UDP Lite for Wireless Video Streaming Amoolya Singh, Almudena Konrad, 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 MultiTracer SocketDUMP RLPDUMP Plotting & Analysis (MATLAB) UDP / UDP Lite Socket Interface H.263+ Encoder RTP IP PPP Packetization RTP UDP / UDP Lite IP PPP De-packetization H.263+ Decoder Socket Interface Fixed Host Unix BSDi 3.0 GSM Base Station GSM Network PSTN Mobile Host Unix BSDi 3.0 SocketDUMP RLP / non RLP

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) UDP Lite (Larzon, Degemark, and Pink) source port # dest port # length / coverage checksum

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) Physical / Radio Link Layer (GSM 9.6 kb/s)

Channel Simulator: WSim WSim Wireless Error Trace Input Video Stream Output Video Stream Allows “easy” performance study of UDP-Lite, and error resilience functionalities Simulates two protocol configurations: –UDP, non-RLP and UDP Lite, non-RLP Uses 215 min of GSM wireless error traces collected in a poor channel environment

Experiment Collect 4480 min of wireless video traces, (~4 min per video) –Bad channel conditions (signal strength ~2-3) Three different network configurations –UDP, RLP –UDP, non-RLP –UDP-Lite, non-RLP 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 Performance Analysis

Experimental Results

End to End Delay

Inter-Arrival Time

Packet Loss

Video Screenshots UDP UDP Lite Experiment Simulation UDP 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 In general, can choose protocol combination appropriate for application UDP Lite /non-RLP Adaptive real-time: vic, vat UDP / RLP Hard real-time: wb, v-conf tolerant & daptive * UDP / RLP Interactive: telnet, web TCP / RLP Protocol ChoiceType of Application Batch: , ftp Example intolerant & rigid *

Provide real-time feedback on channel conditions Provide rate control Incorporate unequal error protection for MPEG4 Future Work