bao cao qos - bui xuan duy - 11cth03 - 1111020290

8/13/2019 Bao Cao QoS - Bui Xuan Duy - 11CTH03 - 1111020290

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B GIO DC V O TO

I HC CNG NGH THNH PH H CH MINH

------------o0o-----------

KHOA CNG NGH THNG TIN

BO CO LAB PHN TCH NH GI MNG

Chuyn : PHN TCH NH GI MNG

GVHD: Nguyn Hong Nam

SVTH: Bi Xun Duy

MSSV: 1111020290

LP : 11CTH03

Tp.H Ch Minh, ngy 17 thng 11 nm 2013


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LI CM N

Li u tin em xin chn thnh cm n s hng dn ca thy Nguyn Hong Nam,khoa Cng Ngh Thng Tin trng H Cng Ngh TP.HCM.

Trong thi gian thc hin bo co thy lun gii p nhng thc mc ca em mt cchnhit tnh v y nht. Thy cho em rt nhiu hiu bit v lnh vc, gii phpmi khi em mi bt u thc hin bo co.

Cho n hm nay, bo co em hon thnh chnh l nh cng ch dy, n c vgip ca thy.

Em cng xin cm n cc thy c trong khoa Cng Ngh Thng Tin cng nh cc thyc trong trng ging dy, gip em c c nhng kin thc nn tng v nhnkin thc chuyn mn em c th hon thnh bo co ny.

Trong qu trnh thc hin bo co do cn thiu kinh nghim cng nh k nng chuynmn nn khng trnh khi nhng thiu st, mong cc thy c b qua.

Sinh vin thc hin

Bi Xun Duy


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MC LC

1> L Thuyt....................................................................................................................... 51.1 Tng Quan v QoS(Quality of Service)..................................................................... 5

1.1.1 Gii thiu............................................................................................................. 51.1.2 nh ngha QoS................................................................................................... 51.1.3 Cc tiu ch nh gi QoS................................................................................... 6

1.1.3.1 tr end to end/ Latency............................................................................ 61.1.3.2 Bin thin tr / Jitter ................................................................................. 61.1.3.3 Bng thng.................................................................................................... 71.1.3.4 mt gi..................................................................................................... 7

1.2 Phn lp lu lng..................................................................................................... 71.2.1 Phn lp lu lng mc lp mng................................................................... 71.2.2 Phn lp lu lng mc lp lin kt d liu.................................................... 9

1.3. Gii php QoS......................................................................................................... 111.3.1 M hnh dch v c gng ti a(Best-effort) ..................................................... 111.3.2 M hnh tch hp dch v(Integrated Services- IntServ) .................................. 11

1.3.2.1 Giao thc dnh trc ti nguyn(RSVP) .................................................... 12

1.3.2.2 Bn tin thng bo v xc nhn li(Error and confirmation message) ......... 131.3.2.3 Teardown Message ...................................................................................... 13

1.3.3 M hnh phn bit dch v(Difference Services- DiffServ) ............................. 141.3.3.1 Trng DS................................................................................................... 161.3.3.2 Chnh sch tng chn(Per- Hop Behaviour - PHB) ................................... 171.3.3.3 Cc thnh phn ca phn bit dch v......................................................... 18

1.3.4 S khc nhau gia m hnh IntServ v DiffServ .............................................. 19

1.4. Qun l tc nghn.................................................................................................... 191.4.1 Cc nguyn nhn gy tc nghn........................................................................ 201.4.2 Cc khi nim hng i..................................................................................... 20

1.4.2.1 Leaky bucket (thng b thng).................................................................... 201.4.2.2 Tail Drop (Ct ui).................................................................................... 211.4.2.3 Token bucket(thng ng th).................................................................... 211.4.2.4 First in First out Queue (Hng i FIFO) ................................................... 22

1.4.2.5 Priority Queue (Hng i u tin (PQ))...................................................... 231.4.2.6 Custom Queue (Hng i t chn (CQ)).................................................... 24


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1.4.2.7 Weighted Fair Queue (Hng i cn bng trng s(WFQ)) ...................... 251.4.3 Congestion Avoidance (trnh nghn mng)...................................................... 31

1.4.3.1 Random Early Detection (RED) ................................................................. 32

1.4.3.2 Weighted Random Early Detection(WRED) .............................................. 34

1.4.3.3 Explicit Congestion Notification (ECN) ..................................................... 38

1.5 Traffic Shaping (iu ha lu lng) v Traffic Policing (gim st lu lng) ..... 401.6 Link efficiency ...................................................................................................... 43

1.6.1 Nn d liu ti v IP Header .............................................................................. 431.6.2 Link Fragmentation and Interleaving ................................................................ 45

2> Thc hnh..................................................................................................................... 46

2.1 M hnh thc hnh................................................................................................... 462.2 Thc hin cu hnh................................................................................................... 462.3 Kt Lun................................................................................................................... 572.4 Ti liu tham kho.................................................................................................... 58


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1> L THUYT 1.1. Tng Quan v QoS (Quality of Service)

1.1.1. Gii thiu

Trc y, khi m internet ch yu l truyn data th ngi ta khng cnquan tm n vic phn bit v u tin cho cc gi tin bi v lc ny bng thngmng v cc ti nguyn khc cung cp cho cc ng dng trong mng, v vycc ISPs s cung cp cho khch hng ca h dch v Best Effort (BE) khi tt c cc khch hng s c i s nh nhau h ch khc nhau loi ktni. y l dch v ph bin trn mng Internet hay mng IP ni chung. Cc githng tin c truyn i theo nguyn tc n tr c c phc v trc m khng quan tm n c tnh lu lng ca dch v l g. iu nydn n rt kh h tr cc dch v i hi tr thp nh cc dch v thi gian thc hay video.Cho n thi im ny, a phn cc dch v ccung cp bi mng In ternet vn s dng nguyn tc B-E ny.

M hnh Best-effort: Trong m hnh Best-effort vic chuyn tip gi tin cthc hin theo th t chng nhn c v khng phn bit gia cc gi tin. Cc ntmng ch thc hin chuyn gi tin nhanh nht c th m khng c bt k s utin ring no. M hnh Best-effort l m hnh mng trong nhng nm 1990 v vn duy tr cho n ngy nay mng internet.

Nhng khi internet cng ngy cng pht trin v pht trin thm cc dchv HTTP, Voice, Video th iu ny s lm cho cht lng ca cc dchv ny gim i r rt v delay ln, jitter ln v khng bng thng truyn, phng n tng bng thng ca mng cng khng gii quyt c vn ny m li cn rt tn km.

Chnh v nhng l do trn m cc ISP tp trung trin khai vic qun l

lu lng v cc qu trnh QoS. 1.1.2. nh ngha QoS

QoS l thut ng c dng nh ngha kh nng cung cp cc cp khcnhau v s bo m dch v i vi nhiu loi lu lng ca mt mng.QoS l mtp cc k thut x l lu lng trong mng truyn s liu nhm m bo cc lolng c yu cu cht lng dch v khc nhau c i x u tin khc nhau.QoS cung cp cc u tin khc nhau i vi tng dng liu, ngi dng, ngdng khc nhau m bo mt mc hot ng n nh ca dng d liu.


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V d: trong mng IP c hai ng dng ph bin l truyn file FTP v dch v giin thoi IP telephony. ng dng IP telephony ni hi d liu phi c truynlin tc, tr thp , cn ng dng FTP th khng yu cu cao v tr, min ltruyn v chnh xc ni dung d liu. thc hin c yu cu ng dng IPTelephony hot ng c n nh cho d xy ra tranh chp ti nguyn khi 2 ngdng cng chy song song hot nghn mng th ta cn phi p dng cc k thut xl v phn loi lu lng v p dng cc chnh sch u tin khc nhau nhm m bo lu lng IP telephony phi c u tin ng truyn cao hn lu lngFTP.

QoS hot ng da trn cc bc c bn sau: Phn lp v dnh du Kim tra chnh sch nh tuyn a vo hng i hoc nh rt

1.1.3. Cc tiu ch nh gi QoS

Hiu qu ca cht lng dch v (QoS) c nh gi da vo cc thng s sau:

1.1.3.1. tr end to end/ Latency

L thi gian cn thit gi tin i t source n destination, trong sutvi cc node trung gian (tc l ta khng quan tm thi gian n ti cc nodetrung gian. Ta nn phn bit delayv latency. Delayl trong tr packet itnode ny n node kia trc tip. VD:nu gi i t node 1 n node 2 trc tipht 10s th ta ni n l delay l 10s. Sau gi i qua node 2, node 3....node n. ht tng cng 100s th lc ny ta ni n l latency = 100s) latency lend to end delay. Delay/latency ph thuc vo khong cch, tc truynd liu, v thi gian xl ca cc node mng.

1.1.3.2. Bin thin tr / Jitter

Jitter l s bin ng v tr khi ta gi cc gi t source ndestination. Chng hn, source ta pht i c 10ms mt gi, th nu ngtruyn l l tng th u thu s nhn c gi sau tr hn gi trc 10ms,nhng v mt l do no (chng hn, do gi i vo cc hng i ca router,gi i theo 1 ng khcv.v) m lm cho thi gian n ca gi sau so vigi trc c th ln hn hoc nh hn 10ms. Gi tr jit ter s l dngnu gi sau n chm hn gi trc 10ms (VD: nu gi 1 nhn c thi im t0=100 v gi 2 nhn c t1=112, nh vy delay s l

12ms v jitter s l 2ms. V nu gi tip theo nhn t2=120, th nh vy delay ca gi l 8ms, v jitter l-2ms). i vi cc ng dng


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nh VoIP th ngi ta khng h mong mun gi tr Jitter l dng, v gitr l tng tt nhin l 0.

