IEEE Communications Magazine • July 2011 185 0163-6804/10/$25.00 © 2010 IEEE INTRODUCTION Currently, Wireless Broadband Access (WBA) technologies are rapidly deployed while the tra- ditional telecom networks are migrating to Inter- net Protocol (IP) technology. The future will witness a clear trend of Fixed Mobile Internet Convergence (FMIC) in Next Generation Net- works (NGN) [1]. To realize this convergence, NGN will employ an open architecture and glob- al interfaces to create a multi-vendor and multi- operator network environment. Moreover, NGN will employ multiple networking technologies for the best service provisioning. While core net- works in NGN are going to employ a common network layer protocol to carry the current and foreseeable future services, the access networks will use a variety of technologies, such as 2G/3G, LTE, WiMAX, UWB, WLAN, WPAN, Blue- tooth, Ethernet cable, DSL, and optical fiber, to meet the diversified requirements from end users. Under the multi-operator, multi-network, and multi-vendor converged network environ- ment, users are expected to experience a hetero- geneous wireline and wireless high-bandwidth ubiquitous network access as well as diversified service provisioning. Since NGN can offer multiple services over a single network, it potentially simplifies network operation and management, and thus opera- tional expenditure (OPEX). While enjoying the benefit of the decreased OPEX, service pro- viders will encounter fierce competition provi- sioned by the availability of fixed-mobile convergence. In order to sustain and sharpen their competitive edges, service providers need to satisfy users’ needs to retain and attract lucra- tive customers. For this reason, service providers may explore management and control decisions based on user Quality of Experience (QoE). As the ultimate measure of services tendered by a network, QoE is defined as the overall accept- ability of an application or service as perceived subjectively by the end-user [2]. Figure 1 illustrates typical constituents in an NGN. The core network consists of four major candidate transport technologies, i.e., ATM, Eth- ernet, IP, and IP/MPLS, where IP-based core networks possess two QoS models (DiffServ and IntServ) standardized by IETF. The access net- works accommodate various wireless and wireline access technologies to provide consistent and ubiquitous services to end users. End-to-End (E2E) communications between users or between a user and an application server may span fixed and wireless mobile networks belonging to multi- ple operators and employing multiple networking technologies with their respective characteristics from different aspects, such as QoS models, ser- vice classes, data rates, and mobility support. The multiplicity of provider domains and diversity of transport technologies pose challenges for net- work interconnection, interworking, and interop- eration, and therefore E2E QoE. QoE includes the complete E2E system effects ranging from users, terminals, customer premises networks, core and access networks, to services infrastruc- tures. Besides the E2E network QoS, QoE is affected by many other factors such as user sub- jective factors, capabilities of terminal devices, properties of the applications, and characteristics of the user’s physical environment. Such a variety of contributing factors of QoE exacerbate the difficulty for assuring E2E QoE. ABSTRACT In next generation networks, voice, data, and multimedia services will be converged onto a sin- gle network platform with increasing complexity and heterogeneity of underlying wireless and optical networking systems. These services should be delivered in the most cost- and resource-efficient manner with ensured user sat- isfaction. To this end, service providers are now switching the focus from network Quality of Ser- vice (QoS) to user Quality of Experience (QoE), which describes the overall performance of a network from the user perspective. High net- work QoS can, in many cases, result in high QoE, but it cannot assure high QoE. Optimizing end-to-end QoE must consider other contribut- ing factors of QoE such as the application-level QoS, the capability of terminal equipment and customer premises networks, and subjective user factors. This article discusses challenges and a possible solution for optimizing end-to-end QoE in Next Generation Networks. ACCEPTED FROM OPEN CALL Jingjing Zhang and Nirwan Ansari On Assuring End-to-End QoE in Next Generation Networks: Challenges and a Possible Solution