A Next Generation Network (NGN) is an advanced, packet-based network that exploits multiple broadband, QoS-enabled transport technologies to provide telecommunication services. The objective of NGN is to focus on users and those service-related functions that are independent of underlying transport-related technologies. With the advent of NGN, services that are currently provided by multiple specific network-centric architectures are migrated toward a single, converged, user-centric communication network. NGN provides AAA (Anytime, Anywhere and Always on) access to users from different service providers with consistent and ubiquitous provision of services as necessary. The principles and requirements of Convergence of Fixed and Mobile Networks (FMC) and IP Multimedia Sub-layer (IMS) are likely to deliver all the desired benefits of NGN and should be carefully examined and studied. This special issue is intended to foster state-of-the-art research in the area of NGN. The issue focuses on a range of NGN-related topics including cross layer design, mobility, security, services, business models, and novel applications associated with their utilization. Contributions to this special issue focus on all aspects of NGN and present novel results and solutions to solve various problems and challenges foreseen in future NGN.

ZigBee is a protocol suite based upon IEEE standard 802.15.4 for the construction of low-rate wireless personal area networks. Since most of ZigBee devices are powered by battery, the power saving is an important issue. In the past several years, many solutions are proposed to extend battery life by reducing device transmitting and receiving time. However, few studies have noticed that most energy is consumed in sensing and monitoring rather than communicating activities, since the data rates in most ZigBee networks are low. Besides, energy will consume the most of those nodes which act as routers or are orphans that cannot join the network. In order to extend the life time of network, we proposed a dynamic topology reformation algorithm. The algorithm consists of a cluster reformation scheme for enhancing connectivity and a self-swapping method for averaging the loading of router nodes and end devices. As the experimental result shows, compared with the ZigBee standard, our method gains 6.02% to 15.13% improvement in network join ratio. And the role swapping balances the power consumption which makes the lifetime of the whole network 1.3 to 1.375 times longer.

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