MC LC

n tt nghip i hc

Mc lc

MC LC

iv

THUT NG VIT TT

1

LI NI U

3

CHNG I - MT S VN TNG QUAN V MNG IP

31.1 Khi nim v mng IP

31.2 M hnh phn lp TCP/IP

71.3 Cu trc tiu IPv4 v IPv6

71.3.1 Cu trc tiu gi tin IPv4

91.3.2 Cu trc tiu gi tin IPv6

111.3.3 a ch IPv4

131.4 Cc mc QoS end to end.

131.4.1 Dch v n lc ti a.

141.4.2 Dch v tch hp (Intergrated Service)

151.4.3 Dch v khc bit (Differentiated Service)

18

CHNG II - CHT LNG DCH V TRONG MNG IP

182.1 Khi nim QoS

202.2 Tr

202.3 Nghn

212.4 Jitter

222.5 Mt gi

23

CHNG III - KIN TRC CQS

233.1 Vn nh tuyn trong mng IP

233.1.1 Khi nim v nh tuyn

243.1.2 Cc phng php nh tuyn.

243.1.2.1 nh tuyn tnh

253.1.2.2 nh tuyn lun phin

263.1.2.3 nh tuyn ng

273.1.3 Mt s giao thc nh tuyn

273.1.3.1 nh tuyn vect khng cch.

293.1.3.2 nh tuyn trng thi lin kt

313.1.3.3 nh tuyn phn lp.

323.1.3.4 nh tuyn khng phn lp.

333.1.3.5 nh tuyn trn c s QoS.

343.2 Cu trc router

373.3 Kin trc CQS

CHNG IV - 41

NG DNG KIN TRC CQS CHO QUN L NGHN TRONG MNG IP

414.1 Ti sao phi qun l nghn.

424.2 Cc chin lc qun l nghn s dng kin trc CQS.

424.2.1 Cc chin lc qun l nghn s dng hng i

424.2.1.1 Chin lc hng i FIFO

424.2.1.2 Chin lc hng i cn bng trng s (WFQ)

584.2.1.3 Chin lc hng i khch hng (CQ)

614.2.1.4 Chin lc hng i u tin (PQ)

634.2.1.5 So snh cc chin lc s dng hng i

644.2.2 Cc chin lc trnh nghn.

654.2.2.1 Random Early Detection

674.2.2.2 Weighted Random Early Detection

684.2.2.3 Random Early Detection vo/ra

694.2.2.4 Adaptive Random Early Detection

704.2.2.5 Flow Random Early Detection

72

KT LUN

73

TI LIU THAM KHO

THUT NG VIT TT

AVB

Available Bit Rate

Tc bt kh dng

BGP4

Border Gateway Protocol version 4

Giao thc cng bin phin bn 4

CIDR

Classess Inter Domain Routing

nh truyn lin vng khng phn lp

CL

Controlled Load

iu khin truyn ti

CQS

Classification, Queuing, Sheduling

Phn loi, hng i, lp lch

DCEF

Distributed Cisco Express Forwarding

Chuyn tip phn phi nhanh ca Cisco

DiffServ

Differentiated Servervice

Dch v khc bit

DWFQ

VIP-Distributed Weighted Fair Queuing

Hng i cn bng trng s phn phi theo VIP

FIFO

First In, First Out

Vo trc ra trc

FIP

Forwarding Information Base

C s thng tin chuyn tip

GS

Guaranteed Service

Dch v m bo

IGRP

Interior Gateway Routing Protocol

Giao thc iu khin cng bn trong

LLC

Logical Link Control

iu khin lin kt logic

LLQ

Low Laytency Queuing

Hng i tr thp

LSA

Link State Advertisements

Thng bo trng thi lin kt

MTU

Maximum Transmission Unit

Khi truyn dn ln nht

NCP

Network Control Protocol

Giao thc iu khin mng

NP

Net Performance

Hiu nng mng

OSPF

Open Sortest Path First

Thut ton tm ng ngn nht u tin

PVC

Permanent Virtual Circuit

Knh o c nh

RED

Random Early Detection

Tch sm ngu nhin

RTP

Real-Time Transport Protocol

Giao thc truyn ti thi gian thc

SLA

Service Level Agreement

Hp ng mc dch v

SVC

Switched Virtual Circuit

Knh o chuyn mch

TCP/IP

Transfer Control Protocol/Internet Protocol

Giao thc iu khin truyn ti / Giao thc lin mng

VBR

Variable Bit Rate

Tc bt bin thin

VIP

Versatile Interface Procesor

B x l giao din a nng

WFQ

Weighted Fair Queuing

Hng i cn bng trng s

LI NI U

Ngy nay mng li vin thng v ang ngy cng pht trin mnh m v rng khp trn th gii. iu t ra mt bi ton l qun l mng vin thng nh th no n hot ng mt cch hiu qu v m bo c cht lng dch v ca mng. i vi mng Internet trc y do nhu cu khch hng cha cao, ch yu l s dng cc dch v truyn thng nh truyn file, th in t, dch v telnet v.v... Do vy m dch v Best Effort l rt hiu qu v m bo c cht lng dch v. Nhng hin nay vi nhu cu truyn a phng tin ang ngy cng pht trin nhanh chng, iu lm xut hin cc dch v Intergrated Service v Differentiated Service. Khi cc dch v ny ra i th yu cu v vn nh tuyn v tc cc router cng phi c nng cao. iu cn thit phi c mt c ch qun l mi v mt kin trc mi qun l router tt hn. p ng yu cu , Kin trc CQS ra i v c ng dng trong mng Internet ngy nay. Ni dung n s nghin cu n kin trc mi ny v mt s ng dng ca kin trc CQS trong vn qun l nghn trong mng IP. n cng thc hin lp trnh m phng xc nh lng bng thng cung cp cho cc lung lu lng IP u tin s dng thut ton WFQ. B cc ca n gm nm chng nh sau:

Chng I: Mt s vn tng quan v mng IP Trnh by m hnh giao thc TCP/IP v cc dch v Best Effort, Intergrated Service, Differentiated Service.

Chng II: Cht lng dch v trong mng IP Trnh by cc thng s cht lng dch v nh: tr, nghn, jitter, mt gi.

Chng III: Kin trc CQS Trnh by vn nh tuyn trong mng IP v kin trc CQS trong router.

Chng IV: ng dng kin trc CQS cho qun l nghn trong mng IP Trnh by cc phng php qun l nghn c s dng kin trc CQS.

Ngoi ra n cng thc hin lp trnh m phng xc nh lng bng thng cung cp cho cc lung lu lng u tin IP s dng thut ton WFQ. Phn ny khng c a vo ni dung n m c a ra mt phn ring.

Trong qu trnh thc hin n, vi nng lc c hn nn chc chn khng trnh khi nhng thiu st. Rt mong c s ng gp kin ca cc thy c gio, ca cc c gi quan tm ti vn c trnh by trong n n c hon chnh hn.

Ti xin chn thnh cm n thy gio Thc s Nguyn Vn t ht sc tn tnh gip v hng dn ti trong qu trnh thc hin n.

CHNG I - MT S VN TNG QUAN V MNG IP

1.1 Khi nim v mng IP

Tin thn ca mng Internet l mng ARPANET ca B quc phng M. Mng ARPANET ra i vi mc ch l kt ni cc trung tm nghin cu ca mt s Vin nghin cu v trng i hc nhm chia s, trao i ti nguyn thng tin. Ban u giao thc truyn thng c s dng l NCP (Network Control Protocol) nhng sau c thay th bi b giao thc TCP/IP (Transfer Control Protocol/ Internet Protocol). B giao thc TCP/IP gm mt tp hp cc chun ca mng, c t chi tit cch thc cho cc my tnh thng tin lin lc vi nhau, cng nh quy c cho u ni lin mng v nh tuyn cho mng.

Trc y, ngi ta nh ngha Internet l mng ca tt c cc mng s dng giao thc IP. Nhng hin nay iu khng cn chnh xc na v nhiu mng c kin trc khc nhau nhng nh cc cu ni giao thc nn vn c th kt ni vo Internet v vn c th s dng y cc dch v Internet. Internet khng ch l mt tp hp cc mng c lin kt vi nhau, Internetworking cn c ngha l cc mng c lin kt vi nhau trn c s cng ng vi nhau v cc quy c m cho php cc my tnh lin lc vi nhau, cho d con ng lin lc s i qua nhng mng m chng khng c u ni trc tip ti. Nh vy, k thut Internet che du chi tit phn cng ca mng, v cho php cc h thng my tnh trao i thng tin c lp vi nhng lin kt mng vt l ca chng.

1.2 M hnh phn lp TCP/IP

TCP/IP l mt b giao thc c pht trin bi cc cc d n nghin cu cp cao (ARPA) ca b quc phng M. Ban u n c s dng trong mng ARPANET. Khi cng ngh mng cc b pht trin, TCP/IP c tch hp vo mi trng iu hnh UNIX v s dng chun Ethernet kt ni cc trm lm vic vi nhau. n khi xut hin cc my PC, TCP/IP li c chuyn sang mi trng PC, cho php cc my PC chy DOS v cc trm lm vic chy UNIX c th lin tc trn cng mt mng. Hin nay TCP/IP c s dng rt ph bin trong mng my tnh, m in hnh l mng Internet.

TCP/IP c pht trin trc m hnh OSI, do cc tng trong TCP/IP khng tng ng hon ton vi cc tng trong m hnh OSI. Chng giao thc TCP/IP c chia thnh bn tng: giao din mng (network interface), lin mng (internet), giao vn (transport) v ng dng (application) c cho nh hnh v 1.1:

ng dng

Trnh din

Phin

Giao vn

Mng

Vt l

Lin kt d liu

M hnh OSI

ng dng

Giao vn

Lin mng

Giao din mng

M hnh TCP/IP

Hnh 1.1: M hnh giao thc TCP/IP v m hnh OSI

Tng ng dng

Tng ng dng cung cp cc dch v di dng cc giao thc cho ng dng ca ngi dng. M s giao thc tiu biu ti tng ny gm:

FTP (File Transfer Protocol): y l mt dch v hng kt ni v tin cy, s dng TCP cung cp truyn tp gia cc h thng h tr FTP.

Telnet (Terminal Network): Cho php cc phin ng nhp t xa gia cc my tnh. Do Telnet h tr ch vn bn nn giao din ngi dng thng dng du nhc lnh tng tc. Chng ta c th nh lnh v cc thng bo tr li s c hin th.

HTTP (Hyper Text Transfer Protocol): Trao i cc ti liu siu vn bn h tr Web.

SMTP (Simple Mail Transfer Protocol): Truyn th in t gia cc my tnh. y l dng c bit ca truyn tp c s dng gi cc thng bo ti mt my ch th hoc gia cc my ch vi nhau.

POP3 (Post Office Protocol): Cho php ly th in t t hp th trn my ch.

DNS (Domain Name System): Chuyn i tn min thnh a ch IP. Giao thc ny thng c cc ng dng s dng khi ngi dng ng dng ny dng tn ch khng dng a ch IP.

DHCP (Dynamic Host Configuration Protocol): Cung cp cc thng tin cu hnh ng cho cc trm, chng hn nh gn a ch IP.

SNMP (Simple Network Managament Protocol): c s dng qun tr t xa cc thit b chy TCP/IP. SNMP thng c thc thi trn cc trm ca ngi qun l, cho php ngi qun l tp trung nhiu chc nng gim st v iu khin trong mng.

Tng giao vn

Tng giao vn chu trch nhim chuyn pht ton b thng bo t tin trnh - ti - tin trnh. Ti tng ny c hai giao thc l TCP v UDP, mi giao thc cung cp mt loi dch v giao vn: hng kt ni v phi kt ni.

Giao thc TCP

TCP thc hin mt s chc nng nh sau: Chc nng u tin l nhn lung d liu t chng trnh ng dng; d liu ny c th l tp vn bn hoc l mt bc nh. Vic u tin TCP lm l chia lung d liu nhn c thnh cc gi nh c th qun l. Sau gn mo u vo trc mi gi. Phn mo u ny c cha a ch cng ngun v cng ch. Ngoi ra n cn cha s trnh t chng ta bit c gi ny nm v tr no trong lung d liu.

Sau khi nhn c mt s lng gi nht nh, TCP s gi xc nhn. V d, nu chng ta pha nhn, v s lng gi c quy nh l 3 th chng ta s gi xc nhn cho pha gi sau khi nhn c 3 gi. u im ca vic lm ny l TCP c kh nng iu chnh vic gi v nhn cc gi tin.

Giao thc UDP

UDP (User Datagram Protocol) l mt giao thc truyn thng phi kt ni v khng tin cy, c dng thay th cho TCP trn IP theo yu cu ca ng dng. UDP c trch nhim truyn cc thng bo t tin trnh - ti - tin trnh, nhng khng cung cp c ch gim st v qun l.

UDP cng cung cp c ch gn v qun l s cng nh danh duy nht cho cc ng dng chy trn mt trm ca mng. Do t chc nng phc tp nn UDP c xu th hot ng nhanh hn TCP. N thng dng cho cc ng dng khng i hi tin cy cao.

Tng lin mng

Tng lin mng trong chng giao thc TCP/IP tng ng tng mng trong m hnh OSI. Chc nng chnh ca tng lin mng l nh a ch logic v nh tuyn gi ti ch. Giao thc ng ch nht tng lin mng l giao thc lin mng IP (Internet Protocol). Ngoi ra cn c mt s giao thc khc nh ICMP, ARP, RARP.

Giao thc IP

IP l mt giao thc phi kt ni v khng tin cy. N cung cp dch v chuyn gi n lc ti a. N lc ti a y c ngha IP khng cung cp chc nng theo di v kim tra li. N ch c gng chuyn gi ti ch ch khng c s m bo. Nu tin cy l yu t quan trng, IP phi hot ng vi mt giao thc tng trn tin cy, chng hn TCP.

Giao thc ICMP

Nh trnh by trn, IP l giao thc chuyn gi phi kt ni v khng tin cy. N c thit k nhm mc ch s dng hiu qu ti nguyn mng. IP cung cp dch v chuyn gi n lc ti a. Tuy nhin n c hai thiu ht: thiu ht iu khin li v thit lp cc c ch h tr; IP cng thit lp c ch truy vn. Mt trm i khi cn xc nh xem router hoc mt trm khc c hot ng khng. Mt ngi qun l mng i khi cn thng tin t mt trm hoc router khc.

Giao thc thng bo iu khin lin mng ICMP (Internet Control Message Protocol) c thit k b p hai thiu ht trn. N c i km vi giao thc IP.

Giao thc ARP

Giao thc phn gii a ch (ARP: Address Resolution Protocol) chuyn i a ch lgic thnh a ch vt l.

