38050 Povo Trento (Italy), Via Sommarive 14

Transcription

1 UNIVERSIY OF RENO EARMEN OF INFORMAION AN COMMUNICAION ECHNOLOGY ovo rento Italy Va Soarve 4 htt:// SUORING SERVICE IFFERENIAION IH ENHANCEMENS OF HE IEEE 80. MAC ROOCOL: MOELS AN ANALYSIS Bo L and Roberto Battt May 003 echncal Reort # I-03-04

2 .

3 Suortng Servce fferentaton wth Enhanceent of the IEEE 80. MAC rotocol: Model and Analy Bo L and Roberto Battt eartent of Couter Scence and elecouncaton Unverty of rento OVO rento Italy e-al: {l battt}@dt.untn.t Abtract. A one of the fatet growng wrele acce technologe rele LAN ut evolve to uort adeuate degree of ervce dfferentaton. Unfortunately current LAN tandard le IEEE 80. trbuted Coordnaton Functon CF lac th ablty. or n rogre to defne an enhanced veron caable of uortng QoS for ulteda traffc at the MAC layer. In th aer we a at ganng nght nto three echan to dfferentate aong traffc categore.e. dfferentatng the nu contenton wndow ze the Inter-Frae Sacng IFS and the length of the acet ayload accordng to the rorty of dfferent traffc categore. e rooe an analy odel to coute the throughut and acet tranon delay. In addton we derve aroxaton to get ler but ore eanngful relatonh aong dfferent araeter. Coaron wth dcrete-event ulaton reult how that a very good accuracy of erforance evaluaton can be acheved by ung the rooed analy odel. Keyword: rele LAN IEEE 80. MAC Servce fferentaton erforance Evaluaton I. Introducton he an obectve of the next-generaton broadband wrele networ to rovon eale ulteda ervce to oble uer. In th context one of the aor challenge of the wrele oble Internet to rovde utable level of Qualty of Servce over I-baed wrele acce networ []. Current aroache to rovde I QoS nclude IntServ [] and ffserv [3] archtecture. he IntServ archtecture defne echan for er-flow QoS anageent and rovde tght erforance guarantee for hgh rorty flow whle the ffserv archtecture defne aggregated behavor for a lted nuber of erforance. h wor uorted by roect ILMA rele Internet and Locaton Manageent funded by rovnca Autonoa d rento

4 clae for whch only tattcal dfferentaton rovded therefore achevng better calng erforance. rele acce ay be condered ut another ho n the councaton ath for the whole Internet. herefore t derable that the archtecture uortng ualty aurance follow the ae rncle n the wrele networ a n the wrelne Internet aurng coatblty between the wrele and wrelne art. A good exale for uch a wrele technology the IEEE 80. trbuted Coordnaton Functon CF tandard [4] whch coatble wth the current bet-effort ervce odel of the Internet. In the lterature erforance evaluaton of 80. ha been executed by ung ulaton [5] or by ean of analytcal odel [6]-[]. Contant or geoetrcally dtrbuted bacoff wndow ze have been condered n [6] [7] and [8]. In [9] an exonental bacoff wth only two tage odeled by ung a two-denonal Marov chan. In [0] a ore general odel that account for all the exonental bacoff rotocol detal rooed. In [] ntead of ung tochatc analy the average value for a varable ued whch reult n an aroxate but effectve analy. In order to uort dfferent QoS reureent for varou tye of ervce a oblty to uort dfferentaton n the IEEE 80. MAC layer a rooed n [] - [5]. In [] a le rorty chee for IEEE 80. ha been rooed where a hgh rorty taton ha a horter watng te when acceng the edu. In [3] a ervce dfferentaton chee rooed. he chee ue two araeter of IEEE 80. MAC the bacoff nterval and the IFS between each data tranon to rovde the dfferentaton. In [4] ervce dfferentaton uorted by ettng dfferent nu contenton wndow for dfferent tye of ervce. he effectvene deontrated by ulaton. he wor n [5] rooe three ervce dfferentaton chee for IEEE 80. CF. he frt one baed on calng the contenton wndow accordng to the rorty of each flow. he econd one agn dfferent Inter-Frae Sacng to dfferent traffc clae. he thrd one ue dfferent axu frae length. Moreover an effectve Contenton ndow C reettng chee to enhance the erforance of IEEE 80. CF analyzed n [6] by extendng the odel rooed n [0]. In [7] both the Enhanced trbuted Coordnaton Functon ECF and the Hybrd Coordnaton Functon HCF defned n the IEEE 80.e draft are evaluated through ulaton. In order to gan a deeer nght nto the odfed IEEE 80. MAC wth ervce dfferentaton uort yte odelng and erforance analy are needed. By buldng on revou aer dealng wth the analy of the IEEE 80. MAC we rooe an

