Comparing performance of SRAMT-LE vs other layered encoding schemes regarding TCP friendliness

Transcription

1 Compang pefomance of SRAMT-LE vs othe layeed encodng schemes egadng TCP fendlness Chstos Bouas, Apostolos Gkamas Reseach Academc Compute Technology Insttute, 61 Rga Feaou St, GR Patas, Geece Compute Engneeng and Infomatcs Dept., Unv. of Patas, GR Patas, Geece e-mal: {bouas, Abstact. In ths pape we descbe a hybd sende and eceve-based adaptaton scheme fo multcast tansmsson of multmeda data usng layeed encodng, whch we call SRAMT-LE (Sende-Receve based Adaptaton scheme fo Multcast Tansmsson usng Layeed Encodng). The most pomnent featues of SRAMT-LE ae ts dstbuted (to sende and eceves) tansmsson ate estmaton algothm and ts nnovatve (Round Tp Tme) estmaton algothm based on one-way delay measuements. SRAMT- LE s usng both a TCP model and an AIMD (Addtve Incease Multplcatve Decease) algothm n ode to estmate a TCP fendly bandwdth shae. We evaluate SRAMT-LE and compae t wth a numbe of smla layeed encodng schemes avalable to the lteatue (PLM, RLC, MLDA). Man concluson of ths evaluaton was that SRAMT-LE has fendly behavo aganst the domnant taffc types of today s Intenet and has a elatve good behavo compang wth the othe layeed encodng schemes avalable to the lteatue. 1. Intoducton The multcast tansmsson of eal tme multmeda data s an mpotant component of many cuent and futue emegng Intenet applcatons, lke vdeoconfeence, dstance leanng and vdeo dstbuton. The heteogeneous netwok envonment that Intenet povdes to eal tme applcatons as well as the lack of suffcent QoS (Qualty of Sevce) guaantees, many tmes foces applcatons to embody adaptaton schemes n ode to wok effcently. In addton, any applcaton that tansmts data ove the Intenet should have a fendly behavo towads the othe flows that coexst n today s Intenet and especally towads the TCP flows that compse the majoty of flows. We defne as TCP fendly flow, a flow that consumes no moe bandwdth than a TCP connecton, whch s tavesng the same path wth that flow ([12]). The methods poposed fo the multcast tansmsson of multmeda data ove the Intenet can be geneally dvded n thee man categoes, dependng on the numbe of multcast steams used: (1) The sende uses a sngle multcast steam fo all eceves ([1], [3], [16]). (2) Smulcast: The sende tansmts vesons of the same vdeo, encoded n vayng degees of qualty. Ths esults to the ceaton of a small numbe of multcast steams wth dffeent tansmsson ates ([8], [6], [4]). (3) The

2 2 Chstos Bouas, Apostolos Gkamas sende uses layeed encoded vdeo, whch s vdeo that can be econstucted fom a numbe of dscete data layes, the basc laye and moe addtonal layes, and tansmts each laye nto dffeent multcast steam ([10], [9], [14], [15]). In ths pape, we befly pesent an adaptaton scheme fo multcast tansmsson of multmeda data ove best effot netwoks, lke the Intenet, whch povdes the most satsfacton to the goup of eceves, wth the cuent netwok condtons. We call ths adaptaton scheme SRAMT-LE (Sende-Receve based Adaptaton scheme fo Multcast Tansmsson usng Layeed Encodng) and t s a hybd sende and eceve-based adaptaton scheme. SRAMT-LE s tyng to tansmt TCP fendly multcast flows wth the use of layeed encodng vdeo. SRAMT-LE ceates n layes (the basc laye and n-1 addtonal layes) and tansmts each laye n dffeent multcast steams, each one wthn cetan bandwdth lmts. The basc laye povdes the basc vdeo qualty and each addtonal laye mpoves the vdeo qualty. A eceve n ode to be able to decode the vdeo layes and pesent the vdeo nfomaton must eceve the laye k and also the layes 1-(k-1) and then we say that the eceve s n laye subscpton level k. Moe nfomaton egadng SMART-LE and a detal evaluaton of SMART-LE can be found n [5]. In ths pape we gve also a detal compason of the SMART-LE wth othe layeed encodng schemes avalable to the lteatue. Man taget of ths compason s to compae the SMART-LE pefomance of the pefomance of othe layeed encodng schemes avalable to the lteatue aganst the followng ctea: TCP fendlness, Stablty, Scalablty and Convegence tme to stable state. The above paametes set outlne well the behavo of a layeed encodng congeston contol scheme. 2. Descpton of SRAMT-LE Wth the use of SRAMT-LE, the sende tansmts multmeda data to a goup of m eceves wth the use of multcast. Sende s usng the layeed encodng appoach, and tansmts the vdeo nfomaton n n dffeent layes (the basc laye and n 1 addtonal layes). The eceves jon the appopate numbe of layes, whch bette sut the equements Sende Opeaton The sende geneates n dffeent laye manages. Each laye manage s esponsble fo the tansmsson of a vdeo laye. Each eceve manage coesponds to a unque eceve. In addton, the synchonzaton seve s esponsble fo the management, synchonzaton and ntecommuncaton between laye manages and eceve manages. We have added an applcaton specfc pat (APP) to the RTCP eceve epots, whch the eceves sent to the RTP/RTCP sesson of the basc laye, n ode to nclude the eceves estmaton about the TCP fendly bandwdth shae n _ tcp the path between the eceve and the sende, the packet loss ate estmaton l n all layes, whch ths eceve s lstenng and the eceve laye subscpton level (the maxmum laye up to whch the eceve s lstenng) k. Receve manages stoe the

