1. Effect of FEC mechanisms in the Performance of Low Bit Rate Codecs in Lossy Mobile Environments Rolando Herrero, PhD Northeastern University, Boston, MA, U.S.A. Martin Cadirola, Director/VP Business Development Ecotronics Ventures LLC, Clarksburg, MD, U.S.A.

2. Background  Developers of Kapanga (Voice/Video/Fax SIP client)  Field work with OEM, QA and military environments  Collaboration with academia © 2014 - IPT Communications Conference - September 29, 2014

3. Motivation © 2014 - IPT Communications Conference - September 29, 2014

4. Motivation © 2014 - IPT Communications Conference - September 29, 2014 Voyager 1 -Launched in 1977 -130 AU from the Sun -14 hours to Tx/Rx -38,000 mph = 61,000 kph

5. Motivation © 2014 - IPT Communications Conference - September 29, 2014 HOW?FEC!

6. Mobile Networks © 2014 - IPT Communications Conference - September 29, 2014 Source: http://www.ice.rwth-aachen.de/ -Multipath loss -Slow/Fast fading channels -Applicable in RT over 3G/4G/LTE Use of Forward Error Correction (FEC) techniques in media transmission are critical here too!

7. Motivation  Mobile networks  Interest in creating real-time QA tools  Room for innovation in improving performance © 2014 - IPT Communications Conference - September 29, 2014

8. Motivation  Work based on Barton, Lemberg, Sarraf, Hamilton, “Performance analysis of packet loss concealment in mobile environments”, in Communications Quality and Reliability (CQR), 2010 IEEE International Workshop Technical Committee.  Network impairments in mobile networks are mostly due to fading, especially in high multipath environments  The characteristics of fading channels are a well known phenomenon and their statistics have been modeled mathematically by a two-state Markov process © 2014 - IPT Communications Conference - September 29, 2014 How do LBR codecs perform in such a mobile network? How can we assess quality of speech?

9. Theoretical Model: Markov Process  2-state Markov Process models a fading channel mobile network environment © 2014 - IPT Communications Conference - September 29, 2014 Model has 2 states: High Packet Loss State (H) Low Packet Loss State (L) Model has 5 parameters: Transition probability from low to high loss states (p) Probability that the channel stays in a high loss state (α) Distance between an RTP packet and the transmission of the corresponding FEC RTP packet in packet times (D) Packet loss probability when the channel is in the low loss state (β) Packet loss probability when the channel is in the high loss state (γ)

10. Experimental Framework  We implemented 2 kinds of FEC techniques in the UA  XOR-based  Optimal for lower bandwidths  Repetition-based  Best quality for higher bandwidths  Assumptions wrt Markov process: β = 0 and γ = 1  All RTP packets are dropped in the high loss state  No RTP packets are lost in the low loss state © 2014 - IPT Communications Conference - September 29, 2014

11. A little FEC background © 2014 - IPT Communications Conference - September 29, 2014 Pn 160 bytes Speech Packet Repetition-based FEC … 160 bytes320 bytes P2 P3 320 bytes P1 XOR-based FEC 160 bytes P1P2 … RTP Payload RTP Header RTP Packet P2-P1 160 bytes For each packet (on each case) P3-P2 P3 160 bytes

12. Experimental Framework  Modify a SIP UA to implement FEC mechanisms under study  Setup UA with Linux box running Netem  Use ITU-based speech waveforms *no tones nor signals*  Use of G.723.1, G.729A, AMR-NB, AMR-WB, EVRC, SILK, Opus © 2014 - IPT Communications Conference - September 29, 2014

13. Experimental Framework  Netem takes the transition probabilities of the two-state Markov model, namely α and p, as input parameters  In order to validate different bursty scenarios the following combination of parameters is considered; α = 0.01, 0.05, 0.1 and 0.15 and p = 0.25, 0.5 and 0.75  In order to minimize latency, in part due to the restrictions imposed by playout buffers in regards to tolerable speech quality, the packet distance between the transmitted RTP and the FEC RTP is D = 2 © 2014 - IPT Communications Conference - September 29, 2014

14. Comparative Analysis © 2014 - IPT Communications Conference - September 29, 2014 Bursty Packet Loss (Repetition-based FEC)

15. Comparative Analysis © 2014 - IPT Communications Conference - September 29, 2014 Bursty Packet Loss (XOR-based FEC)

16. Comparative Analysis © 2014 - IPT Communications Conference - September 29, 2014 Rate-Distortion (for a set of α and p)

17. Conclusions  We presented a framework to evaluate and compare the experimental and theoretical performance of RTP FEC applied to a set of narrowband and wideband codecs in a lossy mobile environment  It can be verified that the experimental probability of success of an endpoint receiving an RTP packet is within 15% of the analytical value (error) obtained by modeling the system with a two-state Markov process  Speech quality scores, based on PESQ and PESQ-WB metrics, follow the probability of decoding success for both when repetition FEC and XOR FEC schemes are used © 2014 - IPT Communications Conference - September 29, 2014

18. Conclusions  When put in the context of rate-distortion plots narrowband codec G.723.1 and wideband codec Opus provide better performance by decoding same quality speech at lower transmission rates  Although the probability of success (from the theoretical model) does not take into account the codec type nor the characteristics of the playout mechanism it provides a good approximation to estimate the overall quality of the communication  When comparing XOR-based vs Repetition-based FEC it is clear that the latter gives better media quality at the cost of significantly increasing the transmission rate  FEC and other error correcting techniques offer improvements to the quality of *any* real-time media application: RTC, any rtp-based communications © 2014 - IPT Communications Conference - September 29, 2014

19. Next Steps  Challenges (as any new technology) -> standarization, unless everybody uses one kind of UA  Continue research on new FEC mechanisms (TurboCodes, Reed Salomon)  Utilization of these techniques in:  UAV communications for civilian and military fields  LTE deployments overseas  Space applications © 2014 - IPT Communications Conference - September 29, 2014 Earth Science Drones/UAV/UAS

20. Thank you! Q & A! © 2014 - IPT Communications Conference - September 29, 2014