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CHNG 4: M PHNG.
4.1 Mc ch ca vic m phng.Mng OBS c nhiu u im ng c quan tm tuy nhin mng OBS cha
tht sc trin khai trong thc t do cn thc hin vic m phng nh gi
nhng cht lng ca mng OBS. Mc tiu ca ti ny l tm hiu cht lng
dch v (QoS) da trn nhng thng sc ginh trc. M phng trong lun
vn cng so snh v nh gi cht lng dch v v xc sut mt gi trong iu kin
ti a vo mng khc nhau.
Phn m phng s thc hin vic m phng mt mng chuyn mch quang
chm OBS vi cc trng hp c cp trong chng III vi cc vn chnh
nh sau: QoS da trn vic ng khi burst, QoS da trn vic xp lch knh
truyn, QoS da trn vic bo hiu, QoS da trn vic gii quyt xung t.
M phng c thc hin bng phn mm m phng OBS4NS chy trn nn
ca phn mm m phng mng NS-2. M phng c thc hin tnh ton xc
sut mt gi v tr vi cc ti lu lng khc nhau. Kt qu m phng sc
a ra di dng th.
4.2 M hnh mng v cc thng s.
M hnh mng m phng c da theo m hnh mng NSFNET (National
Science Foundation Network) ca Hoa K vi 14 node mng. Vic s dng m
hnh ny do mng OBS cha thc sc trin khai trong thc t, hn na mng
NSFNET c s dng kh ph bin trong cc bi nghin cu v mng OBS ca
cc tc gi. Vic la chn mt mng chun c cc nh nghin cu xut so
snh kt qu l cn thit.
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Hnh 4.1 M hnh mng NSFNETSau y l cc thng s chnh trong trong m phng:
- Cc node mng u l cc node kt hp.- Lin kt l song hng vi mi hng c hai knh iu khin v hai
knh d liu. Do mt lin kt c 8 bc sng quang.
- Cc gi n c kch thc cnh l 1250 byte.- Tc truyn dn ca lin kt l 10Gbps.-
Thi gian chuyn mch l 10s
. Cng ngh chuyn mch ton quangc th da trn hai cng ngh l cng ngh chuyn mch gng vi thi
gian chuyn mch hng ms v cng ngh chuyn mch bn dn vi thi
gian chuyn mch vi s . Trng hp m phng ny tc gi gi s rng
chuyn mch ton quang u l cc chuyn mch bn dn.
- Kch thc gi iu khin l cnh v bng 64byte.- Thi gian x l gi iu khin l 2.5 s
4.3 Phn mm m phng mng ns-2
4.3.1 Gii thiu
[17,18,5] Phn mm NS-2 l phn mm m phng mng iu khin s kin
ring r hng i tng c pht trin ti UC Berkely, vit bng ngn ng C++
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v Otcl. Ns-2 l phn mm m phng m ngun mhu ch cho vic nghin cu
mng din rng (WAN) v mng local (LAN). Bn li ch ln nht ca Ns-2 l:
Kh nng kim tra tnh n nh ca cc giao thc mng ang tn ti
Kh nng nh gi cc giao thc mng mi trc khi a vo s dng
Kh nng thc thi nhng m hnh mng ln m gn nh ta khng th thc thi
c trong thc t
Kh nng m phng nhiu loi mng khc nhau
4.3.2 Kin trc ca NS-2
NS thc thi cc giao thc mng nh Giao thc iu khin truyn ti (TCP)
v Giao thc gi ngi dng (UDP); cc dch v ngun lu lng nh Giao thc
truyn tp tin (FTP), Telnet, Web, Tc bit cnh (CBR) v Tc bit thay i
(VBR) ; cc k thut qun l hng i nh Vo trc Ra trc (Drop Tail), D sm
ngu nhin (RED) v CBQ; cc thut ton nh tuyn nh Dijkstra NS cng thc
thi multicasting v vi giao thc lp iu khin truy cp ng truyn (MAC) i
vi m phng LAN.
Hnh 4.2 Tng quan vNS di gc ngi dng
OTcl Script Kch bn OTcl
Simulation Program Chng trnh M phngOTcl B bin dch Tcl mrng hng i tng
NS Simulation Library Th vin M phng NS
Event Scheduler Objects Cc i tng B lp lch S kin
Network Component Objects Cc i tng Thnh phn Mng
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Network Setup Helping Modules Cc m un Trgip Thit lp Mng
Plumbling Modules Cc m un Plumbling
Simulation Results Cc kt qu M phng
Analysis Phn tch
NAM Network Animator Minh ha Mng NAM
Trong hnh trn, NS l B bin dch Tcl mrng hng i tng; bao gm
cc i tng B lp lch S kin, cc i tng Thnh phn Mng v cc m un
Trgip Thit lp Mng (hay cc m un Plumbing).