1.1.3.3. Bng thng

Bng thng l gi tr trung bnh s lng gi tin c truyn qua mng thnhcng trong mt giy. K hiu l kbps hoc Mbps. Bng thng kh dngln nht ca ng lin kt bng gi tr bng thng nh nht ca ccng lin kt m gi tin i qua bng thng nh nht ca ng lin ktnythng l ng lin kt mng WAN.

Mt s tuyn kt ni khc nhng lin ktuplink gia ccswitchhoc router. 1.1.3.4. mt gi

Mt gi xy ra khi cc b nh tuyn trn khng gian b m trong cc giao dinu vo tip nhn thm cc gi tin mi i vo.Mt b nh tuyn c th b qumt s gi tin dnh khng gian cho cc gi tin khc c u tin caohn. Cc b nh tuyn IP thng thng s loi b gi tin v mt s l dokhc 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 chnh c khng gian b m ri cho cc gi i vo v mt s hin tng do gitin b li khung.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. 1.2. Phn lp lu lng

Vic phn lp lu lng c thc hin ti c lp 2 (lp lin kt d liu- Datalinklayer ) v lp 3 (lp mng Network layer ) trong m hnh OSI.

1.2.1. Phn lp lu lng mc lp mng

sp xp cc lung d liu IP thnh cc lp khc nhau nhm phc v cho cc

chnh sch QoS khc nhau, 3 bit u tin trong trng loi dch v (Service Type- ToS ) trong phn IP header ca gi d liu s c s dng. 3 bit ny c gi ltrng IP Precedence v c gi tr mc nh l 0. Trng IP Precedence bng 0, cngha l gi tin ny s c truyn theo kiu hiu qu ti a(Best Effort ). 7 gi trcn li ca trng IP Precedence dng phn chia lu lng IP thnh 7 lp dchv c th t u tin tng dn
http://vi.wikipedia.org/wiki/L%C6%B0u_l%C6%B0%E1%BB%A3nghttp://vi.wikipedia.org/wiki/L%C6%B0u_l%C6%B0%E1%BB%A3nghttp://vi.wikipedia.org/w/index.php?title=Datalink_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Datalink_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Datalink_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Network_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Network_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Network_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=ToS&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=ToS&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=IP_Precedence&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Best_Effort&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Best_Effort&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Best_Effort&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=IP_Precedence&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=ToS&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Network_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Datalink_layer&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=Datalink_layer&action=edit&redlink=1http://vi.wikipedia.org/wiki/L%C6%B0u_l%C6%B0%E1%BB%A3ng


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Hnh1.1 : Cc trng trong IPv4 v IPv6 headers

Hnh1.2 : Cc tham s ca trng ToS trong IPv4 header

Trong trng hp cn thit phi phn chia nhiu hn 8 lp lu lng, 6 bit utin ca trng ToS gi l trng s c s dng. Trng DSCP c gi tr t 0n 63, do n cho php phn chia lu lng IP thnh 64 lp dch v khc nhau.Tuy nhin, mt s thit b mng c c th khng h tr vic phn lp lu lng sdng trng DSCP ny. Thc t, trng IP Precedence l nm trong trng DSCPnn ta khng th cng lc va phn lp lu lng theo IP Precedence v va theoDSCP
http://vi.wikipedia.org/w/index.php?title=ToS&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=ToS&action=edit&redlink=1


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Hnh 1.3: Trng DSCP

1.2.2. Phn lp lu lng mc lp lin kt d liu

Trong phn mo u ca khung d liu lp lin kt d liu khng c trng no phc v cho vic phn lp lu lng. Tuy nhin ta c th phn lu lng da vovic chn thm cc th nh danh VLAN gi l tag theo giao thc 802.1Q/p . Mitag gm 4 byte trong trng gm 3 bit (cu trc chi tit ca tag c trnh bytrong hnh v) c dng phn lp lu lng. Nh vy ti mc lin kt d liuchng ta cng c th phn chia lu lng thnh 8 lp vi cc mc u tin tng dntng t nh khi s dng IP Precedence ti lp mng ca gi tin.

Hnh1.4 : Cu trc tag trong khung d liu 802.1Q/p

Tm li, vic phn lp lu lng d liu c th c thc hin tng data linkhoc network nh m t trong hnh1.4:
http://vi.wikipedia.org/wiki/VLANhttp://vi.wikipedia.org/w/index.php?title=802.1Q/p&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=802.1Q/p&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=802.1Q/p&action=edit&redlink=1http://vi.wikipedia.org/wiki/VLAN


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Hnh1.5 : Phn lp d liu trn 2 tng network v datalink

Mc u tin c 2 tng u c sp xp theo th t t thp n cao, 0 l gitr thp nht, tng ng vi khng thit lp u tin cho gi d liu v 7 l u tin cao nht. Gi tr DSCP (Differentiated Services Code Point ) khng nhngdng phn lp cho lu lng u tin m cn dng ch nh kh nng rt gica phn lp .

Hnh1.6 : Cc gi tr DSCP v u tin tng ng


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Lp cs l nhng gi tr u tin gc (pre-dating DSCP), lp af (assured forwarding)c nh ngha trong RFC 2597 v lp ef (expedited forwarding) c nh nghatrong RFC 2958. V d: lu lng thuc lp af33 s c u tin cao hn lulng thuc lp af21 nhng kh nng mt gi li ln hn lu lng thuc lp af3

1.3. Gii php QoS 1.3.1. M hnh dch v c gng ti a(Best -effort)

y l dch v ph bin trn mng internet, d liu i vo mng u tun theo quytc FIFO (First in first out). Khng c s i x no ca QoS i vi d liu. iuny dn n rt kh h tr cc dch v i hi tr thp nh cc dch v thi giathc hay video.

1.3.2. M hnh tch hp dch v(Integrated Services- IntServ)

c ITEF gii thiu vo gia thp nin 90 vi mc ch h tr cht lng dch vend-to- end, IntServ l kin trc h tr QoS cho cc ng dng trn mng internet. Tt c cc b nh tuyn trn ng truyn ca gi thng tin u-cui phi cci t IntServ m bo cung cp cht lng dch v theo yu cu. thc hic iu , cn phi c mt giao thc ng dng thng bo yu cu QoS ntng b nh tuyn. iu ny c thc hin bi giao thc RSVP.

Mt ng dng s xc nh c tnh ca lung lu lng m n a vo mng ngthi xc nh mt s yu cu v mc dch v mng. c tnh ca lu lng Tspec(Traffic Specification) yu cu mc cht lng dch v Rspec (RequiredSpecification). V th cc b nh tuyn phi c kh nng thc hin cc cng vicsau:

Kim sot (policing): kim tra TSpec ca lu lng, nu khng ph hpth loi b lung.

iu khin chp nhn: kim tra xem ti nguyn mng c p ng cyu cu ca ng dng hay khng. Nu khng th p ng, mng s tchi.

Phn lp (classification): phn loi d liu cn c vo mc yu cu cacht lng dch v ca gi

Hng i v lp lch (queuing v scheduling): a gi d liu vo hngi tng ng v quyt nh hy gi d liu no khi xy ra xung t.

Cc lp dch v: c 2 loi dch v l m bo dch v (Guaranteed Service) vkim sot ti (control load service)

m bo dch v: Cho php gii hn thi gian chuyn tip cc gi dliu n ch trong mt khong thi gian nht nh, m bo s d liu
http://tudiencongnghe.com/Routerhttp://tudiencongnghe.com/Routerhttp://tudiencongnghe.com/RSVPhttp://tudiencongnghe.com/RSVPhttp://tudiencongnghe.com/RSVPhttp://tudiencongnghe.com/Router


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khng b loi b khi hng i y. Thng tin Tspec phi bao gm ccthng s nh: tc nh, kch thc ln nht ca gi d liu. Trong khi thng s quan trng nht ca Rspec l tc dch v. Thng s nycho php xc nh bng thng m lu lng cn khi i trong mng.Thng s ny cng vi cc thng s trong Rspec cho php xc nh thigian tr ln nht c th chp nhn c ca d liu. Nhc im ca lpdch v ny l hiu qu s dng ti nguyn mng thp v n i hi milung lu lng c hng i ring.

Kim sot ti: Cc ng dng ca dch v ny c th chp nhn kh nngmt d liu v thay i tr mt mc nht nh. Lung d liu khi vo mng s c kim tra i chiu vi nhng c t lu lngTspec c ng k. Nu khng ph hp vi cc c t c ngk trc th d liu s c chuyn tip theo phng thc n lc ti

a.

1.3.2.1. Giao thc dnh trc ti nguyn (RSVP) RSVP l giao thc bo hiu cung cp th tc thit lp v iu khin

qu trnh chim gi ti nguyn, hay ni cch khc RSVP cho php ccchng trnh ng dng thng bo cho mng nhng yu cu v mccht lng dch v; v mng s hi p chp nhn hoc khng chpnhn yu cu .

