quality of services chat luong dich vu mang ip

n tt nghip i hc

Tm hiu QoS trong mng IP v ng dng

MC LC 3.2.Loi b gi tin sm theo trng s WRED ..................................................625.5.4.Hng i WFQ..............................................................................105

DANH MC HNH V Hnh 1-1: Mt s cch tip cn nh gi QoS trong mng IP ..............................11 Hnh 1-2: Cc khi chc nng bo m QoS trn cc b nh tuyn mng ..............13 Hnh 2-1: M hnh Best - Effort ...............................................................................19 Hnh 2-2: Nguyn l hot ng ca m hnh tch hp dch v .................................21

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Hnh 2-3: Nguyn l hot ng ca giao thc dnh trc ti nguyn RSVP ............25 Hnh 2-4: Qu trnh x l d tr ti nguyn ca giao thc RSVP ............................26 Hnh 2-5: Nguyn l chuyn tip yu cu d tr ti nguyn ti cc nt ...................27 Hnh 2-6: nh dng thng ip RSVP ....................................................................29 Hnh 2-7: Khun dng i tng RSVP ...................................................................30 Hnh 2-8: Khun dng ca kiu i tng ...............................................................32 Hnh 2-9: Cu trc thng ip PATH .......................................................................33 Hnh 2-10: Cu trc thng ip RESV .....................................................................33 Hnh 2-11: Nguyn l hot ng ca m hnh phn bit dch v DiffServ ...............36 Hnh 2-12: Cc thnh phn chnh trong mt vng DS .............................................37 Hnh 2-13: Chc nng ca Router bin v router li theo m hnh DiffServ ............37 Hnh 2-14: Min DS v vng DS .............................................................................38 Hnh 2-15: K thut chuyn tip nhanh theo tng bc EF PHB ..........................40 Hnh 2-16: M hnh kt hp gia hai m hnh Interv v Differv ..............................42 Hnh 3-1: Trng CoS trong ISL Header .................................................................46 Hnh 3-2: Trng CoS trong 802.1Q Header ...........................................................46 Hnh 3-3: Header ca gi tin IPv4 v trng kiu dch v .......................................48 Hnh 3-4: im m phn bit dch v - DSCP .........................................................48 Hnh 3-5: Phn loi a trng MF .........................................................................49 Hnh 3-6: Phn loi kt hp hnh vi BA ................................................................51 Hnh 3-7: Hng i FIFO .........................................................................................53 Hnh 3-8: Hng i u tin PQ .................................................................................53 Hnh 3-9: Hng i cn bng FQ ..............................................................................54 Hnh 3-10: Hng i xoay vng trng s WRR ........................................................56 Hnh 3-11: V d v k thut phn lung lu lng ca WRR .................................57 Hnh 3-12: Hng i ty bin CQ .............................................................................61 Hnh 3-13: Hng i LLC ........................................................................................63 Hnh 3-14: Nguyn l hot ng ca hng i RED ................................................64 Hnh 3-15: Hin trng loi b gi tin ........................................................................65 Hnh 3-16: Cc thnh phn v nguyn l hot ng ca ECN ..................................68 Hnh 3-17: Trng ECN trong tiu gi tin IP ......................................................69 Hnh 3-18: Trng ECN trong tiu TCP ..............................................................70

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Hnh 3-19: ECN thc hin c ch bt tay TCP gia ngun v ch ..........................70 Hnh 3-20: ECN hot ng sau khi thc hin c ch bt tay TCP ............................70 Hnh 3-21: Cc module ca chnh sch lu lng ....................................................71 Hnh 3-22: Khong thi gian ca hai tham s CIR v CBS ......................................73 Hnh 3-23: Go token C v E trong k thut nh du 3 mu tc n srTCM ....73 Hnh 3-24: Nguyn l hot ng ch m mu ca srTCM ...............................74 Hnh 3-25: Nguyn l hot ng ch r mu ca srTCM .................................75 Hnh 3-26: Cc thnh phn trong k thut nh du 3 mu tc kp trTCM ........76 Hnh 3-27: Nguyn l hot ng ch hot ng m mu .................................76 Hnh 3-28: Nguyn l hot ng ch hot ng r mu ...................................77 Hnh 3-29: Nguyn l hot ng ca nh hng lu lng thun ...........................78 Hnh 3-30: Nguyn l nh hng lu lng bng go r token ..............................79 Hnh 3-31: Nn tiu TCP .....................................................................................80 Hnh 3-32: Nn tiu RTP .....................................................................................80Hnh 3-33: nh hng ca khng nn v nn tiu i vi tr v thng lng .....80

Hnh 4-1: M hnh mng m phng trn Lab ...........................................................82 Hnh 4-2: Kt qu o kim khi cha thc thi QoS ....................................................85 Hnh 4-3: Kt qu o kim khi thc thi QoS ............................................................86 Hnh 4-4: QoS cho mng Campus LAN....................................................................87 Hnh 6-1: M hnh nh x 12 lp lu lng sang 3 lp lu lng ...........................98 Hnh 6-2: M hnh nh x 12 lp lu lng sang 4 lp lu lng ...........................99 Hnh 6-3: M hnh nh x 12 lp lu lng sang 6 lp lu lng ...........................99 Hnh 6-4: Cc bc cu hnh thit b mng theo phng php MQC .....................102

DANH MC CC BNG Bng 1-1: Kiu lu lng v cc vn khi khng thc thi QoS..............................10 Bng 1-2: Phn loi cc lp dch v theo ITU - T ....................................................10 Bng 1-3: Phn loi cc lp dch v theo ETSI ........................................................11 Bng 2-1: Cc kiu dnh trc ti nguyn ca RSVP ..............................................28

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Bng 2-2: ngha cc bt xx v yyy ca kiu i tng ...........................................32 Bng 2-3: Cc lp PHB v cc gi tr DSCP tng ng ...........................................41 Bng 3-1: Gi tr trng CoS v ng dng ...............................................................49 Bng 3-2: Gi tr trng IP Precedence v ngha ..................................................50 Bng 3-3: Gi tr trng ToS v ngha ..................................................................50 Bng 3-4: Cc gi tr DSCP tng ng vi 3 pool v ng dng ca chng ..............51 Bng 3-5: Gi tr IP Precedence v gi tr DSCP tng ng ....................................52 Bng 3-6: Gi tr IP Precedence v gi tr trng s ca hng i WFQ ....................58 Bng 3-7: Mi quan h gia WRED v gi tr u tin (IP Precedence) ...............66 Bng 3-8: Mi quan h gia WRED v gi tr DSCP ...............................................67 Bng 3-9: WRED v cc gi tr Max v Min tng ng vi tc link kh dng ....67 Bng 3-10: Bng yu cu bng thng v kt qu ca nn tiu RTP thoi ............81 Bng 6-1: Bng SLA mu ........................................................................................94Bng 6-2: Bng ty chn cch m ha payload v bng thng yu cu tng ng .......95

Bng 6-3: Bng yu cu cc tham s QoS bo m lu lng Voice ..................95 Bng 6-4: Bng yu cu cc tham s QoS bo m lu lng Video ..................95 Bng 6-5: Bng so sch cc yu cu QoS gia cc loi lu lng ...........................97 Bng 6-6: Bng phn lp lu lng ca Cisco v IETF ...........................................98 Bng 6-7: Switch 2950 version nng cao v version chun h tr QoS .................100 Bng 6-8: Cc dng lnh cu hnh trust ranh gii ...................................................101

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Chng 1 Khi nim, yu cu v cc thng s nh hng n cht lng dch v (QoS) trong mng IPI. Khi nim v QoS v s cn thit ca QoS trong mng IP 1. Khi nim v QoS Cht lng dch v (QoS Quality of Service) l mt khi nim rng v c th tip cn theo nhiu hng khc nhau. Theo khuyn ngh ca Hip hi vin thng quc t ITU-T (International Telecommunication Union) cht lng dch v l tp hp cc kha cch ca hiu nng dch v nhm xc nh cp tha mn ca ngi s dng i vi dch v. Theo IETF [ETSI TR102] nhn nhn cht lng dch v l kh nng phn bit lung lu lng mng c cc ng x phn bit i vi cc kiu lung lu lng, QoS bao gm c vic phn loi cc dch v v hiu nng tng th ca mng cho mi loi dch v. Cht lng dch v c nhn nhn t hai kha cnh: pha ngi s dng dch v v pha nh cung cp dch v mng. Nhn t kha cnh ngi s dng dch v mng, QoS l mc chp nhn cht lng dch v m ngi s dng dch v nhn c t nh cung cp dch v mng i vi cc dch v ring ca h hoc cc ng dng m cc nh cung cp dch v cam kt vi khch hng ca mnh nh: voice, video v d liu. Nhn t kha cnh nh cung cp dch v mng, QoS lin quan ti kh nng cung cp cc yu cu cht lng dch v cho ngi s dng. C hai kiu kh nng mng cn thit cung cp cht lng dch v trong mng chuyn mch gi. Th nht, mng chuyn mch gi phi c kh nng phn bit cc lp lu lng m ngi s dng u cui c th xem xt lu chn mt hoc nhiu lp lu lng trong s cc lp lu lng khc nhau . Th hai, mt khi mng phn bit c cc lp lu lng, n phi c c ch x l khc nhau i vi cc lp khc nhau bng cch bo m vic cung cp ti nguyn v phn bit dch v trong mng. Mc chp nhn dch v ca ngi s dng u cui c xc nh thng qua vic kim tra cc thng s mng nh kh nng mt gi, tr, jitter v xc sut tc nghn. S lng v cc c tnh ca cc tham s trn ph thuc vo cc k thut thc thi QoS khc nhau trn mng.

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2. S cn thit ca QoS trong mng IP Ngy nay Internet v Intranet pht trin rt nhanh km theo l s pht trin nhiu loi dch v khc nhau. Ngi dng s dng Internet c th vi nhiu mc ch khc nhau, c th l mc ch ring hoc c th l mc ch kinh doanh. D liu c truyn i qua mng Internet v s lng ngi s dng mng Internet tng theo hm m. Cc ng dng a phng tin cc ng dng thi gian thc, nh thoi IP (IP Telephony) v h thng hi ngh video (Video conferencing system), IPTV, l cc ng dng mi cn nhiu bng thng hn rt nhiu so vi cc ng dng c s dng rt sm trn Internet, mt khc cc ng dng ny yu cu vic truyn d liu i qua mng phi lin tc, tr thp. Trong khi , cc ng dng truyn thng trn Internet nh WWW, FTP, hoc Telnet, khng chp nhn vic mt gi xy ra, khng yu cu tr cao min sao d liu khi bn nhn nhn c l y v chnh xc ni dung. T rt sm mng IP thc thi nhiu loi dch v mng khc nhau t mng in thoi. u tin, mng IP c thit k mang d liu. khng ging vi voice, d liu khng phi l dch v thi gian thc. D liu c th c lu tr trn mng v pht li sau. Nu d liu pht li b li, th n c th c truyn li. i khi cc dch v truyn d liu c cp n nh l dch v lu v chuyn tip. Cht lng ca cc ng dng thoi ph thuc vo cht lng ng truyn kt ni t u cui n u cui, du hiu ca tn hiu thoi khng c m bo cht lng thng gp nh truyn li, nhiu tn hiu, ting vng, Ngay c vic truyn d liu thi gian thc s dng giao thc thi gian thc RTP (Real Time Protocol) vn ph thuc vo vic tn dng cc ti nguyn c phn pht trn c s giao thc IP. QoS l mt k thut c s dng bo m cc ng dng thi gian thc chy c trn Internet v cc ng dng truyn thng c bo m cht lng tt hn. Bng 1-1 di y cho thy cc du hiu ca mng khi khng c c ch v cc k thut bo m cht lng dch v: Kiu lu lng Voice Cc vn khi khng c QoS Voice nghe kh hiu Voice khng lin tc, ting ni b mo Ngi gi khng bit ngi nhn kt thc cuc gi khi no hay kt thc cha Cuc gi khng kt ni c Hnh nh hin th chp chn

Video

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Data

m thanh khng ng b vi video S di chuyn ca hnh nh chm li D liu c chuyn n khi n khng cn gi tr na. D liu phn hi khng ng so vi ban u Thi gian truyn b gin on lm cho ngi dng tht vng v t b hoc thc hin li dch v Bng 1-1: Kiu lu lng v cc vn khi khng thc thi QoS

II.

Cc yu cu v mt s cch tip cn nh gi QoS trong mng IP

1. Cc yu cu cht lng dch v trong mng IP Mi ng dng u c c tnh ring ca n, do xc nh c yu cu cht lng dch v, h thng thng nhn bit da trn cc lp dch v. Theo quan im ca ITU-T, cc lp dch v c chia nh sau: Lp QoS Cc c tnh QoS 0 Thi gian thc, nhy cm vi jitter, tng tc cao 1 Thi gian thc, nhy cm vi jitter, tng tc cao 2 D liu chuyn tip, tng tc cao 3 D liu chuyn tip, tng tc 4 Tn hao thp 5 Cc ng dng nguyn thy ca mng IP ngm nh Bng 1-2: Phn loi cc lp dch v theo ITU - T Nh vy, theo quan im ca ITU th cc ng dng thi gian thc v cc ng dng c tnh tng tc cao c t ln hng u i vi mng IP, phn ln cc ng dng ny c trin khai trong cc mng chuyn mch hng kt ni (chuyn mch knh v ATM). Trong khi , mng IP nguyn thy khng h tr QoS cho cc dch v thi gian thc. D n TIPHON ca ETSI xut cc lp dch v QoS nh sau: Lp QoS Thnh phn Cc c tnh QoS Hi thoi thi gian Thoi, audio, Nhy cm vi tr v jitter, c gii hn li thc (thoi, video, hi video, a v tn tht gi, tc bt thay i v c ngh video) phng tin nh Lung thi gian thc Audio, video, Tr v jitter c sai s nht nh, sai s nh (qung b) a phng tin Tng tc cn d liu D liu thi gian thc (trnh duyt Web) Phi thi gian thc D liu (Email) i vi li v tn tht, tc bt thay i Nhy cm vi tr, jitter v mt gi, tc bt thay i Khng nhy cm vi tr v jitter, nhy cm vi li

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Bng 1-3: Phn loi cc lp dch v theo ETSI Hng tip cn ca ETSI tp trung vo cc dch v trn mng IP phn ra cc loi dch v yu cu thi gian thc v khng yu cu thi gian thc.2. Mt s cch tip cn nh gi QoS trong mng IP

Cc phng php c bn xc nh cht lng ca dch v mng bao gm qu trnh phn tch, m hnh ha v m phng hoc o trc tip cc thng s mng nh gi. Vic nh gi mc chp nhn dch v hay ni cch khc l vic o kim cc thng s mng c nh gi da trn cc thang im nh gi trung bnh MOS (Mean Opinion Score). MOS dao ng t mc 1 n mc 5 (mc 1 ti, mc 2 ngho, mc 3 cn bng, mc 4 tt, v mc 5 xut sc) v cc nh cung cp dch v da vo mc MOS ny a ra cc mc cht lng dch v ph hp cho dch v ca mnh.

