Access Network

Wireless mesh networks (WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. They provide network access for both mesh and conventional clients. The integration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers. Mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. WMNs are anticipated to resolve the limitations and to significantly improve the performance of ad hoc networks, wireless local area networks (WLANs), wireless personal area networks (WPANs), and wireless metropolitan area networks (WMANs). They are undergoing rapid progress and inspiring numerous deployments. WMNs will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas. Despite recent advances in wireless mesh networking, many research challenges remain in all protocol layers. This paper presents a detailed study on recent advances and open research issues in WMNs. System architectures and applications of WMNs are described, followed by discussing the critical factors influencing protocol design. Theoretical network capacity and the state-of-the-art protocols for WMNs are explored with an objective to point out a number of open research issues. Finally, testbeds, industrial practice, and current standard activities related to WMNs are highlighted.

Even though multiple non-overlapped channels exist in the 2.4GHz and 5GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel. As a result, these networks rarely can fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. This prevents them from being used as an ISP's wireless last-mile access network or as a wireless enterprise backbone network. In this paper, we propose a multi-channel wireless mesh network (WMN) architecture (called Hyacinth) that equips each mesh network node with multiple 802.11 network interface cards (NICs). The central design issues of this multi-channel WMN architecture are channel assignment and routing. We show that intelligent channel assignment is critical to Hyacinth's performance, present distributed algorithms that utilize only local traffic load information to dynamically assign channels and to route packets, and compare their performance against a centralized algorithm that performs the same functions. Through an extensive simulation study, we show that even with just 2 NICs on each node, it is possible to improve the network throughput by a factor of 6 to 7 when compared with the conventional single-channel ad hoc network architecture. We also describe and evaluate a 9-node Hyacinth prototype that is built using commodity PCs each equipped with two 802.11a NICs.

In this paper, we study the performance of route query control mechanisms for the recently proposed Zone Routing Protocol (ZRP) for ad-hoc networks. The ZRP proactively maintains routing information for a local neighborhood (routing zone), while reactively acquiring routes to destinations beyond the routing zone. This hybrid routing approach has the potential to be more efficient in the generation of control traffic than traditional routing schemes.

In this paper we study with simple analytical models the energy-aware management of cellular access networks, trying to characterize the amount of energy that can be saved by reducing the number of active cells during the periods when they are not necessary because traffic is low. When some cells are switched off, radio coverage and service provisioning are taken care of by the cells that remain active, so as to guarantee that service is available over the whole area. We show how to optimize the energy saving, first assuming that any fraction of cells can be turned off, and then accounting for the constraints resulting from the cell layout.

Wireless access to Internet services will become typical, rather than the exception as it is today. Such a vision presents great demands on mobile networks. Mobile IP represents a simple and scalable global mobility solution but lacks the support for fast handoff control and paging found in cellular telephony networks. In contrast, second-and third-generation cellular systems offer seamless mobility support but are built on complex and costly connection-oriented networking infrastructure that lacks the inherent flexibility, robustness, and scalability found in IP networks. In this article we present Cellular IP, a micro-mobility protocol that provides seamless mobility support in limited geographical areas. Cellular IP, which incorporates a number of important cellular system design principles such as paging in support of passive connectivity, is built on a foundation of IP forwarding, minimal signaling, and soft-state location management. We discuss the design, implementation, and evaluation of a Cellular IP testbed developed at Columbia University over the past several years. Built on a simple, low-cost, plug-and-play systems paradigm, Cellular IP software enables the construction of arbitrary-sized access networks scaling from picocellular to metropolitan area networks. The source code for Cellular IP is freely available from the Web (comet.columbia.edu/cellularip).

We define a cyclostationary signature as a feature which may be intentionally embedded in a digital communications signal, detected through cyclostationary analysis and used as a unique identifier. The purpose of this paper is to demonstrate how cyclostationary signatures can be exploited to overcome a number of the challenges associated with network coordination in emerging cognitive radio applications and spectrum sharing regimes. In particular we show their uses for signal detection, network identification and rendezvous and discuss these in the context of dynamic spectrum access. We present a theoretical discussion followed by application-oriented examples of the cyclostationary signatures used in practical cognitive radio and dynamic spectrum usage scenarios. We focus on orthogonal frequency division multiplexing (OFDM) based systems and present an analysis of a transceiver implementation employing these techniques developed on a cognitive radio test platform.