Cc bn tin RSVP c cc b nh tuyn hay cc b chuyn mch trnlin kt gia hai u cui gi v nhn trao i vi nhau p ng yucu v mc cht lng dch v ca ng dng.

RSVP c 2 bn tin c bn: bn tin Path v bn tin Resv. Bn tin Pathmang thng tin v c t lung lu lng Tspec v cc thng tin nh:a ch IP ca nt gi, a ch IP nt nhn, ch s cng UDP. V khinhn c bn tin Path, nt mng ch s gi li bn tin Resv. Bn tinResv s gi km theo phn m t yu cu RSpec ch nh kiu dch vtch hp l kim sot ti hay m bo dch v; ngoi ra cn c du hiunhn dng lung (flow descriptor) m mi b nh tuyn dng nhn

din mi phin chim gi ti nguyn. Khi nhn c bn tin Resv, mi b nh tuyn trung gian s tin hnh qu trnhiu khin chp nhn (admission control). Nu yu cu khng c chp nhn,do khng ti nguyn mng th b nh tuyn s bo li v pha u thu. Nuyu cu c chp nhn th b nh tuyn s gi bn tin Resv n b nh tuyn gi bn tin Path cho n


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Hnh1.7 : M hnh INTSERV

1.3.2.2. Bn tin thng bo v xc nhn li

Ba loi bn tin thng bo li v xc nh li l : bn tin bo li ng i (patherror message Patherr), bn tin bo li yu cu ginh trc ti nguyn (Reservation request error message Resverr) v bn tin chp nhn yu cu ginhti nguyn ( Reservation request Acknowledment message Resvconf) Bn tinPatherr v Resverr c gi ngc li v pha ngi gi to ra li, nhngchng khng m t trng thi ca ng i m chng i qua. Bn tin Patherr chra li trong tin trnh x l trng thi ca ng i v c gi li cho ngi gd liu. Bn tin Resverr ch ra li trong tin trnh x l yu cu ginh ti nguynv c gi n ngi nhn (Trong RSVP ch duy nht ngi nhn mi c ththit lp mt dng d liu RSVP)

Cc bn tin bo li c th bao gm nh sau:

Admission failure Ambigous path

Bandwidth unavailable Bad Flow specification Service not supported

1.3.2.3. Teardown Message

c dng g b trng thi ginh ti nguyn v ng i t tt c cc nodesang trng thi ginh ti nguyn. Teardown message c th c khi to tnode gi hoc node nhn hay mt node bt k no trn ng i ca dng dliu. C 2 loi teardown message c h tr bi RSVP l : path teardown v


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reservation request teardown. Path teardown xa b trng thi ca bn tin path vcc trng thi ginh ti nguyn c kt hp trong ng i ca dng d liu.Reservation request teardown xa b trng thi ginh trc ti nguyn nhng gili ng i ca dng d liu c chnh sa.

Nguyn l cn bn ca m hnh IntServ l dnh ring ti nguyn mng (bngthng, tr) cho tng lung thng tin xuyn sut t ngun n ch. Tinguyn ny c chim dng v khng c tn dng cho bt k mt lungthng tin no. Nu ti nguyn b chim dng m khng dng th hin tng lng ph ti nguyn s xy ra.

Mt c im na l m hnh IntServ m bo cht lng dch v theo lung(flow). Mt lung c xc nh bi cc tham s: a ch IP ngun, IP ch, cng

ngun, cng ch Khi mt lung c thit lp th tng ng vi 1 phinRSVP c thit lp, iu ny dn n mt hn ch l: i vi mng c lulng cao nh mng ISP hoc cc t chc doanh nghip ln th s lng lungc th ln n hng trm ngn lung trong mt thi im v n n hin tnglng ph ti nguyn do bandwidth s dng thit lp knh RSVP ln rt nhiu(RSVP khng phi l lung thoi m ch l thng tin iu khin, bo hiu).

Hn ch ca m hnh IntServ vi h thng mng c s lng lu lng ln: Mcd InServ l m hnh m bo cht lng dch v tuyt i t u cui n ucui (end-to- end), nhng n khng linh hot v kh nng m rng thp nnthng khng c la chn thc hin QoS trong mng c quy m ln. Vvy m hnh IntServ ch thch hp cho nhng mng nh vi t lung lu lng.

1.3.3. M hnh phn bit dch v(Difference Services- DiffServ)

M hnh DiffServ c thit k khc phc nhng hn ch ca m hnh InServ.M hnh DiffServ c kh nng linh hot cao v kh nng m rng ln. Thay vthc hin cht lng dch v xuyn sut v thng nht trn c ng truyn nhm hnh InServ, m hnh DiffServ thc hin cht lng dch v ring l trn tng

router, vi cch thc hin nh vy m hnh DiffServ khng cn phi tin hnh bohiu theo tng lung nn tit kim bng thng v c kh nng m rng ln rt phhp trong m hnh h thng mng ln.


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Hnh1.8 : M hnh DiffServ

Nguyn l hot ng ca DiffServ c th din t nh sau: u tin cc gi tin phn loi ra thnh nhiu nhm u tin t thp n cao ty theo c im ca tngdch v, thit b s tin hnh cung cp ti nguyn theo tng nhm, nhm no c tht cao hn th s c cung cp quyn c s dng ti nguyn u tin hn, tinguyn s c cc nhm thp hn dng nu nhm trn khng s dng na. Tt ccc qu trnh ny s c thc hin ring l trn tng thit b.

Gii php QoS theo m hnh DiffServ c thc hin qua nhng bc sau: nhdu v phn loi gi tin. u tin cc gi tin s c nh du phn bit, sau

c sp xp vo cc nhm (lp) ph hp. Vic nh du v xp lp s gip thchin cc c ch QoS nhng bc sau:

Qun l tc nghn: C ch qun l tc nghn c thc hin trn ccgiao din ca thit b mng. Khi gi tin n cc giao din ny, cc gi tins c phn chia theo tng hng i c mc u tin khc nhau.

Trnh tc nghn: C ch loi b gi tin trc khi n c th gy ra hintng tc nghn.

t ngng:: C ch t ngng trn, ngng di cho bng thng, cth l bng thng s c m bo mt ngng di ti thiu v khi lnhn ngng trn th gi tin c th b loi b hay a vo hng i.

Nn header: Header chim phn ln trong 1 gi tin nhng khng mangthng tin tht s, c ch nn header s gip tit kim c bng thng.

Phn mnh: Cc gi tin d liu thng c di ln, iu ny s gy trv tc nghn. C ch phn mnh s bm cc gi tin n y thnh cc gi tin nh hn trnh tc nghn.


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1.3.3.1. Trng DS

Nhin vo cc hnh 1.2.1b ta thy rng trong IP header c mt trng c tn lToS (Type of Service ). RFC791 m t nh dng ca IP header, bao gm mttrng 8 bit c gi l ToS. Trng ToS ny d nh c dng nh mttrng nh du mt gi tin cc cng c QoS c th x l. Gi tr ToS cchia ra thnh cc trng con, vi 3 bit cao c nh ngha nh IP Precedence(IPP).

V tr bit 3 n bit 6 ca ToS bao gm cc trng c c bt on hay off ch ra mt mc dch v c bit. Bit cui cng (bit 7) khng c nh ngha trongRFC791. Cc c khng c dng thng xuyn, v vy mc ch chnh ca ToSl lu gi cc gi tr u tin ca gi tin IP.

Mt lot cc RFC c gi l Differentiated Services (DiffServ) ra i sau.DiffServ cn nhiu hn 3bit nh du gi tin, v vy DiffServ chun ha mtnh ngha li ca trng ToS. Trng ToS c t tn l trng DifferentiatedServices (DS) v IPP c thay th bng mt trng c di 6bit c gi lDifferentiated Services Code Point (DSCP). Ni cch khc, DSCP l mt cchdin t khc ca chnh trng ToS trong IP header ban u.

Hnh1.9 : IP ToS v trng DS


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6 bit ca trng DSCP c chia thnh 3 phn nhm mc ch gn v qun lcodepoint. Phn 1 vi 32 codepoint c gn cho hot ng chun (StandardAction) , 16 codepoint ca phn 2 c d tr dng hoc s dng trong ni bv 16 codepoint ca phn 3 c sn lc ban u dng hoc s dng trong ni b, nhng c th c dng chun ha cc nhim v nu phn 1 c mt vicodepoint cn kit.

1.3.3.2. Chnh sch tng chn(Per- Hop Behaviour - PHB)

Chnh sch tng chn dng nh hng cho cc b nh tuyn hot ng vicc gi tin cn cht lng dch v. Chnh sch tng chn l cch x l gi tin davo mt s thng s trong phn u ca gi tin. Cc loi chnh sch tng chn :

Chnh sch mc nh (default PHB): trng DSCP trong gi tin s cgn gi tr 0x00 (000000 dng nh phn) v gi tin s nhn s chuyn tipda trn m hnh c gng ti a (best effort) truyn thng.

