PowerPoint Presentation

I. Gii thiu v QoS v ATM1.Tng quan v vai tr ca QoS 1.1. nh ngha QoSTheo khuyn ngh E 800 ITU-T cht lng dch v l Mt tp cc kha cnh ca hiu nng dch v nhm xc nh cp tho mn ca ngi s dng i vi dch v.ISO 9000 nh ngha cht lng l cp ca mt tp cc c tnh vn c p ng y cc yu cu.Trong khi IETF [ETSI TR102] nhn nhn QoS l kh nng phn bit lung lu lng mng c cc ng x phn bit i vi cc kiu lung lu lng, QoS bao trm c phn loi ho dch v v hiu nng tng th ca mng cho mi loi dch v.

Hnh 1.1: Quality of Service1.2. Vai tr ca QoSVi cc xu hng pht trin t cc dch v thng mi in t (e-commerce), vn m bo cht lng dch v cho cc ng dng trn mng Internet tr nn cn thit hn bao gi ht.1.3. Cc thng s QoSThng s QoSCc gi tr v dBng thng (nh nht)64kb/s, 1.5Mb/s, 45Mb/sTr (ln nht)50ms tr vng, 150ms tr vngJitter (bin ng tr)10% ca tr ln nht, 5ms bin ngMt thng tin (nh hng ca li)1 trong 1000 gi cha chuyn quaTnh sn sng (tin cy)99.99%Tnh bo mtM ha v nhn thc trn tt cc c lung lu lng2. Tng quan v ATMATM(ting Anh:Asynchronous Transfer Mode Ch truyn khng ng b) l h thng chuyn mch gi tin tin, c th truyn ng thi d liu,m thanhv hnh nh s ho trn c mngLANv mngWAN.

Hnh 2.1 Gii thiu v ATMy l mt trong nhng phng php kt ni mng WAN nhanh nht hin nay, tc t t 155 Mbit/s n 622 Mbit/s. Cc c trng ca ATM bao gm:* S dng gi d liu (cell) nh, c kch thc c nh (53 byte), d x l hn so vi cc gi d liu c kch thc thay i trong X.25 v Frame Relay.53 bytes gm 48 byte d liu v 5 byte header.* Tc truyn d liu cao, theo l thuyt c th t 1,2 Gbit/s* Cht lng cao, nhiu thp nn gn nh khng cn n vic kim tra li* C th s dng vi nhiu phng tin truyn dn vt l khc nhau (cp ng trc, cp dy xon, cp si quang)* C th truyn ng thi nhiu loi d liuII. m bo cht lng QoS1. 1. Khi nimMt cch tng quan QoS mang ngha l Kh nng ca mng m bo v duy tr cc mc thc hin nht nh cho mi ng dng theo nh cc yu cu ch r ca mi ngi s dng. Nh cung cp dch v mng m bo QoS cung cp cho ngi s dng v thc hin cc bin php duy tr mc QoS khi iu kin mng b thay i v cc nguyn nhn nh nghn, hng hc thit b hay li ng truyn v. vAB NETNET CEQCEQ NP NP NP QoSHnh 1. 1: M hnh QoS tng quanTrong m hnh c c cht lng ca tng mng (NP-Net perfomane) trn ng truyn t u cui ny ti u cui kia. QoS gip cho cc dch v vin thng v nh cung cp mng p ng c cc nhu cu dch v ca khch hng. Cn NP c o trc tip hiu nng trn mng khng chu nh hng ca khch hng v cc thit b u cui. NP yu cu phi c h tr cc kh nng:* Kh nng truy nhp dch v* Kh nng khai thc* Kh nng duy tr* Kh nng tch hp dch v1. 1. 1 Phn cp QoSMt cch t nhin, c nhiu mc QoS khc nhau cng ging nh l c nhiu ng dng vy. Cc ng dng li thay i rt ln thm ch c vi nhng yu cu n gin v bng thng.V d nh tn hiu thoi c th yu cu bt k s liu no trong khong t 8 n 64 Mb/sMt mng cn phi c kh nng cung cp QoS yu cu cho mi ng dng, khng cn bit bng thng cn thit c c nh hay khng. Kh nng v pha mng cp cho cc ng dng cc bo m v QoS v d nh l bo m v bng thng, c xem nh l phn cp QoS ca mng.Phn cp tt QoS s cho php ngi s dng thm ch trong cng mt lp dch v xc nh bng thng h yu cu chnh xc hn. S chnh xc ny mun t c th phi tr gi bng phc tp ca mng, y l l do chnh trong vic gii hn cc tham s QoS v t ra cc lp dch v trong giai on u.

