The expanded scope and attack surface of the today’s multi-tier heterogeneous wireless network (MHWN), which constitutes the basis of our daily life activities, dictates a deeper understanding of how distributed Denial of Service (DDoS) attacks can impact its performance. In this work, we assess the performance of large-scale MHWNs that are subject of random DDoS attacks, considering that i) each tier may support a different radio access technology and spectrum band, and ii) end terminals have limited access to available tiers. Depending on the capability of end terminals to perfectly detect DDoS actors (or not), we provide a solid analytical framework for assessing the impact of different user association policies on both the service probability and the user load distribution per tier. Among others, our numerical analysis highlights the importance of striking a good balance between optimal system-wide service probability and fair load distribution across the tiers of the MHWN.

During the last decade, various Internet of Things (IoT) networks have emerged as an effort to support the constantly increasing need for IoT applications. Focusing on IoT networks that use unlicensed spectrum bands, Low Power Wide Area Networks (LPWANs) are being developed widely. For these networks, one of the most effective technologies is the combination of Long Range (LoRa) / LoRa Wide Area Network (LoRaWAN) protocol stack. In this context, we set up a LoRa/LoRaWAN network in a campus environment and we conducted thorough measurements that allowed us to produce link-level performance analysis. More precisely, the relation between key link-level performance metrics, namely the Received Signal Strength Indication (RSSI) and the Signal to Noise Ratio (SNR) was derived, considering i) the heterogeneous terrain where the measurements were conducted, and ii) the configuration parameters selected, such as the Spreading Factor (SF).

A fundamental technology towards the next generation of mobile networks is the Network Slicing, i.e., the capability to “slice” network resources and functions and to offer isolated end-to-end network services over shared physical infrastructures. From the performance perspective, one of the main challenges in network slicing is the minimisation of the slice set up time; a factor that directly effects a key performance indicator for the 5G networks, namely, the service creation time. Treating a network slice as a set of Virtual Network Functions (VNFs) that are installed in different hosts (central/edge clouds) during the slice creation procedure, we examine a nature-inspired metaheuristic approach for scheduling the VNFs installation process. Simulation results prove that the proposed metaheuristic method can offer high quality solutions for VNF scheduling problems and optimize service creation time for a set of requested network slices, by producing a close-to-optimal scheduling plan, for a large set of VNFs, in reasonable execution time.

Wireless networks are currently proliferated by multiple tiers and heterogeneous networking equipment that aims to support multifarious services ranging from distant monitoring and control of wireless sensors to immersive virtual reality services. The vast collection of heterogeneous network equipment with divergent radio capabilities (e.g. multi-GHz operation) is vulnerable to wireless network attacks, raising questions on the service availability and coverage performance of future multi-tier wireless networks. In this paper, we study the impact of black hole attacks on service coverage of multi-tier heterogeneous wireless networks and derive closed form expressions when network nodes are unable to identify and avoid black hole nodes. Assuming access to multiple bands, the derived expressions can be readily used to assess the performance gains following from the employment of different association policies and the impact of black hole attacks in multi-tier wireless networks.

Over the past years there has been a rapid rise of the mobile communications industry which, combined with the limitations of the current communications networks' structure, necessitates the development of new networks with increased capabilities, so that users can be served with optimal quality of service and network resources utilization. Software Defined Networking (SDN) is a networking approach which transforms the network elements to simple forwarding devices, making decisions centrally. The quality of service perceived by the user, or Quality of Experience (QoE), is considered to be a matter of great importance in software defined networks. This paper presents the SDN QoE Monitoring Framework (SQMF), an SDN application that monitors and preserves the QoE for VoIP and video applications, by periodically monitoring various network parameters and using QoE estimation models.

While video streaming has dominated the Internet traffic, video service providers (VSPs) compete on how to assure the best quality of experience (QoE) to their customers. HTTP Adaptive Streaming (HAS) has become the de facto way that helps VSPs work-around potential network bottlenecks that inevitably cause stallings. However, HAS-alone cannot guarantee a seamless viewing experience, since this highly relies on the mobile network operators' (MNOs) infrastructure and evolving network conditions. Software-defined networking (SDN) has brought new perspectives to this traditional paradigm where VSPs and MNOs are isolated, allowing the latter to open their network for more flexible, service-oriented programmability. This paper takes advantage of recent standardization trends in SDN and proposes a programmable QoE-SDN App, enabling network exposure feedback from MNOs to VSPs towards network-aware video segment selection and caching, in the context of HAS. The video selection problem is formulated using Knapsack optimization and relaxed to partial sub-problems that provide segment encodings that can mitigate stallings. Furthermore, a mobility prediction mechanism based on the Self-similar Least-Action Walk model is introduced, toward proactive segment caching. A number of use cases, enabled by the QoE-SDN App, are designed to evaluate the proposed scheme, revealing QoE benefits for VSPs and bandwidth savings for MNOs.

Towards the new era of communications, direct communications are intensively studied by industry and academia. One of the major challenges in this communication paradigm is the device discovery problem, referring to the mutual detection of neighboring devices prior the establishment of the direct communication. Recognizing the scarcity of the radio resources and the need for frequent discovery transmissions, we propose a validation approach as a complement to the device discovery process. Building on the idea that the neighboring relationship of some devices may last for long time, an enhanced radio resource allocation is applied for those devices, improving the overall performance of the discovery process.

Device-to-device (D2D) discovery is the inextricable prelude for the direct exchange of local traffic between cellular users in proximity. The D2D discovery process can be based on either autonomous actions taken by D2D-enabled devices, also known as network-assisted D2D discovery or core network functionalities to estimate proximity, also known as network-assisted D2D discovery. A key advantage of network-assisted D2D discovery is its potential to reduce the energy, signaling, and interference required for D2D discovery, by exploiting knowledge of the network layout. We analyze the performance of network-assisted D2D discovery in random spatial networks and derive useful guidelines for its design. We derive approximate expressions for the distance distribution between two D2D peers conditioned on the core network's knowledge of the cellular network layout, assuming that the base stations are distributed according to the Poisson point process. The expressions are used to assess the interplay between the D2D discovery probability and key system parameters, such as network intensity and transmit power, as well as to identify conditions to maximize the D2D discovery probability. Numerical results validate the accuracy of our findings and provide insights on the performance tradeoffs of network-assisted D2D discovery.

