1. V. Fodor and Gy. Dan, KTH - Marholmen 2002 End-to-end control for audio-visual communication Viktoria Fodor and György Dán Laboratory for Communication Networks, KTH/IMIT {viktoria,gyuri}@it.kth.se

2. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Outline Overview of audio-visual communication, requirements of QoS provisioning The end-to-end argument Source shaping in networks with small buffers quality differentiation with forward-error correction Future plans

3. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Problem definition Audio-visual communication requires limited packet loss probability, end to end delay and jitter Audio-visual traffic can not be served as best effort How to provide QoS guarantees? –Considering the existing Internet architecture –Following the end-to-end argument

4. V. Fodor and Gy. Dan, KTH - Marholmen 2002 The end-to-end argument Help to define new control functions for new applications (Saltzer, Reed and Clark, ‘81) Control functions: implemented fully inside the network for all traffic necessary for acceptable performance future proof - does not limit future applications Control functions: can not be solved inside the network application specific

5. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Proposed solution Inside the network: –dedicated capacity for a limited set of service class, thus per class scheduling at the routers best effort controlled load - typically for audio-visual communication guaranteed service –separate buffers for the service classes controlled load: small buffers to limit delay and jitter At the network edge - for audio-visual communication: –probe based admission control to limit loss probability (Prof. Gunnar Karlsson, Ingnacio Mas) –traffic control functions to improve performance

6. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Control functions Source shaping Forward-error correction Optimization problem: –there is a limited delay control functions can utilize ({end-to-end delay limit} - {network delay}) –performance of the control functions is proportional to the introduced delay –how to allocate delay to the control functions? performance of source shaping performance of forward-error correction with and without shaping

7. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Source shaping To limit burstiness (peak rate) and thus increase the efficiency of buffering at the nodes Simplest shaper: leaky bucket Introduced delay:  shaper buffer (p,m)(c, p>c>m) B

8. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Performance - source shaping Traffic mix (MPEG) with and without shaping Source shaping can decrease the average loss probability with many orders of magnitude with delay of 20-100ms Shaped flows have lower packet loss probability, ca. half of the loss of unshaped flows at the interesting loss levels

9. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Performance - source shaping Shaped sources have more even loss distribution: –consecutive losses –losses in block of packets –losses in different frame types Shaping improves quality: –decreased average loss –improved loss distribution Relative loss (I) = loss in I / average loss

10. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Forward-error correction Add error correction to a block of packets and regenerate lost packets at the receiver Introduced delay: ~ the block+code size Also increased network load (  increased loss probability) information error code

11. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Performance - forward-error correction Traffic mix with different error correcting capability Error correction provides solution for quality differentiation (with the cost of higher source rate)

12. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Conclusion Efficient audio-video transmission might be possible in networks with little control at the nodes Suggestions – capacity allocation for different service classes –one class for delay and loss sensitive traffic end to end call admission control to limit loss use of small buffers inside the network to limit delay control mechanisms at the edge (shaping + forward error correction) to increase efficiency

13. V. Fodor and Gy. Dan, KTH - Marholmen 2002 Further work Forward-error correction and shaping –mathematical model to combine the two functions Adaptive forward-error correction –with fixed peak rate, changing the source coding rate (signal processing) –with feedback from the destination (control theory)