Chnh sch chuyn tip nhanh (Expedited Forwarding PBH): trngDSCP ca gi tin s c gn gi tr 0x2e (101110 dng nh phn) v vigi tr ny, gi tin s c rt thp, tr thp v bng thng bo m.Chnh sch ny thng c p dng cho cc dch v voice, video , mua bn trc tuyn, cc ng dng thi gian thc yu cu tr thp v bngthng bo m.

Chnh sch chuyn tip bo m (Assured Forwarding PHB): trong chnhsch ny c 4 lp AF, mi lp yu cu s lng bng thng c nh v bm trng. Trong mi lp AF l 3 danh sch tham chiu nh rt ca n.Khi c xung t xy ra, b nh tuyn c th chn gi tin nh rt t thamchiu nh rt ca n.

Hnh1.10 : Cc gi tr ca 4 lp AF


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Mi PHB mang mt gi tr Afxy. Gi tr x cho php xc nh hng i dnh chogi, gi tr y xc nh kh nng mt gi khi xy ra tc nghn hoc tranh chp. Gitr x cng cao th u tin ca gi cng cao, gi tr y cng cao th kh nng mtgi cng cao, x c 4 gi tr v y c 3 gi tr. Cc gi c cng gi tr x (AFx1,AFx2, AFx3) s c a vo cng mt hng i khng b mt th t.

Chnh sch b chn lp (Class selector PHB): chnh sch ny ch dng 3 bit u l IP Precedence ca trng ToS v c 8 gi tr t 0-7 tng ngvi cc u tin khc nhau. Gi tin c gi tr IPP cng ln th u tincng cao

Hnh 1.11: Cc gi tr lp CS

1.3.3.3. Cc thnh phn ca phn bit dch v

B phn loi (Classifier): c dng nhn dng lu lng v phn chia lulng thnh cc loi khc nhau. phn loi gi, ta dng b m t lu lng

phn chia cc gi trong phm vi cc nhm ring bit nh ngha cc gi .Mt s b m t c trng dng phn loi gi bao gm: b giao tip ng vo, u tin IP , DSCP, a ch ngun, a ch ch, cc ng dng.

B dnh du (Marker): hot ng nh du gip cc thit b mng phn loi gihay khung ra vo b m t lu lng c trng. Mt s b m t lu lng s dng nh du gi nh: lp dch v, DSCP, u tin IP. nh du l yut hu dng v n cho php thit b mng d dng nhn ra cc gi tin theo cc lpc trng. Khi k thut cht lng dch v c th ng dng tng thch m bo s ng n vi cc chnh sch cht lng dch v.


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B nh gi (Meter): hot ng gia b phn loi v b iu phi lu lng(traffic conditioner). Cc gi tin nhn c t b phn lp, b nh gi mthuc tnh tc thi ca dng da vo hin trng lu lng . Qu trnh x lc thc hin bi b nh du, b nh dng v b kim sot da trn cc gitin bn trong hoc bn ngoi hin trng.

B nh ng (Shaper): B nh dng v c bn l mt hng i m cho dnglu lng v tr cc gi tin, lm vic ny n lm ty theo 1 hin trng lulng ring bit. Cc gi tin c th b loi b nu b m trng.

B hy (Dropper): dng nh rt cc gi tin ty theo hin trng ca dng. Bhy c th c thc thi nh l mt trng hp c bit ca b nh dng vikch thc b m l 0.

1.3.4. S khc nhau gia m hnh IntServ v DiffServ

1.4. Qun l tc nghn

Qun l nghn l t dng chung xoay quanh cc chin lc hng i khc nhau cdng qun l cc tnh hung khi bng thng yu cu ca ng dng mng vt qutng bng thng cho php. Qun l nghn khng iu khin lu lng khi xy ranghn m iu khin lu lng vo m bo mi loi lu lng u c u tkhc nhau. Cc k thut hng i c dng ph bin l:

First in First out Queuing


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Priority Queuing Custom Queuing Weighted Fair Queuing (WFQ)

Trong 4 k thut hng i trn, Priority Queuing v Custom Queuing i hi nhqun tr phi ln k hoch tnh ton cn thn thc thi v cu hnh chnh xc trnrouter. Nh qun tr phi c 1 s am hiu tt v cc dng lu lng v cch nhu u tin trn cc dng lu lng c th to ra cc chin lc hng ihiu qu. FIFO v WFO th khng cn cu hnh nhiu c th hot ng 1 cchthch hp.

1.4.1. Cc nguyn nhn gy tc nghn Nghn xy ra do lu lng mng qu nhiu dn n y hng i v cc routervt qu kh nng x l. Tng bandwidth ng truyn c th gii quyt nhngch mt gii hn nht nh. V th cc k thut qun l nghn trn nn tng CiscIOS cung cp cho nh qun tr mng kh nng qun l hng i mt cch hiu quv cp pht bandwidth cn thit n cc ng dng c bit khi trng thi nghn tti.

Nghn c th xy ra khi tc ng truyn khng ph hp. Ch yu l khi lulng di chuyn t mng c tc cao nh LAN (100Mbps hay 1000Mbps) sangcc ng truyn c tc thp nh ng WAN (1Mbps hay 2Mbps). S khng ph hp v tc cng xy ra trong mng LAN-LAN, khi lu lng di chuyn tmng LAN c tc 1000 Mbps sang mng LAN c tc ng truyn 100Mbps.

1.4.2. Cc khi nim hng i

Hng i tn ti trong b nh tuyn gi gi tin cho n khi c ti nguyn chuyn tip gi tin ra khi cng ra. Nu khng c tc nghn, gi tin s lp tc chuyn i.

1.4.2.1. Leaky bucket (thng b thng)

Leaky bucket l khi nim kha cho vic hiu v l thuyt hng i. Mt hngi mng c th c so snh nh mt thng m nhng gi tin c vo.Chic thng ny c mt l di y gi tin c th i ra vi mt tc lintc. Trong mi trng mng, tc gi tin ra s l tc ca card giao tip. Nu tc ca gi tin i vo ln hn tc ca gi tin i ra th thng s b yv s xy ra hin tng rt gi, cc gi tin i vo s b nh rt.


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Hnh1.12: Leaky Bucket

1.4.2.2. Tail Drop (Ct ui)

Khi mt lng ln cc gi tin i vo hng i vt qu dung lng ca hng ith s xy ra tc nghn v cc gi tin i vo sau s b nh rt cho n khi ht tcnghn. Cc giao thc tng cao hn s dng phng thc ca n pht hin vx l truyn li cc gi tin b nh rt. Vic nh rt gi tin l vic xy rathng xuyn trong mng v tc ca gi tin i vo (100Mbs Fast Ethernet)nhanh hn tc ca gi tin i ra khi b nh tuyn ( 1.544Mbs T1 interface).

1.4.2.3. Token bucket(thng ng th)

Token bucket l mt thut ton khc uc dng trong QoS, n c m t nhmt h ti nguyn c dng bi mt dch v bt c khi no cn thit. Khc viLeaky bucket (thng b thng) , gi tin i vo s c i ra t nh ch khng phi t y thng nh leaky bucket. Dn dn th s c thm vo thng. Khimt ng dng mun gi d liu ra ngoi mng, n s ly i mt lng th tnng vi lng d liu m n mun gi. Nu trong thng khng c th, ngdng s phi i cho n khi th mi c th gi d liu.


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Hnh1.13: Token Bucket

1.4.2.4. First in First out Queue (Hng i FIFO)

Hng i FIFO l hng i n gin nht da trn kh nng lu tr v chuyntip ca b nh tuyn, gi tin no vo trc th s c ra trc. FIFO l thutton sp xp truyn thng mc nh trong mt s trng hp, v vy khng cn phi cu hnh, nhng n c nhng hn ch nht nh. Hn ch ln nht ca n lkhng c s phn lp cho cc gi tin, khng c s tha thun v bng thngtruyn. FIFO l thut ton u tin c thit k cho vic truyn thng trnmng, nhng i vi nhng mng thng minh ngy nay i hi nhng thut tontt hn cng nh phc tp hn. FIFO c dng ch yu trong m hnh c gngti a (best-effort).

Hnh1.14 : Hng i FIFO

u im: y l k thut n gin v nhanh.


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Hng i u tin cung cp cho ngi qun tr kh nng mnh c th t chilu lng thuc hng i Low. Khi hng i u tin thuc th hng thp khngc phc v v c qu nhiu lu lng hng i cao hn th s xy ra tnhtrng priority starvation (i u tin). Priority starvation l mt cm bynghim trng v kh nng xy ra hin tng i hng i l mt vn ngquan tm khi thit k chin lc hng i u tin.. V vy, vic hiu thut tonhng i u tin v t chc mt k hoch thch hp l mt vn quan trng.Hng i u tin c th phn lp da vo cc gi sau:

Loi giao thc (IP, Appletalk, IPX, etc). Kch c gi tin theo byte. S cng TCP hoc UDP nu l lu lng TCP/IP Card giao tip m gi tin n.

Nhng gi tin khng c phn lp s c t ng xp v hng i Normal. Trong hng i u tin, hng i mc nh thng thng l hng i normal, tuynhin n c th chuyn thnh bt c hng i no khc. Cao hn hng i Highl hng i h thng, nhng ta khng th s dng n.

Round Robin: ln lt ly cc gi theo th t, nhng khng thc hin c s u

tin.