Hnh 1-1: Mt s cch tip cn nh gi QoS trong mng IP Theo khuyn ngh ca ITU-T G107, nh gi cht lng dch v thoi qua IP th nn s dng m hnh E, y l mt m hnh u vit trong vic truyn dn, kt qu ca m hnh E l mt gi tr truyn dn chung gi l nhn t tc truyn dn R (Transmission Rating Factor) th hin cht lng m thoi gia ngi ni v ngi nghe. R dao ng trong khong t 1 n 100 ty thuc vo cc s mng c th. R cng ln th cht lng dch v mng cng cao. i vi dch v mng IP, m hnh E l mt cng c c lc nh gi cht lng dch v. Cc yu t nh hng n s suy gim R nh: tr, ting di jitter, mt gi, v thut ton m ha thng tin. Gi tr u ra ca m hnh E c th chuyn thnh gi tr MOS tng ng nh gi cht lng dch v.

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Mt cch tip cn khc nh gi QoS c nhn nhn t pha mng l tip cn theo m hnh phn lp trong m hnh tham chiu h thng m OSI, c th nh sau:-

Tng ng dng: Cht lng dch v QoS c nhn thc l mc dch v. Khi nim ny rt kh nh lng chnh xc, ch yu da vo nh gi ca con ngi v mc hi lng i vi dch v.

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Tng vn chuyn: Cht lng dch v c thc hin bi kin trc logic ca mng, cc c ch nh tuyn v bo hiu bo m cht lng dch v. Tng mng: Cht lng dch v c th hin qua cc tham s lp mng tng i gn vi cc tham s m chng ta thng gp, c biu din thng qua cc i lng ton hc nh: T l li, gi tr trung bnh, gi tr ln nht ca cc tham s nh bng thng, tr, v tin cy ca lung lu lng.

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Tng lin kt d liu: Cht lng dch v c th hin qua cc tham s truyn dn, t l li thng tin, cc hin tng tc nghn v hng hc ca cc ng lin kt mng.

3. Cc yu cu chc nng chung ca IP QoS Nh trnh by phn khi nim v QoS, cung cp cht lng dch v qua mng IP, mng phi thc hin hai nhim c c bn: (1) Phn bit cc lung lu lng hoc cc kiu dch v ngi s dng a cc ng dng vo cc lp hoc cc lung lu lng phn bit vi cc ng dng khc.

(2) Phn bit cc lp lu lng bng cc ngun ti nguyn v cch c x i vi cc dch v khc nhau trong mt mng.

Nhim v (1) thng c thc hin bi thit b ca ngi s dng mng v ti giao din gia mng v mng. Nhim v (2) c thc thin bi cc b nh tuyn mng. Kh nng thc hin nhim v (2) l s khc bit gia cc cng ngh mng, n th hin cc c im u vit v nhc im ca cc gii php cng ngh khc nhau. Hnh 1-2 ch ra cc yu cu chc nng c th hin trong cc b nh tuyn IP. B nh tuyn IP trn hnh v th hin di gc cc khi chc nng c sp xp theo hng i ca lung d liu t u vo b nh tuyn ti u ra b nh tuyn. Cc gi tin IP i vo t cc cng u vo ca b nh tuyn ti cc khi chc nng nh du gi tin v phn loi gi tin, hai khi chc nng ny ca b nh tuyn thc

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hin nhim v (1). Cc khi chc nng: Chnh sch lu lng, qun l hng i, lp lch gi tin v chia ct lu lng l cc khi chc nng thc hin nhim v (2).Cc gi tin i vo Nhim v 1nh du gi tin

Phn loi gi tin

Chnh sch lu lng

Qun l Nhim v 2 Lp lch gi hng i tin

nh hng lu lng

Cc gi tin i ra

Hnh 1-2: Cc khi chc nng bo m QoS trn cc b nh tuyn mngIII. Cc tham s nh hng n cht lng dch v trong mng IP 1. Bng thng Bandwidth

Bng thng l gi tr trung bnh s lng gi tin c truyn qua mng thnh cng trong mt giy. K hiu l kbps hoc Mbps. Bng thng kh dng ln nht ca ng lin kt bng gi tr bng thng nh nht ca cc ng lin kt m gi tin i qua. Bng thng nh nht ca ng lin kt ny thng l ng lin kt mng WAN. Mt s tuyn kt ni khc nh ng lin kt uplink gia cc switch hoc router. nh hng ca s thiu ht bng thng l g? S thiu ht bng thng l mt trong nhiu nguyn nhn lm gim hiu nng ca cc ng dng trn mng; c bit l cc ng dng d b nh hng bi thi gian nh voice hoc cc ng dng yu cu bng thng cao nh video. Mt s gii php c th ngn chn s thiu ht v ci thin hiu nng ca bng thng:

Tng bng thng: Cch tt nht ngn chn s thiu ht ca bng thng l nng cao tc kt ni ca tt c cc dch v ca nh cung cp dch v vi ngi s dng. Tuy nhin n gp phi mt s iu kin khch quan khin cho phng php ny khng phi l phng php c s dng nhiu nh chi ph cao, thi gian thc thi v gii hn ca cng ngh trong qu trnh nng cp v thc thi. Chuyn tip cc gi tin theo u tin: y l gii php thng c s dng hin nay, n lin quan n vic s dng k thut QoS. S dng phn loi lu lng thnh cc lp QoS, sp xp th t u tin cc lung lu lng quan

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trng v chuyn cc lung lu lng c u tin quan trng trc. y l mt trong nhng k thut c bn ca QoS v hng i. Chi tit v cc k thut ny s c trnh by c th trong bi bo co ny.

Nn: Ti u ng lin kt bng cch nn ni dung ca cc frame nhm tng bng thng kh dng ca lin kt. Nn d liu c th thc hin bng phn cng hoc phn mm qua cc thut ton nn. Ngoi ra, nn tiu (Header) ca gi tin cng l mt phng php c bit hiu qu i vi ng truyn c cc gi tin c t s header/gi tin l ln. V d nh nn tiu ca giao thc truyn ti tin cy TCP v giao thc thi gian thc RTP. Theo kin ca cc chuyn gia th nn ni dung (Payload compression) l phng php nn hiu qu trong mng u cui u cui (end to - end). Trong khi , nn header l phng php hiu qu c s dng trong cc lin kt bc bc (hop-by-hop).

2. tr - Delay tr l khong thi gian trung bnh m gi tin c truyn i t ni gi n ni nhn. Thi gian ny c gi l tr u cui n u cui. Mi thnh phn trong tuyn kt ni t u cui n u cui nh: thit b pht, thit b truyn dn, thit b chuyn mch v nh tuyn u c th gy ra tr. Nhn t gc tng qut th c ba thnh phn gy tr: tr lan truyn, tr x l, v tr hng i.-

Tr lan truyn l tham s c gi tr c nh ph thuc vo phng tin truyn, trong khi tham s tr x l v tr hng i trong cc thit b nh tuyn l cc tham s c gi tr thay i do cc iu kin thc t ca mng.

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Tr x l l khong thi gian cn thit ca mt thit b nh tuyn chuyn mt gi tin t giao din u vo ti hng i u ra v ph thuc vo rt nhiu yu t nh: Tc x l, mc chim dng CPU, phng thc chuyn mch IP, kin trc b nh tuyn v cc c tnh cu hnh giao din u vo v u ra.

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Tr hng i l khong thi gian ca gi tin nm ch ti hng i trong mt thit b nh tuyn. Tr hng i ph thuc vo s lng v kch thc cc gi tin trong hng i v bng thng kh dng trn lin kt u ra ca thit b nh tuyn. Tr hng i cn ph thuc vo k thut xp hng cc gi tin.

Tr lan truyn l thi gian truyn mt gi tin qua lin kt, tr lan truyn thng ch ph thuc vo bng thng kh dng ca lin kt. Cc k thut truy cp CSMA/CD

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cng c th gy thm tr v xc sut tranh chp ti nguyn trong trng hp giao din tin gn ti trng thi tc nghn. Mt s gii php nhm ci thin tr:

Tng bng thng lin kt, bng thng s lm cho hng i ngn li v cc gi tin khng phi i trc khi c truyn i. Tng bng thng cng ng ngha l lm gim tr ni tip nhng mt khc, gii php ny cng lm tng gi thnh ca h thng khi cn nng cp. S dng cc k thut qun l hng i. y l phng php tip cn hiu qu, tn km t chi ph. Cc hng i u tin l mt trong nhng thnh phn ch yu trong cch tip cn ny. Cc k thut x l ca hng i s c trnh by chi tit trong chng 3 ca n ny.

3. bin thin tr - Delay variation/Jitter

L s khc bit v tr ca cc gi tin khc nhau trong cng mt lung lu lng. Cc gi tin trn cng mt lung lu lng khng n ch cng tc m chng c pht i. Nhng gi tin ny c x l, a vo hng i, i ra khi hng i, l ring l v c lp vi nhau. Do , th t i ra ca cc gi tin ny, v tr ca chng c th b thay i. Kt qu ca s tc ng ca bin thin tr i vi cc ng dng thi gian thc nh thoi IP l di tn hiu echo signal, nhiu tn hiu. Mt s gii php nhm lm gim bin thin tr ca lu lng mng:

Tng bng thng lin kt: y l cch tt nht hn ch v khc phc hin tng jitter, tuy nhin gii php ny gp phi mt s im hn ch trn thc t nh thi gian, chi ph v i khi cn hn ch bi cng ngh ca cc thit b truyn dn nng cp h thng. u tin cc gi tin c tr nhy cm v chuyn cc gi tin quan trng trc: thc hin c iu ny th cc gi tin phi qua giai on phn loi hoc nh du gi tin trc khi chng c a vo cc hng i tng ng cho cc loi gi tin v d nh hng i cn bng trng s WFQ (Weighted Fair Queuing), hng i cn bng trng s theo lp CBWFQ (Class-base weighted fair queuing) y l nhng phng php khng tn km chi ph nhng li nng cao c bng thng.

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Thay i u tin ca gi tin: y l trng hp chc chn xy ra, u tin ca gi tin c thit lp khi cc gi tin i vo thit b nh tuyn. Khi gi tin di chuyn t min ny sang min khc, u tin ca cc gi tin ny c th c thay i. V d, gi tin i ra t mng doanh nghip c nh du v i vo mng ca nh cung cp dch v th gi tr u tin ca gi tin phi thay i li bo m cht lng dch v cam kt gia nh cung cp dch v vi mng doanh nghip. Nn ni dung ca gi tin tng 2 v hearder ca giao thc RTP: Nn tng 2 s lm gim kch thc gi tin IP, v n lm gim s lng bt truyn qua mng do n lm tng bng thng kh dng ln. Nn hearder ca giao thc RTP l mt phng php hiu qu cho gi tin VoIP, bi v n lm gim kch thc phn tiu c nh ca giao thc RTP. Vic nn header ca giao thc RTP c xut dnh cho kt ni c bng thng nh hn 2 Mbps. Nn Header lm gim thi gian chim dng CPU t hn hn so vi nn ni dung tng 2 v c hai u c tc dng lm gim delay trong hng i. Tuy nhin, ngay c vic nn header hay nn ni dung tng 2 u to ra thi gian tr cho vic x l.

4. Mt gi Packet loss T l mt gi l t l phn trm s gi tin IP b mt trn tng s ton b s gi IP pha u gi chuyn vo mng cho pha u nhn. Mt gi xy ra khi cc b nh tuyn trn khng gian b m trong cc giao din u vo tip nhn thm cc gi tin mi i vo. Mt b nh tuyn c th b qua mt s gi tin dnh khng gian cho cc gi tin khc c u tin cao hn. Cc b nh tuyn IP thng thng s loi b gi tin v mt s l do khc nh: Loi b gi tin ti hng i u vo v hng i u vo y, loi b cc gi u ra v b m u ra y, b nh tuyn qu ti khng ch nh c khng gian b m ri cho cc gi i vo v mt s hin tng do gi tin b li khung. Cc bin php khc phc vic mt gi ti cc b nh tuyn (Ngoi vic tng bng thng lin kt):

Tng khng gian b m tng thch vi cc ng dng c bng n lu lng cao. Cc k thut hng i thng c s dng trong thc t nh: hng i u tin PQ, hng i cn bng trng s WFQ, hng i cn bng trng s theo lp CBWFQ. Cc k thut ny s c cp chi tit ti chng 3.

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Cc phng php chng tc nghn: nhm loi b gi tin sm trc khi c hin tng tc nghn xy ra, cc hng i RED, WRED c nh gi l phng php chng tc nghn hiu qu trong mng TCP tc cao. Cc k thut ny s c cp chi tit ti chng 3. Thit lp chnh sch lu lng gii hn cc gi tin t quan trng, u tin cc gi tin quan trng hn. Cc k thut ny s c cp chi chng 3.

