UDP Lite for

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UDP Lite for Wireless Video Streaming
Almudena Konrad, Amoolya Singh, and
Anthony Joseph University of California,
Berkeley Jun 19, 2000
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Idea

• Problem
• Current Internet doesnt 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

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Testbed, Protocols, Tools
H.263 Encoder
Socket Interface
UDP / UDP Lite
transparent / non transparent
transparent / non transparent
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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)

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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 N7 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)

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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

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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

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Experimental Results
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End to End Delay
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Inter-Arrival Time
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Packet Loss
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Video Screenshots
Experiment
UDP UDP Lite
Simulation
UDP UDP Lite

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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

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