5 analy odel to coute the throughut and acet tranon delay n a LAN wth Enhanced IEEE 80. trbuted Coordnaton Functon wth uort for ervce dfferentaton. In our analytcal odel ervce dfferentaton uorted by dfferentatng the contenton wndow ze the Inter-Frae Sacng and the acet length accordng to the rorty of each traffc flow. he aer organzed a follow: n Secton II a bref decrton on the IEEE 80. CF and enhanceent gven. In Secton III the odel defned and yte erforance eaure.e. throughut and average acet delay are obtaned. In Secton IV oe aroxaton are condered to obtan ler forula allowng a deeer nght nto the yte. hen dcrete-event ulaton and nuercal reult obtaned fro the analy are reented and dcued n Secton V. II. IEEE 80. trbuted Coordnaton and Enhanceent In the 80. MAC ub-layer two ervce have been defned: the trbuted Coordnaton Functon CF whch uort delay nentve data tranon and the otonal ont Coordnaton Functon CF baed on ollng and ntended to uort delay entve tranon. he bac 80. MAC rotocol the trbuted Coordnaton Functon CF wor a lten-before-tal chee baed on Carrer Sene Multle Acce CSMA wth a Collon Avodance CA echan to avod collon that can be antcated f ternal are aware of the duraton of ongong tranon vrtual carrer ene. Followng a bref uary of the CF rotocol. hen the MAC receve a reuet to trant a frae a chec ade of the hycal and vrtual carrer ene echan. If the edu not n ue for an nterval of IFS the MAC ay begn tranon of the frae. If the edu n ue durng the IFS nterval the MAC elect a bacoff te and ncreent the retry counter. he bacoff te randoly and unforly choen n the range 0 beng the contenton wndow. he MAC decreent the bacoff value each te the edu detected to be dle for an nterval of one lot te. he ternal tart tranttng a acet when the bacoff value reache zero. hen a taton trant a acet t ut receve an ACK frae fro the recever after SIFS lu the roagaton delay or t wll conder the tranon to have faled. If a falure haen the taton rechedule the acet tranon accordng to the gven bacoff rule. If there a collon the contenton wndow doubled and a new bacoff nterval 3

6 elected. At the frt tranon attet et eual to a value C n called nu contenton wndow. After each unucceful tranon doubled u to a axu value C ax C. n he above-decrbed two-way handhang technue for the acet tranon called bac acce echan. Furtherore n order to overcoe the hdden taton roble 80. defne an otonal Reuet-to-end/Clear-to-end RS/CS echan. In the RS/CS echan before tranttng a data frae the ender end a hort RS frae. On recevng the RS frae the recever trant a CS frae edately. he RS and CS frae nclude nforaton about the te reured to trant the next data frae.e. the frt fragent and the correondng ACK reone. herefore other taton cloe to the ender and hdden taton cloe to the recever wll not tart any tranon durng the adverted frae tranon erod. In the aer only the bac acce echan analyzed. he analy ethod can be ealy extended to the cae of RS/CS acce echan. he bac CF ethod not arorate for handlng ulteda traffc reurng guarantee about throughut and delay. Becaue of th weane ta grou E of the IEEE 80. worng grou currently worng on an enhanced veron of the tandard called IEEE 80.e. he goal of the extenon to rovde a dtrbuted acce echan caable of ervce dfferentaton. A new acce echan called Enhanced CF ECF ha been elected [8]. It hown by ulaton that ECF ha better erforance than F and ore calable [9]. In th aer n the nteret of concene we are not ntereted n exlorng all detal of the new rooed tandard but to gan nght nto three of the buldng bloc ued to acheve dfferentaton.e. dfferentatng the nu contenton wndow ze the Inter-Frae Sacng IFS and the length of acet ayload accordng to the rorty of each traffc category. III. erforance Analy A. Syte Modelng e aue that the channel condton are deal.e. no hdden ternal and cature and that the yte oerate n aturaton: a fxed nuber of traffc flow alway have a acet avalable for tranon. Becaue our analy can be ealy extended and for the ae of lcty only two 4

7 dfferent tye of traffc are condered wth n traffc flow for traffc of tye. e aue that tye- traffc ha a hgher rorty than tye- traffc. Let b t be the tochatc roce rereentng the bacoff te counter for a gven traffc flow wth tye. Moreover let u defne for convenence C a the nu contenton wndow for n traffc tye. Let axu bacoff tage be the value uch that C ax. Let t be the tochatc roce rereentng the bacoff tage 0... for a gven traffc flow wth tye. Let IF denote the length of the dtrbuted nter-frae ace IF of traffc flow wth tye. σ the duraton of an ety lot te. Moreover we defne IF IF a the dfference between IF and IF eaured n the nuber of σ ety lot. In th aer t aued that IF IF. Moreover we only conder the cae that an nteger. he ey aroxaton n the odel that at each tranon attet for a traffc flow of tye regardle of the nuber of retranon uffered each acet collde wth contant and ndeendent robablty very accurate f. h auton ha been hown by ulaton to be and n are large [0]. he araeter referred to a condtonal collon robablty the robablty of a collon een by a acet belongng to a traffc flow wth tye at the te of t beng trantted on the channel. e do not aue that. Later our analy reult utfy th auton. In the followng we ue a two-denonal dcrete-te Marov chan to odel the behavor of a traffc flow wth tye. he tate are defned a the cobnaton of two nteger t b }. he Marov chan can be reented a follow ee Fg.a { t Cae : Before acet tranon { } [0 ] [0 ]. Cae : After acet tranon { 0} { 0} {0 0} 5 [0 [0 [0 ] [0 ] [0 ] ]...3