Chng 2 Mt s m hnh bo m cht lng dch v ph bin hin nayHin nay, c 3 m hnh ch yu ang thc thi QoS trn mng IP l m hnh Best Effort (m hnh n lc ti a), m hnh tch hp dch v v m hnh phn bit dch v. Vi m hnh Best Effort, QoS khng c p dng cho cc gi tin truyn i qua mng. Nu nh cc gi tin l khng quan trng, khng cn bit n n ch hay

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khng, v cc gi tin n ch nh th no th m hnh Best Effort l m hnh thch hp thc thi. M hnh tch hp dch v (Integrated service) l m hnh nng cao hiu nng hot ng ca m hnh mng IP bng vic h tr vic truyn cc lu lng thi gian thc v m bo bng thng cho tng lung lu lng ny bng cch d tr ti nguyn t u cui n u cui m bo cho cc lung lu lng thi gian thc c bo m theo yu cu. M hnh phn bit dch v (Differentiated services) khng x l theo tng lung lu lng ring bit, do n khng s dng trng thi ca tng lung trong cc b nh tuyn m n nhm tng lung lu lng ring bit thnh cc nhm hoc cc lp lu lng cng vi cc tham s khc nhau ca QoS li vi nhau. y l m hnh c coi l bc pht trin tip theo nhm khc phc cc hn ch ca m hnh tch hp dch v. I. M hnh Best-Effort M hnh Best Effort l m hnh u tin c p dng cho cc gi tin qua mng Internet. QoS khng c p dng cho cc gi tin truyn i qua mng. N khng phn bit cc gi tin qua mng v phn bit cc dch v cho cc gi tin, cc gi tin c truyn i t im u cui ny sang im u cui khc m khng c bt k mt c ch bo m bng thng hoc thi gian ti thiu ca tr cho cc gi tin. Cc yu cu trn Internet c i x theo nguyn tc n trc, ra trc. iu ny c ngha l tt c cc yu cu c cng u tin v c x l theo chin lc vo trc ra trc. V vy n khng c kh nng dnh trc bng thng cho cc kt ni c bit hoc u tin cho cc yu cu c bit.Lung lu lngLu lng 1 Lu lng 2 Lu lng 3 Lu lng 4 Lu lng 5

IPTt c cc lung lu lng

M hnh Best - Effort

Hnh 2-1: M hnh Best - Effort

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u im ca m hnh Best effort l gn nh khng hn ch kh nng leo thang trn mng. Ch c mt cch duy nht hn ch s leo thang trn mng l hn ch bng thng, trong trng hp ny tt c lu lng n c cng tnh cht nh nhau. Nhc im ca m hnh ny l khng bo m cht lng dch v. Cc gi tin khng c s u tin trong i x. Gi tin quan trng c i x nh cc gi tin bnh thng. II. M hnh tch hp dch v - Integrated Services Model M hnh tch hp dch v c a ra bi nhm lm vic ti IETF tch hp cc dch v khc nhau trn Internet. M hnh ny khng nhng p ng c cc dch v best - effort m cc dch v thi gian thc cng c thc thi qua m hnh ny qua vic h tr chc nng dnh trc bng thng trn internet v cc mng tng tc (Internetworks). Tch hp dch v c pht trin ti u ha mng v s dng ti nguyn cho cc ng dng mi, nh a phng tin thi gian thc yu cu bo m QoS. Bi v tr v tc nghn s lm cho cc ng dng thi gian thc hot ng khng hiu qu trn m hnh Best effort qua Internet. Cc phn mm phc v hi ngh video, qung b video, v hi ngh audio cn cung cp bng thng bo m cht lng ca video v audio. h tr m hnh tch hp dch v, cc Router phi cung cp cc k thut QoS ph hp cho mi lu lng, ph hp vi cc m hnh dch v. lm c iu router phi c chc nng iu khin lu lng (Traffic control). Bao gm cc thnh phn sau: Lp lch gi tin, phn loi gi tin, iu khin u vo.

Lp lch gi tin (Packet scheduler) Vic qun l lp lch cho cc lung gi tin khc nhau c chuyn tip gia cc host v cc Router c thc hin da trn cc lp dch v, s dng cc k thut hng i v thut ton lp lch khc nhau. Lp lch gi tin phi bo m cc gi tin c phn b v chuyn ti u ra theo lut. Ngi thit lp lch cng c th thit lp chnh sch v nh hng cho cc lu lng sao cho cc lu lng phi chc chn ph hp vi cng u ra. Cc k thut lp lch gi tin s c trnh by chi tit ti chng 3 ca bi bo co ny. Phn loi gi tin (Packet classifier)

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Vic phn loi gi tin l vic xc nh lung gi tin IP trong cc Host v cc Router. Sau , cc gi tin s c phn ra cc lp khc nhau. Tt c cc gi tin c cng lp th s nhn c s c x nh nhau trong lp lch gi tin. Vic chn cc gi tin vo mt lp da trn i ch IP ca ngun, ch v s hiu cng bn trong Header ca gi tin hoc a thm s phn loi cho mi gi tin. K thut phn loi gi tin s c trnh by chi tit ti chng 3 trong bi bo co ny.

iu khin lu lng vo (Admission control)

iu khin lu lng vo bao gm cc thut ton gip Router quyt nh vic chp nhn hay khng chp nhn cc lun lu lng i vo Router. Router xc nh nu n c ti nguyn nh tuyn th n chp nhn cc yu cu QoS cho cc lung lu lng mi . Nu n khng ti nguyn nh tuyn th vic chp nhn mt lung mi s nh hng ti cc lu lng cn bo m ti nguyn chp nhn trc , do cc lung ny s b loi b. Nu cc lung gi tin c chp nhn, Router s thit lp ti nguyn d tr b phn loi v b lp lch cc gi tin phc v vic x l cc gi tin c chp nhn bo m yu cu QoS. iu khin u vo c thc thi ti mi Router chp nhn d tr ti nguyn cho cc Host yu cu truyn dch v thi gian thc. Thut ton iu khin u vo phi ph hp vi m hnh dch v. i khi chng ta d mc sai lm khi phn bit hai khi nim iu khin u vo v chnh sch iu khin. Chnh sch iu khin thc hin nhim v xc nh gi tin vi phm tc lu lng hay khng. N bo m cho cc host khng vi phm cc c trng v lu lng c thit lp. Trong khi , iu khin u vo s lin quan ti chnh sch qun l ti nguyn d tr c bo m. Mt s chnh sch s c s dng kim tra chng thc ngi dng cho mt yu cu dnh ring. Cc yu cu khng qua chng thc c th b loi b. 1. Nguyn l hot ng ca m hnh tch hp dch v M hnh tch hp dch v s dng giao thc dnh trc ti nguyn (RSVP Resource Reservation Protocol) bo hiu. C ngha l m hnh tch hp dch v s duy tr kt ni truyn thng gia cc trm u cui qua router bng cch s dng giao thc dnh trc ti nguyn to v duy tr trng thi cc lung lu lng dc theo ng i ca mt lung.

H

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Hnh 2-2: Nguyn l hot ng ca m hnh tch hp dch v Mt ng dng mun gi gi tin i theo lung c d tr ti nguyn nhm bo m cht lng ca gi tin th n thc hin vic truyn i thng ip dnh trc ti nguyn RSVP ti cc nt mng. Giao thc RSVP c gng thit lp mt lung dnh trc cho yu cu QoS , n c th c chp nhn nu cc ng dng ph hp vi chnh sch lu lng v cc Router c th x l cc yu cu QoS. Sau khi truyn i thng ip RSVP ti cc nt mng dnh trc ti nguyn. RSVP s bo cho b lp phn loi v b lp lch gi tin trong mi nt mng x l v truyn cc gi tin theo ng lung ca n. Nu cc ng dng phn pht cc gi tin n b phn loi trong nt u tin, n s nh x lung ny vo lp dch v c th thc hin yu cu QoS, lung ny c ng gi vi a ch IP ca bn gi v c chuyn ti b lp lch gi tin. B lp lch gi tin chuyn tip cc gi tin i n cc giao tip u ra ph thuc vo vic gi tin thuc lp lu lng no n cc Router hoc trm bn pha nhn gi tin. Giao thc RSVP l giao thc n gin, vic dnh trc ti nguyn QoS ch thc thi theo mt hng, t nt gi n nt nhn. Nu ng dng mun kt thc vic dnh trc ti nguyn cho lung d liu, n gi mt thng ip dnh trc ti nguyn (bt cc thng ip bn trong giao thc RSVP nhm xa b d tr v xa b ti nguyn) gii phng ti nguyn d tr thc hin QoS trn tt c cc Router nm trong tuyn ng i ca gi tin. c t ca m hnh tch hp dch v c nh ngha trong RFC 1633. Trong m hnh tch hp dch, mi lung IP c xc nh bi nm tham s sau: a ch IP ch a ch cng ch

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Giao thc nhn dng Protocol identifier a ch IP ngun a ch cng ngun

-

d tr ti nguyn cho mi lung, ng dng ch phi cung cp cc c tnh lung. c tnh lung bao gm cc c tnh lu lng v cc yu cu dch v cho lung . c tnh lu lng bao gm: Tc nh, tc trung bnh, kch thc bng n v cc tham s go r (leaky bucket). Cc yu cu dch v bao gm: bng thng ti thiu v cc yu cu hiu nng nh: tr, jitter, t l mt gi. Cc tham s go r bao gm: Tc token (r) v su ca go r (b). Tham s r xc nh tc di hn ca d liu v c o bng s byte gam d liu IP trong mt giy. Gi tr ca tham s ny c th nm trong khong t 1 byte trn giy n 40 terabyte trn giy. Tham s b xc nh tc bng n d liu cho php ca h thng v c o bng byte. Di gi tr ca tham s b c th nm trong khong t 1 byte n 250 gigabytes. M hnh tch hp dch v xut hai lp dch v b sung cho cc dch v IP truyn thng bao gm: Dch v bo m (Guaranteed Service), c nh ngha trong RFC 2212. Dch v iu khin ti (Controled Load Service), c nh ngha trong RFC 2211. 2. Dch v iu khin ti Controlled Load Service Dch v iu khin ti c a ra h tr cc lp ng dng nhy cm vi s qu ti trn Internet, nh cc ng dng thi gian thc. Nhng ng dng ny hot ng tt di iu kin mng khng qu ti, nhng b suy gim cht lng nhanh chng di iu kin mng qu ti. Nu cc ng dng s dng dch v iu khin ti, hiu nng ca cc lung d liu ring bit ca ng ng dng khng b suy gim nu ti trong mng tng ln. Mi Router trong mng chp nhn yu cu cho dch v iu khin ti phi bo m bng thng v ti nguyn hp l x l cc gi tin yu cu QoS. iu ny c th c thc hin ti b iu khin u vo. Trc khi mt Router chp nhn mt yu cu ti nguyn QoS mi, c bit l cc gi tr ca c tnh lu lng, n phi xc nh tt c cc ti nguyn quan trng, nh bng thng lin kt, khng gian b m ca cng trn Router hoc Switch , v tnh ton kh nng chuyn tip gi tin.

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Lp dch v iu khin ti khng s dng cc tham s xc nh t ch nh bng thng, tr, hoc t l mt gi iu khin. Cc ng dng s dng dch v iu khin ti phi lun m bo lng gi tin b mt v tr gi tin l lun nh. Dch v iu khin ti ch h tr vic iu khin QoS cho lu lng tun theo c tnh lu lng c cung cp ti thi im thit lp. iu ny c ngha l cc dch v bo m ch p dng cho cc gi tin tun theo lut ca th go r trn tt c cc thi gian ca cc giai on (T), s lng d liu c gi i khng vt qu rT + b. Dch v iu khin ti c thit k cho cc ng dng chp nhn s lng gi tin b mt v tr hp l, nh audio v hi ngh video qua mng. 3. Dch v bo m Gruaranted Service M hnh dch v bo m cung cp cc chc nng bo m cc datagram s n ch trong khong thi gian c phn pht v khng b mt gi do lung b trn hng i. Dch v bo m c s dng cho cc ng dng cn bo m mt datagram s truyn n pha nhn khng chm hn mt khong thi gian no sau khi n c truyn i t pha ngun. Dch v bo m ch c s dng nu n c h tr bi cc Router trong tuyn ng dnh trc ti nguyn. Bo m dch v a li cho cc ng dng tr nh nht. Nh cp, tr trong mng IP c ba phn chnh: Tr ng truyn c nh, tr x l v tr hng i. Tr truyn c nh ph thuc vo vic chn ng thng qua cc k thut nh tuyn. Tr hng i c xc nh bi dch v bo m v n c iu khin bi hai tham s: go r (c bit l kch thc go r b) v bng thng R c yu cu dnh trc. Trong m hnh dch v bo m, cc c tnh lu lng v cc yu cu dch v c s dng thit lp mt lung d tr. c tnh lu lng c c trng bi cc tham s go r. Cc yu cu lu lng bao gm tham s R, c trng cho bng thng cho lung d tr. 4. Giao thc dnh trc ti nguyn RSVP 4.1. Gii thiu chung v RSVP Giao thc dnh trc ti nguyn RSVP c nh ngha trong RFC 2205. RSVP l mt giao thc thit lp ti nguyn d tr cho QoS IP. N h tr c IPv4 v IPv6 v n cng p dng cho c hai phng thc chuyn pht tin a hng v n hng (multicast and unicast) trn mng IP. Trong giao thc dnh trc ti nguyn RSVP, ti nguyn c dnh trc theo cc hng c lp (n hng). h tr cc kt

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ni kp, nh hi ngh video hoc hi ngh audio, th mi bn gi cng l mt bn nhn, iu ny l cn thit thit lp hai phin RSVP cho mi trm. Trm ngun v trm ch trao i thng ip RSVP thit lp cc trng thi chuyn tip v phn loi gi tin ti mi nt. Trng thi ca ti nguyn c d tr ti cc nt RSVP khng c nh v n c thit lp li mt cch nh k (c lm ti thng xuyn theo nh k) thng thng l khong 30s. RSVP khng phi l mt giao thc nh tuyn m l mt giao thc bo hiu. Cc thng ip RSVP c chuyn i trn cng ng dn cng vi cc gi tin IP da trn bng nh tuyn trong b nh tuyn IP. thit lp mt ti nguyn dnh trc vi RSVP, my nhn gi mt yu cu d tr ti nguyn n my gi, ph thuc vo kh nng ca h thng ca h. V d, mt my trm tc nhanh v mt PC tc chm mun nhn mt lung video MPEG cht lng cao vi 30 frame trn mt giy, v tc ng truyn d liu l 1.5 Mbps. My trm c CPU gii m lung video , nhng PC c th gii m c 10 frame trn mt giy m thi. Nu my Server Video gi cc thng ip ti hai thit b nhn ny th n c th p ng c tc truyn cc lung video l 1.5 Mbps, my trm c th p ng c yu cu dnh trc ti nguyn 1.5 Mbps . Nhng my PC th khng cn bng thng cho lung ca n bi v n khng th gi m c tt c cc frame. Do my PC phi gi mt yu cu d tr ti nguyn cho cc lung vi 10 frames trn mt giy v bng thng 500 kpbs.4.2. Nguyn l hot ng ca RSVP

Mt phin lm vic ca giao thc dnh trc ti nguyn RSVP c xc nh bi 3 tham s sau: - a ch ch - Nhn dng giao thc Protocol indentifier- S hiu cng ch

Hnh 2-3 di y m t nguyn l hot ng ca giao thc dnh trc ti nguyn RSVP.

