1. 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
이주경

2. 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

3. 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

4. LOSS MODELING
The Gilbert Model

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

6. LOSS MODELING(con’t)

7. 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

8. 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)

9. 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

10. 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

11. 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

12. 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)

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

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

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

16. 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