3 Compang pefomance of SRAMT-LE vs othe layeed encodng schemes egadng TCP fendlness 3 last value of _ tcp, l and k fom the eceve, whch epesent, and these nfomaton s used fo the adjustment of layes tansmsson ates. When a eceve manage eceves a RTCP eceve epot fom the eceve (whch epesents) s usng the packet loss ate l to estmate the tansmsson ate AIMD of the eceve wth the use of an AIMD (Addtve Incease Multplcatve Decease) algothm (whch has been pesented n [2]). In addton, the eceve manage s usng the analytcal model of TCP pesented n [12] n ode to estmate a TCP fendly bandwdth shae n the path between the eceve and the sende: If the eceve expeences packet losses, a TCP fendly bandwdth shae (n bytes/sec) s estmated wth the use of the equaton (1) (whee t s the sende estmaton fo between that eceve and the sende), and l s the packet loss ate that the eceve epots): = t 2 2 l + 4t 3 P 3l mn(1,3 ) l (1 + 32l ) 8 If the eceve does not expeence packet losses, n ode to estmate a TCP fendly bandwdth shae l _, the tcp l _ must not be nceased moe than a packet / tcp. Fo ths eason eceve manage calculates the new value of by addng ( T / t ) packets (whee T s the tme space between the cuent and the last eceve epot of eceve ) to the pevous value of (the s expessed n bytes/sec): T = l _ tcp + P (2) ( 2 t ) Then the eceve manage selects as eceve s pefeed tansmsson ate the mnmum of the,, _ : _ tcp AIMD l tcp = mn(,, ) (3) _ tcp AIMD Each tme one eceve manage eceves a eceve epot n the basc laye sesson fom the eceve, whch epesents, nfoms synchonzaton manage n ode to adjust the layes tansmsson ates. The adjustment of layes tansmsson ates has as taget to poduce TCP fendly cumulatve tansmsson ate fo any laye subscpton level k. Fo ths eason the synchonzaton manage polls the values of the eceves that ae lstenng only to basc laye (laye 1) and sets as tansmsson ate of laye 1 the mnmum value of of the eceves that ae lstenng only to laye 1 basc laye. Then polls the values of the eceves that ae lstenng up laye 2 and sets as tansmsson ate of laye 2 the mnmum values of laye 2 Ths pocedue epeats fo all the layes: laye 1 = mn( ) fo all eceve lstenng up to laye 1 (basc laye) fo all eceve lstenng up to laye 2 laye 2 = mn( ) laye 1 mnus the (1). laye 1 (4)

