VIPER – Voice over IP with Enhanced Resiliency Abstract: VoIP call quality is subject to Internet conditions, and users may experience periods of low quality if there is high traffic or link failures. The goal of this project, VoIP with Enhanced Resiliency (VIPER), is to reduce the likelihood of users experiencing bursts of unacceptable voice quality. The approach taken leverages the fact that there are multiple paths for point-to-point communications over the Internet, and that not all of them are likely to suffer from connectivity problems at the same time. Hence, VIPER uses packet-level diversity, sending voice packets over multiple paths instead of relying only on one particular path. University of Pennsylvania Department of Electrical and Systems Engineering Authors: Joseph Coyne ESE ‘10 Ji Kim ESE ’10 Kevin Sin ESE ‘10 Grace Tay ESE ’10 TEAM #4 Advisor: Prof. Roch Guerin DEMO TIMES: Thursday, April 22 rd, 2010 AM: 11:00, 11:30 PM: 1:30, 2:00 Problem Statement Voice over Internet Protocol (VoIP) has become increasingly popular due to the increased global Internet infrastructure, the ease-of-use of VoIP programs, and the low costs of making long-distance calls. However, while VoIP is usable, its performance is not yet acceptable to replace the public phone network. On average, VoIP is unintelligible for 5-10 minutes a day, which is an order of magnitude more than the public phone network. Additionally, there is a 6.2% chance that users making a long VoIP call will be forced to hang up within the first hour due to network outages. VIPER aims to improve the reliability and resiliency of VoIP by implementing packet-level diversity over multiple Internet paths instead of the single-path routing used by conventional VoIP applications. Solution: Diversity Encoding and Multipath Routing VIPER uses diversity coding so the receiver is able to fully reconstruct the original data even if not all data packets are received. VIPER implements two diversity schemes: the (2,3,2) and (3,6,4) schemes for different levels of protection against Internet failures. In the (2,3,2) scheme, at the Sender, 2 voice packets undergo diversity encoding to generate 3 data packets which are sent via 3 relays to the Receiver. The Receiver is able to recover the original voice data completely if it receives at least 2 of the 3 packets sent correctly. Similarly, in the (3,6,4) scheme, 6 data packets are generated from 3 voice packets, and the Receiver is able to recover the original voice data completely if at least 4 of the 6 packets sent are received correctly. A (1,1,1) case was also created to simulate the direct-path routing of conventional VoIP programs. For testing failure scenarios, the 1 relay would behave like a congested router or a bad link and drop or delay a certain amount of packets so the receiver would not receive them on time. Project Goals Under both normal Internet conditions and simulated worst- case scenarios, when compared to the direct-path case, the VIPER application should provide: 1.Higher voice quality, measured using the Mean Opinion Score (MOS). 2.A lower voice packet loss rate. Results: Lower Voice Packet Loss The voice packet loss rates at the Receiver for the single- path VoIP system and VIPER were also measured in a series of drop rate simulations at the Relays. As shown in Figure 5, under the same drop rate conditions, the percentage of voice packets received is higher with VIPER than with the single-path system. Figure 3: VIPER in a (2,3,2) call. Figure 5: Voice Packet Loss Results. Figure 4: MOS Score Results. Conclusion VIPER has shown that packet-level diversity and multipath routing improves the resiliency of a VoIP system to network failures. VIPER provides a broad framework that can be built upon for further applications: This framework could be very useful for other real-time Internet applications such as streaming video. The (2,3,2) and (3,6,4) schemes guarded against failures on one path and failures on two paths, respectively. More complex diversity schemes could be applied to further reduce the overhead of extra packets sent over the network. VIPER was set up using computers as relays for different paths in the Internet. This multipath routing could be extended to using multiple wireless access points. Internet SenderReceiver Router Figure 1: Normal VoIP uses the default path. Figure 2: VIPER uses diversity encoding and multipath routing to improve resiliency against link failures. In the (2,3,2) scheme, even if one link fails, there is no loss of voice packets. Internet SenderReceiver Relay 3 Relay 2 Relay 1 Only packets through Relays 1 and 3 are received MOSRatingPerceived Quality 4—5ExcellentToll Quality 3—4GoodCell Phone Quality < 3FairUnacceptable < 2BadUnintelligible Results: Higher Voice Quality The Mean Opinion Score (MOS) is the industry standard for measuring call quality. Human judges rate VoIP voice samples on a scale of 1 (bad) to 5 (Excellent) and the MOS score is derived by taking the mean of these scores. Different drop rate scenarios were presented to ten unbiased judges who evaluated the MOS score at the Receiver. The results in Figure 4 show that under the same drop rate conditions, VIPER provides a higher average MOS score and hence higher voice quality.