Methods of Handling Packet Loss for Multimedia Applications

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Methods of Handling Packet Loss for Multimedia
Applications

• by Hansen Bow

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Contents

• Introduction
• Sender Methods
• Receiver Methods
• Interactive Methods

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Introduction

• Channels can introduce bit and erasure errors
• Variable length coding can be desynchronized
• MPEG-2
• 15 pictures in GoP
• loss in one frame messes up rest of frames in
  group
• cannot really use TCP protocol because results in
  sawtooth patterns in transmission rate

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Sender-Based Repair

• Forward Error Correction
• Interleaving
• Retransmission

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Forward Error Correction

• Media independent
• block or algebraic codes
• Media dependent
• primary and secondary encoding
• multiple description coding
• joint source and channel coding
• robust waveform and entropy coding
• Congestion Control
• layered encoding sent to different groups

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Interleaving

• Prerequisite
• Unit size smaller than packet size
• Units interleaved at encoder and returned to
  order at decoder
• Disperses effect of packet losses

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Retransmission

• only host closest to failure issues request
• subsidiaries repress request to avoid implosion

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Error Concealment

• Insertion-based repair
• Interpolation-based repair
• Regeneration-based repair

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Insertion-based repair

• Splicing together of streams
• Silence substitutions
• Noise substitution
• Repetition

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Interpolation-based repair

• Account for changing characteristics of signal
• Motion-compensated temporal prediction
• maximally smooth recovery
• Time scale modification

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Regeneration-based repair

• Based on compression algorithm
• one way DC and lowest five AC coefficients
  estimated from top and bottom of neighboring
  blocks rest forced to zero

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Interactive modes

• Adjusting transmission rate according to feedback
  information
• withdraw congestion before packet loss
• Selective encoding
• tell encoder locations of damaged parts
• encoder adapts encoding strategy to match with
  prediction
• Retransmission without waiting
• interpolation at decoder during retransmission
• reverse calculate what current scene is when
  encoder information arrives