn mch gi tin t ingress router n egress router m khng cn phn tch a ch IP

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QoS trong MPLS

ch c trong gi tin. Do , i vi mi gi tin c chuyn tip s c mt nhn c thm vo, nhn ny s m trch cc vn chuyn tip gi tin n ch, cc vn v QoS, v.v... ngha l chuyn tip gi tin da trn nhn. Bt k s thay i no trong tin trnh quyt nh s c thng bo cho router khc trong mng thng qua vic phn phi mt nhn mi. l l do ra i ca MPLS (Multiprotocol Label Switching) - cng ngh chuyn mch nhn a giao thc. 1.2 MNG MPLS MPLS l cng ngh thng dng trong mng core, bi v trong mng core l ni m mi d liu ca ca cc mng thu bao u v y trc khi ti ch, v vy n s chu mt ti trng rt ln nu ch s dng cc cng ngh bnh thng th vic xy ra nghn mng l khng th trnh khi, mng MPLS c th p ng c cc yu cu khc khe trn, n s dng chuyn mch nhn (Swithcing Label) ch khng routing nh mng IP. Mt mng MPLS in hnh:

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QoS trong MPLS

Hnh 1.3: Mng MPLS Mng MPLS y s gm c ba loi router CE (Customer Equipment hay router khch hng), PE ( Provider Equipment hay router bin nh cung cp ) v P ( Provider hay router bn trong nh cung cp dch c ), cc router P v mt phn PE s chy MPLS, cc router CE v mt phn PE cn li s chy cc giao thc khc ( c th l IP, Frame-Relay, ATM).

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CHNG 2: TNG QUAN V MNG MPLS 2.1 Gii thiu: Ngy nay mng my tnh pht trin rng khp, c bit l mng Internet n tr thnh ph bin trn ton th gii. V n ang pht trin c v s lng ln cht lng, bn cnh vic tng vt s user trong mng th vic gia tng dch v cng l vn rt ln, trc y nu nh ta ch c nhu cu truyn data th by gi ta cn truyn c tn hiu thoi tn hiu video v mt s dch v m rng khc, Vi mng Internet truyn thng th ngun ti nguyn v bng thng v tc l hn ch, v vy thc hin truyn tn hiu thoi v video c cht lng l khng th. Nhiu mng th h mi hn ra i nh:Frame-Relay, ISDN, ATM, chng gii quyt phn no nhng yu cu trn nhng vn cn nhiu hn ch, theo pht trin ca cng ngh mng MPLS ra i vi tng dng nhn chuyn mch n gii quyt v khc phc nhng hn ch m cc mng trc y vn cn tn ti nh: Tc , bng thng khng hu ch, delay. Mng MPLS l s k tha v kt hp ca routing thng minh trong mng IP v chuyn mch tc cao trong mng ATM, c c routing layer 3 (IP) v switching layer 2 (VPI/VCI ca ATM). MPLS l c ch chuyn mch nhn do Cisco pht trin v c IETF chun ha, h tr kh nng chuyn mch, nh tuyn lung thng tin mt cch hiu qu. MPLS l mt cng ngh kt hp c im tt nht gia nh tuyn lp ba v chuyn mch lp hai cho php chuyn ti cc gi rt nhanh trong mng li (core) v nh tuyn tt mng bin (edge) bng cch da vo nhn (label). MPLS l mt phng php ci tin vic chuyn tip gi trn mng bng cc nhn c gn vi mi gi IP, t bo ATM, hoc frame lp hai. Phng php chuyn mch nhn gip cc Router v MPLS-enable ATM switch ra quyt nh theo ni dung nhn tt hn vic nh tuyn phc tp theo a ch IP ch. MPLS kt ni tnh thc thi v kh nng chuyn mch lp hai vi nh tuyn lp ba, cho php cc ISP cung cp nhiu dch v khc nhau m khng cn phi b i c s h tng sn c. Cu trc MPLS c tnh mm do trong bt k s phi hp vi cngSVTH: TRN VN TR 6 GVHD: ThS TRNG TN C ANH

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QoS trong MPLS

ngh lp hai no. MPLS h tr mi giao thc lp hai, trin khai hiu qu cc dch v IP trn mt mng chuyn mch IP. MPLS h tr vic to ra cc tuyn khc nhau gia ngun v ch trn mt ng trc Internet. Bng vic tch hp MPLS vo kin trc mng, cc ISP c th gim chi ph, tng li nhun, cung cp nhiu hiu qu khc nhau v t c hiu qu cnh tranh cao. Li ch ca MPLS - Lm vic vi hu ht cc cng ngh lin kt d liu nh IP, ATM. - Tng thch vi hu ht cc giao thc nh tuyn v cc cng ngh khc lin quan n Internet. - Hot ng c lp vi cc giao thc nh tuyn (routing protocol). - Tm ng i linh hot da vo nhn(label) cho trc. - H tr vic cu hnh qun tr v bo tr h thng (OAM). - C th hot ng trong mt mng phn cp. - C tnh tng thch cao. c im mng MPLS - Khng c thnh phn giao thc pha host. - MPLS ch nm trn cc router. - MPLS l mt giao thc c lp nn c th hot ng vi cc giao thc mng khc IP nh IPX, ATM, Frame-Relay, PPP hoc trc tip vi tng Data Link. - nh tuyn trong MPLS c dng to cc lung bng thng c nh tng t nh knh o ca ATM hay Frame Relay. - MPLS n gin ho qu trnh nh tuyn, ng thi tng cng tnh linh ng vi cc tng trung gian.

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QoS trong MPLS

Mt s ng dng ca MPLS: Internet c ba nhm ng dng chnh: voice, data, video vi cc yu cu khc nhau. Voice yu cu tr thp, cho php tht thot d liu tng hiu qu. Video cho php tht thot d liu mc chp nhn c, mang tnh thi gian thc (realtime). Data yu cu bo mt v chnh xc cao. MPLS gip khai thc ti nguyn mng t hiu qu cao. Mt s ng dng ang c trin khai l: MPLS VPN: Nh cung cp dch c c th to VPN lp 3 dc theo mng ng trc cho nhiu khch hng, ch dng mt c s h tng cng cng sn c, khng cn cc ng dng encrytion hoc end-user. MPLS Traggic Engineer: Cung cp kh nng thit lp mt hoc nhiu ng i iu khin lu lng mng v cc c trng thc thi cho mt loi lu lng. MPLS QoS (Quality of service): Dng QoS cc nh cung cp dch v c th cung cp nhiu loi dch v vi s m bo ti a v QoS cho khch hng. im vt tri ca MPLS so vi cc m hnh IP over ATM - Khi hp nht vi chuyn mch ATM, chuyn mch nhn tn dng nhng thun li ca cc t bo ATM - chiu di thch hp v chuyn vi tc cao. Trong mng a dch v chuyn mch nhn cho php chuyn mch BPX/MGX nhm cung cp dch v ATM, Frame Replay v IP Internet trn mt mt phng n trong mt ng i tc cao. Cc mt phng (Platform) cng cng h tr cc dch v ny tit kim chi ph v n gin ha hot ng cho nh cung cp a dch v. ISP s dng chuyn mch ATM trong mng li, chuyn mch nhn gip cc cc dng Cisco, BPX8600, MGX8800, Router chuyn mch a dch v 8540 v cc chuyn mch Cisco ATM gip qun l mng hiu qu hn xp chng (overlay) lp IP trn mng ATM. Chuyn mch nhn trnh nhng rc ri gy ra do c nhiu router ngang hng v h tr cu trc phn cp (hierarchical structure) trong mt mng ca ISP.

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QoS trong MPLS

S tch hp: MPLS xc nhp tnh nng ca IP v ATM ch khng xp chng lp IP trn ATM. MPLS gip cho c s h tng ATM thy c nh tuyn IP v loi b cc yu cu nh x gia cc c tnh IP v ATM. MPLS khng cn a ch ATM v k thut nh tuyn. tin cy cao hn: Vi tc chuyn mch, MPLS c kh nng cung cp cho mng s an ton v nhanh chng, m bo d liu khng b tht thot nhiu, ngoi ra cn c cc c ch v cc mode trong k thut MPLS gip bo mt cho thng tin khch hng. Trc tip thc thi cc loi dch v: MPLS s dng hng i v b m ca ATM cung cp nhiu loi dch v khc nhau. N h tr quyn u tin IP v loi dch v (class of servicecos) trn chuyn mch ATM m khng cn chuyn i phc tp sang cc lp ATM Forum Service. H tr hiu qu cho Mulicast v RSVP: Khc vi MPLS, xp lp IP trn ATM ny sinh nhiu bt li, c bit trong vic h tr cc dch v IP nh IP muticast v RSVP( Resource Reservation Protocol - RSVP). MPLS h tr cc dch v ny, k tha thi gian v cng vic theo cc chun v khuyn khch to nn nh x xp x ca cc c trng IP&ATM. Gim ti trn mng li: Cc dch v VPN hng dn cch MPLS h tr mi thng tin nh tuyn phn cp. Hn na,c th tch ri cc nh tuyn Internet khi li mng cung cp dch v. Ging nh d liu VPN, MPLS ch cho php truy sut bng nh tuyn Internet ti im ra vo ca mng. Vi MPLS, k thut lu lng truyn bin ca AS c gn nhn lin kt vi im tng ng. S tch ri ca nh tuyn ni khi nh tuyn Internet y cng gip hn ch li, n nh v tng tnh bo mt

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Kh nng iu khin lu lng: MPLS cung cp cc kh nng iu khin lu lng sng dng hiu qu ti nguyn mng. K thut lu lng gip chuyn ti t cc phn qu ti sang cc phn cn ri ca mng da vo im ch, loi lu lng, ti, thi gian, Cc hnh thc hot ng ca MPLS: Mng MPLS dng cc nhn chuyn tip cc gi. Khi mt gi i vo mng, Node MPLS li vo nh du mt gi n lp chuyn tip tng ng (FEC Forwarding Equivalence Class) c th. Trong mng MPLS nhn iu khin mi hot ng chuyn tip. iu ny c nhiu thun li hn s chuyn tip thng thng: 1. S chuyn tip MPLS c th thc hin bng cc b chuyn mch (switch), c th tra cu (lookup) thay th nhn m khng nh hng n header lp mng. Cc b chuyn mch ATM thc hic cc chc nng chuyn cc t bo da trn gi tr nhn. ATM-switch cn c iu khin bi mt thnh phn iu khin MPLS da vo IP (IP-base MPLS control element) nh b iu khin chuyn mch nhn (LSC - Label Switch Controller). 2. Khi mt gi vo mng n c chuyn n lp chuyn tip tng ng (FEC Forwarding Equivalence Class). Router c th s dng thng tin gi, nh cng vo (ingress) hay giao tip (interface). Cc gi i vo mng c gn cc nhn khc nhau. Quyt nh chuyn tip c thc hin d dng bi router ng vo. iu ny khng c trong s chuyn tip thng thng, v s xc nh l trnh ca cc router khc vi thng tin l trnh trn gi. 3. Mng c qun l lu lng buc gi i theo mt con ng c th, mt con ng cha c s dng. Con ng c chn trc hoc ngay khi gi i vo mng tt hn s la chn bi cc thut ton nh tuyn thng thng. Trong MPLS, mt nhn c th c dng i din cho tuyn, khng cn km trong gi. y l dng c bn ca MPLS Traffic Engineering.

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QoS trong MPLS

4. "Lp dch v (Class of service)" ca gi c xc nh bi nt MPLS vo (ingress MPLS node). Mt nt MPLS vo c th hu tuyn hay sa i lch trnh iu khin cc gi khc nhau. Cc trm sau c th nh li rng buc dch v bng cch thit lp PHB (per-hop behavior). MPLS cho php (khng yu cu) u tin mt phn hoc hon ton ca lp dch v t nhn. Trng hp ny nhn i din cho s kt hp ca mt FEC vi u tin hoc lp dch v. y l dng c bn ca MPLS QoS. 2.2 Cng ngh chuyn mch 2.2.1 Nhn MPLS Thay th c ch nh tuyn lp ba bng c ch chuyn mch lp hai. MPLS hot ng trong li ca mng IP. Cc Router trong li phi enable MPLS trn tng giao tip. Nhn c gn thm vo gi IP khi gi i vo mng MPLS. Nhn c tch ra khi gi ra khi mng MPLS. Nhn (Label) c chn vo gia header lp ba v header lp hai. S dng nhn trong qu trnh gi gi sau khi thit lp ng i. MPLS tp trung vo qu trnh hon i nhn (Label Swapping). Mt trong nhng th mnh ca khin trc MPLS l t nh ngha chng nhn (Label Stack). 1. Cng thc gn nhn gi tin l: Network Layer Packet + MPLS Label Stack 2. Khng gian nhn (Label Space): c hai loi. Mt l, cc giao tip dng chung gi tr nhn (per-platform label space). Hai l, mi giao tip mang gi tr nhn ring, (Perinterface Label Space). B nh tuyn chuyn nhn (LSR Label Switch Router): ra quyt nh chng k tip da trn ni dung ca nhn, cc LSP lm vic t v hot ng gn nh Switch. 3. Con ng chuyn nhn (LSP Label Switch Path): xc nh ng i ca gi tin MPLS. Gm hai loi: Hop by hop signal LSP - xc nh ng i kh thi nht theo kiu best effort v Explicit route signal LSP - xc nh ng i t nt gc.