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Hnh 2-3: Nguyn l hot ng ca giao thc dnh trc ti nguyn RSVP Trm gi gi thng ip PATH ti trm ch cho mt lung hay cn gi l mt phin truyn thng. Thng ip PATH cha cc c trng ca lung s c gi i, thng ip PATH i qua cc Router trn ng dn ti ch, cc Router ng k nhn dng lung v c tnh lung vo c s d liu. Thng ip RESV c pht ngc tr li t my nhn ti my gi, cc Router xc nhn v chnh sa thng tin yu cu c gi trong thng ip PATH v RESV. Khi my nhn nhn c thng ip PATH, n gi tr li thng ip RESV. Thng ip RESV mang thng tin ti nguyn d tr ca ng n m gi tin IP s chuyn qua. Ti mi nt mng, mt yu cu d tr ti nguyn tri qua hai hot ng: a) D tr ti nguyn QoS trn ng lin kt ca n vi cc nt khc. Thng ip RSVP x l v chuyn cc yu cu d tr ti nguyn ti b iu khin u vo v b chnh sch iu khin c thit lp trn nt mng. B iu khin u vo s kim tra nu Router c ti nguyn thit lp d tr cho mt QoS yu cu mi, v chnh sch iu khin s kim tra nu ng dng c yu cu chng thc cho QoS hay khng. Nu mt trong cc b kim tra b li, vic d tr ti nguyn s b loi b v thng ip RSVP s x l tr v mt thng ip li ResvErr ti my nhn. Nu c hai b kim tra ti nguyn v yu cu chng thc l hp l th nt mng s dng thng tin ca trng FITERSPEC trong thng ip RESV thit lp vicThng ip RESV

phn loi gi tin v s dng thng tin trong trng FLOWSPEC trong thng ip RESV thit lp vic lp lch gi tin. Sau , b phn loi gi tin s nhn cc gi tin thuc vo lung tng ng ca n, v b lp lch s Chng thc yu cu QoS c nhn cc xc nh trong trng FLOWSPEC. FLOWSPEC FLOWSPEC RSVP trn Router.Xc nh Router v lp QoS Xc nh Router v lp QoS B lp lch gi tin ng dng ? FILTERSPEC FILTERSPEC Chnh sch iu khin Thng ip RESV

Hnh 2-4 m t qu trnh x l d tr ti nguynTi nguyn thc d tr ti nguyn ca giaonh tuyn? iu khin u vo

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Hnh 2-4: Qu trnh x l d tr ti nguyn ca giao thc d tr ti nguyn RSVP b) Chuyn tip yu cu d tr ti nguyn ti cc nt khc. Sau khi b iu khin u vo v chnh sch iu khin kim tra thnh cng, mt yu cu d tr ti nguyn c truyn n my nhn. Trong mi trng truyn a hng, mt my nhn c th nhn d liu t nhiu my gi. Tp hp cc my gi a ra cc yu cu dnh trc ti nguyn c gi l ngun pht cc yu cu. Cc yu cu d tr ti nguyn c chuyn i t mt nt sau khi Hop trc n p ng vic d tr t cc yu cu ti nguyn. lm c iu ny, mt phn l v k thut iu khin lu lng c th xc nh cc c tnh lung theo tng bc (hop by - hop). Mt yu t quan trng khc l, trong mi trng mng a hng, vic d tr ti nguyn Router thuc cc nhnh khc nhau, nhng cng mt my gi, th cc Router ny s gi cc thng ip tr li ti mt Router m my gi ang kt ni v trn Router ny c mt im c gi l ni hp nht (Merge) cc thng ip. im hp nht ny l cn thit bo m ti nguyn trn cc Router. Tc l, mt yu cu d tr ti nguyn l thnh cng trong mi trng mng a hng khi tm mt im m ti nguyn n c bng hoc ln hn ti nguyn yu cu. Ti im ny, yu cu ti nguyn c hp nht cng vi ti nguyn c sn ti mt a im v khng cn phi chuyn i ni khc.

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Hnh 2-5: Nguyn l chuyn tip yu cu d tr ti nguyn ti cc nt Kiu d tr ti nguyn ny ch hp l nu tt c cc Router trn ng truyn h tr RSVP. Nu tn ti mt Router khng h tr vic d tr ti nguyn th dch v khng c m bo trn ng truyn , bi v c trng n lc ti a c ci t mc nh trn cc Router. Router ny c gi l im tht c chai i vi lung lu lng. RSVP duy tr trng thi mm trn cc Router v Host, tc l vic d tr ti nguyn b hy b nu RSVP khng gi thng ip lm ti cho cc ng i h tr vic d tr ti nguyn. iu ny gip Router thay i thng tin nh tuyn lin tc lm tng hiu nng nhn dng thng ip mi v cc lung lu lng mi.4.3. Cc kiu dnh trc ti nguyn ca RSVP

C 3 kiu d tr ti nguyn c nh ngha bi t chc IETF trong RFC 2205 (xem bng 2-1). iu khin my gi chu trch nhim la chn cc my gi. C hai kiu iu khin my gi c nh ngha l:

Kiu la chn hin (explicit selection): lit k danh sch ton b cc my gi Kiu la chn i din (wildcard selection): tt c cc my gi trong phin

iu khin chia s ti nguyn thc hin vic iu khin cc ng x ti nguyn d tr cho cc my gi khc nhau trong cng mt phin truyn thng. C hai kiu iu khin chia s ti nguyn c nh ngha, l: Kiu dnh trc ti nguyn phn bit: ti nguyn dnh trc c to ra cho tng my gi. Kiu dnh trc ti nguyn chia s: mt ti nguyn c chia s bi nhiu my gi. La chn my gi Ti nguyn dnh trc Phn bit Chia s

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Hin (Explicit) Kiu b lc c nh (FF) Kiu chia s hin (SE) i din (Wildcard) Khng c nh ngha Kiu lc i din (WF) Bng 2-1: Cc kiu dnh trc ti nguyn ca RSVP Da vo bng cc kiu dnh trc ti nguyn, chng ta nhn thy c 4 kh nng c t hp t cc cch thc iu khin chia s ti nguyn v lu chn my gi. Tuy nhin, c mt kiu khng c nh ngha v chng ta c 3 kiu dnh trc ti nguyn, l: Kiu b lc c nh (Fixed-Filter Style), kiu chia s hin (SE Shared-Explicit Style), v kiu b lc i din (Wildcard-Filter Style).

Kiu b lc i din - WF: kiu dnh trc ti nguyn ny thit lp mt ti nguyn d tr cho tt c cc my gi trong cng mt phin. D tr ti nguyn i din chuyn tip ti nguyn n tt c cc my gi. Nu mt my gi mi xut hin trong phin truyn, v d, mt thnh vin mi gia nhp vo h thng hi ngh qua video, th vic d tr ti nguyn c m rng thm cho my gi mi ny. Kiu lc c nh FF: l s kt hp gia d tr ti nguyn phn bit v la chn my gi hin. iu ny c ngha l mt ti nguyn d tr ring bit c to ra cho cc gi d liu t mt my gi. Cc gi tin t cc my gi khc nhau trong cng mt phin khng chia s ti nguyn d tr. Kiu chia s ti nguyn hin SE: l s kt hp gia kiu chia s ti nguyn d tr v la chn my gi hin. iu ny c ngha l mt ti nguyn bao bc cc lung t mt nhm nh trong danh sch tt c cc my gi. Do , mt danh sch my gi phi bao gm c yu cu d tr ti nguyn t cc my nhn. 4.4. nh dng thng ip RSVP

nh dng thng ip RSVP bao gm mt tiu chung v cc trng chc nng th hin cc i tng nh hnh 2-6 (a) di y. Mi i tng c cu trc bi tiu i tng v ni dung i tng.

(a)

(b)

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Hnh 2-6: nh dng thng ip RSVP nh dng tiu chung gm cc trng nh hnh 2-6 (b) bao gm:- Version: 4 bt, cho bit s hiu phin bn RSVP - Flag c: 4 bt. Cha c gi tr c c nh ngha - Kiu bn tin (kiu thng ip): l trng 8 bt xc nh cc kiu thng ip

RSVP bao gm: o Path - S dng yu cu dnh trc ti nguyn o Resv Gi phn hi li khi nhn thng ip Path thit lp v duy tr vic d tr ti nguyn. o PathErr Thng bo li thng ip Path o ResvErr Thng bo li thng ip Resv o PathTear S dng xa b ti nguyn khi mng theo hng i c thit lp. o ResvTear S dng xa b ti nguyn khi mng theo hng v. o ResvConf l mt thng ip ty chn, gi ngc li ti pha my gi bn tin RESV xc nhn rng ti nguyn d tr xc nh thc s c thit lp.- Tng kim tra RSVP (RSVP Checksum) Trng 16 bt. Tng kim tra

c th c s dng bi my nhn thng ip RSVP pht hin li trong vic truyn thng ip RSVP. Nu trng tng kim tra c gi tr ton b l 0, iu ny th hin khng cn kim tra thng ip c truyn i.- Send_TTL (Thi gian sng Time To Live) Trng 8 bt, s dng

gi thi gian sng ca gi tin IP.- D phng (Reserved) Trng 8 bt d phng - Chiu di bn tin RSVP (RSVP Length) Trng 16 bt cho bit tng

di ca thng ip RSVP bao gm tiu chung v tt c cc i tng ca lung. chiu di c m bng byte. Khun dng i tng RSVP nh hnh 2-7, gm 32 bt tiu v cc ni dung i tng c di thay i. Cc i tng RSVP c t chc thnh lp i tng v kiu i tng.

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Hnh 2-7: Khun dng i tng RSVP Trong :- Trng ch th di (Length) Trng 16 bt bao gm chiu di i

tng. N phi l b s ca 4. Chiu di ti thiu l 4 bt.- Trng Class-Number Trng 8 bt, nh ngha cc lp i tng. Bao

gm cc lp i tng sau (c nh ngha trong RFC 2205):o

NULL i tng NULL c Class-Number = 0. di ca i tng ny ti thiu l 4, nhng c th l b s ca 4. i tng NULL c th xut hin bt c ni no trong th t cc i tng ca thng ip RSVP. My nhn t chi nhn ni dung ca i tng ny. Session - i tng Session cha a ch IP ch, ID giao thc IP, v cng ch nh ngha mt phin cho i tng khc trong cng lung. i tng Session c yu cu c trong mi thng ip RSVP. RSVP_HOP i tng RSVP_HOP cha a ch IP ca nt mng gi chnh thng ip ny v interface logic u ra. i vi thng ip hng i (v d nh thng ip PATH), i tng RSVP_HOP miu t mt i tng HOP lin trc n. i vi thng ip hng v (v d nh thng ip RESV), i tng RSVP_HOP miu t mt i tng HOP k tip. Time_Values i tng Time_Value cha thi gian lm ti thng ip PATH v thng ip d tr ti nguyn. Nu cc thng ip ny khng c lm ti trong mt khong thi gian xc nh, trng thi ng i PATH v trng thi d tr ti nguyn s b hy b.

o

o

o

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Style i tng Style nh ngha kiu d tr ti nguyn v mt vi thng tin ring bit khng c trong m t lung lu lng v m t b lc. i tng Style l bt buc trong cc thng ip RESV. Flowspec y l i tng xc nh cc yu cu QoS trong thng ip d tr ti nguyn. N m t c tch lung bao gm cc tham s ca lung dnh cho dch v iu khin ti: Tc go r Token (my nhn yu cu dnh trc ti nguyn), kch thc go r Token (My nhn yu cu dnh trc ti nguyn), Tc d liu nh (My gi yu cu dnh trc ti nguyn), vv. Filterspec i tng Filterspec xc nh gi d liu c nhn QoS trong i tng Flowspec, tc l n m t c tnh b lc. Sender_Template i tng ny cha a ch IP my gi v chn thm cc thng tin trong mt knh truyn thng s dng cho mt my gi nht nh. N m t khun dng gi tin ca i tng gi. V i tng ny l bt buc c trong tt c cc thng ip ng i PATH. Sender_Tspec i tng ny nh ngha cc c trng lu lng ca mt lung d liu t mt my gi. i tng ny l bt buc c trong tt c cc thng ip ng i PATH. Adspec i tng Adspec c s dng cung cp cc thng tin qung b cho module iu khin lu lng trong cc nt mng s dng giao thc RSVP theo ng i. Error_Spec i tng ny xc nh cc thng ip li nh thng ip li ng i PathErr hoc thng ip li dnh trc ti nguyn ResvErr, hoc thng ip li chng thc ResvConf. Policy_Data i tng ny cha thng tin cho php module chnh sch lu lng quyt nh vic cho php kt hp ti nguyn hay khng. N c th c s dng trong cc thng ip PATH, RESV, PathErr, hoc thng ip ResvErr. Integrity (Tnh ton vn d liu v ton vn ni dung thng ip RSVP) i tng ny cha d liu c m ha chng thc trong cc nt mng v kim tra li ni dung thng ip RSVP.

o

o

o

o

o

o

o

o

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Scope i tng Scope cha thng tin danh sch hin cc my gi c gi i. i tng ny c th xut hin trong cc thng ip Resv, ResvErr, hoc thng ip ResvTear. Resv_confirm i tng ny cha a ch IP ca my nhn c yu cu chng thc cho vic d tr ti nguyn. N c th c s dng trong thng ip RESV v Resvconf.

o

- C-Type Trng C-Type m t kiu i tng trong Class number. -

Ni dung i tng (Object contents) Trng ni dung i tng ph thuc vo kiu i tng v c di ti a l 65,528 byte.

