Methods of Handling Packet Loss for Multimedia Applications by Hansen Bow

Contents Introduction Sender Methods Receiver Methods Interactive Methods

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

Sender-Based Repair Forward Error Correction Interleaving Retransmission

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

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

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

Error Concealment Insertion-based repair Interpolation-based repair Regeneration-based repair

Insertion-based repair Splicing together of streams Silence substitutions Noise substitution Repetition

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

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

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