s dng NS-2, user lp trnh bng ngn ng kch bn OTcl. User c th
thm cc m ngun Otcl vo NS-2 bng cch vit cc lp i tng mi trong
OTcl. Nhng lp ny khi sc bin dch cng vi m ngun gc. Kch bn
OTcl c th thc hin nhng vic sau:
Khi to B lp lch S kin Thit lp M hnh mng dng cc i tng thnh phn Mng Bo cho ngun lu lng khi no bt u truyn v ngng truyn gi
trong b lp lch s kin
Thut ng plumbing c dng ch vic thit lp mng, v thit lp mt
mng ngha l xy dng cc ng d liu gia cc i tng mng bng cch thit
lp con tr neighbour cho mt i tng chn a ch ca i tng tng
ng. Module plumbing OTcl trong thc t thc hin vic trn rt n gin.
Plumbing lm nn sc mnh ca NS.
Thnh phn ln khc ca NS bn cnh cc i tng Thnh phn Mng l
B lp lch S kin. B lp lch S kin trong NS-2 thc hin nhng vic sau:
T chc Bnh thi M phng Hu cc s kin trong hng i s kin Triu gi cc Thnh phn Mng trong m phng
Ph thuc vo mc ch ca user i vi kch bn m phng OTcl m kt
qu m phng c thc lu tr nh file trace. nh dng file trace sc ti
vo trong cc ng dng khc thc hin phn tch:
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File nam trace (file.nam) c dng cho cng c Minh ha mng NAM
File Trace (file.tr) c dng cho cng c Ln vt v Gim st M phng
XGRAPH hay TRACEGRAPH
Hnh 4.3Lung cc skin cho file Tcl chy trong NS
NAM Visual Simulation M phng o NAM
Tracing and Monitoring Simulation M phng Ln vt v Gim st
C++ v OTclHnh sau biu din kin trc chung ca NS. User c th tng tng mnh
ang ng gc tri di, thit k v chy cc m phng trong Tcl. Tcl dng cci tng m phng trong OTcl. Cc i tng B lp lch S kin v hu ht cc
i tng Thnh phn Mng thc thi bng C++ v sn c cho OTcl qua mt lin kt
OTcl. Lin kt OTcl ny c thc thi dng TclCL. Tt c lm nn NS, b bin
dch Tcl mrng hng i tng v cc th vin m phng mng.
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Hnh 4.4 Kin trc ca NS-2
NS s dng hai ngn ng lp trnh: Ngn ng kch bn (Tcl Tool
Command Language, c l tickle) v Ngn ng lp trnh h thng (C/C++)
NS l tng bin dch Tcl chy cc kch bn Tcl
Bng cch s dng C++/OTcl, b m phng mng phi hon ton l hng
i tng
Hnh sau ch ra cc i tng C++ c lin kt OTcl. Khi , nu chng to
nn mt phn cp th cc i tng OTcl cng c mt phn cp tng ng nh vy.
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Hnh 4.5 C++ v OTcl: Si ngu
TclCL l ngn ngc s dng cung cp lin kt gia C++ v OTcl.
Cc kch bn Tcl/OTcl c vit thit lp v cu hnh topology ca mng. TclCL
cung cp lin kt gia phn cp lp, khi to i tng, ni kt bin v gi lnh.
Hnh 4.6 TclCL hotng nhlin kt gia A v BVic s dng hai ngn ng v B m phng cn thc hin hai vic khc
nhau.
Mt mt l v cc m phng cho cc giao thc yu cu mt ngn ng lp
trnh h thng c th tnh ton mt cch hiu qu cc byte, cc tiu packet v cc
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thut ton thc thi ang chy trn mt tp d liu ln. Vi tc v ny, run-time
speed (tc thi gian chy thc) l quan trng trong khi turn-around time (thi
gian thay i) th t quan trng hn. Turn-around time bao gm thi gian chy m
phng, thi gian tm li, thi gian sa li, thi gian bin dch li v thi gian chy
li.
Mt khc, khi nghin cu mng th rt cn quan tm n cc tham s v cc
cu hnh c thay i nhng khng ng k, hay quan tm n cc scenario (tnh
hung) cn khm ph tht nhanh chng. Trong tc v ny th iteration time (thi
gian lp li, tc l thi gian hay i m hnh v chy li) l quan trng hn. V cu
hnh ch chy mt ln lc bt u m phng nn run-time trong tc v ny r rng
km quan trng hn.
Dng C++ :
M phng giao thc chi tit yu cu ngn ng lp trnh h thng Thao tc trn byte, x l gi, thc thi thut ton Tc thi gian thc l quan trng nht Thc hin bt k vic g m cn phi x l tng packet ca mt
lung.
Thay i hnh vi ca lp C++ ang tn ti theo nhng hng khng c lng trc.
V dng OTcl :
M phng nhng thng s hay cu hnh thay i Tham d nhanh mt s tnh hung Thi gian tng tc (thay i m hnh hay chy li) l quan trng Cu hnh, thit lp hay nhng g ch lm mt ln. Thc hin nhng ci ta mun bng cch thao tc trn cc i tng
C++ ang tn ti.