4 4 Chstos Bouas, Apostolos Gkamas laye n = mn( ) laye n 1 fo all eceve lstenng up to laye n In addton, the sende ncludes to all the RTP packets, whch tansmts, the tansmsson ate of all the layes. Ths nfomaton can be used fom the eceves n ode to change the subscpton level and accommodate bette the equements. 2.2 Receve Opeaton Each eceve measues the followng paametes of the path, whch connects t wth the sende: (1) Packet loss ate ( l ): The eceve calculates the packet loss ate dung the ecepton of sende layes based on RTP packets sequence numbes. (2) estmatons ( e ): The eceve makes an estmaton fo the between t and the t sende based on one way delay measuements wth the use of RTP packets tmestamps. The eceve emulates the behavo of a TCP agent wth the use of the analytcal model of TCP pesented n [12] and estmates a TCP fendly bandwdth shae evey tme. If the eceve expeences packet losses s usng the _ tcp followng equaton n ode to estmate a TCP fendly bandwdth shae (n bytes/sec): _ tcp = e t 2 e 2 l + 4t 3 P 3l mn(1,3 ) l(1+ 32l ) 8 If the eceve does not expeence packet losses, n ode to estmate a TCP fendly bandwdth shae, the _ must not be nceased moe than a packet / _ tcp tcp. Fo ths eason eceve calculates the value of (n bytes/sec): _ tcp = _ tcp 1 + e t P _ tcp (5) wth the followng equaton Each tme the eceve sends a eceve epot to the sende, usng the RTP/RTCP sesson of the basc laye, ncludes the aveage value of snce last eceve _ tcp epot. In addton the eceve has the capablty to add o emove layes based on the nfomaton that gathes tself and the nfomaton that sende ncludes n to RTP packets. The eceves laye subscpton changes ae synchonzed at the end of a specfc tme peod T epoch, whch we call epoch. The eceve change the laye subscpton (add o emove layes) usng the followng pocedue: At the end of each epoch, each eceve compaes the value of the, wth the cumulatve tansmsson ates of the sende layes and change ts laye subscpton level up to laye k n ode to satsfy the followng constant: <= k _ tcp laye j j= 1 _ tcp (6) (7)

5 Compang pefomance of SRAMT-LE vs othe layeed encodng schemes egadng TCP fendlness 5 We declae as unsuccessful laye change the stuaton when a eceve jons (o leaves) a laye and afte a sot tme peod ( T change ) dop (o add) agan ths laye. Dung ou pefomance evaluaton, we obseve that the unsuccessful laye changes by the eceves cause nstablty to the opeaton of SRAMT-LE and must be avoded. In ode to avod unsuccessful laye changes by the eceves, when a eceve makes an unsuccessful laye change we avet the eceve to make the laye change, whch was unsuccessful, fo the next k 2 *T tme (whee k the numbe of contnuant unsuccessful laye changes snce the last successful laye change). Due to fact that T change affects lnealy the value k 2 *T and the k affects the value of change 2 k *Tchange exponentally, we set T change to 5 seconds but othe values of T can also be used. change change 2.3 SMART-LE detals In ths paagaph we pesent some detals egadng the opeaton of SMART-LE (moe detaled nfomaton can be found n [5]): Packet Loss Rate Estmaton: In ode to pevent a sngle spuous packet loss havng an excessve effect on the packet loss estmaton, eceves smooth the values of packet loss ate usng the followng flte, whch computes the weghted aveage of the m most ecent loss ate values l m,. l Estmatons: When a eceve eceves a RTP packet fom a sende laye, uses an algothm based on one way measuements n ode to estmate the Round Tp Tme () between the sende and the eceve. Extensons to RTP/RTCP: RTP povdes an extenson mechansm to allow ndvdual mplementatons that eque addtonal nfomaton to be caed n the RTP data packet heade. SRAMT-LE uses the extenson mechansm of RTP n ode to add to the addtonal felds n to RTP heade and new applcaton specfc pat (APP) to the RTCP epots. Synchonzaton of steam changes: Smla eseach has shown ([10]) that, f the eceves synchonze the laye changes, the synchonzaton poblems can be mnmzed. Fo ths eason the eceves laye changes ae synchonzed n the end of each epoch. Scalablty ssues: In ode to ensue that, when the goup of the patcpants nceases, the sende wll collect feedback nfomaton epesentng all the eceves, we use the patal suppesson method poposed n [11] to contol the tansmsson of the RTCP epots. 3. Compang SRAMT-LE wth othe layeed encodng schemes In ths secton we compae the pefomance of SRAMT-LE mechansm wth othe mechansm founded to the lteatue egadng the followng paametes: TCP