Mt lp i tng c yu cu bi thng ip RESV c lp kiu bn tin STYLE vi class-num = 8. Lp ny c mt i tng vi C-Type = 1. Kiu i tng nh ngha kiu dnh trc ti nguyn. Hnh 2-8 m t khun dng ca kiu i tng.

Hnh 2-8.: Khun dng ca kiu i tng Kiu dnh trc ti nguyn c nh ngha bi 5 bt cui cng. Trong o, 2 bt u tin xx nh ngha kiu iu khin chia s ti nguyn v 3 bt sau yyy iu khin la chn my gi. ngha ca cc bt c th hin di bng sau: Bt xx 00 01 10 11 iu khin chia s Bt yyy iu khin la chn my gi D phng 000 D phng Ti nguyn phn bit 001 La chn i din (Wildcard) Ti nguyn chia s 010 La chn hin D phng 011-111 D phng Bng 2-2: ngha cc bt xx v yyy ca kiu i tng

4.5. Thng ip PATH

Thng ip PATH m t thng tin truyn thng qua a ch IP ngun v a ch IP ch, cng vi mt s c tnh ca ng i c th hin trong cc i tng RSVP_HOP v TIME_VALUE. Khun dng ca gi tin s c chuyn i tng thch vi cc kiu b lc c m t trong i tng SENDER_TEMPLATE, cc c tnh lung ca cc ng dng t my gi c m t trong i tng SENDER_TSPEC. Cu trc thng ip PATH c th hin di hnh 2-9: SVTH: H c Lnh - 47133042 29

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Hnh 2-9: Cu trc thng ip PATH4.6. Thng ip RESV

Thng ip RESV mang yu cu dnh trc ti nguyn theo tng bc t my gi n my nhn dc theo ng i ngc li vi ng i ca thng ip PATH ca lung d liu trong cng mt phin. Cc i tng trong thng ip RESV nhm xc nhn v sa i mt s yu cu ca thng ip PATH cho ph hp vi hin trng ca mng. Hnh 2-10 m t cu trc ca thng ip RESV.

Hnh 2-10: Cu trc thng ip RESV 4.7. u v nhc im ca m hnh tch hp dch v M hnh tch hp dch v c thit k nhm cung cp cht lng dch v cho cc ng dng kt ni im im qua mng khng ng nht. iu ny c ngha l m hnh tch hp dch v h tr cc kiu mng khc nhau v cc thit b khc nhau. N thc thi ti cc nt mng, nh Router, cn thng tin cung cp cc yu cu dch v cho cc lung QoS im im. Thng tin c thit lp trn Router thng qua vic thc thi giao thc d tr ti nguyn RSVP. RSVP l mt giao thc bo hiu, n yu cu cc nt mng t u cui ti u cui theo ng i dnh trc ti nguyn bo m chc chn rng lung d liu s nhn c s lng bng thng cn thit. Mc d RSVP c s dng yu cu ti nguyn t mng, tch hp dch v nh ngha cc kiu dch v cn thit, xc nh s lng ti nguyn yu cu v quyt nh ti nguyn yu cu c hiu lc.

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Di y l mt im hn ch ca m hnh tch hp dch v trn Internet:

M hnh ny hot ng khng hiu qu trong trng hp mt Router no trn ng i khng ti nguyn nhn v ng k d tr cho mt lung no . Trong trng hp ny, Router ny c xem l nt tht trong mng. M hnh tch hp dch v hot ng da trn trng thi lung v x l tng lung. Nu s lng lung tng ln t ngt, n phi dnh s lng ti nguyn tng ng p ng vi s tng ln ca cc lung . Ti nguyn ny s b chim dng v khng c tn dng cho bt k mt lung no khc. Nu ti nguyn b chim dng ny m khng dng th hin tng lng ph ti nguyn s xy ra.

M hnh tch hp dch v s dng giao thc dnh trc ti nguyn RSVP bo hiu. Khi mt lung c thit lp th tng ng vi mt phin RSVP c thit lp, iu ny dn n mt hn ch l: i vi mng c lu lng cao nh mng ISP hay cc t chc doanh nghip ln th s lng lung lu lng c th ln ti hng trm, hng ngn lung trong mt thi im v dn n hin tng lng ph ti nguyn do bng thng c s dng thit lp knh RSVP ln rt nhiu. Do , n khng c la chn thc hin QoS trong mng c quy m ln. N ch thch hp cho nhng mng nh vi lung lu lng t hoc mng cn u tin ti nguyn cho lung lu lng ring. u im ca m hnh tch hp dch v:

M hnh ny bo m cht lng dch v theo tng lung d liu t u cui n u cui cn bo m QoS, nh Thoi IP, h thng video qua mng, vv.

M hnh tch hp dch h tr vic iu khin u vo, iu ny cho php mt mng c th t chi mt phin RSVP mi nu mt Interface trong ng i khi b hn ch v ti nguyn. Thng ip RSVP yu cu QoS theo tng lung. Trong yu cu ny, vic chng thc ngi dng (chng thc i tng) v chnh sch lu lng cn thit (chnh sch ca cc i tng) c gi i. T mng c th cung cp cc c ch bo n cho cc lung .

Cho php cc Host yu cu tng lung v xc nh s lng ti nguyn cn thit trn ng i t u cui n u cui, bao gm vic phn hi v thng tin ti nguyn u vo.

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Thng ip RSVP bo cho cc thit b mng bit v cc tham s ca lung (a ch IP v s hiu cng). Mt s ng dng s dng s hiu cng ng, v d nh cc ng dng hot ng da trn giao thc H.323, cc ng dng ny c th gy kh khn cho cc thit b mng nhn din. h tr iu ny, k thut NBAR ca Cisco a ra b sung giao thc dnh trc ti nguyn RSVP cho cc ng dng s dng s hiu cng ng nhng khng s dng giao thc RSVP.

III. M hnh phn bit dch v - Differentiated Services Model (DiffServ)

1. Gii thiu tng quan v m hnh phn bit dch v M hnh phn bit dch v (DiffServ) c pht trin bi nhm lm vic v phn bit dch v trong IETF. Mc tiu pht trin ca DiffServ l nhm cung cp cc lp dch v khc nhau cho cc lu lng trn Internet, do n h tr nhiu loi ng dng v tip nhn cc yu cu kinh doanh ring trn Internet. S khc bit gia m hnh tch hp dch v v m hnh phn bit dch v l DiffServ cung cp c ch phn bit cc dch v trn Internet m khng cn trng thi ca tng lung v bo hiu ti cc Hop. Trong DiffServ, cc lu lng trn Internet c chia thnh cc lp dch v khc nhau tng tng vi cc yu cu QoS khc nhau. V trong DiffServ, bng thng v cc ti nguyn mng khc nhau c ch nh trong cc lp lu lng. Mt khc, DiffServ hng ti x l tng vng dch v phn bit (DS domain) thay v x l t u cui ti u cui nh trong m hnh tch hp dch v. DiffServ ch cung cp s ng x phn bit lin quan ti cc lp lu lng khc nhau, v vy DiffServ khng cung cp mc QoS c th. m bo mt s mc cht lng dch v QoS c th, iu khin u vo c h tr ti bin ca min phn bit dch v DS iu khin cc lung lu lng i vo mng. Khng ging nh m hnh tch hp dch v s dng giao thc bo hiu RSVP dnh trc bng thng dc theo ng i, QoS trong m phn bit dch v c cung cp theo hng cung cp ti nguyn hn l dnh trc ti nguyn. Thnh phn trung tm ca m hnh phn bit dch v l tha thun mc dch v (SLA) gia nh cung cp dch v v ngi s dng. DiffServ nh ngha mt s tham s m ngi s dng hiu r cho cc ng dng ca h trong SLA nh: Tha thun iu kin lu lng (Traffic Conditioning Agreement - TCA), m t s lc v cc tham s lu lng (cc tham s go r), cc tham s hiu nng (thng lng, tr,

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mc tn tht gi), cch thc x l cc cc gi tin khng ph hp vi tha thun, v cc k thut nh du, nh hng lu lng.2. Nguyn l hot ng v kin trc ca m hnh phn bit dch v

2.1. Nguyn l hot ng ca m hnh phn bit dch v Hnh 2-11m t cc bc c bn trong vic cung cp cc dch v DiffServ:SLA Cc gi tin ca ngi dngDSCP3 DSCP2 DSCP1

Hng i PHB

Cng ra Phn loi gi tin BA

Interface ca ngi dng

B nh tuyn IP

Hnh 2-11: Nguyn l hot ng ca m hnh phn bit dch v DiffServ Cc gi tin ngi s dng c nh du DSCP (hoc cha c nh du) i n Router, Router kim tra trng DSCP ca cc gi tin v phn loi cc gi tin theo phng php phn loi hnh vi kt hp - BA. Cc gi tin phn loi thnh cc lp BA c chuyn tip theo hnh vi tng bc - PHB (Per Hop Behavior) c nh ngha trc cho cc BA. Mi PHB c th hin bi gi tr DSCP v c x l nh nhau i vi cc gi tin trong cng lp BA. Cc yu cu chung ca QoS nh: chnh sch lu lng, nh hng lu lng, loi b gi tin, qun l hng i, lp lch gi tin c p dng ti bc ny ca m hnh phn bit dch v. 2.2. Kin trc ca m hnh phn bit dch v Kin trc ca m hnh phn bit dch v c nh ngha trong RFC 2475. Trong , mt mng IP c chia thnh cc min phn bit dch v (vit tt l min DS DS Region), trong mt min DS c mt hoc nhiu vng phn bit dch v (vit tt l vng DS DS Domain) k tip nhau. Mt vng DS gm c cc b nh tuyn h tr c ch phn bit dch v, cn gi l cc nt DS, hot ng vi cng mt chnh sch cung cp dch v. Mt vng mng IP hoc vng IP c mt ng bin, mt vng DS c phn ranh gii bi mt ng bin DS (DS Boundary). Mt nt DS t ti ng bin DS c xc nh l nt bin DS (DS Boundary node); v mt nt DS bn trong vng DS c gi l nt bn trong DS (DS interior node).

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C hai kiu nt bin DS: nt bin li vo v nt bin li ra. Nt bin li vo l nt bin DS t li vo ca vng DS, v nt bn li ra l nt bin DS c t li u ra ca vng DS theo hng truyn t my gi sang my nhn. Cc lu lng i vo mt vng DS thng qua nt bin u vo v i ra mt vng DS thng qua nt bin u ra. Hnh 2-12 cho chng ta thy r v cc thnh phn chnh trong mt vng DS

Hnh 2-12: Cc thnh phn chnh trong mt vng DS Cc nt bin DS thc thi vic phn loi v iu khin lu lng u vo bo m rng cc gi tin qua vng DS c nh du thch hp la chn mt PHB t mt nhm PHB c h tr trong phm vi vng DS . Cc nt trong vng DS hay cn gi l cc nt li thc hin vic la chn cch ng x chuyn tip cho cc gi tin da trn im m dch v DSCP ca chng, sp xp vo mt trong cc PHB theo yu cu. Hnh 2-13 m t chc nng ca Router bin v router li trong vng DS.

Hnh 2-13: Chc nng ca Router bin v router li theo m hnh DiffServ Mt min DS c mt hoc nhiu vng DS lin k nhau c cc chnh sch qun tr khc nhau. Do , mt min DS c th cung cp DiffServ qua cc b nh tuyn trn mng di nhiu chnh sch qun tr khc nhau. Tng qut, mi vng DS thc thi cc chnh sch v PHB ca chng. Mi vng c th s dng im m phn bit dch v DSCP ch nh cc kiu lu lng. cung cp DiffServ qua min DS, cc vng DS ngang hng trong min DS c th thit lp mt mc tha thun dch v SLA cha tha thun lu lng TCA ph hp ti cc

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Interface gia cc vng DS. Mt s vng DS trong mt min DS c th k tha mt chnh sch cung cp dch v chung v c th h tr tp hp chung cc nhm PHB v cch sp xp im m phn bit dch v DSCP, v vy c th loi b qui nh lu lng gia cc vng DS trong mt min DS.

Hnh 2-14: Min DS v vng DS 3. K thut nh du gi tin trong m hnh phn bit dch v M hnh phn bit dch v DiffServ s dng trng kiu dch v (Type of Service - ToS) trong Header IPv4 v trng lp lu lng (Traffic Class - TC) trong Header IPv6 nh du gi tin. Khi c IPv4 v IPv6 c thc thi trn cc b nh tuyn Router v cc Router ny hot ng trong vng DS, cc trng ToS v TC c thay th bng trng phn bit dch v ( DiffServ field - DS) 8 bt. Trong 8 bt ny, 6 bt c s dng nh du gi tin v 2 bt cui cng l d phng. 6 bt s dng nh du gi tin c c gi l im m phn bit dch v DSCP. Chi tit v trng DS v DSCP c trnh by ti mc 5.1.3 trong bi bo co ny. Nh vy, cc gi tin mun nh du thc thi theo m hnh phn bit dch v th chng ta phi thit lp gi tr ca trng DSCP.3.1. K thut hnh vi theo tng bc - PHB

M hnh phn bit dch v DiffServ s dng phng php phn loi gi tin kt hp hnh vi (BA Behavior Aggregate). Trong phng php nh du gi tin BA, cc gi tin c nh u ch da trn gi tr ca trng im m phn bit dch v DSCP. Cc gi tin c nh du trong mt BA nhn c cng cch x l nh nhau trong vic chuyn tip gi tin.

