QoS-Factor Transmission Control Mechanism for Voice over IP Network based on RTCP-XR Scheme

Transcription

1 QoS-Fator Transsson Control Mehans for Voe over IP Network based on RTCP-XR Shee Jnsul K, Seung Ho Han, Hyun-Woo Lee, Won Ryu, and Mnsoo Hahn Abstrat Wth the nreasng deand for Internet telehony serves by usng the Voe over IP (VoIP) tehnology, tehnques for QoS-fator ontorng over IP networks are requred to anage the seeh qualty of VoIP serves onstantly. Ths aer resents an end-to-end bdretonal transsson ontrol ehans to anage QoS-fators suh as jtter, delay, aket loss rate, et., based on the RTCP-XR shee. Also, we roose and odfy the standard RTCP-XR shee defned by IETF to erfor better qualty ontorng of VoIP serve. In order to evaluate the newly roosed RTCP-XR shee for VoIP serves, we easure n real-te the qualty degree of the reeved seeh sgnal whle alyng our roved Paket Loss Conealent (PLC) algorths n a G.729A ode usng an leented Sesson Intaton Protool (SIP)- based SoftPhone and a 1-ort gateway. And then, for the aurate QoS delverng evaluaton of the RTCP-XR Shee we aled alls through the PSTN to SIP gateways, SIP gateways to the PSTN, and SIP gateways to SIP gateways. The exerental results onfr that the aled VoIP serve n real envronents wth the QoS-fator transsson ontrol ehans aheve a suffent auray for qualty ontorng of VoIP serves 1. Index Ters VoIP, QoS, Seeh Qualty, RTCP-XR, PLC, PESQ, E-Model I. INTRODUCTION As the nterests n suortng IP ounaton treendously nrease, a varety of IP-based real te ulteda alaton serves suh as the VoIP and the MMoIP have been develoed radly n resdental and enterrse ounaton arkets beause of ther attratve serve enhaneents and ost savngs. Moreover, aordng to the dsovery of avalable and sutable audovsual serves over IP, researhes on the Qualty of Serve (QoS) for varous ulteda alaton serves are requred. An ortant fator for VoIP QoS ontrol tehnque nvolves the rate ontrol, whh s based largely only on network arents suh as the aket loss rate or the delay due to the network ongestons [1], [2]. The 1 Ths work was suorted by the KT (Korea Teleounaton) Cor. n South. Korea. Jnsul K, Hyun-Woo Lee, Won Ryu are wth the BN Interworkng Tehnology Laboratory, BN Serve Researh Grou, BN Researh Dvson, ETRI, Daejeon, Korea (e-al: jsetr@etr.re.kr, hwlee@etr.re.kr, wlyu@etr.re.kr). Seung Ho Han and Mnsoo Hahn are wth the Seeh and Audo Inforaton Laboratory, the Inforaton and Counatons Unversty, Daejeon, Korea. (e-al: sae0128@u.a.kr, shahn@u.a.kr). seond ortant fator s based on the fator that dfferent arts of seeh have dfferent eretual ortane and eah art of seeh does not ontrbute equally to the overall voe qualty [3]. Hene, n our aroah, voe akets that are eretually ore ortant are arked,.e. aqure rorty. If there s any ongeston, the akets are less lkely to be droed than akets that are of less eretual ortane. The rorty arkng based QoS shees are oen loo ones and do not ake use of hanges n the network arents. To easure the seeh qualty we adot the well-known PESQ (Peretual Evaluaton of Seeh Qualty) algorth, whh s one of objetve eretual voe qualty easureent tehnques, based on the ITU-T seeh qualty evaluaton standards [4]. Nonntrusve ethods do not need a referene sgnal and are arorate for ontorng the real traff. The ITU-T E- odel [5] s the ost wdely used non-ntrusve voe qualty easureent ethod and ay be used to redt the onversatonal MOS (Mean Onon Sore) dretly fro the IP network and the ternal araeters [6]. The Real-te Transort Protool (RTP) and RTP Control Protool (RTCP) ounatons use the RTCP- Reever Reort to feedbak IP network ondtons fro RTP reevers to RTP senders. However, the orgnal RTCP rovdes overall feedbak on the qualty of end-to-end networks as a whole [7]. The RTP Control Protool Extended Reorts (RTCP-XR) s a new VoIP anageent rotool whh defnes a set of etrs