PERFORMANCE OF VERTICAL HANDOVERS IN HETEROGENEOUS WIRELESS SYSTEMS UTILIZING IEEE 802.21 Liljana Gavrilovska, Vladimir Atanasovski, Valentin Rakovic, Ognen Ognenoski and Aleksandar Momiroski Faculty of Electrical Engineering and Information Technologies, University “Ss Cyril and Methodius” Karpos 2 bb, 1000, Skopje, Macedonia phone: + (389) 2 3099 114, fax: + (389) 2 3064 262, email: liljana@feit.ukim.edu.mk web: www.feit.ukim.edu.mk ABSTRACT Mobile and broadband wireless access networks (e.g. 3G, B3G, WiMAX, WiFi) constant development enlarges the spectrum of possible user applications. It opens potentials for the operators to increase their service portfolio and for the users to experience context-rich and personalized ser- vices. Therefore, the interoperability between different wire- less networks and the enabling of seamless Vertical Hand- overs (VHOs) become crucial cornerstones. This paper deals with a simulation performance analysis of VHOs utilizing the lately emerging IEEE 802.21 standard for heterogeneous access environments. The simulation results show that the implementation of the IEEE 802.21 standard yields lower VHO latencies allowing for a “make-before-break” VHO approach in heterogeneous environments. 1. INTRODUCTION The evolution and the emerging variety of different hetero- geneous wireless network platforms with different properties require integration into a single platform capable of support- ing transparent and seamless user roaming, while not inter- rupting active communications. This process is followed by the development of new user devices designed to deal with the various network platforms and protocols. The 4G para- digm [1] defines a seamless concept which is cost effective, simple, operable and personalized according to the users’ needs. It should support the paradigm shift from technology centric to user centric concepts and should provide “any- time, anywhere, anyhow and always-on” connectivity in a seamless manner. The key behind successful resolution of many commu- nication challenges in future wireless systems is in the inter- operability, both on network and user level, Fig. 1, [2]. The interoperability offers network providers and users a possi- bility to choose between alternative wireless access net- works based on different criteria, Fig. 1. Fig. 1. The network selection decision A key enabling technology of the interoperability in heterogeneous networks is the lately emerging IEEE 802.21 standard [3]. Prior to its introduction, the Vertical Handovers (VHOs) in heterogeneous environments depended heavily on pure Mobile IP [4] (or related protocols) functionalities leading to high handover latencies and, thus, high discon- nection times and high number of dropped packets during VHOs. The main target of the IEEE 802.21 standard is the seamless mobility through heterogeneous environments, i.e. the ability of a user to transit through different Radio Access Technologies (RATs) without the need to restart the connec- tion every time he switches to a different network. The ac- tual implementation of the standard requires knowledge on the network types in question, the policy rules to be fol- lowed, the roaming criteria etc. This paper deals with a simulation performance analysis of VHOs in heterogeneous environments exploiting IEEE 802.21. Section 2 briefly elaborates on the main IEEE 802.21 framework components, while section 3 presents and discusses related work in the field and preliminary simula- tion results of VHO performance with the utilization of IEEE 802.21. Finally, section 4 concludes the paper. 2. IEEE 802.21 FRAMEWORK The IEEE 802.21 is focused on handover facilitation be- tween different wireless networks in heterogeneous envi- ronments regardless of the type of medium. The standard names this type of VHO as Media Independent Handover (MIH). The goal of IEEE 802.21 is to better and ease the mobile nodes’ usage by providing uninterrupted handover in heterogeneous networks. For this purpose, the handover procedures can use the information gathered from both the mobile terminal and the network infrastructure. The heart of the 802.21 framework is the Media Inde- pendent Handover Function (MIHF), Fig. 2. The MIHF will have to be implemented in every IEEE 802.21 compatible device and will be responsible for communication with dif- ferent terminals, networks and remote MIHFs providing abstract services to the higher layers using a unified inter- face (L2.5 functionalities). MIHF defines three different services: Media Independent Event Service (MIES), Media Independent Command Service (MICS) and Media Inde- pendent Information Service (MIIS). MIES provides events