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QoS trong MPLS

Nhn l gi tr c chiu di c nh dng nhn din mt FEC no . S kt hp gia FEC v nhn c gi l nh x nhn - FEC. MPLS c thit k s dng bt k mi trng v hnh thc ng gi lp 2 no, hu ht cc hnh thc ng gi lp 2 l da trn frame, v MPLS ch n gin thm vo nhn 32 bit gia mo u lp 2 v lp 3, gi l shim header. Phng thc ng gi ny gi l Frame-mode MPLS. ATM l mt trng hp c bit s dng cell c chiu di c nh. Do nhn khng th c thm vo trong mi cell. MPLS s dng cc gi tr VPI/VCI trong mo u ATM lm nhn. Phng thc ng gi ny c gi l Cell-mode MPLS. Nhn ca gi tin i ra l nhn ng ra, tng t cho nhn ca gi tin i vo l nhn ng vo. Mt gi tin c th c c nhn ng ra v ng vo, c th c nhn ng vo m khng c nhn ng ra hoc l ngc li. Thng thng, mt gi tin c th c nhiu nhn c gi l chng nhn (lable stack). Cc nhn trong chng nhn c t chc theo kiu chng nhn LIFO (last-in, first-out). Mt gi tin khng c gn nhn c xem l c chiu su chng nhn bng 0. Chiu su d ca chng nhn tng ng vi trnh t ca nhn trong chng nhn vi nhn 1 y chng nhn v nhn d nh ca chng nhn. (Trong khun kh lun vn ny ch trnh by ng gi MPLSPPP v LAN lp tuyn d liu). Nhn MPLS l mt s t ph, n da trn tng VPI/VCI ca mng ATM nhng cao cp hn, gm 32 bit.

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Hnh 2.1: Nhn MPLS + Label: Trng ny gm 20 bit, nh vy chng ta s c hn 1 t nhn khc nhau s dng, y chnh l phn quan trng nht trong nhn MPLS n dng chuyn tip gi tin trong mng. + Experimemtal (EXP): Trng ny gm 3 bit, n dng mapping vi trng ToS hoc DSCP trong gi tin ti thc hin QoS. + Stack (S): Ch c 1 bit, khi mt gi tin i qua mt tunnel, n s c nhiu hn 1 nhn gn vo, khi ta s mt stack nhn, bit S ny dung ch ra rng nhn ny c nm y Stack khng, nu y th S=1, ngc li S=0.

Hnh 2.2: Nhn ca stack + Time-to-live (TTL): Trng ny nh trng TTL trong IP header, khi chuyn tip gi tin nu nh router khng tm thy destination m vn c chy trong mng th s xy ra loop lm nghn mng (congestion). TTL dng khc phc iu ny, gi tr ban u

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ca n l 255, mi khi i qua mt router th gi tr ny s gim i 1, nu nh gi tr ny gim v 0 m gi tin vn cha ti ch th n s b rt (dropped). Khi gi tin n router bin th trng TTL trong IP header s gim i mt v copy qua trng TTL trong nhn MPLS, gi tr ny s gim dn khi i qua mng MPLS, khi ra khi mang MPLS th trng nay li c copy qua trng TTL trong IP header, nu gi tr l 0 th gi s b rt (drop). Cc gi tr qui c cho trng TTL: 0: Chnh n (Host gi tin n chnh n) 1: Trong cng mt subnet 32: Trong cng mt site (Mt mng) 64: Trong cng mt vng (C cng AS) 128: Trong cng mt mt lc a 255: Khng gii hn Cc cch ng gi tin:

Hnh 2.3: Nhn lp 2

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Nh vy: i vi mng IP cch ng gi tin s l Ethernet hay PPP v nhn l mt shim c chn vo nh trnh by trn. i mng Frame-Relay nhn s l gi tr DLCI, vi mng ATM th nhn s l VPI hoc VCI. Cc loi nhn c bit - Untagged: gi MPLS n c chuyn thnh mt gi IP v chuyn tip n ch. - Nhn Implicit-null hay POP: Nhn ny c gn khi nhn trn (top label) ca gi MPLS n b bc ra v gi MPLS hay IP c chuyn tip ti trm k xui dng. Gi tr ca nhn ny l 3 (trng nhn 20 bit). Nhn ny c dng trong mng MPLS cho nhng trm k cui. - Nhn Explicit-null: Ch mang gi tr EXP, gi tr nhn bng 0, c gn gi gi tr EXP cho nhn trn (top label) ca gi n. Nhn trn c hon i vi gi tr 0 v chuyn tip nh mt gi MPLS ti trm k xui dng. Nhn ny s dng khi thc hin QoS vi MPLS trong m hnh Pipe Mode. - Nhn Aggregate: vi nhn ny, khi gi MPLS n n b bc tt c nhn trong chng nhn ra tr thnh mt gi IP v thc hin tra cu trong FIB xc nh giao tip ng ra cho n. 2.2.2 Chuyn tip gi tin trong MPLS Thut ton chuyn tip nhn (Label Forwarding Algorithm) B chuyn nhn s dng mt thut ton chuyn tip da vo vic hon i nhn. Nt MPLS ly gi tr trong nhn ca gi va n lm ch mc n LFIB. Khi gi tr nhn tng ng c tm thy, MPLS s thay th nhn trong gi bng nhn ra (outgoing label) v gi gi qua giao tip ng ra tng ng n trm k c xc nh. Nu nt MPLS cha nhiu LFIB trn mi giao tip, n s dng giao tip vt l ni gi n chn mt LFIB c th phc v chuyn tip gi. Cc thut ton chuyn tip thng thng s dng nhiu thut ton nh unicast, multicast v cc gi unicast c thit lp bit ToS. Tuy nhin, MPLS ch dng mt thut ton chuyn tip da trn s hon i nhn (Label swapping). Mt nt MPLS truy xut b nh n ly ra cc thng tin nh quyt nh

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dnh ra ti nguyn cn thit chuyn tip gi. Kh nng chuyn tip v tra cu tc nhanh gip chuyn nhn (label switching) tr thnh cng ngh chuyn mch c tnh thc thi cao. MPLS cn c th dng chuyn vn cc giao thc lp ba khc nh IPv6, IPX, hoc Apple Talk. Cc thuc tnh ny gip MPLS c th tng thch tt vi vic chuyn i cc mng t IPv4 ln IPv6. Thc hin chuyn tip d liu vi MPLS gm cc bc sau:

Gn nhn MPLS (trn LSR). Giao thc phn phi nhn (LDP - label distribution protocol hay TDP - tag distribution protocol ) thc hin gn nhn v trao i nhn gia cc LSR trong min MPLS thit lp cc phin lm vic (session). Vic gn nhn c th gn cc b trn router hoc trn giao tip ca router.

Thit lp LSP gia LSR/E_LSR. Mc nh trn router s dng LDP.

Trong cc mng thun ty th vic chuyn tip gi tin c thc hin bng cch tra bng routing c trong mi router, cng vic ny thc hin layer 3, n tn kh nhiu thi gian cho cc router trong vic tra bng routing nu nh bng ny c kch thc ln (trong mng bnh thng bng ny c th c ti vi trm ngn router). Trong nguyn l nh tuyn c in, th tm ra next hop mi router phi thc hin vic tra bng routing nh sau:

Hnh 2.4: Chuyn tip IPSVTH: TRN VN TR 16 GVHD: ThS TRNG TN C ANH

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Nh trn hnh v ta thy: c c thng tin v mng 10.0.0.0/8 th cc router trong mng phi thng xuyn update cho nhau v tnh trng up hay down ca mng ny, vic update ny cn ty vo k thut p dng cho mng l Link-state hay Distance vector, nhng ni chung n chim mt lng bng thng khng mong mun trong mng, sau khi c bng routing th gi gi tin n ch cc router phi tra bng routing mi khi gi tin ti n chuyn tip n next hop. V vy trong MPLS s khng thc hin nh vy, vic chuyn tip nhn trong MPLS s thc hin layer 2, n khng phi tra bng routing nn s rt nhanh chng tm ra next hop tip theo.

Hnh 2.5: Chuyn tip MPLS Theo hnh v trn, th vic chuyn tip gi tin trong MPLS ch thc hin trn nhn, mi khi gi tin n router cc router s thc hin vic gn nhn (router bin), swap nhn (router core), v pop nhn (router bin), vic ny thc hin layer 2 rt nhanh chng (chng ta s tm hiu k hn cc phn sau). 2.2.3 Cc bng tra FIB v LFIB Bng tra FIB (Forwarding information based) s nh x t mt gi tin IP khng nhn thnh gi tin MPLS c nhn ng vo ca router bin hoc t gi tin IP khng nhn thnh gi tin IP khng nhn ng ra ca router bin, bng ny c hnh thnh t bng routing table, t giao thc phn phi nhn LDP v t bng tra LFIB.

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Hnh 2.6: Bng tra FIB v LFIB Bng tra LFIB (Label Forwarding Information Based) l bng cha ng thng tin cc nhn n cc mng ch, mt gi tin c nhn khi i vo mt router n s s dng bng tra LFIB tm ra hop k tip, ng ra ca gi tin ny c th l gi tin c nhn cng c th l gi tin khng nhn. Hai bng tra FIB v LFIB c gi tr nh bng routing table trong mng IP, nhng trong mng IP th bng routing table c s entry rt ln khong vi ngn, cn vi FIB v LFIB s nhn m n nm gia rt t khong vi chc l ti a. 2.3 CU TRC MPLS C hai c ch hot ng trong MPLS l: a. C ch Frame Mode C ch ny c s dng vi cc mng IP thng thng, trong c ch ny nhn ca MPLS l nhn thc s c thit k v gn cho cc gi tin, trong mt phng Control plane s m nhim vai tr gn nhn v phn phi nhn cho cc route gia cc router chy MPLS, v trong c ch ny cc router s kt ni trc tip vi nhau

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qua 1 giao din Frame mode nh l PPP, cc router s s dng a ch IP thun ty trao i thng tin cho nhau nh l: Thng tin v nhn v bng nh tuyn routing table. Cn vi mng ATM hay Frame-relay chng khng c cc kt ni trc tip gia cc interface, ngha l khng th dng a ch IP thun trao i thng tin cho nhau, v vy ta phi thit lp cc knh o gia chng (PVC - permanent virtual circuit) b. C ch cell mode. Thut ng ny dng khi c mt mng gm cc ATM LSR dng MPLS trong mt phng iu khin trao i thng tin VPI/VCI thay v dng bo hiu ATM. Trong kiu t bo, nhn l trng VPI/VCI ca t bo. Sau khi trao i nhn trong mt phng iu khin, mt phng chuyn tip, router ng vo (ingress router) phn tch gi thnh cc t bo ATM, dng gi tr VCI/CPI tng ng trao i trong mt phng iu khin v truyn t bo i. Cc ATM LSR pha trong hot ng nh chuyn mch ATM chng chuyn tip mt t bo da trn VPI/VCI vo v thng tin cng ra tng ng. Cui cng, router ng ra (egress router) sp xp li cc t bo thnh mt gi. Trong :

GFC (Generic Flow Control): iu khin lung chung VPI (Virtual Path Identifier): nhn dng ng o VCI (Virtual Channel Identifier): nhn dng knh o PT (Payload Type): Ch th kiu trng tin CLP (Cell Loss Priority): Chc nng ch th u tin hu b t bo HEC (Header error check): Kim tra li tiu .

