Optimal Adaptive Voice Smoother with Lagrangian Multiplier Method for VoIP Service

Transcription

1 Optmal Adaptve Voe Smoother wth Lagrangan Multpler Method for VoIP Serve Shyh-Fang HUANG, Er Hsao-uang WU and Pao-Ch CHANG Dept of Eletral Engneerng, Computer Sene and Informaton Engneerng and Communaton Engneerng Natonal Central Unversty, Tawan Astrat: - VoIPs, emergng tehnologes, offer hgh-qualty, real-tme voe serves over IP-ased roadand networs. Pereved voe qualty s a ey metr for VoIP applatons that s manly affeted y IP networ mparments suh as delay, jtter, and paet loss. Playout uffers at the reevng end an ompensate for the effets of jtter ased on a tradeoff etween delay and loss. Adaptve smoothng algorthms are apale of dynamally adjustng the smoothng sze y ntrodung a varale delay ased on the networ parameters to avod the qualty deay prolem. Ths paper ntrodues an effent and feasle pereved qualty method for uffer optmzaton to aheve the est voe qualty. Ths wor formulates an onlne loss model that norporates uffer szes and apples the Lagrangan Multpler approah to optmze the delay-loss prolem. Dstnt from the other optmal smoothers, the proposed optmal smoother, sutale for most odes, arres the lowest omplexty. Smulaton experments onfrm that the proposed adaptve smoother aheves sgnfant mprovement n the voe qualty. Key-Words: - Adaptve voe smoother, VoIP, uffer re-synhronzaton, delay/loss trade off 1 Introduton Wth the growng popularty of the Internet, whh s tradtonally used n delverng data only, novel multmeda serves, suh as delay ounded voe and vdeo streamng applatons are feasly and easly delvered y roadand paet networs, suh as ale modem, dgtal susrer lne, et. The next generaton networ, le an ALL-IP networ, s evolvng to ntegrate all heterogeneous wred and wreless networs and provde seamless worldwde molty. In an All-IP networ, one revoluton of the new generaton Internet applatons wll provde VoIP serves that people an tal freely around through the mole-phones, the destops and VoIP telephones at any tme and plae. Unfortunately, the IP-ased networ does not guarantee the avalale andwdth and assure the onstant delay jtters (.e., the delay varane) for real tme applatons. In other words, ndvdual transmsson delays of a gven flow of paets n a networ may ontnue to hange sujet to vared traff load and dfferent routng paths aused y ongestons, so that the paet networ delays for a ontnuous seres of ntervals (.e. talspursts) at the reever may not e the same (.e. onstant) as the sender. In addton, a paet delay may our y the sgnal hand-out or the dfferene of andwdth transportaton n wreless/fxed networs. The voe smooth tehnology usually employs jtter uffers to pre-store some voe paets for playout. A hardware deve or software proess that elmnates jtter aused y transmsson delays n an Internet telephony (VoIP) networ. For delay senstve applatons, a domnant porton of paet losses mght e lely due to delay onstrant. A late paet, whh arrves after a delay threshold,.e. the playa tme, s treated as a lost paet. A tght delay threshold not only degrades the qualty of playa ut also redues the effetve andwdth eause a large fraton of delvered paets are dropped. In fat, delay and loss are normally not ndependent of eah other. In order to redue the loss mpat, a numer of applatons wll enlarge smoothng uffers to redue the qualty degradaton aused y loss paets. However, a large uffer wll ndue exessve end-to-end delay and deterorate the multmeda qualty n nteratve real-tme applatons. Therefore, a tradeoff s requred etween nreased paet loss and uffer delay to aheve satsfatory results for playout uffer algorthms. For pereptual-ased uffer optmzaton shemes for VoIP, voe qualty s used as the ey metr eause t provdes a dret ln to user pereved QoS. However, t requres an effent, aurate, and ojetve way to optmze pereved voe qualty. Ths paper ntrodues a new delay-loss smoother that employs the Lagrange multpler method to optmze the voe qualty y alanng the delay and the loss. Lagrange multpler method s often used to optmze the trade off prolems. The ontrutons of ths paper are three-fold: () A new

