Video streaming over the Internet is becoming very popular and

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1 Streamng MPEG-4 AudoVsual Objects Usng TCP-Frendly Rate Control and Unequal Error Protecton Toufk Ahmed 1, Ahmed Mehaoua 1 and Vncent Lecure CNRS-PRSM LabUnversty of Versalles CRAN lab CNRS UMR 739 Unversty Henr Poncaré of Nancy 1, 45 av des Etats-Uns, Faculté des Scences BP 239, F-7835, Versalles, France F-5456 Vandoeuvre-lès-Nancy Cedex, France Abstract Ths artcle descrbes a far and robust vdeo streamng framework over IP networks It s based on an MPEG4 Audo-Vsual Object (AVOs) classfcaton, TCP-Frendly transport and out-of-band unequal forward error protecton Accordng to network congeston feedback, vdeo source servers dynamcally adjust ther bt rates by addng and droppng MPEG-4 AVO to conform to the TCP-Frendly Rate Control (TFRC) algorthm and by takng nto consderaton meda semantc relevancy Thus, an accurate MPEG-4 Access Unt (AU) parttonng and packetzaton can be performed to cope wth decodng error propagaton and network bandwdth fluctuaton Fnally, AVOs requrng smlar network QoS level are automatcally classfed, packetzed and mapped to one of the avalable IP DffServ PHB (Per Hop Behavors) Smulaton results show a sgnfcant mprovement regardng to user-perceved vdeo qualty, packet loss recovery and bandwdth share farness Keywords: Adaptve vdeo streamng, IP, TCP-Frendly, QoS, FEC I INTRODUCTION Vdeo streamng over the Internet s becomng very popular and t s competng wth tradtonal TCP based applcatons for bandwdth utlzaton As a result, Network stablty and traffc farness become crtcal ssues On the other hand, next generaton Internet wll be characterzed by Qualty of Servce (QoS) capabltes It s commonly accepted that IP Dfferentated Servces (DffServ) wll be hghly deployed n the next generaton IP networks Recent researches on transmttng vdeo over IP demonstrate that DffServ s a strong canddate for supportng realtme vdeo communcatons Works presented n [1], [2], [3], and [4] clearly state that IP Dffserv s the most sutable model for delverng nteractve and streamed vdeo content over Internet at a large scale The QoS-capablty cannot be acheved effcently wthout mechansms to ensure a far share of network resource between realtme (UDP-based) and non-real tme (TCP-based) IP servces Those mechansms are known as TCP-frendly transport protocols In ths paper, we propose an ntegrated transmsson archtecture that effcently combnes FEC and TCP-Frendly mechansms to guarantee both, a hgh vsual qualty level of the played-out MPEG-4 Audo-Vsual streams and a far share of the bandwdth The control of the qualty of the vdeo servce s performed at the vdeo streamng sources through three schemes Frst, an adaptve MPEG-4 Access Unt (AU) parttonng and packetzaton protocol that classfy MPEG4 AudoVsual Objects (AVO) accordng to ther mportance for the vdeo scene Second, vdeo servers perform an unequal and out-of-band forward error protecton to senstve Access Unts to deal wth IP packet loss and error propagaton Thrd, servers adjust ther transmsson rate based on network congeston control nformaton, accordngly to the TCP-Frendly Rate Control scheme (TFRC) Ths source bt rate adjustment leads to a far share of network resources wth other TCP/IP connectons The vdeo servers tag and stream the most relevant IP packets embeddng AVO data accordng to ther relevancy to the servce (e, low or hgh drop precedence) Less mportant AVO are transmtted only f bandwdth avalablty Consequently, ths ntegrated vdeo streamng archtecture provdes a sgnfcant mprovement for the control of the end-to-end QoS Performance evaluaton s carred out through smulaton The remander of ths paper s as follows: Secton II presents an overvew of MPEG-4 framework and the IP vdeo streamng framework Secton III descrbes the proposed IP vdeo streamng archtecture Secton IV focuses on the AVO protecton scheme usng Unequal Error Protecton based on audovsual relevancy Performance evaluaton and analyss s presented n secton V We fnally conclude n Secton VI II MPEG-4 AVO STREAMING OVER IP A MPEG-4 Object based Codng Bascally, an MPEG-4 scene conssts of one or more audo vsual