Measurement and Comparative Analysis of UDP Traffic over Wireless Networks Sumit Maheshwari, K. Vasu, C. S. Kumar*, Sudipta Mahapatra, Department of Electronics and Electrical Communication Engineering *Department of Mechanical Engineering Indian Institute of Technology Kharagpur, Kharagpur, WB, India Abstract - With the increasing usage of mobile devices to ubiquitously access heterogeneous applications in wireless Internet, the measurement and analysis of Internet traffic has become a key research area. In this paper, we present the results and analysis of our measurements for CBR and VBR traffic over UDP in GPRS, UMTS and Wi-Fi networks carried over Vodafone-India and BSNL-India networks. We focus on Inter-Packet Arrival Time (IPRT) and Inter-Packet Transmission Delay (IPTD) and observe that the later has a significant impact on the round trip delay. It is also observed that choice of optimal IPTD for a particular application provides better QoS (Quality of Service) by avoiding congestion in the network. Numerical parameters for Weibull and Normal distribution are also presented in order to represent such traffic. Keywords- GPRS; UMTS, Wi-Fi, traffic measurement; 1 Introduction The transport layer provides a mechanism for the exchange of data between end systems. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are two main transport protocols which provide connection- oriented and connectionless services respectively. TCP ensures reliable and ordered data delivery while also introducing processing overhead and bandwidth limitations due to congestion and flow control mechanisms. The lightweight UDP neither provides reliable delivery nor suffers from processing overhead and bandwidth limitations and hence is used in time-sensitive applications because dropping packets is preferable to waiting for delayed packets, which may not be an option in a real-time system like Voice over IP (VoIP), IPTV, video on demand and online gaming. Although TCP is still the popular protocol in the Internet, with the increasing demand of real-time applications, which have specific Quality of Service (QoS) requirements like low delay, jitter and packet loss, UDP is gaining in popularity [1]. The self-similar nature of Internet traffic [2][10] allows researchers to measure and analyze characteristics of both flow level and packet level traffics which give a key to synthetically generate and use similar traffic for various applications, which is a time consuming process otherwise. Wireless Internet traffic traces contain inherent information about user behaviour, interaction between users, wireless channel, applications and protocols. Thus, analysis of traces is more important than analytical modeling of wireless protocols alone. Though immensely rewarding, analyzing the statistical characteristics of wireless traffic is difficult partly due to the unfamiliar characteristics of wireless network traffic [3]. Wi-Fi and GPRS are two prime modes of accessing Internet via mobiles under the category of wireless Internet; others being 3G and WiMAX which are still gaining pace in terms of usage and accessibility in India [7]. Therefore, results of real-time measurement and analysis of traffic traces of GPRS and Wi-Fi networks can be utilized for better capacity management, congestion avoidance and testing before deployment of future networks. Real-time applications prefer UDP over TCP. VoIP for example uses some standard codec like G.711 etc based upon the bandwidth available. By suitably varying the Inter- Packet Transmission Delay (IPTD) depending upon the codec used, congestion at the network can be significantly reduced even for data applications over UDP. Packet switched networks have great advantages over circuit switched networks. One is that the bandwidth of the circuit is not limited to a small set of fixed allowed rates and the other is that it supports Variable Bit Rate (VBR) traffic [9]. VBR traffic makes efficient use of available bandwidth and thus its analysis becomes important. A comparative analysis of traffic over different networks like Vodafone GPRS, BSNL GPRS, BSNL UMTS and Wi-Fi gives an insight into the practical scenario and helps operators to implement better resource planning and congestion avoidance mechanisms. Traffic measurements can be carried out at various levels like byte, packet, flow, session. Our measurements are carried out in the packet-level in view of the following benefits as compared to the other higher level methods: (a) most of the network problems (loss, delay, jitter etc.) occur at the packet level; (b) packet-level approach is independent of protocols being used; (c) traffic at the packet-level remains observable even after encryption made by different protocols. The measurement and analysis done in this paper has the following salient features: (a) non-cooperative