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M hnh DiffServ hot ng c bn l da trn tng bc v da trn nh ngha PHB trong mi Router. Tuy nhin, cung cp DiffServ cho mi vng DS, PHB trong mi Router c th c thit k, v cch tt nht l p ng tt c cc yu cu QoS u cui n u cui. PHB c th k sao cho c th kt hp c vi k thut chnh sch lu lng, nh hng lu lng, iu khin u vo. Mt nh cung cp dch v s dng mt PHB xc nh bng thng v cc yu cu ti nguyn khc. Do , mt PHB c th c nh ngha trong nhm ca cc yu cu ti nguyn mng (bng thng, kch thc b m), u tin ca cc PHB c so snh vi nhau trong cng mt Router, v cc thng s hiu nng ( tr, jitter, v mt gi). to ra cc hnh vi chuyn tip gi tin c nh ngha theo quy tc ng x tng bc PHB, cc k thut bo m QoS bn trong Router nh AQM, lp lch gi tin v cc yu cu khc c trnh by trong chng 3 c p dng. Mt PHB ca mt Router c th khng cn ph thuc vo nguyn tc chung m c th c pht trin vi cc k thut ring ca nh cung cp thit b mng. C hai loi PHB c nh ngha trong RFC 2598 l: Chuyn tip nhanh hnh vi tng bc (Expedited forwarding (EF) PHB) v chuyn tip bo m hnh vi tng bc (Assured forwarding (AF) PHB). 3.2. Chuyn tip nhanh PHB Expledited Forwarding (EF) PHB Chuyn tip nhanh EF PHB ban u c m t trong RFC 2598, sau c thay th bi RFC 3246. Vi EF PHB, Cc gi tin c chuyn tip vi t l mt gi thp, tr thp v jitter thp. EF PHB yu cu mt s bo m v s lng bng thng ca cng lin kt i ra c th a ra c cc hnh vi ph hp p ng c kh nng tn hao thp, tr thp v bin tr thp. iu ny c th thc thi c bng cch cung cp cho t u cui ti u cui cc ng o ring virtual leased lines hoc ph dch v. V tr c sinh ra do thi gian m cc gi tin trong b nh m v hng i lu, mt b nh tuyn EF phi bo m rng cc lu lng EF c a n b nh m c kch thc nh v tn ti trong thi gian ngn. Tc u ra ca Router phi bng hoc ln hn u vo. Khi xy ra hin tng qua ti, nt bin vng DS khng cho php cc dng lu lng EF i vo trong min v n s gy ra hin tng tc

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nghn ti cc b inh tuyn trong vng DS. Vn ny c iu chnh thng qua vic xc nh mc dch v tha thun SLA v xc nh lu lng truyn c iu kin. Hnh 2-15 th hin qu trnh chuyn tip gi tin theo phng php chuyn tip nhanh theo tng bc EF PHB.

Hnh 2-15: K thut chuyn tip nhanh theo tng bc EF PHB Ti cc nt bin ca vng DS, cc gi lu lng EF c chnh sch theo gi tr tha thun SLA. Hng i FF phi c kch thc b m v bng thng cng u ra cc lung lu lng EF ra vi tc phc v v tc lung lu lng EF i vo l . h tr EF PHB qua mt min DS t u cui ti u cui, bng thng ti cc cng u ra ti cc Router li v cc b m EF phi tha mn tc phc v lun ln hn tc vo . Cc lung khng phi l EF l cc lung dch v n lc ti a. Vi cc k thut lp lch gi tin c trnh by ti mc 5.3, chuyn tip EF PHB m bo c tnh u tin cho cc lung lu lng theo yu cu. Mt cch tip cn khc thc thi EF PHB l s dng cc bin th ca hng i WFQ phn loi cc lu lng chuyn tip EF. Khi EF PHB c s dng cho cc dch v thi gian thc nh voice v video v cc dch v thi gian thc s dng giao thc UDP thay v s dng giao thc TCP, th hng i RED khng thch hp cho hng i FF. Bi v cc ng dng s dng giao thc UDP l giao thc truyn thng phi kt ni khng tin cy, n khng c c ch phn hi, loi b cc gi tin ngu nhin RED s loi b cc gi tin tha. Trong tng lai, k thut qun l hng i ng (AQM Active Queue Management) s thay th cho giao thc UDP, AQM tng t nh phng php ECN c s dng cho giao thc TCP. 3.3. Chuyn tip bo m PHB Assured Forwarding (AF) PHB

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Chuyn tip bo m (AF) PHB c m t trong RFC 2597. Mc ch ca AF PHB l phn pht gi tin tin cy, do tr v jitter l hai tham s khng quan trng bng tham s mt gi tin. V vy, AF PHB thch hp cho cc dch v phi thi gian thc nh cc ng dng s dng giao thc TCP. AF PHB bao gm 4 lp chuyn tip, AF1, AF2, AF3 v AF4. Vi mi lp AF, cc gi tin sau khi c nh du c a vo 3 lp con vi 3 mc u tin loi b gi tin, mi lp AF c gn mt lng bng thng v khng gian b m nht nh, nh vy chng ta c tng cng 12 lp con AF. Bng 2-3 hin th 4 lp AF v 12 lp con AF v cc gi tr ca trng DSCP tng ng vi 12 lp con c a ra trong RFC 2597. Lp PHB AF4 Gi tr DSCP 100010 (34) 100100 (36) 100110 (38) AF3 011010 (26) 011100 (28) 011100 (30) AF2 010010 (18) 010100 (20) 010110 (22) AF1 001010 (10) 001100 (12) 001110 (14) EF 101110 (46) Bng 2-3: Cc lp PHB v cc gi tr DSCP tng ng Mt mc dch v c nh ngha khi s dng cc lp AF, s lng v cht lng khc nhau gia cc lp AF c th thy r bi s lng bng thng v khng gian b m khc nhau trong 4 lp AF. Khng ging nh EF, hu ht cc lu lng AF l cc lu lng khng phi l thi gian thc, s dng giao thc TCP v k thut hng i RED ph hp s dng cho AF PHB. 4 lp ca AF PHB c th thc thi nh 4 hng i. Bng thng cng u ra c chia cho 4 hng i AF. Vi mi hng i AF, cc gi tin c nh du bng 3 mu hoc 3 mc u tin loi b gi tin. IV. S kt hp gia m hnh tch hp dch v v phn bit dch v trong vn bo m cht lng dch v Lp con PHB AF41 AF42 AF43 AF31 AF32 AF33 AF21 AF22 AF23 AF11 AF12 AF13 u tin loi b gi Thp Trung bnh Cao Thp Trung bnh Cao Thp Trung bnh Cao Thp Trung bnh Cao

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tng c bn y l s dng c hai m hnh cung cp cht lng dch v t u cui n u cui m vn bo m cht lng dch v c thit lp. ng thi cho php tng kh nng m rng mng khi cn thit. V vy, trong phn ny s phn tch mt cch tng qut nguyn l hot ng ca hai m hnh bo m cht lng dch v; m hnh tch hp dch v v m hnh phn bit dch v, t chng ta p dng cc chnh sch, k thut bo m dch v qua hai m hnh khc nhau ny. C th, y p dng kin trc ca m hnh tch hp dch v (Intserv) truyn thng tin gia u cui n u cui thng qua mt hoc nhiu vng phn bit dch v (DiffServ). Cc Router hoc cc Host chy trong mng theo m hnh Intserv kt ni vi nhau qua cc vng phn bit dch v. Trong cc vng phn bit dch v, cc Router c thc thi vi cc PHB c th cung cp vic iu khin cc lu lng. Tng s lng ca lu lng t nhn vo trong vng DiffServ c th c hn ch bi mt chnh sch c th ti cc Router bin ca mng DiffServ. C hai cch tip cn cho vic kt ni mng Intserv vi mng DiffServ:

Ti nguyn trong vng DiffServ s dng giao thc bo hiu RSVP Ti nguyn trong vng DiffServ khng s dng giao thc bo hiu RSVP

Hnh 2-16 l mt v d minh ha cho m hnh kt hp gia hai m hnh bo m cht lng dch v.

Hnh 2-16: M hnh kt hp gia hai m hnh Interv v Differv M hnh ny bao gm hai mng Intranet c s dng giao thc RSVP c kt ni vi nhau qua cc vng DiffServ. Trong cc mng Intranet trn, cc my trm s dng RSVP truyn cc thng s yu cu QoS vi my trm mng Intranet khc chy cc ng dng yu cu QoS.

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Cc mng Intranet bao gm cc Router bin R1 v R4, chng kt ni ti vng Diffser qua interface. Chng c kt ni vi cc Router bin R2 v R3 ca vng DiffServ. Giao thc bo hiu RSVP c thit lp bi cc ng dng yu cu dch v trn cc my trm (v d, host A). Vic iu khin lu lng trn my trm c th c thc thi bng cch nh du trng DSCP trong cc gi tin c truyn i v nh hng lu lng c truyn i da trn cc yu cu QoS trong mng Intserv. Thng ip bo hiu RSVP t u cui ti u cui c thay i gia cc my trm trong cc mng Intranet. Do , vic d tr ti nguyn c thc thi hon ton bn ngoi vng DiffServ. Cc Router bin hot ng nh cc tc nhn (agent) iu khin u vo ca mng DiffServ. Chng x l cc thng ip bo hiu t cc my trm trong c hai mng intranet v p dng chnh sch iu khin u vo. iu khin u vo c thc thi da trn cc ngun ti nguyn kh dng trong vng DiffServ. N ch c nh ngha trong cc chnh sch ca cc cng ty, t chc s dng mng Intranet. V cc Router bin R2 v R3 khng quan tm n giao thc RSVP. Cc Router ny iu khin v chp nhn cc gi tin da trn trng DSCP v s tha thun iu khin ton b lu lng ca cc my trm truyn qua. Mng DiffServ h tr vic iu khin ton b cc lu lng v gi s chng s dng k thut phn loi a trng MF. Do , bt k thng ip RSVP no cng s i qua vng mng DiffServ mt cch trong sut m nh hng n hiu nng ca mng DiffServ khng ng k. Cng vic tip theo l vic nh x cc kiu dch v v thit lp cc tham s (cc tham s m t lung lu lng) trong mng Intserv ti mng DiffServ. Mng DiffServ s dng k thut hnh vi tng bc PHB hoc thit lp cc PHB, mt nh x ca cc gi tr tham s m t lung lu lng trong mng Intserv c nh ngha ph hp vi iu c a ra trc . Gi tr nh x l mt bt kt hp trong trng DSCP. Tuy nhin, nh x ny c cn nhc qua vic qun l bng thng trong mng DiffServ. Cc Router trong mng DiffServ u bit gi tr DSCP. Cu hi t ra l lm th no cc gi tr DSCP s c truyn b n cc Router ny? C hai la chn:

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Cc gi tr DSCP c th c nh du ti Router bin ca vng DiffServ. Trong trng hp ny, chng c th c nh du li ti Router bin u ra ca vng DiffServ. nh du DSCP c th xy ra trong mt my trm hoc mt Router trong mng Intranet. Trong trng hp ny, vic nh x gi tr DSCP t Router bin mng Intranet ti mng DiffServ l cn thit truyn thng gia cc thit b ca hai mng khc nhau ny.

Di y l cc bc ch cho chng ta thy lm th no cc ng dng t c s h tr QoS t u cui n u cui:1) Trm A, kt ni vo mng Intranet, yu cu mt dch v t my trm B nm

mt mng Intranet khc. C hai mng Intranet ny kt ni vi nhau qua mng DiffServ. 2) My trm A, pht ra thng ip PATH RSVP, m t cc lu lng mong mun ca ng dng c yu cu gi i. 3) Thng ip PATH c gi qua mng Intranet ti R1. Cc thit b mng trong mng intranet nhn c v thc hin x l.4) Trng thi thng ip PATH c nh ngha ti Router R1, v c truyn

ti Router R2 trong mng DiffServ.5) Thng ip PATH b l i trong mng DiffServ ti Router R2 v R3. N

c gi n R4 trong mng Intranet v ti my trm B. 6) Khi my trm B nhn c thng ip PATH, mt thng ip RESV RSVP c to ra, cho bit lng ti nguyn p ng cho cc kiu lu lng . 7) Thng ip RESV c gi ngc li n mng Differv.8) Thng ip c truyn i mt cch trong sut qua mng DiffServ ti

Router R1.9) Ti R1, thng ip RESV bt u qu trnh x l iu khin u vo. C

ngha l cc yu cu ti nguyn trong yu cu RSVP ban u c so snh vi ti nguyn kh dng trn mng DiffServ ti mc dch v tng ng trong mng DiffServ. Mc dch v tng ng ny c xc nh bi chc nng nh x t mng Intserv ti DiffServ. Ti nguyn kh dng c xc nh thng qua SLA gia hai mng.

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Nu R1 chp nhn yu cu, thng ip RESV c chp nhn v cho

php gi ti my gi, my trm A. R1 cp nht bng nh tuyn ca n cng vi vic gim dung lng vn c trn Interface c lin quan khi chp nhn mc dch v yu cu.11)

Nu thng ip RESV khng b loi b bi bt k mt node thit lp

RSVP trc trn mng Intranet, th n s c nhn li ti my trm A.