that ontans nforaton for assessng the VoIP all qualty by the IETF [8]. The RTCP-XR an be leented as software ntegrated nto IP hones and gateways nexensvely and then, essages ontanng key all-qualty-related etrs are exhanged erodally between IP hones and gateways. However, n order for ontorng the QoS-fator on end-toend VoIP networks, the RTCP-XR s nsuffent to estate the seeh qualty beause t doesn t have any seeh qualty ontorng funtonalty. To solve ths roble we roose the udate of soe oonents n RTCP-XR shee. Paket loss ours nherently n an IP network due to the network haratersts suh as the delay, the jtter, and network ongestons. The aket loss stands ssng seeh sales for a te nterval at reever and brngs about the degradaton of the reeved seeh qualty. Sne transsson s a real-te roess, t s ossble to retranst the ssed data when the data s ssed. A onealent tehnque s requred for the ssed aket reonstruton. Seeh odes have ther own PLC ehanss aganst the aket loss. At the reever, a new /06/$ IEEE Authorzed lensed use lted to: Korea Advaned Insttute of Sene and Tehnology. Downloaded on Deeber 7, 2009 at 21:38 fro IEEE Xlore. Restrtons aly.

2 seeh sgnal s generated to redue the effet of aket loss by utlzng the PLC ehans [9]. In ths aer, for the QoS anageent and ontorng of the seeh qualty durng utual onversatons over IP networks, we roosed an end-to-end bdretonal transsson ontrol ehans to anage the QoS-fators suh as the jtter, the delay, and the aket loss rate on a odfed RTCP-XR shee. The newly resented QoSfator transsson ontrol ehans s assessed wth the erforane analyss of the roosed PLC algorths n VoIP seeh oders. Varous tyes of aket losses are generated by the Error Inserton Deve (EID) and then the PESQ s used to evaluate both the orgnal and the roosed PLC algorth n G.729. Also, to easure and reort the R- fators, our exerents sefy the QoS erforane wth the objetve easureent ethod over the IP network,.e., E-Model. Fg. 1. VoIP network arhteture II. VOIP NETWORK ARCHITECTURE AND PROCEDURE FOR QOS-FACTOR MANAGEMENT A. VoIP Syste Arhteture Hstorally, voe has been delvered, ether wreless or wred, n a dedated, one-to-one rut swthed anner. Ths s beause of the unque requreents voe traff laes on a network. It requres the low lateny and jtter erforane of a voe all, but laes hgh deands on the data aaty at the sae te. To guarantee the QoS for VoIP serves we roosed a new arhteture wth a QoS easurng server. Our roosed arhteture, Fg. 1 s desgned wth a SoftPhone and a 1-ort gateway as the an User Agent (UA) whh arres QoS easureent oonents. Our network also nludes SIP servers and a QoS-fator ontorng server for the all and QoS ontrol. B. Real-te QoS-Fator Measureent and Transsson Beause resent IP networks are not desgned to suort the QoS, the qualty easureent beoes ore ortant and urgent for ore relable hgher qualty ulteda serves over IP networks. We exlore the at of the ndvdual aket loss, the delay, and the jtter on the eretual seeh qualty n VoIP systes. The VoIP serve qualty evaluaton s arred out by frstly enodng the nut seeh re-odfed wth gven network araeter values and then deoded to generate degraded outut seeh sgnals. In order to obtan an end-to-end (E2E) MOS between the aller-ua and the allee-ua, we aly the PESQ and the E-Model ethod. In detal, to obtan the R fators for E2E easureent over the IP network we need to get Id, Ie, Is and Ij. Here, Ij s newly defned as n equaton (1) to reresent the E2E jtter araeter. R fator = R0 Is Id Ij Ie + A (1) Fg. 2. Proedure of QoS-Fator easureent and transsson The ITU-T Reoendaton rovdes ost of the values and ethods to get araeter values exet Ie for the G.729A ode, Id and Ij. Frst, we obtan Ie value after the PESQ algorth aled. Seond, we aly the PESQ values to Ie value of R-fator as shown n Fg.2. We easure the E2E Id and Ij fro our urrent network envronent. By