A scheduling Algorithm for Interactive Video Streaming in UMTS Networks R. Laraspata, D. Striccoli, P. Camarda DEE–Politecnico di Bari v. Orabona, 4 – 70125, Bari, Italy Email:{r.laraspata, d.striccoli, p.camarda}@poliba.it; Abstract—The importance of a Variable Bit Rate (VBR) video transmission on UMTS networks is increasing in time. The bursty nature of VBR traffic complicates the design of efficient mechanisms for video retrieval, transport, and provisioning to achieve a high bandwidth utilization and reduce the negative effects of bandwidth fluctuations in wireless channels. To this aim, several scheduling algorithms can be successfully implemented. They regulate data transmission to reduce the rate variability peculiar of VBR streams. At client side, scheduled data are temporarily stored in the client buffer before being decoded on the terminal. In this work, a novel scheduling algorithm, the Scheduling Algorithm for Interactive Video (SAIV) is presented and analyzed. It is an algorithm thought for VBR stream transmission in UMTS networks that takes into account the user interactivity. Scheduling is performed ”online”, over relatively small video segments to reduce delays. SAIV dynamically varies the sampling frequency of the Real Time Control Protocol (RTCP) feedbacks that carry information on the client buffer status. The sampling frequency is modulated according to the difference between the calculated buffer fill level at server side and the real buffer fill level at client side. The latter is exploited to reschedule data with the updated information. Numerical results testify the SAIV effectiveness compared to the classical SLWIN online algorithm already known by literature, in some simulation scenarios of real interest. Keywords: Adaptive Scheduling, UMTS, VBR video, RTCP feedback, User interactivity. I. I NTRODUCTION For several years mobile and fixed networks, as Internet, were not communicating each other. Nowadays, services to end users provide a diversified and personalized range of applications to anyone, anywhere, anytime. Users can combine telecommunications, information technology and entertain- ment services that various operators offer. The main aim of the Universal Mobile Telecommunication System (UMTS) is to combine the most important trend of telecommunications market and allow customers to access efficiently to a wide range of data and applications. In this way, the standard meets the growing needs of mobility, flexibility and opportunity of choice. UMTS standard [1] provides to mobile users the same several multimedia applications, typically used in wired networks. UMTS network supports both pre-existing services and offers quite new revolutionary services including broad- band Internet access. It implements interactive and multimedia services in addition to voice, text, picture and audio/video contents that the Global System for Mobile Communications (GSM) standard already provided. All of these services were independent applications until now. Traditionally telecom- munication environments have been integrated with vertical business and technology segmentation. In 3G communication system a horizontally seamless layer service network integrates the Internet transport Protocol (IP) into a mobile service envi- ronment, making new opportunities for IP-based mobile appli- cations [2]. The 3G system provides many different services with different Quality of Service (QoS) guarantees. UMTS service classes require end-to-end QoS support. For this reason the Third Generation Partnership Project (3GPP) labels four main QoS classes to data bearer. One of this is the streaming class [3]. Thanks to the increasing transmission capacities of wireless communication networks, video streaming becomes an interesting and feasible application. End users can click on a link using web browser on their mobile devices and play the selected video clip. The client can start playing the video few seconds after the first part of the multimedia contents have received and before the download from the streaming server is completed [4]. Both the highly fluctuating conditions of wireless links and the limited amount of buffering on mobile terminals strongly influence the correct delivery of audio and video contents to the terminals. Despite the highly variable bandwidth conditions of wireless channel and the relatively high data bit rates, UMTS systems should ensure continuous and lossless data delivery. 3GPP standardized the mobile packet-switched streaming service, commonly referred to as the 3G-PSS standard [5]. Figure 1 shows a simplified UMTS architecture for packet-switched operations [6][7]. Fig. 1. Packet-switched architecture in UMTS network PRE-PRINT VERSION