Extending an Open Media-Streaming Platform to Support Differentiated ServicesS.Zoi D. LouKatos, P. Papageorgiou, P. Stathopoulos, N.Mitrou Ece Department National Technical University of AthensGreece
OutlineIntroductionRelated WorkDiffServ Aware Architectural ExtensionsQuality Evaluation MetricsExperimental Evaluation of the Enhanced Platform on a DiffServ Lab TestbedFuture Work
IntroductionState-of-the-art multimedia technology gives the potential to author complex networked multimedia applications, composed of multiple media streams.Although network level QoS do exist, the deployment of QoS mechanisms to such applications is still very limited.This is mainly because the definition of portable QoS specifications is still an open issue.
Introduction (contd.)There are several application level QoS frameworks have appeared so far (e.g. DMIF and Winsock 2 API), but studies are restricted to single stream traces, and simulated networks.What is needed is the ability of the application to define its own quality parameters, in such a way that perceived quality is also captured.
Introduction (contd.) Best-Effort - Best-Effort does not provide QoS, because there is no reordering of packets. Differentiated Services (DiffServ) - DiffServ, as the name suggests, differentiates between multiple traffic flows. Integrated Services (IntServ) - IntServ is often referred to as Hard QoS, because it can make strict bandwidth reservations. Needs signaling first. Must be configured on every router along a path. QoS Services
Introduction (contd.)In order to support the quality of differentiated service in the IP network, DS Field (DiffServ Field) was proposed by IETF in RFC2427.
DSCP : DiffServ CodepointCU : Currently Unused
- Introduction (contd.)The DiffServ network uses DSCP to classify data packets and forwarding them according to the corresponding PHB (Per Hop Behavior).IETF has proposed three kinds of PHB : DF (Default Forwarding) PHB - also called Best-Effort , DSCP : 000000 EF (Expedited Forwarding) PHB - also called Premium service , DSCP : 101110 AF (Assured Forwarding) PHB - AFij , 1
Related WorkThe differentiated Services (DiffServ) framework supports the differentiation of packets, not only belonging to different competitive streams, but also within the same stream.This is achieved by marking the ToS byte of each packet header.
Related Work (contd.)In MPEG-4 encoding, high compression is achieved at the cost of low error resistance and several error resilience mechanisms are foreseen by the standard such as resynchronization and data partitioning. resynchronization
Related Work (contd.)At user level, perceived quality is evaluated by using subjective methods. However, these can be costly, and time-consuming to give quantifiable results.In the case of audio a set of methods of quality evaluation have been proposed, and they are take into human psychoacoustics.In the case of video, many evaluation of the pictures based on the Peak Signal-to-Noise Ratio (PSNR).
Related Work (contd.)MPEG4IP The MPEG4IP project is an open-source platform, incorporation additional open source tools from other parties. The client side mainly comprises the player and the decoders, while the server side comprises the following components : - A toolkit for off-line encoding of MPEG-4 compatible streams. - An application (mp4live) for capturing, real-time encoding and streaming video and audio content. - A streaming server, the open source Apple`s Darwin Streaming Server (DSS)
DiffServ Aware Architectural ExtensionsThe QoS Framework for real application -QCompiler is adopted in this work.
DiffServ Aware Architectural Extensions (contd.)High-level application specification layer user quality are defined, for example High, Medium, and Low.
With a quality study component has been developed inside the MPEGIP platform, QoS violation effects (e.g. losses, delays) can be simulated and previewed on a media stream before this is transmitted to the network.
DiffServ Aware Architectural Extensions (contd.)Next, the quality degradation observed in a pre-encoded video stream, in the following scenarios : Scenario 1 (no error resilience) : The 5th packet of the first I frame is lost. Scenario 2 (no error resilience) : The last packet of the first I frame is lost. Scenario 3 (with error resilience) : The 5th packet of the first I frame is lost. Scenario 4 (with error resilience) : The last packet of the first I frame is lost. Scenario 5 (with error resilience) : The last packet of the 3rd P frame is lost.
DiffServ Aware Architectural Extensions (contd.)
DiffServ Aware Architectural Extensions (contd.)The Metadata Compilation Layer and the Binding Layer In order to enhance mp4live application with packet differentiation extensions, a dedicated marking component was implemented. This component is capable of differently labelling parts of the produced bitstream with arithmetic values corresponding to different quality levels. This values will be assigned to the corresponding packets as ToS values by the binding layer, during packetization.
DiffServ Aware Architectural Extensions (contd.)VOP : Video Object Plane
DiffServ Aware Architectural Extensions (contd.)The Run-Time Metadata execution layer metadata descriptions are parsed and different QoS levels are assigned to different network classes, i.e. ToS mapping to DifferServ classes.
Quality Evaluation MetricsIt becomes apparent that packet level metrics (e.g. % packet loss rate) cannot give an accurate estimation of the final perceived quality.In the case of video, spatial and temporal effects of losses on frames are of interest to map user perceived quality.
Quality Evaluation Metrics(contd.)In the case of Internet telephony, the perceived quality after bursty packet losses is often worse than when the occurrences of these losses are adequately spaced.To address this problem, the finite horizon QoS criterion call (m,k)-firm guarantee was proposed.In the case of video streams, the (m,k) criterion is meaningless at packet level. On the contrary it is meaningful at frame level, as the frame is the entity mostly perceived by human eye.
Experimental Evaluation of the Enhanced Platform on a DiffServ Lab TestbedExperiments Platform topology
MPEG4IP QoS extention DSS a DiffServ enabled router (AF PHB implemented) MPEG4IP QoS extention
Experimental Evaluation of the Enhanced Platform on a DiffServ Lab Testbed (contd.) Encoding parameters of a video stream : Frame rate :10fps, Resolution : 176 X 144, Encoding rate : 500kbps
Experimental Evaluation of the Enhanced Platform on a DiffServ Lab Testbed (contd.)The video stream encoded with and without error resilience, is experimentally evaluated under Best Effort and DiffServ configurations.Error resilience mechanisms are based on resynchronization markers, for I frames and data partitioning for P frames.
Experimental Evaluation of the Enhanced Platform on a DiffServ Lab Testbed (contd.)Queue statistic
Conclusions and Future WorkMore sophisticated packet-marking policies for unequal protection based on stream semantics, such as objects extracted with video segmentation algorithms will be explored.The use of metadata descriptions for defining portable QoS specification will also be explored within this QoS framework based on content description technologies, such as XML.
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