In this paper we present our vision on future uses of the Media Independence paradigm developed within the IEEE 802.21. We argue that this specification is an excellent starting point for future applications that require the handling of heterogeneous technologies. The current IEEE 802.21 standard facilitates media independent handovers by providing higher layer mobility management functions with common service primitives for all technologies, thus hiding the technology specifics of the lower layers. In this paper we claim that such a media independent abstraction can be useful for functions other than handovers and advocate for extending the IEEE 802.21 standard to cover these additional functions. We concentrate on a particular scenario currently being discussed in the 802.21 WG, the Spectrum Optimization & White Spaces. We first identify the key challenges that need to be addressed in order to satisfy the requirements of these scenarios by means of a media independence abstraction. Then, based on the requirements identified, we outline a proposal for a media independent service layer architecture.

The Pervasive Computing field is almost always addressed from application, middleware, sensing or Human Computer Interaction perspective. Thus, solutions are usually designed at application level or involve developing new hardware. Although current layered network architectures (mainly TCP/IP stack) have enabled internetworking of lots of different devices and services, they are neither well-suited nor optimized for pervasive computing applications. Hence, we firmly believe that we should have an underlying network architecture providing the flexible, context-aware and adaptable communication infrastructure required to ease the development of ubiquitous services and applications. Herein, we propose a clean slate network architecture to deploy ubiquitous services in a Pervasive and Ubiquitous Computing environment. The architecture is designed to avoid hierarchical layering, so we propose a serviceoriented approach for a flow-oriented context-aware network architecture where communications are composed on the fly (using reusable components) according to the needs and requirements of the consumed service.

In recent years multitechnology-enabled terminals have become available. Such multimode terminals pose new challenges to mobility management. In order to address some of these challenges, the IEEE is currently working on a new specification on media-independent handover services (IEEE 802.21 MIH). The main aim of this specification is to improve user experience of mobile terminals by enabling handovers between heterogeneous technologies while optimizing session continuity. In this article we provide an overview of the current status of the IEEE 802.21 specification.

The availability of multiple technologies, with micro and macro wireless cells, for network access combined with terminals capable of exploiting such diversity in wireless access requires the development of new mechanisms for optimized handover procedures. Appealing solutions should support network controlled handovers through heterogeneous technologies, preferably combined with a cross-layers two/three design. The IEEE 802.21 working group is currently standardizing the methods and the protocol potentially able to provide such a solution. In this paper we analyze the impact of signaling timing on network controlled handovers execution and performance in this environment. Through an extensive simulation study, we obtain results, that can be exploited in both terminal and handover procedure designs.

Envisioning a future where mobile terminals equipped with one or more network devices are able to roam across wireless or wired networks, in a diverse macro and micro wireless cells environment, requires the development of enhanced methods to control IP-based mobility. These methods should consider traditional terminal mobility (mainly due to user movement) as well as mobility across heterogeneous networks in the presence of semi-static users. For this to become reality, a cross layer interaction is required starting from a potentially large diversity of layer two access technologies up to the common IP layer, allowing the exchange of messages between terminals and network components. Furthermore, traditional host mobility driven concepts need to evolve, and include more stringent mobile operator requirements in context of fully driven network controlled mobility. This paper presents and evaluates a novel framework design, based on the IEEE 802.21 future standard, encompassing network driven as well as host driven mobility. This paper evaluates signalling aspects, algorithm design and performance issues.

The integration of wireless LAN technology in mobile devices such as cellular phones, PDAs or laptops has become a user need due to its popularity in providing high speed wireless Internet access at a low cost. Such devices though should meet users' expectations with regard to QoS, i.e., guarantee a reasonable voice quality when VoIP is used, and power saving efficiency, i.e., standby and calling times should be similar to the ones of cellular phones. The IEEE 802.11e standard, which extends the 802.11 wireless LAN MAC layer with QoS and power saving enhancements, should be the most appropriate solution to address users' wishes in those devices. In this paper, we focus on the 802.11e functionality likely to be included in mobile devices in the short-term, EDCA for QoS and U-APSD for power saving, and evaluate the performance improvements and associated costs of two possible configurations of U-APSD as compared to the 802.11 power save mode. In addition, the dependency between the QoS and power saving enhancements obtained with U-APSD and the available channel capacity is analyzed considering three different scenarios: 802.11b, 802.11b+g and 802.11g. The evaluation is based on our proposed implementation of U-APSD: Static U-APSD (SU-APSD). The main conclusions that can be drawn from our results are that U-APSD significantly outperforms the 802.11 power save mode in all considered performance metrics and that the performance enhancements obtained with U-APSD are independent of the available channel capacity.