Weighted Round Robin: cng ln lt ly cc gi tin hng i nh RoundRobin, nhng thc hin s u tin bng cch: hng i c mc u tin cao cly nhiu gi tin hn hng i c mc u tin thp, vic ly nhiu hay t c thquy nh bng s gi tin ly ra mi hng, hoc thi gian phc v cho mi hngtrong 1 chu k.

1.4.2.6. Custom Queue (Hng i t chn (CQ))

khc phc s cng nhc ca hng i u tin, nh qun tr c th dng hngi ty chn thay th. Hng i ty chn cho php nh qun tr nh du utin cho lu lng m khng gy ra vic thiu hng i thp nh hng i utin. Vi Hng i ty chn, nh qun tr c th to ra 16 hng i cho cc lulng u tin, b lp lch ca hng i ty chn khng c ty chn phc vmt hng i u tin- nh hng i u tin cao V th hng i ty chnkhng cung cp dch v vi tr hon ln v lu lng nhy vi s thay i. Blp lch hng i ty chn thc hin dch v tun hon trn mi hng i, bt ut hng i 1, hng i ty chn ly cc gi t hng i cho n khi tng s byte

ch nh cho mi hng i vt ngng. Sau khi hng i phc v nhiu byte hay


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hng i khng cn gi no, hng i ty chn di chuyn n hng i tip theov lp li tin trnh.

Hnh1.16: Custom Queue

Router thc hin vic a gi tin vo hng i da vo thut ton round-robin,sp xp li tng byte cu hnh c m t mi hng i trong tng chu k. Tnnng ny m bo rng khng c ng dng no (hay nhm ng dng c th no)c th hot ng cao hn kh nng m h thng cp pht cho chng khi ngtruyn ang tnh trng qu ti. Ging nh Priority Queue, Custom Queue ccu hnh tnh v khng t ng cp nht li cc thay i ca mng.

1.4.2.7. W eighted Fair Queue (Hng i cn bng trng s(WFQ))

WFQ l chin lc hng i mc nh cho cc card giao tip c tc thp.WFQ l phng php cp pht bng thng u cho tt c cc lu lng. WFQsp xp cc lu lng mng vo nhng dng to nn cuc hi thoi trn mng bng cch dng s kt hp ca cc tham s. Cc cuc hi thoi TCP/IP c xcnh da vo cc tham s sau:

Giao thc IP. a ch IP ngun. a ch IP ch.

Cng IP ngun. Cng IP ch.


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Trng ToS (Type of Services).

Qua vic theo di cc dng d liu, router c th bit c dng no cn nhiu bng thng nh FTP hoc dng no nhy cm vi tr nh Telnet. C 256 hngi mc nh c dng khi s dng WFQ.

Bi v WFQ phn cc gi tin vo cc dng lu lng khc nhau v sau acc dng ny vo trong nhng hng i khc nhau, router s c s hng i khcnhau. S hng i ny nhiu hn bt k cc cng c hng i khc (tc l cccng c hng i khng x l theo dng lu lng). C ch nh thi ca WFQdng cc thut ton hon ton khc vi cc thut ton ca cc cng c hng ikhc im n c th qun l mt s lng ln cc hng i. Mc ch tng thca WFQ c tm tt nh sau:

Cc dng c cng u tin IPP (IP Precedence) ca gi tin IP s ccp cng mt mc bng thng, bt chp c bao nhiu byte trong midng lu lng.

i vi nhng dng c nhng gi tr IPP khc nhau, cc dng c utin IPP cao hn s c cp mt lng bng thng cao hn.

Hnh 1.17: Weighted Fair Queue

- Tin trnh nh thi WFQ

t c mc ch cp pht bng thng, WFQ dng b nh thi kh ngin. B nh thi s ly gi tin c ch s tun t thp nht sequence numberSN (cn gi l thi gian hon thnh) khi n cn chuyn gi tin k tip n hng


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i phn cng. C ch WFQ s gn mi gi tin mt ch s tun t SN khi gitin i vo hng i WFQ. Tin trnh gn ch s tun t SN cng l mt phnquan trng trong c ch nh thi ca WFQ. B nh thi WFQ s tnh ton chs tun t SN da trn nhiu thng s ca dng lu lng, bao gm c chiudi v u tin IPP ca gi tin. Cng thc tnh ch s tun t SN ca mt gitin trong mt dng lu lng l nh sau:

SN=ch s SN trc +(trng s weight*chiu di gi tin mi).

Trong trng s c tnh nh sau:

Weight=32384/(I P_Precedence+1)

Cng thc trn c tham chiu n chiu di ca gi tin mi, trng s ca dnglu lng v gi tr SN trc . Bng cch xem xt chiu di gi tin, vic tnhton s tun t SN c th dn n mt ch s SN rt cao cho nhng gi tin ckch thc ln v ch s tun t SN thp hn cho nhng gi tin c kch thcnh hn. Vi vic bao gm lun ch s tun t SN ca gi tin trc tronghng i, cng thc ny s tnh ra ch s SN ln hn cho nhng gi tin tronghng i c mt s lng ln gi tin. Bng cch gn trng s (IPP+1), ccgi tin cc u tin IPP cao s c kt qu SN thp hn. Hnh di y s mt hai gi tin c gn hai ch s tun t nh th no. Tnh ton ch s tun tSN ca mt gi tin th d dng. Tuy nhin gi tin u tin trong mt dng lulng no th khng c ch s tun t SN ca gi tin tr c dng trongcng thc tnh ton trn. Cng thc m t rng ch s tun t SN ca gi tincui cng c a vo hng i cng th c dng nh l ch s tun t SNcho dng mi theo sau.

Sau khi cc ch s tun t SN c gn, cn li, cng vic chn gi tin no gii phng ca b nh thi tr nn n gin. N s ly gi tin c ch s SNthp nht gia tt c cc hng i.

- Chnh sch loi b gi tin ca WFQ, s hng i v chiu di hng i

Trong hot ng ca router, mc d a cc lu lng vo cc hng itng ng, nhng nu lu lng i qua router vn tip tc tng cao, bt bucrouter s phi tin hnh vic loi b bt gi tin gim bt nghn. WFQ dngtin trnh hai bc gi l loi b cui hng c b sung (modified tail drop) chn la khi n o th loi b gi tin. Theo tn gi, tin trnh ny khc vi tintrnh loi b cui hng thng thng.

u tin, WFQ s xem xt gii hn tuyt i ca tt c cc gi tin trong

hng i gia tt c cc hng i, gii hn ny gi l hold-queue limit. Nu mt gi tin n hng i v gii hn hold-queue ti, gi tin s b


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loi b. Quyt nh khng da trn mt hng duy nht nhng trnton h thng hng i ca WFQ. Ni cch khc, gii hn hold-queueny l mt ch s ton cc, c tnh ton tng th gia cc hng iWFQ.

Th hai l WFQ s xem xt chiu di ca mt hng i m trong nhng gi tin s c a vo. Trc khi a mt gi tin vo hng i,mc ngng congestive discard threshold (CDT) s c kim tra vichiu di thc s ca hng i . Nu hng i l di hn CDT, mtgi tin s b loi b, nhng c th khng phi l nhng gi tin mi n.Gi tin c ch s tun t cao nht trong tt c cc hng i ca WFQ s b loi b.

Nhng gi tin va n s i qua tin trnh ny, nhng trong mt nhnh ca

thut ton, gi tin mi n s khng b loi b, thay vo , mt gi tin khctrong mt hng i khc s b loi b. Mt cch c bn, nu gi mi n cn phi i vo mt hng i vt qu CDT, WFQ s loi b gi tin c ch stun t cao nht t bt k hng i no. Gi tr CDT phi gn bng bi s ca2. IOS s khng chp nhn bt k gi tr no khc. WFQ c th c cu hnhdng ti a 4096 hng i, gi l dynamic queue. Mi khi c mt dng lulng, router s to ra mt dynamic queue truyn dng lu lng trn. Khix l. xong mt dng lu lng hng i s b hu. Thm vo , WFQ gitm hng i n cho cc lu lng c to ra bi router. WFQ dng mt mctrng s rt thp cho cc hng i ny u tin cho cc cc lu l ng ca hthng. Ngoi ra, c mt vi hng i trong s 4096 hng i c th c dng bi Resource Reservation Protocols (RSVP) gi bng thng. RSVP dng cc bo hiu gi phn bng thng ti thiu cho nhng dng lu lng c bittrong mt h thng mng, da ch yu vo cc cng c hng i thc shin thc c tnh nng gi bng thng. WFQ, CBWFQ, v LLQ h trRSVP.

- Class-Based WFQ (CBWFQ)

Cisco to ra Class- Based WFQ (CBWFQ) v Low- Latency Queuing (LLQ), sdng cc k thut PQ, CQ v WFQ v c thm vo vi c im khc. CBWFQdnh ring bng thng cho tng hng i v dng k thut WFQ cho cc gi tintrong lp mc nh. LLQ thm vo trong CBWFQ khi nim hng i u tin,nhng khng ging nh PQ, LLQ ngn cc hng i c u tin cao khi vic b ri vo trng thi cht.