obnng Ie, Id and Ij, the fnal R fator ould be outed for the E2E QoS erforane results. Fnally, obtaned R fator s reonverted to MOS by usng equaton (2), whh s redefned by the ITU-T SG12. R6.5: MOS R100: MOS1 R R R R100: MOS III. QOS-FACTOR TRANSMISSION CONTROL MECHANISM BASED IN RTCP-XR SCHEME A. Oeraton Proedure wth Voe Paket Transsson The RTP rotool s used for transttng real-te data nforaton and the RTCP, for sendng the ontrol nforaton. The an funton of the RTCP s to rovde a detaled reresentaton of the voe akets exhanged durng an RTP sesson. Its struture nludes the sender reort (SR) and the reever reort (RR) transtted erodally to all artants n the sesson. It as at rovdng a feedbak on the qualty of the transsson (e.g., delay jtter, average aket loss, et.), where transtters (2) Authorzed lensed use lted to: Korea Advaned Insttute of Sene and Tehnology. Downloaded on Deeber 7, 2009 at 21:38 fro IEEE Xlore. Restrtons aly.

3 send sender reorts and reevers send reever reorts usng the RTCP-XR. Whle the SR nludes transsson and reeton nforaton for atve senders n the sesson, the RR would also ontan the reeton nforaton for non-atve senders. The QoS easureent server reeves the QoS-fator and reorts the to the QoS-ontorng nterfae every 2-seond. Fg. 2 also shows that the roedure of the RTP/RTCP/RTCP-XR aket transsson wth the QoS easureent roedure. B. Conversatonal Seeh Qualty Montorng wth Modfed RTCP-XR Shee For the onversatonal seeh qualty we have develoed an RTCP-based aket struture to rovde an end-to-end bdretonal transsson ontrol that an reort the delay, the jtter, and the aket losses n a tely anner. Our aket struture s slar to the RTCP-XR, whh s rarly defned to rovde ore detaled statsts, artularly for ultast alatons [8]. In our ase, the RTCP-XR shee was sefally desgned to reort the delay, the jtter, and the aket losses for every frae of voe sgnal. Also, the loss and the dsard rates are desgned to be alulated for eah sesson at the endreever n order to get real-te easured values. The orgnal RTCP-XR aket tye defned an be used for seeh qualty ontorng. However, t s not falar wth real-te seeh qualty reortng for bdretonal onversaton through VoIP networks. We odfed the RTCP-XR aket shee n order for onversatonal seeh qualty reortng and ontorng beause ounaton serves lke the VoIP ust be reognzed as the utual onversaton one. For the delay ontorng as one of the sgnfant QoSfator BT-5 s foratted wth both sub-blok 1 and subblok 2. SSRC_1 and SRRC_2 are for the sender and the reever nubers whh s defned randoly. The DLRR n sub-blok 1 reorts the one way delay between the sender and the reever. The DLRR n sub-blok 2 reorts the round tr delay whh s easured usng the one way delay nforaton fro DLLR n sub-blok 1. Fg. 3 shows the essage forat-ii of BT-5 for delay ontorng. In Fg. 4, nforaton of the jtter and the akets s ontrolled n BT- 6. At frst, n order to anage the jtter, we ategorze t nto three levels of n_jtter, ax_jtter, and ean-jtter. Those are reorted as the uulatve effets of jtter values obtaned through the jtter buffer n our ases. Seond, to get the real-te utual ounaton seeh qualty ontorng feld of aket ount nforaton of the RTP/RTCP s nluded n the reort blok. The Tx/Rx RTP Pakets forat n BT-6 s desgned for ontorng sender/reever RTP. The Rx RTCP Pakets are the RTCP XR akets whh are reeved at the QoS easureent server, and the Tx RTCP Pakets are the RTCP XR akets whh are sent fro the SoftPhone (or 1ort Gateway) to the QoS easureent server. The bdretonal QoS-fator s also easured n real-te and reorted to the QoS- Montorng deve. The fnal result value of the uulatve aket loss s also nluded n our BT-6 shee. The forat of our BT-7 shee s slar to the standard RTCP-XR. However, the loss and the dsard rates are outed as soon as the all sesson stats by usng the uulatve akets ontrolled by BT-6. The