Wireless LAN hotspots are becoming widely spread. This, combined with the availability of new multi-mode terminals integrating heterogeneous technologies, opens new business opportunities for Mobile Operators. Scenarios in which 3G coverage is complemented by Wireless LAN deployments are becoming available. Therefore all IP based networks are ready to offer a new variety of services across heterogeneous access. However, to achieve this, some aspects still need to be analyzed. In particular, how and when to execute handovers in order to minimize service interruptions and maximize the use of the most appropriate technologies according to user's preferences (for example, a user may prefer to use a lower cost technology if available). This paper presents a simulation study of handover performance between 3G and Wireless LAN access networks. The mobile devices are based on the IEEE 802.21 cross layer architecture and use Wireless LAN signal level thresholds as handover criteria.

This paper evaluates, through an extensive simulation study, a flexible framework for centralized network-based handover control across wireless heterogeneous access. For handover decision-making algorithm, implemented in network elements, the approach encompasses events reported by the terminal side (e.g. radio conditions) as well as events reported by the network side (e.g. load change in the access). Based on standard contributions within the IEEE 802.21 Working Group we investigate and design the functionalities required for efficient network to network communication focusing on optimal device configuration and reliable transport. The study verifies that i) the signaling overhead introduced by the proposed framework does not impact negatively handover performance while allowing network reporting and ii) the implemented re-transmission mechanism reduces messages loss even under congestion conditions.

WLAN hot-spots are becoming widely spread. This, combined with the availability of new multi-mode terminals integrating heterogeneous technologies, opens new business opportunities for mobile operators. Scenarios in which 3G coverage is complemented by WLAN deployments are becoming available. Thus, true all-IP based networks are ready to offer a new variety of services across heterogeneous access. However, to achieve this, some aspects still need to be analyzed. In particular, the effect of the terminal speed on the detection and selection process of the preferred access network is not yet well understood. In fact, efficiency of vertical handovers depends on the appropriate configuration of mobile devices. In this paper we present a simulation study of handover performance between 3G and WLAN access networks showing the impact of mobile users' speed. The mobile devices are based on the IEEE 802.21 cross layer architecture and use WLAN signal level thresholds as handover criteria. A novel algorithm to dynamically adjust terminals' configuration is presented.

The integration of the wireless LAN technology in mobile devices as cellular phones or PDAs has become a user need due to its popularity in providing high speed wireless Internet access at a low cost. Such devices though should meet users' expectations with regard to QoS, e.g., guarantee a reasonable voice quality when VoIP is used, and power saving efficiency, e.g., standby and calling times should be similar to the ones of cellular phones. IEEE 802.11e defines QoS and power saving enhancements that should allow the wireless LAN technology address users' wishes in such specific devices. However, there are several questions that need to be answered in order to assess whether the additional complexity introduced by these mechanisms would be justified by a relevant performance improvement. With our work we contribute to answer these questions by i) identifying the likely 802.11e functionality to be implemented in mobile devices in the short-term (EDCA+U-APSD) ii) proposing a specific implementation of the U-APSD mechanism (SU-APSD) and iii) evaluating the performance improvement obtained as compared to 802.11 standard power save mode.

Increasing popularity of services for mobile users, diversity of radio access technologies and availabi lity of multi-technology enabled terminals, are facts th at amongst others point to an upcoming Future Internet scenario where several access technologies coexist. The recently published IEEE 802.21 standard (1), aims at improving handover performance between heterogeneous technologies. This paper reviews new scenarios and subsequent issues that are not addres sed by the base standard which might be object of study for the research community in the upcoming years.