Device-to-Device (D2D) communications enable direct exchange of localized traffic between cellular users in proximity. Nonetheless, the employment of D2D communications heavily relies on the capability of the cellular devices to infer on their proximity. In this paper, we analyze the performance of network- assisted D2D discovery in random cellular networks and derive optimal deployment strategies for transforming the today's cellular network, which is optimized for coverage and capacity, into a D2D- centric network where the discovery and communications between cellular devices will be orchestrated by the core network. In this direction, we develop an analytical framework that exploits existing knowledge of the cellular network topology and effectively estimates the probability that two tagged devices are in proximity, a.k.a. D2D discovery probability. Also, we identify conditions under which the D2D discovery probability is maximized and assess the key performance trade-offs inherent to network-assisted D2D discovery.

Currently, cellular networks are evolving towards providing high quality mobile services in a ubiquitous manner. In this direction, increased robustness is required to face fluctuations at the service quality that follow traffic demanding events, such as an earthquake or a blackout. Dealing with this challenge, we propose a cross-layer scheme, which handles the traffic changes by adjusting dynamically the encoding rate at the application layer. The rate adjustments target at controlling the impact on the provided Quality of Experience (QoE), i.e., the key metric for assessing the perceptual quality of a provided service. The performance analysis conducted revealed a smooth QoE adaptation to traffic changes with quite low signaling cost for the exchange of the rate adaptation commands.

Today's heterogeneous wireless network (HWN) is a collection of ubiquitous wireless networking elements (WNEs) that support diverse functional capabilities and networking purposes. In such a heterogeneous networking environment, proximity estimation will play a key role for the seamless support of emerging applications that span from the direct exchange of localized traffic between homogeneous WNEs (peer-to-peer communications) to positioning for autonomous systems using location information from the ubiquitous HWN infrastructure. Since most of the existing wireless networking technologies enable the direct (or indirect) estimation of the distances and angles between their WNEs, the integration of such spatial information is a natural solution for robustly handling the unprecedented demand for proximity estimation between the myriads of WNEs. In this paper, we develop an analytical framework that integrates existing knowledge of the HWN layout to enable proximity estimation between WNE supporting different radio access technologies (RATs). In this direction, we derive closed-form expressions for the distance distribution between two tagged WNEs given partial (or full) knowledge of the HWN topology. The derived expressions enable us to analyze how different levels of location-awareness affect the performance of proximity estimation between WNEs that are not necessarily capable of communicating directly. Optimal strategies for the deployment of WNEs, as means of maximizing the probability of successful proximity estimation between two WNEs of interest, are presented, and useful guidelines for the design of location-aware proximity estimation in the nowadays HWN are drawn.

In this paper, we present a novel framework for virtualizing the Long Term Evolution (LTE) base stations to improve the user performance and lower the downlink interference. Our proposal, referred to as “OpeNB”, is an attempt to utilize the benefits of Software Defined Networking (SDN) and OpenFlow, introducing network virtualization in LTE networks with an adaptable, highly extensible, and less invasive manner. The proposed solution consists of a novel network architecture and a mechanism that allows the virtualization of LTE base stations depending on the network state. Simulation results show that the proposed framework improves the average interference, throughput and packet loss experienced by the end users.

To address the challenging issues of energy-efficiency and seamless connectivity in heterogeneous networks, 3GPP and IEEE have recently incorporated several architectural and functional enhancements to the baseline operation of their standards for cellular and wireless local area network access, respectively. Based on the 3GPP Access Network Discovery and Selection Function (ANDSF) and the advanced measurement capabilities provided by the IEEE 802.11-2012 and the 3GPP Long Term Evolution - Advanced (LTE-A) Standards, we propose an ANDSF-assisted energy-efficient vertical handover decision algorithm for the heterogeneous IEEE 802.11-2012 / LTE-A network. The proposed algorithm enables a multi-mode mobile terminal to select and associate with the network point of attachment that minimizes its average overall power consumption and guarantees a minimum supported quality of service for its ongoing connections. System-level simulation is used to evaluate the performance of the proposed algorithm and compare it to that of other competing solutions.

Device-to-Device (D2D) communications are currently attracting high interest from industry and academia, targeting at new commercial and public safety proximity services (ProSe). A major challenge under consideration is the device discovery problem, i.e., the problem of meeting the communication peers in time, frequency and space. In line with the current standardization efforts from the 3rd Generation Partnership Project (3GPP), we propose a centrally controlled device discovery scheme which consists of an application layer procedure and a set of access level enhancements. The target of the application layer procedure is to enable the ProSe discovery services, while the access level enhancements ensure the spectrum resources required for discovery transmissions. Evaluation results illustrate the impact of consuming cellular resources for device discovery on cellular network performance, while reveal the potential performance gains for the cellular network due to the introduction of the ProSe communications.

Femtocells will play a key role for the wide adoption of the LTE-Advanced system, as they bring the access network closer to the end user in a cost-effective manner. This disruptive communication paradigm, however, dictates the use of advanced interference and mobility management algorithms to cope with the dense yet unplanned network layout. In this paper, we present an interference-aware handover decision algorithm for the LTE-Advanced femtocell network, which utilizes standard signal measurements to select the candidate cell that a) attains the minimum required channel gain for sustaining service continuity and b) minimizes the mean UE transmit power for a prescribed mean SINR target. The proposed algorithm attains backwards compatibility with the LTE-Advanced system, as it is deployed by using the private mechanism for non-standard use. Based on the evaluation methodology of the Small Cell forum, we validate the performance of the proposed algorithm and compare it against that of other state-of-the-art algorithms.