8 Euaton. account for the fact that the bacoff te decreented at the begnnng of each lot te. Euaton. account for the fact that a collon occur and the taton double the bacoff te. Euaton. odel the fact that once the bacoff tage reache the value t not ncreaed n ubeuent acet tranon. Euaton.3 account for the fact that a new acet followng a ucceful acet tranon tart wth bacoff tage 0. Let aue that IF dfferent fro IF and therefore larger accordng to our defnton. hen IF exre after the lat tranon tye- traffc flow edately te nto ther bacoff tage whle tye- traffc flow ut tll wat for the end of the longer nter-frae ace IF. raffc of tye ha a chance of beng trantted only f all traffc of hgher rorty of tye elect a bacoff te uffcently large that IF alo exre before tranon tarted. hen th event occur coetton to acce the channel deterned by the nu aong bacoff counter of all actve traffc flow. Of coure the event never occur n aturated condton and tye- traffc coletely tarved f the dfference larger than the axu contenton wndow ze for tye- traffc. e odel th roce by addng a euence of hold tate that tye- traffc ut enter before obly tartng to decreent the bacoff counter. herefore we odel the behavor of a tye- traffc flow wth a three denonal Marov chan. he tate are defned a the cobnaton of three nteger t b t d } where { t 0 d t. hat to ay for a noral tate t b 0} the correondng hold tate { t further ub-dvded nto tage. herefore f d t > 0 the condered traffc flow watng at oe tage of the hold tate. For better undertandng the tate tranton of dfferent taton carryng dfferent tye of traffc we gve an exale for the tate tranton of two dfferent tye of traffc flow n Fg.. In the exale for lcty we aue that there are only two traffc flow n the yte. Flow carre tye- traffc and Flow carre tye- traffc. Moreover the IF dfference between nter-frae earaton. In the fgure tate for the two traffc flow are labeled n the correondng te lot. In the te lot fro t to t Flow at tate { 0} and t begn endng a acet. Flow at tate { 00}. Fro t to t 3 after the endng of the acet Flow begn another bacoff roce. At the ae te Flow te nto the hold tate { 0} to wat for the end of IF. Fro t 3 to t 4 Flow further decreae t bacoff counter fro to. Flow reue t bacoff roce and decreae t bacoff counter fro to. Fro t 4 to t 5 both Flow 6

9 and Flow try to end acet at the ae te. herefore a collon occur. Fro t 5 to t 6 Flow begn a new bacoff roce n order to end the acet agan. Flow te nto hold tate {00}. Fro t 6 to t 7 Flow begn a new bacoff roce n order to end the collded acet agan. Flow contnue t bacoff roce by decreang t bacoff te fro 5 to 4. In the followng we decrbe the tate tranton atheatcally: Cae : Before acet tranon ee Fg. b { 0 0} { 0} { d d} { 0 } { d} d [ ] d [ ] where 0 ] [0 ] [. robablty of lence the robablty that all the other traffc flow do not trant under the condton that the condered traffc flow at the tate of { 0}. Note that the condered traffc flow not at the tate of tranon. the robablty that all the tye- traffc flow do not trant. In order to ae the odel tractable we aue that regardle of the dfferent tage for dfferent hold tate an ndeendent contant robablty. h auton ha been hown by our ulaton to be very accurate f not o large that tye- traffc flow are alot tarved by tye- traffc flow. Euaton 3. account for the fact that the bacoff counter decreented at the begnnng of each lot te f all traffc flow are not n the tate of tranon. Euaton 3. ean that for the condered tye- traffc flow f there are oe other traffc flow n the tate of tranon durng the at te lot t next tate a hold tate. If the condered traffc flow at a hold tate t trant nto the next hold tate wth robablty ee euaton 3.3. Or t goe bac to the frt hold tate wth robablty becaue of the tranon of at leat one tye- traffc flow durng the at te lot ee euaton 3.5. Euaton 3.4 how that for the condered traffc flow the traffc flow wll te nto noral tate after the lat hold tate wth robablty. Cae : After acet tranon ee Fg. c 7

10 { 0 00} { 0 d 0 d} { 0 0 } { 0 0 } {0 0 0 } { 0 0 d} d [ ] < [0 [0 d [ ] [0 ] ] ] where 0 ]. Euaton 4. account for the fact that after the tranon of a acet [ the condered tye- traffc flow te nto hold tate wth robablty. If the condered traffc flow at a hold tate t trant nto the next hold tate wth robablty ee euaton 4. or t goe bac to the frt hold tate wth robablty becaue of the tranon of at leat one tye- traffc flow durng the at te lot ee euaton 4.6. Euaton 4.3 account for the fact that a collon occur and the taton carryng tye- traffc double the bacoff te after t endng of a acet. Euaton 4.4 odel the fact that once the bacoff tage reache the value t not ncreaed n ubeuent acet tranon. Euaton 4.5 account for the fact that a new acet followng a ucceful acet tranon tart wth bacoff tage 0. Fro the above decrton on the tate tranton for traffc flow we can ee that wth the ntroducton of the acet collon robablte and hold tate for tye- traffc flow and robablte and t oble to olve the Marov chan of a traffc flow ndeendently. B. hroughut Analy Frt we olve the Marov chan for tye- traffc. Let 0 ] and [ 0 ] be the tatonary dtrbuton of the chan. It eay to fnd that [ and < <