objects called AVOs Each of them s characterzed by temporal and spatal nformaton Each Vdeo Object (VO) may be encoded n a scalable (mult-layer) or non scalable (sngle layer) form A layer s composed of a sequence of a Group of Vdeo-Object-Plane (GOV) A Vdeo Object Plane (VOP) s smlar to the MPEG-2 frame VOP supports ntra coded (I-VOP) temporally predcted (P-VOP) and b drectonally predcted (B-VOP) [5] To take benefts from the object-based compresson, we have proposed n [6] an ntellgent adaptaton to cope wth network congeston and end termnal heterogenety We proposed to classfy MPEG-4 AVOs at the vdeo server from most mportant AVO to least mportant ones Several methods have been used for objects classfcaton Durng scene creaton, one can affect the adequate prortes to each object n the scene For scenes wth no assgned object prortes, MPEG-4 object descrptors or MPEG-7 QoS descrptors metadata have been used to provde the relevant nformaton needed to handle object prorty The classfcaton process s very mportant n order to apply adaptve vdeo streamng and unequal error protecton to dfferent vdeo streams AVO requrng dfferent level of QoS and handlng traffc prortzaton n the network level are automatcally classfed and mapped to one of the IP DffServ PHB supported by the IP network Detals on the classfcaton process and model are out of the scope of ths artcle Readers can refer to [6] for more nformaton B MPEG-4 System Layer The MPEG 4 vdeo codng provdes an object-based representaton of vdeo by allowng the codng of audo-vsual object Each audo-vsual object s coded separately Texture and shape codng n MPEG-4 are very smlar to the codng of frames n MPEG-2 In a partcular AVO, the dfferent parts of the vdeo data stream have not the same mportance for the qualty of the decoded vdeo The damages caused by some data loss n a reference pcture (I-VOP or P-VOP) wll affect subsequent pcture(s) due to nterframe predctons Subsequently, I-Frame must be protected more than P-Frame and P-Frame more than B-Frame Let us consder now the example of vdeo object coded wth layered wavelet transform technques The most mportant layer contans the low frequency sub-band of the pcture, called Base Layer (BL) Other layers, whch represent a herarchcal level of resoluton of the wavelet transform, are less mportant These layers are called Enhancement Layers (EL) Ths s the second step of preparng AU to be transmtted over the network It operates wthn a sngle audo-vsual object The frst step s handled by the classfcaton layer whch classfes the object among them As we sad, the result of the classfcaton s a set of AVOs sorted accordng to ther mportance n the scene We affect a fnal prorty to each AU to apply an unequal error protecton Ths prorty reflects both the prorty of partcular AVO n the scene and the prorty of a sngle frame type (I, P, B or herarchcal stream f any BL or EL) We chose a scale of 1 levels of prorty (p [,99], the hgher value beng assocated to the most mportant AU) that can be applcable to a large number of meda encodng scheme C IP Vdeo Streamng Control Schemes By classfyng MPEG-4 AVO, we provde a frst level of scalablty called object scalablty It gves the server the ablty to add and drop vdeo objects dynamcally and deal wth network

2 congeston ntellgently In ths paper we propose an ntegrated archtecture for uncast vdeo streamng usng the followng mechansms: (1) An AVO classfcaton mechansm to generate MPEG4 access unts (2) A mechansm for addng and droppng AVO accordng to network congeston and TCP-frendly rate control, that s performed by the server to adjust transmsson rate whle beng far to other network traffc (3) An out-of-band and unequal FEC sgnalng to mnmze packet loss mpact on vdeo qualty These mechansms are ntegrated and collaborate wth each others to guarantee a hgh level of protecton durng vdeo transmsson and network congeston perods III ADAPTIVE AVO STREAMING USING TCP-FRIENDLY The vdeo qualty adaptaton mechansm s based on TFRC [7] It operates as follows: The recever measures the loss rate and feeds ths nformaton back to the sender Ths s acheved by a modfed verson of RTP (Real-tme Transport Protocol) and RTCP (Real-tme