Device-to-Device (D2D) communications provide the means to users of cellular networks for spatially reusing licensed spectrum by establishing direct connections. Considering the benefits for operators and consumers, a plethora of resource and interference management approaches in the literature deal with parallel cellular and D2D transmissions. However, this feature is not yet supported by modern cellular systems, such as the Long Term Evolution (LTE). The current paper targets at filling this gap by enabling D2D transmissions in LTE networks. Standardized LTE capabilities are utilized to provide a comprehensive framework on which existing or future resource and interference management schemes for D2D communications may be applied. The proposed framework is assessed under a moderate scenario where the cellular resource management policy is not affected. Results show that multiple D2D connections can be established in parallel to cellular uplink transmissions, while a satisfactory percentage of the cell region is available for spatial spectrum reuse.

ABSTRACT Modern wireless orthogonal frequency division multiple access (OFDMA) systems incorporate dynamic resource allocation (DRA), adaptive modulation and coding (AMC), and power control (PC) to exploit multiuser diversity and achieve higher system throughput. In the literature, only a few proposed algorithms deal with the contiguous DRA problem according to which a contiguous collection of resources can be allocated to each user. This paper formulates this high complexity problem, provides a suitable decision metric and a simple yet efficient solution. The proposed algorithm allocates in each step a contiguous collection of resources to the pending user that leads to the highest estimated correctly received number of bits. Simulation results show that, in this way, considerably improved performance can be achieved in terms of overall system throughput, spectral efficiency, and served traffic. Copyright © 2010 John Wiley & Sons, Ltd.

Resent measurements and reports show that in most cases licensed spectrum is used sporadically resulting in large unutilized spectrum portions. Opportunistic spectrum access (OSA) is a promising solution providing methods to identify and exploit these portions. Most existing OSA proposals provide ways for unlicensed users to access the licensed spectrum. This paper describes a novel approach where licensed users of an infrastructure-based system exploit features of their system to detect spatial spectrum opportunities. Focusing on an interference-free solution, an alternative opportunistic operation mode is provided, allowing licensed users to increase utilization of their own spectrum.

The IEEE 802.16e standard provides a high degree of flexibility for setting up and operating mobile WiMAX networks in metropolitan environments. While the standard supports differentiated Quality of Service (QoS), crucial functions such as traffic scheduling and slot allocation are left as open issues to the research community. This paper focuses on these two features, that consist an NP-Hard problem, and provides an integrated solution. The key component of the proposal is the “Colored OFDMA Frame Registry Tree Scheduler” (CO-FRTS) that achieves QoS-aware resource allocation by using an advanced tree structure to prepare the creation of time frames, and reduce processing requirements. An extended simulation model reveals the improved performance of the proposed solution, compared to other competent proposals.

A “Smart Spaces System”, called MITOS, for improved user connectivity in large wireless LAN installations is proposed. MITOS extends the scope of resource management to the dynamic relocation of nomadic users: the system suggests to a user the best location to move to for obtaining a satisfactory quality of service level, when the controlling access point of its current location becomes congested. The system monitors the traffic and user location across the network, and formulates the appropriate relocation proposal urging specific users to move to better locations at reasonable distances. Two enhancements to the basic MITOS system are introduced for maintaining an almost uniform load level across the considered infrastructure: the first uses microeconomic concepts, while the second borrows game theoretic mechanisms from the Santa Fe Bar problem. Simulation results on the efficiency of the proposed schemes are provided.

A cross-layer mechanism to improve the performance of real-time applications over IEEE 802.16e metropolitan area networks is presented. The proposed mechanism uses channel quality and service quality information from the physical and medium access control layers, respectively, to determine the most suitable burst profile, transmission power level and media encoding rate for a connection, or even initialize a handover execution. The main contribution of this mechanism is the integration of the handover initiation into the cross layer logic, aiming to improve the overall system performance. Extensive simulation results show that the proposed mechanism offers significant performance improvement in terms of packet loss rate, power consumption, throughput, and system capacity.

Abstract In this paper, an efficient cross‐layer design that performs joint adaptation of the physical (PHY) and application layers of a mobile WiMAX network is proposed. The design takes into account channel state and performance information from the PHY and medium access control (MAC) layers, respectively. It uses a decision algorithm to evaluate this information, specify unfavorable conditions regarding low channel quality and increased congestion, and take measures by coordinating modulation order, transmission power, and media encoding rate, toward improved overall quality of service (QoS) offered to the user. Extensive simulation results show that the proposed design achieves considerably reduced packet loss and power consumption, combined with increased throughput as compared to a typical mobile WiMAX system. Copyright © 2008 John Wiley & Sons, Ltd.

The requirement for ubiquitous service access in wireless environments presents a great challenge in light of well-known problems like high error rate and frequent disconnections. In order to satisfy this requirement, we propose the integration of two modern service technologies: Web Services and Mobile Agents. This integration allows wireless users to access and invoke semantically enriched Web Services without the need for simultaneous, online presence of the service requestor. Moreover, in order to improve the capabilities of Service registries, we exploit the advantages offered by the Semantic Web framework. Specifically, we use enhanced registries enriched with semantic information that provide semantic matching to service queries and published service descriptions. Finally, we discuss the implementation of the proposed framework and present our performance assessment findings.

Recent studies indicate the presence of a significant amount of idle licensed spectrum, in different time periods and geographic locations. Prompted by the latest regulatory changes and radio technology advances, dynamic spectrum access is becoming increasingly attractive, for alleviating the spectrum scarcity problem in the unlicensed bands. We study the dynamic spectrum access in a CDMA environment. We assume that users selfishly switch from one frequency band to another, so as to maximize their individual benefit, and model the studied problem as a non-cooperative game. We propose a probabilistic, distributed strategy with which users might share the available re sources to satisfy their quality of service requirements, and minimize their transmitted power. The comparison of the proposed strategy against other alternative strategies shows that it combines fast convergence, efficiency and stability, while its simplicity makes it practical for a real network.