MPLS chia thnh 2 mt phng 2.3.1 Control plane (trao i thng tin nh tuyn v label) Mt phng iu khin MPLS chu trch nhim to ra v lu tr LIB. Tt c cc nt MPLS phi chy mt giao thc nh tuyn IP trao i thng tin nh tuyn n cc nt

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MPLS khc trong mng. Cc nt MPLS enable ATM s dng mt b iu khin nhn (LSC Label Switch Controller) nh router 7200, 7500 hoc dng mt mun x l tuyn (RMP Route Processor Module). Cc giao thc nh tuyn Link-state nh OSPF v IS-IS l cc giao thc c chn v chng cung cp cho mi nt MPLS thng tin ca ton mng. Trong cc b nh tuyn thng thng, bn nh tuyn IP dng xy dng b lu tr chuyn mch nhanh (Fast switching cache) hoc FIB .Tuy nhin vi MPLS, bn nh tuyn IP cung cp thng tin ca mng ch v subnet prefix. Cc giao thc nh tuyn link-state gi thng tin nh tuyn (flood) gia mt tp cc router ni trc tip, thng tin lin kt nhn ch c phn phi gia cc router ni trc tip vi nhau bng cch dng giao thc phn phi (LDP Label Distribution Protocol) hoc TDP (Cisco proproetary Tag Distribution protocol). Cc nhn c trao i gia cc nt MPLS k cn xy dng nn LFIB. MPLS dng mt mu chuyn tip da trn s hon i nhn kt ni vi cc node iu khin khc nhau. Mi node iu khin chu trch nhim nh du v phn phi mt tp cc nhn cng nh lu tr cc thng tin iu khin c lin quan khc. Cc giao thc cng ni (IGP Interior Gateway Potocols) c dng xc nhn kh nng n c, s lin kt, v nh x gia FEC v a ch trm k (next-hop address). 2.3.2 Data plane (chuyn tip gi tin da trn label) Mt phng chuyn tip s dng mt c s thng tin chuyn tip nhn (LFIB - Label Forwarding Information Base) chuyn tip cc gi. Mi nt MPLS c hai bng lin quan n vic chuyn tip l: c s thng tin nhn (FIB - Forwarding Information Base) v LFIB. FIB cha tt c cc nhn c nt MPLS cc b nh du v nh x ca cc nhn ny n cc nhn c nhn t lng ging (MPLS neighbor) ca n. LFIB s dng mt tp con cc nhn cha trong FIB thc hin chuyn tip gi.

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Hnh 2.7: Data plane v Control Plane Cc thnh phn data plane v control plane ca MPLS: Cisco Express Forwarding (CEF) l nn tng cho MPLS v hot ng trn cc router ca Cisco. Do , CEF l iu kin tin quyt trong thc thi MPLS trn mi thit b ca Cisco ngoi tr cc ATM switch ch h tr chc nng ca mt phng chuyn tip d liu. CEF l mt c ch chuyn mch thuc s hu ca Cisco nhm lm tng tnh n gin v kh nng chuyn tip gi IP. CEF trnh vic vit li overhead ca cache trong mi trng li IP bng cch s dng mt c s thng tin chuyn tip (FIB Forwarding Information Base) quyt nh chuyn mch. N phn nh ton b ni dung ca bng nh tuyn IP (IP routing table), nh x 1-1 gia FIB v bng nh tuyn. Khi router s dng CEF, n duy tr ti thiu 1 FIB, cha mt nh x cc mng ch trong bng nh tuyn vi cc trm k tip (next-hop adjacencies) tng ng. FIB trong mt phng d liu, ni router thc hin c ch chuyn tip v x l cc gi tin. Trn router cn duy tr hai cu trc khc l c s thng tin nhn (LIB Label Information Base) v c s thng tin chuyn tip nhn (LFIB Label Forwarding Information Base). Giao thc phn phi s dng gia cc lng ging MPLS c nhim v to ra cc ch mc (entry) trong hai bng ny. LIB thuc mt phng iu khin v c giao thc phn phi nhn s dng khi a ch mng ch trong bng nh tuyn c nh x vi nhn nhn c t router xui dng. LFIB thuc mt phng d liu v cha nhn cc b (local label) n nhn trm k nh x vi giao tip ng ra (outgoing interface), c dng chuyn tip cc gi c gn nhn. Nh vy, thng tin v cc mng n c do cc

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giao thc nh tuyn cung cp dng xy dng bng nh tuyn (RIB - Routing Information Base). RIB cung cp thng tin cho FIB. LIB c to nn da vo giao thc phn phi nhn v t LIB kt hp vi FIB to ra LFIB. 2.4 PHN PHI NHN TRONG MPLS 2.4.1 TDP Trc y, trong qu trnh "thai nghn" ra MPLS, Cisco a ra cng ngh tag-switching v h tr t IOS 11.1CT. MPLS c h tr bi cc router cisco t IOS 12.1(3)T. Tag-switching chnh l tin thn ca mpls nn rt ging, ch c mt s khc bit nh: Giao thc s dng phn phi nhn ca tag-switching l TDP - s dng tcp/udp port 711, cn mpls l LDP s dng tcp/udp port 646. cho php chuyn mch nhn hot ng th IOS 11.1 l tag-switching ip, IOS 12.1 l mpls ip. C php lnh ty vo IOS. 2.4.2 LDP MPLS l th h sau ca tag-switching, n s dng giao thc LDP phn phi nhn, hot ng nh TDP ch khc l n s dng LDP phn phi nhn, LDP phi c cu hnh trn tng interface chy MPLS, cc lng ging ca chng s t ng nhn ra cc interface c chy LDP kt ni vi chng. S dng UDP broadcast v mulicast tm ra cc lng ging ca chng. kch hot LDP MPLS trn cc router ta dng cc lnh sau: P1#config t P1(config)#ip cef P1(config)#mpls ip P1(config-if)#interface serial 0/0 P1(config-if)#mpls ip Trong mt min MPLS, mt nhn gn ti mt a ch (FIB) ch c phn phi ti cc lng ging ngc dng sau khi thit lp session. Vic kt ni gia mng c th vi nhn cc b v mt nhn trm k (nhn t router xui dng) c lu tr trong LFIB v LIB.SVTH: TRN VN TR 22 GVHD: ThS TRNG TN C ANH

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2.4.3 S duy tr nhn MPLS C hai ch duy tr nhn: Ch duy tr nhn t do (liberal label retention mode): duy tr kt ni gia nhn v mng ch nhng khng lu gi trm k cho ch n . LSR c th chuyn tip gi ngay khi IGP hi t v s lng nhn lu gi rt ln cho tng ch n c th nn tn b nh. Ch duy tr nhn thng xuyn (conservative label retention mode): duy tr nhn da vo hi p LDP hay TDP ca trm k. N hy cc kt ni t LSR xui dng m khng phi trm k ca ch n ch nh nn gim thiu c b nh. 2.4.4 Routing vi nhn Gi s ta c mt mng n gin nh sau trong Router A l Ingress router (router bin ng vo), Router C l Egress router (router bin ng ra).

Hnh 2.8: Mng MPLS y s trnh by cch cc router xy dng bng FIB v LFIB cho Network X l mng m cn truyn d liu n.

Phng thc gn v phn tn nhn gm nhng bc nh sau: Step 1: Giao thc nh tuyn (OSPF hay IS IS ) xy dng bng routing table.

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Step 2: Cc LSR ln lt gn 1 nhn cho mt dest-IP trong bng routing Table

Step 3: LSR ln lt phn tn nhn cho tt c cc router LSR k cn. Step 4: Tt c cc LSR xy dng cc bng LIB, LFIB, FIB da trn label nhn c.

u tin cc router s dng cc gii thut nh tuyn nh OSPF hay IS IS tm ng i cho gi tin ging nh mng IP thng thng v xy dng nn bng routing- table cho mi router trong mng. Gi s, y router A mun n mng X th phi qua router B, B chnh l Next-hop ca router A n mng X.Routing table of A Network Next-hop X B Routing table of B Network Next-hop X C Routing table of C Network Next-hop X D

AFIB on A Network Next hop Label X B

B

C

D

E

Network X Routing table of E Network Next-hop X C

Sau khi bng routing table hnh thnh, cc router s gn nhn cho cc ch n m c trong bng routing table ca n, v d y router B s gn nhn bng 25 cho mng X, ngha l nhng nhn vo c gi tr 25 router B s chuyn n n mng X.Routing table of B Network Next-hop X C

Router B gn nhn 25 Router B gn nhn 25 cho X cho X C D

A

B

E

Network X

Router B phn tn nhn 25 cho tt c cc router LSR k cn n vi ngha Nu bn mun n X th hy gn nhn 25 ri gi n ti, cng lc bng tra LIB hnh thnh trong router B v c entry nh hnh sau.SVTH: TRN VN TR 24 GVHD: ThS TRNG TN C ANH

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Cc router LSR nhn c nhn c t router hng xm s cp nhp vo bng LIB, ring vi router bin (Edge LSRs) s cp nhp vo bng LIB v c FIB ca n.

Cng ging nh B, router C s gn nhn l 47 cho Network X v s qung b nhn ny cho cc router k cn, C khng qung b cho router D v D khng chy MPLS.

Cng lc router C hnh thnh 2 bng tra LIB v LFIB c cc entry nh trn. Sau khi nhn c qung b ca router C, router B s thm nhn 47 va nhn c vo trong bng

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tra FIB v LIB ng thi xy dng bng tra LFIB c cc entry nh hnh v, router E ch thm nhn 47 vo trong LIB v FIB.

Nh vy ta c c ng i t bin router A n mng cn n l mng X, hay ni cch khc mt LSP hnh thnh. By gi gi tin c th truyn theo ng ny ti ch nh sau: Mt gi tin IP t mng IP n router bin Ingress, router A s thc hin tra bng FIB ca n tm ra nexthop cho gi itn nay, y A s gn nhn 25 cho gi tin ny theo entry c trong bng FIB ca n v s gi ti next hop l router B n mng X.

Gi tin vi nhn 25 c truyn n cho router B, router B s tra bng LFIB ca n v tm ra gi tr nhn ng ra cho gi tin c nhn ng vo 25 l 47, router B s swap nhn thnh 47 v truyn cho next hop l router C.

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Gi tin vi nhn 47 c truyn n router C, router C s tra bng LFIB ca n v tm ra hot ng tip theo cho gi tin c nhn vo 47 l s pop nhn ra khi gi tin v truyn cho next hop l router D, nh vy gi tin n D l gi tin IP bnh thng khng nhn.

Gi tin IP ny n D, router D s tra bng routing table ca n v truyn cho mng X.

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CHNG 3: TNG QUAN QoS Trc y, khi m internet ch yu l truyn data th ngi ta khng cn quan tm n vic phn bit v u tin cho cc gi tin bi v lc ny bng thng mng v cc ti nguyn khc cung cp cho cc ng dng trong mng, v vy cc ISPs s cung cp cho khch hng ca h dch v best-effort (BE) khi tt c cc khch hng s c i s nh nhau h ch khc nhau loi kt ni. y l dch v ph bin trn mng Internet hay mng IP ni chung. Cc gi thng tin c truyn i theo nguyn tc n trc c phc v trc m khng quan tm n c tnh lu lng ca dch v l g. iu ny dn n rt kh h tr cc dch v i hi tr thp nh cc dch v thi gian thc hay video. Cho n thi im ny, a phn cc dch v c cung cp bi mng Internet vn s dng nguyn tc Best Effort ny. Nhng khi internet cng ngy cng pht trin v pht trin thm cc dch v HTTP, Voice, Video th iu ny s lm cho cht lng ca cc dch v ny gim i r rt v delay ln, jitter ln v khng bng thng truyn, phng n tng bng thng ca mng cng khng gii quyt c vn ny m li cn rt tn km QoS (Quanlity of Service) l mt khi nim dng cp n tt c cc kha cnh lin quan n hiu qu hot ng ca mng. QoS bao gm hai thnh phn chnh: + Tm ng qua mng nhm cung cp cho dch v c yu cu. + Duy tr hiu lc hot ng ca dch v. Hai m hnh cung cp cht lng dch v c s dng ph bin ngy nay l: + M hnh dch v tch hp IntServ (Intergrated Services). + M hnh dch v phn bit DiffServ (Differentiated Services). C nhiu nguyn nhn gii thch ti sao m hnh IntServ khng c s dng theo kp mc pht trin ca Internet. Thay vo , IntServ ch c s dng ph bin trong cc m hnh mng vi quy m nh v trung bnh. Trong khi , DiffServ li l m hnh cung cp cht lng dch v c kh nng m rng. C ch hot ng ca m hnh ny bao gm qu trnh phn loi lu lng v ti thnh phn bin mng, qu trnh xp hngSVTH: TRN VN TR 28 GVHD: ThS TRNG TN C ANH

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ti mi nt mng v x l hu gi trong li mng. Trong , phn ln cc qun l x l c thc hin ti thnh phn bin mng m khng cn phi lu gi trng thi ca cc lung lu lng trong li mng. Cc k thut QoS trong mng IP.