C CBWFQ v LLQ u dng tu chn phn loi mnh, bao gm c NBAR.CBWFQ v LLQ dng cu hnh tng t nhau, s khc nhau nm ch cu lnh bandwidth hay cu lnh priority c dng. CBWFQ v LLQ dng class-map


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phn loi v dng policy map to ra mt tp hp cc nhm lu lng dngtrn mt cng. Cc lp nh ngha trong policy map s dng mt hng i. Thutng hng i v class thng thng dng qua li khi lm vic vi LLQ vCBWFQ. Ngha l, c th m ch n mt lp lu lng no bng c thutng queue hay class.

V d: khi cu hnh

R1(config)# class-map http

R1(config-cmap)# match access-group 101

Theo v d trn th lu lng Web (HTTP) c phn loi vi cu lnh class-mapkt hp vi access control list (ACL). CBWFQ v LLQ h tr 64 hng i (64class). Chiu di hng i ti a c th thay i, vi gi tr ti a v chiu dimc nh thay i ty thuc vo router v tng s b nh c dng. C hai uc mt hng i c bit gi l hng i mc nh. Hng i ny tn ti ngay ckhi n khng c cu hnh. Nu mt gi tin khng thuc v nhm no c cuhnh trong mt policy map, IOS s t gi tin vo hng i mc nh.

c im ca CBWFQ: CBWFQ h tr nhiu class phn loi lu lng vo cc hng i FIFO

tng ng vi n. Tail drop cng l c ch loi b gi tin mc nh ca CBWFQ. CBWFQ m bo mt t l ti thiu ca bng thng n tng hng i. Nu

tt c cc hng i c mt s lng ln gi tin, mi hng i s nhn phntrm bandwidth ngm nh bi cu hnh. Tuy nhin, nu mt vi hng i ltrng v cc hng i ny khng c nhu cu bng thng trong mt khongthi gian ngn, bng thng c cp pht tng ng vi cc nhm lulng khc.

c im c th ca CBWFQ c th hin trong bng sau:


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Bng 1.18: c im ca CBWFQ

- Low-Latency Queuing (LLQ)

i vi nhng ng dng cn tr thp, Low-Latency Queuing (LLQ) l chnla tt. LLQ tm kim v hnh ng ging nh CBWFQ trn hu ht mi phngdin, ngoi tr yu t l LLQ cho php mt s hng i hot ng nh cc hngi c tr thp. LLQ cho php cc hng i c u tin cao (ging nh PQ).LLQ lun phc v cc gi tin trong nhng hng i ny trc.

LLQ c th c dng trong cc tnh hung khc nhau. Nu mt chnh sch policy map c t nht mt LLQ, chnh sch policy map c th xem nh ang

hin thc LLQ, v hng i c gi l LLQ. Mt hng i LLQ cn cgi l PQ v c tnh hot ng ging PQ.

Khi LLQ thm vo mt hng i c tr thp vo c ch CBWFQ, n cnggip ngn nga hin tng hng i cht ca PQ. LLQ kim sot hng i datrn bandwidth c cu hnh. Bandwidth cp cho mt hng i LLQ va l mc bandwidth m bo ti thiu, va l mc bandwidth ti a. Kt qu l, cc gi tinc th c gii phng khi hng i c tr thp nhng s c vi gi tin bloi b ngn nga cc hng i khc ri vo trng thi cht v khng c xl. Hot ng ca LLQ c th hin trong hnh sau:


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Hnh1.19: Hot ng ca k thut hng i LLQ

LLQ cho php nhiu hng i c cu hnh nh PQ. LLQ t cc gi tin t cchng i LLQ vo mt hng i bn trong. V vy, cc gi tin trong cc hng iu tin khc nhau vn c phc v trc nhng gi tin trong cc hng ikhng u tin, nhng n s c phc v da trn thi gian gi tin n trong bt

k hng i u tin no. Dng nhiu hng i u tin do policy kim sot bandwidth. Khi kim sot bandwidth ca mt lp mt mc no v vi lplu lng khc mc khc, dn n c nhiu mc hiu chnh khc nhau choLLQ. V d nu hoch nh cho d liu video v voice, c th t cc loi d liuny vo cc hng i LLQ ring bit v c hai loi d liu ny s c tr thp,ng thi ngn nga d liu video chim bandwidth ca voice v ngc li.

1.4.3. Congestion Avoidance (trnh nghn mng)

Truyn d liu khi mng ang b nghn s gy ra nhiu vn nghim trng. Vd, delay ca cc gi tin tng ln cao, cc gi tin phi cnh tranh vo hng iv ch cho n khi c th c gi i, khi hng i y m cc gi tin li lintc n router, cui cng lm cho cc gi tin s b nh rt theo hin tng taildrop. Cc thit b u cui khng bit ni xy ra nghn mng. i vi cc thit bu cui th s nghn mng c hiu l delay tng. Cc giao thcthuc layer 4 (TCP/UDP) s dng b m thi gian v phng php truyn li.Do , cc giao thc ny phn ng li vi delay ln bng cch truyn li cc gtin. c bit l giao thc TCP, ni nhn gi s khng th bo cho pha pht cc gi b mt nn khi c li xy ra th s phi thc hin truyn li ton b cc gi tin tron

ca s (window size). Tt c nhng nguyn nhn trn s lm cho hiu sut ca hthng mng gim xung.


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khc phc vn trn th c th s dng cc cng c QoS sau: Random Early Detection (RED) Weighted Random Early Detection(WRED) Explicit Congestion Notification (ECN)

1.4.3.1. Random Early Detection (RED)

Khi nghn mng xy ra th cc gi tin s b nh rt theo hin tng tail drop.Random Early Detection (RED) l mt cng c gip gim vic mt gi tin trongh thng mng. RED gim st chiu di hng i v loi b mt s gi tin tronghng i ci tin hiu sut ca mng.Thay v ch hng i y (nguyn nhn

chnh gy ra hin tng tail drop), RED s lm rt mt s gi tin trc khi hngi y. RED chn ra gi tin c th s b nh rt v sau nh rt vi gi tinmt cch ngu nhin.

t c tng nu trn th cng c RED phi thc hin c 2 vic sau: RED phi pht hin hin tng hng i c du hiu b nghn (b y) mt

cch nhanh chng.

RED hay khng v nh rt bao nhiu phn trm gi tin trong hng i.

pht hin hng i c du hiu y th RED nh ngha ra cc khi nimAverage queue depth (kch thc hng i trung bnh) v Actual queue depth(kch thc hng i hin ti). Kch thc hng i trung bnh l s lng gi tintrung bnh c tnh t kch thc hng i hin ti v s kch thc hng itrung bnh trc . Kch thc hng i hin ti l s lng thc t ca cc gitin trong hng i ti mt im c th. Cng thc tnh s kch thc hng itrung bnh nh sau:

Kch thc hng i trung bnh mi = (kch thc hng i trung bnh trc *(1-2- n)) + (kch thc hng i hin ti * 2-n)

Gi tr mc nh ca n l 9.

Theo thi gian th s kch thc hng i hin ti thay i lin tc v nhiu hnsovi s kch thc hng i trung bnh. S kch thc hng i trung bnh lunc thay i sao cho ph hp vi s thay i ca s kch thc hng i hinti. iu ny c th hin trong hnh sau y:


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Hnh1.20: So snh kch thc hng i hin ti vi kch thc hng i trung bnh

Sau khi c c s kch thc hng i trung bnh mi, RED tin hnh so snhs ny vi hai ngng s lng gi tin trong hng i (c th c cu hnh ttrc). l minimum threshold (ngng thp nht) v maximum threshold(ngng cao nht). Kt qu so snh nh sau:

Kch thc hng i trung bnh mi < minimum threshold: Khng c nghnxy ra v khng c gi tin no b nh rt (No Drop).

Minimum threshold < kch thc hng i trung bnh mi < maximumthreshold: C nghn xy ra v RED ngu nhin nh rt cc gi tin (khng phi l tt c cc gi tin Random Drop). T l phn trm gi tin b nh rtln nht c tnh da trn Mark Probability Denominator (MPD). MPDc cu hnh trn IOS router. Cng thc tnh ton l 1/MPD. V d, MPDc cu hnh l 10 th t l phn trm gi tin b nh rt ln nht l 10%(1/10). Ni cch khc, t l phn trm gi tin b nh rt giao ng t 0%n 10%.

Average queue depth > maximum threshold: C nghn xy ra v tt c gitin mi (chun b vo hng t) u b nh rt (full Drop). Trng hp nytng t nh hin tng tail drop.


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Hnh1.21: RED nh rt gi tin bng Average queue depth, minimum thresholdv maximum threshold

1.4.3.2. Weighted Random Early Detection(WRED)

V c bn th Weighted Random Early Detection (WRED) ging vi RED.WRED pht hin hin tng hng i c du hiu b nghn v tnh t l phntrm gi tin b nh rt cng da trn cc khi nim:

Average queue depth (kch thc hng i trung bnh). Minimum threshold (ngng thp nht). Maximum threshold (ngng cao nht). Mark Probability Denominator (MPD).