Beyond 3G wireless systems will be vested with dynamic reconfiguration capabilities capable of adapting their protocol stacks during runtime to optimize spectrum utilization and, thus, better meet the ever-changing service demands. For protocol stack reconfiguration to become a practical capability, a language for modeling, expressing and circulating data essential to reconfigurable protocol stacks is necessary. We present a generic object-oriented information model for describing the feasible combinctions of protocol layers into protocol stacks. The model supports the derivation of an associated ontology specified in standard W3C semantic languages (OWL). We introduce a novel algorithm for discovering all the feasible protocol layer combinations that render valid protocol stacks, thus facilitating the selection of suitable ones. We assess the performance of a prototypical implementation of our algorithm used to discover feasible protocol stack combinations for the GPRS, UMTS and IMS access standards. Finally, we present our conclusions and provide directions for future work.

In the framework of the LIAISON (location bAsed services for the enhancement of wOrking enviroNment) IP project the existing legendary charging functionality is complemented with new features fulfilling the emerging charging requirements for an integrated environment providing mobile workers with location-based services. In that scope, LIAISON introduces the LIAISON customised billing module (namely the LCBM), an integrated customised billing module, which collects the charging information from each, potentially different, business domain, calculates the charges that are due to each involved business entity and shares the respective revenues. The LCBM covers the emerging requirements of an integrated environment enabling LIAISON solution to provide mobile workers with advanced location-based services. It receives charging information from heterogeneous environments through open application programming interfaces (APIs), applies the appropriate pricing policy based on the user or/and service profile and calculates the apportioning revenues between the actors.

To meet the growing requirements for resource management schemes in the context of mobile and wireless computing, path prediction algorithms are gaining more attention and are being extensively examined. Path prediction allows the network to enhance the user quality of service. A parametric dimensioning of a path prediction algorithm based on learning automata is presented. The algorithmic parameter values are optimised for maximum prediction accuracy. Furthermore, two add-on mechanisms of the path prediction algorithm are introduced, and their performance is evaluated through simulations.

The proliferation of WLANs and the ubiquitous coverage of cellular networks have resulted in several integration proposals towards 4G networks. Among them, the tight- coupled WLAN/UMTS architectures promise seamless service continuity to users and enhanced network performance. Most of these solutions assume that only one interface is active at a time, while much fewer consider the concurrent use of both WLAN and UMTS interfaces as this is expected to consume more energy. This paper presents a detailed description of power consumption for the two different tight-coupled WLAN/UMTS approaches based on the states of the wireless devices. A simple analytical model is provided for estimating the power consumption in each approach, while a simulation model measures the power needs for more complicated cases. Moreover, the enhancement due to a power-saving mechanism in WLAN is also assumed in the system and useful deductions are provided about the average power consumption per mobile terminal.

Radio resources management in integrated cellular and wireless networks is a very complex and important issue. Although a number of proposals exist in the literature that present considerable improvement in several aspects, they also present some disadvantages that affect their implementation and deployment. In an attempt to tackle this, we propose a simple distributed algorithm that enables terminals to build prioritised lists of target access network independently for each of their connections. The algorithm also provides specific details on how the core network components can treat each connection based on a number of parameters, which are of paramount importance for the operators. The final choice is a trade-off between the user preferences, the terminal capabilities, the network load and the location and speed of the terminal. The algorithm is designed to provide an easy method for defining user preferences. Finally, we provide an initial evaluation of the signalling load required inside the core network to support the proposed decision making mechanism and make suggestions on the best functional architecture of the radio resource management entities.

The technological race of boosting legacy and developing new air-interfaces, recent advancement of core network architectures, and evolution from software-defined and cognitive radio to reconfigurable systems put new complexions on the definition of "next-generation". This contribution envisages Next-Generation Mobile Networks as the class of multi-radio cognitive systems capable of absorbing the heterogeneity of wireless access, with advanced reconfiguration capabilities moved from edges to the core. Inline with 3GPP IMS rationale and ETSI TISPAN design extensions, a unified subsystem for offering reconfiguration services is proposed, adopting a multiplane and layer-based approach with clear separation of control and management concerns. The paper presents the signalling between the terminal and network elements in the course of an exemplary staged reconfiguration process, and discusses design and deployment advantages when introducing the so-called Reconfiguration Support Subsystem in Beyond 3G portfolios.

A scheme for the proactive allocation of network resources to mobile users, based on a pricing framework, is proposed. The objective is the reduction of service discontinuation events attributed to handovers in the cellular infrastructure. The future base station, where network resources have to be reserved proactively, is determined by means of a path prediction algorithm. The network receives a fee for providing the advance reservation service to the user. The exact price is determined after a sequential bargaining procedure, modeled as a two-person non-cooperative game between the mobile user and the network The efficiency of the proposed scheme is evaluated through simulations.

We consider the uplink power control problem in a single cell, multi-user, CDMA wireless data system and formulate it as a cooperative game. We use the Nash bargaining solution concept, in order to determine the socially optimum solution, which is both Pareto efficient and fair. In our formulation, the BS plays the role of the arbitrator, Le., solves the power control problem, and broadcasts the relevant information to all users in order to enforce convergence to the optimal operating point. The comparison of the cooperative scheme to the non-cooperative scheme shows significant reduction in the transmission power of the mobile terminals.