Transport Control Protocol) Each RTP packet has a tmestamp and a sequence number that allow the recever to compute the packet loss and the sender to compute the RTT The loss rate and the RTT are then fed nto the TFRC module to get the approprate transmsson rate (cf Eq 1 below) The sender then adds or drops audo-vsual objects and the assocated layers f any, to adjust ts transmsson rate to match the target rate (e, allowed rate) The calculated rate s obtaned by usng the TFRC equaton [8]: s R TCP (Eq1) 2bp 3bp 2 RTT + t RTO (3 ) p(1+ 32 p ) 3 8 Where RTCP s the target transmsson rate or the allowed transmsson rate, s s the packet sze, RTT s the round trp tme, p s the loss rate, t RTO s the TCP retransmsson tmeout value and b s the number of packets acknowledged by a sngle TCP acknowledgement A Add / Drop of Audo-Vsual Objects Let S be a set of MPEG-4 AVOs contanng n AVOs O j, wth j {1, 2 n} Wthout loss of generalty, we assume that these objects are sorted n a decreasng order of prorty usng our Classfcaton process Each object O j may consst of m j layers (m j 1) Note that lower layers wthn an object have hgher prortes than hgher layers Let P be the functon that returns the prorty of a partcular object or layer Wthout loss of generalty, we assume that: j,1 j < n : P(O j+1 ) P(O j ) (Eq2) j,1 j < n, l,1 l < m j : P(L j,l + 1 ) < P(L j,l ) L j,l s the Layer number l of the Object O j By usng formula (2) we can construct an Audo-Vsual Entty set called E composed of all object layers ordered by ther prortes E= {L 1,1, L 1,2 L 1,m1, L 2,1, L 2,2 L 2,m2,, L n,1, L n,2 L n,mn} We wll n note E as follows: E= {e 1, e 2,,e W} wth w= E = m j The server adds a new audo-vsual entty as soon as the target rate exceeds the current sendng rate of current enttes plus the new entty Assume that the server s streamng k enttes at tme t We assume also that the clent has suffcent resources to play all the enttes beng sent by the server Therefore, at tme t +1 the server can add a new entty whle the followng condton (3) s satsfed: k+1 R +1 (e j ) R TCP (Eq3) Wth the same manner, when the estmated throughput of the TCP sesson ndcates that the vdeo server s transmttng more data than t should, then the vdeo server must reduce ts sendng rate by droppng one or more audo-vsual enttes Therefore, the server drops enttes whle the followng condton (4) s satsfed: k R +1 (e ) > j R TCP (Eq4) IV AVO PROTECTION USING FEC Error reslence of each Elementary Stream assocated to one AVO can be enhanced when the senstve data s protected whereas the less mportant data s none or less protected, as shown n [9], [1] Paper [11] and [12] specfy how error protecton s unequally appled to dfferent part of the vdeo stream We extend ths dea n case of object based codng (e, MPEG-4 AVO) In ths case, the classfcaton process specfes how assgnng prorty levels to each Access Unts wthn an AVO From such classfcaton, an Unequal Error Protecton (UEP) mechansm can be performed through forward error correcton It s qute obvous that the most mportant AVO data must be protected as strongly as possble aganst packet loss durng transmsson Ths secton presents frst Reed Solomon codes and then our proposal for protectng MPEG-4 AVO A Reed-Solomon FEC Codes The am of Reed-Solomon (RS) codes s to produce at the sender n blocks of encoded data from k blocks of source data n such a way that any subset of k encoded blocks suffces at the recever to reconstruct the source data [13] RS code s called an (n, k) code RS code (n, k) s defned over the Galos Feld GF(2 q ) where each block contans q bts The codeword length n s restrcted by n 2 q 1 We choose q to be 8 bts and therefore n 255 Wth ths value for q, encodng and decodng are processed easer Let x = x x k-1 be the source data, G an (k n) generator matrx of the (n, k) RS code, and y the encoded data Then, y s gven by: y = G x (Eq5) G conssts of two parts The frst part s the (k k) dentty matrx I k The second part s an (h h) matrx, wth h=n-k G s gven by (6) 8 k 8 n G : GF(2 ) GF(2 ) x a y = x G, G = [I F ] k k,h wth F k,h = { f r,c } a matrx ( k h) r 1 and f = c, r [ 1,k ], c [ 1,h] (Eq6) r,c When G s used as generator matrx, the