MODELLING OF VERTICAL HANDOVER FROM UNTRUSTED WLAN NETWORK TO LTE Grebeshkov Alexander*, Zaripova Elvira § , Roslyakov Alexander*, Samouylov Konstantin § * Department of Automatic Telecommunication Povolzhskiy State University § Department of Applied Probability and Informatics of Telecommunications and Informatics Peoples’ Friendship University of Russia (RUDN University) 23 Leo Tolstoy st., Samara 443010, Russian Federation 6 Miklukho-Maklaya st., Moscow 117198, Russian Federation Email: grebeshkov-ay@psuti.ru, arosl@mail.ru E-mail: zaripova_er@rudn.university, samuylov_ke@rudn.university KEYWORDS Vertical handover, 3GPP access network, LTE, modelling, simulation, untrusted WLAN. ABSTRACT Nowadays, operators offer telecommunication services at a very high level. For the support of the best quality of service it would be reasonable to implement a handover to another radio access network cell in the same territory, a so-called vertical handover (VHO), by transferring the user connection and IP session from the current access network to a new network. In this paper, we analyze vertical handovers from an untrusted WLAN network to an LTE network. This type of handover from an untrusted WLAN network is the most difficult because of the many nodes of an LTE network related to authorization and resource allocation. The paper includes a synthesis of the basic procedures for the session setup and LTE resource allocation. Unlike other papers, we represent a complicated VHO procedure as a sequence of at least 40 signalling messages from the discovery of a new network for the VHO to its full completion at the target LTE network. We also propose a vertical handover time estimation method for the said VHO procedure. We perform numerical experiments on realistic data. INTRODUCTION Modern wireless access networks can be characterized as heterogeneous and ubiquitous with overlapping and seamless mobile and IP–connectivity. Enhanced quality of service (QoS) for the delivery of multimedia services can be made through a handoff to the best network from the point of view of such criteria as increasing received signal strength (RSS), decreasing handover latency, increasing available bandwidth, optimal power consumption, satisfaction of user preferences with some decision schemes (Ahmed et al., 2014). Handover process is categorized into vertical handover (VHO) and horizontal handover (HHO). Horizontal handover occurs in homogeneous network. This type of handover is well researched. A vertical handover occurs when user equipment (UE) switches between the cells of two different networks located on the same territory but which support different radio access technologies. During a VHO process, the UE can fetch a new physical connection and a new IP session. In (Abdoulaziz et al., 2012), the VHO time (or latency) is discussed as one of the main parts of a handover process because a mobile terminal may leave the WLAN area before the VHO to a 3GPP network will be completed. In (Yu et al. 2013) there is a case with lost or buffering packets due to a time out in the WLAN–3GPP VHO. Since VHO time has a clear impact on QoS and mobility, an analytical estimation of VHO time should be useful for reasonability analysis of VHO decision making in real time. This paper is organized as follows: the “VHO standardizations and specifications” section is devoted to the analysis of current VHO standards and technical specifications. The “WLAN–LTE VHO procedure design” section includes information on a step–by–step time-dependent VHO procedure. The ”Mathematical modelling of VHO procedures” section includes an analytical model of the discussed VHO procedure. A numerical example for initial realistic data is shown in the ”Numerical experiment” section. VHO STANDARDIZATIONS AND SPECIFICATIONS One of the main technical specifications which considers VHO architecture, principles and scenarios is the (3GPP TS 23.402 2016). This standard has been designed for non-3GPP access network interconnection with an Evolved 3GPP Packet Switched (EPS) domain. This technical specification describes an IP–based protocol for evolved UMTS Terrestrial Radio Access Networks (E–UTRAN). EPS may provide the UE with assistance data and policies about available networks for VHO by establishing secure communication in the form of an IP tunnel between the UE and the EPS core. This means that the security aspects of a 3GPP access and non– 3GPP (non–compliant access with 3GPP specification) need to be taken into consideration for the VHO procedure and VHO time estimation. Some security aspects of VHOs are described in (3GPP TS 33.222 Proceedings 31st European Conference on Modelling and Simulation ©ECMS Zita Zoltay Paprika, Péter Horák, Kata Váradi, Péter Tamás Zwierczyk, Ágnes Vidovics-Dancs, János Péter Rádics (Editors) ISBN: 978-0-9932440-4-9/ ISBN: 978-0-9932440-5-6 (CD)