11 where [ 0 ] and [ 0 ]. Becaue taton carryng tye- traffc ut be n hold tate too. hold exreed a we have 00 7 [ ] τ defned a the robablty that a taton carryng tye- traffc trant n a randoly choen lot te. e have τ 0 8 [ ] leae refer to [0] for detaled dervaton on euaton 5 to 8. For tye- traffc let 0 ] [ 0 ] tatonary dtrbuton of the chan. e derve and [ < < and [ ] be the where and [ 0 ]. Furtherore t can be ealy found that 0 0 > 0 0 where 0 ]. leae refer to the Aendx for the detaled dervaton of euaton 9 to [. Fro above three euaton we can ee that all the tate robablte can be exreed by 000. Becaue we can have: [ ] Let u defne hold a the robablty that all taton carryng tye- traffc are n hold tate. e ehaze that f one taton carryng tye- traffc n hold tate all the other 9

12 hold Moreover we defne τ a the robablty that a taton carryng tye- traffc trant n a randoly choen lot te under the condton that t not n hold tate. herefore we have Now we can exre 00 0 τ 4 [ ] the robablty that all the other traffc flow excet for the condered tye- traffc flow are not n the tate of tranon a follow n n τ τ 5 the robablty that all the traffc flow wth tye- are not tranttng can be gven a n τ 6 th the above robablte defned we can exre the acet collon robablte and a n n τ [ τ ] te te 7 n n τ τ 8 Cobnng euaton 8 to 8 and by ung SOR nuercal ethod [0] we can get all the value for τ τ and hold. In order to derve the yte throughut we defne Q a the robablty that there are a nuber of tye- taton and a nuber of tye- taton tranttng wthn a randoly elected lot. For Q 00 wth no tranttng taton we have n n Q 00 τ [ τ ] 9 For Q 0 wth only one tye- taton tranttng we have hold hold n n Q 0 nτ τ [ τ ] hold hold 0 For Q 0 wth only one tye- taton tranttng we have Q0 n n τ hold nτ τ For Q c c c c 0 whch ean that there are oe collon occurrng between tye- traffc flow we have 0

13 n c n c n Q c c τ τ [ hold hold τ ] c For Q c c c c c we have n τ n 3 c n c c nc c hold c τ c τ τ Q c he noralzed yte throughut S can be defned and exreed a: Average ayload trantted n a lot te S Average length of a lot te S S Q0 E[ Len ] Q0 E[ Len ] Q00 σ Q0 Q0 Q c c 0c n 0c n c c c c c where S and S denote the throughut contrbuted by tye- and tye- traffc flow reectvely. E ] the average duraton to trant the ayload for tye- traffc the [ Len ayload ze eaured wth the te reured to trant t. For lcty wth the auton that all acet of tye- traffc have the ae fxed ze we have σ the duraton of an ety te lot. of a ucceful tranon of a acet of a tye- traffc flow. 4 E Len ] Len [. ee Fg. 3 the average te of a lot becaue can be exreed a HYheader MACheader E[ Len ] SIF δ ACK IF δ 5 where δ the roagaton delay. c c refer to Fg. 3 the average te the channel c ened buy by each taton durng a collon caued by ultaneou tranon of c tye- taton and c tye- taton. It can be exreed a and c c HYheader MACheader ax[ θ c Len θ c Len IFS δ 6 c ] θ x 0 x > 0 x 0 C. acet elay Analy For the ualty of ervce of real-te ulteda t ortant to now the te that a acet ut wat for tranon over the IEEE 80. MAC. By analyzng the acet delay we can derve an uer bound for the average delay.

14 For a tye- traffc flow we defne that the whole erod of te wthn ee euaton 5 ent to end a acet. herefore for a tye- traffc flow we defne acet delay a the average te erod between the ntant of t fnhng endng the forer acet to the ntant of begnnng to end the next acet. herefore doe not nclude the tranon te for a acet ee Fg. 4. In Fg. 4 detaled tng relatonh between acet endng te and acet delay are llutrated. Baed on Fg. 4 t can be ealy found that there a le relatonh between the throughut S : and S [ Len ] 7 n E herefore for tye- traffc flow can be gven a E[ ] 8 Len IV. Aroxate Analy In the above two ecton we have analyzed the yte throughut and acet delay n aturaton tate. In order to gan a deeer nght nto the whole yte we ae oe aroxaton to get ler but ore eanngful relatonh aong dfferent araeter. In the followng dcuon t aued that 0 that we only conder the cae that IF IF. e tart fro euaton 7 and 8. Becaue 0 hold ut alo be 0. herefore we can ealy derve n τ τ It can be een that f τ τ then one ut have τ 9 whch utfe our forer auton that condtonal acet collon robablte of dfferent tye of traffc flow ay be dfferent fro each other. hen the nu contenton wndow ze >> and >> the tranon robablte τ and τ are all that τ << andτ <<. herefore fro euaton 9 we have the followng aroxaton 30 under the condton of >> and >>. Furtherore when >> >> and

