The 7 th International Conference for Informatics and Information Technology (CIIT 2010) ©2010 Institute of Informatics. ANALYSIS OF VOICE OVER IP DURING VERTICAL HANDOVERS IN HETEROGENEOUS WIRELESS AND MOBILE NETWORKS Kire Jakimoski Toni Janevski Ss. Cyril and Methodius University, Faculty of Electrical Engineering and Information Technologies Ss. Cyril and Methodius University, Faculty of Electrical Engineering and Information Technologies Skopje, Republic of Macedonia Skopje, Republic of Macedonia ABSTRACT Roaming across different heterogeneous technologies such as 802.11, WiMAX and UMTS will become a requirement of future networking devices, especially for Voice over IP traffic, which nowadays is one of the most important services regarding the performance evaluation of wireline and wireless networks. In this paper we perform a study on the performance of voice packet transmissions during vertical handovers between 3G- HSPA, WiMAX (IEEE 802.16) and WLAN (IEEE 802.11) wireless networks. In particular, we analyze the performance metrics, such as handover latency and packet loss, for obtaining the effects of vertical handover on the mobile node performance, by using the recommended parameter values for link triggers and router configuration in IEEE 802.21 standard. Results show that the handover latency is severely impacted by the choice of the time interval parameters on the link layer, especially in the case of UMTS to WiMAX vertical handover. Packet loss is also analyzed in order to have the best optimization in vertical handovers between UMTS, WiMAX and WLAN, for Voice over IP traffic. I. INTRODUCTION Next-generation wireless networks have been envisioned as an IP-based infrastructure with the integration of various wireless access networks such as IEEE 802.11 wireless local area networks (WLANs), IEEE 802.16 wireless metropolitan area networks (WMANs), and Universal Mobile Telecommunications System (UMTS). Heterogeneous wireless networks need to cooperate to provide users with seamless mobility and required quality of service (QoS). Mobile nodes can automatically switch the connectivity between different types of networks. The vertical handover occurs when the connection to a mobile user changes from one network to the other during a call. The process of deciding and executing a vertical handover is more complex than a horizontal handover with a network such as the case that a mobile user switches its home base station. IEEE 802.21 [1] defines a media-independent handover (MIH) framework that can significantly improve handover between heterogeneous network technologies. The standard defines the tools required to exchange information, events, and commands to facilitate handover initiation and handover preparation. IEEE 802.21 does not attempt to standardize the actual handover execution mechanism. Therefore, the MIH framework is equally applicable to systems that employ mobile IP at the IP layer as to systems that employ Session Initiation Protocol (SIP) at the application layer. On the other hand, in the recent past, there has been a tremendous increase in the popularity of VoIP services as a result of huge growth in broadband access. The same VoIP service poses new challenges when deployed over a heterogeneous wireless network while enabling users to make voice calls during vertical handovers using mobile nodes with different interfaces. In this paper, through an extensive simulation study, the effect of DCD/UCD interval (WiMAX MAC layer parameter) on vertical handover performance for VoIP traffic according IEEE 802.21 standard has been investigated. In the simulation environment, terminals move according to the different random trajectories. Performance of vertical handovers is measured based on vertical handover latency and packet loss. According to the 802.21 standard, the handover algorithm configures the power thresholds, and then handovers are triggered by signals received from lower layers. We analyze the effect of the DCD/UCD interval on vertical handover latency and packet loss between UMTS/WiMAX/WLAN networks. The results indicate that the choice of DCD/UCD interval has great impact on the VoIP QoS during vertical handover between UMTS and WiMAX with the IEEE 802.21 specification. This paper is organized as follows: Section II is the introduction to the VoIP and G.723.1 codec used in the simulations. Section III shows the simulation scenario. Simulation model, simulation parameters and handover performance metrics are explained in details. Section IV gives the results and analysis from the simulations and finally Section V concludes this paper. II. VOIP TRAFFIC In the context of IP networks, telephony services are known as Voice over IP (VoIP). A VoIP flow depending on the encoding employed, such as G.711, G.723.1 or G.729, can generate data rates between 5.33 and 64 Kbps. Packets are generated isochronously at the supported packetization rate through the real time protocol (RTP) containing a fixed size payload. To maintain a conversation at good quality levels, a VoIP flow requires low packet loss rates. Loss rates up to 10% may be tolerated depending on the type of packet concealment technique employed by the decoder on the side of the receiver. To sustain intelligibility of VoIP communications the total end-to-end delay should remain below 150 ms or lower, for highly interactive conversations. Delays in the range of 150-400 ms are considered acceptable, although the