Khi mt trm hoc router cn tm a ch vt l ca mt trm hoc mt router khc trn mng, n gi gi yu cu ARP. Gi ny cha a ch vt l v a ch lgic ca ngun v a ch IP ca ch. Do ngun khng bit a ch vt l ca ch nn yu cu ny c gi qung b.

Mi trm v router trn mng u nhn v x l yu cu ARP ny, nhng ch c trm ch nhn ra a ch IP ca n v gi tr li ARP li cho ngun. Gi tr li cha a ch lgic v a ch vt l ca ch. Gi tr li ny c gi thng (gi unicast) ti trm yu cu (ngun) s dng a ch vt l c trong gi yu cu ARP

Giao thc RARP

Giao thc phn gii a ch ngc (RARP: Reverse Address Resolution Protocol) chuyn i a ch vt l thnh a ch lgic. N c s dng trong trng hp mt my bit a ch vt l ca mnh nhng li khng bit a ch IP. Khi my c bt, yu cu RARP c to ra v c gi qung b trn mng cc b. Mt my khc trn mng bit v mi a ch IP s tr li yu cu bng bn tin tr li RARP. My yu cu RARP phi chy chng trnh RARP khch v my tr li RARP phi chy chng trnh RARP ch.

Tng giao din mng

Tng giao din mng tng ng vi tng lin kt d liu v tng vt l trong m hnh OSI. Tng ny cung cp giao tip vi mng vt l. N bao gm tt c cc thnh phn phn cng ca c s h tng mng, v thc hin vic kim sot li d liu phn b trn mng vt l, to cc kt ni vt l n h thng cp trong thi gian thch hp, to khung thng tin. Tng ny khng nh ngha mt giao thc ring no c m h tr tt c cc giao thc chun v c quyn. V d nh: Ethernet, Token Ting, FDDI, X25, wireless, Async, ATM, SNA

1.3 Cu trc tiu IPv4 v IPv6

1.3.1 Cu trc tiu gi tin IPv4

Tiu IP c thm vo sau khi n nhn c thng tin ca tng chuyn vn hoc tng ng dng, sau n c a xung tng lin kt d liu truyn i trn mt phng tin nht nh. Chiu di ca tiu IP c th t 20 bytes n 60bytes trn cc ng i nu nhng chc nng l chn c s dng. Cu trc tiu c ch ra trn hnh 1.2 nh sau:

012345678910111213141516171819202122232425262728293031

VersionIHLToS

Total Length

Fragment offset

Flags

Identification

TTLProtocol

Header Checksum

Source IP Address

Destination IP Address

Options and Padding

..

Hnh 1.2: Tiu IPv4

Version: Ch ra phin bn ca giao thc hin hnh IPv4, c s dng my gi, my nhn, cc b nh tuyn cng thng nht v nh dng lc d liu.

IHL (Identifed Header Length): Trng xc nhn di tiu cung cp thng tin v di tiu ca gi tin, thng thng tiu c di 20 octets.

TOS (Type Of Service): Trng kiu phc v di 8 bit n gm 2 phn. Trng u tin v kiu phc v. Trng u tin gm 3 bit dng gn mc u tin cho cc gi tin, cung cp c ch cho php iu khin cc gi tin qua mng. Cc bit cn li dng xc nh kiu lu lng gi tin khi n chuyn qua mng, nh c tnh tr, thng qua v tin cy. Vo khong cui nm 1990, IETF nh ngha li ngha ca cc bit trong trng TOS, th hin mt tp hp cc dch v khc bit. Thng qua 6 bit u tin thit lp 64 im m (codepoint) nh x vo mt s dch v c s, 2 bit cn li trng. Tuy nhin trng d liu ny c s dng nh th no th cn tu thuc rt nhiu vo kin trc mng, v chnh bn thn mng Internet khng m bo cht lng phc v QoS, nn y n thun ch l tiu ch yu cu ch khng phi l tiu ch i hi i vi cc b nh tuyn.

TL (Total length): trng hin th tng di gi tin di 16 bit, n s dng xc nh chiu di ca ton b gi IP. Chiu di ln nht mt gi IP cho php l 65535 octets.

Identification: Trng d liu nhn dng ny di 16 bit. Trng ny c my ch dng pht hin v nhm cc on b chia nh ra ca gi tin. Cc b nh tuyn s chia nh cc gi tin nu nh n v truyn tin ln nht ca gi tin MTU (Maximum Transmission Unit) ln hn MTU ca mi trng truyn (Mi trng m gi tin c truyn dn trn ). MTU ca mi trng truyn c nh ngha nh l kch c ca gi IP ln nht m n c th c mang i trong mt khung lin kt d liu (Tng lin kt d liu truyn cc khung thng tin c ghp knh v thng tin ny c cha ng trong cc khe thi gian TS). Vic hp li cc on tin c thc hin ti my ch ch.

S chia ct gi tin to thm cng vic cho cc b nh tuyn v cc my ch u cui. Mt k thut c tn l tm tuyn ng cho n v truyn gi tin ln nht (Path MTU Discovery) c a ra, to kh nng cho mt my ch gi tin c th tm ra mt MTU rng nht c th, theo con ng t ngun ti ch m khng cn bt k qu trnh chia ct gi tin no khc.

Flags: Trng c cha 3 bit c s dng cho qu trnh iu khin phn on, bit u tin ch th ti cc b nh tuyn cho php hoc khng cho php phn on gi tin, 2 bit gi tr thp c s dng iu khin phn on, kt hp vi trng nhn dng, trng phn on xc nh gi tin nhn c sau qu trnh phn on.

Fragment Offset: Trng phn on mang thng tin v s ln chia mt gi tin, kch thc ca gi tin ph thuc vo mng c s truyn tin, tc l di gi tin khng th vt qu MTU ca mi trng truyn.

TTL (Time-to-live): Trng thi gian sng ca gi tin c s dng ngn cc gi tin lp vng trn mng. N c vai tr nh mt b m ngc, trnh hin tng tr gi tin qu lu trn mng. TTL cng s dng xc nh phm vi iu khin, qua vic xc nh xem mt gi c th i c bao xa trong mng. Bt k gi tin no c vng TTL t gi tr bng 0 th gi tin s b b nh tuyn hu b v thng bo li s c gi v trm pht gi tin.

Protocol: Trng ny c dng xc nhn giao thc tng k tip mc cao hn ang s dng dch v IP di dng con s.

H-Check sum: trng kim tra tng di 16 bit, c tnh ton trong tt c cc trng ca tiu IPv4 (ToS, HL, TL...). Mi khi gi qua b nh tuyn, cc trng la chn c th b thay i v trng TTL s b thay i. Cho nn mt gi tin khi qua cc b nh tuyn th trng kim tra tng cn phi c tnh ton v cp nht li m bo tin cy ca thng tin nh tuyn.

Source Address- Destination Address: Trng a ch ngun v a ch ch c cc b nh tuyn v cc gateway s dng nh tuyn cc n v s liu, lun lun i cng vi gi tin t ngun ti ch.

Options v Padding: C di thay i, dng thm thng tin tu chn v chn y m bo s liu bt u trong phm vi 32 bit.

Ngoi ra, tiu IP cng c th cha cc chc nng m n cn c x l trn mi b nh tuyn dc theo ng truyn. Tuy nhin, cc chc nng ny khng c s dng qu nhiu bi v bt k ci g thm vo phn tiu ca gi tin, u yu cu mt qu trnh x l ph i vi mi b nh tuyn trung gian. Thng thng, cc bn ghi tuyn ng s c thm vo trong trng la chn.

1.3.2 Cu trc tiu gi tin IPv6

Din n IP phin bn 6 c bt u vo thng 7-1999 bi 50 nh cung cp Internet hng u vi mc ch pht trin giao thc IPv6, n s ci thin cht lng v bo mt ca Internet, thit lp mt c cu cho th k mi. IPv6 c bit quan trng khi cc thit b tnh ton di ng tip tc gia tng trong thp k ti.

Do s thay i v bn cht ca Internet v mng thng mi m giao thc lin mng IP tr nn li thi. Trc y, Internet v hu ht mng TCP/IP cung cp s h tr cc ng dng phn tn kh n gin nh truyn file, mail, truy nhp t xa qua TELNET, song ngy nay Internet ngy cng tr thnh a phng tin, mi trng giu tnh ng dng, dn u l dch v WWW (World Wide Web). Tt c s pht trin ny b xa kh nng p ng cc chc nng v dch v ca mng IP. Mt mi trng lin mng cn phi h tr lu lng thi gian thc, k hoch iu khin tc nghn linh hot v cc c im bo mt m IPv4 hin khng p ng c y . Cu trc tiu gi tin IPv6 c cho nh hnh v 1.3:

012345678910111213141516171819202122232425262728293031

VersionTraffic Class

Flow Label

Hop Limit

Next Header

PayLoad Length

Source Address (128 bit)

Destination Address (128 bit)

..

Data

..

Hnh 1.3: Khun dng tiu IPv6

Version: Ch ra phin bn IPv6 (4 bits).

Traffic Class: Lp lu lng (8 bits), s dng phn phi mc u tin lu lng Internet.

Flow Label: Nhn lung (20 bits), c dng xc nh cch x l c bit t ngun ti ch theo th t gi.

Payload Length: di ti tin (16 bits). Xc nh di ca s liu trong gi. Khi thit lp v 0 th l cch chn ti ln khi chuyn theo tng chng .

Next Header: Tiu k tip (8 bits). Xc nh giao thc ng gi tip theo. Cc gi tr tng thch vi cc gi tr dng trong trng giao thc IPv4.

Hop Limit: Gii hn bc nhy (8 bits), mi b nh tuyn, khi chuyn gi gi tr ny s gim i 1, nu gi tr ca trng ny l 0 th gi s b loi b. Trng chc nng gii hn bc nhy thay cho trng TTL trong tiu IPv4.

Source address: a ch ngun IPv6 (128 bit).

Destination address: a ch ch IPv6 (128 bit).

Th gii ang i mt vi vic thiu a ch IP cho cc thit b mng, a ch di 32 bit khng p ng c s bng n ca mng. Thm na, IPv4 l giao thc c, khng p ng nhng yu cu mi v bo mt, s linh hot trong nh tuyn v h tr lu lng, IPv6 c thit k bao gm nhng chc nng v nh dng m rng hn IPv4 gii quyt vn ny. Tt c cc a ch s dng trong Internet u phi duy nht. Vi phng thc nh a ch hin nay th vic thiu a ch s xy ra sm hn. IPv6 l mt giao thc thay th c kh nng duy tr s pht trin ca Internet, gii quyt vn khng gian a ch IP: 3,4x1038 so vi khong 4 t a ch IPv4 v nhng thuc tnh khc ca Internet.

IPv6 khng ch c kh nng m rng a ch m cn h tr kin trc mng hnh thang, pht trin bo mt v tnh ton vn d liu, nng cao cht lng dch v QoS v tnh bo mt, nh tuyn n gin v c tnh t ng nh cu hnh.

Vi khng gian a ch v cng ln n cho php cc nh thng mi trin khai cc h thng thit b mng bn v di ng mt cch hiu qu. S linh hot trong nh tuyn vi cc a ch ca nt, thit b nh v theo cu trc cy v kh nng t nh cu hnh v pht hin cc thit b xung quanh.

1.3.3 a ch IPv4

Mi trm trong mng Internet u c c trng bi mt s hiu nht nh gi l a ch IP. a ch IP c s dng trong lp mng nh tuyn cc gi tin qua mng. Do t chc v ln ca cc mng con trong lin mng khc nhau nn ngi ta chia a ch IP thnh cc lp A, B, C, D.

Lp A: cho php nh danh ti 126 mng, vi ti a 16 triu host trn mi mng. Lp ny c dng cho cc mng c s trm cc ln.

Lp B: cho php nh danh ti 16384 mng vi ti a 65534 host trn mi mng.

Lp C: cho php nh danh c khong 2 triu mng vi ti a 254 host trn mt mng. Lp ny c dng cho cc mng c t trm.

Lp D: c dng gi cc IP datagram ti mt nhm cc host trong lin mng.

Cc lp ny c th hin nh hnh v 1.4:

0NNNNNNN

Host ID

Host IDHost ID

10NNNNNN

Network ID

Host IDHost ID

110NNNNN

Network ID

Network IDHost ID

1110NNNN

Multicast MulticastMulticast

07152331

Lp A

Lp B

Lp C

Lp D

Hnh 1.4: Phn lp a ch IP

Phn mng l mt cng ngh c s dng chia mt a ch mng IP n ra thnh mt s cc mng con. y l mt hnh thc m rng m hnh a ch. iu ny cho php mt di a ch IP ln c chia ra thnh cc di a ch nh hn v c phn n nhiu v tr khc nhau m khng gp kh khn g so vi vic yu cu mt a ch lp mng ring cho mi v tr. Cch x l phn mng ny c thc hin bng cch phn chia phn my ch ca lp a ch IP cho tng mng con. Cng nh a ch phn lp c in, ranh gii gia phn mng (tin t mng + mng con) v cc phn my ch th c xc nh bi mt mt n mng con. Khi cn c thm mt vng nhn dng phn mng subnetID (subnet Identifier) nh danh cc mng con . Vng subnetID s nm trong vng nhn dng my ch hostID c. Vn mng con s gp phn gii quyt cho cc bng nh tuyn trong cc b nh tuyn thc hin n gin hn trong qu trnh tm kim a ch.

S phn mng chia mt a ch IP n thnh cc mng con. Mt mng siu nh c to thnh bi vic tng hp nhiu mng con, to thnh mt a ch chung cho cc mng . Vic tng hp ny to ra hai u im sau:

Gim kch c ca cc bng nh tuyn c duy tr bi cc b nh tuyn cng vi vic gim s lng cc u vo mng trn lp ring bit.

To ra kh nng s dng hiu qu khng gian a ch IP cha c s dng bng cch ch cp a ch cho mt mng khi n cn.

Khi cc a ch lp con gn nhau th c biu din li bng mt k hiu tin t mang v khi ny c gi l khi nh tuyn lin vng khng phn lp CIDR (Classess Inter Domain Routing).

CIDR c tc dng:

Gim tc cp pht cc a ch IP ca mng Internet cho cc mng con.

Gim s ng vo cc b nh tuyn ca mng ton cu.

Cc t chc gi y mong mun rng mt a ch Internet s c phn chia thnh cc khi CIDR hn l cc a ch c chia lp nh truyn thng c m t trn.

1.4 Cc mc QoS end to end.

Ni n cc mc dch v l ni n cc kh nng QoS end to end thc t, ngha l kh nng mt mng thc hin nhu cu dch v bi lu lng mng ring end to end hoc edge to edge. Cc dch v khc nhau mc QoS chnh xc ca chng. C ba mc QoS end to end c th c cung cp thng qua mng hn hp: Dch v n lc ti a, dch v khc bit v dch v tch hp.