auray of eah aket ountng n real-te s ortant. Eseally, for te synhronzaton we set our exeuton te of both the SoftPhone and the 1-ort gateway to the NTP (Natonal Te Protool). That s, the host syste te s synhronzed wth the natonal standard te. Fnally, by alyng the QoS-fator obtaned fro the bdretonal seeh qualty easureent MOS-LQ and MOS-CQ s defned searately for the lstenng qualty and the onversatonal qualty. Other fators n BT-7 are just added to the standard forat shee as shown n Fg. 5. Fg. 3. QoS-fator: BT=5 delay ontorng for transsson ontrol Fg. 4. QoS-fator: BT=6 jtter, akets for transsson ontrol Fg. 5. QoS-fator: BT=7 loss & dsard late, MOS-LQ, & -CQ for transsson ontrol Authorzed lensed use lted to: Korea Advaned Insttute of Sene and Tehnology. Downloaded on Deeber 7, 2009 at 21:38 fro IEEE Xlore. Restrtons aly.

4 IV. PROPOSED PLC ALGORITHMS When aket losses our over IP networks, the PLC algorth eloyed n G.729A reonstruts lost seeh fraes based on the revously reeved seeh nforaton [9]. In ths aer, two tehnques are roosed to onstrut a new PLC algorth for G.729A. One adatvely utlzes both-sde nforaton for lost fraes based on the lass lassfaton. The other s the adatve gan ontrol aordng to the average agntude varaton aross the fraes. We aly the algorth to our syste to rove akets loss oensaton n both off-lne test envronent n whh the deoder s odfed by our PLC algorth and real-te envronent, by the transsson ontrol ehans based on the RTCP-XR shee wth gven QoS-fators. A. Adatve Utlzaton of Both-sde Inforaton Our roved PLC algorth uses adatvely both-sde nforaton for lost fraes wth the buffer to store a sueedng frae. When both-sde nforaton s avalable, the roosed PLC algorth odfes the LSP (Lne Setru Pars) nterolaton oeffents for frst subfrae based on the lass of the last good frae. The last good frae s lassfed nto ether the lass A or the lass B by the deson tree. To ake out deson tree, we use the CART (Classfaton And Regresson Tree) [10] and analyze 1000 Korean dalogue seeh. The ZCR (Zero Crossng Rate) [11], the rato between the average agntude [11] of the urrent frae and that of the adjaent frae, the average agntude rato between the subfraes n urrent frae, and rato between the frst value and the seond value of the autoorrelaton funton [11] are evaluated as the feature araeters. In the lass A, the odfed LSP nterolaton s gven as q q q (3) (revous) (future) , 1,...,10 where q s the -th LSP oeffent for the urrent lost frae, (revous) q, for the revous frae, and (future) q, for the future frae. And, n the lass B, the odfed LSP nterolaton s gven as q q q. (4) (revous) (future) , 1,...,10 B. Adatve Gan Control The PLC algorth eloyed n G.729A attenuates the adatve and fxed odebook gans as follows. fator based on the varaton of average agntudes between revous two fraes. The varaton s evaluated by G. G I n nreasng ase and G D n dereasng ase are resetvely alulated by 2E E 2E E G, G 2 (6) I D E 1 E 1 where E s the average agntude, and s the frae ndex. The adatve and fxed odebook gans are attenuated by the new fators as follows. G g g g g 0.7 1: 0.98, 0.9 G g g g g (-1) (-1) I 1: 0.988, 0.92 (-1) (-1) GD g g g g (-1) (-1) D 0.7 : 0.977, 0.88 V. SIMULATION SURROUNDINGS Ths aer evaluates the erforane of the QoS-fator transsson ontrol ehans wth the roosed PLC algorth under dfferent aket loss sulatng ondtons. The PLC algorth s tested n both n off-lne envronent and real-te envronent wth G.729A. In the off-lne envronent, Fg. 6 shows the exerental roedure. Frst, seeh data are enoded n the enoder. Seond, aket losses are generated by the EID. Thrd, enodng fles are deoded wth and wthout aket losses. Fnally, deodng fles wth aket losses are evaluated wth the referene seeh deoded wthout a aket loss n the seeh qualty evaluaton odule. In real-te envronent, our VoIP syste ales the QoS-fator transsson