15 we have the followng aroxaton baed on euaton 8 and 4 Fro euaton 9 0 and 4 we have S S Q0 E[ Q0 E[ Len Len τ τ ] nτ τ E[ ] n τ τ E[ Len Len ] nτ E[ ] n τ E[ Len Len ] n E[ ] n E[ Len Len ] ] 3 3 hen fro the above euaton we have E[ Len 33 E[ Len ] ] he above euaton hold under the condton of 0 >> and >> and. e can ee that the throughut dfferentaton anly deterned by the calng of nu contenton wndow ze and the length of acet ayload. Moreover fro euaton 8 we can ee that under the condton 3 E << whch alway hold when the nuber of traffc flow n >> we have E[ Len ] [ Len 34 E[ Len ] Euaton 34 another ortant aroxaton relatonh obtaned. e can ee that acet delay dfferentaton aong dfferent tye of traffc flow anly deterned by the rato of the correondng nu contenton wndow ze. Aung that all the and E ] are fxed then fro euaton and 8 [ Len we can ealy arrve at the followng concluon: E[ Len ]. can be lnearly exreed by that. herefore reache t E[ ] axu value when reache t axu value. hat to ay there a cae where all throughut and the total throughut S of the yte reach ther axu value at alot the ae confguraton. can be lnearly exreed by that. herefore reache t. Len ]

16 nu value when reache t nu value. hat to ay there a cae where all the acet delay reach ther nu value at alot the ae confguraton. 3. hen all throughut reach ther axu value all the wll reach ther nu value at alot the ae confguraton. he above roerte how that by calng dfferentaton and ae the whole yte ealy controllable. and E ] one can obtan ervce [ Len V. Reult And cuon In th ecton by ung our analy odel we nvetgate the effect of the dfferent araeter on the traffc dfferentaton and we valdate the analy auton by coaron wth a dcrete-event ulaton of the yte. In addton we ae the range of valdty of the aroxated forula obtaned n the revou analy. e roceed by frt conderng the effect of varyng a ngle crucal araeter on the erforance dfferentaton and then by conderng the valdty of the aroxated forula for the cae of eual nter-frae earaton. In our exale we aue that two tye of traffc coext n the yte. he araeter for the yte are uarzed n able baed on IEEE 80.b. able. Syte araeter MAC Header 7 bt HY Header 9 µ ACK bt HY header Channel Bt Rate Mb roagaton elay µ Slot e 0 µ SIFS 0 µ IFS 30 µ he uroe of the frt ere of exerent to verfy the accuracy of our analy odel and ae the effect of varyng the nter-frae earaton on the erforance. o th end we ee all other araeter eual and only change the value of. In Fg. 5 and Fg. 6 we valdate our rooed analy odel by coarng ulaton reult and nuercal reult. For our ulator whch leented by ung C we conder that there are 0 4

17 taton each carryng only one traffc flow. 5 of the carry tye- traffc and the other carry tye- traffc. In the ulaton deal channel condton.e. no hdden ternal and cature are aued. he other araeter are et a follow: 64 8 and 5 E[ Len ] E[ Len ] 000byte. fferent ulaton value are obtaned by varyng the IFS dfference. Each ulaton value are obtaned by runnng our dcrete-event ulator to ulate the actual behavor of the yte wthn the erod of 5 hour. For each ont we run the ulator for 0 te wth 0 dfferent rando eed. Sulaton reult how that the tandard devaton of the reult caued by ung dfferent rando eed le then one ercent for each ont and therefore not vble n the fgure. In Fg. 5 throughut S S and S veru IFS dfference are hown. In Fg. 6 average acet delay and the overall average acet delay er traffc flow n n are hown veru the IFS dfference. Fro thee two fgure t can be n n een that the ulaton reult agree very well wth the theoretcal one. e can alo ee that the aller the better the ulaton reult agree wth the nuercal one whch ugget that the accuracy of our auton of the robablty beng a contant accurate and reaonable for th cae. On the other hand when ncreae the dfference between ulaton reult and nuercal one becoe ore evdent. In order to undertand the reaon let u conder an extree cae where the axu contenton wndow ze C ax for tye- traffc aller than. It evdent that n th cae after the erod of tranon of a acet or collon between oe acet t entrely oble for tye- traffc flow to get acce to the channel. In th cae the bacoff roce for tye- traffc flow wll not roceed fro one noral tate to another. However by referrng to Fg. b and euaton 5 and 6 t can be found that n ot cae one can alway get otve and nonzero and whch ean that the bacoff roce of tye- traffc flow wll alway go on and tye- traffc flow wll eventually acce the channel even n the above extree cae. herefore our odel only an aroxaton needed to ae our odel tractable. Moreover extenve ulaton how that our odel very accurate a long a tye- traffc flow are not heavly tarved by tye- traffc. Fro thee two fgure we can uantfy the dfferentatng effect caued by. th the ncreae of ore channel reource are allocated to tye- traffc flow and alo the average acet tranon delay for tye- traffc decreae. hen becoe larger the rate for the erforance roveent of tye-