blocks of encoded data nclude a verbatm copy of the source It smplfes the reconstructon of source data when few losses are expected B Unequal Error protecton (UEP) usng adaptve RS codes We assgn prorty to each AU to apply an unequal error protecton to the data Prorty reflects both the semantc mportance of the AVO wthn the scene and mportance of partcular vdeo codng structures such as frame type (I, P, B or herarchcal stream f any BL or EL) Of course, UEP ncreases the traffc load due to control overhead To correctly control the volume of transmtted data, we propose to control the proporton of FEC overhead wth a rato parameter called r, for each level of prorty We assume that movng from one level prorty to other ncreases by a 1 percent ths rato So, we chose a scale of 1 levels of prorty (p [99]) Then, the rato r can be defned by: r = 1 p ( Eq 7) Therefore, the traffc overhead s lmted to 1 percent (e, r=1) for the data flow of prorty 1, to 2 percent (e, r=2) for the data flow of prorty 2, to 1 percent for the data flow of prorty 1, and so on Such fne scale provdes a greater granularty for control of the traffc overhead that can be applcable to a large number of meda encodng scheme Let us consder U, the th Access Unt n the flow of prorty p The man block of the proposed UEP s to determne the values n and k n such a way that the (n, k ) RS code s effcent The value k s defned as the number of packets n whch U s broken when no error protecton s performed The value n depends on the prorty p It depends also on the length m of U because the traffc overhead ntroduced by redundant data does not become excessve Once the effcent (n, k ) RS code s found, the codng step begns We also nvestgate packetzaton process known as block of packets that was ntroduced n [14] and adapt t to MPEG-4 Object Plan Data of U s placed n k horzontal packets (S 1, S 2 S k) Each packet has the same sze of t bytes Paddng s added to the last

3 packet f m s not a multple of k Then the (n, k ) RS code s appled across these packets, vertcally We generate h =n -k redundant packets (R 1, R 2 R h) After appendng the RS codes, result packets are transmtted horzontally wth a FEC header Fnally, the packet can be transmtted over RTP FEC header contans both the U sequence number and the values n and k of the RS code In case of packet losses, the decoder needs ths nformaton to decode correctly the receved packets If the number of lost packets s not more than h, then the decoder wll be able to recover U Otherwse, U s completely lost Fgure 1 shows the format of packets sent on the IP network d bytes 4 bytes t bytes IP/UDP/RTP FEC header payload S headers j or R j seq n k Fgure 1: Header nformaton and vdeo packet format In order to fnd the effcent value n for the (n, k ) RS code, we proceed as follow: Let ς U be the reserved byte-budget for error protecton It depends on the number of bytes used to send U when no error protecton s performed It s gven by: ς = r (k d + m ) (Eq U 8) Where d s the packet header sze (e, when RTP s used wth the proposed UEP, d = ( ) = 44 bytes) The relaton between the real byte-budget spent on error protecton, ς U, and the RS code to be used can be stated as follows: ς = n t m + d (n k ) (Eq 9) U The error margn between ς and ς s ς = ς ς, that can be AVO 1 L 1, 1 AVO 2 L2,1 AVO j L j, k AVO n L 1,n Add or Drop Transmsson rate VoD Server + smoothng TFRC Une qual FEC IP Dffserv Marker IP Dffserv Network Object Layers L 1,1 L 1,2 L 1,m 1 L 2,1 RTP L 2,2 RTCP L 2,m2 L n,1 L n,2 L n,mn Audo-Vsual Objects AVO 1 AVO 2 AVO n VoD Clent Fgure 2: The MPEG-4 Vdeo Streamng System Model AVO Composton B Smulaton Model Intensve smulatons are conducted to evaluate our MPEG-4 streamng wth TCP-frendly transport mechansm and error protecton scheme We have used NS2 and we have developed an MPEG-4 Server (NS2 Agent) and an MPEG-4 clent (NS2 Agent) The server reads and sends the dfferent MPEG-4 AVOs found n vdeo trace fles to the clent though the IP Dffserv network We used the network archtecture shown n Fgure 3 to smulate a uncast servce provded by the MPEG-4 server attached to the node S The server sends data to the clent attached to