Hnh 3.1: Cc k thut QoS trong mng IP Nguyn nhn thnh cng ca giao thc IP chnh l s n gin ca n. Mi tnh nng phc tp c ci t ti u cui mng cn mng li th n gin. B nh tuyn trong mng s cn c vo a ch IP v cc nt trong mng tm nt mng k tip c nhn gi. - Nu hng i dnh cho nt mng k tip qu di, thi gian tr ca gi d liu s ln. Nu hng i y khng cn ch trng gi d liu s b hy. - Nh vy, mng IP ch cung cp m hnh dch v n lc ti a _best effort service_c ngha l mng s khai thc ht kh nng trong gii hn cho php, nhng khng m bo tr v mt mt d liu. V vy, khi c nhiu lung lu lng truyn i trong mng v vt qu kh nng ca mng, dch v khng b t chi nhng cht lng dch v gim: thi gianSVTH: TRN VN TR 29 GVHD: ThS TRNG TN C ANH

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tr tng, tc gim v mt d liu. Do , mng IP khng thch hp vi nhng ng dng yu cu thi gian thc. Ngoi ra, vi thng tin a im (multicast) ng thi phc v hng triu khch hng th hin nay mng IP khng thc hin c. Nu c th trin khai tt thng tin qung b c th tch hp pht thanh truyn hnh vo mng IP. - S ra i cc giao thc cht lng dch v QoS cung cp cho mng cc tnh nng gip mng c th phn bit c cc lu lng c i hi thi gian thc vi cc lu lng c tr, mt mt hay bin ng tr (jitter). Bng thng s c qun l v s dng hiu qu c th p ng nhng yu cu v cht lng ca cc lung lu lng. Mc tiu ca QoS l cung cp mt s mc d bo v iu khin lu lng. - Trong cc mng s liu, QoS c nh gi qua cc tham s chnh sau: sn sng ca dch v tr (delay). bin ng tr (jitter) Thng lng hay bng thng T l tn tht gi (packet loss rate): t l cc gi b mt, b hy, v b li khi i trong mng. Hin nay, c hai loi cht lng dch v c bn: Dnh trc ti nguyn (Resource Reservation) vi m hnh Tch hp dch v IntServ (Intergrated Service). Ty theo yu cu ca dch v v chnh sch qun l bng thng m mng s cung cp ti nguyn phc v cho tng ng dng. S u tin (Prioritization) vi m hnh cc dch v phn bit ( DiffServ-Differentiated Service). Lu lng vo mng c phn loi v c cung cp theo ch tiu ca chnh sch qun l bng thng. Cht lng dch v c p dng cho tng lung d liu ring bit hoc mt nhm lung. Lung c xc nh da vo 5 thng tin: giao thc lp vn chuyn. a ch IP ngun. a ch IP ch.30 GVHD: ThS TRNG TN C ANH

SVTH: TRN VN TR

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3.1 CU TRC QoS Khi ni n QoS ta s ngh ngay ti cc k thut hng i nh: Weighted Fair Queuing (WFQ), hay Custom Queuing (CQ), nhng tht ra n c nhiu hn th, ngoi hng i QoS cn c cc k thut khc gm: nn (compression), policing v shaping, loi gi (drop packet), v mt s khc. V sao chng ta li cn QoS? Nh trc y, khi m nhu cu s dng mng ca con ngi cha cao bi v s mi m, cha ph bin v cc ng dng cha nhiu th lu lng trn mng c th p ng cho hu ht cc ng dng lc by gi, nhng khi n tr nn ph bin s ngi dng nhiu v cc ng dng cng tng ln th ti nguyn bng thng mng tr nn thiu ht, iu ny s dn ti vic mt gi ng k khi truyn qua mng, khc phc iu ny th QoS ra i vi nhim v u tin cho cc ng dng thi gian thc bng cch cp pht thm bng thng v t chng mc u tin cao hn cc ng dng khc. Nu mt mng khng p dng QoS th s xy ra cc trng hp nh sau:

Hnh 3.2: D liu vi khng QoS QoS s nh hng ti cc thng s mng nh: Bandwidth (Bng thng), Delay (tr), Jitter (Bt n nh), Loss ( mt gi). Cc mng ngy nay u phi s dng QoS m bo cht lng dch v, tuy nhin vi mi ng dng th cn c cc mc QoS khc nhauSVTH: TRN VN TR 31 GVHD: ThS TRNG TN C ANH

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Hnh 3.3: Mc yu cu QoS cho cc loi d liu Cc thng s QoS + tr ton trnh Delay: tr qu mc t u cui n u cui khin cuc m thoi bt tin v mt t nhin. Mi thnh phn trong tuyn truyn dn: my pht, mng li, my thu u tham gia lm tng tr. ITU-TG.114 khuyn co tr ti a theo mt hng l 150 ms m bo thoi c cht lng cao. + tr pha Jitter: nh lng tr trn mng i vi tng gi khi n my thu. Cc gi c pht i mt cch u n t Gateway bn tri n c Gateway bn phi cc thi khong khng u. Jitter qu ln s lm cho cuc m thoi t qung v kh hiu. Jitter c tnh trn thi gian n ca cc gi k tip nhau. B m Jitter c dng gim tc ng tri st ca mng v to ra dng gi n u n hn my thu.

Cng thc tnh jitter:

Di = ( Ri Si ) - ( Ri-1 Si-1 ) Di = ( Ri Ri-1 ) ( Si Si-1 )

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Di

n

i

n + mt gi Packet Loss: c th xy ra theo cm hoc theo chu k do mng b nghn lin tc. Mt gi theo chu k n 5-10% s gi pht ra c th lm cht lng thoi xung cp ng k. Tng cm gi b mt khng thng xuyn cng khin m thoi gp kh khn. + Mt trnh t gi Sequence Error: nghn trn mng chuyn mch gi c th khin gi chn nhiu tuyn khc nhau i n ch. Gi c th n ch khng ng trnh t lm cho ting ni b t khong. Cc bc thc hin QoS:

Hnh 3.4: Cc bc thc hin QoS 3.1.1: Dch v tch hp IntServ ng trc nhu cu ngy cng tng trong vic cung cp dch v thi gian thc (thoi, video) v bng thng cao (a phng tin), dch v tch hp IntServ ra i. y l s pht trin ca mng IP nhm ng thi cung cp dch v truyn thng Best Effort v cc dch v thi gian thc. Sau y l nhng ng lc thc y s ra i ca m hnh ny:

+ Dch v c gng ti a khng cn p ng na, ngy cng c nhiu ng dng khc nhau, cc yu cu khc nhau v c tnh lu lng c trin khai, ng thi ngi s dng

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cng yu cu cht lng dch v ngy cng cao hn. Cc ng dng a phng tin ngy cng xut hin nhiu. + Mng IP phi c kh nng h tr khng ch n dch v m cn h tr a dch v ca nhiu loi lu lng khc nhau t thoi, s liu n video. Ti u ha hiu sut s dng mng v ti nguyn mng. + m bo hiu qu s dng v u t. Ti nguyn mng s c d tr cho lu lng c u tin cao hn, phn cn li s dnh cho s liu best effort. Cung cp dch v tt nht. + M hnh IntServ cho php nh cung cp mng tung ra nhng dch v tt nht, khc bit vi cc i th cnh tranh khc.

Hnh 3.5: M hnh mng IntServ - M hnh IntServ c IETF gii thiu vo gia thp nin 90 vi mc ch h tr cht lng dch v t u cui ti u cui. Cc ng dng nhn c bng thng ng yu cu v truyn i trong mng vi tr cho php.

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- Trn thc t giao thc RSVP l giao thc duy nht dng bo hiu cho m hnh IntServ. V th i khi ngi ta lm ln dng RSVP ni v IntServ.Tht ra, IntServ l kin trc h tr cht lng dch v mng, cn RSVP l giao thc bo hiu cho IntServ. - Ngoi giao thc bo hiu, m hnh tch hp dch v cn nh ngha thm mt s lp dch v. - Mt ng dng s xc nh c tnh ca lung lu lng m n a vo mng ng thi xc nh mt s yu cu v mc dch v mng. c tnh lu lng Tspec (Traffic Specification) v yu cu mc cht lng dch v Rspec (Required Specification). V th cc b nh tuyn phi c kh nng thc hin cc cng vic sau: Kim sot ( bng cc policing): kim tra TSpec ca lung lu lng; nu khng ph hp th loi b lung. iu khin chp nhn: kim tra xem ti nguyn mng c p ng c yu cu ca ng dng hay khng. Nu khng th p ng, mng s t chi. Phn lp (Classification): phn loi gi d liu cn c vo mc yu cu cht lng dch v ca gi. Hng i v lp lch (queuing and scheduling): a gi d liu vo hng i tng ng v quyt nh hy gi d liu no khi xy ra xung t. a. Cc lp dch v C hai loi dch v: m bo dch v (Guaranteed Service) v kim sot ti (Control load service). a.1 m bo dch v - Cho php gii hn thi gian chuyn tip cc gi d liu n ch trong mt khong thi gian nht nh, m bo s d liu khng b loi b khi hng i y. - Thng tin Tspec phi bao gm cc thng s nh: tc nh, kch thc ln nht ca gi d liu. Trong khi thng s quan trng nht ca Rspec l tc dch v. Thng s ny cho php xc nh bng thng m lu lng cn khi i trong mng. Thng s nySVTH: TRN VN TR 35 GVHD: ThS TRNG TN C ANH

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cng vi cc thng s trong Rspec cho php xc nh thi gian tr ln nht c th chp nhn c ca d liu. - Nhc im ca lp dch v ny l hiu qu s dng ti nguyn mng thp v n i hi mi lung lu lng c hng i ring. a.2 Kim sot ti - Cc ng dng ca dch v ny c th chp nhn kh nng mt d liu v thay i tr mt mc nht nh. Lung d liu khi i vo mng s c kim tra i chiu vi nhng c t lu lng Tspec c ng k. Nu khng ph hp vi cc c t c ng k trc th d liu s c chuyn tip theo phng thc n lc ti a. b. Giao thc dnh trc ti nguyn RSVP - RSVP l giao thc bo hiu cung cp th tc thit lp v iu khin qu trnh chim gi ti nguyn, hay ni cch khc RSVP cho php cc chng trnh ng dng thng bo cho mng nhng yu cu v mc cht lng dch v; v mng s hi p chp nhn hoc khng chp nhn yu cu . - Cc bn tin RSVP c cc b nh tuyn hay cc b chuyn mch trn lin kt gia hai u cui gi v nhn trao i vi nhau p ng yu cu v mc cht lng dch v ca ng dng. - RSVP c 2 bn tin c bn: bn tin Path (hay Request) v bn tin Resv. Bn tin Path (hay Request) mang thng tin v c t lung lu lng Tspec v cc thng tin nh: a ch IP ca nt gi, a ch IP nt nhn, ch s cng UDP. V khi nhn c bn tin Path (hay Request), nt mng ch s gi li bn tin Resv. Bn tin Resv s gi km theo phn m t yu cu RSpec ch nh kiu dch v tch hp l kim sot ti hay m bo dch v; ngoi ra cn c du hiu nhn dng lung (flow descriptor) m mi b nh tuyn dng nhn din mi phin chim gi ti nguyn. - Khi nhn c bn tin Resv, mi b nh tuyn trung gian s tin hnh qu trnh iu khin chp nhn (admission control). Nu yu cu khng c chp nhn, do khng ti nguyn mng th b nh tuyn s bo li v pha u thu. Nu yu cu c chp

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nhn th b nh tuyn s gi bn tin Resv n b nh tuyn gi bn tin Path (hay Request) cho n. - Ngoi ra, RSVP l giao thc mm, c ngha l cc bn tin Path (hay Request) v Resv s c gi li sau khong thi gian nht nh duy tr lu di s chim gi ti nguyn. Nu sau khong thi gian ny khng c bn tin no gi i, s d tr ti nguyn s b xa b. - Mt khc, lu lng RSVP c th i qua b nh tuyn khng h tr RSVP. Ti nhng b nh tuyn ny dch v c phc v theo m hnh n lc ti a. - Ni tm li, RSVP ng vai tr quan trng trong qu trnh trin khai vic chuyn ti nhiu dch v nh: m thanh, hnh nh v d liu trong cng mt h tng mng. Cc ng dng c th la chn nhiu mc cht lng dch v khc nhau cho lung lu lng ca mnh. c. Kin trc IntServ - Cu trc ca cc b nh tuyn v cc b chuyn mch c h tr RSVP trong mng

Hnh 3.6: M hnh dch v IntServ - Nh vy ta thy cu trc gm cc khi: Khi iu khin lu lng bao gm: b phn loi (Classifier), b lp lch gi (scheduler).

Khi iu khin thu nhn v thit lp d tr (set up).

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- u tin cc ng dng a ra yu cu lp dch v: m bo dch v hoc kim sot ti ng thi t ng dn v chim gi ti nguyn mng cho vic truyn d liu. Khi iu khin thu nhn s xem xt c th p ng c cc yu cu m dch v a ra hay khng. B phn loi tin hnh phn loi v a cc gi d liu nhn c vo hng i ring. B lp lch s lp cch x l p ng yu cu v cht lng dch v.