18 traffc decreae and at the ae te erforance for tye- traffc becoe wore whch ndcate that a very large not uch helful to rove the yte erforance. he uroe of the econd ere of exerent for the cae 0 to verfy the range of valdty of the aroxated forula derved n the aer. In the exerent two cae have been hown. In cae we et E[ Len ] E[ Len ] 000byte. In cae dfferent acet ayload for two tye of traffc have been et.e. E[ Len ] 000byte and E[ Len ] 00byte. Other araeter are et a follow: 56 n n 5. Fg. 7 and Fg. 8 how a coaron between throughut and acet delay obtaned by ung accurate theoretcal forula and thoe obtaned by ung aroxate forula. In Fg. 7 the value of that when E[ E[ not large that Len Len ] ] are coared wth thoe of not very all the rato E[ E[ Len Len ]. e can ee ] can be aroxated by farly well whch verfe our aroxaton ade n euaton 33. Furtherore we can verfy that the length of the acet ayload ha an edate effect on the throughut dfferentaton between dfferent traffc clae. In Fg. 8 the value of are coared wth thoe of. Agan we can ee that when not large the rato can be aroxated by farly well whch verfe our aroxaton ade n euaton 34. Moreover we notce that the correondng value of for two dfferent cae are overlaed the axu dfference between thee two cae are le then one ercent whch ndcate that acet ayload alot ha no nfluence on the value of 6. hat to ay calng the length of acet ayload ha lttle effect on the dfferentaton of acet delay between the dfferent traffc clae. Let u now conder the otzaton of the overall erforance of the yte. In the forer ecton n the cae of 0 and by ung the aroxated forula we ont out that there a cae where all throughut and the total throughut S of the yte reach

19 ther axu value at alot the ae confguraton. And we alo ont out that there a cae where all acet delay reach ther nu value at alot the ae te. In Fg. 9 and Fg. 0 thee concluon are verfed by ung nuercal reult. In thee fgure we ee the rato contant and change the value n order to ee the varaton of throughut and acet delay of dfferent tye of traffc. In thee two fgure two cae have been hown. Moreover axu throughut ont and nu acet delay ont are hown. Fro Fg.9 we can ee that for a artcular cae S reache ther axu value alot at the ae whch verfe our frt concluon ade n the forer ecton. And fro Fg. 0 we can ee that for a artcular cae reache ther axu value alot at the ae whch verfe our econd concluon ade n the forer ecton. Moreover by checng thee two fgure together we can fnd that and correondng reach ther otal ont at exactly the ae whch n turn utfe our thrd concluon ade n the forer ecton. Fro thee two fgure by coarng cae and cae we fnd that a exected the yte becoe ore table wth the ncreae of axu bacoff tage and. h becaue that wth larger and acet collon rate dro whch ncreae the utlzaton of the whole yte. Let u now conder the effect of the traffc xture on the erforance. o th end we fx the total nuber of flow and vary the relatve orton of hgh- veru low-rorty flow. In Fg. and Fg. we ee the total nuber of traffc flow contant and change the nuber n of tye- traffc flow n the cae of 0. In Fg. throughut and veru the nuber of tye- traffc flow n are hown. fferent curve are for dfferent value of the nu contenton wndow ze. In Fg. the acet delay and for two tye of traffc are hown n the ae confguraton. Fro Fg. and Fg. we can ee that wth the decreae of tye- traffc flow gan rorty over tye- traffc flow: throughut becoe larger than and acet delay becoe aller than. herefore ore bandwdth reource are allocated to tye- traffc. However we can ee that n the cae of large n uch a n > 40 both the erforance on throughut and acet delay are wore than n the cae of 56 whch ndcate that rovdng ervce dfferentaton wth very large nuber of traffc flow belongng to hgher rorty 7

20 grou ae the yte erforance wore than n the cae of no ervce dfferentaton uort. In th cae erforance of all traffc flow no atter f they belong to hgher or lower rorty clae becoe wore. he reaon can be ealy exlaned by referrng to Fg. 3 that how the acet collon rate and for two tye of traffc. e can ee that wth the ncreae of n collon rate and ncreae dratcally therefore reducng the bandwdth utlzaton. On the other hand fro Fg. 3 t can be een that wth the ncreae of the dfference between and decreae n agreeent wth the aroxaton obtaned n euaton 30. Moreover referrng to Fg. and Fg. f the nuber of traffc flow wth hgher rorty all both throughut and acet delay for hgher rorty traffc flow are roved gnfcantly wth only all nfluence on the other traffc flow wth lower rorty. he above reult ndcate that the nuber of traffc flow wth hgher rorty ut be controlled to a utable fracton of the total traffc by utable acce control chee. Fnally when one conder leentng oe real yte to uort ervce dfferentaton lcty hould alo be condered. It alway the cae that the ler the chee the lower the yte cot. In our odel three ervce dfferentaton uortng echan are analyzed. By adotng the chee of dfferentatng nu contenton wndow ze and acet ayload of dfferent traffc tye le relatonh ext aong throughut and acet delay whch helful to lfy the degn of the whole yte. On the other hand n order to ae the yte a le a oble one hould lt the nuber of araeter that can be aduted. On the whole by ung the analy odel rooed n th aer we can obtan deeer nght whch ortant and helful to the degn of real yte. However the leentaton ue of real yte are beyond the coe of th aer although they are very ortant reearch toc for our future wor. VI. Concluon e rooed an analy odel to coute the throughut and acet tranon delay n a LAN wth enhanced IEEE 80. trbuted Coordnaton Functon whch uort ervce dfferentaton. In our analytcal odel ervce dfferentaton uorted by calng the contenton wndow the Inter-Frae Sacng IFS and the acet length accordng to the rorty of each traffc flow. Coaron wth ulaton reult how that good accuracy of erforance evaluaton can be acheved by ung the rooed odel. 8