Phn cp l mt kha cnh quan trng khc ca QoS. Phn cp xc nh cc thng s QoS tt n mc no m ngi s dng c th nh r cho cc ng dng c th. Nu mng cung cp QoS khng tiu chun th n c th gii hn ngi s dng truy nhp vo mng.1. 1. 2 Bo m QoS m bo cht lng, ta thc hin 3 vn sau:* Cc c ch m bo cht lng dch v ti cc nt mng: Cc thut ton xp hng (queueing), c ch nh hnh lu lng (traffic shapping), cc c ch ti u ho ng truyn, cc thut ton d on v trnh tc nghn. * Phng thc bo hiu QoS gia cc nt mng phi hp hot ng m bo cht lng dch v t u cui ti u cui. * Chnh sch QoS v cc chc nng tnh cc, qun l iu khin v phn pht QoS cho cc lu lng i qua ton mng. 1. 1. 3 Cc tham s QoS Thng s QoSCc gi tr v dBng thng (nh nht)64kb/s, 1. 5Mb/s, 45Mb/sTr(Ln nht)50ms tr vng, 150ms tr vngJitter (Bin ng tr)10%ca tr ln nht, 5ms bin ngLoss (Mt thng tin)-cc nh hng ca li1 trong 1000 gi cha chuyn giaoTnh sn sng (tin cy)99. 99%Bo mtM ho v nhn thc trn tt c cc lung lu lng Bng 1.1.3 Cc tham s QoS1. 1. 3. 1 Bng thng (nh nht)Bng thng ch n gin l thc o s lng bt trn giy m mng sn sng cung cp cho cc ng dng Khi c s dng nh l mt tham s QoS bng thng l yu t ti thiu m mt ng dng cn hot ng.V d, thoi PCM cn bng thng l 64kb/s iu ny khng to ra khc bit khi mng xng sng c kt ni 45Mb/s gia cc nt mng ln. Bng thng cn thit c xc nh bi bng thng nh nht sn c trn mng. Cc ng dng thoi nh thoi PCM 64kb/s c gi l cc ng dng gii hn tr . Thoi PCM 64kb/s ny s khng hot ng tt hn nu c bng thng 128kb/s. Loi thoi ny ph thuc hon ton vo thng s tr QoS mng c th hot ng hiu qu. 1. 1. 3. 2. TrTr lin quan cht ch vi bng thng . Vi cc ng dng gii hn bng thng th bng thng cng ln tr s cng nh. i vi cc ng dng gii hn tr nh l tn hiu thoi 64kb/s, tham s QoS tr ln nht cc bit gp phi khi truyn qua mng.Mi quan h gia bng thng v tr trong mng c ch ra trong hnh v sau:Khung = X bitng bit"t1 = bit u tin vot1 = bit u tin ra(a)(b)Khung = X bitng bit"t1 = bit cui cng rat1 = bit u tin raTrong phn (a), t2 t1 = s giy tr. Trong phn (b), X bit/( t2 t1)=bit/s bng thng. Nu c nhiu bng thng hn tc l c nhiu bit n hn trong mt n v thi gian th tr tng th nh hn. Bng thng v tr ca mng c mi quan h vi nhau v c th tnh ton ti nhiu ni trong mng, thm ch t u cui ti u cuiBng thng c nh ngha l s bit ca mt khung chia cho thi gian tri qua k t khi bit u tin ri khi mng cho ti khi bit cui cng ri khi mng. Bng thng bin i tc l tr cng bin i trn mng . Cc nt mng c nhm vi nhau cng c th ng gp vo s thay i ca tr. Ti cc nt mng u c qu trnh xp hng. Tr xy ra do cn thi gian chuyn gi ti hng i u ra (output queue) v tr do gi b gi trong hng i.

Tuy nhin vi cc thut ton xp hng c u tin c th gim tr xung di 10ms. Ngoi ra cng c th k n tr khi cc bridge, switch v router chuyn d liu, n ph thuc vo tc ca h thng mch, CPU cng nh kin trc bn trong cc thit b mng. Tham s QoS tr ch xc nh c tr ln nht m khng t bt k mt gii hn nh hn no cho tr ca mng.