V d nh cc link l nhng i tng OTcl lin kt cc m un delay (tr
hon), queueing (hng i) v possibly loss (kh nng mt mt). Cn nu mun
thc hin nhng vic chuyn nghip hn th cn phi to ra i tng C++ mi.
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Hu ht nh tuyn c vit bng OTcl (d thut ton Dijkstra li vit bng
C++). M phng HTTP c tng lung bt u ti OTcl nhng vic x l tng gi
li c vit bng C++. Phng php ny chy tt cho n khi c n 100 lung bt
u thi gian m phng mi giy. Ni chung, nu phi triu gi Tcl nhiu ln mi
giy th c l nn chuyn sang C++.
V phng din m ngun, NS-2 c vit vi 100k dng m lnh C++, 70k
dng m Tcl v 20k dng ti liu.
4.3.3 Cc c tnh ca NS-2
NS-2 thc thi nhng tnh nng sau:
Cc k thut qun l hng i Router nh DropTail, RED, CBQ,
Multicasting
M phng mng khng dy
c pht trin bi Sun Microsystems + UC Berkeley (D n Daedalus)
Thuc mt t (di ng, adhoc, GPRS, WLAN, BLUETOOTH), v tinh Chun
IEEE 802.11 c thc m phng, cc giao thc Mobile-IP v adhoc nh DSR,
TORA, DSDV v AODV
Hnh vi ngun traffic www, CBR, VBR
Cc agent truyn ti UDP, TCPnh tuyn
Lung packet
M hnh mng
Cc ng dng Telnet, FTP, Ping
Cc packet tracing trn tt c cc link v trn cc link xc nh
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4.4 Phn mm m phng mng quang OBS4NS
4.4.1 Gii thiu.
Ns-2 kh y cho vic m phng mng thng thng, tuy nhin li t h
tr cho lp quang v m phng mng OBS v trong OBS cc burst d liu c
chuyn mch ton quang, khng b delay hay x l ti cc node mng. V l do ,
phn mm mrng OBS4NS chy trn nn NS-2 c xy dng gii quyt vn
m phng mng ton quang. Phn mm m phng mng OBS4NS c cc tc
gi trng i hc Vigo-Ty Ban Nha xy dng v pht trin phn ln cc chc
nng phc v tng i y cho m phng mt mng OBS hon chnh.
Phn mm OBS4NS c kh nng:
- To cc node bin, node li v node kt hp
- To cc lin kt WDM.
- Thc hin qu trnh ng khi.
- Thc hin nh tuyn.
- Thc hin vic gii quyt xung t bng bm, chuyn hng v phn
on burst.
- Thc hin vic lp lch knh truyn LAUC, LAUC-VF,..
4.4.2 Cc module trong OBS4NS.Phn mm OBS4NS c xy dng t cc module sau:
Module to node mng (ObsNode)Cc node trong mng OBS bao gm node bin v node li. Phn mm ny
cng xy dng mt module to cc node ny trong mng, cc node mng trong
phn mm ny l node unicast khng h trnode multicast.
- Node bin
Ng vo ca node bin l lu lng ly t module to lu lng. Cc thngs ca lu lng tu thuc vo lu lng a vo. Gi tr ng ra ca node bin l
cc burst d liu, gi iu khin, thng tin vng i ngn nht, bc sng cho
gi iu khin v burst d liu.
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Hnh di y m t kin trc ca node bin v node li trong OBS4NS.
Hnh v cho thy nhng phn ging nhau trong khi xy dng i tng m phng
l c node bin v node li u s dng chung thnh phn to kt ni
(Connector/ObsLink) v s dng bin entry_ xc nh li vo. Phn khc nhau
gia node bin v node li l node bin c phn giao din lp MAC cn node
li c chuyn mch quang khi (Classifier/ObsSwitch)
Hnh 4.7 Giao din lp MAC
Giao din n lp MAC l thnh phn c bn ca node bin c nhim v
nhn lu lng t khi to lu lng (lu lng c to ra bng mt s module
trong NS-2). N phn loi gi n theo ch n (Classifier/Addr) v theo lp dch
v (Classifier/CoS). Kn bng khi (Agent/Burstifier) c chc nng tp trung
cc gi tin lp cao vo bm ri to thnh burst d liu cng vi vic pht gi
iu khin. Cui cng l b lp lch knh truyn (ChannelScheduler) chn mt bc
sng thch hp cho burst d liu ng ra. Node bin ch c b gii ng khi
(Agent/Deburstifier) tch cc gi tin t burst d liu nhn c.
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Thnh phn quan trng nht ca giao din lp MAC l b ng khi
(Agent/Burstifier). Cc bin s cho bng khi quyt nh vic ng khi nh th
no:
MaxDBsize_ : ng khi theo tiu chun v dung lng ti a.