Hnh 3.7: Trao i thng tin vi IntServ

Hnh 3.8: Trao i thng tin vi IntServ Hnh v trn l cch thc hot ng ca RSVP, cc ng dng a ra yu cu mc cht lng dch v dnh cho lung lu lng xc nh qua giao din dch v ng dng. B iu khin thu nhn v thit lp d tr p ng yu cu ca cc ng dng bng cch to ra cc bn tin ca giao thc RSVP yu cu chim gi ti nguyn. Bn tin ny s i

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qua cc b nh tuyn nm trn ng dn t u gi n u thu. Ti mi b nh tuyn, khi iu khin thu nhn s tin hnh qu trnh iu khin chp nhn kt ni, quyt nh xem c th p ng c yu cu cht lng dch v m ng dng a ra hay khng. Nu c, b nh tuyn s da vo thng tin trong bn tin RSVP cu hnh cho b iu khin lu lng. - Chng ta xem xt kin trc ca m hnh tch hp dch v cng nh mt giao thc rt quan trng RSVP. M hnh ny cho php trin khai cc ng dng thi gian thc v lu lng truyn thng trn cng mt h tng mng. 3.1.2: Dch v phn bit DiffServ

Hnh 3.9: M hnh mng DiffServ - Cu trc ca m hnh DiffServ bao gm nhiu lp dch v v mi lp s c cung cp mt lng ti nguyn xc nh. - V d trong mng bao gm hai lp dch v: n lc ti a v u tin (premium). iu ny c ngha l nhng gi d liu thuc lp u tin s c cung cp cht lng dch v tt hn: d liu c m bo, t mt hn v c tr thp hn. - im khc nhau gia m hnh DiffServ v IntServ: IntServ dng giao thc bo hiu thng bo cho cc nt mng cht lng dch v m lung yu cu. Vi m hnh DiffServ,

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trn mi gi d liu s cha thng tin xc nh lp dch v. Thng tin ny c gi l im m dch v phn bit DSCP (Differentiated Service Code Point) ca tiu IP, tin thn l vng ToS (Type of Service). Nh vy trn l thuyt chng ta c tt c 64 lp dch v khc nhau nhng trong thc t s lng lp dch v t hn nhiu. - Cu hi t ra y l cc b nh tuyn s lm g khi nhn gi d liu vi gi tr DSCP no ? - Gi tr DSCP cho bit yu cu cht lng dch v m gi d liu yu cu mng cung cp hay ni cch khc DSCP xc nh mt hnh vi hop PHB (Perhop behavior). Ngoi nhng gi tr PHB chun, trong ni b mt mng c th nh ngha ring nhng gi tr PHB. Sau y l mt s gi tr PHB chun: Gi tr mc nh (Default): tng ng vi yu cu n lc ti a. Chuyn tip nhanh EF (Expedited Forwarding): gi d liu c gi tr ny s c thi gian tr nh nht v mt gi thp nht. Chuyn tip bo m AF (Assured Forwading): mi PHB mang mt gi tr AFxy. Gi tr x cho php xc nh hng i dnh cho gi, gi tr y xc nh mc u tin hay ni cch khc l kh nng mt gi khi xy ra hin tng nghn mch hoc tranh chp. Nh vy, nu cc gi c nh du AF11, AF12, AF13 th chng c xp chung vo mt hng i nhng mc u tin ca cc gi AF13 thp hn v xc sut mt cao hn. Ring cc gi AF2y c hng i khc gi AF1y. S lng AF PHB l 12, trong x c 4 gi tr v y c 3 gi tr. V iu quan trng cn phi nhc n l cc gi AFx1, AFx2, AFx3 s c a vo cng mt hng i khng b mt th t. -Mi thit b nh tuyn s lu gi mt bng nh x gi tr DSCP ca gi vi gi tr PHB, t xc nh phng thc x l gi.

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Hnh 3.10: M hnh DiffServ ti bin v mng li 3.1.3 S khc nhau gia IntServ v DiffServ Trong mt mng s dng QoS, chng ta c th khng cn dng n IntServ hay DiffServ m mng vn chy bnh thng, tuy nhin nu c ng dng DiffServ hay IntServ vo th s cho kt qua tt hn nhiu, v c th m bo cht lng dch v cao hn. DiffServ ra i khc phc cc khuyt im ca IntServ, gia chng c nhng s khc nhau: DiffServ IntServ

Khng dng bt k giao thc bo hiu no Dng giao thc bo hiu RSVP dnh dnh trc bng thng mng, do vy trc bng thng mng, do s tn ti tit kim c bng thng mng. nguyn mng v ch.

C th s dng cho mng ln v c mng Ch c th s dng cho mng c nh vi nh vi s lu lng rt ln t tn ti nguyn mng Xt u tin gi trn tng chn s lng lu lng nh Tn nhiu ti nguyn mng Khi to mt knh truyn trc khi truyn

Kh nng m rng mng cao v phc v Kh nng m rng mng thp v phc c a dch v t dch c. Hnh 3.11: S khc nhau gia DiffServ v IntServ

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3.2 PHN LOI V NH DU QoS l kh nng cung cp cc mc x l khc nhau hng n cc lp lu lng ring. Trc khi cc ng dng hay cc k thut QoS c p dng, lu lng phi c nhn bit v sp xp vo trong cc lp khc nhau. Thit b mng s dng s phn loi nhn bit lu lng theo cc lp ring bit. Sau khi lu lng mng c sp xp, vic nh du c thc hin bng cch gn th cho cc gi ring bit cc thit b mng khc c th thc hin cc chc nng QoS cho cc gi khi chng di chuyn thng qua mng. 1. Phn loi: - Phn loi c thc hin nhn dng lu lng v phn chia lu lng thnh cc lp khc nhau. phn loi gi, ta dng b m t lu lng phn chia cc gi trong phm vi cc nhm ring bit nh ngha cc gi . Mt s b m t c trng dng phn loi gi bao gm: b giao tip ng vo, u tin IP (IP Precedence), DSCP, a ch ngun hay a ch ch v cc ng dng. Sau khi gi c nh danh, chng c kh nng c tin hnh cc chc nng QoS trn mng. - Vi vic s dng phn loi gi, nh qun tr mng c th phn vng lu lng mng thnh nhiu mc u tin hay nhiu lp dch v. Khi b c t lu lng c s dng phn loi, lu lng ngun ng tham gia tho thun cc gii hn v mng s thc hin cc giiSVTH: TRN VN TR 42 GVHD: ThS TRNG TN C ANH

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hn vi vic m bo v cht lng dch v. Cc k thut cht lng dch v khc nh gim st lu lng, nn dng lu lng v k thut hng i s dng b m t lu lng m bo gi ng tho thun. Vic phn loi nn c t bin mng. 2. nh du: - Hot ng nh du cho php cc thit b mng phn loi gi hay khung (frame) da vo b m t lu lng c trng. Mt s b m t lu lng c s dng nh du gi nh: lp dch v (CoS), DSCP, u tin IP, nhm QoS, chuyn mch nhn a giao thc (MPLS). Vic nh du c s dng thit lp thng tin trong tiu gi lp 2 hay lp 3. - Vic nh du gi hay khung cng vi vic phn loi cho php thit b mng d dng phn bit cc gi hay khung c nh du. nh du l yu t hu dng v n cho php thit b mng d dng nhn dng cc gi hay khung theo cc lp c trng. Khi k thut QoS c th ng dng tng thch m bo s ng n vi cc chnh sch qun tr QoS. 3.2.1 Phn loi (classification) Phn loi l vic cc gi tin s c a vo nhng hng i khc nhau mi khi ti router, IOS ca router bng cch ny hay cch khc phi phn bit c cc gi tin khc nhau vi u tin khc nhau a vo cc hng i thch hp, n phi bit c gi tin no c RTP (Real time protocol) headers shape (nh hng) cho gi tin nhm cung cp bng thng cho lu lng l voice. IOS phi phn bit c u l VoIP v u l data, lm iu ny th n phi s dng Phn Loi (Classification). c th phn loi c gi tin, thng thng phi kim tra mt s trng trong headers, sau khi phn loi, mt QoS tool s a gi tin vo hng i thch hp, hu ht s phn loi nhm phn bit u l gi tin VoIP v u l gi tin khng phi VoIP.

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Hnh 3.12: S phn loi gi tin Trong hnh trn ta thy: Vic phn loi c thc hin tt c cc router trn links kt ni, router R3 sau khi phn loi s a vo hng i Queuing v sau l shaping (nh hng). Q1, Q2, Q3, Q4 ln lt l cc mc a tin, y ta thy voice c mc a tin cao nht. bng th 2 l shaping police ta s tm hiu phn sau. Ta c th dng mt s tools phn loi, v d nh dng ACLs: Vi ACL 101 cho php gi tin loi no s c xp vo hng i th 1, vi ACL 102 cho php goi tin loi khc s c xp vo hng i th 2, Sau khi c phn loi, cc gi tin s c nh du (marking), vic nh du s nh du vo mt trng trong IP header, sau khi gi tin c nh du, cc tools cn li trong QoS s s dng du tin hnh phn loi cc chng tip theo. Hai trng dng nh du l IP Precedence v Differentiated Service Code Point (DSCP), chng ta s tm hiu k chng trong Chng 4.

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Mt s Tools cho phn loi v nh du:

Hnh 3.12: Tool cho phn loi v nh du

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y ta dng ACLs phn loi gi tin, ta s phn d liu thnh 3 loi l:Voice (ACL 101), HTTP (ACL 102), FTP (ACL 104), SMTP (ACL 105), v Besteffort (ACL 103). PE1(config)#access-list 101 permit udp any any range 16384 32768 ///ACL cho Voice PE1(config)#access-list 102 permit tcp any any eq www PE1(config)#access-list 103 permit ip any any PE1(config)#access-list 104 permit tcp any any eq ftp PE1(config)#access-list 105 permit tcp any any eq smtp 3.2.2 nh du (Marking) nh du l mt k thut dng to ra s phn bit gia cc gi tin ca cc loi d liu khc nhau trong khi thc hin QoS, vic nh du s thc hin trn cc mt s trng c trong gi tin nh IP precedent, DSCP, EXP, QoS group, QoS discard. Vic nh du thng c thc hin sau khi gi tin c phn loi, Sau khi phn loi gi tin ta s nh du vo gi tin mt gi tr, c th l gi tr IP precedent, DSCP hay EXPCc gi tr c nh du s c dng phn loi gi tin chn tip theo v thc hin QoS. V d di y s nh du gi tin Voice vi gi tr EXP l 5, HTTP l 3, FTP v SMTP vi EXP l 2 v Best Effort l 0: PE1(config-pmap)#class Voice-dscp PE1(config-pmap-c)#set mpls experimental topmost 5 PE1(config-pmap-c)#exit **** PE1(config-pmap)#class HTTP-dscp PE1(config-pmap-c)#set mpls experimental topmost 3 PE1(config-pmap-c)#exit ****SVTH: TRN VN TR 46 GVHD: ThS TRNG TN C ANH

///ACL cho HTTP (www) ///ACL cho Best-effort ///ACL cho ftp ///ACL cho smtp

Lun vn tt nghip PE1(config-pmap)#class smtp-dscp PE1(config-pmap-c)#set mpls experimental topmost 2 PE1(config-pmap-c)#exit **** PE1(config-pmap)#class ftp-dscp PE1(config-pmap-c)#set mpls experimental topmost 2 PE1(config-pmap-c)#exit **** PE1(config-pmap)#class best-effort-dscp PE1(config-pmap-c)#set mpls experimental topmost 0 PE1(config-pmap-c)#exit

QoS trong MPLS

Vic nh du thng xy ra ti ng vo ca interface, ti y gi tin s c thu nhn v thc hin nh du li (remark) nu cn thit, du va nh s tn ti trong cc hng i ng ra ca router ny v trn ng truyn ti ch tip theo. Thc cht ca vic nh du l ta s set cc gi tr trong gi tin ln cc gi tr thch hp m ta cho l hp l.

Mt s trng dng cho nh du:SVTH: TRN VN TR 47 GVHD: ThS TRNG TN C ANH

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Hnh 3.13: Trng nh du 3.3 CC K THUT HNG I (CLASSIFICATION & QUEUING) V tc s l cc gi tin ca router l chm hn nhiu so vi s lng gi tin n v cn truyn i, v vy cc gi tin cn phi xp hng v i trong mt hng di nu nh khng mun b drop, do k thut hng i cn c p dng cho cc router. Thng th hng i ch xy ra ng ra ca router khi ta gi l hng i ng ra (output queuing), nhng i khi hng i cng xy ra ng vo ta gi l hng i ng vo (input queuing).

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Hnh 3.14: Hng i trong router Hnh trn l mt v d v hng i, ng vo vi 4 gi tin kch thc 1500 byte mi gi, y ta c hai hng i :hng th 1 ang c 3 gi tin ang ch v bng thng ca hng ny l 25% tng bng thng, hng th 2 ch c 1 gi tin ang ch vi bng thng l 75%, nh vy gi tin no s c gi trc? Tht ra gi tin no c gi trc l ty thuc vo mc u tin ca hng i v hng i nh th no so vi cc hng i khc.