21 In artcular we evaluated the throughut and acet delay. It hown that:. he ettng of C n for dfferent tye of traffc flow have gnfcant nfluence on the throughut and acet delay. One tye of traffc gan rorty over other tye of traffc through a aller nu contenton wndow ze. More channel reource are occued wth a aller acet delay.. raffc flow wth horter IFS obtan hgher rorty to acce to the channel reource. However exceve IFS value caue very long acet delay for traffc flow wth lower rorty borderng on tarvaton. 3. he length of acet ayload of dfferent tye of traffc drectly nfluence the bandwdth allocaton aong dfferent tye of traffc flow. However the dfferentaton of acet ayload ze ha lttle nfluence on the dfferentaton of acet delay. Let u note that n noy channel condton the tycal tuaton n wrele LAN longer ayload uffer a hgher error robablty and th fact ay dcourage alyng ayload length varablty a a dfferentaton echan. 4. he nuber of traffc flow wth hgher rorty ut be lted to antan the yte worng at a hgh erforance rege by utable acce control or rcng chee. See for exale [] for a oble adatve chee to regulate the arorate nuber of tranttng taton. 5. By adotng the chee of calng nu contenton wndow ze and acet ayload aroxate and le relatonh ext aong throughut acet delay and length of acet ayload of dfferent traffc tye whch can be ued for the otal degn of the whole yte. By ung the rooed odel three dfferent ervce dfferentaton chee have been analyzed. he chee are not utually excluve. he arorate choce and ettng of araeter for the control of a real-world yte ncludng acce control an nteretng area of future reearch that can be beneft fro the analy reented n th aer. Reference [] Y. Cheng and. H. Zhuang ffserv reource allocaton for fat handoff n wrele oble Internet IEEE Councaton Magazne vol. 40 no [] R. Braden. Clar and S. Shener Integrated ervce n the Internet archtecture: an overvew IEF RFC 633 Jun [3] S. Blae. Blac M. Carlon E. ave Z. ang and. e An archtecture for dfferental 9

22 ervce IEF RFC 475 ec [4] rele LAN Medu Acce Control MAC and hycal Layer HY ecfcaton IEEE Standard 80. Aug [5] J. enller M. Schlager A. Fetag and A. olz erforance tudy of acce control n wrele LAN IEEE 80. FMAC and ESI RES 0 HIERLAN Moble Networ and Alcaton vol [6] H. S. Chhaya and S. Guta erforance odelng of aynchronou data tranfer ethod of IEEE 80. MAC rotocol rele Networ vol [7]. S. Ho and K. C. Chen erforance evaluaton and enhanceent of the CSMA/CA MAC rotocol for 80. wrele LAN roceedng of IEEE IMRC ae awan Oct [8] F. Cal M. Cont and E. Gregor IEEE 80. wrele LAN: Caacty analy and rotocol enhanceent roceedng of INFOCOM 98 San Francco CA March 998 vol [9] G. Banch L. Fratta and M. Olver erforance analy of IEEE 80. CSMA/CA edu acce control rotocol roceedng of IEEE IMRC ae awan Oct [0] G. Banch erforance analy of the IEEE 80. dtrbuted coordnaton functon IEEE Journal on Selected Area In Councaton vol. 8 no. 3 March 000. [] Y. C. ay and K. C. Chua A Caacty Analy for the IEEE 80. MAC rotocol rele Networ [] J. L. Sobrnho and A. S. Krhnauar trbuted ultle acce rocedure to rovde voce councaton over IEEE 80. wrele networ roceedng GLOBECOM [3] J. eng and R.S. Chang A rorty chee for IEEE 80. CF acce ethod IEICE ranacton n Councaton vol. 8-B no. Jan [4] A. Vere A.. Cabell M. Barry and L. H. Sun Suortng Servce fferentaton n rel acet Networ Ung trbuted Control IEEE Journal on Selected Area In Councaton vol. 9 no. 0 Oct [5] I. Aad and C. Catellucca fferentaton Mechan for IEEE 80. roceedng of IEEE Inforco [6]. Hatao C. Shduan. Yong L. Keng and M. Jan IEEE 80. dtrbuted coordnaton functon CF: analy and enhanceent roceedng of ICC [7] S. Mangold S. Cho. May O. Klen G. Hetz and L. Stbor IEEE 80.e wrele lan for ualty of ervce roceedng of the Euroean rele Feb 00. [8] M. Benvente G. Cheon M. Hoehen A. Sngla H. eunen and M.entn ECF rooed draft text IEEE worng docuent 80.-0/3r March 00. [9] A. Lndgren A. Alut and O. Schelen Evaluaton of ualty of ervce chee for IEEE 80. wrele LAN roceedng of IEEE Conference on Local Couter Networ LCN 00 Noveber [0] G. Bolch S. Grener H. de Meer and K.S. rved Queueng Networ and Marov Chan: Modelng and erforance Evaluaton wth Couter Scence Alcaton ley-intercence [] Roberto Battt Marco Cont Enrco Gregor Mala Sabel rce-baed Congeton-Control n -F Hot Sot roceedng of Ot 03 March INRIA Soha-Antol France