ontrol ehans based on the RTCP-XR shee for the QoS-fator anageent and ontorng. Fg. 7 outlnes the onfguraton for the VoIP syste test envronent under test. Both the orgnal and roosed PLC algorths are tested eah other nteratvely usng the SoftPhone and 1ort gateway. Seeh Coder Enoder Deoder EID Fg. 6. Exerental roedure Seeh Qualty Evaluaton Module PESQ sore (7) g g g g (5) (-1) (-1) 0.98, 0.9 where s the subfrae ndex, g s the fxed odebook gan, and g s the adatve odebook gan. The roosed PLC algorth odfes the attenuaton Fg. 7. Confguraton of sulaton envronent alyng roosed QoS-fator shee and roved PLC algorth Authorzed lensed use lted to: Korea Advaned Insttute of Sene and Tehnology. Downloaded on Deeber 7, 2009 at 21:38 fro IEEE Xlore. Restrtons aly.

5 A. Paket Loss Desgn A ounaton hannel an be odeled by the Glbert- Ellot odel [12] or the Bellore odel [13]. In the sulaton, we use the STL (Software Tool Lbrary) nluded n ITU-T Reoendaton G.191 [14] to odel aket losses. The STL rovdes the EID whh generates losses based on the Glbert-Ellot odel and the Bellore odel. A varous atterns of losses an be generated by the odfaton of araeters n the EID. To odel varous aket loss envronents, we desgn burst and rando aket losses wth 1%, 3%, 5%, 10%, and 15% loss rates and t s onsdered that a aket ontans 1 seeh frae, 2 seeh fraes, or 3 seeh fraes. B. Perforane Evaluaton For PLC algorth erforane evaluaton, we use the syste evaluaton ethod whh s PESQ defned by ITU- T Reoendaton P.862 for objetve assessent of qualty. After oarng an orgnal sgnal wth a degraded one, the outut of PESQ rovdes a sore fro -0.5 to 4.5 as a MOS-lke sore. The referene seeh for the real-te envronent sulaton and the off-lne envronent sulaton s the orgnal seeh and the deoded seeh wthout any aket loss, resetvely. In the real-te envronent, after gettng the PESQ, t s used for E-Model evaluaton ethod as we enton above. Fnally, the MOS s aqured. We use 200 Korean dalogue seeh utteranes fro 2 ale and 2 feale seakers as test data. The duraton of eah utterane s about 10 seonds. VI. SIMULATION RESULTS The sulaton results show that the roosed PLC algorth outerfors that eloyed n G.729A for both off-lne and real-te envronents. The sulaton shows that the roosed QoS-fator transsson ontrol ehans based on the odfed RTCP-XR shee aheves uh better result for seeh qualty than other VoIP systes whh use standard shee durng bdretonal talk n IP network envronent. TABLE I PESQ RESULT FOR OFF-LINE ENVIRONTMENT PLC Orgnal Proosed Loss tye 1f 2f 3f 1f 2f 3f 1% Rando Burst 3% % % % % % % % % TABLE II RESULT FOR REAL-TIME ENVIRONMENT PLC Orgnal Proosed Loss tye PESQ R MOS PESQ R MOS 0% Rando 3% % % % Burst 3% % % Fg. 8. MOS results for rando losses n the real-te envronent Fg. 9. MOS results for burst losses n the real-te envronent A. PESQ Measureent n Off-lne Test Envronent Table I shows the results of the PLC erforane evaluaton n PESQ sores. In the table, f refers to frae er aket. As the roosed PLC algorth s aled, the PLC erforane s roved. At 1f, the dfferene of the degree of roveent sore between rando losses and burst losses s not large. PESQ sores are nreased by on the average. On the other hands, at 2f and 3f, the degree of roveent for rando losses s hgher than that for burst losses beause of the aketzaton effet. At 2f, the degree of the roveent for rando losses s whle that for burst losses s on the average. At 3f, the degree of the roveent s for rando losses and for burst losses, resetvely. B. PESQ, R-fator and MOS Measureent n the Real-te Envronent In Table II, the PLC erforane evaluaton results for the real-te envronent are suarzed as the PESQ, the R-fator, and the MOS. The roosed PLC aheves the Authorzed lensed use lted to: Korea Advaned Insttute of Sene and Tehnology. Downloaded on Deeber 7, 2009 at 21:38 fro IEEE Xlore. Restrtons aly.

