On Traffic Characteristics and Bandwidth Requirements of Voice over IP Applications Sanaa Sharafeddine 1 , Anton Riedl 1 , Josef Glasmann 1 and Jürgen Totzke 2 1 Institute of Communication Networks, Munich University of Technology Arcisstr. 21, 80290 Munich, Germany {Sharafeddine, Riedl, Glasmann}@ei.tum.de 2 Siemens AG Schertlinstr. 8, 81359 Munich, Germany Juergen.Totzke@siemens.com Abstract Voice over IP (VoIP) services will play an important role in future IP networks, promising cost savings and new revenue sources to operators and service providers. To provide quality of service guarantees, certain mechanisms need to be implemented which support predictable packet handling, bandwidth allocation, and call admission control. In order to configure these mechanisms, a solid understanding of VoIP traffic characteristics and its respective bandwidth requirements is necessary. In this paper, we characterize traffic traces generated by various VoIP applications. According to the H.323 standard, the characteristics are described by means of token bucket parameters which are then used to derive the required service rates for individual traffic flows. While in most cases sources send out fairly steady packet streams, there are situations where software-based clients emit rather bursty traffic resulting in unreasonably high bandwidth needs. On basis of these traffic flows, we investigate the effects that token bucket parameters have on the bandwidth demand and discuss tradeoff possibilities in order to reduce it. 1. Introduction Voice over IP (VoIP) is evolving with a great potential of providing improved network efficiency, cost savings, and diverse value-added services as compared to traditional telephony systems. In enterprise environments with often two separate networks for voice and for data services, the provisioning of multiple service types over a common IP network infrastructure appears to be very promising to reduce operational costs. In any case, for VoIP to be accepted by the customers, its availability and its quality of service (QoS) will have to be comparable to circuit-switched telephony systems. However, based on today’s conventional IP technology, only bandwidth over- provisioning can assure a certain degree of QoS in closely defined network domains with limited number of users. And even then, large bandwidth links cannot guarantee a faultless service without phases of degradation. Therefore, traffic-engineering methodologies have been developed which take into account the characteristics and requirements of various traffic types and which handle the corresponding packets accordingly. Especially voice traffic is very sensitive to QoS impairment and, therefore, requires special treatment within the IP network. In order for traffic-engineering mechanisms to work properly, the characteristics of the sources have to be known. Only then it is possible to keep up QoS by either reserving appropriate bandwidth shares or performing call admission control based on allocated capacities. Therefore, it is necessary that a traffic source either knows its characteristics and then specifies the traffic profile to the network before sending, or a set of standard characteristics is assumed and preconfigured. Thus, traffic models are needed to accurately describe the traffic and to derive its bandwidth requirements. In this paper, we present measurements and characterization results for various VoIP applications in different situations. While VoIP coders usually produce quite deterministic traffic behavior, it has been observed that traffic flows sent by software-based clients show different properties in some cases. Based on a general network architecture, we analyze the effects of traffic characteristics mainly from a perspective of network dimensioning. The paper is organized as follows: In Section 2, we introduce the VoIP system model and describe the individual components. In Section 3, the characterization framework and the dimensioning approach are presented. Measurement and analysis results are given in Section 4. Section 5 covers tradeoff considerations between service quality and bandwidth requirements. Finally, Section 6 concludes the paper. Proceedings of the Eighth IEEE International Symposium on Computers and Communication (ISCC’03) 1530-1346/03 $17.00 © 2003 IEEE