1.4.1 Dch v n lc ti a.

Dch v Best Effort hon ton ph hp vi cc ng dng khng yu cu cht ch v thi gian v s phn phi gi c kh nng d on trc. Nh l cc ng dng c khuynh hng pht sinh bng n d liu hoc t nht c th chu c s bng n. Vi TCP, mng c th x l nhiu ng dng khi khng ch bng n m cn chu ng s mt gi.

Cy ng dn ngn nht thit lp kt ni ch ra. Ngay c khi tham s ca giao thc nh tuyn l mt c tnh c y ngha nh tr tng chng hay bng thng kh dng th mng cng khng m bo tnh sn sng thc t ca ti nguyn (nh bng thng kt ni v kh nng router) dc ng dn ti mt thi im cho trc. Bi v m hnh edge/core tch ri, cc giao thc nh tuyn IP khng th tc ng ti nhu cu thay i nng ng cc lung lu lng end to end bng n trn mng. Trong mng IP thng thng, bng thng kh dng thc t hoc tr trn mt s chng cho ph thuc vo ln trn s linh ng ca tng lung lu lng qua mng ti mt thi im.

Mt router IP thng thng phn nh bn cht nh ngha dch v n gin ca mng IP Best Effort. Nhim v c bn ca mt router IP l chuyn mt gi m n nhn c ra khi mt giao din, thc hin tm kim bng chuyn tip da trn a ch ch ca gi v chuyn gi ti router chng k tip nh ch ra. Router c gng thc hin cng vic nhanh ti mc n c th. Tuy nhin router quan tm ti ni gi gi m t khi quan tm ti vic khi no gi gi. iu n gin l n thc hin theo nguyn l hng i FIFO.

1.4.2 Dch v tch hp (Intergrated Service)

ng trc nhu cu ngy cng tng trong vic cung cp cc dch v thi gian thc (thoi, video) v bng thng cao (a phng tin) dch v tch hp IntServ ra i. y l s pht trin ca mng IP nhm ng thi cung cp dch v truyn thng n lc ti a v cc dch v thi gian thc (minh ho trn hnh 1.5). ng lc thc y m hnh ny ch yu do nhng l do c bn sau y:

Dch v n lc ti a khng cn tt na: ngy cng c nhiu ng dng khc nhau c nhng yu cu khc nhau v c tnh lu lng c trin khai, ng thi ngi s dng ngy cng yu cu cao hn v cht lng dch v.

Cc ng dng a phng tin ngy cng xut hin nhiu: mng IP phi c kh nng h tr khng ch n dch v m phi h tr tch hp a dch v ca nhiu loi lu lng khc nhau t thoi, s liu n Video.

Ti u ho hiu sut s dng mng v ti nguyn mng: m bo hiu qu s dng v u t. Ti nguyn mng s c d tr cho lu lng c u tin cao hn, phn cn li s dnh cho s liu n lc ti a.

Cung cp dch v tt nht: m hnh dch v IntServ cho php nh cung cp mng cung cp c dch v tt nht khc bit vi cc nh cung cp cnh tranh khc.

ng dngSetup

Lp lchPhn loi

Setup

Giao thc nh

tuyn/

Database

Lp lchPhn loi

iu khin

chp nhn/

Cng bc

Data

IP Data

Cc bn tin Setup t trc

Hnh 1.5 : M hnh dch v tch hp

Trong m hnh ny c mt s thnh phn tham gia nh sau:

Giao thc thit lp: Setup cho php cc my ch v cc router d tr ng ti nguyn trong mng x l cc yu cu ca cc lung lu lng ring, RSVP, Q.2931 l mt trong nhng giao thc .

c tnh lung: xc nh cht lng dch v QoS s cung cp cho lung ring bit. Lung c nh ngha nh mt lung cc gi t ngun n ch c cng yu cu v QoS. V nguyn tc c th hiu c tnh lung nh bng tn ti thiu m mng bt buc phi cung cp m bo QoS cho lung yu cu.

iu khin lu lng: trong cc thit b mng (my ch, router, chuyn mch) c thnh phn iu khin v qun l ti nguyn mng cn thit h tr QoS theo yu cu. Cc thnh phn iu khin lu lng ny c th c khai bo bi giao thc bo hiu nh RSVP hay nhn cng. Thnh phn iu khin lu lng bao gm:

iu khin chp nhn: xc nh thit b mng c kh nng h tr QoS theo yu cu hay khng.

Thit b phn loi (Classifier): nhn dng v la chn lp dch v - da trn ni dung ca mt s trng nht nh trong mo u gi.

Thit b lp lch (Scheduler): cung cp cc mc cht lng dch v QoS trn knh ra ca thit b mng.

Cc mc cht lng dch v cung cp bi IntServ bao gm:

Dch v bo m GS: bng tn dnh ring, tr c gii hn v khng b tht thot gi tin trong hng i. Cc ng dng cung cp thuc loi ny c th k n: hi ngh truyn hnh cht lng cao, thanh ton ti chnh thi gian thc v.v...

Dch v kim sot ti CL: khng m bo v bng tn hay tr nhng khc n lc ti a im khng gim cht lng mt cch ng k khi ti mng tng ln. Ph hp cho cc ng dng khng nhy cm lm vi tr hay mt gi nh truyn multicast audio/video cht lng trung bnh.

1.4.3 Dch v khc bit (Differentiated Service)

Vic a ra m hnh IntServ c v nh gii quyt c nhiu vn lin quan n QoS trong mng IP. Tuy nhin trn thc t, m hnh ny khng thc s m bo c QoS xuyn sut (end-to-end). c nhiu c gng thay i iu ny nhm t c mt mc QoS cao hn cho mng IP v mt trong nhng c gng l s ra i ca DiffServ. DiffServ s dng vic nh du gi v xp hng theo loi h tr cc dch v u tin qua mng IP. Hin ti IETF c mt nhm lm vic DiffServ a ra cc tiu chun RFC v DiffServ.

Nguyn tc c bn ca DiffServ nh sau:

nh ngha mt s lng nh cc lp dch v hay mc u tin. Mt lp dch v c th lin quan n c tnh lu lng (bng tn min - max, kch c burst, thi gian ko di burst)

Phn loi v nh du cc gi ring bit ti bin ca mng vo cc lp dch v.

Cc thit b chuyn mch, router trong mng li s phc v cc gi theo ni dung ca cc bit c nh du trong mo u ca gi.

Vi nguyn tc ny, DiffServ c nhiu li th hn so vi IntServ:

Khng yu cu bo hiu cho tng lung.

Dch v u tin c th p dng cho mt s lung ring bit cng mt lp dch v. iu ny cho php nh cung cp dch v d dng cung cp mt s lng nh cc mc dch v khc nhau cho khch hng c nhu cu.

Khng yu cu thay i ti cc my ch hay cc ng dng h tr dch v u tin. y l cng vic ca thit b bin.

H tr rt tt dch v VPN.

Tuy nhin c th nhn thy DiffServ cn vt qua mt s vn nh:

Khng c kh nng cung cp bng tn v tr m bo nh GS ca IntServ hay ATM.

Thit b bin vn yu cu b Classifier cht lng cao cho tng gi ging nh trong m hnh IntServ.

Vn qun l trng thi classifier ca mt s lng ln cc thit b bin l mt vn khng nh cn quan tm.

Chnh sch khuyn khch khch hng trn c s gi cc cho dch v cung cp cng nh hng n gi tr ca DiffServ.

M hnh DiffServ ti bin v li c m t trong hnh 1.6 sau y:

Phn loi

a byte

Chnh sch

nh du

gi

Hng i, qun

l lp lch

Phn loi DS

byte

Hng i, qun l

Lp lch

Router bin

Router li

Hnh 1.6: M hnh DiffServ ti bin v li ca mng

M hnh DiffServ bao gm mt s thnh phn nh sau:

DS-Byte: byte xc nh DiffServ l thnh phn ToS ca IPv4 v trng loi lu lng IPv6. Cc bit trong byte ny thng bo gi tin c mong i nhn c thuc dch v no.

Cc thit b bin (router bin): nm ti li vo hay li ra ca mng cung cp DiffServ.

Cc thit b bn trong mng DiffServ.

Qun l cng bc: cc cng c v nh qun tr mng gim st v o kim m bo SLA gia mng v ngi dng.

Cc mc cht lng dch v cung cp bi dch v DiffServ bo gm:

Expedited forwording

Assured forwording

Trng dch v khc bit

Trong mng DiffServ octet ToS ca gi tin IPv4 tr thnh trng dch v khc bit (Differentiated servervice Field). Trong 6 bit ca octet ToS c to nn mt im m ho DiffServ mi (DSCP) nh ch ra trn hnh 1.7. V nh vy v mt l thuyt cho php phn loi ti 26 trng hp khc nhau.

DSCP

CU

0

57

Hnh 1.7: Trng dch v khc bit

DSCP: Differentiated Services Code-Point.

CU: Currently unused.

CHNG II - CHT LNG DCH V TRONG MNG IP2.1 Khi nim QoS

Khuyn ngh ca CCITT l E800 a ra mt tnh cht chung ca QoS (Quanlity of Service): Hiu ng chung ca c tnh cht lng dch v l xc nh mc hi lng ca ngi s dng i vi dch v.

Khuyn ngh ETR300 003 ca ETSI chia v ci tin nh ngha ca ITU thnh cc nh ngha nh hn, n ph hp vi cc yu cu v quan im ca cc nhm khc nhau trong vin thng. Cc nh ngha l:

Yu cu QoS ca ngi s dng/khch hng.

ngh QoS ca nh cung cp dch v.

Vic thc hin QoS bi cc nh cung cp dch v.

S cm nhn QoS ca ngi s dng/khch hng.

Yu cu QoS ca nh cung cp dch v.

Nh vy mt cch tng qut 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 c ch r ca mi ngi s dng. Mt trong nh ngha ny chnh l cha kho hiu c QoS l g t gc nhn ca nh cung cp dch v mng. 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 lin kt v.v QoS cn c cung cp cho mi ng dng ngi s dng c th chy ng dng , v mc QoS m ng dng i hi ch c th c xc nh bi ngi s dng, bi v ch ngi s dng mi c th bit c chnh xc ng dng ca mnh cn g hot ng tt. Tuy nhin, khng phi ngi s dng t ng bit c mng cn phi cung cp nhng g cn thit cho ng dng, h phi tm hiu cc thng tin cung cp t ngi qun tr mng v chc chn rng, mng khng th t ng t ra QoS cn thit cho mt ng dng ca ngi s dng.

Cc nh cung cp dch v mng a ra thng tin c t v gi tr thc t ca cc thng s QoS theo mt trong hai cch sau. Vi mi trng knh o c nh (PVC: Permanent Virtual Circuit), cc gi tr ca cc tham s QoS c th ch n gin c ghi bng vn bn v trao li cho i din ca nh cung cp dch v mng. Khch hng vi nh cung cp dch v tho thun vi nhau v cch thc s dng. QoS c hiu lc trn PVC khi PVC sn sng. Vi mi trng knh o chuyn mch (SVC: Switched Virtual Circuit), cc gi tr ca thng s QoS c gi cho nh cung cp dch v trong bn tin bo hiu thit lp cuc gi, n l mt phn ca giao thc bo hiu c s dng cung cp dch v chuyn mch trn mng. C hai phng php u c s dng trong mng. Phng php PVC cho php QoS c cung cp trong mt min ln hn, trong khi phng php SVC i hi QoS trn mt kt ni cho trc v c thit lp lin tc.

Nu mt mng c ti u hon ton cho mt loi dch v, th ngi s dng t phi xc nh chi tit cc thng s QoS. V d, vi mng PSTN, c ti u cho thoi, khng cn phi xc nh bng thng hay tr cn cho mt cuc gi. Tt c cc cuc gi u c m bo QoS nh c quy nh trong cc chun lin quan cho in thoi. m bo cht lng mng trong mt mi trng dch v hp ng thng c biu hin theo hnh thc tho thun mc dch v (SLA: Service Level Agreement) c thit lp gia khch hng v nh cung cp dch v. SLA c th l mt phn ca hp ng dch v hay l mt ti liu c lp hon ton. SLA a ra cc yu cu ca khch hng v cc hnh pht i vi nh cung cp trong trng hp xy ra s c. SLA cng cung cp mt phng php thun tin cho khch hng so snh cc dch v do cc nh cung cp dch v khc nhau a ra.

Vy trong tt c nhng iu nu v phn cp QoS, m bo cht lng v SLA, iu no phi c thc hin cc dch v thi gian thc trn mi trng IP, v d nh VoIP? Vn l bn cht nh hng IP l mt mng n lc ti a do "khng tin cy" khi yu cu n m bo v QoS. Cch tip cn gn nht cc nh cung cp dch v IP c th t ti m bo QoS hay SLA gia khch hng v ISP l vi dch v mng IP qun l c. Thut ng qun l c y l bt c ci g m nh cung cp dch v qun l thay mt cho khch hng.

Hnh v 2.1 sau y biu din mt m hnh QoS tng quan.

``

APAP

QoS

Mng

Mng

NP

NP

NP

Hnh 2.1 M hnh QoS tng qut

Trong hnh v, NP (Net Performance: hiu nng mng) l nng lc v hiu qu ca mt mng c th. N bao gm kh nng ng x ca mng, tnh hiu qu ca mng v cht lng phc v m mng cung cp. Trnh nhm ln gia NP v QoS. AP (Access Point) l im truy nhp mng.

Cc thng s xc nh QoS l cc c tnh tr, nghn, Jitter, mt gi, v.v Sau y chng ta s tm hiu tng c tnh .

2.2 Tr

Tr (latency, delay) l c tnh ch lng thi gian cn thit mt gi tin di chuyn t ngun ti ch (tr end to end). Tr end to end l kt hp ca ba loi tr: tr truyn lan, tr qu trnh, v tr xp hng.

Tr truyn lan

Tr truyn lan do tc truyn tn hiu trong mng gy nn. V d tc cc in t truyn truyn lan trong cp ng l 125000 mile/giy. Nh vy mt mng cp ko di lin tc na vng tri t c tr truyn lan mt chiu vo khong 70ms. Loi tr ny l c th d on trc.

Tr qu trnh

Tr qu trnh l tr gy ra bi qu trnh x l ca cc thit b trong mng (nh cc thit b chuyn mch, router), v nhiu yu t khc nh qu trnh ng gi, nnTr qu trnh nh hng rt ln ti mng chuyn mch gi trong c mng IP.

