Wenyu Jiang , Henning Schulzrinne 2002.11.12 이주경 Comparison and Optimization of Packet Loss Repair Methods on VoIP Perceived Quality under Bursty Loss Wenyu Jiang , Henning Schulzrinne 2002.11.12 이주경

Abstract VoIP Gilbert loss model Packet loss degrades the perceived quality of voice of IP Packet loss tends to come in bursts Gilbert loss model Packet interval FEC, LBR Present a method of optimizing the packet interval

Introduction Packet Loss Repair and Recovery FEC LBR(Lower Bit-rate Redundancy) Redundant data but lower quality version of the same audio MOS(Mean Opinion Score) Common VoIP quality metric 1 ~ 5 :bad, poor, fair, good, excellent

LOSS MODELING The Gilbert Model

LOSS MODELING(con’t) Loss Burstiness vs. FEC Performance

LOSS MODELING(con’t)

Related work : THE E-MODEL Analytical model for predicting voice quality Impairment factor Delay, loss, echo, loudness, frequency Each factor is mapped to a score

MOS TEST EXPERIMENT DESIGN Object Random vs. bursty(Gilbert) loss model Compare FEC and LBR, mostly under Gilbert loss MOS with or without FEC under a wide range of loss probabilities(pu), loss burstiness(pc) and packet intervals(T)

MOS TEST EXPERIMENT DESIGN Design of an Optimal LBR mechanism LBR Main audio codec decoder state drift Packet alignment order - optimized LBR Main audio codec packet loss시 Redundant audio decoding Reencoding it using a duplicate main encoder Finally decoding it again using the main decoder Packet alignment order

MOS TEST RESULTS Test Set N1: Random vs. Bursty Loss FEC(R) FEC(R) LBR(R) FEC(B) FEC(B) LBR(R) LBR(B) LBR(B) LBR(optimal) LBR

MOS TEST RESULTS(con’t) Test N1 : Quality of FEC vs. LBR AMR+LBR Figure 13 - MOS(FEC) > MOS(LBR) - bit exact form - sudden switch between low and high audio quality Figure 14 - FEC(2,1) code has best quality

MOS TEST RESULTS(con’t) Test N2 : MOS Quality vs. Loss Burstiness and Packet Interval Without FEC Different Packet interval (a), (b) Different Burstness (c), (d)

MOS TEST RESULTS(con’t) Test N2 : MOS Quality vs. Loss Burstiness and Packet Interval MOS of FEC vs. Packet Interval T

MOS TEST RESULTS(con’t) Comparison with the E-model MOS R value R= 92.4- Id - Ie

MOS TEST RESULTS(con’t) Optimizing Packet Interval with Delay Impairment

Conclusion and Future work Evaluation study on the effect of random and bursty packet loss Generally : MOS(random loss) > MOS(bursty loss) MOS(FEC) vs. MOS(LBR) Larger packet interval improves FEC quality Based on E-model Trade off between FEC delay and listening quality Future Work Determining the reason of MOS test results Accurate FEC MOS test FEC : bandwidth overhead and delay