6 PESQ gan of 0.1 for all tyes of loss. The orresondng gans for the R-fators and the MOSs are aheved by ths PESQ gans. Fnally, even though the MOS s not roved for burst losses at hgh loss rates, the MOS gan of 0.1 s generally aheved as shown n Fg. 8 and Fg. 9. Thus, the roveent of the erforane n the real-te envronent s also onfred. VII. CONCLUSION In ths aer we have roosed an end-to-end bdretonal QoS-fator transsson ontrol ehans to anage the seeh qualty n real-te on odfed RTCP- XR shee for QoS ontorng of utual onversatons over IP networks. The newly resented QoS-fator transsson ontrol ehans s assessed wth the erforane analyss of the roosed PLC algorths n off-lne and real-te envronent. The seeh qualty erforane evaluaton onfrs that our roosed PLC algorth outerfors the one n the G.729A seeh ode. The future dreton of ths researh wll be further evaluatons and verfatons of the odfed RTCP-XR n ore olex onverged networks. REFERENCES [1] R. Eejae, M. Handley and D. Estrn, RAP: An End-to-end Ratebased Congeston Control Mehans for Realte Streas n the Internet, Pro. IEEE INFOCOM, USA, Marh [2] F. Bertell, G. Rugger and G. Shebra, TCP-Frendly Transsson of Voe over IP, Proeedngs of IEEE Internatonal Conferene on Counatons, New York, USA, Arl [3] J. C. De Martn, Soure-drven Paket Markng for Seeh Transsson over Dfferentated-Serves Networks, Proeedngs of IEEE ICASSP 2001, Salt Lake Cty, USA, May [4] ITU-T Reoendaton P.862, Peretual evaluaton of seeh qualty (PESQ), an objetve ethod for end-to-end seeh qualty assessent of narrowband telehone networks and seeh odes, Feb [5] ITU-T Reoendaton G.107, The E-Model, a outatonal odel for use n transsson lannng, [6] R.G. Cole and J. H. Rosenbluth, VoIP over IP Perforane Montorng, Journal on Couter Counatons Revew, vol 31, no.2, Arl [7] H. Shulzrnne, S. Casner, R. Frederk and V. Jaobson, RTP: A Transort Protool for Real-Te Alaton, IETF RFC 3550, July [8] T. Fredan, R. Caeres, A. Clark, RTP Control Protool Extended Reorts, IETF RFC 3611, Nov [9] ITU-T Reoendaton G.729 Annex A, Codng of seeh at 8 kbt/s usng onjugate-struture algebra-ode-exted-lnearredton (CS-ACELP), Nov [10] R. O. Duda, P. E. Hart, D. G. Stork, Pattern Classfaton, JOHN WILEY&SON, 2001, [11] L. R. Rabner, R. W. Shafer, Dgtal Proessng of Seeh Sgnals, Prente Hall, [12] Mushkn, M, Bar-Davd, I, Caaty and odng for the Glbert-Ellot hannels, IEEE Transatons on Inforaton Theory, Vol. 35, Nov. 1989, [13] Vjay K. Vara, Testng Seeh Coders for Usage n Wreless Counatons Systes, Proeedngs of IEEE worksho on Seeh Codng for Teleounaton, Ot. 1993, [14] ITU-T Reoendaton G.191, Software tools for seeh and audo odng standardzaton, Nov Jnsul K was born n Nawon, Chonbuk, South Korea, n He reeved the B.S. degree n outer sene fro Unversty of Utah, Salt Lake Cty, Utah, USA, n 2002, and the M.S. degree n dgtal eda engneerng fro Inforaton and Counatons Unversty (ICU), Daejeon, South Korea, n Sne 2005, he has been workng as a researher n Broadband onvergene Network Interworkng Tehnology Laboratory, Eletrons and Teleounatons Researh Insttute (ETRI), Daejeon, Korea. Hs researh nterests nlude Moblty, NGN, Multeda Counaton and Voe/Vdeo over IP. Seung Ho Han was born n Seoul, South Korea, n He reeved the B.S. degree n avons engneerng fro Hankuk Avaton Unversty, Kyongg, South Korea, n 2003, and the M.S. degree n eletrons engneerng fro Inforaton and Counatons Unversty (ICU), Daejeon, South Korea, n He s urrently workng toward Ph.D. degree n shool of engneerng at ICU. Hs researh nterests nlude seeh odng, and VoIP. Hyun-Woo Lee was born n Seoul, South Korea, n He reeved the B.S. degree n eletrons engneerng fro Hankuk Avaton Unversty, Kyongg, South Korea, n 1993, and hs M.S. and Ph.D. degree n ounaton and nforaton engneerng fro Hankuk Avaton Unversty, Kyongg, South Korea, n 1995 and Sne 1995, he has been workng as senor researher, n Broadband onvergene Network Interworkng Laboratory, Eletrons and Teleounatons Researh Insttute (ETRI), Daejeon, Korea. Hs researh nterests nlude Moblty, Wreless LAN, Interworkng Tehnology and VoIP. Won Ryu was born n Busan, South Korea, n He reeved the B.S. degree n the deartent of outer sene & statsts fro Pusan Natonal Unversty, Busan, South Korea, n 1983, and the M.S. degree n the deartent of outer sene & statsts fro Seoul Natonal Unversty, Seoul, South Korea, n 1988, resetvely, and hs Ph.D. degree n nforaton engneerng fro SungKyunKwan Unversty, Kyongg, South Korea, n Sne 1989, he has been jonng as a researher and urrently he s a rojet leader n the Broadband onvergene Network Interworkng Researh Laboratory, Eletrons and Teleounatons Researh Insttute (ETRI), Daejeon, Korea. Hs researh nterests nlude All-IP based Convergene Serve & Control Plane, Moblty, NGN, Wre/Wreless Interworkng Tehnology, and VoIP. Mnsoo Hahn was born n Seoul, South Korea, n He reeved the B.S. and the M.S. degrees n eletral engneerng fro Seoul Natonal Unversty, Seoul, South Korea, n 1979 and 1981, resetvely, and the Ph.D. degree n eletral and eletrons engneerng fro Unversty of Florda, Florda, USA, n Fro 1982 to 1985, he was wth Korea Researh Insttute of Standards and Sene (KRISS), Deajeon, South Korea. Fro 1990 to 1997, and he was wth Eletrons and Teleounatons Researh Insttute (ETRI), Deajeon, South Korea. In 1998, he has been a faulty eber of the Shool of Engneerng, Inforaton and Counatons Unversty (ICU). Currently, he s a Full Professor n Shool of Engneerng, ICU and a Dretor n Dgtal Meda Laboratory, ICU. Hs researh nterests nlude seeh and audo odng, seeh synthess, nose reduton and VoIP. Reently, he s loated general har for Seeh Engneerng County, South Korea. Authorzed lensed use lted to: Korea Advaned Insttute of Sene and Tehnology. Downloaded on Deeber 7, 2009 at 21:38 fro IEEE Xlore. Restrtons aly.