Max_packets_ : ng khi theo tiu chun v s lng gi ti a trong burst.
Time_out_ : ng khi theo tiu chun thi gian ti a.
Np_ : s lng gi trong mt burst thc tc pht i.
Size_ : dung lng thc tc pht i.
Hnh 4.8 Giao din lp MAC
Khi mt burst d liu c a vo mng, mt gi iu khin c to ra
cho burst ny. Gi iu khin ny c gi vo mng ngay tc khc cn burst d
liu phi i trong bm mt khong thi gian b mi c pht i. Thi gian b
c tnh nh sau:
extraiTxioffsetswitchBHPprocioffset TTTTnTT +++++= )()1)(max( 1,1,,
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Vi
n: s bc nhy t ngun n ch.
i: mc u tin dch v.
)max( BHPprocT : thi gian x l gi iu khin ti mi node. Nu chng ta gi
s rng thi gian x l gi iu khin cc i ti mi node l bng nhau k c node
ngun th tng thi gian x l gi iu khin l )max( BHPprocT (n+1)
switchT : thi gian chuyn mch ti mi node trung gian
1, ioffsetT : thi gian offset time ca burst c mc u tin cao hn.
1, iTxT
: thi gian truyn burst c mc u tin cao hn ti a. iu ny to ras cch ly 100% gia cc lp dch v.
- extraT : l thi gian pht sinh do cc tnh hung khc v c tnh nh say:
+++=randomBHPqueuedeflBHPprocextra
TTnTT )max(
defln : l s ln chuyn hng ti a ca mt burst theo mt phng thc
chng loop.
BHPqueueT : l thi gian gi iu khin cn phi cha trong hng i.
: l khong thi gian rt nh, l khong thi gian bo v, cho php chuyn
mch chuyn t trng thi hot ng sang trng thi cu hnh li.
randomT : l khong thi gian c to ngu nhin trong mt khong no
ng vai tr mt thng s ngu nhin no trong mng.
Max_bhp_queue_time_: bin ny cho php ci t BHPqueueT
Extra_random_time_: bin ny cho php ci t randomT
Extra_fixed_time_: bin ny gii hn s bin i randomT v 1, iTxT
Equal_offset_: cho php gi tr offset time ca cc lp dch v khc nhau
bng nhau.
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Bhp_struct_map_: cho php gi iu khin c th sa li khi thng tin v
burst trn ng truyn b thay i (v d nh burst b rt mt phn).
Bhp_size_: bin thit lp kch thc gi iu khin.
Segmentation_: cho php phn on burst trong min in.
Max_segmentation_: s lng on ln nht trong mt burst.
Min_segmentation_size_: kch thc ti thiu ca mi on.
Stats_ : cho php gi chc nng thng k.
Hnh 4.9 Thi gian offset
- Node li
Thnh phn ch yu ca node li l n viu khin chuyn mch SCU v
ma trn chuyn mch quang OXC.
Cc thnh phn ny thuc lp Classifier/ObsSwitch
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SCU
OXC
BHP
DB
Ng ra
(Classifier/ObsSwitch)
Hnh 4.10 Node li trong OBS4NS
Chng trnh xy dng SCU vi cc bin s sau:
Bhp_proc_time_: thi gian x l gi iu khin.
Channel_schedule_: chn la loi lp lch knh truyn.
Multipath_: cho php chn la nhiu ng i hay khng.
Deflection_ : cho php SCU cu hnh cho OXC chuyn hng burst trong
vic gii quyt xung t.
Segmentation_: cho php SCU cu hnh cho OXC phn on burst trong vic
gii quyt xung t.
Max_segmentation_size_: kch thc nh nht cho mi on.
Switch_time_: thi gian chuyn mch ca ma trn chuyn mch quang.
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- Node kt hp
Ngoi node bin v node li vi cc chc nng ring bit, phn mm cn xy
dng mt node kt hp bao gm c chc nng node bin ln chc nng node li.
Giao din ktni n lp
MAC
Node li OBS
Agent
Agent
Agent
Ng ra Ng ra
Ng
vo
Node kt hp
(Connector/ObsLink)
(Classifier/TypeSwitch)
Gii a hp(Classifier/Port)
IP
OBS
Hnh 4.11 Node kt hp
T hnh ta thy node kt hp c th x l hai loi lu lng IP v burst d
liu. Classifier/TypeSwitch c nhim v xt xem lu lng n l IP hay l burst, t
a ra quyt nh lu lng ny x l phn no (node li hay node bin).
Cc thng s lin quan khc c cu hnh ging nh cu hnh i vi node
bin v cu hnh i vi node li.
Module to lin kt trong mng (Connector/ObsLink)Do lin kt trong mng OBS l cc lin kt WDM nn trong xy dng
chng trnh cng c chc nng to lin kt WDM. Lin kt WDM trong chng
trnh to nn cc bin s sau:
ndc_: s knh d liu.
ncc_: s knh iu khin.