2 method s for optmzng voe qualty for VoIP and s easly appled to new odes. () Dfferent from the other optmal smoothers, our optmal smoother has the lowest omplexty wth O ( n). () A smple sheme of the uffer resynhronzaton to effently avod the uffer overflow. The remander of ths paper s organzed as follows: In Seton 2, we overvew the related researh wors. In Seton 3, we ntrodue the proposed novel adaptve smoother. In Seton 4, the detaled desrpton of the uffer re-synhronzaton soluton s shown. In Seton 5, the smulaton results n smoothers are depted. Fnally, onlusons are drawn. 2. Related Wor The wdely deployed Internet s usually la of performane guarantee to aheve the adaptalty and salalty. One of the greatest hallenges to VoIP s voe qualty and the eys to aeptale voe qualty nlude andwdth and delay. The studes of the lteratures made on the degradaton of the voe qualty onsder the effet of paet loss, ut less of efforts onsder that of paet delay. Reently, the researh efforts aout the haratersts of the end to end paet transmsson delay have een ntated n some lteratures [1] [2]. Wthn lterature on tng delays, the use of Pareto dstruton n [1] s omputng the dstruton parameters and reuldng the new dstruton to t the next paet delay, and the use of neural networ models to learn traff ehavors [2]. The use of Pareto dstruton or a neural networ model requres relatvely hgh omplexty or a long learnng perod. Therefore, we onsder the smoothers [3]-[9] whh employ statstal networ parameters related wth the voe haraterst,.e. loss, delay and talspurt that have sgnfant nfluene to the voe qualty. They detet delay spe n traff and quly alulate the requred uffer sze to eep the qualty as good as possle. The Spe Deteton (SD) Algorthm has een studed y many researhers [3]-[9]. A delay spe s defned as a sudden and sgnfant nrease of networ delay n a short perod often less than one round-trp. Ths algorthm adjusts the smoothng sze,.e. playa delay, at the egnnng of eah tal-spurt. The results of ths algorthm are therefore ompared to the results otaned heren. The SD Algorthm n [3] used the gap-ased method to detet delay spes. For a voe sesson of N paets and L talspurts, defne t, a, n, p as the sender tmestamp, reever tmestamp, numer of paets, and playout tme for paet of talspurt. The SD Algorthm uses estmatons of the mean networ delay, d, and varane, v, for paet of talspurt to adapt the playout. The mean estmaton of networ delay s ased on the RFC 793 algorthm (see [7]), whle the varane s estmated usng a measure of the varaton n the delays as suggested y Van Jaoson n the alulaton of the round trp estmates for the TCP retransmt tmer (see [3]). These estmatons are reomputed eah tme a paet arrves, ut only used when a new talspurt s ntated. In the deteton of a new talspurt, oth algorthms use the most reent values of d and v to alulate the playout tme of the frst paet usng Eq. (1). For all susequent paets wthn the same talspurt s used to alulate ther playout tme ( p ). p = t + d + γ v (1) where t represents the tme at whh paet of talspurt s generated at the sendng host and γ s a onstant fator used to set the playout tme to e far enough eyond the delay estmate suh that only a small fraton of the arrvng paets ould e lost due to late arrval. The value of γ = 4 s used n smulatons [3]. The estmates are reomputed eah tme a paet arrves, ut only appled when a new tal-spurt s ntated. The mean networ delay d and varane v are alulated ased on a lnear reursve flter haraterzed y fators α and β d = d + (1 )n If n > d-1 v = v + (1 ) d n (2) d = d + (1 )n If n d-1 v = v + (1 ) d n where n s the end-to-end delay ntrodued y the networ and typal values of α and β are.9982 and.75 [3], respetvely. The deson to selet α and β s ased on the urrent delay ondton. The ondton n > d represents networ ongeston (SPIKE_MODE) and the weght β s used to emphasze the urrent networ delay. On the other hand, n d represents networ traff s stale, and α s used to emphasze the long-term average. In estmatng the delay and varane, the SD Algorthm uses only two values α and β that are smple ut may not e adequate, partularly when the traff s unstale. For example, an under-estmated prolem s when a networ eomes p