WRED tnh kch thc hng i trung bnh, tnh t l phn trm gi tin b nhrt v kt qu so snh gia kch thc hng i trung bnh, minimum threshold,maximum threshold tng t vi RED.

im khc bit gia WRED v RED l WRED quyt nh nh rt gi tin cnda trn gi tr IP Precedence hay DSCP. Trong khi RED th thc hin nh rtcho gi tin khng c nh du u tin vi gi tr IP Precedence hay DSCP.WRED c mc nh vi gi tr IP Precedence l 0. Khi tt c cc gi tin cgn gi tr IP Precedence l 0 th WRED hot ng tng t nh RED. iu nyc th hin trong hnh sau:


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Hnh1.22: WRED mc nh vi cc gi tin c gi tr IP Precedence l 0

Theo hnh1.22, gi s kch thc hng i trung bnh mi tnh c l 20. Ccgi tin mi vi gi tr IP Precedence l 0 c a vo hng i. Nu kch thchng i trung bnhdi 20 (minimum threshold) th WRED khng nh rt gitin. Nu kch thc hng i trung bnhtng t 20 n di 40 (maximumthreshold), WRED nh rt cc gi tin v t l phn trm nh rt gi tin l t 0%

n 10% (1/MPD). Khi kch thc hng i trung bnhvt ngng 40, WRED b tt c cc gi tin.

Trong trng hp, cc gi tin c gn cc gi tr u tin khc nhau th WREDthit lp minimum threshold,maximum thresholdv cc gi tr MPD khc nhauda trn gi tr IP Precedence hay DSCP. Xt v d c th trong hnh sau:

Hnh1.23: V d WRED vi cc gi tin c gi tr IP Precedence l 0 v 3


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Theo hnh1.23 , thc hin nh du cc gi tin vi 2 gi tr IP Precedence 0 v IPPrecedence 3. Gi s kch thc hng i trung bnh mi tnh cl 20,maximum threshold l 40. Cc gi tin c nh du vi gi tr tr IP Precedence0 c minimum t hreshold l 20, MPD l 10. Cc gi tin c nh du vi gi tr tr IP Precedence 3 c minimum threshold l 30, MPD l 20. Cc gi tin mi vigi tr c a vo hng i.

Nu kch thc hng i trung bnh tng ln, xt cc trng hp sau: 20 < kch thc hng i trung bnh < 30: Cc gi tin gn gi tr IP

Precedence 0 s b WRED nh rt v minimum threshold l 20, cn ccgi tin gn gi tr IP Precedence 3 vn cha b WRED nh rt vminimum threshold l 30.

30 < kch thc hng i trung bnh < 40: WRED nh rt thm cc gi tingn gi tr IP Precedence 3. T l phn trm nh rt cc gi tin gn gi trIP Precedence 0 l t 0% n 10% (1/10). T l phn trm nh rt cc gitin gn gi tr IP Precedence 0 l t 0% n 5% (1/20).

Kch thc hng i trung bnh > 40: Tt c cc gi tin u b nh rt.

Qua v d trn cho thy cc gi tin c nh du u tin cao th c t l bnh rt thp hn. iu ny m bo hn cho cc gi tin c u tin cao. Ccgi tr minimum threshold, maximum threshold, MDP c mc nh trn

IOS router da trn gi tr IP Precedence hay DSCP c th hin qua hai bngsau:

Bng 1.24: Cc gi tr minimum threshold, maximum threshold, MDP da trn IPPrecedence


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Bng 1.25: Cc gi tr minimum threshold, maximum threshold, MDP da trnDSCP

WRED qun l vic loi b gi tin da trn kch thc hng i. WRED ch sdng vi cc loi hng i First-in, first-out (FIFO), Class-Based WFQ(CBWFQ), LowLatency Queuing (LLQ). Gi tin i vo hng i sau khi c phn loi v nh du s c WRED pht hin nghn.

Cc cu lnh cu hnh c bn v WRED c th hin trong bng sau:

Bng 1.26: Cc lnh cu hnh c bn v WRED


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1.4.3.3. Explicit Congestion Notification (ECN)

Explicit Congestion Notifica tion (ECN) l phng php trnh nghn mng chyu cho cc gi tin TCP. ECN trnh nghn mng da trn vic nh du vo IPheader. Thay v nh rt gi tin ngay mt cch ngu nhin nh RED v WREDth ECN nh du cc gi tin vi du hiu tc nghn thng bo cho thit b cui bit. ECN nh du IP header bng 2 bits cui (trong 8 bits) ca trngType Of Service (ToS). Nu trong m hnh DiffServ, y l 2 bit ECN trongtrng DSCP.

Hnh1.27: 2 bits ECN trong trng DSCP

Theo hnh 1.27, 2 bits ECN l ECT (ECN Capable Transport) v CE(Congestion Experienced). Bit ECT c thit lp bi ngun lu lng TCP.Router da vo bit ny bit gi tin c c nh du ECN khng. Bit ECT

c bt ln 1 thng bo tc nghn cho cc thit b u cui. Bit CE giprouter pht hin tc nghn trong mng khi bit ny c thit lp vi gi tr l 1.ECN nh du TCP header bng 2 bits ca trng Reserved field. l cECNEcho (ECE) v c Congestion Window Reduce (CWR). C ECE c thit lp gip cc thit b u cui (gia my gi v my nhn) tha thun 2 bit ECNv nhau. C CWR c s dng bo cho my gi gim s lng thng tintruyn xung v bo cho my nhn bit l my gi gim kch thc ca struyn d liu xung ( congestion window CWND).


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Hnh1.28: Trng Reserved trong TCP header

Hnh1.29: V d c th v hot ng ca ECN

Theo hnh1.29 , thc hin kt ni TCP gia 2 thit b u cui (Client 2 vServer1). Hot ng c th ca ECN nh sau:

(1) Client 2 thit lp mt kt ni TCP n Server1. C Client2 v Server1u s dng ECN. Client2 thit lp gi tr 2 bit ECN (ECT v CE) trong IPheader l 01 (ECT = 0, CE = 1).


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(2) Router s dng WRED pht hin nghn. WRED ngu nhin chn ccgi tin nh rt. V c cu hnh ECN nn router kim tra cc gi tin vtm ra cc gi tin c nh du 2 bits ECN. Sau , router thit lp li 2 bits ECN vi gi tr l 11 (ECT = 1, CE = 1) cho cc gi tin ny v truyni thay v nh rt.

(3) Gi tin c truyn n Server1 vi gi tr ca 2 bit ECN vn l 11. (4) Server1 nhn c cc gi tin c gi tr ca 2 bit ECN l 11. Trong gi

tin gi tr v cho Client2 t Server1 s c Server1 nh du vo TCPheader. Bit c nh du y l c ECE vi gi tr c thit lp l 1. 2 bits ECN c xem l khng quan trng trong gi tin tr v.

(5) Gi tin tr v Client2 n router. Nhng ti y router khng kim tracc bits cn nh du trong gi tin v cng khng thit lp li cc bits ny.

(6) Client2 nhn gi tin tr v vi c ECE c thit lp gi tr l 1 trongTCP header. Sau , Client2 gim kch thc CWND liu xung 50%. (7) Client2 thng bo Server1 bit Client2 gim kch thc CWND

xung 50% bng cch gi gi tin nh du vo TCP header cho Server1.Cc bits c nh du y l 2 bits ECN vi gi tr l 01 (ECT = 0, CE =1) v c CWR vi gi tr l 1.

1.5. Traffic Shaping (iu ha lu lng) v Traffic Policing (gimst lu lng)

Traffic Shaping (TS) v Traffic Policing (TP) l mt phn quan trng ca cht lngdch v QoS. TS v TP dng o tc truyn hoc nhn d liu. TS l cng ciu ha lu lng, gip cho cc gi tin c gi theo ng tc cu hnh. Nicch khc, khi gi tin i ra khi router th tc truyn tng th ca gi tin ny khng vt qua mt gii hn nh ngha. m bo tc truyn ca cc gitin khng vt qua gii hn nh ngha, TS lm gim tc ca cc gi tin ny bng cch a chng vo cc hng i iu ha (cc hng i ny khc vi cc hngi mm trn cc cng ca router). Sau , router mi tip tc gi cc gi tin trntheo ng tc nh ngha.

TP l cng c khng ch lu lng. TS o tc truyn ca gi khi gi tin vo v ramt cng ca router. Nu tc truyn vt qu tc cu hnh, router s loi b s lng gi tin sao cho tc cu hnh khng b vt qua. Hoc router cngc th nh du cc gi tin sao cho cc gi tin ny c th b loi b v sau. V d,ISP cung cp dch v v cho khch hng c th gi cc gi tin vi mt tc x (tc cam kt gia ISP v khch hng). Tuy nhin, nu khch hng gi cc gi tin vitc 10x th TP s lm rt cc gi tin . TS ngn chn khch hng s dng vtqu bandwidth cho tha thun (k c trong trng hp ISP vn kh nng qunl nhng lu lng ny).

TS v TP thng xy ra bin gia gia 2 loi m hnh mng.


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V d, xt m hnh mng sau:

Hnh1.30: V d m hnh mng minh ha cho Policing v Shaping

Theo hnh5 a, mnh ha m hnh mng ca mt cng ty A. TS v TP xy ra cc bin mng gia:

R1 vi FRS1 (link1). FRS2 vi R2 (link 2). R3 vi ISP-R1 (link 3).