The proliferation of wireless access technologies, mostly wireless LANs, along with the ubiquitous coverage of cellular networks, has spurred many researchers to consider schemes for integrated network provision. In overlaying network environments, flexible resource management and service continuity during handover play a crucial role in the quality-of-service seen by the user. This paper describes an integrated UMTS/WLAN architecture that manages to establish every connection in a mobile terminal through the most appropriate access network, based on both network policies and user preferences. Moreover, connections are handed over independently between UMTS and WLAN, aiming at seamless service continuity. A detailed simulation model is used to measure the performance of the proposed architecture against existing schemes

IEEE 802.16 is considered today as the most promising technology, to provide extension of wireless broadband communications into metropolitan environments. One of the main design challenges in 802.16 is the introduction of an efficient traffic scheduler that handles resource allocation in the wireless interface. This paper proposes such a scheduler, referred to as the "frame registry tree scheduler", that aims at providing differentiated treatment to data connections, based on their QoS characteristics. The scheduler uses a tree structure in order to prepare time frame creation and reduce processing needs at the beginning of each time frame. Simulation results show that the proposed scheduler can attain considerable improvement in terms of throughput and packet losses

A flow rejection algorithm for the dynamic resource reservation protocol (dRSVP) protocol is proposed. dRSVP is an enhanced version of RSVP, aiming at providing dynamic quality-of-service (QoS) support in a variable bandwidth environment (e.g., wireless) through guarantees of ranges of bandwidth instead of specific values. Flow rejection occurs when the channel quality decreases to a level that even the minimum bandwidth requirements per flow cannot be fulfilled. The proposed algorithm aims at improving the flow dropping probability of dRSVP, without affecting the bandwidth utilization. Its operation is based on setting priority classes and rejecting the minimum required number of flows per class, in order to guarantee QoS to the remaining. Both mathematical analysis and simulation results show that the overall flow dropping probability can be significantly reduced.

A flow rejection algorithm for the dynamic RSVP (dRSVP) is proposed. dRSVP is an enhanced version of RSVP, aiming at providing dynamic quality of service (QoS) support in a variable bandwidth environment through guarantees of ranges of bandwidth instead of specific values. Flow rejection occurs when the channel quality decreases to a level that even the minimum bandwidth requirements per flow cannot be fulfilled. The proposed algorithm aims at significantly improving the flow dropping probability, without affecting the bandwidth utilization. Its operation is based on setting priority classes and rejecting the minimum required number of flows per class, in order to guarantee QoS to the remaining. Both mathematical analysis and simulation results show that the overall flow rejection probability can be significantly reduced.

SIP is evolving as the dominant protocol for multimedia call control in IP networks and is expected to be widely deployed in the near future. Using SIP for supporting mobility in SIP-based networks appears as a very attractive alternative to mobile IP, taking advantage of existing SIP infrastructure and signaling, while avoiding duplication of functionality. However, existing proposals for supporting mobility with SIP are not efficient in handling micro-mobility and do not cater for all types of traffic. In this paper, we introduce hierarchical mobile SIP (HMSIP), for efficient micro-mobility management in SIP environments. HMSIP is a SIP-based scheme that builds on existing IP mobility protocols, aiming at integrating their key concepts in the most beneficial way. Our proposed scheme minimizes the handoff latency and the backbone signaling overhead, while catering for all types of traffic. Moreover, HMSIP can be effectively combined with micro-mobility schemes for QoS flows, producing, thus, a complete micro-mobility solution for SIP flows with QoS guarantees.

Future mobile communication systems beyond 3rd generation (3G) are expected to signal the transition from inflexible, vertical infrastructures to reconfigurable, horizontally integrated networks that incorporates a vast, ubiquitous space of devices and radio technologies and will be able to deliver to end-users a previously unimaginable range of valuable services. A fundamental characteristic for systems and services that operate in such a pervasive, heterogeneous environment is context-awareness that enables dynamic adaptation according to rapidly changing situational parameters. Challenging technical issues, however, need to be solved on the route to realization of this feature, including the optimal representation, placement, replication and management of the corresponding context information. This paper discusses some of these problems and introduces data management schemes that facilitate the seamless incorporation of re-usable situation-awareness functionality into a middleware platform for beyond 3G service delivery and management.

Over the last years, a number of mechanisms have been proposed for scheduling different types of traffic over base stations-oriented wireless and mobile systems. The majority of these mechanisms focus on access control in the base station-to-mobile units part of the wireless and mobile system. Recent proposals for the unlicensed spectrum in the 5GHz band have redefined the problem, since base stations, operated by different operators in overlapping geographical areas, need access resolution mechanisms to allocate wireless resources. This issue is addressed here, and a novel mechanism for dynamic channel allocation in unlicensed wireless LANs (WLANs) or public area wireless networks (PAWNs) environments is presented. The proposed method exploits the learning automata technique for the efficient allocation of wireless resources in a distributed manner. Nearby base stations that compete to access and reserve time on separate frequencies are driven by the output of a learning automaton, which determines the available carrier illustrating minimal competition. The paper discusses contention resolution disciplines while the learning automaton algorithm as well as its knowledge base structure are also discussed and evaluated.

The operation of TCP in wireless-mobile environments is discussed. After briefly presenting previous efforts to ameliorate TCP performance in the considered environments, we propose a new mechanism for tackling the slowdown problems caused by handovers. Our mechanism is based on stochastic datagram relocation. Traffic destined to the mobile terminal is tunneled to and cached into adjacent cells according to the output of a path prediction algorithm. To reduce the associated overhead, only percentages of inbound traffic are copied to the cell's neighborhood on the basis of estimated probabilities. The time scheduling for datagram relocation is also taken into account. Simulations of the proposed architecture show substantial performance improvements for TCP traffic.

A platform for the simulation of mobility functions (e.g., protocols, and application architectures) is presented. This platform, named RMPG, is based on the assumption that real humans exhibit considerable spatial and temporal regularity in their moves. We base our simulation environment on the random way-point algorithm incorporated in the ns tool. Using the Java-based RMPG we performed a series of simulations by considering a path prediction algorithm as a mobility function. We present our results.

The last decade of the 20/sup th/ century has been witness to remarkable technological developments in the area of wireless communication technologies. Following the commercial deployment-and subsequent worldwide success-of 2/sup nd/ generation mobile telecommunication systems, such as GSM, standardization bodies, industry partners and regulatory fora from around the globe joined forces in producing the standards for 3/sup rd/ generation mobile telecommunication systems. In parallel, the academic research community has been gradually shifting its focus in defining the scope of 4/sup th/ generation systems. The present paper highlights fundamental concepts and presents key market developments in 4/sup th/ generation mobile communication environments. It outlines their major high level requirements and identifies the fundamental building blocks of 4/sup th/ generation system architectures in terms of technological solution sets. Finally, it proposes a set of priorities for the 4/sup th/ generation research agenda.

