Performance Evaluation of VoIP in Different Settings Tom Christiansen Ioannis Giotis Shobhit Raj Mathur

Outline How does VoIP work in the Internet today? How is VoIP quality measured? Which network parameters affect the performance of VoIP? How does the speech quality of VoIP depend on these parameters? How can the existing VoIP technology be improved?

How does VoIP work? Audio Sampling Audio Encoding Codec Network Protocol Audio Decoding Network Protocol 128 kbps RTP over UDP 5 – 30 kbps

VoIP Quality Metrics Signaling quality  Measure of the call setup performance Delivery quality  Latency  Jitter  Packet Loss Call quality  Perceived quality E-model – Analytical model which generates an R-value MOS (Mean Opinion Score) – Related to the R-value

VoIP Quality Metrics R-valueMOSUser satisfaction 5Even better than the real thing Like calling next door A decent phone call Some users dissatisfied Many users dissatisfied Tin cans and a string 2Can you hear me now ? 1Try the Pony Express instead

VoIP Measurements Using Brix Networks’ VoIP testing tool A total of 600 experiments were run over a period of two weeks. Types of networks  UW Gigabit Ethernet  Wireless at UW  Cable (Comcast)  Dial-up from home Destinations  Boston  Helsinki  London  Montreal  San Jose  Sydney

Quantifying the quality degradation UW LAN average MOS, G.711Cable average MOS, G average MOS, G.729Dial-up average MOS, G.729

Traceroute Analysis Edges are the bottlenecks in today’s Internet.  Last hop delay in the case of a dialup connection is the same as the intercontinental delay! On slow networks like dialups, an increase in the geographical distance degrades the MOS due to higher latency. UW LAN to LondonDial-up to London

What we can conclude LAN>Cable>802.11>dial-up, as expected. LAN and cable are great !  Negligible degradation due to the network Dial-up is somewhat useable.  Main cause of degradation is latency, caused due to the delay over the last hop is in-between and has lots of issues.  Main cause of degradation is packet discards (delayed packets and garbled packets). Other traffic causes serious degradation even on cable  Background downloads severely affect speech quality

Future improvements Adaptive VoIP clients  Variable codec parameters based on network condition QoS guarantees from the OS  Priority over other traffic at the end hosts Forward Error Correction  Research shows that we can achieve significantly better quality with FEC in “lossy” connections  Especially useful for  Adaptive FEC (variable code rate)

Conclusions It does work ! But still not ready to take over land lines. In our report  More details on VoIP quality metrics  Explicit quantification of the degradation factors for each type of networks.  Possible improvements to VoIP based on our analysis of the experimental results

Thank You Questions?