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dc_bandwidth_: bng thng knh d liu.
cc_bandwidth_: bng thng knh iu khin.
delay_: tr lan truyn trn mi lin kt.
Module n v truyn dn trong mng (ObsPacket)
Hai n v truyn dn trong mng l gi iu khin OBS_BHP v burst d
liu OBS_DB, burst d liu trong OBS4NS khng phi l mt gi c th nh trong
NS-2, chng trnh m phng ch xt hai gi tr vim bt u DB_START v kt
thc DB_END ca mi burst. C th trong chng trnh hai gi tr ny l hai bin
NULL, iu ny lm cho vic x l burst d liu nhanh hn v thch hp cho vic
x l ca my tnh.
OBS_BHP: chng trnh s to ra gi iu khin vi cc thng s sau:
Id_: bin s nhn din mi gi BHP.
Db_start_time_: thi im bt u ca burst.
Db_end_time_: thi im kt thc ca burst.
Channel_: gi BHP ny sa n knh no.
Ttl_: thi gian sng ca gi BHP.
Offset_obs_bhp_: thng s v thi gian b.
Stats_: bin gi module thng k.
Id_ Db_start_time_ Db_end_time_ Channel_ Ttl_ Offset_obs_bhp_ Stats_
OBS_DB: Chng trnh to ra burst d liu vi cc thng s sau:
Type_: cho bit l DB_START hay DB_END.
Id_: s nhn din burst, cng ch s vi OBS_BHP tng ng.
Src_: a ch node ngun.
Dst_: a ch node ch.Channel_: burst ny sc a ln knh no.
Stats_: bin gi module thng k.
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Phn Dbpayload i din cho phn d liu ca burst c pht i bao gm 3
bin s lin quan:
Np_: s gi tin thc t trong mt burst.
Size_: kch thc thc t ca burst
Number_DB_: s lng on trong mt burst d liu trong trng hp ng
khi kiu phn on.
Module lp lch knh truyn (ChannelScheduler)Khi mt burst d liu c to ra hoc khi n i qua cc node trung gian, n
cn c sp xp n mt bc sng no ng ra. Ba phng thc lp lch c
nhiu nh nghin cu quan tm nht c xy dng trong OBS4NS l: FFUC,
LAUC v LAUC-VF.
ChannelScheduler/FFUC: Thut gii lp lch knh l FFUC.ChannelScheduler/LAUC: Thut gii lp lch knh truyn l LAUC.
ChannelScheduler/LAU_VF: Thut gii lp lch knh truyn l LAUC-VF.
Module nh tuyn (ObsRoute)
OBS4NS tnh ton ng i da trn gii thut ng i ngn nht SPF. Mi
node mng cng vi cc lin kt to ra mt topo mng. Sau mi node mng s
lu tr mt bng cc node ln cn ca n. Vic tnh ton ng i ngn nht t
node ny n node kia ban u da vo s chng tm ng i ngn nht. Nunh vic tm ng i da vo s bc nhy tm c nhiu hn mt con ng
n ch th con ng ngn nht c chn chnh l con ng c tr lan
truyn nh nht.
Module thng k (stats)
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Trong phn mm OBS4NS burst d liu khng phi l mt gi c th nh
trong NS-2, chng trnh ch m phng hai gi tr thi im bt u v kt thc mi
burst, do khng tha ra kt qu bng file trace nh NS-2. Phn mm OBS4NS
h trvic theo di kt qu bng mt module thng k. Cc bin trong hm thng
k ny gm:
Get-global-stats-collector: Dng thng k tt c cc gi i vo h thng.
Get-flow-stats-collector:Dng thng k tt c cc gi i vo theo tng
lung ring r
4.5 Cc trng hp thc hin m phng.
TRNG HP 1: QoS da trn vic thay i cc thng sng gi. [20,1]:
Vic thc hin vic so snh cc thng sng gi khc nhau c thc hin di
tiu chun drop policy (DP) v phn mnh gii quyt xung t (SDP). Hai tiu
chun ny c cp n trong chng II.
Mt ngng vi hai mc u tin: Trong phn ny chng ta gi s mng
mang hai lp lu lng chy trn hai lp dch v vi hai mc u tin khc nhau:
lp 1 c mc u tin thp, lp 2 c mc u tin cao, tc gp i lp 1.
Vic thit lp mt thng s ngng cho tt c cc burst d liu trong mng ln lt
l:100, 150, 300 gi trong burst. Chng ta snh gi kh nng mt gi ca cc tia vo mng vi cc thng s ngng khc nhau.
TRNG HP 2: QoS da trn vic thay i cc tiu chun xp lch knh.
[10]: Vic thc hin m phng nh gi QoS da trn vic thay i cc tiu chun
xp lch knh vi s dng tiu chun drop policy v phn mnh gii quyt xung
t vi mt ngng ng gi cnh. Mng OBS m phng mang hai lp dch v.