Mobility and QoS provision are the two most important burdens to solve before IP becomes truly ubiquitous. Mobile IP and RSVP (resource reservation protocol) are the most visible proposals for those problems. Their interoperability, though, is inefficient. To ameliorate the compatibility problem and performance gap, we have proposed the introduction of the RSVP mobility proxy (see Paskalis, S. et al., "RSVP Mobility Proxy", Internet Draft, 2001; Workshop on Wireless Local Networks, 2001). We present a performance evaluation of our scheme versus the plain RSVP operation.

A dynamic network-based virtual private network (VPN) deployment, which is established between the general packet radio services (GPRS) border gateway and a corporate intranet gateway, is presented and analyzed. By relying on a sequence of concatenated protection mechanisms (GPRS ciphering and VPN deployment), it is possible to provide secure remote access to mobile users without requiring an extra tunnel overhead on the radio link or the implementation of computationally intense encryption algorithms in the mobile station. The VPN functionality is based on IPsec. For VPN initialization and key agreement procedures, an Internet key exchange (IKE) protocol proxy scheme is proposed, which enables the mobile user to initiate a VPN, while shifting complex key negotiation to the network infrastructure. The required enhancements for security service provision can be integrated in the existing network infrastructure, and therefore, the proposed security scheme can be used as an add-on feature of the GPRS.

An analytic estimation on the performance of a proposed decentralized multiple access technique for radio resource management of self-organized base stations (BSs) is presented. the proposed distributed dynamic channel reservation (DDCR) method applies to multicarrier wireless ATM LANs, where base stations act as hubs to offer wireless ATM access to mobile terminals (MTs). The method is suitable for unlicensed wireless nodes, and especially in scenaria when BSs with different providers are installed in a common coverage area. The paper evaluates etiquette rules, contention disciplines, medium access control (MAC) mechanisms and carrier selection rules through simulations.

The operation of TCP in wireless/mobile environments is considered. After briefly presenting previous efforts to ameliorate TCP performance in the considered environments, we propose a new mechanism for tackling the problems caused by handovers. Our mechanism is based on stochastic datagram relocation. Traffic destined to the mobile terminal is tunneled to adjacent cells according to the output of a path prediction algorithm. To reduce the associated overhead, only percentages of inbound traffic are copied to the cell's neighborhood on the basis of estimated probabilities. Through simulations, we have measured the effects that stochastic datagram relocation has on TCP dynamics.

Article Share on Using proxy cache relocation to accelerate Web browsing in wireless/mobile communications Authors: Stathes Hadjiefthymiades University of Athens, Dept. of Informatics and Telecommunications, Panepistimioupolis, Ilisia, Athens, 15784, Greece University of Athens, Dept. of Informatics and Telecommunications, Panepistimioupolis, Ilisia, Athens, 15784, GreeceView Profile , Lazaros Merakos University of Athens, Dept. of Informatics and Telecommunications, Panepistimioupolis, Ilisia, Athens, 15784, Greece University of Athens, Dept. of Informatics and Telecommunications, Panepistimioupolis, Ilisia, Athens, 15784, GreeceView Profile Authors Info & Claims WWW '01: Proceedings of the 10th international conference on World Wide WebMay 2001Pages 26–35https://doi.org/10.1145/371920.371927Published:01 April 2001Publication History 34citation983DownloadsMetricsTotal Citations34Total Downloads983Last 12 Months4Last 6 weeks0 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Publisher SiteGet Access

A distributed multiple access technique for radio resource management is presented. The proposed distributed dynamic channel reservation (DDCR) method applies to multicarrier wireless ATM LANs, where base stations act as hubs to offer wireless ATM access to mobile units. The method is suitable for unlicensed wireless systems, where base stations are installed in a common coverage area. According to the proposed approach, base stations compete to access and reserve time on separate frequencies, using a dynamic TDMA/TDD technique, combined with listening and competing periods. Etiquette rules, contention disciplines and medium access control mechanisms are proposed. Procedures for terminal association and registration, and solutions for the hidden terminal problem are introduced. Finally, the performance of the presented contention disciplines is evaluated and compared through simulations.

The scarce available bandwidth and the unpredictable, variable bit rate traffic in modern packet-switched wireless LANs, require an efficient channel allocation scheme. In this paper we make an overview of traditional call-by-call dynamic channel assignment (DCA) methods and propose a novel DCA method that aims at assigning channels in a more dynamic way, based on the quality-of-service (QoS) required by different connections. Although the method can be applied in different wireless environments, here it is used in a wireless ATM LAN, in conjunction with a TDMA/TDD medium access control protocol. Simulation results at the end of the paper show that this kind of methods can improve significantly the performance of the system.

A centralized approach for dynamic channel assignment (DCA) in wireless systems is presented. The proposed method applies to structured wireless LANs, where base stations act as hubs to offer wireless access to mobile terminals. We focus on wireless ATM LANs, although the method applies also to other packet-based systems, offering quality-of-service (QoS) guarantees. A central scheduler for DCA (CSDCA) is introduced for the dynamic assignment of resources to the requesting base stations. This scheduler takes into account mutual interference constraints of the base stations, current resource usage, and delay constraints of active connections. Simulation results have shown the improved performance attained by the proposed method.

A centralized approach for dynamic channel assignment (DCA) in wireless ATM system is presented. The proposed approach applies to structured wireless ATM LANs, where base stations act as hubs to offer wireless access to mobile units. An intradomain DCA entity (IADCA) is introduced for the dynamic assignment of resources to the requesting base stations, taking into account mutual interference constraints and current resource usage. The IADCA entity is based on two different reservation disciplines and multiple assignment policies when candidate carriers are available. Simulation results for a number of scenarios are presented to assess the performance of the proposed approach.