V d, trong sn phm Cisco IOS VoIP, b x l tn hiu s (DSP) pht ra mu thoi sau mi 10 ms khi dng G.729. Hai mu thoi ny (c hai u tr 10 ms) c t vo mt gi. Do vy gi b tr 20 ms. Mt khong thi gian tin x l 5 ms l cn thit khi dng G.729, dn n tr ban u l 25 ms cho frame thoi u tin.

Cc nh ch to c th quyt nh s lng mu m h s gi vo trong mt gi. Bi G.729 dng cc mu thoi 10 ms, nn mi mt s gia tng mu l lm cho thi gian tr ca frame tng ln 10 ms. Trn thc t Cisco cho php ngi dng t la chn s mu t vo trong mi frame.

Tr xp hng.

Trong mng chuyn mch gi vic s dng cc hng i s gy ra mt loi tr l tr hng i. S d c loi tr ny l do trong qu trnh xp vo hng i cc gi phi ch x l c ra khi hng i. Trong trng hp lu lng mng thp (hng i khng b y) th cc gi c th c x l ngay. Nhng khi mng xy ra nghn (hng i b y) th cc gi s phi ch mt thi gian x l mi c th c truyn i v qu trnh i ny c th rt lu tu vo tnh trng nghn ko di hay khng.

Tr gy ra qu trnh xp hng ny l khng th d on trc v thng giao ng theo mt m hnh nghn.

2.3 Nghn

Chng ta bit rng router l im quy t v phn chia lu lng ca hng chc, hng trm, thm ch hng nghn lung gi. Lu lng cc lung gi n l lun lun thay i. Nu nh cc lung lu lng n ng thi cng mt lc m n cng nh hng ti mt u ra, m kh nng x l v tc giao din u ra khng p ng kp thi, tc l tc n ln hn tc i th s c nghn xy ra.

V d, lu lng hi t t nhiu ng lin kt Ethernet 100 Mbps c th d dng vt qu kh nng ca cc lung OC 3/STM 1,55 Mbps, hoc lu lng t mt ng kt ni T3/E3 c th ng thi yu cu chuyn tip ra cng nhiu ng lin kt T1/E1 nh hn. x l nhng iu , tt c cc router kt hp cc b m (hng i) ni b trong chng lu gi cc gi d ra cho n khi chng c th gi tip v pha trc. Vic ny s gy ra tr cng vo.

2.4 Jitter

Mt cch n gin jitter l s thay i khong thi gian gia cc gi. Jitter l mt vn ch tn ti trn cc mng gi. V d c mt lng gi c truyn i (gi s l gi thoi) trong mi trng IP. Ngi gi mong i cc gi ny c chuyn i mt cch tin cy v cch nhau mt khong thi gian khng i (chng hn 20ms). Thc t cc gi ny c th b tr hon khi i qua mng v khng th n ch vo cc thi im cch u nhau nh khi gi i. V d, chng c th khng nhn c sau mi 20 ms nh ch ra trn hnh 2.2. lch gia thi im mong i v thi im nhn c gi thc s c gi l jitter.

``

A

A

BC

BC

D1

D2 = D1D3 D2

My ngun

My ch

My ch truyn

Khe nhn

Mng

Hnh 2.2: Hin tng jitter.

Trn hnh v cho thy thi lng cn phi gi gi A v gi B l bng nhau (D1 = D2). Gi C vp phi mt thi gian tr trn mng v nhn c vo thi im tr hn so vi thi gian d nh. y l l do tn ti b m jitter, b m ny che i s thay i thi gian tr.

iu cn lu l jitter v tr khng phi l mt s vic, cho d c nhiu jitter trong mng gi c th lm tng tng thi gian tr trong mng. Bi v cng c nhiu jitter th cng phi tng b m jitter b vo bn cht t nhin khng th d on c ca mng gi.

Nu mng s liu ca chng ta tt v c phng nga thch hp th jitter trong mng khng phi l tr ngi ln v b m jitter khng ng gp lng ng k vo tng tr.

Cc tem thi gian RTP c dng trong phn mm Cisco IOS xc nh mc jitter no xut hin trong mng.

B m jitter i khi cn c gi l hng i ng (dynamic queue). Hng i ny c th tng ln hay gim xung theo hm m tu vo khong thi gian gia cc gi.

2.5 Mt gi

Mt vn khc l mt gi. Nh chng ta bit cc router thng ch c mt kh nng m gii hn, giai on duy tr nghn c th lm cho b m t ti gii hn ca chng. Khi cc gi i vo b m m khng gian b m ht th cc gi phi b thi hi cho n khi b m tr li kh dng. iu ny s lm cho pha thu khng nhn c gi. N cng gy nn tr cng vo khi thc hin truyn li.

CHNG III - KIN TRC CQS3.1 Vn nh tuyn trong mng IP

3.1.1 Khi nim v nh tuyn

nh tuyn l qu trnh tm ng i t mt ngun n mt ch cho trc. Ngun v ch y c th l mt my tnh, c th l my fax, hay ni chung l bt k mt thit b no tham gia vo qu trnh vn chuyn v truyn nhn thng tin trong mng. nh tuyn m bo cho thng tin c truyn i trn mng ti c ch cn n ca n. Qu trnh ny cn phi thc hin theo mt tiu ch nht nh chn ra c mt ng i ti u (chng hn nh ng i ngn nht).

Thit b thc hin vic nh tuyn l router (hay b nh tuyn). Trong mi b nh tuyn s c mt bng nh tuyn ghi li trng thi ca mng v cc thng tin hnh mng t router c quyt nh chn ng i ti u nht theo tiu ch nh trc. Cn thng tin v a ch s c ghi trong tiu gi tin.

Hnh v 3.1 sau y biu din mt qu trnh truyn tin c thc hin trong mng t mt my tnh X n mt my tnh Y thng qua cc router. M hnh phn lp di biu din qu trnh truyn gi tin trong cc lp theo m hnh OSI.

``

Application

Presenlation

Session

Transport

Network

Data Linhk

Physical

Network

Data Linhk

Physical

Network

Data Linhk

Physical

Network

Data Linhk

Physical

Application

Presenlation

Session

Transport

Network

Data Linhk

Physical

X

ABC

Y

X

A

B

C

Hnh 3.1: Qu trnh truyn tin trong mng.

3.1.2 Cc phng php nh tuyn.

3.1.2.1 nh tuyn tnh

L phng php nh tuyn khng s dng cc giao thc nh tuyn. Cc nh tuyn n mt mng ch s thc hin mt cch c nh khng thay i trn mi b nh tuyn. Mi khi thc hin mt vic thm bt cc mng phi thc hin thay i li cu hnh trn mi b nh tuyn. To hng c nh l phng thc n gin nht, trong mi b nh tuyn ca mng cha cc bng to hng c nh. Cc bn to hng ny cung cp cho chng tt c cc thng tin cn phn hng cho cc gi qua mng. Hnh v 3.2 l mt v d v nh tuyn c nh:

F

`

`

`

`

`

`

B

C

D

E

R1

R2

R3

R4

1

2

3

4

1

2

3

Hnh 3.2: Nguyn tc nh tuyn tnh.

m t s lm vic ca n ta xc nh bng nh tuyn cho b nh tuyn R2, R3 theo phng php nh tuyn tnh nh sau:

Thit b

u cui

Tuyn

A

B

C

D

E

F

3

3

3

4

2

1

Thit b

u cui

Tuyn

A

B

C

D

E

F

3

3

4

1

2

2

R2R3

Bng 3.1: Bng nh tuyn tnh cho R2 v R3.

u im ln nht ca nh tuyn c nh l cu hnh mng chm, c ngha l tnh chu n hi ca mng s tt hn dn ti vic on hiu nng mng v sa li nhanh hn. Trong nh tuyn tnh cc b nh tuyn khng cn trao i cc thng tin tm ng cng nh c s d liu nh tuyn. Do n c s dng trong trng hp cn che du mt phn ca lin mng (v l do an ton). Trong trng hp mng ch c mt ng dn duy nht tip cn vi n (mng ny cn c gi l stub network) th cng ch cn mt tuyn tnh l . Hnh 3.3 biu din mt mng nh vy:

`

`

Mng ct

R1

R2

ng kt ni

duy nht

Hnh 3.3: S dng nh tuyn tnh cho mng ct.

3.1.2.2 nh tuyn lun phin

Phng php nh tuyn lun phin c biu din trong hnh v 3.4 di y. Gia bt k hai nt mng no cng c nhiu hn mt tuyn. Nguyn tc nh tuyn lun phin nh sau: khi tt c cc mch thuc tuyn u tin bn th tuyn th hai c chn; nu tuyn th hai bn th tuyn th ba c chn v c nh vy cho ti khi tm c tuyn ri hoc s mt cuc gi .

Phng php ny rt hiu qu trong vic ti u ho s dng cc knh trung k v thng c p dng gia cc tng i in t s SPC.

`

`

R1

R2

R3

R4

R5

Tuyn th 1

Tuyn th 2

Tuyn th 3

Hnh 3.4: Nguyn tc nh tuyn lun phin.

3.1.2.3 nh tuyn ng

nh tuyn ng l nh tuyn da trn thng tin v trng thi hin thi ca mng. Thng tin trng thi c th d on v tuyn ng c th thay i khi cu hnh mng hoc lu lng mng thay i. Thng tin nh tuyn cp nht vo trong cc bng nh tuyn ca cc node mng trc tuyn v p ng tnh thi gian thc nhm trnh tc nghn cng nh ti u hiu nng mng. C hai phng php nh tuyn ng c s dng l: nh tuyn ng theo thi gian v nh tuyn ng theo trng thi mng.

nh tuyn ng theo thi gian c p dng trong nhng vng mng c lu lng thay i theo thi gian trong ngy v s thay i theo mt quy lut nht nh. Phng php nh tuyn ny m bo tnh linh hot v hiu qu cho vic s dng s dng knh trung k di tc ng ca s thay i lu lng mng thc t theo thi gian trong ngy.

nh tuyn ng theo trng thi mng c s dng rng ri trong mng vin thng. Vi phng php ny vic chn tuyn s hon ton t ng theo trng thi lu lng mng hin thi. Vic chn tuyn ny c iu khin bi mt trung tm iu hnh mng.

u im ln nht ca nh tuyn ng l n c th thit lp tuyn ng ti tt c cc thit b trong mng, t ng thay i khi tuyn ng cu hnh mng thay i, chng hn nh khi:

- Thm thit b v a ch mng mi.

- Loi b thit b v a ch khi mng.

- T ng cu hnh ph hp vi s thay i mng.

Hnh 3.5 cho chng ta thy c mt trong nhng u im ca nh tuyn ng. y qu trnh nh tuyn t ngun ti ch c th c la chn mt trong hai ng. C th i theo ng X -> R1 -> R2 -> R4 -> Y hoc X -> R1 -> R3 -> R4 -> Y. Gi s ban u n ang i theo ng th nht. Nu trong qu trnh truyn thng tin th mng b li tuyn . Lc ny Router R1 s t ng cp nht v thay i li bng nh tuyn v chuyn hng truyn tin theo ng th hai m khng lm gin on qu trnh tuyn tin. iu ny l khng th c trong nh tuyn tnh. Trong nh tuyn tnh nu xy ra s c trn ng truyn th qu trnh truyn tin s b gin on cho ti khi s c c khc phc.

`

`

X

R2

R3

R4

Y

Hnh 3.5: Kh nng thay th tuyn ca nh tuyn ng

nh tuyn ng s dng cc giao thc nh tuyn thc hin xy dng nn cc bng nh tuyn trn cc b nh tuyn. Cc giao thc nh tuyn ng c chia thnh hai nhm chnh l: Giao thc nh tuyn vector khong cch v giao thc nh tuyn trng thi lin kt. Ngoi ra cn c mt s giao thc lai ghp nh: Giao thc nh tuyn phn lp, giao thc nh tuyn khng phn lp v giao thc nh tuyn trn c s QoS. Sau y chng ta s nghin cu cc giao thc nh tuyn .

3.1.3 Mt s giao thc nh tuyn 3.1.3.1 nh tuyn vect khng cch.

Theo giao thc ny, cc router s nh k chuyn thng tin c trong bng nh tuyn n cc router ln cn ni trc tip vi n v cng theo nh k nhn cc bng nh tuyn t cc router ln cn. Sau khi nhn cc bng nh tuyn t cc router ln cn n s so snh vi bng nh tuyn hin c v quyt nh v vic xy dng li cc bng nh tuyn theo thut ton ca tng giao thc hay khng. Trong trng hp phi xy dng li, router sau s gi bng nh tuyn mi cho cc router ln cn v cc router ln cn li thc hin cc cng vic tng t. Cc router t xc nh cc router ln cn trn c s thut ton v cc thng tin thu c t mng.

T vic cn thit phi gi cc bng nh tuyn mi cho cc router ln cn v cc router ln cn li phi gi bng nh tuyn mi ca n, nh tuyn lp vng c th xy ra nu s hi t v trng thi bn vng ca mng din ra chm trn mt cu hnh mi. Cc router s dng k thut b m nh thi m bo khng ny sinh vic xy dng mt bng nh tuyn sai. C th din gii iu nh sau:

- Khi mt router nhn c mt cp nht t ln cn ch rng mt mng c th truy xut trc y nay khng th truy xut c na, router nh du tuyn khng th truy xut v khi ng mt b nh thi.

- Nu ti bt k thi im no m trc khi b nh thi ht hn mt cp nht c tip nhn cng t ln cn ch ra rng mng c truy xut tr li, router nh du mng c th truy xut v gii phng b nh thi.

- Nu mt cp nht n t mt b nh tuyn ln cn khc vi gi tr nh tuyn tt hn gi tr nh tuyn c ghi cho mng ny, router nh du mng c th truy xut v gii phng b nh thi. Nu gi tr nh tuyn ti hn th cp nht c b qua.

- Khi b nh thi m v khng th gi tr nh tuyn mi c xc lp, router c bng nh tuyn mi.

Vic tnh ton tuyn trong giao thc vector khong cch s dng thut ton tm ng ngn nht theo k thut phn tn m in hnh l thut ton chn ng Ford & Fulkerson. K thut chn ng ny cho php ta tm tt c cc con ng i ngn nht t tt c cc nh ti mt nh cho trc. Gii thut ny c thc hin bng cc bc lp, sau k bc, mi nh c nh du bi mt cp gi tr (nk(v), Dk(v)), trong :

Dk(v) l gi tr cc tiu t nh v n ch ti bc th k.

Nk(v) l nh tip theo trn con ng t v n ch ti bc th k.

Qu trnh lp s dng li khi cp nh du ca mi nh c gi nguyn khng thay i na. Thut ton Ford & Fulkerson c m t nh sau:

- u vo:

th c hng G = (V, E) vi n nh.

a(u,v) l ma trn trng s khng m.

s l nh ch.

