63963435 48467914 Quality of Services Chat Luong Dich Vu Mang IP

8/3/2019 63963435 48467914 Quality of Services Chat Luong Dich Vu Mang IP

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n tt nghip i hc Tm hiu QoS trong mng IP v ng dng

MC LC3.2.Loi b gi tin sm theo trng s WRED ..................................................62

5.5.4.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 ...................................................................30Hnh 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 .................................57Hnh 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 ....73Hnh 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 .....................................................................................80

Hnh 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 6-4: 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 btxx vyyy 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 ..................................................................50Bng 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 Mintng 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 ........................................................................................94

Bng 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 1Khi 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 QoSCht 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 chx 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 hmm. 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 Cc vn khi khng c QoSVoice Voice nghe kh hiu

Voice khng lin tc, ting ni b moNgi gi khng bit ngi nhn kt thc cuc gi khi no

hay kt thc cha

Cuc gi khng kt ni cVideo Hnh nh hin th chp chn

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m thanh khng ng b vi videoS di chuyn ca hnh nh chm li

Data D liu c chuyn n khi n khng cn gi tr na.D liu phn hi khng ng so vi ban uThi gian truyn b gin on lm cho ngi dng tht

vng v t b hoc thc hin li dch vBng 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 QoS0 Thi gian thc, nhy cm vi jitter, tng tc cao1 Thi gian thc, nhy cm vi jitter, tng tc cao2 D liu chuyn tip, tng tc cao3 D liu chuyn tip, tng tc4 Tn hao thp5 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 dngny 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 QoSHi thoi thi gian

thc (thoi, video, hingh video)

Thoi, audio,

video, aphng tin

Nhy cm vi tr v jitter, c gii hn li

v tn tht gi, tc bt thay i v cnh

Lung thi gian thc

(qung b)

Audio, video,

a phng tin

Tr v jitter c sai s nht nh, sai s nh

i vi li v tn tht, tc bt thay iTng tc cn d liu

thi gian thc (trnh

duyt Web)

D liu Nhy cm vi tr, jitter v mt gi, tc

bt thay i

Phi thi gian thc

(Email)

D liu 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 qutrnh 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.- 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.

- 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 acc 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, nth 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).

Hnh 1-2: Cc khi chc nng bo m QoS trn cc b nh tuyn mng

III.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 vingi 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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Nhim v 1

Nhim v 2 Cc gitin i ra

Phn loigi tin

nh dugi tin

Chnh schlu lng

Qun lhng i

Lp lch gitin

nh hnglu lng

Cc gitin i vo


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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 cnghoc 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.

- 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 ura.

- 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 ngngha 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 phithay 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 gii 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.

SVTH: H c Lnh - 47133042 13


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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 ccgi 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 nay

Hin 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

SVTH: H c Lnh - 47133042 14


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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 tu 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.

Hnh 2-1: M hnh Best - Effort

SVTH: H c Lnh - 47133042 15

M hnhBest - Effort

Lu lng 1Lu lng 2Lu lng 3Lu lng 4Lu lng 5

Lung lu lng

IP

Tt c cc lunglu lng


16/112


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 bnhthng.

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 cchost 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 sc 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 cukhng 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.

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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 gimt 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 cholung . 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 titrong 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 dchv 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 tithng 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 ngctr 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 khinu 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 vic

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 nhn cc yu cu QoS c

xc nh trong trng FLOWSPEC.

Hnh 2-4 m t qu trnh x l d tr ti nguyn ca giao thc d tr ti nguyn

RSVP trn Router.

SVTH: H c Lnh - 47133042 22B phn loi

gi tin

B lp lch gitin

iu khin u

vo

Xc nhRouter vlp QoS

Xc nhRouter vlp QoS

Thng ip RESVThng ip RESV

FLOWSPECFLOWSPEC FILTERSPECFILTERSPEC

Chng thcng dng ?

Ti nguynnh tuyn?

Chnh sch iukhin

Data


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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 tinguyn 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 tmc 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 trcPhn 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 thnghi 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 nguynd 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 ipRSVP 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 trac 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 RSVPTrong :

- 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.

o 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 ipRSVP.

o 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.

o 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.

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o 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.

o 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 sca 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.

o 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.

o 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.

o 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 ctrong tt c cc thng ip ng i PATH.

o 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.

o 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.

o 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.

o 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.