the node C R1 uses A Two Rate Three Color Marker (TR3CM) to mark the background traffc evenly among the dfferent Assured Forwardng class Recall that the MPEG-4 vdeo packets are marked at the source (e, the vdeo server) that knows well the characterstc of each vdeo stream FTP Snk FTP B/packet Mbt/s 1 Mbt/s 5 ms 5 ms 1 Mbt/s 5 ms U U S R1 C U U 1 Mbt/s 5 ms 1 Mbt/s TR3CM postve or negatve It cumulates along the data access unt arrvals MPEG-4 5 ms 1 Mbt/s MPEG-4 Usng the formula (8) and (9), the fluctuaton of the error margn can be wrtten as:, =1 (Eq ς ( n ) = (r +1) m n t + (r k n + k ) d +ς ( n 1 ), > 1 1) To respect the constrant gven on traffc overhead, the best value n s the one that provdes the smallest error margn n formula (1) Then, n s obtaned by: mn ς ( ) n n such that n ℵ, n k, m,k,t Wth the proposed UEP, the RS code evolves dynamcally so the network bandwdth s correctly controlled accordng to vdeo applcaton requrement V PERFORMANCE EVALUATION A IP Vdeo Streamng System archtecture Fgure 2 depcts the proposed MPEG-4 vdeo streamng system It s composed of a vdeo server and clent The server streams MPEG4 vdeo to the end termnal through an IP network usng RTP Two RTP sessons are created, the frst sesson handles AVO stream and the second one handles FEC stream The clent decodes and composes the orgnal MPEG-4 scene based on receved AVO streams and FEC data Each AVO s coded separately so the decodng process decodes also each AVO separately and then the composton module composes the orgnal scene The target transmsson rate of the vdeo server s calculated by the TFRC module Ths nformaton s sent to the add/drop module whch adapts the vdeo transmsson rate usng add/drop algorthms Dffserv Marker module handles the markng of the dfferent RTP Server core R2 1 Mbt/s 5 Mbt/s 5 ms 5 ms 5 ms 2 CBR 4 Null Fgure 3: Network Smulaton Topology Clent C MPEG-4 Vdeo Traffc Characterzaton The MPEG-4 traffc s obtaned from the MPEG-4 trace fle presented n [16] In our smulaton, the MPEG-4 presentaton was obtaned by usng a set of AVOs components We smulate an MPEG-4 scene composed of the followng AVO: (1) AO (audo speech), (2) VO1 (background), (3) VO1 (speaker) and (4) VO3 (logo) These objects are sorted as follows: AO has the prorty 1, t s the most mportant object n ths scene It s marked wth Dffserv PHB AF11 (low drop precedence) VO1 and VO2 have the prorty 2 They are marked wth Dffserv PHB AF12 (medum drop precedence) Each Object s composed of 3 layers (one base layer and 2 enhancement layers) VO3 has the prorty 3, t s the least mportant object n ths scene It s marked wth Dffserv PHB AF13 (hgh drop precedence) Fgure 4 shows the bt-rate of the MPEG-4 vdeo objects that can be sent from the MPEG-4 server to the clent durng a perod of 12 seconds Audo Object Player VO1 BL VO1 EL1 VO1 EL packet wth Dffserv Code Pont before enterng the Dffserv Audo Object Vdeo Object 1 network It mplements and algorthm that better takes nto account VO2 BL VO2 EL1 VO2 EL2 the characterstcs and the relevance of MPEG-4 AVOs Senstve 8 8 data streams wll undergo a processng prvlege from the Dffserv 6 6 routers Most mportant AVOs n the scene are marked wth low 4 4 drop precedence Least mportant AVOs are marked wth hgh drop 2 2 precedence, and so on Vdeo Object 2 Vdeo Object 3 VO3

4 4 Fgure 4: Instantaneous throughput of MPEG-4 AVOs layers Fgure 5: Correctly decoded AVO rato vs Background traffc throughput Packet loss rses when usng our FEC-based UEP because UEP AU types Object Type Prorty ncreases the MPEG-4 packet-stream throughput by 7 % For ths reason, there s more packet losses n scenaro 3 compared to VO1 BL VO1 EL1 VO1 EL2 scenaro 4, for a gven network load However, the redundant UEP Audo Object nformaton better recovers lost packet at the recever Consequently, 8 8 a partcular Access Unt can be restored Falures n the decodng 6 6 process are rather dstrbuted toward the less mportant objects, and 4 4 then UEP reduces the effects of spatal and temporal errors 2 2 propagaton Fgure 5 shows that the decoded object rato of scenaro 3 s always better than scenaro Audo Object Vdeo Object 1 Second measurement concerns only the adaptaton mechansm n