- u ra:

N(v) ghi nhn nh trc v trn ng i n ch.

Dk(s) ghi li ng i ngn nht.

Gii thut:

Bc 0 (khi to):

D0(s) = 0;

Bc k (tnh v cp nht):

Vi mi v khc s (ch), cp nht li Dk(v) nh sau:

Dk(v) = min[Dk 1(w) + l(v,w)]

Vi w thuc Nv, trong Nv l tp cc nt ln cn ca v.

Cp nht nk(v) nh sau:

nk(v) = w1;

vi w1 tho mn biu thc:

Dk 1(w1) + l(v, w1) = min[Dk 1(w) + l(v, w)]

Kim tra iu kin lp:

Nu tn ti Dk(v) khc Dk 1(v) th tip tc bc k+1. Ngc li th kt thc qu trnh tnh ton.

3.1.3.2 nh tuyn trng thi lin kt

Cc gii thut nh tuyn trng thi lin kt cn c gi l nh tuyn ng dn ngn nht OSPF (Open Shortest Path First). N duy tr mt c s d liu phc tp cha thng tin v cu hnh mng. Trong khi gii thut vector khong cch khng c thng tin c bit g v cc mng xa v cng khng bit cc router xa, gii thut trng thi lin kt bit c y v cc router xa v bit c chng lin kt vi nhau nh th no. Giao thc nh tuyn trng thi lin kt s dng:

- Cc thng bo v trng thi lin kt LSA (Link State Advertisements).

- Mt c s d liu v cu hnh mng.

- Gii thut OSPF v cy OSPF sau cng.

- Mt bng nh tuyn lin h cc ng dn v cc cng n tng mng.

Hot ng tm hiu khm ph mng trong kiu nh tuyn trng thi lin kt c thc hin nh sau:

- Cc router trao i cc LSA cho nhau. Mi router bt u vi cc mng c kt ni trc tip ly thng tin.

- Mi router ng thi vi cc router khc tin hnh xy dng c s d liu v cu hnh mng bao gm tt c cc LSA n t lin mng.

- Gii thut OSPF tnh ton ng i mng c th t n. Router xy dng cu hnh mng lun l nh mt cy, t n l gc, gm tt c cc ng dn c th n mi mng trong ton b mng ang chy giao thc nh tuyn trng thi lin kt. Sau n sp xp cc ng dn ny theo chin lc chn ng dn ngn nht.

- Router lit k cc ng dn tt nht ca n v cc cng dn n mng ch trong bng nh tuyn ca n. N cng duy tr cc c s d liu khc v cc phn t cu hnh mng v cc chi tit v hin trng ca mng.

Khi n thay i v cu hnh mng, router u tin nhn bit c s thay i ny gi thng tin n cc b nh tuyn khc hay n mt router nh trc c gn l tham chiu cho tt c cc router trn mng lm cn c cp nht.

- Theo di cc ln cn ca n, xem xt c hot ng hay khng, v gi tr nh tuyn n ln cn .

- To mt gi LSA trong lit k ca tt c cc router ln cn v gi tr nh tuyn i vi cc ln cn mi, cc thay i trong gi tr nh tuyn v cc lin kt dn n cc ln cn c ghi.

- Gi gi LSA ny i sao cho tt c cc router u nhn c.

- Khi nhn mt gi LSA, ghi gi LSA vo c s d liu sao cho cp nht gi LSA mi nht c pht ra t mi b nh tuyn.

- Hon thnh bn ca lin mng bng cch dng d liu t cc gi LSA tch lu c v sau tnh ton cc tuyn dn n tt c cc mng khc s dng thut ton OSPF. C hai vn cn lu vi giao thc nh tuyn trng thi lin kt l:

Hot ng ca cc giao thc nh tuyn trng thi lin kt trong hu ht cc trng hp u yu cu cc router dng nhiu b nh v thc thi nhiu hn so vi giao thc nh tuyn theo vector khong cch. Cc yu cu ny xut pht t vic cn thit phi lu tr thng tin ca tt c cc ln cn, c s d liu mng n t cc ni khc v thc thi cc thut ton nh tuyn trng thi lin kt. Ngi qun l mng phi m bo rng cc b nh tuyn m h chn c kh nng cung cp cc ti nguyn cn thit ny.

Cc nhu cu v bng thng cn phi tiu tn khi ng s pht tn gi trng thi. Trong khi khi ng qu trnh khm ph tt c cc router dng cc giao thc nh tuyn trng thi lin kt gi cc gi LSA n tt c cc b nh tuyn khc. Hnh ng ny lm trn ngp mng khi m cc router ng lot yu cu bng thng v tm thi lm gim lng bng thng kh dng dng cho lu lng d liu thc c nh tuyn. Sau khi khi ng pht tn ny, cc giao thc nh tuyn trng thi lin kt thng ch yu cu mt lng bng thng ti thiu gi cc gi LSA kch hot s kin khng thng xuyn nhm phn nh s thay i cu hnh mng.

Vic tnh ton tuyn trong giao thc nh tuyn trng thi lin kt s dng thut ton chn ng ngn nht theo k thut chn ng tp trung m in hnh l thut ton Dijkstra. Thut ton a ra tm ng i ngn nht t nh s n tt c cc nh cn li trong th c hng da trn c s gn cho cc nh cc nhn tm thi (khc vi thut ton Ford & Fulkerson tm ng i t tt c cc nh n mt ch).

Thut ton Dijkstra c m t nh sau:

- u vo:

th c hng G = (V, E) vi n nh.

s thuc V l nh xut pht.

a[u, v] l ma trn trng s.

d(v) l khon cch t nh xut pht s n v.

- u ra:

Truoc[v] ghi nhn nh i trc v trong ng i ngn nht t s n v.

Bc 0 (khi ng):

N0 = {s};

D0(v) = l(s, v); vi v khng thuc N0.

Bc k (tnh v cp nht):

Nk = Nk 1 + {w};

Trong w tho mn biu thc:

Dk 1 (w) = min[Dk 1 (v)]

vi v khng thuc Nk 1

Cp nht:

Vi mi v khng thuc Nk:

Dk(v) = min[Dk 1 (v), Dk 1 (w) +l(w, v)]

Kim tra iu kin lp:

Nu Nk khc vi V th lp bc k + 1 ngc li th dng qu trnh tnh ton.

3.1.3.3 nh tuyn phn lp.

Giao thc nh tuyn phn lp thc hin tun t cc phng php vector khong cch tnh ton tuyn. Cc mt n nh tuyn khng pht hnh trn mng theo chu k.

Khi s dng giao thc nh tuyn phn lp, tt c cc mng con trn cng mt mng chnh (lp A,B,C) cng dng chung mt mt n mng. Tu thuc vo cc gi tin cp nht nh tuyn, b nh tuyn chy giao thc nh tuyn phn lp theo mt trong cc phng php sau:

Nu thng tin nh tuyn trong cng mt mng v c cu hnh trn cng mt giao tip nhn tin, b nh tuyn t mt n mng c cu hnh trn mt n nhn. Nu thng tin nh tuyn nm trn mng khc cng c cu hnh trn mt nhn, b nh tuyn s p dng mt n ngm nh (theo lp a ch). Cc giao thc nh tuyn phn lp nh RIPv1 v IGRP, chuyn i tuyn trn mng con trong cng mt mng. iu ny l c th v tt c cc mng con trong mt mng ln l c cng mt mt n mng v cng mt mt n nh tuyn.

Khi tuyn c trao i vi mng ln cn, cc thng tin v mng con cng s c chuyn theo, v mt n nh tuyn ca cc mng khc s khng c bit. Kt qu, cc thng tin v mng lm vic t mng ny c th tng kt (sumerized) thnh ng bin phn lp nh s dng mt n nh tuyn ngm nh cp nht vo bng nh tuyn. To ra tuyn tng kt (sumary) ti ng bin ca mng chnh c x l t ng bi cc giao thc nh tuyn phn lp. Tng kt ti cc im khc trong mng khng c thc hin bi cc giao thc nh tuyn phn lp.

Khi thc hin phn lp mng con ti im chuyn tip vi cc giao thc nh tuyn phn lp, cn phi ch ci t cc mt n mng con ti tt c cc giao tip trong vng nh tuyn phn lp. iu ny yu cu cc b nh tuyn mng con phi c pht hnh chnh xc.

S dng mt n mng con c nhng nhc im t gc ch nh vng a ch hiu qu. Vi 27 bit mt n, ch ra s host khong 30 trm trn mi mt phn on Ethernet, khng phi tt c 30 host cng c s dng trn ng lin kt ni tip (S0,S1).

3.1.3.4 nh tuyn khng phn lp.

Cc giao thc nh tuyn khng phn lp gm cc mt n nh tuyn vi cc hng pht hnh (advertisement).

Giao thc nh tuyn khng phn lp c coi nh l cc giao thc nh tuyn th h tip theo ca cc giao thc nh tuyn phn lp, v n c thit k nh a ch nhm gii hn ca cc giao thc nh tuyn phn lp. Mt trong nhng gii hn c bn nht ca nh tuyn phn lp l mt n nh tuyn khng c trao i trong qu trnh x l cp nht nh tuyn, yu cu cng mt mt n nh tuyn cho tt c cc mng lm vic.

Cc gii hn khc ca giao thc nh tuyn phn lp tip cn nh mt nhu cu tng kt cc mng phn lp. Vi cc mt n nh tuyn ngm nh ti ng bin mng. Trong mi trng khng phn lp, x l tng kt c iu khin nhn cng v c th xc nh bt c mt v tr bit no trn mng. Cc giao thc nh tuyn khng phn lp s dng cp nht lp tc hc cc s thay i topo mng. iu khin ni dung bng nh tuyn, cc hng tng kt c th c to ra. Thit k phn cp s dng OSPF cho php tng kt ti bt k bit no, nhng gii hn cu hnh tng kt trn mt s loi thit b c bit, nh cc b nh tuyn ng bin vng. V cc hng mng con c chun b qua vng nh tuyn, cc tng kt c yu cu gi kch thc bng nh tuyn.

3.1.3.5 nh tuyn trn c s QoS.

Giao thc nh tuyn trn c s QoS c gng to nhiu php o vo ti nguyn khi xy dng bng chuyn tip ca mng. Giao thc ny tng c nghin cu trong nhiu nm v thng bt u bng mt s tha nhn rng mng c xy dng t cc router IP n lc ti a. Bt u t s tha nhn ny nh tuyn n thng s dng nh c mt s hn ch khi tha nhn p ng nhu cu QoS c nh ca mi trng a dch v.

Mt thng s c th c xem l mt loi gi tr v mi kt ni (chng) c mt gi tr tng ng. Giao thc nh tuyn n lc tm kim nhng ng dn vi tng gi tr ca tt c cc kt ni t ngun n ch c th l nh nht. Tuy nhin gi tr ny khng th l i din ng quan tm v cn thit cho tt c cc loi lu lng. Phi chng n i din cho tr ca ng lin kt, bng thng, kh nng mt gi hoc c th l chi ph hin ti cho vic gi gi qua ng lin kt . Chn la mt trong s chng ta s t c mt s la chn ph hp vic tm kim lu lng, trong khi s la chn lu lng khc l lng ph ti nguyn.

Chng hn, mt mng xem tr l mt thng s. ng dn ngn nht lc ny ph hp vi cc ng dng c yu cu thi gian thc cht ch. Nhng chng khng n l. Mng cng hon ton c th c s dng cc ng dng d liu bng n truyn thng m s quan tm ti n t hn l tr. Lu lng t cc ng dng khc ny cng i theo cc ng dn ngn nht vi tr nh nht, thm ti trng vo cc router n lc ti a dc theo ng dn. Mt tc ng khng thun li l lu lng bng n chim cng khng gian hng i c s dng bi lu lng thi gian thc, s tng ln ca jitter v tr trung bnh bi tt c cc lu lng qua cc router. Cch tip cn ny cng gy nh hng n s chnh xc ca gi tr tr m giao thc nh tuyn s dng quyt nh ng dn ngn nht.

nh tuyn trn c s QoS to nhiu cy ng dn ngn nht bao gm hnh hin thi ca cc router v cc ng lin kt vi mi cy s dng mt t hp tham s khc nhau nh n v kt ni. Mc tiu l gim thiu s cng tn ti khng cn thit trong router ca lu lng vi yu cu QoS m rng khc. Cc gi vi yu cu tr nghim ngt sau c chuyn tip bng cch s dng cy c xy dng vi tr nh l mt thng s. Cc gi khng yu cu thi gian thc c th xy dng cy theo kiu khc (chng hn nh gim gi tr cui cng ca ng dn ti mc cc tiu). Mt vi vn thc t tn ti trong vic nh tuyn trn c s QoS l:

Mi router cn c nhiu bng chuyn tip (hoc chc nng tng t) trn biu din ch dn chng tip theo trn c s a ch ch ca mi gi. Mi ch dn c mt loi cy ngn nht. Cc trng thm vo trong tiu gi c s dng chn mt chng tip theo c th kt hp vi a ch ch ca gi. iu ny gy kh khn cho vic thit k c ch truyn dn chng tip theo.

Mt s tng ln trong giao thc nh tuyn trn xut hin bi v cng vic ca router phi chu ng mt c th ca mi giao thc cho mi cy ngn nht duy nht. Yu cu lm cho thi gian tp trung gi ca router trong mng tng ln mt khong thi gian ngn no (chng hn khi cc kt ni n hoc i hoc gi tr ca chng thay i) thi gian tp trung tng ln nhiu hn nu giao thc nh tuyn c yu cu tnh ton cy da trn nhiu thng s cng mt lc.

Cc thng s nh tr hoc bng thng kh dng ph thuc nhiu vo lu lng hin thi i qua mng. Mt cy ng dn ngn nht xy dng vi gi tr tr c nh hnh mt cch c nh c th tr nn li thi khi lu lng bt u chy qua mng. Khng c quy c cho vic cp nht gi tr mi kt ni vi cc s o thi gian thc hp l, to ra mt s lo s l thuyt iu khin thc - mi gi tr cp nht c th l kt qu tnh ton li cy ng dn ngn nht kt hp dn n vic tip tc x l ti trng trn tt c cc router.

iu th v l s pht trin ca cc router vi kin trc CQS mt mc no lm gim nhu cu nh tuyn trn c s QoS. V d s dng tr nh mt thng s gi tr. By gi ch rng vi mi router c t nht hai hng i trn mt giao din u ra. Mt cho lu lng nhy cm vi tr, mt cho tt c cc lu lng cn li. Tt c cc lu lng u c nh tuyn theo ng dn vi tr thp nht. Tha nhn cc router phn loi lu lng ph hp vo hai hng i , dch v nhn c vi lu lng nhy cm vi tr khng ph thuc vo s bng n ca tt c cc loi lu lng khc. iu chng t mt s quy c v giao thc nh tuyn IP n thng s khi kt hp vi cc router da vo kin trc QoS c th chu ng c nhiu mc khc nhau ca dch v. iu ch yu c ni y l kh nng thch ng tn ti dc theo mt cy n cung cp tt c nhng ngi tham gia.

