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UDP Lite for Wireless Video Streaming Almudena Konrad, Amoolya Singh, and Anthony Joseph University of California, Berkeley Jun 19, 2000 Idea Problem • Current Internet doesn’t support bit error resilient codecs Goal • Support real-time streaming applications over noisy channels, such as wireless Proposed Solution • Provide link/transport layer alternatives to support error resilient video codecs Testbed, Protocols, Tools H.263+ Encoder H.263+ Decoder Packetization De-packetization RTP RTP Socket Interface Socket Interface UDP / UDP Lite UDP / UDP Lite IP IP PPP PPP transparent / non transparent transparent / non transparent GSM Network Mobile Host Unix BSDi 3.0 PSTN Fixed Host Unix BSDi 3.0 GSM Base Station SocketDUMP SocketDUMP MultiTracer RLPDUMP Plotting & Analysis (MATLAB) UDP Lite (Larzon, Degemark, and Pink) • Flexible checksumming scheme allows corrupted data to be transmitted to the application • “length” field in UDP header replaced by “coverage” field • Specifies how many bytes of payload to checksum • Implemented in BSDi 3.0 kernel (Keith Slower) 0 7 8 source port # length / coverage 15 dest port # checksum Physical / Radio Link Layer (GSM 9.6 kb/s) Transparent Mode • no error control mechanism Non-Transparent Mode • Uses RLP (Radio Link Protocol), a semi-reliable ARQ protocol – Link resets after N=7 number of re-transmissions • Fixed frame size of 30 bytes (6 bytes header) – Reliability at the cost of additional end-to-end delay • Window size of 62 frames • Error recovery mechanisms – Select - Reject (initiated by receiver) – Checkpointing (initiated by sender) Channel Simulator: WSim Wireless Error Trace Input Video Stream WSim Output Video Stream • Allows “easy” performance study of UDP-Lite, and error resilience functionalities • Simulates two protocol configurations: – UDP, non-transparent and UDP Lite, transparent • Uses 215 min of GSM wireless error traces collected in a poor channel environment Performance Analysis Experiment • Collect 4480 min of wireless video traces, (~4 min per video) – Bad channel conditions (signal strength ~2-3) • Three different network configurations – UDP, non-transparent – UDP, transparent – UDP-Lite, transparent • For each trace, we calculated metrics – end-to-end, inter-arrival time ,loss rate and throughput • For each metric, we calculated statistics – mean & std dev Simulation • Run Wsim on “mom” video stream using a wireless error trace of 1.5% BLER Experimental Results End to End Delay 2.5 Mean & Std Dev End-to-End Delay (s) 2.0 1.726 1.5 1.0 0.511 0.5 0.377 0.0 UDP, non-transparent UDP, transparent UDP Lite, transparent Inter-Arrival Time 0.70 Inter-arrival Time (s) Mean & Std Dev 0.65 0.60 0.601 0.594 0.597 0.55 0.50 UDP, non-transparent UDP, transparent UDP Lite, transparent Packet Loss Mean & Std Dev Packet Loss (%) 3% 2.09% 2% 1.05% 1% 0.00% 0% UDP, non-transparent UDP, transparent UDP Lite, transparent Video Screenshots Experiment UDP Simulation UDP UDP Lite UDP Lite Discussion & Conclusions • Reliability at link layer causes delay • Strict checksumming of UDP causes poor “error resilience” at application • UDP Lite (with GSM in transparent mode) provides – less end to end delay – constant jitter – higher throughput – lower packet loss … than UDP (with GSM in non-transparent mode) • In general, can choose protocol combination appropriate for application Type of Application intolerant & rigid* tolerant & daptive* Example Protocol Choice Batch: email, ftp TCP / RLP Interactive: telnet, web UDP / RLP Hard real-time: wb, v-conf UDP / RLP Adaptive real-time: vic, vat UDP Lite /transparent Future Work • Provide real-time feedback on channel conditions • Provide rate control • Incorporate unequal error protection for MPEG4