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o 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.

o 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 sdng trong thng ip RESV v Resvconf.

- 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 tngKiu 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 iu khin chia s Bt yyy iu khin la chn my gi00 D phng 000 D phng01 Ti nguyn phn bit 001 La chn i din (Wildcard)10 Ti nguyn chia s 010 La chn hin

11 D phng 011-111 D phngBng 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 tngSENDER_TSPEC. Cu trc thng ip PATH c th hin di hnh 2-9:

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Hnh 2-9: Cu trc thng ip PATH

4.6. 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 vcho 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 tnglung. 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 lunglu 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 ccng 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 tinguyn 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:

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 DSRegion), 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).

SVTH: H c Lnh - 47133042 33

Cc gi tin cangi dng

DSCP1DSCP2DSCP3

Interface ca ngidng

SLA

B nh tuyn IP

Hng i PHB

Cng ra

Phn loigi tin -BA


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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 DSCc 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 leasedlines 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 tia. 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, ccgi 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 Lp con PHB u tin loi b gi Gi tr DSCP

AF4 AF41 Thp 100010 (34)AF42 Trung bnh 100100 (36)AF43 Cao 100110 (38)




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 lthi 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

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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 chngta 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 thcthi 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 ccgi 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 binmng 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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10) 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 lpRSVP trc trn mng Intranet, th n s c nhn li ti my trm A.

SVTH: H c Lnh - 47133042 42


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Chng 3

Cc k thut bo m cht lng dch v trong mng IP

I. 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 kt hp hnh vi (Behavior Aggregate classification) BA1. Phn loi a trng (Multi Field classification) MF

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.

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 vi

Hnh 3-2: Phn loi kt hp hnh vi BA

SVTH: H c Lnh - 47133042 43

Cc gi tin i vo

Phn lp kt hphnh vi

(BA Classifier)

Phn lp kt hphnh vi

(BA Classifier)

DSCP 1DSCP 2DSCP 3

.

BA

a ch nguna ch chTrng DS

Nhn dng giao thcCng ngun/chGiao din u vong dng

Phn lpa trng

(MF Classifier)

Phn lpa trng

(MF Classifier)

Cc lpgi tin


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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 choim 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 liuTrng 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 nhdu 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.

SVTH: H c Lnh - 47133042 45
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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 Mc ch s dng hoc cc ng dng7 Dnh ring cho vic qun l ti nguyn v nh tuyn

(Reserved for management traffic and routing data)6 Dnh ring cho vic qun l ti nguyn v nh tuyn

(Reserved for management traffic and routing data)5 Voice4 Video3 Tn hiu cuc gi (Call signaling)2 u tin d liu cao (High priority data)1 u tin d liu va (medium priority data)

0 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

(Gi tr u tin)

ngha

7 (111) iu khin mng (Network control)6 (110) iu khin mng tng tc (Internetwork control)5 (101) Ti hn, ti a (Critical)4 (100) Truyn cc nhanh cho php ghi (Flash override)3 (011) Truyn nhanh (Flash)

2 (010) Ngay lp tc tc thi (Immediate)1 (001) u tin (Priority)

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0 (000) 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 ngha8 (1000) tr thp nht (Minimize delay)4 (0100) Thng lng cao nht (Maximize throughput)2 (0010) tin cy cao nht (Maximize relibility)1 (0001) Chi ph thp nht (Minimize Monetary cost)0 (0000) 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 dng1 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. Trongkhi , 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(IP Precedence)

Gi tr im m phnbit (DSCP)

ngha

0 - (000) 0 (000000) Gi tr mc nh, khng c tnh u tin

gi tin1 (001) 8 (001000) CS1 u tin2 (010) 16 (010000) CS2 Ngay lp tc3 (011) 24 (011000) CS3 Truyn nhanh4 (100) 32 (100000) CS4 Truyn rt nhanh, cho php ghi 5 (101) 40 (101000) CS5 Ti a, ti hn

6 (110) 48 (110000) CS6 iu khin mng tng tc Internet7 (111) 56 (111000) CS7 iu khin mng - network

SVTH: H c Lnh - 47133042 48


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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 v

63963435 48467914 Quality of Services Chat Luong Dich Vu Mang IP

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