case of TCP-frendly transport mechansm Fgure 6 show a scenaro VO2 BL VO3 VO2 EL1 of a network sesson shared wth eght FTP stream and one vdeo VO2 EL2 8 8 streamng sesson FTP starts streamng at tme t=3s and stops at tme t=9s We can see n ths Fgure that the network resources are 6 6 farly shared among the dfferent connectons The mportant AVO s always present Vdeo Object 3 s present when there are suffcent resources n the network Vdeo Object 2 Vdeo Object 3 Base Layer, I-frame Vdeo p=2 EL1 Layer, P-frame Vdeo p=1 EL2 Layer, B-frame Vdeo p= Voce Sample Audo p= The table above shows the prorty level of each AU Wth respect to ths error protecton polcy, the nserton of redundant data generates a global network traffc overhead equal to 7 % n ths scene D Smulaton Scenaros We perform smulatons wth dfferent parameters accordng to these scenaros: Scenaro 1: our proposed combned error protecton scheme (e, AVO protected wth Unequal Error Protecton and transmtted over IP Dffserv Network usng TCP-frendly mechansm) Both mechansms are based on AVOs prortes Scenaro 2: AVO (wthout error protecton) transmsson over IP Dffserv and wthout TCP-frendly mechansm Scenaro 3: AVO transmsson usng Unequal Error Protecton (based on the descrbed prorty) usng TCP-frendly Transport mechansm (TFRC) Scenaro 4: AVO transmsson wthout any error protecton usng TCP-frendly Transport mechansm (TFRC) In each scenaro, we vary gradually the network load by CBR traffc and by usng n FTP traffc each tme n order to get more nformaton on the behavor of the dfferent mechansms E Results Analyss In order to hghlght the effcency of our combned error protecton scheme, we perform three measurements The frst measurement concerns the worthness of FEC-based unequal error protecton (UEP) We study the contrbuton of ths mechansm on error reslence assocated to each AVO Fgure 5 shows the results of the comparson between the decoded object rato for scenaro 4 (no error protecton) and scenaro 3 (UEP) The X-axs represents the throughput of the background traffc As expected, the quantty of the AVOs decoded at the recever sde decreases when the network load ncreases because t entals more packet losses Decoded Object Rato No Error Protecton FEC-based UEP Background Traffc (Mbt/s) MPEG-4 FTP1 FTP2 FTP3 FTP4 FTP5 FTP6 FTP7 2 FTP Fgure 6: Effect of the Source Rate adaptaton mechansm The contrbuton of TCP-frendly mechansm on error protecton assocated to each AVO s also consdered In scenaro 1 1% of packets loss were recovered by our UEP scheme In ths case, DffServ network provdes a dfferentated level of QoS for each vdeo stream dependng to ts prorty class It s vsble for these scenaros that the losses happen manly on the lower prorty streams (e, O1 and some background traffcs whch are marked wth hgh drop precedence) When best effort servce s used, loss approxmately follows a unform dstrbuton Ths s due to the IP best Effort routers that use Drop Tal queue management polcy When the queue s full, all the ncomng packets are dropped wth the same probablty In contrast, DffServ network provdes a dfferentated level of QoS for each stream dependng to ts prorty class VI CONCLUSION We descrbed a new adaptve vdeo streamng framework for delverng MPEG-4 content over next generaton IP networks wth dfferentated servces support MPEG-4 vdeo streams based on Audo Vsual Objects (AVOs) are automatcally classfed, packetzed and streamed over the network accordng to data semantc relevancy and network resource avalablty Combned wth a FECbased Unequal Error Protecton and a TCP-frendly transports mechansm, the proposed vdeo streamng system shows a sgnfcant mprovement regardng to user-perceved qualty, packet loss recovery and bandwdth share farness REFERENCES [1] T Ahmed, G Burdant, A Mehaoua, Delverng of MPEG-4 Multmeda Content Over Next Generaton Internet, IFIP/IEEE MMNS, October 21 [2] J Shn, J Won Km and C-C Jay Kuo, Content-Based Packet Vdeo Forwardng Mechansm n Dfferentated Servce Networks, IEEE PV, May 2 [3] M Albrecht, M Köster, P Martn, M Frank, End-to-end QoS Management for Delay-senstve Scalable Multmeda Streams over DffServ, n Proc 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