18th Telecommunications forum TELFOR 2010 Serbia, Belgrade, November 23-25, 2010. Abstract — Multi-access mobile devices and overlapping wireless network deployments have emerged as a next generation network fixture. Mobile devices should be capable of handing over between heterogeneous networks seamlessly and automatically. On the other side, the Voice-over-IP protocol (VoIP) and video has attracted a great deal of attention in the field of wireless mobile networks. In this paper we study the vertical handover latency of voice packet transmissions and video traffic during the vertical handovers between UMTS (HSPA), WiMAX (IEEE 802.16) and WLAN (IEEE 802.11) networks. Furthermore, we analyze throughput and packet loss results during VHOs between UMTS and WiMAX considering the effects of DCD/UCD interval, and detect the best values for this parameter. Keywords — Handover, Latency, Packet Loss, Throughput, UMTS, Video, VoIP, WiMAX, WLAN. I. INTRODUCTION ROVIDING users of multi-interface devices the ability to roam between different access networks is becoming a key requirement for service providers. The availability of multiple mobile broadband access technologies, together with the increasing use of real-time multimedia applications, is creating strong demand for handover solutions that can seamlessly and securely transition user sessions across different access technologies. A key challenge to meeting this growing demand is to ensure handover performance, measured in terms of latency and loss. The main purpose of IEEE 802.21 standard is to enable handovers between heterogeneous technologies (including IEEE 802 and cellular technologies) without service interruption, hence improving the user experience of mobile terminals. The aim of the handover procedure is to maximize the service continuity by providing seamless maintenance of active communications when the user changes its point of attachment to the network, either wired or wireless. To avoid unacceptable disruptions to ongoing communications, the network should establish the link to the new point of attachment prior to releasing the previous link. Such soft handover would prevent any perceptible interruption, for example during a voice call. IEEE 802.21 provides a framework that allows higher Kire Jakimoski, M.Sc. is Ph.D. student at the Faculty of Electrical Engineering and Information Technologies, Ss. Cyril and Methodius University, Karpos 2 bb, 1000 Skopje, Macedonia, (e-mail: kire_jakimoski@yahoo.com). Dr. Toni Janevski is Professor at the Faculty of Electrical Engineering and Information Technologies, Ss. Cyril and Methodius University, Karpos 2 bb, 1000 Skopje, Macedonia, (e-mail: tonij@feit.ukim.edu.mk). levels to interact with lower layers to provide session continuity without dealing with the specifics of each technology. Packet losses and delay due to vertical handover between heterogeneous mobile and wireless networks can significantly degrade the end-to-end VoIP call quality. Thus, optimization of the parameter values for link triggers and router configuration in IEEE 802.21 is crucial to have the best vertical handover performance metrics results in order to have non interruptible VoIP traffic between the users during vertical handovers. In this paper we optimize the vertical performance metrics results (vertical handover latency, packet loss and throughput) during vertical handover process between UMTS, WiMAX and WLAN for VoIP (codec G.723.1) and video traffic, using ns-2 simulator and package from NIST [1]. The delay contributed by the synchronization component in the WiMAX standard is the most significant during the vertical handover process. Because of this, the effect of the interval of the MAC management messages (downlink and uplink channel descriptor – DCD/UCD) on delay, throughput and packet loss results of the VoIP traffic is researched and optimized. Throughput performances are also analyzed through 15 random simulations with different random trajectories of the mobile terminal for different DCD/UCD intervals. Results are presented which illustrate that significant improvements in vertical handover latency and packet loss for VoIP G.723.1 codec between UMTS and WiMAX are achievable with DCD/UCD optimization. Throughput performances of different random simulations during vertical handover between UMTS and WiMAX for two DCD/UCD intervals show that throughput results during vertical handover are improved if we use lower DCD/UCD interval. This paper is organized as follows: Section II is the introduction to the VoIP (G.723.1 codec) and video traffic used in the simulations. Section III presents the simulation model used for the researching. Section IV gives the results and analysis from the simulations and finally Section V concludes this paper. II. VOIP AND VIDEO TRAFFIC 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 QoS Challenges of Real Time Traffic during UMTS/WiMAX/WLAN Vertical Handovers Kire Jakimoski and Toni Janevski, Senior Member, IEEE P 324