6 6 fendlness, Stablty, Scalablty and Convegence tme to stable state. The above paametes set outlne well the behavo of a layeed encodng congeston contol scheme. We compae the SMART-LE wth the followng layeed encodng schemes: PLM ([9]): PLM stands fo Packet pa eceve-dven Layeed Multcast and s based on a cumulatve layeed scheme and on the use of packet pa to nfe the bandwdth avalable at the bottleneck to decde whch ae the appopate layes to jon. PLM assumes that the outes ae multcast capable but does not make any assumpton on the multcast outng potocol used. PLM s eceve dven, so all the buden of the congeston contol mechansm s at the eceves sde. The only assumpton we make on the sende s the ablty to send data va cumulatve layes and to emt fo each laye packets n pas (two packets ae sent back-to-back). PLM s hghly scalable due to the eceve-dven cumulatve layeed scheme. PLM does not eque ethe any sgnalng o feedback. MLDA ([14]): MLDA stands fo Multcast enhanced Loss-Delay based Adaptaton algothm. MLDA s a hybd sende and eceve-based adaptaton scheme that combnes on the one hand vaous well known concepts fo multcast congeston contol such as eceve-based ate calculaton, layeed tansmsson and dynamc nto a unfed congeston contol achtectue. Scalablty n MLDA s based on patal suppesson method. RLC ([15]): RLC stands fo Receve-dven, Layeed Congeston contol algothm. RLC s desgned to suppot one-to-many communcaton to potentally lage sets of eceves wth dffeent bandwdth equements. RLC uses a heachcal, layeed scheme fo data tansmsson, whee eceves can jon to one o moe multcast goups to eceve data at a ate appoxmately matchng the bandwdth to the souce - ths tanslates nto dffeent qualty levels n the case of multmeda steams, o n faste tansfe tmes fo elable data communcaton. Scalablty n RLC comes fom full decentalzaton of functonalty: each eceve takes congeston contol decsons autonomously. Bandwdth (bps) Tme (sec) SRAMT-LE TCP Two Fg. 1. Bandwdth dstbuton on C1-C3 bottleneck lnk Fgue 1 shows the bandwdth dstbuton to bottleneck lnk shaed by SRAMT- LE and a TCP connecton wth the same tme. As ths fgue ndcate that SRAMT-LE s n geneal fa towads to TCP connectons and teats the heteogeneous goup of the eceves wth faness. SRAMT-LE behaves as s expected, and shaes the avalable bandwdth wth the TCP connecton wth the same delay. The behavo of SRAMT-LE ( seekng fo avalable bandwdth and eacton to congeston) leads some tmes to get moe bandwdth shae than TCP and some tmes to get less bandwdth shae than TCP, but n long tem both the SRAMT-

7 Compang pefomance of SRAMT-LE vs othe layeed encodng schemes egadng TCP fendlness 7 LE and the TCP flows get the appoxmately the same bandwdth shae of the bottleneck lnks. Fg. 2. PLM pefomance aganst TCP taffc Fg. 3. RLC pefomance aganst TCP taffc Fg. 4. MLDA pefomance aganst TCP taffc Fgue 2 shows how the PLM shaes a bottleneck lnk ntally wth one TCP connectons and late on wth two TCP connectons. The smulaton scenao was the followng: Intally the fst TCP connectons tansmts data and at the 20 th second stats the tansmsson of the PLM sesson and fnally at the 60 th second stats the tansmsson of the second TCP connecton ove the bottleneck lnk. As fgue 2 shows, the PLM sesson adapts all most pefectly to the avalable bandwdth n pesence of TCP flows. Compang the PLM behavo wth the SMART-LE behavo