The introduction of ATM in wireless CPN environments (WATM) necessitates the design of mobility related protocols, since the existing versions of B-ISDN signalling (ITU-T Q.2931, ATMF UNI 3.1) do not provide the means for terminal mobility. Such protocols can be deployed either as extensions to the standard signalling capabilities or as individual solutions that have little or no impact on existing infrastructures (switches, signalling software, etc.). In this paper, after presenting a WATM architecture, we study the problem of the switching/rerouting of the signalling connections that need to be performed whenever a mobile terminal crosses cell boundaries (handover, location update). Registration and forward hard handover algorithms are proposed.

The medium access control (MAC) protocol and the underlying traffic scheduling mechanism for the radio interface are critical components of a wireless ATM network, aiming to provide ATM-like quality of service (QoS) guarantees over the air. A traffic scheduling algorithm for a wireless ATM customer premises network is proposed. The algorithm operates in the mobile terminals, and complements a centralized scheduling mechanism operating in the base stations, for improved performance. The proposed algorithm is delay oriented to meet the requirements of the various traffic classes defined by the ATM architecture. The system performance improvement attained by the proposed algorithm is evaluated via simulations.

The introduction of ATM in wireless CPN environments (WATM) necessitates the design of mobility signaling protocols, since the existing versions of B-ISDN signaling do not support terminal mobility. These protocols can be deployed as overlay solutions that have little or no impact on existing infrastructures (switches, signaling software, etc.). We present a WATM architecture and discuss the design of a mobility management and control protocol (MMC). After presenting what procedures the protocol specifies for the forward handover scenario we provide simulation results related to the performance of the system.

A wireless intelligent ATM access system is explored from a signaling protocol viewpoint. The proposed architecture is consistent with the B-ISDN user-network interface (UNI) signaling structure as a wireless local area network to access the ATM core network infrastructure, and can be adapted to cater also for a wireless broadband access network for future mobile telecommunication systems. Emphasis is placed on taking advantage of well-developed protocol standards, where appropriate, to allow the easy introduction of the proposed architecture in the real world. The evaluation of the signaling performance of the system captures the effect of the proposed structure on the performance of call and mobility control and yields results, which fall within acceptable signaling performance measures.

In this paper, a multiservice, local-area, wireless access ATM system is explored from a signaling protocol viewpoint. The signaling architecture considered here follows the signaling structure of broadband ISDN (B-ISDN) user-network interface (UNI), thus offering the possibility for integration of the wireless ATM access system into fixed B-ISDN. It is shown that the use of the employed signaling structure substantially simplifies the call/bearer and handover control. The evaluation of the signaling protocol architecture yields results, which fall within acceptable ATM signaling performance measures. A comparison with alternate access signaling configurations is also carried out to quantify the relative gains.

The multiple access problem as characterized by infinite user population and a slotted-time channel is examined, and an algorithm that utilizes a control mini-slot is proposed. The stability region of the proposed algorithm is determined and compared to the random access algorithm with the highest known throughput. A break-even point is also given.

Analyzes the throughput of a centralized packet receiver which utilizes multiuser detection in an unslotted contention channel. The receiver is capable of demodulating all overlapping, unit-length packets, provided that the T-length packet headers do not overlap, and at most K packets overlap at any one time. If one of these conditions is violated, the remainder of the busy period is assumed to be unresolvable. Assuming that the aggregate packet arrival process is Poisson, the authors analyze the throughput as a function of the total offered load (/spl lambda/), the maximum number of resolvable overlapping packets (K), and the fractional header duration (T). They derive an iterative expression for the throughput for K=2 or 3, generalizable to larger K, which permits solution of the throughput to arbitrary accuracy. A closed form solution is given for the case K=2 and T=0.5. The authors provide bounds on the throughput for arbitrary K, /spl lambda/, and T, which are more convenient than the exact approach for T>0 or large K. Numerical results illustrate the improvement in throughput due to multiuser detection, and suggest a technique for finding the minimum complexity multiuser receiver (minimum K) as a function of other system parameters.>

A key issue in future wireless access networks is the design of multiaccess protocols that enable dispersed voice and data terminals to efficiently share the terminal-to-base radio channel. A promising class of multiaccess protocols for wireless access is that of reservation random access (RRA) protocols, in which voice talkspurt packets and data packets are statistically multiplexed over TDMA frames. Voice terminals obtain reservations for their talkspurts using a random access protocol. An analysis method for evaluating the performance of a class of RRA protocols is developed. The method is based on a Markovian model, whose stationary solution is obtained via an iterative computational procedure based on matrix decomposition techniques. Subject to a maximum delay constraint, the voice packet dropping rate and distribution of the number of packets dropped from a talkspurt are evaluated for three RRA protocol examples, and comparisons are made with the performance of an ideal hypothetical multiplexer. The transient performance of RRA protocols is evaluated by simulating their response to sudden changes in the number of active voice terminals. Finally, suggestions for the design of integrated voice/data RRA protocols are made.>

Two mechanisms for shaping private network traffic in asynchronous transfer mode (ATM) broadband ISDN (B-ISDN) are proposed and analyzed. The shapers utilize the information about the network policer and implement a form of priority service to assure satisfactory levels of cell loss and delay for traffic streams with differing service requirements multiplexed into a policed ATM virtual path. The performance of the shapers is analyzed using stochastic-fluid methods and Markov-modulated models of bursty traffic sources. The numerical results illustrate the performance benefits and flexibility obtainable through the use of the proposed shapers in comparison to a simple policed path without traffic shaping.>

Future metropolitan area networks (MANs) will need a shared-medium backbone with capacity up to many gigabits per second to support the communication requirements of large numbers of users over distances of hundreds of kilometers. Efficient medium access control protocols for this future MAN environment are needed. The authors introduce and analyze a new protocol for unidirectional bus networks, in which bandwidth allocation and access fairness are adaptively controlled by the head end of the bus on the basis of traffic measurements. The proposed protocol can control the admitted traffic of a particular type to a desired fraction of the bus capacity and at the same time enforce access fairness faster than other existing protocols, such as the one used in the recently approved IEEE 802.6 MAN standard.>