23 Aendx: ervaton on Euaton 9 0 and Fro Fg. b for ]0 0 [ < we have < A. Fro above euaton we have ]0 [0 0 < A. Moreover for the cae of 0 ] 0 [ we have < A.3 then ] [ A.4 By cobnng euaton A. and A.4 euaton can be obtaned. Next we ubdvded our dcuon nto three dfferent cae: Cae : when 0 < < Fro the decrton on the Marov chan for tye traffc flow we have A.5 Fro above euaton we have

24 A.6 In euaton A.6 let 0 one derve A.7 and then A.8 Cae : when e have 0 00] 00 [ ] 00 [ A.9 Fro euaton A.9 we have 0 00] 00 [ 0 A.0 By ettng 0 fro above euaton and euaton A.7 we have A. Cobnng euaton A.7 and A. we can obtan euaton 9. Moreover we have A. Cae 3: 0 e have the followng euaton

25 A.3 then A.4 Fro euaton 9 the above euaton can be reduced nto the followng euaton A.5 Fro euaton A.8 A. and A.5 we can obtan euaton 0.

26 - / / -... / /... / / Fg. a Marov odel of bacoff roce for tye traffc Fg. b ranton out of tate {0} for tye traffc / - / '0... ' [0 0 ] [ ] Fg. c ranton out of tate {00} for tye traffc 4

27 ... t t t3 t4 t5 t6 t7... Flow {0} {0} {0} {00} {5} {4} Flow {00} {0} {00} {000} {00} {30} Note: Flow : Carryng tye traffc wth 8 Flow : Carryng tye traffc wth 8 Fg. An exale for tate tranton of two dfferent tye of traffc flow Header ayload SIF ACK IF Header ayload IF c c c Fg. 3 Coonent for and c c c Start Bacoff for the current acet Start Bacoff for the next acet elay Header ayload SIF ACK IF... Start Bacoff for the current acet ye traffc elay Header ayload SIF ACK IF elay elay elay ye traffc Fg. 4 Analy of the acet delay elay Hold State... Start Bacoff for the next acet 5

28 S 0.6 hroughut S S and S S S Nuercal reult Sulaton reult E[ Len ]E[ Len ]000 byte n 5 n IF dfference Fg. 5 hroughut S S and S veru Nuercal reult Sulaton reult 000 Average acet elay 00 E[ Len ]E[ Len ]000 byte n 5 n IF dfference Fg. 6 Average acet delay and veru 6

29 / *E[ Len ]/ *E[ Len ] cae 000 rato of throughut / 00 cae 0 Cae : 0 E[ Len ]E[ Len ]000 byte 56 n n 50 Cae : E[ Len ]000 byte E[ Len ]00 byte 56 n n rato of contenton wndow ze / Fg. 7 Rato of throughut / veru rato of contenton wndow ze / rato of acet delay / 00 0 / / Cae : E[ Len ]E[ Len ]000 byte 56 n n 50 Cae : E[ Len ]000 byte E[ Len ]00 byte 56 n n 50 cae cae rato of contenton wndow ze / Fg. 8 Rato of acet delay / veru rato of contenton wndow ze / 7

30 Cae : / 8 Cae : / 8 8 Otal ont for Cae Otal ont for Cae acet ayload 000 byte n 0 n 400 S throughut S S and S cae cae cae Cae Cae Cae S S nu contenton wndow ze for tye traffc 0.0 Fg. 9 hroughut S S and Sveru contenton wndow ze acet delay and Cae Cae Cae Cae Cae : / 8 Cae : / 8 8 Otal ont for Cae Otal ont for Cae acet ayload 000 byte n 0 n nu contenton wndow ze for tye traffc Fg. 0 acet delay and veru contenton wndow ze 8

31 and : throughut er traffc flow acet ayload 000 byte 56 n n n : nuber of traffc flow of tye Fg. hroughut and veru the nuber of traffc flow n and : acet delay acet ayload 000 byte 56 n n n : nuber of traffc flow of tye Fg. acet delay and veru the nuber of traffc flow n 9

32 and : acet collon rate acet ayload 000 byte 56 n n n : nuber of traffc flow of tye Fg. 3 acet collon robablte and veru the nuber of traffc flow n 30