8 8 we can daw the followng conclusons: PLM has moe stable tansmsson ate and change ts tansmsson ate n steps compang wth SMART-LE whch can not keep ts tansmsson ate stable and changed t contnues dung the ente expement (fgue 1). In long tem, we can say that n the case of PLM, TCP taffc gets moe bandwdth that the PLM taffc but n the case of SMART-LE, TCP and SMART-LE taffcs ae shae almost them equally the avalable bandwdth. In ode to summaze, both PLM and SMART-LE have good behavo aganst the TCP taffc wth PLM offeng a moe stable tansmsson ate and SMART-LE offeng moe fa bandwdth shang. In addton, the PLM has a fast convegence tme to the stable state afte the tansmsson of the TCP taffc to the bottleneck lnk. The man dsadvantage of PLM s the fact that assumes that the outes of netwok testbed suppot some knd of a fa queung mechansm that allocates each flow a fa bandwdth shae. Only unde ths assumpton, s t possble to use PLM fo congeston contol. The fact that the Intenet oute does not suppot fa queung mechansms at the moment (and t s not expected to suppot fa queung mechansms n lage scale to the nea futue) has as esult the dffcult lage scale deployment of PLM to the Intenet. Fgue 3 shows how the RLC shaes a bottleneck lnk wth TCP taffc. The smulaton scenao ncludes the tansmsson of 8 RLC sessons togethe wth 8 TCP connectons ove a bottleneck lnk. As fgue 3 shows, RLC s slghtly moe aggessve than TCP, but ths was expected as RLC consdes closely spaced losses as a sngle event, wheeas TCP does not. On the othe hand, TCP and RLC do not stave each othe when competng. Compang the RLC behavo wth the SMART-LE behavo we can daw the followng conclusons: Both RLC and SMART-LE have some fluctuaton on the tansmsson ates but they keep elatve stable the tansmsson ates. In addton, t s obvous that SRAMT-LE has moe fendly behavo aganst TCP taffc than RLC has. In addton, both RLC and SMART-LE have smla convegence tmes to the stable state. In ode to summaze, SMART- LE has bette behavo aganst the TCP taffc compang wth RLC and ths s because the TCP analytcal model used by SMART-LE s moe accuate than the TCP analytcal model used by the RLC. On the othe hand, the RLC has a much moe smple mplementaton compang wth SMART-LE. Fgue 4 shows how the MLDA shaes a bottleneck lnk wth TCP taffc. Fgue 4 shows the bandwdth shae between MLDA and TCP taffc n the bottleneck lnk. As fgue 4 shows, the MLDA has fendly behavo aganst TCP taffc most of the smulaton tme but n some cases ethe the TCP taffc staves MLDA taffc o MLDA taffc staves TCP taffc (most of the stave cases). Compang the MLDA behavo wth the SMART-LE behavo we can daw the followng conclusons: The SMART-LE behavo s fendle that MLDA behavo aganst TCP taffc manly due to the fact the SMART-LE taffc does not stave TCP taffc as MLDA taffc does n some cases. In addton, MLDA has long convegence tmes to the stable state compang wth SMART-LE. Moeove, both MLDA and SMART-LE do not keep the tansmsson ates stable but they have fluctuaton on the tansmsson ates. In ode to summaze, both MLDA and SMART-LE have smla behavo but the MLDA has the dawback of bg convegence tme to the stable state and stavng of TCP taffc n some cases.

9 Compang pefomance of SRAMT-LE vs othe layeed encodng schemes egadng TCP fendlness 9 Table 1 summazes the compason of SMART-LE aganst the othes layeed encodng schemes. As ths table shows, SMART-LE has good pefomance aganst TCP taffc and n geneal tems has good pefomance compang wth the othe layeed encodng schemes. The man dawback of the SMART-LE mechansm s the fact that SMART-LE has fluctuaton on ts tansmsson ate and t s not keep ts tansmsson ate stable. Ths has as esult the TCP connectons also to have fluctuaton on the tansmsson ates as eacton to the contnues changng netwok condtons due to the above mentons SMART-LE behavo. Table 1. Compason of SMART-LE wth the othe layeed encodng schemes Paamete / SMART- PLM RLC MLDA Mechansm LE TCP fendlness Vey Good Good modest Good Stable No Yes Yes No tansmsson ate Convegence Relatve fast Vey fast Relatve Modest tme fast Stable opeaton Yes Yes Yes No Lmtatons No fa No No queung mechansm n outes Scalablty Well - patal suppesson method Well - not eque feedback fo the clent Well - not eque feedback fo the clent Well patal suppesson method 4. Concluson - Futue Wok In ths pape, we pesent the behavo nvestgaton of the SRAMT-LE, a mechansm fo multcast tansmsson of adaptve multmeda data n a heteogeneous goup of eceves wth the use of layeed encodng. SRAMT-LE s usng a hybd sende and eceve-based adaptaton scheme and uses both a TCP model and an AIMD algothm to estmate a TCP fendly bandwdth shae. We nvestgate the behavo of SRAMT-LE though a numbe of smulatons. We compae also the behavo of SRAMT-LE wth othe layeed encodng schemes avalable to the lteatue. Man concluson of the evaluaton was that SRAMT-LE has fendly behavo aganst the domnant taffc types (TCP taffc) of today s Intenet and good behavo dung congeston condton. In addton SRAMT-LE povdes good pefomance compang wth othe layeed encodng schemes avalable to the lteatue. Ou futue wok ncludes the nvestgaton of the fluctuatons n SRAMT-LE tansmsson ate n ode the SMART-LE to tansmt moe smooth tansmsson ates. In addton, we plan to nvestgate to dynamcally addng moe layes nstead of the statc numbe of layes that SRAMT-LE suppots now. Moeove we plan to mplement a pototype of SRAMT-LE and evaluate ts opeaton ove the eal Intenet

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