COMP 249 Advanced Distributed Systems Multimedia Networking Performance of Multimedia Delivery on the Internet Today Kevin Jeffay Department of Computer Science University of North Carolina at Chapel Hill jeffay@cs.unc.edu November 9, 1999 http://www.cs.unc.edu/~jeffay/courses/comp249f99 1 Performance on the Internet Today Outline Internet u A prototypical videoconferencing system» Architecture» Quality-of-service requirements u Performance metrics» Understanding end-to-end latency u Some typical experimental results u Conclusions? 2
Performance on the Internet Today conferencing performance requirements Internet u No more than 25 ms end-to-end, one-way latency u Continuous audio u Minimum of 1 frames per second video throughput u Loosely synchronized playout ± 8 ms skew 3 conferencing Performance Requirements Understanding end-to-end latency Transmit/ Digitize Compress Synchronize Decompress Display Frame n Frame n+1 Frame n+2 33 66 1 133 167 2 Time Sender s Pipeline Receiver s Pipeline 4
Understanding End-to-End as a measure of continuity of playout Digitize Compress Transmit/ Synchronize Decompress Display Frame n Time 33 66 1 133 167 25 2 15 1 5 5 1 15 2 25 3 35 4 Time (in 33 ms frame-times) 5 Understanding End-to-End as a measure of continuity of playout Acquisition Pipeline Transport System Sending Digitization Compression... Network Transport Network Driver Driver Sender Display Pipeline Transport System Receiving Display Display Decompressioression... Network Transport Network Driver Driver Receiver 6
Understanding End-to-End as a measure of continuity of playout Digitize Compress Transmit/ Synchronize Decompress Display Frame n Time 33 66 1 133 167 25 2 15 1 5 Combined Sender/Receiver Hardware Pipeline 5 1 15 2 25 3 35 4 Time (in 33 ms frame-times) 7 Understanding End-to-End Audio performance u To provide lip synchronization, audio must be delayed to wait for video Processing Digitize Compress Transmit Decompress Display Audio Processing Time 1 2 3 4 5 6 1 2 3 4 5 6 acquisition/ Transmit playout compression 33 66 1 133 167 8
Understanding End-to-End as a measure of lip synchronization Audio 25 2 15 1 5 Combined Hardware Pipeline 5 1 15 2 25 3 35 4 25 2 15 1 5 Combined Sender/Receiver Hardware Pipeline 5 1 15 2 25 3 35 4 Time (in 33 ms frame-times) 9 Understanding End-to-End as a measure of delay-jitter u Delay-jitter increases playout latency latency = p latency = 3p Sender Receiver Display initiation points Playout gaps 1
Understanding End-to-End as a measure of delay-jitter u Recall that actual playout time is not a function of the arrival time, only of the end-to-end delay» The key application decision is how long to delay the initial sample prior to playout Sender NTP clock RTP clock t Receiver Receive Playout RTCP Message t RTP Message sample generation time + local clock synchronization correction sender packaging delay network delay + + + jitter-buffer delay = sample playout time end-to-end latency 11 Understanding End-to-End as a measure of delay-jitter Sender Receiver 4 3 2 1 Combined Hardware Pipeline 25 5 75 1 125 15 175 2 Time (in 66 ms frame-times) 12
Understanding End-to-End Network v. application latency 4 3 2 1 Combined Hardware Pipeline 25 5 75 1 125 15 175 2 Delivery 4 3 2 1 Combined Hardware Pipeline 25 5 75 1 125 15 175 2 Time (in 66 ms frame-times) 13 Network v. Application Is application induced latency bad? 4 3 2 1 Combined Hardware Pipeline 25 5 75 1 125 15 175 2 Audio 4 3 2 1 Media Acquisition Pipeline 25 5 75 1 125 15 175 2 Time (in 33 ms frame-times) 14
conferencing on the Internet Today ProShare TM performance on the Internet 4 35 3 25 2 15 1 16 14 12 1 8 6 4 2 5 Throughput (frames/sec) Audio 1 2 3 4 5 6 Packet Loss Packet Loss 1 2 3 4 5 6 Audio 8 Audio 7 6 5 4 3 2 1 1 2 3 4 5 6 8 7 6 5 4 3 2 1 1 2 3 4 5 6 15 conferencing on the Internet Today ProShare TM performance on the Internet 4 35 3 25 2 15 1 8 7 6 5 4 3 2 1 5 Throughput (frames/sec) Audio 1 2 3 4 5 6 Packet Loss 1 2 3 4 5 6 8 7 6 5 4 3 2 1 1 2 3 4 5 6 8 Audio 7 6 5 4 3 2 1 1 2 3 4 5 6 16
conferencing on the Internet Today What s the problem? u Where is data being delayed and lost? Internet 17 conferencing on the Internet Today What s the problem? u Do we need more bandwidth or just better management of the existing bandwidth? Requirements (performance, scale) insufficient Internet sufficient but scarce abundant 198 199 2 Hardware in year X 18
Where do we go from here? Two fundamental approaches insufficient sufficient but scarce abundant u Provide true quality-of-service through reservation of in the network» Requires coordination amongst all parties v admission control v policing v... u Provide best-effort service by adapting media streams» Monitor & provide feedback on performance» Bias transmission and processing of media to ameliorate the effects of congestion 19