- M phng mng OBS vi tiu chun xp lch knh LAUC.-
M phng mng OBS vi tiu chun xp lch knh FFUC.- M phng mng OBS vi tiu chun xp lch knh LAUCVF.
TRNG HP 3: QoS da trn vic gii quyt xung t.[1]: trng hp
ny s thc hin m phng mng OBS mang hai lp traffic vi hai mc u tin
khc nhau. Cc tiu chun gii quyt xung t c s dng l DP, SDP, DFSDP,
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DFDP, SFDP. Chng ta snh gi kt qu da trn kh nng mt gi ca lu
lng a vo mng vi mt ngng ng gi cnh.
TRNG HP 4: QoS da trn tn hiu u tin: Vic m phng s thc
hin trn mng OBS vi hai tn hiu c s dng l JET v JIT. Chng ta cng s
nh gi kt qu da trn kh nng mt gi vi cc mc lu lng khc nhau.
TRNG HP 5: Trng hp ny cp n tr do chuyn mch OBS
gy ra. Trng hp ny xt n 3 tnh hung:
- Tnh hung th nht: mng chuyn mch quang chm OBS chai lp dch v, lp dch v th nht c u tin thp hn lp th hai,
lp lch knh truyn LAUCVF, gii quyt xung t DP, ngng 100.
- Tnh hung th hai: mng chuyn mch quang chm OBS chai lp dch v, lp dch v th nht c u tin thp th hai, lp lch
knh truyn LAUCVF, gii quyt xung t SDP, ngng 100.
- Tnh hung th ba: mng chuyn mch quang chm OBS chai lp dch v, lp th nht c u tin thp hn lp th hai, s dng
giao thc bo hiu JET, lp lch knh truyn LAUCVF, ngng 100.
4.6 Xy dng kch bn m phng.
4.6.1 Lu xy dng kch bn m phng.
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Bt u
Ktthc
Ly ngun cho m phng
To m hnh mng NSFNET
Thit lp cc thng s mng
Khi to cc bin
Thit lp cc thng s SCU giiquyt xung t
a lu lng vo mng trnmi cp node
Thu thp kt qu
Kt thc lu lng
S gi gi
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4.6.2 Cc bc thc hin m phng.
Ly ngunPhn mm m phng OBS4NS xy dng tng i y cc th vin cn
thit cho vic m phng mt mng quang, chng ta gi li cc ngun cn thit cho
vic m phng bng cch trng dn n cc th vin nh sau:
Source {ng dn n th mc obs4ns-3.4}/tcl/lib/ns-obs-lib.tcl
Source {ng dn n th mc obs4ns-3.4}/tcl/lib/ns-obs-node.tcl
Source {ng dn n th mc obs4ns-3.4}/tcl/lib/ns-obs-link.tcl
Source {ng dn n th mc obs4ns-3.4}/tcl/lib/ns-obs-stats.tcl
Source {ng dn n th mc obs4ns-3.4}/tcl/lib/ns-obs-defaults.tcl
Khi to cc binKhai bo cc bin c nh ngha bn ngoi kch bn m phng a
ti vo mng. Bin load thay i t 0,1 (Erlang) n 1 (Erlang). i vi mi loi
lu lng thi im pht gi u tin ph thuc vo hm ngu nhin. Hm ngu
nhin ny to ra mt s ngu nhin da vo bin seed.
Set load [lindex $argv 0] //a ti vo mng
Set opt(seed) [lindex $argv] // Khi to cc s ngu nhin.
To i tng m phng mi.Set ns [new Simulator]
To cc node mng.Nh cp trong chng 2, mt mng OBS gm c cc node bin, node
li v node kt hp. Phn mm OBS4NS-3.4 h trvic xy dng cc node mng
nh sau:
Set c($i) [$ns ObsCoreNode $ncc $ndc ChannelScheduler/$stype CoS]
// Khi to cc node liSet e($i) [$ns ObsEdgeNode $ncc $ndc ChannelScheduler/$stype CoS]
// Khi to node bin.
Set h($i) [$ns ObsHybridNode $ncc $ndc ChannelScheduler/$stype CoS]
// Khi to cc node kt hp
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Trong :
ChannelScheduler/$stype: loi lp lch knh truyn.
Ndc: s lng knh d liu ng ra ca mi node.
Ncc: s knh iu khin ng ra ca mi node.
CoS: s mc dch v.
To cc lin kt trong mng.Sau khi to cc node mng bc tip theo chng ta s xy dng cc lin kt
trong mng to nn mt topology mng hon chnh. Cu lnh to lin kt song
hng gia hai node mng c dng nh sau:
$ns duplex-obs-link $c($i) $c($j) $ncc $ndc $d ChannelScheduler/$stype
Trong :
C($i): node th i
C($j): node th j
d: khong cch gia node th i v node th j, n v km.
duplex-obs-link: lin kt l song hng.