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Hnh 3.15: Cc k thut hng i v so snh gia chng

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3.3.1 First In-First Out Queuing - Hng i FIFO khng c s phn loi v tt c cc gi u thuc v cng mt lp. Mt b nh tuyn hay b chuyn mch cn cc hng i xut gi cc gi trong khi ch b giao tip sn sng gi gi. Trong khi cc cng c hng i khc th hin cc tnh nng khc, nh sp xp trt t cc gi, hng i FIFO ch cung cp mt ngha gi cc gi trong khi chng ch ri khi mt cng giao tip (interface). Hng i FIFO s dng mt hng i n cho b giao tip. V ch c mt hng i nn khng cn phn lp quyt nh khi gi i vo. V cng khng cn lp lch ban u cho hng i ly gi tip theo. Ch quan tm n cch cu hnh chiu di hng i FIFO trnh tc ng n tr v mt gi. - Hng i FIFO s dng k thut hy gi cui hng i quyt nh khi no b gi hay cho gi vo hng i. Nu cu hnh mt hng i di hn, nhiu gi c th t trong hng i, ngha l hng i t kh nng y. Nu khng gian hng i cn trng nhiu th gi t b mt. Tuy vy, vi mt hng i di, tr v bin ng tr ca gi tng. Vi hng i ngn, tr hon t xut hin hn, nhng hng i FIFO n s y nhanh chng, lc ny cc gi mi s b hy b.

Hnh 3.16: Hng i FIFO Lp lch hng i FIFO: - Sau khi gi i vo hng i th b nh tuyn s s dng thut ton lp lch duy tr cng vic. Lp lch FIFO l thut ton lp lch truyn thng c s dng trong Internet, y lSVTH: TRN VN TR 51 GVHD: ThS TRNG TN C ANH

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thut ton lp lch n gin nht. Trong thut ton ny b lp lch truyn cc gi theo th t n v hy cc gi khi hng i y. Tuy nhin, b lp lch gi khng c s

phn bit gia cc ngi s dng. V vy n khng th phn phi cho mt s user tr trung bnh thp hn cc ngi dng khc. Mi ngi dng trong cng lp dch v chu cng mt tr bin thin (jitter delay). Ngoi ra, bin ng tr c xu hng tng ln khi s chng tng ln v tr hng i ca gi cc chng khc nhau khng tng quan vi nhau. - Vi FIFO, tr trung bnh ca mt ngi s dng c th tng ln nu tng tc n ca tt c ngi s dng tng ln. - Tuy nhin vic s dng k thut hng i FIFO c cc nhc im: FIFO khng hon ton tin cy khi mt lung khng mong mun tranh ginh vi cc lung c u tin thp. Cc lung khng mong mun gi mt s lng ln cc gi (a s cc gi b hu b). Trong khi , cc lung vi u tin thp gi mt s lng gi xc nh v hu ht chng b hy bi v hng i lc no cng y do cc lung khng mong mun chim ht khng gian hng i. S bng n cao hay thp gy ra tnh trng y hng i FIFO. Cc gi i vo mt hng i y phi ch mt thi gian di trc khi chng c truyn. Nhng thi im khc, hng i c th trng v cc gi trong cng mt lung khng b tr hon. - Cc u im ca k thut hng i FIFO y l k thut n gin v nhanh. N c h tr trn tt c cc nn tng. Hng i FIFO c h tr trong tt c cc phin bn ca Cisco IOS. cu hnh cho hng i FIFO ta phi unable tt c cc k thut hng i khc c trong interface . Mc nh th WFQ (Weighted Fair Queuing) s c p dng cho cc interface v n chy tc E1 (khong 2M). - disable WFQ ta dng cu lnh no fair-queue, Khi disable tt c cc k thut hng i c trong interface th FIFO s mc nhin c s dng.

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- chn chiu di cho hng i ta dng cu lnh hold-queue x out.

V d: R3(config)#int s 0/0 R3(config-if)#no fair-queue R3(config-if)#^Z R3#sh int s 0/0 Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial Description: connected to FRS port S0. Single PVC to R1. MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 // disable WFQ ;

Encapsulation FRAME-RELAY, loopback not set Keepalive set (10 sec)

LMI enq sent 80, LMI stat recvd 73, LMI upd recvd 0, DTE LMI up LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0 LMI DLCI 1023 LMI type is CISCO frame relay DTE Broadcast queue 0/64, broadcasts sent/dropped 171/2, interface broadcasts 155 Last input 00:00:02, output 00:00:03, output hang never Last clearing of "show interface" counters 00:13:48 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue :0/40 (size/max) //hng i FIFO c dng //Kch c hng i ng ra l 40 gi tin.

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Lun vn tt nghip 30 second input rate 0 bits/sec, 0 packets/sec 30 second output rate 0 bits/sec, 0 packets/sec 235 packets input, 14654 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 2 input errors, 0 CRC, 2 frame, 0 overrun, 0 ignored, 0 abort 264 packets output, 15881 bytes, 0 underruns 0 output errors, 0 collisions, 6 interface resets 0 output buffer failures, 0 output buffers swapped out 10 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up

QoS trong MPLS

+Thay i chiu di hng i ng ra thnh 50 gi tin: R3(config)#int s 0/0 R3(config-if)#hold-queue 50 out R3(config-if)#^Z ! R3#sh int s 0/0 Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial ! Lines omitted for brevity Queueing strategy: fifo Output queue :0/50 (size/max) //chiu di hng i l 50 : ! Line omitted for brevity

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3.3.2 Priority Queuing

Hnh 3.17: Cch ly gi tin ca hng i PQ - Tnh nng c bit ca PQ l b lp lch. PQ lp lch lu lng m bo hng i u tin lun c phc v trc. Vi 4 mc u tin: cao, trung bnh, bnh thng, v thp. Nu hng i u tin cao lun c mt gi ang ch, b lp lch lun lun ly cc gi trong hng i u tin cao. Nu hng i u tin cao khng c gi no ang ch nhng c trong hng i u tin trung bnh, mt gi trong hng i ny s c ly v tin trnh c nh th tip tc. - B lp lch PQ c mt s thun li v hn ch. Cc gi trong hng i u tin cao c th t 100% bng thng lin kt, vi tr hon nh v bin ng tr nh. Tht ra, khi nghn

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mch, cc gi trong hng i u tin thp tn nhiu thi gian phc v. Khi lin kt tc nghn, cc ng dng ngi dng c th ngng lm vic nu cc gi t trong hng i u tin thp. - PQ phn lp cc gi da trn ni dung ca cc tiu . N s dng ti a 4 hng i. Ch p dng chnh sch hy gi cui hng i (tail drop), mt khc sau khi phn lp cc gi, nu

hng i tng ng y, cc gi b b. Mt khc, chiu di mi hng i l nguyn nhn nh hng n tr v mt gi. Tht ra, PQ c th thit lp chiu di hng i tr v gi tr 0, c ngha l chiu di hng i khng gii hn. (khng gii hn c ngh l khi b nh tuyn ra ngoi vng nh, cc gi khng th lp lch, tuy nhin chng ta gp vn rc ri hn vic lp lch cho gi nu b nh tuyn ngoi vng nh.)

Hnh 3.18: Tin trnh gi gi tin ca PQ 1. PQ c th phn lp cc gi s dng danh sch iu khin truy cp ACL vi giao thc lp 3. PQ cng c th so trng trc tip khng cn s dng ACL, u vo, chiu di gi v cng TCP v UDP. 2. Hy b gi cui hng i l chnh sch b gi mc nh. 3. S hng i cc i l 4. 4. Chiu di hng i cc i c th l 0, ngha l hng i c chiu di khng xc nh theo l thuyt. Mc nh l 20, 40, 60 v 80 tng ng vi cc hng i u tin cao,trung bnh, bnh thng v thp.SVTH: TRN VN TR 56 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip 5. Bn trong mt hng i, PQ s dng hng i FIFO.

QoS trong MPLS

6. Khi lp lch cc hng i, PQ lun phc v cc hng i u tin cao trc.

- Khi ng xut khng tc nghn (ni mt cch khc TX khng y), cc gi mi t vo TX mt cch trc tip. Khi TX y, PQ th hin vic lp lch. Khi tt c cc hng i PQ truyn ht cc gi (TX khng y), tc nghn du i. Cc gi mi n li vo TX, cho n khi n y tr li, n s khi ng tin trnh hng i vi PQ. - PQ lm vic tt trong cc chnh sch QoS cn x l mt loi lu lng vi kh nng phc v tt nht. Tuy nhin, dch v PQ vi cc hng i thp gim nhanh chng, lm cho PQ khng thit thc cho hu ht cc ng dng hin nay. Chng hn, vic chy mt kt ni FTP, mt trnh duyt web, mt cuc gi NetMeeting, v 2 cuc gi VoIP khi xut, cc kt ni TCP vi lu lng HTTP v FTP thng xuyn vt qu thi gian cho php. Bng tm tc tnh nng PQ:

3.3.3 Custom Queuing Custom Queuing (CQ) l k thut hng i ra i sau PQ, khng ging nh PQ, CQ s phc v cho tt c cc hng i c trong interface ca n thm ch khi sy ra nghn mng. CQ c tt c 16 hng i, nh vy n cho php ti a 16 lp dch v (va cho cc loiSVTH: TRN VN TR 57 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip

QoS trong MPLS

dch v ngy nay). CQ cn khng cung cp cho mt hng i c bit no c mc u tin cao hn cc hng i khc v cng khng u tin hng i no c low delay, low jitter, low loss

CQ cung cp mt lng bng thng ngang nhau cho tt c cc hng i, vic lp lch ca CQ nh sau:

Hnh 3.19: Cch ly gi tin ca CQ CQ s kim tra ln lt cc hng i, bt u t hng i th 1, CQ s ly gi tin t hng i ny cho ti khi s gi tin m n ly vt qu hoc bng gi tr cho php, sau khi hng i ny c phc v vi s gi tin nhu trn hoc hng i ny khng c gi tin th CQ s chuyn qua phc v cho hng i k tip v qu trnh lp li nh trn. CQ khng cho php cu hnh bng thng cho tng hng i m ch cho php cu hnh s gi tin s ly th hng i . V d: ta thit k s ly 10000 bytes cho mi hng i v ta c 5 hng i tt c, nh vy mi hng i s chim dng bng thng l 20% (10000/50000). By gi nu ta thit k c 5 hng i: hai hng u tin s c phc v vi s bytes l 5000, hai hng tip theo l 10000, v hng th 5 l 20000, nh vy hng th nht v th hng mi hng s nhn bng thng l 10% (5000/50000), hai hng tip theo mi hng nhn l 20% (10000/50000) v th 5 l 40% trn tng bng thng ca link. Khi thc hin gi gi tin, gi s trong hng i th 4 khng c gi tin no ang ch, ch c hng i 1,2,3 v 5 l c gi tin ang ch, khi bng thng s c phn pht li nh sau: hng i th nht nhn 12.5%, th 2 12.5%, th 3 25%, th 4 0% v th 5 l 50%.SVTH: TRN VN TR 58 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip

QoS trong MPLS

Ta tnh nh sau: Hng i th 1 : 5000*100 =12.5% 40000 5000*100 =12.5% 40000 1000*100 =25% 40000 2000*100 =50% 40000

Hng i th 2:

Hng i th 3:

Hng i th 4:

Qu trnh gi gi tin ca CQ:

Hnh 3.20: Qu trnh gi gi tin ca CQ 1.CQ phn loi gi tin bng cc ACLs hoc bng cc k thut khc. 2.Tail drop l k thut CQ dng chng nghn. 3.Ti a l 16 hng i. 4.Ta c th set kch c ca hng i v ti 0 (ngha l chiu di l v hn).SVTH: TRN VN TR 59 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip 5.Bn trong mt hnh i CQ s dng FIFO.

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6.Khi lp lch cho gi tin, CQ s xoay vng cho cc hng i (phc v cho hng ny xong th ti hng hng khc). c im ca CQ : + Khng thch hp cho cc mng cn low delay, low jitter,... + Khng th dnh trc bng thng cho link. + Khng cung cp hng i u tin. + Khng thch hp cho Voice + Cho php cc hng i c phc v xoay vng. +Cho php cc hng i bnh ng nhau.

Hnh 3.21: Bng tm tt CQ 3.3.4 Weighted Fair Queuing WFQ l k thut hng i mc nh trong router Cisco, n khc vi cc hng i PQ v FIFO cc im sau:

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+ N khng cho php cu hnh phn loi, WFQ phn loi gi tin theo flow, mt flow bao gm nhiu gi tin c cng ch n v cng ngun, cng port ch v port ngun. S

khng c cu hnh no r rang cho n. + Tnh nng lp lch: WFQ da vo flow, do vy nhng flow no c u tin cao hn th s c pht trc. + Mi flow l mt hng i, v vy s hng i trong WFQ c th ln ti 4096 hng i ln hn rt nhiu so vi PQ hay FIFO. Vi WFQ ta c ti a l 4096 hng i trong 1 interface ca router, s hng i ny cng chnh l s flow chy vo router. V d: ta c 5 flow l Voice, 2 kt ni HTTP, 2 kt ni FTP th khi ta s c 5 hng i trong router, nh vy s hng i thay i theo s flow, chng khng c nh nh trong cc k thut khc

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Hnh 3.22: Cch ly gi tin ca WFQ

Hot ng ca WFQ nh sau:

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Hnh 3.23: Tin trnh gi gi tin ca WFQ +Khi gi tin vo interface, n s c phn loi thnh cc flow theo 5 thng s: - IP source - IP destination - port source - port destination - Giao thc lp 4 n s dng l g (TCP hay UDP) WFQ da vo cc trng nh DSCP, ToS phn loi gi tin v a n vo cc hng i khc nhau. Nhng gi tin c IP precedent hay DSCP cao hn s c mc u tin cao hn. Hai vn quan trng trong WFQ l : a. i x cng bng vi tt c cc flow ang tn ti : Gi s ta c bng thng l 128 kbps v c 10 hng i ang tn ti, mi hng i s nhn c bng thng l 12.8 kbps. Nu s hng i l 100 th mi hng i s nhn bng thng l 1.28 kbps. Mt vn tn ti y l s qu cng bng ca WFQ, gi b. s trong s 10 hng i trn hng i th 1 cn bng thng l 5 kbps v hng i th 2 cn bng thng l 30 kbps, nhng v WFQ ch cp bng thng cho mi hng i l 12.8 kbps, nh vy hng i th 1 d bng thng n s lun c phc v tt nht, ngha l low delay, low jitter, low loss v s gi tin trong hng i ca n

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Lun vn tt nghip ca n s rt ln. c.