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Chng 3 Cc k thut bo m cht lng dch v trong mng IPI. Phn loi gi tin Packet Classification

Phn loi gi tin l phng php c s dng nhm cc gi tin IP li vi nhau theo lp dch v. im bt u vic phn lp lu lng c th t ti thit b u cui. Trong mng, cc gi tin c la chn da trn cc trng phn header ca gi tin IP, cc trng ny cng c s dng cho vic nh du gi tin nh: Giao din u vo, IP Precedence, im m dch v khc bit (Differentiated Services Code Point), a ch ngun hoc a ch ch v cc ng dng. C hai kiu phn loi gi tin:

Phn loi a trng (Multi Field classification) MF Phn loi a trng (Multi Field classification) MF

Phn loi kt hp hnh vi (Behavior Aggregate classification) BA 1. Phng php phn loi a trng hot ng nh hnh 3-1. Trong phng php phn loi a trng, cc gn tin c phn loi da trn t hp cc gi tr ca mt hoc nhiu trng trong phn Header ca gi tin IP. Thm vo trng Header ca gi tin cc tham s khc nh nhn dng giao din nh ngha u vo, tham s ny c s dng tt cho mc ch phn loi gi tin.a ch ngun a ch ch Trng DS Nhn dng giao thc Cng ngun/ch Giao din u vo ng dng

(MF Classifier)

Phn lp a trng

Cc lp gi tin

Hnh 3-1: Phn loi a trng MF 2. Phn loi kt hp hnh vi (Behavior Aggregate classification) BA Phng php phn loi kt hp hnh vi thc hin vic phn loi gi tin ch da trn trng cha gi tr im m dch v phn bit (DiffServ Code Point - DSCP). Hnh 3-2 m t hot ng ca phng php phn loi gi tin kt hp hnh viBA

Cc gi tin i vo

Phn lp kt hp hnh vi(BA Classifier) (BA Classifier)

DSCP 1 DSCP 2 DSCP 3 .

Hnh 3-2: Phn loi kt hp hnh vi BA SVTH: H c Lnh - 47133042 43

n tt nghip i hc II.nh du gi tin Marking


nh du gi tin l phng php thit lp gi tr bt nh phn thch hp vo cc trng c bit trong phn Header ca gi tin IP phn bit kiu ca gi tin IP vi cc gi tin IP khc. V d, mt gi tin IP c th phn bit vi gi tin IP khc qua a ch ngun, a ch ch, hoc kt hp c hai. V d khc, thit lp gi tr c bit cho im m dch v (DSCP) ca trng IP Precedence ca gi tin. Cc gi tin IP i n cng u vo ca mt Router c th c nh du li hoc khng . Nu cc gi tin c nh du, nhng cc gi tr c nh du khng hp l vi chnh sch c thit lp trong Router ang thc hin chuyn gi th cc gi tin c th c nh du li. Nu gi tin chuyn qua nhiu vng dch v phn bit, cc gi tin s c nh du theo cch ph hp vi cc mc tha thun dch v (SLA - Service Level Agrrement) gia cc vng. Nu gi tin i vo Router m cha c nh du, n c th c nh du nhn gi tr thch hp vi chnh sch ca Router. Vic nh du gi tin c s dng thit lp cc gi tr trong phn Header ca gi tin IP ti tng lin kit d liu v tng mng trong m hnh OSI. Tng lin kt d liu Trng lp dch v (CoS - Class of Service) c s thit lp 8 gi tr nh phn khc nhau. Trng CoS l mt trng nm trong header ca ng trunk trong ISL v 802.1Q. Chuyn mch nhn a giao thc (MPLS Multi Protocol Lable Switching) s dng trng EXP mang 3 bt u tin, 3 bt ny dng nh x IP Precedence vo mt nhn MPLS. Frame Relay s dng bit DE nh du gi tin, v ATM dng bt CLP nh du gi tin. Tng mng S dng 3 bt u tin trong trng loi dch v (Service Type) trong phn Header ca gi tin IPv4. 3 bt ny c gi l trng IP Precedence v c gi tr mc nh l 0. Trng IP Precedence c gi tr bng 0 c ngha l cc gi tin s c truyn i theo kiu khng c cam kt cht lng dch v. im m phn bit dch v s dng 6 bt cao nht trong trng ToS nh du.

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1. Lp dch v - Class of Service (CoS)

Cc Router v Switch hin ny c th nh du v tc ng ln trng 3 bt ca cc gi tin IP khi c chuyn xung tng 2 (Tng lin kt d liu trong m hnh OSI) , trng 3 bt gi l CoS, nm bn trong Header Ethernet. Trng CoS ch tn ti bn trong khung Ethernet khi cc ng trunk 802.1Q v ISL (Inter-Switch Link) c s dng. Chng ta c th s dng trng CoS thit lp 8 gi tr nh phn khc nhau nh du gi tin ging nh IP Precedence v DSCP trong Header ca gi tin IP nhm mc ch b phn loi gi tin c th phn loi cc gi tin khc nhau vo cc nhm khc nhau thc hin cc k thut QoS. Thc t CoS c hai trng khc nhau; mt trng bn trong ng Header ca ng trunk 802.1Q (Chun IEEE 802.1Q dng 3 bt u trong 2 byte ca trng tag control) v mt trng Header ISL (ISL l giao thc c quyn ca Cisco- dng 3 bt cui t 1 byte ca trng User).

Hnh 3-3: Trng CoS trong ISL Header

Hnh 3-4: Trng CoS trong 802.1Q Header Nh vy CoS c th c nh du v c dng phn loi khi:

Th nht, khi chng ta mun p dng QoS cho mng ring o VLAN, ng trunk phi c thit lp v chng ta ng gi tin IP theo kiu 802.1Q hoc ISL. Th hai, gi tin phi c chuyn i t tng 3 (Tng mng), thit b chuyn dng thc hin vic ny l Router (hoc Switch layer 3) v Switch.

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Hnh di y cho chng ta thy 8 gi tr CoS khc nhau, mi gi tr tng ng vi mt kiu ng dng hoc mc ch s dng khc nhau, trong CoS c hai gi tr 6 v 7 c dnh ring cho vic qun l lu lng v nh tuyn d liu. CoS 7 6 5 4 3 2 1 0 Mc ch s dng hoc cc ng dng Dnh ring cho vic qun l ti nguyn v nh tuyn (Reserved for management traffic and routing data) Dnh ring cho vic qun l ti nguyn v nh tuyn (Reserved for management traffic and routing data) Voice Video Tn hiu cuc gi (Call signaling) u tin d liu cao (High priority data) u tin d liu va (medium priority data) Khng u tin d liu n lc ti a (Best effort data) Bng 3-1: Gi tr trng CoS v ng dng

2. IP Precedence v kiu dch v - Type of Service Trng IP Precedence l 3 bt u tin v ToS l 4 bt k tip sau trng IP Precedence trong trng Service type trong Header ca gi tin IP.

Hnh 3-5: Header ca gi tin IPv4 v trng kiu dch v Nh vy, vi 3 bt ca trng IP Precedence chng ta c 8 gi tr khc nhau tng ng vi 8 mc u tin khc nhau i vi cc gi tin IP, da trn mc u tin cc b nh tuyn a ra cc quyt nh chuyn tip cc gi tin qua mng. IP Precedence ngha iu khin mng (Network control) iu khin mng tng tc (Internetwork control) Ti hn, ti a (Critical) Truyn cc nhanh cho php ghi (Flash override) Truyn nhanh (Flash) Ngay lp tc tc thi (Immediate) u tin (Priority) (Gi tr u tin) 7 (111) 6 (110) 5 (101) 4 (100) 3 (011) 2 (010) 1 (001)

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Bnh thng (Routine) Bng 3-2: Gi tr trng IP Precedence v ngha

Da trn bng 3-2 chng ta thy, th t u tin cao nht c gn cho cc gi tin c gi tr u tin l 6 v 7 c s dng iu khin mng (giao thc nh tuyn), iu ny nhm mc ch m bo cc gi lin quan ti iu khin v ti cu hnh mng lun c c hi chuyn qua mng cao nht, ngay c trong nhng trng hp tc nghn cc b xy ra. Cc gi c th t u tin thp nht l cc gi s c loi b khi c hin tng tc nghn xy ra. Cng vi trng IP Precedence, trng ToS xc nh th t u tin theo mc tiu cht lng dch v tng ng vi: thng lng (Throughput), tr (Delay) hoc tin cy (Reliability). ToS 8 (1000) 4 (0100) 2 (0010) 1 (0001) 0 (0000) ngha tr thp nht (Minimize delay) Thng lng cao nht (Maximize throughput) tin cy cao nht (Maximize relibility) Chi ph thp nht (Minimize Monetary cost) Dch v bnh thng (Normal service) Bng 3-3: Gi tr trng ToS v ngha

3. im m phn bit dch v - DiffServ Code Points (DSCP)

Khi chng ta thit lp cho Router hot ng theo m hnh phn bit dch v th 8 bt trng kiu dch v (khng phi trng ToS 4bits) trong Header ca gi tin IPv4 v trng lp lu lng (TC Traffic class) trong Header ca gi tin IPv6 c thay th bi trng phn bit (DS - DiffServ) nh du gi tin. Trng DS c 8 bt, 6 bt u c s dng nh du phn bit cc gi tin c gi l trng im m dch v (DS Code Point DSCP) v 2 bt cui cng dng d phng trong tng lai.

Hnh 3-6: im m phn bit dch v - DSCP

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6 bt trng DSCP cung cp 64 gi tr DSCP khc nhau. RFC 2474 chia 64 gi tr ca DSCP ny thnh 3 khi c gi l cc pool. Pool im m DSCP ng dng 1 xxxxx0 Tiu chun (Standard action) 2 xxxx11 Th nghim/ni b (Experimental/Local user) 3 xxxx01 Th nghim/ni b (Experimental/Local user) Bng 3-4: Cc gi tr DSCP tng ng vi 3 pool v ng dng ca chng Pool 1 gm cc im m DSCP c s dng cho ton cu, pool 2 c s dng cho mc ch th nghim v cc b. Cc gi tin DiffServ trong mng Intranet ring c th nh u trng DSCP thuc pool 2. Trng DSCP thuc pool 2 ch c ngha cc b trong mng Intranet v khng c chp nhn ngoi vng Intranet. Bt cui cng ca DSCP thuc pool 1 l 0, cc gi tr cn li l ty (c th l 1 hoc 0). Do , trng DSCP thuc pool 1 c s lp dch v ln ti 32. Trong khi , hai bt cui cng ca trng DSCP ca pool 2 v 3 ln lt l 11 v 10 do s lp dch v c th h tr l 16. Trng DSCP thuc pool 3 c ngha tng t nh trng DSCP pool 2, tuy nhin c s khc bit l trng DSCP thuc pool 3 c th a ln s dng ton cu, nu cn thit. h tr cc Router truyn thng ch s dng trng kiu dch v trong gi tin IPv4, 8 gi tr DSCP ca pool 1 c ch nh l trng IP Precedence xem bng 3-5. 8 gi tr DSCP ca pool 1 ny c s dng cho mc ch trn c xem nh l lp chn lc cc im m (Class Selector Code Point - CSCP). 3 bt cui ca CSCP lun mang gi tr 000. Do , CSCP c dng xxx000. Gi tr mc nh ca DSCP l 000000, vi gi tr ny cc dch v c i x nh nhau, khng c tnh u tin v n thuc dch v n lc ti a Best Effort. Gi tr u tin Gi tr im m phn ngha (IP Precedence) bit (DSCP) 0 - (000) 0 (000000) 1 (001) 2 (010) 3 (011) 4 (100) 5 (101) 6 (110) 7 (111) 8 (001000) CS1 16 (010000) CS2 24 (011000) CS3 32 (100000) CS4 40 (101000) CS5 48 (110000) CS6 56 (111000) CS7 Gi tr mc nh, khng c tnh u tin gi tin u tin Ngay lp tc Truyn nhanh Truyn rt nhanh, cho php ghi Ti a, ti hn iu khin mng tng tc Internet iu khin mng - network

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Bng 3-5: Gi tr IP Precedence v gi tr DSCP tng ng III. Lp lch gi tin Packet Scheduler Lp lch cc gi tin IP th hin cch thc thit lp th t cc gi tin i ra khi cc hng i, da trn cc c tnh ca cc cng u ra, cc gi tin s c phn b v chuyn ti cng u ra theo lut thit lp trong cc k thut lp lch cho cc gi tin. K thut lp lch l mu cht trung tm ca cht lng dch v v cng l thc o cng ngh gia cc nh cung cp thit b mng. Cc gi tin n ti cc cng u vo c ch tuyn da vo bng nh tuyn trn Router ti cc cng u ra v ti ch. Ti mi cng u ra, cc gi c phn loi v xp hng i ra. Mt s kiu hng i lp lch thng s dng gm: Hng i vo trc ra trc (First In First Out), hng i u tin (Priority Queuing), hng i cn bng (Fair Queuing), hng i quay vng theo trng s (Weight Round Robin), hng i cn bng theo trng s (Weight Fair Queuing), v hng i cn bng trng s theo lp (Class based WFQ).1. Hng i vo trc ra trc FIFO (First in, First out)

Hng i FIFO l k thut hng i mc nh trong cc b nh tuyn, cc gi tin sau khi c phn loi c a vo trong mt hng i n v cc gi tin c gi ra u ra theo ng th t m cc gi tin i vo.