Dng lnh $ns compile-obs hon tt vic lin kt gia cc node mng.
Thit lp cc thng s mng. m phng hot ng ca mng OBS, chng ta s thit lp cc thng s
mng theo cc ginh ban u. Cc thng s cn thit lp l bng thng lin kt,
cc thng sng khi (burst assembly), cc thng s b kt ni quang cho OXC,
cc thng siu khin chuyn mch SCU.
Connector/ObsLink dc_bandwidth // thit lpbng thng knh d liu.
Connector/ObsLink cc_bandwidth // thit lp bng thng knh iu
khin.
Agent/Burstifier set max_db_size_ [expr 1250*$number] // ng khitheo kch thc ti a vi number l s lng gi tin trong mt burst.
Agent/Burstifer set timeout_ //ng khi theo tiu chun thi gian.
Agent/OXC switch_time // thit lp thi gian chuyn mch.
Agent/Burstifier set bhp_size_ // thit lp kch thc gi iu khin.
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Agent/SCU max_bhp_proc_time // thit lp thi gian x l gi iu khin.
Agent/Burstifier set max_segmentations_ // thit lp s lng on ti
a khi phn on mt burst.
Agent/Burstifier set min_segmentable_size_ // thit lp kch thc nh
nht ca mi on.
Agent/Burstifier set segmentation_ // thit lp cc thng s cho php
gii quyt xung t trong bng khi bng phn on burst.
Agent/SCU set signalling_ // thit lp k thut bo hiu.
y l phn quan trng nht trong vic m phng, vic xc lp cc thng s
ca b kt ni quang cho OXC v cc thng s iu khin chuyn mch SCU
quyt nh vic thay i cc thng s QoS trn mng.
a lu lng vo mng.Bc tip theo l a ti vo mng vi lu lng a vo mng theo phn
b Poisson:
Set rate [expr $load*$ndc*$n_link*[Connector/ObsLink
dc_bandwidth]/$n_app]
// Tc ca mi lung lu lng c tnh ra t ti a vo mng.
Set Poi($i$j) [new Application/Traffic/Poisson]// To lu lng theo phn b Poisson.
$Poi($i$j) set rate_ $rate
// Gn tc cho lu lng.
$Poi($i$j) set packetSize_
// Gn kch thc gi.
Set udp($i$j) [$c($i) set burstifier_([$c($j) id]:QoS)
// To udp gn lu lng vi QoS l th t lp dch v.$Poi($i$j) attach-agent $udp($i$j)
//t lu lng trn tt c cc cp node.
$udp($i$j) set-traffic-generator $Poi($i$j)
$ns at 0.0 $udp($i$j) start
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// cho php bt u chy lu lng khi mi bt u chy m phng.
Kt thc lu lng.M phng c gi s s kt thc khi s gi pht i vo mng t n con s
nh mong mun. Phn mm OBS4NS ch xc nh cc bin su vo v u ra
nn trong phn ny phi gi chc nng thng k thc hin vic m gi
set sc [$ns get-global-stats-collector k]
// khi to bin sc ghi nhn cc s kin, k l s th t ca lp dch v
$sc set-counter-convergence IP_IND 1000000
// m phng kt thc khi d liu c a vo mng t n mc 1 triu gi.
Stats stop-command stop
// gi hm stop kt thc m phng.
$ns at [RouteLogic/ObsRoute transit_time] $ns enable-stats
// cho php gi chc nng thng k trong thi gian thc hin m phng.
Hm stop c to ra nh sau:
Proc stop {} {
Global ns udp
$ns at-now $udp($i$j$k) stop
// Kt thc pht burstSet now [$ns now]
$ns at [expr $now +0.2] finish
// ch0.2s sau khi cc burst n ch ri mi kt thc m phng
Kt thc m phng v ly kt qu.Sau khi kt thc m phng, s thu thp kt qu v ghi kt qu ny vo mt
file text.
To hm finish nh sau:Proc finish {} {
Global ns sc
Set ip_snd [expr [$sc get-counter-value IP_SND]]
// ly s lng gi c pht i.
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Set ip_rcv [expr [$sc get-counter-value IP_RCV]]
// ly s lng gi nhn c.
Set ip_drop [expr $ip_snd - $ip_rcv]
// tnh s lng gi b rt.
Set ip_p [expr 1.0*$ip_p/$ip_snd]
// tnh xc sut mt gi.
Set file [open results.txt a]
// khi to mt file ghi kt qu.
Puts $file $ip_p
// ghi kt qu xc sut mt gi vo mt file
Exit 0
}
Bt u chy m phng.