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lc no cng rt t. Vi hng i th 2 thiu bng thng v vy delay, jitter v loss

Cung cp thm bng thng cho nhng flow c mc u tin cao hn (higher IP precedent hay higher DSCP) : Vn vi gi s trn 128 kbps cho 10 flow. By gi gi s c 5 flow vi IP precedent bng 0, v 5 flow vi IP precedent bng 1, 5 flow IP precedent 1 c mc u tin cao hn 5 flow IP precedent 0 theo t s bng thng phn phi l 2:1, flow IP precedent 1 s nhn bng thng l 17 kbps gp i flow IP precedent 0 l 8.5 kbps, cch tnh t s ny nh sau: BW cho IP precedent 1 1+1 2 = = BW cho IP precedent 0 0+1 1

+ Sau khi c phn loi gi tin s c tnh gi tr SN (Sequence number) nh sau: SN = SN (trc ) + Weight*length SN : Sequence number Weight : trng s ca gi tin , Weight=32384 / (IP_Precedence+1) Length : Chiu di gi tin Bng gi tr ca Weight:

Hnh 3.24: Bng gi tr Weight

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Lun vn tt nghip SN nh sau: SN = 0 + 1500*32384 = 48576000 -

QoS trong MPLS

V d: Vi gi tin c SN trc l 0, chiu di l 1500 byte v precedent l 0 ta s tnh

Sau quyt nh c drop gi tin hay khng da vo 2 thng s (cn gi l Tail drop):

-

Hold-queue: Nu gi tin l ny l gi m lm vt mc hold-queue (tng s gi tin trong tt c cc hng i) th n s b drop.

-

CDT: (Congestion discard threshold) l s gi tin ti a trong mt hng i, gi tr ny c th cu hnh cho php t 1 n 4096.

+ Tip theo cc gi tin nu khng b drop s a vo hng i v ch pht i + Khi nm trong hng i cc gi tin s c lp lch (scheduler logic), qu trnh lp lch da vo SN ca gi tin, precedent v volume (S gi tin ang c trong mt hng i). Nhng gi tin c SN cng nh, precedent cng ln, v volume cng nh s c chn forward trc. Th t u tin nh sau: u tin l SN, sau l precedent, v cui cng l volume.

Hnh 3.25: Tnh ton SN

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Lun vn tt nghip V d:

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Ta c 4 hng i l flow 1, flow 2, flow 3, flow 4, vi kch thc mi gi tin l 1500 byte, 1000 byte, 500 byte, 100 byte. Mi hng i c 4 gi tin vi precedent l 0, gi s SN trc ca cc gi tin l 0, nh vy ta tnh c cc gi tr SN nh hnh sau:

Hnh 3.26: Th t gi gi tin Khi th t forward gi tin l: 13, 5, 14, 15, 6, 1, 16, 7, 9, 2, 8, 3, 4, 11, 12. V d cu hnh cho WFQ:

Hnh 3.27: V d v mng c dng WFQ

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Lun vn tt nghip R3#conf t R3(config)#int s 0/0 R3(config-if)#fair-queue R3(config-if)#^Z R3#sh int s 0/0 Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial Description: connected to FRS port S0. Single PVC to R1. MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 9/255, rxload 8/255 Encapsulation FRAME-RELAY, loopback not set Keepalive set (10 sec)

QoS trong MPLS

LMI enq sent 171, LMI stat recvd 163, LMI upd recvd 0, DTE LMI up LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0 LMI DLCI 1023 LMI type is CISCO frame relay DTE Broadcast queue 0/64, broadcasts sent/dropped 378/2, interface broadcasts 347 Last input 00:00:01, output 00:00:00, output hang never Last clearing of "show interface" counters 00:28:46 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 8249 Queueing strategy: weighted fair Output queue: 126/1000/64/8249 (size/max total/threshold/drops) Conversations 6/7/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated)

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Lun vn tt nghip Available Bandwidth 1158 kilobits/sec 5 minute input rate 52000 bits/sec, 97 packets/sec 5 minute output rate 58000 bits/sec, 78 packets/sec 36509 packets input, 2347716 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 1 input errors, 0 CRC, 1 frame, 0 overrun, 0 ignored, 0 abort 28212 packets output, 2623792 bytes, 0 underruns 0 output errors, 0 collisions, 5 interface resets 0 output buffer failures, 0 output buffers swapped out 10 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up R3#show queueing fair Current fair queue configuration: Interface Discard Dynamic Reserved Link Priority

QoS trong MPLS

threshold queues queues Serial0/0 Serial0/1 64 64 256 256 0 0 8 8

queues queues 1 1

R3#show queueing fair int s 0/0 Current fair queue configuration: Interface Discard Dynamic Reserved Link Priority

threshold queues queues Serial0/0 64 256 0 8

queues queues 1

R3# show queue s 0/0

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Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 11027 Serial0/0 64 256

Queueing strategy: weighted fair Output queue: 79/1000/64/11027 (size/max total/threshold/drops) Conversations 4/8/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) Available Bandwidth 1158 kilobits/sec ! Next stanza lists info about one of the VoIP calls (depth/weight/total drops/no-buffer drops/interleaves) 37/5397/1359/0/0 Conversation 15, linktype: ip, length: 64 source: 192.168.3.254, destination: 192.168.2.251, id: 0x013B, ttl: 253, TOS: 184 prot: 17, source port 16772, destination port 19232 ! Next stanza lists info about one of the VoIP calls (depth/weight/total drops/no-buffer drops/interleaves) 37/5397/1359/0/0 Conversation 125, linktype: ip, length: 64 source: 192.168.3.254, destination: 192.168.2.251, id: 0x0134, ttl: 253, TOS: 184 prot: 17, source port 16638, destination port 19476 ! Next stanza lists info about one of the HTTP TCP connections (depth/weight/total drops/no-buffer drops/interleaves) 1/10794/36/0/0 Conversation 33, linktype: ip, length: 1404 5397 10794 source: 192.168.3.100, destination: 192.168.1.100, id: 0xFF50, ttl: 127,

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Lun vn tt nghip TOS: 72 prot: 6, source port 80, destination port 1067 ! Next stanza lists info about one of the HTTP TCP connections

QoS trong MPLS

(depth/weight/total drops/no-buffer drops/interleaves) 2/10794/34/0/0 Conversation 34, linktype: ip, length: 1404 source: 192.168.3.100, destination: 192.168.1.100, id: 0xFF53, ttl: 127, TOS: 88 prot: 6, source port 80, destination port 1068 ! Notice the TOS values versus the weight in the last two stanzas! R3#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R3(config)#int s 0/0 R3(config-if)#fair-queue 100 64 10 R3(config-if)#hold-queue 500 out R3(config-if)#^Z ! R3#show interface serial 0/0 Serial0/0 is up, line protocol is up Hardware is PowerQUICC Serial Description: connected to FRS port S0. Single PVC to R1. MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, reliability 255/255, txload 9/255, rxload 8/255 Encapsulation FRAME-RELAY, loopback not set Keepalive set (10 sec) LMI enq sent 198, LMI stat recvd 190, LMI upd recvd 0, DTE LMI up

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Lun vn tt nghip LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0 LMI DLCI 1023 LMI type is CISCO frame relay DTE

QoS trong MPLS

Broadcast queue 0/64, broadcasts sent/dropped 442/2, interface broadcasts 406 Last input 00:00:01, output 00:00:00, output hang never 10794 Last clearing of "show interface" counters 00:33:14 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12474 Queueing strategy: weighted fair Output queue: 95/500/100/12474 (size/max total/threshold/drops) Conversations 5/6/64 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) Available Bandwidth 1158 kilobits/sec ! lines omitted for brevity R3#show queueing fair Current fair queue configuration: Interface Discard Dynamic Reserved Link Priority

threshold queues queues Serial0/0 Serial0/1 100 64 64 256 10 0 8 8

queues queues 1 1

3.3.5 Class-Based Weighted Fair Queuing Class-Based Weighted Fair Queuing (CBWFQ) l k thut hng i ra i sau WFQ, n ging vi WFQ ch: Cho php s dng WFQ ngay bn trong mt hng i ca n, nhng khc vi WFQ ch: CBWFQ s dng Class phn loi cn WFQ s dng flow.

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Lun vn tt nghip CBWFQ c th cu hnh bng thng thc s cho mt hng i.

QoS trong MPLS

Hnh 3.28: Tin trnh gi gi tin ca CBWFQ T tri sang phi: 1.CBWFQ phn loi gi tin bng ACLs, MPLS EXP, Port. 2.Quyt nh drop gi tin bng cc k thut Tail drop hoc WRED 3.S hng i ti a l 64 v chiu di hng i ti a l 64, cc gi tr ny l mc nh ta c th set ty theo mun. 4.Bn trong mi hng i ta c th dng FIFO hoc WFQ. Ch : WRED l k thut hng i dng chng nghn, n tt cho mt s loi d liu nhng cng khng tt cho cc d liu nh Voice hay Video v cc d liu ny cn khng b rt trong mi trng hp. CBWFQ vt tri hn cc hng i WFQ ch: N phn loi gi tin theo Class ch khng theo flow, nh vy d dng cho ta thit k hn.

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Hnh 3.29: cc hng i ca CBWFQ Bng tm tt CBWFQ:

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Cu hnh CBWFQ:

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Kim tra li cu hnh:

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3.3.6 Low-latency Queuing Low latency Queueing (LLQ) l mt k thut hng i m n cho php gi tin c phc v vi cht lng cao nht (low delay, low jitter, low loss ).N n gin cu hnh v n gin hiu. LLQ khng phi l mt hng i tch bit vi cc k thut hng i khc, n c s dng bn trong mt k thut hng i no lm tng tnh u tin cho hng i ny, nhng hng i c dng LLQ th n c i x ging nh hng i PQ, nhng vi PQ th n khng m bo bng thng cho cc hng i khc cn vi LLQ th mc d vn c hng i u tin nhng n vn m bo bng thng cho cc hng i khng c LLQ.

Hnh 3.30: Tin trnh gi gi tin ca LLQ Hoc:SVTH: TRN VN TR 77 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip

QoS trong MPLS

Theo nh gin trn th LLQ s hot ng khng khc g so vi PQ bi v n lun phc v hng i c mc u tin cao hn, ch khi no hng i ny khng cn gi tin th

n mi chuyn sang hng i khng c u tin. khc phc iu ny LLQ s lm nh sau:

Hnh 3.31: Tin trnh gi gi tin ca LLQ ci thinSVTH: TRN VN TR 78 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip

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Nh vy mi khi hng i LLQ vt qu tc cho php hay bng thng cho php th cc gi tin trong hng i ny s b rt v chuyn qua phc v cho hng i khc. Nh vy hng i LLQ ch c th hot ng tc c thit lp t trc v khng th tranh chp vi cc hng i khc khi n cn thm bng thng, vy cc hng i khc c m bo v bng thng. Nh vy LLQ l hng i lun c phc v trc nhng n c cc chnh sch ngn chn vic tranh chp bng thng vi cc hng i khc khi xay ra vt qua tc cho php. Hng i LLQ c ngha rt ln trong cc d liu l Voice, Videov n cho php cc d liu ny nhn c s phc v tt nht c th: low delay, low jitter, low loss.. V d cu hnh LLQ: cu hnh mt hng i LLQ bn trong mt hng i no ta dng cu lnh sau: priority {bandwidth-kbps | percent percentage} [burst] V d: PE1(config-pmap)#class Voice-EXP

PE1(config-pmap-c)#priority 512 PE1(config-pmap-c)#exit

///Mc u tin cao nht

Vi cu hnh ny, mt hng i ca CBWFQ l Voice-EXP c cu hnh thm bn trong l hng i LLQ vi bng thng l 512 kbps. Khi hng i ny s c mc u tin cao nht trong tt c cc hng i. Bng tm tt cc k thut hng i:

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Bng trn cho ta tm tt v cc hng i v cc k thut drop mc nh ca chng, ct cui cng l s hng i ti a cho mi loi hng i.