Lung d liu i vo

Phn loi gi tin

Hng i FIFO

Cng ra

B lp lch

IP Router

Hnh 3-7: Hng i FIFO Do , cc gi tin n trc s c ph v trc, hng i FIFO c xem nh hng i vo trc phc v trc (First come, First served - FCFS). Hng i FIFO mc nh c bt ln trn tt c cc Interface v c bng thng mc nh ln hn 2 Mbps. u im chnh ca hng i FIFO l hng i n gin, khng cn s dng thut ton iu khin. N ch l mt b m n gin, c th lu tr cc gi tin i vo v gi cc gi tin i ra theo th t m chng i vo. FIFO i x vi tt c cc gi tin

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theo cng mt cch, v vy n thch hp vi m hnh mng Best - Effort (m hnh mng n lu ti a). Nhc im chnh ca hng i FIFO l khng phn bit c cc lp lu lng. Do , n khng th cung cp cc c ch i x ring cho cc lu lng khc nhau, tt c cc lung lu lng s b suy gim cht lng khi tc nghn xy ra. 2. Hng i u tin PQ (Priority queuing) Hng i FIFO a tt c cc gi tin vo trong mt hng i n, khng phn bit cc lp lu lng. Hng i u tin c a ra nhm khc phc nhc im ca hng i FIFO. Trong hng i PQ, c N hng i c to ra theo u tin t 1 n N. Th t lp lch c xc nh bi th t u tin v khng ph thuc vo v tr ca gi tin. Cc gi tin trong hng i th i c x l khi khng cn gi tin no trong hng i th i-1.Lung d liu i voHng i PQ1 Hng i PQ2

Hng i PQ3

Cng ra

Phn loi gi tin

Hng i PQ N

IP Router

Hnh 3-8: Hng i u tin PQ Ging nh hng i FIFO, hng i PQ c u im chnh l rt n gin; n a ra phng php n gin phn bit cc lp lu lng. Nhc im chnh ca hng i PQ l lun hng ti x l hng i c u tin cao hn trc, do cc hng i c u tin thp hn c th khng c c hi c x l. V vy phi quan tm v lu khi chng ta p dng hng i PQ trong cc b nh tuyn. Trong b nh tuyn ca Cisco, Hng i PQ c th phn loi cc gi tin vo mt trong 4 kiu hng i: hng i mc cao (High queue), hng i mc va (Medium queue), hng i mc bnh thng (Normal queue) v hng i mc thp (Low queue). B lp lch thc hin vic lp lch cc lu lng theo mc hng i. Mi lp lu lng s dng mt hng i FIFO, v vy cc gi tin b loi b nu mt hng i b y. 3. Hng i cn bng FQ (Fair queuing)

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Hng i cn bng cn c gi l hng i da trn lung lu lng. Trong FQ, cc gi tin n c phn loi thnh N hng i. Mi hng i nhn 1/N bng thng kh dng u ra. B lp lch kin tra cc hng i theo chu k v b qua cc hng i rng. Mi khi b lp lch ti mt hng i, mt gi tin c truyn ra khi hng i. Hng i cn bng rt n gin, n khng yu cu mt k thut ch nh bng thng phc tp no. Nu mt hng i mi c thm vo N hng i c trc to mt lp lu lng mi, b lp lch s t ng t li bng thng ca mi hng i bng 1/(N+1). n gin chnh l u im chnh ca hng i cn bng.Lung d liu i voHng i 1

Vng trn th t (Round Robin order)

Hng i 2

Hng i 3

Cng ra

Phn loi gi tin

Hng i N

B lp lch

IP Router

Hnh 3-9: Hng i cn bng FQ Hng i cn bng c hai nhc im chnh: Th nht, khi bng thng u ra c chia thnh N hng i th tng ng mi hng i s c bng thng l 1/N, nu cc lp lu lng u vo c yu cu bng thng khc nhau, th FQ khng th phn b li bng thng u ra theo yu cu bng thng ca cc lp lu lng u vo. Th hai, kch thc gi tin khng c quan tm trong FQ, trong khi , kch thc cc gi tin li nh hng n s phn b bng thng thc t, thm ch b lp lch vn hot ng theo nguyn tc cn bng (mi hng i s c 1/N bng thng, b lp lch s kim tra theo chu k n tng hng i, mt gi tin s c truyn i khi b lp lch ti thm). V d, nu mt hng i no chim d cc gi tin c kch thc ln hn cc hng i khc, th hng i ny phi c bng thng u ra ln hn bng thng u ra ca cc hng i khc (1/N). Gi s mt hng i FQ c 4 hng i tng ng vi 4 lung lu lng 1, 2, 3, v 4. Kch thc trung bnh ca cc gi tin ca 4 lung lu lng tng ng l 200, 100, 400 v 300 byte, theo th t, bng thng chia s ca cc cng u ra tng ng vi 4 lung ny s l; Lung 1 = 200/1,000 = 20%; Lung 2 = 100/1,000 = 10%; Lung 3 = 400/1,000 = 40%; Lung 4 = 300/1,000 = 30 %;

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4. Hng i xoay vng theo trng s - WRR (Weighted Round Robin)

Hng i xoay vng theo trng s WRR c a ra nhm gii quyt nhc im th nht ca hng i cn bng FQ. WRR chia bng thng cng u ra ca cc lp lu lng u vo ph hp vi bng thng yu cu. Nguyn l hot ng ca WRR theo hnh 3-10. Cc lu lng i vo c nhm thnh n lp v bng thng cng u ra c phn b cho n lp ny theo trng s thch hp c xc nh bi bng thng yu cu cho n lp ny. Tng trng s ca cc lp phi bng 100%.m

Wi =1

i

= 100%

Trong : m l s lp lu lng, Wi l % trng s ca lp i. Vi mi mt lp lu lng, cc lung lu lng ring c lp lch theo nguyn tc hng i cn bng FQ. t s lng hng i FQ trong lp i l Ni, tng s hng i FQ trong lc WRR c tnh theo cng thc:

Trong , m l tng s lp lu lng ca cc lp.S lng hng i FQLp 1

Vng trn th t (Round Robin order)

Lung d liu i vo

N1

W1Lp i Cng ra

Phn loi gi tin

Ni

WiLp nB lp lch

Nn

Wn

IP Router

Hnh 3-10: Hng i xoay vng trng s WRR Nh hnh trn, hng i xoay vng theo trng s WRR gm hai lp lp lch quay vng.

Lp th nht, cc lp t 1 n n c thm bi b lp lch theo vng th t. Lp th hai, cc hng i trong mt lp c b lp lch thm theo th t vng khi b lp lch dng li ti mt lp.

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Bng thng cng u ra tnh theo % c gn bi lp i, trng s lp i (Wi) th hin lng thi gian tiu tn ca b lp lch cho lp i. V d, Wi = 20% c ngha l b lp lch s tiu tn 20% chu k thi gian quay vng cho lp i. Vi cc hng i FQ trong lp i, thi gian cho cc hng i l cn bng, v vy lng thi gian cho mt hng i trong Ni hng i l 1/Ni. Trng s cho mi hng i FQ c tnh nh sau:

Trong , Wij l trng s hng i j trong lp i, Wi l trng s ca lp i, Ni l s hng i FQ trong lp i. T cng thc trn chng ta c th vit li thnh: Wi = Wij x Ni hay:Wi = Wijj=1 Ni

Trng s ca lp i (Wi) s c tnh bng tng cc yu cu lu lng trong lp i. WRR s dng Wi thay cho 1/n nh trong trng hp s dng hng i FQ, to n lp lu lng vi cc yu cu bng thng cng u ra khc nhau. y chnh l bc ci thin ca WRR so vi FQ nhm trnh c nhc im th nht ca hng i FQ. V d (xem hnh 3-11di y)

Hnh 3-11: V d v k thut phn lung lu lng ca WRR WRR c 2 lp, Class 1 v Class 2. Tng bng thng cng u ra l 200 Mb/s. trong , 40% bng thng cho cng u ra ca Class 1trong tng bng thng u ra v 60% bng thng cho cng u ra ca Class 2. Class 1 c 2 lung, Class 2 c 8 lung. Gi s cc lung ny c cng kch thc gi tin. Bng thng cng u ra u ra ca cc lp c xc nh nh sau: Class 1: 80 mb/s. Mi lung c 40 mb/s (Class 1 c 2 lung) Class 2: 120 mb/s. Mi lung c 15 mb/s (Class 2 c 8 lung)

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Gi s cc lung c kch thc gi tin ln lt nh sau: 100, 400, 100, 200, 300, 500, 400, 200, 100 v 200 byte. Bng thng u ra cho mi lung trong tng s 10 lung c xc nh nh sau: Lung 1 = 20% x (100/500) = 4% Lung 3 = 80% x (100/2000) = 4% Lung 5 = 80% x (300/2000) = 12% Lung 7 = 80% x (400/2000) = 16% Lung 9 = 80% x (100/2000) = 4% Lung 2 = 20% x (400/500) = 16% Lung 4 = 80% x (200/2000) = 8% Lung 6 = 80% x (500/2000) = 20% Lung 8 = 80% x (200/2000) = 8% Lung 4 = 80% x (200/2000) = 8%

5. Hng i cn bng trng s - WFQ (Weight Fair Queuing) Mc d hng i xoay vng trng s WRR khc phc c nhc im th nht ca hng i FQ, nhng WRR cha gii quyt c s nh hng ca kch thc gi tin i vi bng thng chia s, bi v WRR s dng hng i FQ trong cc lp. Hng i cn bng trng s WFQ c a ra nhm gii quyt nhc im th hai ca hng i FQ. Trong WFQ, ging nh trong hng i FQ, cc lung lu lng u vo c nhm vo m hng i (WFQ phn loi gi tin da trn cc lung. Mi lung bao gm tt c cc gi tin c cng a ch ngun, a ch ch, v cng cng ngun v cng ch). Tuy nhin, bng thng cng u ra c phn b ti m hng i theo trng s c xc nh bi cc yu cu bng thng ca m lp lu lng thay v chia u v trng s phi bng 100%:

Trong , m l s lp lu lng trong WFQ v Wi l phn trm trng s ca lp i. Trong FQ, mi hng i gi i mt gi tin khi b lp lch gh thm. Trong WFQ, b lp lch gi i cc gi tin t cc hng i da trn vic tnh ton thi gian kt thc ca cc gi tin. Hng i WFQ nn c bt trn Interface nu bng thng trn cc Interface nh hn 2 Mbps. Bng 3-6 l cc gi tr u tin IP c nh x tng tng vi trng s ca chng khi cu hnh.

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Bng 3-6: Gi tr IP Precedence v gi tr trng s ca hng i WFQ6. Hng i cn bng trng s phn lp CB WFQ (Class-Base WFQ)

Hng i cn bng trng s phn lp CB WFQ tng t nh hng i quay vng theo trng s WRR. Trong CB WFQ, ging vi WRR, Cc lu lng i vo c nhm thnh m lp v bng thng cng u ra c phn b cho m lp ny theo trng s thch hp c xc nh bi bng thng yu cu cho m lp ny. Tng trng s ca cc lp phi bng 100%. Ti im ny, CB WFQ v WRR l nh nhau. im khc bit ca CB WFQ so vi WRR l cch s dng c ch hng i cn bng theo trng s WFQ ti cc lp i thay v s dng c ch hng i cn bng FQ.IV. Vn tc nghn, phng php qun l v trnh tc nghn trong mng IP 1. Vn tc nghn Congestion

Tc nghn c th xut hin nhiu v tr khc nhau trong mng v l kt qu ca mt s nguyn nhn sau: Thi gian ch x l, cc gi tin xp hng trong hng i qu ln. Nu cc lung gi tin t ngt i vo t nhiu Interface v tt c u mun i ra cng mt ng nn hng i s b y (do phi lu gi tin v chuyn tip gi tin ). Nu kh nng x l ca cc nt mng yu hay ni cch khc CPU ti cc Router x l chm cc yu cu s dn n tc nghn. Kch thc b m ca hng i qu nh. Nu b m khng dung lng lu cc lung gi tin th mt s gi tin s b mt. Vic tng dung lng b nh m ln c l s c ch, nhng Nagle cho rng nu cc Router c lng b nh khng xc nh th s tc nghn chng tt hn t no m ngc li tr ln xu i do s bn sao c gi tng ln, lm tng lu lng thng tin ni nhn gi tin. tr ln, tn sut li mng cao v s chnh lch v bng thng gia cc lin kt (v d: bng thng lin kt ca mng LAN cao hn bng thng lin kt mng WAN)

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lm tng s lng gi tin ti cc interface u vo ca cc router bin trong mng WAN lm cho kh nng tc nghn trong mng tng ln, v cng ng ngha vi vic s lng gi tin b loi b cng tng ln nu cc Router bin khng c c ch hnh x hp l. 2. Qun l tc nghn Congestion management Qun l tc nghn l mt gii hn tng qut, n bao gm cc k thut hng i khc nhau c s dng qun l bng thng yu cu ca cc ng dng mng, bng thng ca cc ng dng mng ny vt qu tng bng thng m n c th cung cp cho mng. Qun l tc nghn khng iu khin tc nghn trc khi n xy ra m n ch kim sot tc nghn ang tn ti v x l tc nghn tc nghn khng xy ra khi cc lung lu lng mi i vo. Cc thut ton hng i c s dng sp xp lu lng, xc nh u tin ca cc lu lng v a chng ra ng lin kt u ra. Cc k thut qun l tc nghn ch yu l cc k thut hng i nh: Hng i vo trc ra trc FIFO, hng i u tin PQ, hng i ty bin CQ, hng i cn bng trng s WFQ, hng i cn bng trng s theo lp CB WFQ v hng i LLQ. K thut x l gi tin ca cc hng i FIFO, PQ, WFW v CB WFQ c trnh by ti mc III ca chng 3 ca bn n, di y ch trnh by tnh nng ca cc hng i ny trong vai tr qun l tc nghn v u, nhc im ca chng trong vn n qun l tc nghn. Ngoi ra, cc hng i: CQ v LLQ cng c dng qun l tc nghn cng s c trnh by di y.2.1. Hng i vo trc ra trc FIFO

FIFO l k thut hng i mc nh trn hu ht cc Interface trn thit b Router ca Cisco (ch c cu hnh trn cc Interface Serial c bng thng ln hn 2 Mbps). FIFO khng h tr bt k s u tin no cho cc gi tin i vo. Bt k lu lng no i vo b m trc th c truyn i ra Interface trc. Khi s lng lu lng i vo t interface tng ln th n c th lm cho hng i FIFO b y, khi hng i s thc hin ct bt phn ui khi cc lu lng tip tc i vo cho n khi n x l cc gi tin trc v khng gian b m n nhn cc gi tin mi i vo. Kiu hng i ny c hiu qu cao v ph hp cho cc ng lin kt c dung lng cao, chng s khng c nhiu tr hoc tc nghn khi s dng hng i FIFO. FIFO lu tr cc gi tin khi mng b tc nghn v chuyn tip chng theo th t chng i

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