Assessing the user-perceived quality of packet voice in networks with mobile users

• Authors: Cristina Hristea Seibert;Fouad A. Tobagi
• Venue: MSWIM '03 Proceedings of the 6th ACM international workshop on Modeling analysis and simulation of wireless and mobile systems
• Year: 2003

As the Internet becomes the medium of choice for transporting integrated data, voice and video traffic, it is crucial that the quality of service approaches the level seen in networks traditionally employed for carrying these various traffic types. For example, the quality of voice communication in the Internet should approach the toll-quality levels experienced in the public switched telephone network (PSTN). Mobile wireless users have become a common sight across the world, and have motivated the need for further evolving the Internet protocols and infrastructures, originally intended for fixed users, into new realizations capable of supporting portable and even mobile users at various speeds and across many geographical areas [10]. In particular, with mobile users comes the need for user tracking protocols that work seamlessly for all roaming needs and application characteristics.In this paper, we show that existing explicit and implicit schemes for user tracking in packet networks with mobile users can lead to poor quality of voice streaming applications. Implicit tracking schemes, such as the transparent learning protocol employed by layer-2 switches employ timeout-based caches which can lead to voice clips and/or echo and other delay impairments for interactive applications such as packet voice. Explicit tracking schemes such as binding updates employed by Mobile IP [9] or the tracking protocol used in HAWAII [8] are plagued by control overhead, delayed updates and large tracking databases which also degrade voice call quality and increase the cost of the network.To resolve these challenges we propose a number of techniques to improve user tracking in packet networks with the goal of attaining toll-quality. First, we propose an optimization which limits the propagation of explicit tracking information to entities that can receive them in a timely manner. Second, the lifetime value used by the implicit protocol is jointly tuned to account not only for the user mobility rate but also for the impact of packet loss on voice call performance. Finally, an adaptive tracking strategy is proposed that dynamically alternates between explicit and implicit tracking according to the load in the network. While other hybrid implicit and explicit protocols have been proposed in the past, this work is the first to target packet voice traffic. We demonstrate the benefits of these techniques by simulating a large network carrying many packet voice calls and measuring the user perceived quality of the voice calls.