Ct th 2 l cc k thut lp lch cho gi tin trong mi hng i. Cc trng dng phn loi ca cc k thut hng i:

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3.4 nh hng v chnh sch (Shaping and policing) nh hng v cc chnh sch l mt mt phn khng th thiu trong cc k thut QoS, cc chnh sch s gip cho cc gi tin c c cc mc u tin ph hp vi c im ca n v s drop gi tin khi tc vt qua mc so vi cu hnh, Chnh sch do k s thit k cho cc loi d liu khc nhau, n ty thuc vo cm tnh ca ngi k s v ph thuc vo tha thun gia nh cung cp dch v v khch hng. Trong khi nh hng s gip cho cc gi tin nhn c s phc v ng theo tc nh hnh n khng drop gi tin m ch lm cho gi tin chm li khng b vt qu tc cho php. C hai cng c shaping v policing u o tc truyn hoc nhn d liu. Policing c kh nng loi b nhng gi tin d tha m bo tc truyn khng vt qu tc tho thun.

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Lun vn tt nghip nh hnh.

QoS trong MPLS

Shaping sp xp cc gi d tha ny vo hng i, v ri i ra khi hng i tc

Trong c hai trng hp, c hai cng c u ngn lu lng khng c vt qu tc bit c nh ngha bi ngi qun tr. Mt l do c in la chn shaping l khi thit b u kia ca ng truyn ang thc hin policing. V d: gi s R1 thuc mt doanh nghip v R2 thuc ISP. R1 gi gi ti R2 v R2 thc hin policing, loi b nhng lu lng vt qu tc xbps. ISP c th la chn gim st ti R2 bo v mng trnh khi vic chp nhn qu nhiu lu lng. R1 c th c cu hnh shaping lu lng gi ti R2 sao cho lu lng ny tc bng vi tc pha gim st R2, thay v d liu tha b R2 loi b. Ni tm li, shaping v policing c th ng vai tr quan trng trong trng hp router c th gi nhiu lu lng hn s cho php ca hp ng lu lng. Shaping ch lm chm li tc truyn gi khng vt qu hp ng lu lng. Policing loi b nhng gi khng vt qu hp ng lu lng.

Hnh 3.32: So snh gi policing v shaping

Theo hnh nh trn ta thy vi policing th n ch ng x vi cc gi tin vt qua tc cho php bng cch drop chng tc vn m bo v vy ng ra c dng rng ca. Cn

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vi Shaping th n cho ng ra mt hn bi v n khng ng x vi cc g itn vt qu tc m n s lm cho cc gi tin chm li v m bo tc cho trc. V d cu hnh policing v shaping: + Cu hnh theo policing: class-map match-all IP match ip precedence 3 class-map match-all VoIP match ip precedence 5 policy-map child class VoIP priority 128 class IP priority 1000 policy-map parent class class-default police 3300000 103000 103000 conform-action transmit exceed-action drop service-policy child + Cu hnh theo Shaping: policy-map parent class class-default shape average 3300000 103000 0 service-policy child.

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Lun vn tt nghip CHNG 4 : DIFFSERV QoS TRONG MPLS 4.1 TRNG DS

QoS trong MPLS

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4.1.1 Trng ToS

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QoS trong MPLS

Hnh 4.1: Trng ToS Trc khi c DiffServ th trng IP header trong gi tin IP c mt trng ToS, y l trng duy nht dng thc hin QoS, trng ToS gm 8 bit (1 byte) t bit 0 n bit 2 l IP precedent, 3 bit dng set u tin cho gi tin v ta thc hin QoS da trn 3 bit ny, 4 bit tip theo l trng ToS n cha mt s cc thng ip nh: Bit 3: 0 = Normal Delay, 1 = Low Delay.

Bits 4: 0 = Normal Throughput, 1 = High Throughput. Bits 5: 0 = Normal Relibility, 1 = High Relibility. Bit 6-7: Reserved for Future Use.

SVTH: TRN VN TR

87


Lun vn tt nghip

QoS trong MPLS

ngha ca cc bit precedent: 111 - Network Control 110 - Internetwork Control 101 - CRITIC/ECP 100 - Flash Override 011 - Flash 010 - Immediate 001 - Priority 000 Routine V trng precedent ch c 3 bit nh vy s to ra 8 t hp cho ta thc hin QoS, theo cc chuyn gia ca cisco nh vy l t cho cc mng ln, v vy DiffServ ra i vi trng DSCP di hn l 6 bit. 4.1.2 Trng DSCP Trng DSCP c to ra t trng IP precedent bng cch ly thm 3 bit trong trng ToS lm thnh 6 bit thc hin QoS, vi 6 bit ny ta c th to ra t hp 64 gi

SVTH: TRN VN TR

88


Lun vn tt nghip bit 6 v 7 tm thi khng s dng.

QoS trong MPLS

tr khc nhau trong QoS, nhiu hn rt nhiu so vi precedent. T bit 0 ti bit 5 l bit DSCP,

Hnh 4.2: Trng DSCP Nhng thc ra ngi ta khng dng ht 64 gi tr ny m ch dng 21 gi tr v c phn chia thnh 3 loi l: AF, CS v EF nh bng sau: (xem hnh trang sau)

SVTH: TRN VN TR

89


Lun vn tt nghip

QoS trong MPLS

Hnh 4.3: Bng gi tr DSCP

SVTH: TRN VN TR

90


Lun vn tt nghip 4.1.3 nh x t DSCP sang EXP C hai cch nh x t DSCP sang EXP: 1. nh x theo E_LSP :(EXP-infered-PSC-LSP)

QoS trong MPLS

Vic nh du s c thc hin trn trn trng EXP trong nhn gi tin, gi tr DSCP 6 bit s c nh x vo trng EXP 3 bit theo ch c 8 lp c th dng phn loi. V DSCP c 64 gi tr cn EXP ch c 8 gi tr nh vy s c nhiu gi tr trng nhau, Vic nh x ny thc ra c th do ngi k s thc hin, h c th ty thch chn cc gi tr gia hai trng DSCP v EXP nhng Cisco khuyn co s dng cc gi tr sau:

Hnh 4.4: nh x t DSCP sang EXP Hoc c th theo bng sau:

SVTH: TRN VN TR

91


Lun vn tt nghip

QoS trong MPLS

Vi vic nh x nh trn ta s c nhng kh khn nh sau khi thc hin QoS:

SVTH: TRN VN TR

92


Lun vn tt nghip

QoS trong MPLS

Hnh 4.5: Gi gi tin theo E_LSP

y ta thy khi A1 v A3 gi gi tin n ch A2 vi gi tr DSCP ln lt l AF 31 v AF 33, Khi n mng MPLS n s c nh du li vi troung2 EXP u l 3, nh vy c hai s c i x nh nhau khng ai u tin hn ai, y l im kh khn trong E_LSP v c nhng lc ta cn phi u tin cho mt gi trong hai gi ny vi mc u tin cao hn. trnh iu ny ta cn phi thc hin QoS cn thn trnh s trung lp khng cn thit, v d sau s trnh c iu ny ngay c khi d liu c gi t cng mt ch:

SVTH: TRN VN TR

93


Lun vn tt nghip

QoS trong MPLS

Hnh 4.6: Gi gi tin theo E_LSP y, hai loi d liu A v C t A1 gi ti A2, d liu A vi AF 31 d liu C vi EF, khi r rng C s c mc u tin cao hn A v s cho cht lng cao hn A.

2. nh x theo L_LSP: (Label-only-infered-PSC LSP) V vi cch nh x E_LSP ch c th thc hin QoS vi 8 lp trong khi DSCP cho php ti 64 t hp, v vy c mt cch nh x khc c th cho nhiu lp hn thc hin QoS l L_LSP. Vi L_LSP th nhn ca gi tin khng ch ng vai tr l gi tr chuyn mch m cn thc hin QoS, cn trng EXP c s dng cho cc chnh sch drop gi tin.SVTH: TRN VN TR 94 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip

QoS trong MPLS

Mi LSP ring bit c th c thit lp cho mi PHB. Vi nhng LSP nh vy, PSC (PHB Schedule) c bo hiu tng minh ti ln thit lp nhn, sau LSR c th suy ra t gi tr nhn PSC c p t cho gi tin. Trng EXP ch c s dng khi p t gi tr u tin nh rt cho gi tin. Phng php ny c gi l Label-only-infered-PSC LSP, hay cn gi l L _LSP v PSC c th c suy ra t gi tr nhn m khng cn bt k thng tin no khc (bt chp gi tr trng EXP ). 4.2 PHB (PER-HOP BEHAVIORS)

4.2.1 Default PHB Default PHB hay cn gi l Best-effort (BE) c gi tr DSCP l 000000, lp ny thng c s dng cho cc d liu m ta cha bit r v n, khi sau khi phn loi tt c d liu bit th cn cc d liu cn li s l BE. 4.2.2 Class-Selector PHB

SVTH: TRN VN TR

95


Lun vn tt nghip

QoS trong MPLS

S dng 8 bit DSCP, 3 bit cui lun l 0, ngha l cc gi tr nh phn ca CS s c dng xxx000, do c tt c 7 gi tr CS :CS1, CS2, CS3, CS4, CS5, CS6, CS7. S dng mc u tin cng ln cng tt (bigger is better)

4.2.3 Assured Forwarding PHB Assured Forwarding PHB c dng nh sau : Afxy, vi x l Class cn y l cp drop gi tin. Trong mt Class th gi tr y cng ln th s d b drop hn, ngha l : dP(AF13) >= dP (AF12) >= dP(AF11) dP :drop precedent

C th biu din cc gi tr AF nh sau: AFxyzab0, vi xyz c th l 001, 010, 011, 100 tng trng cho 4 Class v ab c th l 01, 10, 11 tng trng cho dP.

Hnh 4.7: Cc gi tr AF

4.2.4 Expedited Forwarding PHB Ch c mt gi tr DSCP duy nht EF s qui nh thi gian delay nh nht, jitter thp nht v cung cp cht lng dch v cao nht, bt k traffic no vt qu tc qui nh s b discard. Gi tr EF c khuyn co l 101110SVTH: TRN VN TR 96 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip

QoS trong MPLS

4.3 DIFFSERV TUNNELING MODES TRONG MPLS NETWORKS DiffServ Tunnueling modes cho php nh cung cp dch v qun l QoS hiu qu hn ni m cc router s chy MPLS trong mt mng MPLS. DiffServ Tunneling modes c cc mode sau: +Pipe mode +short pipe mode +Uniform mode Cc mode trn dng qun l cc router khch hng, router bin v router nh cung cp dch v. Cc tnh nng c cung cp bi MPLS DiffServ Tunneling modes : +To ra mt ng hm QoS xuyn qua nh cung cp dch v (Gi tin QoS s c trong sut t bin n bin). +Trng EXP c th c nh du thay cho cc trng IP precedent hay DSCP. +C th qun l router CE ca nh khch hng. MPLS DiffServ Tunneling modes c nhng li ch nh sau : +Cung cp thm cc tnh nng QoS bng cch to ra trng MPLS EXP thc hin QoS trong sut qu trnh gi tin c chuyn tip bng nhn. +Ta c th thit t PHB (Per hop behavior : ng x tip theo cho gi tin) cho gi tin theo mun.

+Pipe mode v short pipe mode cung cp s trong sut data i xuyn qua nh cung cp. +Cho php to mt Explicit NULL LSP trong Pipe mode, vi tnh nng ny th gi tin s c QoS bng EXP ngay ti router bin u vo. +Trong Pipe v short Pipe mode khch hng s c cc nh du gi tin ca ring mnh v ISP s gi nguyn cc nh du ny khi gi tin i qua mng.SVTH: TRN VN TR 97 GVHD: ThS TRNG TN C ANH

Lun vn tt nghip s nh du li gi tin khi n i qua mng ca ISP. Hn ch MPLS DiffServ Tunneling modes : +Khng cung cp L-LSP, cho php E-LSP.

QoS trong MPLS

+Trong Uniform mode khch hng s khng c nh du cho gi tin ca ring mnh, ISP

+V EXP ch c 3 bit nn s cung cp ti a l 8 class cho gi tin hay ni cch khc n cho php ti a l 8 PHB. 4.3.1 Pipe Model vi Explicit NULL LSP: Trong m hnh Pipe nh cung cp dch v cung cp cho khch hng VPN s cam kt v cht lng dch v i vi lu lng i gia router CE ny n router CE khc trong cng VPN. V cc node trung gian trong mng backbone (router P) hon ton b che du i. Cc gi tin i qua ng hm phi vn chuyn hai mng thng tin Diff-serv: + Thng tin Diff-serv c ngha vi cc node trung gian dc LSP. Thng tin ny cn c gi l thng tin Diff

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