3.2 Cu trc router

Mt router thng thng c cc khi ch nng c bn sau (xem hnh 3.6):

Khi a giao din.

Khi chuyn tip.

Khi qun l.

Khi chuyn tip

Khi qun l

S liu thng k, bn

tin t cc router khc

Cc cp nht ni b

bn tin ti cc router

khc

,

In put

Out put

In put

In put

In put

Out put

Out put

Out put

Hnh 3.6: Cu trc chung ca router

Giao din vo nhn cc gi n t cc router khc, v khi chuyn tip chuyn cc gi ti giao din ra ph hp (da vo a ch ch ca mi gi). Mi giao din sau s dng cc c ch kt ni ring truyn dn cc gi ti cc router (hoc host) k tip dc theo ng dn. Khi mt router cho rng nghn ni ang tng ln mt cch tht thng, cc gi c th b loi b hoc b nh du nh l mt iu kin ch r trng thi ny ti cc mng xung quanh n. Hot ng ca tng gi trong khi chuyn tip (chn giao din u ra v p ng nghn) ch yu c iu khin bi khi qun l.

Khi chuyn tip da vo mt bng FIB (Forwording Information Base) chuyn cc gi ti u ra ph hp. Vi mi a ch ch c th, mt s tm kim xc nhn tin t di nht c nh dng qua FIB. Nu mt xc nhn c tm thy, li vo tng ng ch cho khi chuyn tip bit giao din u ra no c th nhn gi. Nu khng tm thy c ngha l gi b rt. Ni dung ca FIB phn nh trng thi hin ti ca cu trc mng IP xung quanh router, c xc nh bi cc giao thc nh tuyn IP chng hn nh Giao thc OSPF (Open Sortest Path First) v Giao thc cng bin phin bn 4 (BGP4: Border Gateway Protocol version 4) - chy trn khi qun l.

Ch : vic bit cu trc mng xung quanh cho php mt FIB ca chng k tip nhn c t vic tnh cy ng dn ngn nht v t bit tt c cc ch/tin t.

R rng hnh 3.6 l mt m hnh c tnh tru tng cao. Cc router in hnh ban u thng c mt CPU trung tm ring iu khin tt c cc chc nng qun l v chuyn tip gi. T khi cc router pht trin theo hng cu trc phn tn, tt c cc thit k u nhm loi b hoc gim nh hng ca hin tng tht nt chai. Trong cc router backbone, khi chuyn tip c phn phi gia cc mu card giao din ni lin vi nhau bi c cu chuyn mch tc cao hoc mt mt bng pha sau [KLS98][KESH98][DSRTER]. Tuy nhin, tt c cc router c trnh t cc bc chung m mt gi phi i qua trong khi x l gi.

Ngy nay, QoS tr nn quan trng, qu trnh chuyn tip c thit k li nhm mang li thut li hn khi router gi gi. Hnh 3.7 cho ta mt ci nhn tng quan v qu trnh x l xy ra trong khi chuyn tip trong hnh 3.6. Thng thng, mt gi phi tri qua ba giai on chnh sau:

Phn loi v tm kim FIB (thit lp nhn dng gi v tm giao din u ra).

Kim sot v nh du (phn nh li trong trng hp gi khng n trong mt khung thi gian ph hp).

Xp hng v lp thi gian biu (chuyn tip gi ti cc kt ni chia s hay quy tc nh hnh lu lng hoc loi b n khi quy tc iu khin nghn).

Giai on phn loi gi s dng router thit lp trng hp tng qut cho cc gi n sau. Mc d hu ht trng hp c s dng thit lp c tnh iu khin thi gian (kim sot, nh du, xp hng v lp lch), mt vi trng hp thm vo c th c s dng thay i quyt nh chuyn tip. Chng hn, mt router tin tin c th h tr nhiu FBI (i din cho cy ng dn ngn nht da trn n v khc) v la chn gia chng, bng cch s dng cc thng tin khc trong phn tiu ca gi (nh a ch ngun chng hn). Mt cch tng t hay ti thiu mt mi quan h ng thng tn ti gia mt trng hp ca mt gi (thit lp qua mt phn loi gi) v cc loi ca n.

Output

Interface

Input

Interface

Policing &

Marking

Switch

Fabric

Queuing &

Scheduling

Forwarding

Table (s)

FBI

FBI

FBI

Packet

Classification

IP header

FBI

IP payload

Tnh hung gi nh hng n qu trnh sau

Hnh 3.7: Qu trnh x l gi trong khi chuyn tip.

3.3 Kin trc CQS

Trn y chng ta tm hiu mt kin trc chung ca router, kin trc ny tng c s dng rng ri trong mng vin thng ni chung v mng Internet ni ring. Tuy nhin vi s pht trin mng li vin thng nhanh chng v rng khp hin nay i hi phi tng cng kh nng x l, v tng tc cho cc router, cng nh cn phi a thm vo cc c tnh mi nhm qun l lu lng mt cch linh hot v mm do hn ng thi p ng c y yu cu QoS ca cc loi lu lng dch v mi. y chng ta cp n mt kin trc l kin trc CQS. y l mt kin trc mi c a vo router nhm nng cao kh nng qun l ca router ng thi tng kh nng gii quyt vn tc nghn xy ra router v n ch c trong mng dch v khc bit. Kin trc ny c cho nh hnh v 3.8:

Queue

Queue

Queue

Queue

Classify

Port 1

Port N

Schedule

Hnh 3.8: Kin trc CQS.

Theo kin trc ny, cc gi n c phn loi theo u tin hoc theo mt tiu ch no ri chng c cho vo cc hng i tng ng khc nhau. Cui cng, cc hng i phi chia s tt c kh nng ca kt ni u vo m chng a vo. Nhu cu ny bao hm vic thm vo mt c ch lp lch xen cc gi t mi hng i v nh vy cc kt ni truy cp vo mt cch c kh nng d on v iu khin c.

Phn loi

C ch phn loi gi ca mt router nh hng trc tip n nhn t m n c th tch cc lp hoc cc loi lu lng IP khc nhau. Trong thc t, tnh trng ca mt gi tin ph thuc vo c hai thng tin c mang bi chnh bn thn gi v thng tin tnh hnh mng nhn c t giao din ca n (c th l chng tip theo ca n c quyt nh t vic tm kim FIP). Vic phn loi da trn cc kho phn loi v cc quy tc phn loi. Kho phn loi m mt nhm N bit trong tiu gi tin. N bit ny c th phn bit c 2N loi (hoc lp) gi khc nhau. Qu trnh kt hp cc kho phn loi i hi phi da trn nhng quy tc nht nh. Cc quy tc ch r s kt hp cc kho c gi l quy tc phn loi. Mt kha khng th di tu - b nh ca mt router bt buc phi gii hn s lng thng tin trng thi m n c th lu gi nhn bit lp. (Tuy nhin ngha ca cc bit tn ti trong trng phn loi c th t hn nhiu so vi 2N trng hp gii quyt). Thi gian x mi gi kt hp trong tng bc phn loi cng tng ln theo chiu di kha (mc d khng phi lun theo ng thng), iu c th lm gim hiu sut ca router. Mt khc mt kho khng th qu ngn 2N phi bng hoc ln hn gi tr cc tiu ca lp lu lng yu cu bi mng c thit k.

Ngoi tr cc trng c phn loi, giai on phn loi phi c kh nng gi c tc nhn gi nh [KLS98]. Cho n khi trng thi ca gi c thit lp, th hng i c th khng c cung cp. Khi m giai on phn loi chm hn tc nhn gi th hng i FIFO xut hin trc giai on phn loi.

Hu ht cc s phn loi hn hp in hnh s dng mt kho bao gm nhiu trng trong tiu gi IP c ch gii nh l phn loi a trng (MF). Kho ny c th thm mt vi hoc tt c cc trng thng nh ngha mt lung IP thng thng l a ch ngun v a ch ch, trng giao thc, v ch s cng TCP/UDP ngun v ch. Phn loi MF cung cp s lng ln nht cc trng hp cho cc giai on x l k tip ca router. Tuy nhin, khi mt ngi thit k mng tin rng ch mt s lp lu lng nh cn phn bit ti mt vi chng cho trc, gii php thng c n nh cho mt nhm bit ti mt v tr c nh trong tiu gi c phn loi. Octet ToS ca IPv4, octet TC ca IPv6 v trng dch v khc bit hon ton ph hp trong trng hp ny.

Qun l hng i

Mi lp lu lng c yu cu c im lp lch ring phi c t trong chnh hng i ca n vi mi gi trc tip ti hng i thch hp s dng thng tin tnh hung thu thp c t tng phn loi trc . Khng c cc hng i ring bit n khng th c kh nng cho tng lp lch sau phn bit gia nhiu lp lu lng cnh tranh mt ng kt ni n. Mt chc nng b qun l hng i l chu trch nhim thit lp v duy tr hng i v phng thc hng i trong router. Chc nng ny bao gm bn hot ng c bn:

Thm mt gi vo hng i c ch r bng tnh hung ca gi (nh c thit lp trong tng phn loi) nu hng i khng y.

Loi b mt gi nu hng i y.

Loi b mt gi khi c yu cu bi b lp lch.

Gim st la chn s chim dng hng i (s gi hoc byte chim dng hng i) v da vo mt trong cc bc thc hin sau gi mc chim dng thp:

+ Loi b mt gi (hoc khng chn thm mt gi) khi hng i y

+ nh du mt gi khi hng i bt u y.

Ti mt vi im mi hng i cng b y (thm ch trong khi khng gian c sn cho hng i khc tng ln) m bo rng khng mt lp lu lng no dng tt c khng gian nh hn ch ca router to hng i.

Tuy nhin, phi m bo khng mt hng i no b b i. Thm vo mt vi chim dng trung bnh ca hng i c th c gi mc thp. Vic qun l hng i tch cc c thi hn thng p dng phng php gim st v iu khin chim dng hng i trung bnh. chim dng trung bnh thp c hai li ch:

Tn ti cc hng i tiu th s bng n lu lng khng th trnh khi m khng lm mt gi. Hot ng vi mt chim dng trung bnh cao lm gim khng gian sn c tiu th s bng n.

Tr trung bnh c b qua bi s phn chia lu lng mt hng i cho trc tng ln cng vi s tng chim dng hng i. Gi cho chim dng gim gip gi cho tr end to end gim.

Lp lch

Lp lch iu khin c trng thi gian ca vic lu thot gi khi mi hng i - thng ti giao din u ra hng ti router hoc host tip theo, nhng cng c th l ti cc im hng i trong mt router. Cc router truyn thng ch c mt hng i n trn mt giao din kt ni u ra. Nh vy lp lch c nhim v n gin l li cc gi ra khi hng i nhanh bng kh nng kt ni c th chuyn c. Trong cc router c kin trc CQS, mi giao din c mt tng b lp lch chia s kh nng cha ca kt ni u ra gia s kt hp cc hng i trong giao din. Chia s kt ni t c mt s sp xp lch bi khi no v xy ra nh th no, cc gi c ko ra khi hng i v truyn i.

Bi v tnh hung ca mt gi (hoc mt lp lu lng) iu khin hng i no m n c t trong , b lp lch ch yu cng ch quyn u tin tng i, hn ch tr, hoc bng thng ch nh gia cc lp lu lng khc nhau. Mt b lp lch c th thit lp bng thng kh dng nh nht cho mt lp c bit bng cch m bo rng cc gi c ly ra khi hng i c quan h vi cc lp mt cch thng thng. Mt b lp lch cng c th cung cp nh hng tc (li dng bng thng c php cc i cho lp c bit). Bng cch gii hn tn s trong hng i ca lp no c phc v ph thuc vo thit k ca mt b lp lch, n c th p t hai gii hn bng thng di v trn trn mi hng i hoc p t gii hn trn cho mt s hng i v gii hn di cho mt s hng i khc.

Cc thut ton lp lch thng tho thun gia s thc hin n gin v c trng thi gian mong mun. Tt c cc thit k b lp lch c nhng kiu dch v c trng ca ring n cch m n la chn hng i dch v. B lp lch n gin nht tp trung vo hng i phc v trong mt s hng i d on trc, vic tp trung vo dch v khong cch hn l cng sut thu c. Cc b lp lch tin tin hn cho php tng i hoc ton b bng thng thit lp cho mi hng i v chng tip tc lp rp vo cc kiu dch v ca chng m bo bng thng trung bnh hoc tr t c bi mi hng i gii hn trong cu hnh.

Phn tip theo chng ta nghin cu cc chin lc qun l hng i s dng kin trc CQS. V mc nhin t y chng ta tha nhn cc router u c kin trc CQS.

CHNG IV - NG DNG KIN TRC CQS CHO QUN L NGHN TRONG MNG IP4.1 Ti sao phi qun l nghn.

Cc mng hn hp thm vo nhiu giao thc khc nhau s dng bi cc ng dng, vic tng nhu cu lu lng u tin theo th t cc ng dng thi gian cht ch thch hp trong khi vn s dng cc nhu cu ca cc ng dng ph thuc thi gian t hn nh dch v truyn file. Cc loi lu lng khc nhau chia s mt ng d liu qua mng c th nh hng ln nhau theo cch m n tc ng ti s thc hin ng dng ca chng. Nu mng c thit k h tr cc loi lu lng khc nhau nhm chia s mt ng d liu n gia cc router chng ta phi ch vic s dng k thut qun l nghn m bo i x cng bng gia cc loi lu lng.

Sau y l mt s nhn t m rng cn ch xc nh c hoc khng nh hnh QoS qun l nghn:

Mc u tin lu lng c bit quan trng cho cc ng dng tc v, nhy cm vi tr - v d hi ngh truyn hnh nhiu bn Cc ng dng ny yu cu mc u tin cao hn cc ng dng truyn file. Tuy nhin, s dng WFQ m bo rng tt c cc lu lng c i x mt cch cng bng theo trng s ca n v trong mt cch linh ng. Chng hn, WFQ s dng nhu cu ca ng dng tc ng ln nhau m khng k n ng dng truyn file.

Mc u tin c hiu qu tt nht trn cc kt ni WAN m t hp lu lng bng n v tc thp hn tng i c th dn nghn ngn hn.

Ph thuc vo kch thc gi trung bnh, mc u tin c hiu qu tt nht khi p dng cho cc kt ni T1/E1 hoc cc kt ni c tc thp hn.