A movable boundary protocol is proposed for integrating packet voice and data in unidirectional bus networks. The head station on the bus learns the number of ready-to-transmit voice stations by reading a 'request' bit in the header of the received packets and allocates the exact number of voice slots needed in each frame. The protocol guarantees that the maximum delay to transmit a voice packet will be less than the round-trip propagation delay at the head station plus twice the time needed to form the packet. The average data packet delay is evaluated via approximate analysis and simulation, for the case in which the voice-reserved slots in a frame are contiguous and for the case in which they are evenly distributed.>

The authors introduce and analyze a protocol for unidirectional bus networks in which bandwidth allocation and access fairness are adaptively controlled by the head end of the bus on the basis of traffic measurements. The proposed protocol can control the admitted traffic of a particular type to a desired fraction of the bus capacity and at the same time enforce access fairness faster than other existing protocols, such as the one used in the recently approved IEEE 802.6 metropolitan area network (MAN) standard.>

A token-ring local area network (LAN) with an infinite number of nodes uniformly distributed around the ring is considered. A token that circulates around the ring at a constant speed stops to serve fixed length packets that are generated by the nodes. It is assumed that the cumulative arrival process of packets constitutes a two-dimensional Poisson process. Given a fixed point on the ring, called the origin, the first-order statistics of the interarrival times of packets at the origin are obtained in the form of their Laplace-Stieltjes transform.>

The interconnection of two single-hop random-access networks is considered. In each network a station, called the bridge node, receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link, for subsequent broadcasting to the users of that network. In each network, the bridge node shares the available broadcast channel with the local users either via contention or via frequency division. Under the infinite population Poisson user model, conditions for the stability of the interconnected system are derived.>

A stack random access algorithm for CSMA (carrier sense multiple access) and CSMA/CO (CSMA with collision detection) channels is presented. The algorithm adapts its operation to the characteristics of the channel at hand by means of two parameters. Utilizing the regenerative character of the induced packet delay process, a lower bound on the algorithm's maximum stable throughput and very tight upper and lower bounds on the mean packet delay are derived. The packet delay distribution is estimated using the regenerative simulation method. The proposed algorithm is inherently stable, easy to implement, and combines high performance with modest channel monitoring requirements.>

The use of a switch for the interconnection of two high-speed token-ring LANs to avoid congestion at the bridge caused by the large bridge processing time is proposed. A simple network access method is described, and the delay performance of the switch-connected system is analyzed and compared with that of the bridge-connected system. For high-speed token-ring LANs, the comparison shows that the bridge will be a bottleneck unless its processing time is significantly reduced. The proposed interconnection using the switch eliminates the bottleneck problem and, depending on the bridge processing time, it can attain better delay performance than the bridge-connected system over a wide range of system parameters.>

The interconnection of CSMA/CD LANs using an N-port bridge is considered. The stability and throughput-delay performance of the interconnected system is analyzed approximately by decomposing it into N consistent but otherwise independent LAN subsystems. The performance of a LAN subsystem with bridge priority is evaluated, and the results are used for the performance evaluation of the interconnected system. Simulation results indicate that the decomposition approach provides reasonably accurate performance prediction. The bridge interconnection system is compared to a system in which the bridge is replaced by a repeater, and the performance advantages of the former system over the latter are quantified.>

The interconnection of token-ring local area networks (LANs) via store-and-forward bridges is considered. The mean-packet-delay performance of a system of token rings connected in series is analyzed by approximating the interarrival times at the bridges by renewal processes. The approximation gives simple formulas for the mean waiting times and agrees reasonably well with simulation results in most of the cases considered. Also, the conditions under which the performance of a single token-ring LAN can be improved by partitioning it into bridged subrings are investigated. It is found that splitting can improve performance as long as the fraction of the internetwork traffic is below a threshold which depends on the total input traffic.>

An analysis is presented of the delay performance of the n-ary stack algorithm, an easy-to-implement random-access algorithm that uses collision-no-collision binary feedback and requires only limited feedback sensing by the users. Utilizing the regenerative character of the stochastic processes that are associated with the random-access system, tight upper and lower bounds on the mean packet delay and on the packet delay variance are derived. It is shown that the algorithm with n=3 has the best delay characteristics. Simulation results for the percentiles of the packet delay distribution are given.>

The interconnection of two local area networks, each of which connects a large population of users via a carrier-sense multipleaccess (CSMA) channel is considered. In each network, a bridge node receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link; the bridge node of the destination network queues these internetwork packets for subsequent broadcasting to the local users. For the multiplexing of the user transmissions and the bridge node transmissions on the available broadcast channel in each network, frequency division, and contention are considered. The throughput-delay characteristics of the interconnected system operating under the above multiplexing techniques are found and comparisons are made. It is shown that contention multiplexing can yield system performance comparable to that of frequency division multiplexing, while requiring no hardware or software modification of either network in the interconnected system.

Random multiple-access algorithms are used to control the accessing of a common communication channel by a large population of bursty channel users. For such algorithms, the induced transmission delay is a key performance measure. A systematic method for finding the delay characteristics of random multiple-access algorithms, whose delay process is regenerative, is presented. The method uses a powerful result from the theory of regenerative processes, in effect, to reduce the problem of determining the delay moments to the problem of solving denumerable dimensional systems of linear equations. Techniques for finding tight bounds on the solutions of such systems are presented. The "0.487" algorithm is used to exemplify the method.

This paper considers the interconnection of two local area networks, each of which connects a large population of users via a carrier-sense multiple-access (CSMA) channel. In each network a bridge node receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link; the bridge node of the destination network queues these internetwork packets for subsequent broadcasting to the local users. The available broadcast channel in each of the two networks is frequency divided into a bridge node subchannel, used for bridge node transmissions, and a CSMA user subchannel, used for user transmissions. For the interconnected system, stability conditions, optimal bandwidth allocations, and throughput delay characteristics are found. Also it is shown that the performance of a single CSMA network can be substantially improved by partitioning it into smaller interconnected networks.

A conjecture and corrects some inaccuracies of the convergence bounds that were derived in a previous paper.