Bt u chy m phng bng lnh:
$ns
4.7 Kt qu m phng.
Cc s liu t vic chy m phng c biu din di dng th. Nhng
th ny c v bng phn mm matlab 6.5.TRNG HP 1: QoS da trn cc thng s ngng ng khi (burst
assembly). Vic m phng ly 3 mc ngng l 100, 150, 300 trn hai lp dch v,
vi hai tc khac nhau. Lp dch v th nht c u tin thp, lp dch v th
hai c tc gp i lp th nht v c u tin cao. Tiu chun gii quyt xung
t l drop policy (DP) v Phn mnh gii quyt xung t (SDP), giao thc bo
hiu l JET.
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Hnh 4.13 Kt qu m phng da trn cc thng sng khi 100, 150, 300
v gii quy
t xung
t d
a trn tiu chu
n DP.
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Hnh 4.14 Kt qu m phng da trn cc thng sng khi 100, 150, 300
v gii quyt xung t da trn tiu chun SDP.Nhng kt qu trn cho thy rng trong c hai trng hp DP v SDP cho
nhng kt qu sau:
- Thng sng khi cng ln kh nng mt gi cng cao.- Lu lng a vo cng cao kh nng mt gi cng ln.- Burst c u tin cao t mt gi hn so vi burst c u tin thp.Trng hp ng khi vi tiu chun SDP cho mt gi thp hn trong
trng hp ng khi theo tiu chun DP.TRNG HP 2: QoS da trn cc thng s xp lch knh. Vic m phng
thc hin trn hai lp dch v vi hai mc u tin khc nhau da trn tiu chun
lp lch knh l FFUC, LAUC, LAUCVF vi ngng l 100 gi. Hai tiu chun
gii quyt xung t l SDP v DP, giao thc bo hiu l JET.
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Hnh 4.15 Kt qu m phng da trn cc thng sxp lch knh FFUC,
LAUC, LAUCVF v gii quyt xung t da trn tiu chun DP.
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Hnh 4.16 Kt qu m phng da trn cc thng sxp lch knh FFUC,
LAUC, LAUCVF v gii quyt xung t da trn tiu chun SDP.
Trong cc trng hp trn cho cc kt qu sau:
- Tiu chun lp lch knh LAUCVF cho mt gi thp nht.- Lu lng a vo cng ln kh nng mt gi cng ln.- Lp dch v c u tin cao cho mt gi thp hn rt nhiu sovi lp dch v c u tin thp.
- Tiu chun gii quyt xung t SDP cho mt gi t hn so vi DP.
TRNG HP 3: QoS da trn vic thay i cc tiu chun gii quyt xung
t. Cc tiu chun gii quyt xung t ln lt l: DP, SDP, DDP, SDDP, DSDP.
Ngng ng khi l 100, tiu chun lp lch knh l LAUCVF, giao thc bo hiu
l JET.
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Hnh 4.17 Kt qu m phng da trn cc tiu chun gii quyt xung t.
Cc m phng trn cho nhng kt qu sau:
- Hai tiu chun gii quyt xung t DSDP v SDDP cho khnng mt gi thp.
- Ti a vo mng cng cao kh nng mt gi cng cao.- Lp dch v c u tin cao kh nng mt gi thp hn lp
dch v c u tin thp.
TRNG HP 4: QoS da trn cc thng s bo hiu. M phng s dng
hai giao thc bo hiu l JET v JIT vi hai lp dch v khc c mc u tin
khc nhau, ngng ng khi l 100, tiu chun gii quyt xung t l DP v SDP.
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Hnh 4.18 Kt qu m phng da trn thng sbo hiu vi tiu chun gii
quyt xung t DP.
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Hnh 4.19 Kt qu m phng da trn cc thng sbo hiu vi tiu chun
gii quyt xung t SDP.Cc m phng trn cho cc kt qu:
- JET cho mt gi thp hn JIT.- Ti a vo mng cng ln kh nng mt gi cng thp.- Lp dch v c u tin cao t mt gi hn lp dch v c
u tin thp.
- Tiu chun SDP cho mt gi t hn so vi DP.
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TRNG HP 5: Xem xt tr trung bnh do chuyn mch quang chm
gy ra.
Hnh 4.20 : Delay trn mng OBS vi hai lp dch v, lp lch knh tryn LAUCVF,gii quyt xung t DP, ngng 100
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Hnh 4.21: Delay trn mng OBS vi hai lp dch v, lp lch knh tryn LAUCVF,gii quyt xung t SDP, ngng 100
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Hnh 4.22: Delay trn mng OBS vi hai lp dch v, lp lch knh tryn LAUCVF,ngng 100, giao thc bo hiu JET
Nhn xt: Trong c ba trng hp trn cho thy nhng lp c u tin cao
hn cho tr trung bnh t hn. Lu lng a vo mng cng cao tr trungbnh cng gim xung. K thut bo hiu JET v JIT c tr gn ging nhau
nhng JET c tr thp hn so vi JIT do phng php ng k tr hon, gii
phng bng thng tt hn. SDDP cho tr cao hn so vi DP v cn nhiu thi
gian x l hn.
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