Nu ngi dng cc ng dng ang chy qua mng thy rng khng thi gian p ng, chng ta phi ch s dng c tnh qun l nghn. c tnh qun l nghn l rt linh ng. Tuy nhin, cn phi ch nu mt kt ni WAN b nghn lin tc th mc u tin lu lng c th khng gii quyt c vn . Thm bng thng vo c th l gii php ph hp.

4.2 Cc chin lc qun l nghn s dng kin trc CQS.

4.2.1 Cc chin lc qun l nghn s dng hng i

4.2.1.1 Chin lc hng i FIFO

Trong mt dng n gin hng i FIFO (cn c bit n nh l hng i first-come, first-served: FCFS) bao hm vic m v chuyn tip cc gi theo th t khi chng n.

FIFO khng a ra khi nim v mc u tin hay loi lu lng v do khng to ra quy nh v mc u tin gi. Ch c mt hng i v tt c cc gi c i x nh nhau. Cc gi c gi ra khi giao din theo th t chng n.

Khi FIFO c s dng, cc ngun i x km (ill-behaved) c th dng tt c bng thng, ngun bng n c th gy ra tr trong lu lng nhy cm vi thi gian hoc lu lng quan trng v lu lng quan trng c th b loi b bi lu lng quan trng hn chim y hng i.

Khi khng c hng i khc c cu hnh th tt c cc giao din ngoi tr giao din serial E1 (2,048 Mbps) v thp hn s dng FIFO mt cch mc nh (giao din serial E1 v thp hn s dng WFQ mt cch mc nh).

FIFO l mt phng php hng i nhanh nht v n c hiu qu cho cc kt ni ln c t tr v nghn ti thiu. Nu kt ni rt t b nghn th ch cn dng hng i FIFO l .

4.2.1.2 Chin lc hng i cn bng trng s (WFQ)

Phn ny trnh by ba loi hng i WFQ sau:

Flow-Based Weighted Fair queuing (WFQ)

VIP-Distributed Weighted Fair queuing (DWFQ)

Class-Based Weighted Fair Queuing (CBWFQ)

Phn ny cng trnh by cc c trng lin quan sau:

IP RTP Priority

Frame Relay IP RTP Priority

Hng i tr thp (Low Latency Queuing)

Flow-Based Weighted Fair Queuing

WFQ l mt phng php lp lch linh hot cung cp s phn phi bng thng cn bng ti tt c lu lng mng. WFQ p dng quy tc u tin hoc trng s nhn dng cng nh phn loi lu lng cc cuc thoi v xc nh lng bng thng bao nhiu cp cho mi cuc thoi sao cho n cn i vi cc cuc thoi khc. WFQ l mt thut ton trn c s lung lp lch ng thi lu lng tng tc trc hng i gim thi gian p ng v chia s cn bng bng thng cn li cho cc lung bng thng cao. Ni mt cch khc, WFQ cho php c lu lng dung lng thp, nh cc phin Telnet, v u tin lu lng dung lng cao, nh cc phin FTP. WFQ cho php truyn file ng thi s dng dung lng kt ni cn bng; ngha l khi truyn nhiu file xy ra, th vic truyn c cp bng thng c kh nng so snh c. Hnh 4.1 biu din qu trnh lm vic ca WFQ.

Cc gi vo

Phn loi

S lng cu hnh

ca hng i

Hng i

truyn dn

Cc gi ra

Cc ti nguyn b

m hng i

Flow-base Classification:

a ch ngun v a

ch ch

Giao thc

B nhn dng phin

(cng/socket)

Xc nh trng s bng:

QoS yu cu (IP Precedence,

RSVP)

Nghch o thng qua mc

lung

Frame Relay FECN, BECN, DE

(cho lu lng Frame Relay)

Lp lch cn

bng trng s

Hnh 4.1: Weighted Fair Queuing

WFQ khc phc mt lot cc hn ch ca hng i FIFO. Khi FIFO c hiu qu, lu lng c gi i theo th t n nhn c m khng k vic tiu th bng thng hay tr kt hp. Kt qu l truyn file v cc ng dng mng dung lng cao khc thng to ra chui cc gi d liu kt hp. Cc gi lin quan ny c bit n nh l cc dng gi. Cc dng gi l cc nhm gi c khuynh hng cng nhau i qua mng. Cc dng gi ny c th chim tt c bng thng kh dng, v ly i bng thng ca cc lung lu lng khc.

WFQ cung cp vic qun l mc u tin lu lng mt cch nng ng vo bn tin cho mt cuc thoi. WFQ lm t dng gi trong mt cuc thoi m bo rng bng thng c chia s mt cch cn bng gia cc cuc thoi ring v lu lng dung lng thp c truyn i trong mt thi gian c hiu lc.

WFQ phn loi lu lng vo cc lung khc nhau da vo a ch tiu gi, bao gm cc c tnh nh a ch mng ngun v mng ch hay a ch MAC, giao thc, cng ngun, cng ch, ch s phin bn, gi tr nhn dng kt ni data-link Frame Relay v gi tr ToS. C hai loi lung lu lng: phin bng thng cao v phin bng thng thp. Lu lng bng thng thp c mc u tin hiu qu trn lu lng bng thng cao, v lu lng bng thng cao chia s dch v truyn dn cn xng theo trng s c n nh. Lung lu lng bng thng thp gm phn ln lu lng, dch v u i nhn c, cho php ton b ti trng c php i vo c gi trong thi gian thch hp. Lung lu lng dung lng cao chia s dung lng cn li mt cch cn bng.

WFQ t cc gi ca cc cuc thoi khc nhau vo cc hng i cn bng trc khi truyn dn. Th t di chuyn t cc hng i cn bng c xc nh bi thi gian thc s ca gi tr bit cui cng ca mi gi n.

Cc bn tin mi cho cc lung bng thng cao c loi b sau khi ngng bn tin tc nghn c xc nh. Tuy nhin, cc lung bng thng thp bao gm cc bn tin iu khin cuc thoi, th c tip tc xp vo d liu. Kt qu l hng i cn bng i khi c th cha nhiu bn tin hn theo l thuyt theo ch s ngng.

WFQ c th qun l cc lung d liu kp, nh l cc lung d liu gia cc cp ng dng, v lung d liu n nh voice hay video.

Thut ton WFQ cng nhm vo vn tnh cht tr quay vng bin thin. Nu nhiu cuc thoi dung lng ln cng hot ng, th tc truyn v thi gian n c to ra nhiu kh nng d on. WFQ nng cao cc thut ton nh l cc kin trc mng h thng (SNA: Systems Network Architecture), iu khin kt ni logic (LLC: Logical Linhk Control) v iu khin nghn TCP v c trng bt u chm.

Flow-Base WFQ c s dng nh mt phng thc hng i tu chn trn hu ht cc giao din serial c cu hnh hot ng hoc thp hn tc lung E1.

WFQ cung cp gii php cho tnh hung mong mun cung cp thi gian p ng ph hp cho cc ngi dng mng khc nhau m khng thm lng bng thng d tha. WFQ t ng thch nghi vi iu kin lu lng mng thay i.

Hn ch

WFQ khng h tr tunneling v mt m ho bi v c tnh ny lm thay i thng tin ni dung gi m WFQ yu cu cho vic phn loi.

WFQ v u tin IP

WFQ nhn bit mc u tin IP. N c th nhn ra cc gi u tin cao c nh du quyn u tin bi b chuyn tip IP v c th lp lch cho chng nhanh hn, cung cp thi gian p ng cao hn cho lu lng ny. V nh vy khi mc u tin tng ln, th WFQ cp nhiu bng thng hn cho cuc thoi trong sut thi gian nghn.

WFQ n nh mt trng s cho mi lung, n xc nh th t truyn dn cho cc gi c xp hng trong hng i. Trong s ny, cc trng s thp hn c phc v trc. Vi chun WFQ Cisco IOS, mc u tin IP phc v nh l mt b chia cho tha s trng s ny.

Ging nh CQ, WFQ gi mt s byte nht nh t mi hng i. Vi WFQ, mi hng i ph hp vi mt lung khc nhau. Trong mt chu k qua tt c cc lung, WFQ gi i mt s byte ngang bng vi mc u tin ca lung cng vi mt.

S ny ch c s dng nh mt t s xc nh bao nhiu byte/gi gi i. Tuy nhin, vi mc ch hiu c WFQ, vic s dng s ny nh l s m byte c kh nng. V d, lu lng c gi tr trng u tin IP l 7 nhn mt trng s thp hn lu lng c gi tr trng u tin IP l 3, l, mc u tin trong th t truyn dn. Cc trng s l nghch o ca gi tr trng u tin IP.

xc nh bng thng phn phi cho mi hng i, ta chia tng ch s m byte ca tt c cc lung cho ch s lung. Chng hn, nu c mt lung th mi mc u tin, mi lung s nhn thm mc u tin + 1:

1+2+3+4+5+6+7+8 = 36

Nh vy lu lng c mc u tin 0 s nhn 1/36 ca bng thng, lu lng c mc u tin 1 s nhn 2/36, v lu lng c mc u tin 7 s nhn 8/36.

Tuy nhin, nu c 18 lung mc u tin 1 v cc mc u tin cn li u l mt th tng ch s lc ny l:

1+2(18)+3+4+5+6+7+8 = 70

Lu lng mc u tin 0 s nhn 1/70, mi lung mc u tin 1 s nhn 2/70, v c nh vy.

Khi mi lung c thm vo hay bt i th bng thng phn phi thc t s thay i mt cch lin tc.

WFQ vi giao thc dnh trc ti nguyn (RSVP)

RSVP s dng WFQ phn chia khng gian b m, lp lch cc gi v m bo bng thng cho cc lung dnh trc. WFQ lm vic vi RSVP gip cung cp cc dch v QoS m bo v khc bit.

RSVP l giao thc chun Internet IETF cho php mt ng dng dnh trc bng thng mng mt cch linh ng. RSVP cho php cc ng dng yu cu mt QoS ring cho mt lung d liu. Thc hin y Cisco cho php RSVP c khi u trong mng s dng nh hnh proxy RSVP.

RSVP l giao thc bo hiu chun duy nht c thit k m bo bng thng mng t u cui n u cui cho cc mng IP. Cc host v cc router s dng RSVP thc hiu yu cu QoS cho cc router dc ng dn ca lung d liu v duy tr trng thi router v host cung cp dch v c yu cu, thng l bng thng v tr. RSVP s dng mt tc d liu trung bnh, s lng d liu ln nht m router s duy tr trong hng i, v QoS cc tiu xc nh s dnh trc bng thng.

WFQ hoc Weighted Random Early Detection (WRED) hot ng nh l mt s chun b ca RSVP, iu chnh phn loi v lp lch gi yu cu cho cc lung dnh trc. S dng WFQ, RSVP c th to ra mt dch v m bo cc dch v tch hp.

WFQ v Frame Relay

Trng s WFQ c thc hin bi bit loi b thch hp Frame Relay, cc bit khai bo nghn tng minh chuyn tip (FECN) v cc bit khai bo nghn tng minh phn hi khi lu lng c chuyn mch bi module chuyn mch Frame Relay. Mi ln nghn c nh du, cc trng s c s dng bi thut ton c bin i cuc thoi bt gp nghn gi i khng thng xuyn.

Nhng iu cn lu :

Mc d WFQ thch nghi mt cch t ng vi iu kin lu lng mng thay i, n khng a ra mc iu khin r rng trn s phn phi bng thng m CQ v CBWFQ a ra.

VIP-Distributed Weighted Fair Queuing

DWFQ l phin bn tc cao ring ca WFQ hot ng trn VIP. N c h tr trn cc router sau vi mt VIP2-40 hoc mt b x l giao din ln hn:

Cc dy Cisco 7000 vi RSP7000

Cc dy Cisco 7500

Mt b x l giao din VIP2-50 c gii thiu khi tc dng tp hp ca b thch ng cng trn VIP ln hn DS3. Mt card VIP2-50 c yu cu cho cc tc OC-3.

s dng DWFQ, th chuyn mch DCEF (Distributed Cisco Express Forwarding) phi c cho php trn giao din. Nhiu thng tin trn CEF c a vo ch dn cu hnh dch v chuyn mch Cisco IOS v tham kho lnh cc dch v chuyn mch Cisco IOS.

Ch : Vic thc hin VIP-Distributed WFQ khng ging nh WFQ thc hin trn tt c cc nn tng khc.

C hai dng ca DWFQ l: Flow-Based DWFQ v Class-Based DWFQ

Flow-Based DWFQ

Vi flow-based DWFQ, cc gi c phn loi bi lung. Cc gi c cng a ch ngun, a ch ch, cng TCP hoc UDP ngun, cng TCP hoc UDP ch, giao thc, v trng ToS thuc cng mt lung (Tt c cc gi khng phi gi IP c xem nh lung 0).

Mi lung tng ng vi mt hng i u ra ring bit. Khi mt gi c n nh ti mt lung, n c t vo hng i ca lung . Trong sut thi gian nghn, DWFQ phn phi s chia s bng thng ngang bng nhau cho mi hng i hot ng.

Flow-based DWFQ cng c gi l hng i cn bng bi v tt c cc lung c nh trng s mt cch cn bng v c phn chia bng thng cn bng. Trong chiu hng thc hin ca DWFQ, cc trng s khng c n nh cho cc lung. Vi DWFQ, cc host i x tt c bo v t cc host i x km.

Class-Based DWFQ

Trong class-based DWFQ, cc gi c n nh ti cc hng i khc nhau da trn nhm QoS ca chng hoc mc u tin IP trong trng ToS.

Cc nhm QoS cho php tu chn chnh sch QoS. Mt nhm QoS l mt phn loi ni ca cc gi c s dng bi router xc nh nhng gi no c i x bi cc c tnh QoS nht nh, nh l DWFQ v CBR (Committed Access Rate). S dng vic truyn b mt chnh sch CAR hoc chnh sch QoS qua BGP n nh cc gi ti cc nhm QoS.

Nu mun phn loi cc gi ch da vo hai bit u tin IP cp thp, th s dng ToS-based DWFQ.

nh r mt trng s cho mi lp. Trong giai on nghn, mi nhm c cp mt phn trm bng thng u ra ngang bng vi trng s ca lp. V d, nu mt lp c n nh mt trng s l 50, cc gi t lp ny s c cp t nht 50% bng thng trong sut giai on nghn. Khi giao din khng b nghn th cc hng i c th s dng mt lng bng thng kh dng.

Chnh sch loi b

DWFQ duy tr du hiu ca s gi trong hng i v tng s gi trong cc hng i.

Khi tng s gi di mc gii hn chung, th cc hng i c th m nhiu gi hn gii hn hng i ring.