Trong cc bin mng trn th u c mt s tha thun v tc truyn d liu giacng ty A vi dch v Frame Relay v ISP. R2 s dng ng truyn 1.544Mbps(T1 ) v R1 s dng ng truyn 128Kbps ti mng Frame Relay (FRS2 v FRS1).Tuy nhin, tc CIR gia R1 v R2 c th ch l 64Kbps. iu tng t khi R3 ktni vi ISP bng ng fastEthernet (100Mbps). Trong khi , ISP ch cung cpng truyn 2Mbps theo tha thun. R1, R2, R3 s gi d liu ra mt cng vi tc ln lt l 128Kbps, 1.544Mbps, 100Mbps (ng vi tc vt l). Do , vicgi cc gi tin vt qu tc cho php xy ra. Lc ny, c th s lm tng delayv packet loss. TS v TP s gip ngn chn cc hin tng nu trn.

Vic s dng TS v TP c th hin c th trong bng sau:


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Bng 1.31: S dng Policing v Shaping


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1.6. Link efficiency

Bandwidth v delay l 2 vn nh hng nhiu nht n QoS. Link efficiency cth gip gim bt nh hng ca 2 vn trn khi thc hin QoS cho mt h thngmng. Link efficiency gm 2 cng c chnh:

Nn d liu ti v IP Header: Lm gim s bits d liu truyn. Cc gi tin sc y i nhanh hn.

Link Fragmentation and Interleaving (chia nh gi tin v u tin truyn): Cngc ny chia nh gi tin ln ban u thnh nhiu gi tin nh hn trc khi gi.

1.6.1. Nn d liu ti v IP Header

i vi IOS router th nn gm 2 phn chnh: nn d liu ti v nn IP header. Nnd liu ti nn c IP header v d liu ti, trong khi nn IP header ch nn IPheader. Do , nn d liu ti c th cung cp mt t l nn ln cho cc gi tin c kch thc ln vi rt nhiu d liu ngi dng trong so vi nn IP headerthng dng cho cc gi tin c kch thc nh. Nn d liu ti v nn IP headeru yu cu kh nng p ng v CPU v b nh ca router.

Hnh1.32: Nn d liu ti v IP header

Xt v d c th v cng c nn s lm gim nh hng ca Bandwidth nh sau:

Hnh1.33: V d nh hng ca Bandwidth khi khng s dng cng c nn


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Theo hnh1.6.1 b , cc gi tin yu cu Bandwidth 80Kbps cho vic truyn nhngng truyn (trong trng hp ny) ch c 64kbps, nu khng s dng cng cnn th hng i s hng i s y (hng i First-in, first-out FIFO l hng imc nh trong router Cisco) v s c gi tin b rt.

Nu kt hp thm cng c nn (gi s vi t l l 2:1) th cc gi tin yu cuBandwidth 80Kbps cho vic truyn th sau khi nn, cc gi tin ch cn 40kbps. Ving truyn 64kbps m lu lng cn ti l 40 kbps th cc gi tin s khng brt. iu ny c th hin trong hnh sau:

Hnh1.34: V d gim nh hng ca Bandwidth khi s dng cng c nn

Cc cu lnh cu hnh c bn v cng c nn c th hin trong bng sau:

Bng 1.35: Bng cc lnh cu hnh c bn v cng c nn


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1.6.2. Link Fragmentation and Interleaving

Khi routre gi mt gi tin ra khi mt interface th router s gi c nguyn gi. Vvy, khi mt gi tin c kch thc ln n trc, gi tin c kch thc nh n sau phi ch cho n khi router gi xong gi tin c kch thc ln. Do nh hng cadelay gi tin nh n sau c th s b nh rt. Loi delay c th nh rt gi tin y l Serialization delay. V Serialization delay ph thuc vo kch thc ca gitin. Cng c Link Fragmentation and Interleaving (LFI) gim vic nh rt cc gitin nh n sau bng cch chia nh gi tin ln n trc thnh nhiu gi tin nh vcho gi tin nh n sau truyn xen k vi cc gi tin b chia nh t gi tin ln.

Xt v d c th sau:

Hnh1.36: V d khi gi tin ln n trc khng c chia nh

Theo hnh1.36 , gi tin ln n trc c kch thc 1500 bytes, c router gi rakhi mt interface trc. Gi tin nh n sau vi kch thc 60 c th s b nhrt do Serialization delay.

Hnh1.37: V d v cng c chia nh gi tin v truyn xen k

Theo hnh1.37 , gi tin th 1 (1500 bytes) n trc, c chia nh thnh 3 gi tin(P1F1, P1F2, P1F3). Gi tin th 2 (200 bytes) n sau nhng vn c truyn itrc hai gi tin P1F2, P1F3. Nn nu gi tin th 1 vi kch thc 1500 bytes


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khng c chia nh th gi tin th 2 s phi i gi th 1 truyn xong th mic gi i. V gi tin th 2 c th b rt do delay.

2> THC HNH 2.1. M hnh thc hnh

Hnh 2.1: m hnh lab

Yu cu:

1/ Xy dng dch v VOICE, WEB v FTP ti my Server

2/ S dng SDM thit lp u tin trn cc Router cho cc ng dng theo mc sau:

VOICE chim 50% bng thng WEB chim 20% bng thng FTP chim phn bng thng cn li

2.2. Thc hin cu hnhTrn R3 ta s cu hnh ng nhp vo SDM:

R3(config)# username xuanduy privilege 15 password duy123

R3(config)# ip http server

R3(config)# ip http secure-server

R3(config)# ip http authentication local


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R3(config)# line vty 0 4

R3(config-line)# privilege level 15

R3(config-line)# login local

R3(config-line)# transport input telnet ssh

Tip theo ta s ci t SDM:

Hnh 2.2: ci SDM ln my tnh v router

Hnh 2.3: nhp IP, username v password ca router cn cu hnh


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Hnh 2.4: Chn loi ci t ca SDM

Hnh 2.5: Chn vng ci t SDM


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Hnh 2.6: SDM sau nh c ci t

Hnh 2.7: G a ch router mun cu hnh


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Hnh 2.8: G User Name v Password ca router SDM kt ni n

Hnh 2.9: SDM kt ni n router


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Hnh 2.10: Thng tin ca router kt ni SDM

Hnh 2.11 : Chn cng cu hnh SDM


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Chn S1/0 lm ng Out v tip tc Next. Khi hon hnh ta qua tab Edit QoSPolicy chnh sa theo yu cu bi

Theo yu cu ta s cu hnh VOICE l 50%, HTTP 20% v FTP l cn li

Hnh 2.12: Cu hnh dch v voice

Hnh 2.13: Cu hnh dch v http


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Hnh 2.14: Cu hnh dch v ftp

Hnh 2.15: R3 sau khi c cu hnh


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Hnh 2.17: Show policy- map ca R3

Tip theo ta s tin hnh th nghim bng cch bt 3 dch v ln chy cng 1 lc vxem tin trnh QoS v lu lng c phn chia cho tng dch v

Hnh 2.18: Gi polycom cho my Server t myClient


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Hnh 2.19: Giao thc RTP bt c khi gi polycom

Hnh 2.20: Tin hnh DoSHTTP Server


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Hnh 2.21: Giao thc http bt c khi ang DoS

Hnh 2.22: S dng FillZila ng nhp vo FTP server v download


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Hnh 2.23: Giao thc FTP-DATA bt c khi ang download t FTP server

Hnh 2.24: Kt qu bng thng thu c trn NetFlow

2.3. Kt Lun Kt qu t c

Gii php chia u bng thng quy nh cho tng dch v.


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C th iu chnh bng thng cho tng dch v cho ph hp vi nhu cu sdng.

Gip tnh trng b tt nghn gim ti thiu.

Trin khai c 1 h thng nh.

2.4. Ti liu tham kho

http://nhatnghe.com/forum/showthread.php?t=24937

http://www.youtube.com/watch?v=PXwa1NfDwY8

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.1_1

3_ea1/configuration/guide/swqos.html

http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfmcli2.html

http://vnpro.org/forum/showthread.php/12260-Nhu-c%E1%BA%A7u-v%E1%BB%81-QoS-v%C3%A0-c%C3%A1c-m%C3%B4-h%C3%ACnh-QoS
http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfmcli2.htmlhttp://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfmcli2.htmlhttp://vnpro.org/forum/showthread.php/12260-Nhu-c%E1%BA%A7u-v%E1%BB%81-QoS-v%C3%A0-c%C3%A1c-m%C3%B4-h%C3%ACnh-QoShttp://vnpro.org/forum/showthread.php/12260-Nhu-c%E1%BA%A7u-v%E1%BB%81-QoS-v%C3%A0-c%C3%A1c-m%C3%B4-h%C3%ACnh-QoShttp://vnpro.org/forum/showthread.php/12260-Nhu-c%E1%BA%A7u-v%E1%BB%81-QoS-v%C3%A0-c%C3%A1c-m%C3%B4-h%C3%ACnh-QoShttp://vnpro.org/forum/showthread.php/12260-Nhu-c%E1%BA%A7u-v%E1%BB%81-QoS-v%C3%A0-c%C3%A1c-m%C3%B4-h%C3%ACnh-QoShttp://vnpro.org/forum/showthread.php/12260-Nhu-c%E1%BA%A7u-v%E1%BB%81-QoS-v%C3%A0-c%C3%A1c-m%C3%B4-h%C3%ACnh-QoShttp://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfmcli2.html

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