3 sped, ut the delay n s just elow the d, the SD Algorthm wll judge the networ to e stale and wll not enter the SIPKE_MODE. 3 Optmal Smoother wth Delay-Loss Trade off The proposed optmal smoother s derved usng the Lagrangan method to trade off the delay and loss. Ths method nvolves, frst, uldng the traff delay model and the loss model. Seond, a Lagrangan ost funton Q s defned usng ths delay and the loss models. Thrd, the Lagrangan ost funton Q s mnmzed and thus the delay and loss optmzed soluton s otaned. f (t) Smoothng tme Loss Delay Fg. 1 The relaton of smoothng delay and loss 3.1 Traff Delay and Loss Models For pereved uffer desgn, t s rtal to understand the delay dstruton modelng as t s dretly related to uffer loss. The haratersts of paet transmsson delay over Internet an e represented y statstal models whh follow Exponental dstruton for Internet paets (for a UDP traff) has een shown to onsstent wth an Exponental dstruton [1]. In order to derve an onlne loss model, the paet end-to-end delay s assumed as an exponental dstruton wth parameter 1 µ at the reevng end for low omplexty and easy mplementaton. The proalty dstruton funton (PDF) of the delay dstruton F ( t ) an also e represented y [11][12] tu F ( t ) = 1 e (3) and the proalty densty funton (pdf) of the delay dstruton f (t ) s df( t ) tµ f ( t ) = = µ e. (4) dt In a real-tme applaton, a paet loss that s solely aused y extra delay an e derved from the delay model f (t ). Fgure 1 plots the delay funton f (t ), whh shows that when the paet delay exeeds the smoothng tme; the delayed paet s t regarded as a lost paet. The loss funton l () an e derved from Fg. 1 as µ t µ µ l( ) = f ( t )dt = ( e ) = e + e = e (5) From Eqs. (4) and (5), we otan the delay and loss funtons that wll e used n Lagrangan ost funton. 3.2 Optmal Delay-Loss Adaptve Smoother To express the orrespondng qualty for a gven voe onneton, a Lagrangan ost funton Q s defned ased on the delay and the loss model l () Q( ) = + K l( ) (6) where Q ( ) represents the negatve effet on voe qualty,.e., mnmzng Q yelds the est voe qualty. K s a Lagrange multpler where the loss eomes more sgnfant as K nreases. The K value has sgnfant nfluene on the optmzaton proess. We wll dsuss the vald range of the value n ths seton and the suggested value n the next seton. Here, one a smoothng tme s spefed, the µ loss l( ) = e an e alulated from Eq. (5). The Lagrangan ost funton n Eq. (6) yelds µ Q( ) = + K e (7) The dfferental equaton dq d s assgned to zero that mnmzes Q to yeld the smoothng tme, ( ) = µ ln Kµ (8) where s the est smoothng tme for alanng the delay and the loss. Afterwards, the smoother an provde est qualty, onsderng oth the delay and the loss effets, ased on the alulated smoothng tme. The alulated smoothng tme s a funton of K and µ. µ denotes a IP-ase networ delay parameter (end-to-end delay) and an e measured at the reever, ut K s gven y users or applatons. The alulated smoothng tme must e wthn an allowale range to ensure that the end-to-end delay s aeptale. Here, D max s defned as the maxmum aeptale end-to-end delay and the alulated smoothng tme must e etween and ( Kµ ) 1 µ Dmax D max ln. (9) Aordngly, the permssle range of vald K n the Lagrange multpler Q funton n Eq. (8) s µ µ e D max K µ. (1) 3.3 Suggeston of K Parameter

4 In ths seton the relatonshp etween the voe qualty and loss s further studed. Based on the prevous seton dsussons, we now K parameter s tghtly related wth voe qualty. In other words, for a gven (Mean Opnon Sore) of speeh qualty, the allowale range of K an further e restrted. Many studes revealed the dffulty of determnng the mathematal formula that relates the voe qualty, delay, and loss. Aordng to [13], the loss degrades the voe qualty more remaraly than does the delay, so the qualty-loss relatonshp s frst emphaszed [14][15]. In these studes, an empral Eq. (11) was otaned y experments wth many traff patterns for tng the voe qualty that mght e degraded y the traff loss ( loss ) ( +1) = ln loss opt (11) where opt s voe ode related, representng the optmum voe qualty that the ode an aheve, s a onstant that s ode dependent, and loss s a perentage rato tmes 1. Followng ths approah, anyone an estmate a spef empral rule wth spefed voe odes and networ envronments. Equaton (11) also mples that the networ loss rate must e ept lower than or equal to the defned loss to ensure the ted. Equaton (11) s rewrtten to yeld Eq. (12), opt loss = 2 (12) Notaly, the l (t ) funton s a perentage ut loss s not. Therefore, l (t ) s multpled y 1 to yeld loss = 2 opt l( t ) = e µ 1 (13) From Eq. (13), the smoothng tme s opt 2 ln µ. (14) 1 From Eqs. (8) and (14), the suggested range for K s 1 µ K. (15) opt ( 2 ) When K s assgned a value that s more than the threshold n Eq. (15), the desgn of the smoother s manly domnated y the loss effet. For a gven, a sutale an e suggested and an optmal uffer sze an e determned.. delay (ms) Paet Numer (a) The delay of traff 4. Smulaton Varane Tal Spurt () The varane of traff Fg. 4 VoIP traff pattern 4.1 Smulaton Confguraton A set of smulaton experments are performed to evaluate the effetveness of the proposed adaptve smoothng sheme. The OPNET smulaton tools are adopted to trae the voe traff transported etween two dfferent LANs for a VoIP envronment. Nnety personal omputers wth G.729 traffs are deployed n eah LAN. The duraton and frequeny of the onneton tme of the personal omputers follow Exponental dstrutons. Ten fve-mnute smulatons were run to proe the aone networ delay patterns, whh were used to trae the adaptve smoothers and ompare the effets of the orgnal wth the adapted voe qualty latter. Fg. 3 shows the typal networ topology n whh a T1 (1.544 Mps) aone onnets two LANs, and 1 Mps lnes are onneted wthn eah LAN. The propagaton delay of all lns s assumed to e a onstant value and wll e gnored (the dervatve value wll e zero) n the optmzaton proess. The uffer sze of the ottleneed router s assumed to e nfnte sne the performane omparson of adaptve smoothers wll e affeted y overdue paet loss (over the deadlne) and not affeted y the paet loss n router uffer. The networ end-to-end delay of a G.729 paet wth data frame sze (1 ytes) and RTP/UDP/IP headers (4 ytes) s measured for ten fve-mnute smulatons y employng the OPNET smulaton networ. Tale 1 summarzes the smulaton parameters. Fgure 4(a) and 4() lst one of the end-to-end traff delay patterns and the orrespondng delay varanes for VoIP traff oserved at a gven reever.

5 LossRate (%) Delay (ms) Smoothers Ave. Delay Talspurt SD Optmal Fg. 5 The tng tme of smoothers smoothers SD Optmal Tale 2 shows that the Optmal smoother performane aheves a hgh average SSNR and has the sgnfant mprovement n the voe qualty over SD smoother, sne the proposed optmal smoother truly optmzes wth the delay and loss mparments. The SSNR an only represent the loss mpat, ut hardly represent the delay mpat. Therefore, a Lagrangan ost funton s utlzed to onsder the delay and loss mpats to the qualty degradaton for varous smoothers. In order to mantan the normal voe qualty over the networ, the ted, = 3 s requred. Aordng to [14] and G.729, s set as.25 n formula (15) and the µ s set as the frame rate 1 ms for G.729 at the sender. The Lagrange multpler value K = 43 s alulated from the formula (15). Fgure 7 shows the qualty degradaton of smoothers. From the Tale 3, we an oserve that the optmal smoother has the lower Lagrangan ost value than SD smoother. Spefally, we an oserve the optmal smoother has 23% mprovement of the qualty degradaton on SD smoother Tal Spurt Fg. 6 The paet loss rate of smoothers 4 3 Smoothers SD Optmal 4.2 Predted Smoothng Tme and Loss Rate n Smoothers In ths seton the auray of the ted end-to-end delay tme and loss rate among these smoothers are ompared. The mean delay s used to oserve the traff pattern n partular. In Fg. 5 and Fg. 6, we an oserve that the ted tme of the SD smoother s very lose to the mean delay and the loss rate s hgher than optmal smoother. The SD smoother uses a large value of fxed β to deal wth varous traff ondtons and emphasze a long-term mean delay d, so the ted delay wll e lose to the mean delay. A etter hoe for n s proaly the maxmum delay n the last talspurt that an suffently represent the worst ase of urrent networ ongeston and avod an under-estmated delay. 4.3 Qualty Degradaton wth the Lagrangan Cost Funton The test sequene s sampled at 8 Hz, seonds long, and nludes Englsh and Mandarn sentenes spoen y male and female. Tale 2 lsts the mean delay, mean loss rate, and SSNR measured n a voe qualty test wth varous smoothers. SSNR [16][17] s used as an evaluaton tool eause t orrelates etter wth and t s relatvely smple to ompute. Lagrangan Cost (ms) Talspurt Fg. 7 The qualty degradaton of smoothers 4.4 Qualty Sore wth the E-model The E-model s a omputatonal model, standardzed y ITU-T n G.17, G.19 and G.113 [18] whh uses the varous transmsson parameters to t the sujetve qualty of paetzed voe. Therefore, t s essental for the passve montorng agent to tra the performane of ths hannel. In the E-model, a ratng fator R represents voe qualty and onsders relevant transmsson parameters for the onsdered onneton. It s defned n [18] as: R = Ro Is Id Ie _ eff + A (17) where Ro denotes the as sgnal-to-nose rato; Is denotes the sum of all mparments assoated wth the voe sgnal; Id represents the mparments due to delay of voe sgnals; Ie _ eff denotes the equpment mparments, dependng on the low t rate odes (Ie, Bpl) and paet loss (Ppl) levels;