Khi tng s gi t ti gii hn chung th giao din bt u cng p gii hn cc hng i ring. Mt s gi mi n khi mt hng i vt qu gii hn hng i ring ca n th s b loi b. Cc gi trong hng i s khng b loi b, ngay c khi nu hng i vt qu gii hn ring.

Trong mt s trng hp, tng s gi trong tt c cc hng i a ra cng nhau c th vt qu gii hn chung.

Nhng hn ch

S dng DWFQ vi lu lng IP. Tt c lu lng khng phi IP c i x nh l mt lung n v trc c t trong cng hng i.

DWFQ c mt s hn ch sau:

C th c cu hnh trn giao din nhng khng th cu hnh trn giao din con.

Khng h tr bo mt ATM AAL5-MUX v AAL5-NLPID.

Khng h tr trn knh Ethernet nhanh, giao din tunnel hay cc giao din logic khc nh Multilink PPP (MLP).

Khng th cu hnh trn giao din tng t nh RSP-based PQ, CQ hoc WFQ.

Class-Based Weighted Fair Queuing

CBWFQ a ra chc nng hot ng WFQ chun cung cp h tr cho cc lp lu lng ngi dng t nh ngha. Vi CBWFQ, chng ta nh ngha cc lp lu lng da trn cc chun ph hp bao gm cc giao thc, danh sch iu khin truy cp (ACLs: Access Control Lists) v cc giao din vo. Cc gi tho mn chun ph hp cho mt lp to thnh lu lng cho lp . Mt hng i dnh ring cho mi lp v lu lng thuc mt lp c a thng ti hng i cho lp .

Ch mt lp c nh ngha theo chun kt hp ca n, chng ta c th n nh cc tham s ca n. m t mt lp, chng ta n nh bng thng, trng s v gii hn gi cc i cho n. Bng thng n nh cho mt lp l bng thng m bo cp cho lp trong thi gian nghn.

m t mt lp chng ta cng ch r gii hn hng i cho lp , l s gi ti a cho php tch t trong hng i cho mi lp. Cc gi thuc mt lp l i tng bng thng v gii hn hng i m t lp.

Sau khi mt hng i t c gii hn hng i cu hnh ca n, vic xp vo hng i ca cc gi thm vo s dn ti vic b phn ui hoc b gi, ph thuc vo chnh sch lp no c cu hnh.

Vic loi b phn ui c s dng cho cc lp CBWFQ tr khi chng nh hnh chnh sch cho mt lp mt cch r rng t vic s dng WRED loi b cc gi nh l mt phng tin trnh nghn. Ch rng nu s dng loi b gi WRED thay v vic loi b phn ui cho mt hoc nhiu lp bao gm mt bn chnh sch, th phi m bo WRED khng c cu hnh cho giao din m chng ta gn cho chnh sch dch v .

Nu mt lp tu chn c cu hnh vi lnh cu hnh lp bn chnh sch bng thng, th tt c lu lng khng c phn loi c t vo mt hng i n v a ra vic gii quyt theo bng thng c cu hnh. Nu mt lp lu lng mc nh c cu hnh vi lnh fair-queue, th tt c lu lng khng c phn loi tr thnh lung c phn loi v gii quyt n lc ti a cho trc. Nu khng phi lp lu lng mc nh c cu hnh, th sau bng cch ngm nh lu lng khng kt hp mt s lp c cu hnh l lung c phn loi v gii quyt n lc ti a cho trc. Mi khi mt gi c phn loi, tt c cc c ch tiu chun c th c s dng phn bit dch v gia cc lp p dng.

S phn loi lung l s gii quyt WFQ tiu chun. Ngha l cc gi c cng a ch ngun, a ch ch, cc cng TCP hoc UDP ngun hay cng TCP hoc UDP ch c phn loi nh thuc cng lung. WFQ cung cp mt s chia s cn bng bng thng ti mi lung. Flow-based WFQ cng c gi l hng i cn bng bi v tt c cc lung c nh trng s cn bng.

Vi CBWFQ, a ra hng i cn bng WFQ tiu chun, trng s theo l thuyt cho lp tr thnh trng s ca mi gi ph hp chun kt hp ca lp. Cc gi n ti giao din u ra c phn loi theo b lc chun ph hp m chng ta nh ngha, sau mi gi c n nh mt trng s thch hp. Trng s cho mt gi thuc mt lp ring c xut pht t bng thng m chng ta n nh cho lp khi chng ta cu hnh n; vi kh nng ny trng s cho mt lp l do ngi dng t cu hnh.

Sau khi trng s cho mt gi c n nh, th gi c xp vo hng i trong hng i lp ph hp. CBWFQ s dng cc trng s c n nh cho cc gi c sp xp m bo hng i lp c phc v cng bng.

Cu hnh mt chnh sch lp l cu hnh CBWFQ - dn ti ba qu trnh sau:

nh ngha cc lp lu lng xc nh chnh sch phn loi (cc bn phn loi).

Qu trnh ny xc nh bao nhiu loi gi c phn bit t cc lp lu lng khc.

Cc chnh sch kt hp l cc c im lp vi mi lp lu lng (cc bn lu lng).

Qu trnh ny i hi cu hnh ca cc chnh sch p dng cho cc gi thuc mt trong cc lp c nh ngha trc y qua mt bn lp. Vi qu trnh ny chng ta cu hnh mt bn chnh sch ch r chnh sch cho mi lp lu lng.

Chnh sch bt buc ti cc giao din (cc chnh sch phc v).

Qu trnh ny yu cu chng ta kt hp mt bn chnh sch ang tn ti hoc chnh sch dch v, vi mt giao din p dng mu chnh sch ring bit cho bn ti giao din .

Cp bng thng CBWFQ

Tng ton b bng thng phn b trn mt giao din khng th vt qu 75% ca tng bng thng kh dng trn giao din . 25% bng thng cn li c s dng cho phn tiu khc, bao gm c phn tiu lp 2, lu lng nh tuyn v lu lng n lc ti a. Bng thng cho lp tu chn lp CBWFQ chng hn c dng t 25% bng thng cn li. Tuy nhin trong mt s trng hp mun s dng hn 75% ca bng thng giao din cho cc lp, chng ta c th chng ln 75% tng cc i c phn b ti tt c cc lp hoc cc lung s dng lnh max-reserved-bandwidth. Nu mun chng ln 75%, phi s dng mt cch cn thn v m bo c bng thng cn li h tr n lc ti a, lu lng iu khin v tiu lp 2.

Khi ATM c s dng chng ta phi ch vic t bo ATM yu cu tiu khng c thm vo. V d, hy ch trng hp m trong mt lp cn m bo bng thng trn mt ATM PVC. Cn c kch thc gi thng thng cho mt lp l 256 byte v lp cn 100 kbps (trong di dch ti 49 pps) bng thng c m bo. Mi gi tin 256 byte phi c phn chia vo cc t bo gi i trn mt VC, c tng ln l 6*53=318 byte. Trong trng hp ny, t bo ATM cn c phn u phi l 62 byte hoc 49*62*8=24,304 kbps. Khi cu hnh CBWFQ trong v d ny m bo tng tt c bng thng lp c cu hnh t hn bng thng VC t nht 24,304 kbps m bo ti trng mong mun m bo cho lp c cu hnh (trong v d ny, ch c mt lp). Nu cn mt s lp th tng tt c phn u lp cn phi c c lng v thm vo tng tt c cc bng thng lp c cu hnh. Tng ny cn phi nh hn bng thng VC m bo cho s m bo ti trng yu cu.

Ti sao s dng CBWFQ

Sau y l mt s yu t cn ch khi s dng CBWFQ:

Cp bng thng CBWFQ cho php ch r s lng bng thng chnh xc c cp cho mt lp lu lng ring. Vic a bng thng kh dng vo giao din, cn phi cu hnh ti 64 lp v iu khin s phn phi gia chng, m khng phi l trng hp vi flow-based WFQ. Flow-based WFQ p dng cc trng s cho lu lng phn n vo cuc thoi v xc nh mi cuc thoi c cp bng thng bao nhiu tng xng vi cc cuc thoi khc.Vi flow-based WFQ trng s ny v s phn loi lu lng ph thuc vo gii hn bi mc quyn u tin 7.

Coarser granularity v scalability CBWFQ cho php chng ta xc nh nhng g thnh lp mt lp da vo tiu chun vt qu ranh gii ca lung. CBWFQ cho php chng ta s dng cc danh sch v giao thc iu khin truy cp hoc tn giao din u vo xc nh lu lng no c phn loi, bng cch cung cp coarser granularity. Chng ta khng cn s phn loi lu lng cn li trn mt c s lung. Hn na, chng ta c th cu hnh ti 64 lp ring bit trong chnh sch dch v.

CBWFQ v RSVP

RSVP c th c s dng cng vi CBWFQ. Khi c RSVP v CBWFQ c cu hnh cho mt giao din, RSVP v CBWFQ hot ng c lp vi nhau, chng hot ng nh khi chng hot ng mt mnh. RSVP tip tc lm vic ngay c khi CBWFQ khng c mt.

Hn ch

Vic cu hnh CBWFQ trn mt giao din vt l ch c th thc hin nu giao din trong mt mode hng i mc nh. Cc giao din Serial E1 v thp hn s dng WFQ mt cch mc nh cc giao din khc s dng hng i FIFO mc nh. Vic cho php CBWFQ trn giao din vt l cho qua cc phng php hng i giao din mc nh. Vic cho php CBWFQ trn mt ATM PVC khng cho qua phng php hng i mc nh.

Nu cu hnh mt lp trong bn chnh sch s dng WRED cho vic loi b gi thay v loi b phn ui, th phi m bo rng WRED khng c cu hnh trn giao din m chng ta c nh gn lin vi chnh sch phc v.

nh hnh v chnh sch lu lng hin nay khng h tr vi CBWFQ.

CBWFQ c h tr trn cc kt ni ATM VBR (Variable Bit Rate) v AVB (Available Bit Rate). N khng c h tr trn cc kt ni UBR (Unspecified Bit Rate).

CBWFQ khng h tr cc giao din con Ethernet.

IP RTP Priority

c trng quyn u tin IP RTP cung cp mt s hng i u tin cht cho d liu nhy cm vi tr nh thoi . Lu lng thoi c th nhn bit bi ch s cng giao thc truyn dn thi gian thc (RTP: Real-Time Transport Protocol) v c phn vo mt hng i u tin cu hnh bi lnh ip rtp priority. Kt qu l thoi c phc v nh l mc u tin cht trong giao din vi lu lng phi thoi.

c trng quyn u tin IP RTP m rng v ci thin thm cc kh nng cung cp bi lnh ip rtp reserve bng cch cho php thay i mt dy cc cng UDP/RTP m lu lng ca chng c m bo dch v u tin cht trn mt s hng i hoc lp khc s dng cng giao din u ra. Quyn u tin cht c ngha l nu cc gi tn ti trong hng i u tin th chng c sp xp li v gi i trc - trc khi cc gi trong hng i khc c sp xp li. Chng ta nn s dng lnh ip rtp proirity thay cho lnh ip rtp reserve cho cc cu hnh thoi.

c tnh mc u tin IP RTP khng yu cu phi bit cng ca cuc gi. Hn na, c tnh cho chng ta kh nng nhn dng phm vi cc cng m lu lng a vo hng i u tin. Ngoi ra chng ta c th thay i ton b th t cng thoi 16384 ti 32767 m bo rng tt c lu lng thoi u sn sng cho dch v u tin cht. Quyn u tin IP RTP c bit hu ch trn cc kt ni tc thp m c bit l thp hn 1,544 Mbps.

c tnh ny c th c s dng chung vi WFQ hoc CBWFQ trn cng giao din i ra. Trong bt k trng hp no th lu lng ph hp th t cc cng trn l thuyt cho hng i u tin c m bo quyn u tin cht trn cc lp CBWFQ hoc cc lung WFQ khc; cc gi trong hng i u tin lun lun c phc v trc:

Khi c s dng chung vi WFQ, th lnh ip rtp priority cung cp mc u tin cht cho thoi v lp lch WFQ c p dng cho cc hng i cn li.

Khi c s dng chung vi CBWFQ, th lnh ip rtp priority cung cp mc u tin cht cho thoi. CBWFQ c th c s dng thit lp cc lp cho cc loi lu lng khc (nh SNA) cn c dnh bng thng v cn c i x tt hn n lc ti a v khng nh u tin cht; cc lu lng phi thoi c phc v cn bng da trn trng s c n inh cho cc gi trong hng i. CBWFQ cng c th h tr flow-based WFQ trong lp CBWFQ mc nh nu c cu hnh nh vy.

Bi v cc gi thoi thng c kch thc nh v giao din cng c th c cc gi ln i ra, c tnh phn mnh v chn kt ni (LFI: Fragmentation and Interleaving) cng phi c cu hnh trn cc giao din tc thp hn. Khi cho php LFI th cc gi d liu ln c ct ra cc gi thoi nh c th chn vo gia cc on d liu to ra mt gi d liu ln. LFI ngn cn mt gi thoi t nhu cu i cho n khi mt gi ln c gi. thay th, gi thoi c th c gi i trong mt lng thi gian ngn hn.

Cp bng thng IP RTP Priority

Nu mun hiu v hot ng ca n v s dng c tnh IP RTP Priority mt cch ng n, iu quan trng l phi ch c trng chnh sch v iu khin u vo. Khi s dng lnh ip rtp priority hnh thnh hng i u tin cho thoi, cn phi ch r gii hn bng thng cht. Lng bng thng ny c m bo cho lu lng thoi i vo hng i u tin. (Trong trng hp ny chng ta s dng c tnh IP RTP Priority vi CBWFQ hoc WFQ).

Ch : IP RTP Priority khng c iu khin u vo cho tng cuc gi. iu khin u vo l mt c s chung. V d, nu cu hnh cho 96 kbps, IP RTP Priority m bo 96 kbps sn c dnh ring. N khng ch m bo cho 4 cuc gi 24 kbps nhn c. Cuc gi th 5 cng c th nhn c nhng v 5 cuc gi ch c 96 kbps, nn cht lng cuc gi s b gim xung (mi cuc gi ch nhn c 96/5 = 19.2 kbps). Nh vy trong v d ny ngi dng phi m bo ch 4 cuc gi thc hin ti cng mt thi im.

IP RTP Priority gn nh kim sot vic s dng bng thng cho hng i u tin, m bo rng s lng c cung cp khng vt qu mc trong trng hp xy ra nghn. Thc t IP RTP Priority kim sot lung mi giy. IP RTP Priority ngn chn vic truyn dn cc gi thm vo mt khi bng thng cung cp c dng ht. Nu nhn ra rng s lng bng thng c cu hnh b qu, th IP RTP Priority loi b cc gi, iu ny l khng tt i vi lu lng thoi. Chnh sch ng ch n