6 Advantage fator A s no relaton to all other transmsson parameters. The test sequene follows the onfguraton of seton 5.3 and the parameters of Ro, Is and A use the default settng that were suggested y [18]. Fg. 8 shows the E-model sore R of the voe qualty. It shows that the optmal method has the sgnfant mprovement n the voe qualty over SD smoother. 6. Conluson For new-generaton VoIP serves, a dynam smoothng algorthm s requred to address IP-ased networ delay and loss. Ths wor proposes an optmal smoothng method to otan the est voe qualty y Lagrangan lost funton whh s a trade off etween the negatve effets of the delay and the loss. The uffer re-synhronzaton algorthm s also proposed to prevent uffer overflow y sppng some slent paets of the tal of tal-spurts. It an effently solve the msmath etween the apture and the playa los. Numeral examples have shown that our proposed method an ontrol the playout tme to alane the target delay and loss. Referenes: [1] V. Brazausas and R. Serflng, Roust and effent estmaton of the tal ndex of a one-parameter pareto dstruton, North Ameran Atuaral Journal avalale at Apr. 2. [2] P. L. Ten and M. C. Yuang, Intellgent voe smoother for slene-suppressed voe over nternet, IEEE JSAC, vol.17, no.1, pp.29-41, Jan [3] R. Ramjee, J. Kurse, D. Towsley, and H. Shulzrnne, Adaptve playout mehansms for paetzed audo applatons n wde-area networs, Pro. IEEE INFOCOM, pp , June [4] D. R. Jese, W. Matrag, and B. Samad, Adaptve play-out algorthms for voe paets, Pro. IEEE Conf. on Commun., vol.3, pp , 21. [5] J. Pnto and K. J. Chrstensen, An algorthm for playout of paet voe ased on adaptve adjustment of talspurt slene perods, Pro. IEEE Conf. on Loal Computer Networs, pp , Ot [6] Y. J. Lang, N. Farer, and B. Grod, Adaptve playout shedulng usng tme-sale modfaton n paet voe ommunatons, Pro. IEEE Conf. on Aousts, Speeh, and Sgnal Proessng, vol.3, pp , 21. [7] A. Kansal and A. Karandar, Adaptve delay estmaton for low jtter audo over Internet, IEEE GLOBECOM, vol.4, pp , 21. [8] A. K. Anandaumar, A. MCree, and E. Pasoy, An adaptve voe playout method for VOP applatons, IEEE GLOBECOM, vol.3, pp , 21. [9] P. DeLeon and C. J. Sreenan, An Adaptve tor for meda playout ufferng, Pro. IEEE Conf. on Aousts, Speeh, and Sgnal Proessng, vol.6, pp , [1] J. C. Bolot, Charaterzng end-to-end paet delay and loss n the nternet, Journal of Hgh-Speed Networs, vol. 2, pp , De [11] F. Huener, D. Lu and J. Fernandez, Queueng performane omparson of traff models for nternet traff, IEEE GloeCom, Sydney, vol.1, pp Nov [12] K. Fujmoto, S. Ata and M. Murata, Statstal Analyss of Paet Delays n the Internet and ts Applaton to Playout Control for Streamng Applatons, IEICE Trans. Commun., vol.e84-b, no.6, pp , June 21 [13] K. Nouho and I. Kenzo, Pure delay effets on speeh qualty n teleommunatons, IEEE JSAC, vol.9, no.4, May [14] B. Duysurgh, S. Vanhastel, B. De Vreese, C. Petrsor, and P. Demeester, On the nfluene of est-effort networ ondtons on the pereved speeh qualty of VoIP onnetons, Pro. Computer Communatons and Networs, pp [15] L.Yamamoto, J. Beerends, KPN Researh, Impat of networ performane parameters on the end-to-end pereved qualty, EXPERT ATM Traff Symposum avalale at to/ pulatons.html, Sep [16] P. J. W. Melsa, R. C. Youne, and C. E. Rohrs, Jont mpulse response shortenng for dsrete multtone transevers, IEEE Trans..Communatons, vol. 44, no. 12, pp , De [17] N. M. Hosny, S. H. El-Ramly, M. H. El-Sad, Novel tehnques for speeh ompresson usng wavelet transform, The Internatonal Conferene on Mroeletrons, pp , Nov [18] ITU-T Reommendaton G.17, The E-model, a Computatonal Model for use n Transmsson Plannng, Mar., 23.