Recently, peer-to-peer (P2P) networks have emerged as an attractive solution to enable large-scale content distribution without requiring major infrastructure investments. While such P2P solutions appear highly beneficial for content providers and end-users, there seems to be a growing concern among Internet Service Providers (ISPs) that now need to support the distribution cost. In this work, we explore the potential impact of future P2P file delivery mechanisms as seen from three different perspectives: i) the content provider, ii) the ISPs, and iii) individual content consumers. Using a diverse set of measurements including Bit-Torrent tracker logs and payload packet traces collected at the edge of a 20,000 user access network, we quantify the impact of peer-assisted file delivery on end-user experience and resource consumption. We further compare it with the performance expected from traditional distribution mechanisms based on large server farms and Content Distribution Networks (CDNs).

The architecture for the Beyond 3rd Generation (B3G) or 4th Generation (4G) wireless networks aims to integrate various heterogeneous wireless access networks. One of the major design issues is the support of vertical handoff. Vertical handoff occurs when a mobile terminal switches from one network to another (e.g., from WLAN to CDMA 1xRTT). The objective of this paper is to determine the conditions under which vertical handoff should be performed. The problem is formulated as a Markov decision process with the objective of maximizing the total expected reward per connection. The network resources utilized by the connection are captured by a link reward function. A signaling cost is used to model the signaling and processing load incurred on the network when vertical handoff is performed. The value iteration algorithm is used to compute a stationary deterministic policy. For the performance evaluation, voice and data applications are considered. The numerical results show that our proposed scheme performs better than other vertical handoff decision algorithms, namely: Simple Additive Weighting (SAW), Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), and Grey Relational Analysis (GRA).

Wireless mesh networks (WMNs) are low-cost access networks built on cooperative routing over a backbone composed of stationary wireless routers. WMNs must deal with the highly unstable wireless medium. Thus, routing metrics and protocols are evolving by designing algorithms that consider link quality to choose the best routes. In this work, we analyze the state of the art in WMN metrics and propose a taxonomy for WMN routing protocols. Performance measurements of a wireless mesh network deployed using various routing metrics are presented and corroborate our analysis.

Since the energy crisis and environmental protection are gaining increasing concerns in recent years, new research topics to devise technological solutions for energy conservation are being investigated in many scientific disciplines. Specifically, due to the rapid growth of energy consumption in ICT (Information and Communication Technologies), lot of attention is being devoted towards "green" ICT solutions. In this paper, we provide a comprehensive survey of the most relevant research activities for minimizing energy consumption in telecom networks, with a specific emphasis on those employing optical technologies. We investigate the energy-minimization opportunities enabled by optical technologies and classify the existing approaches over different network domains, namely core, metro, and access networks. A section is also devoted to describe energy-efficient solutions for some of today's important applications using optical network technology, e.g., grid computing and data centers. We provide an overview of the ongoing standardization efforts in this area. This work presents a comprehensive and timely survey on a growing field of research, as it covers most aspects of energy consumption in optical telecom networks. We aim at providing a comprehensive reference for the growing base of researchers who will work on energy efficiency of telecom networks in the upcoming years.

The hybrid wireless-optical broadband-access network (WOBAN) is a promising architecture for future access networks. Recently, the wireless part of WOBAN has been gaining increasing attention, and early versions are being deployed as municipal access solutions to eliminate the wired drop to every wireless router at customer premises. This architecture saves on network deployment cost because the fiber need not penetrate each end-user, and it extends the reach of emerging optical-access solutions, such as passive optical networks. This paper first presents an architecture and a vision for the WOBAN and articulates why the combination of wireless and optical presents a compelling solution that optimizes the best of both worlds. While this discussion briefly touches upon the business drivers, the main arguments are based on technical and deployment considerations. Consequently, the rest of this paper reviews a variety of relevant research challenges, namely, network setup, network connectivity, and fault-tolerant behavior of the WOBAN. In the network setup, we review the design of a WOBAN where the back end is a wired optical network, the front end is managed by a wireless connectivity, and, in between, the tail ends of the optical part [known as optical network unit (ONU)] communicate directly with wireless base stations (known as "gateway routers"). We outline algorithms to optimize the placement of ONUs in a WOBAN and report on a survey that we conducted on the distribution and types of wireless routers in the Wildhorse residential neighborhood of North Davis, CA. Then, we examine the WOBAN's routing properties (network connectivity), discuss the pros and cons of various routing algorithms, and summarize the idea behind fault-tolerant design of such hybrid networks.

The integration of optical and wireless systems is considered to be one of the most promising solutions for increasing the existing capacity and mobility as well as decreasing the costs in next-generation optical access networks. In this paper, several key enabling technologies for hybrid optical-wireless access networks are described, including optical millimeter-wave (mm-wave) generation, upconversion, and transmission in a downlink direction, and full-duplex operation based on wavelength reuse by using a centralized light source in an uplink direction. By employing these enabling technologies, we design and experimentally demonstrate an optical-wireless testbed that is simultaneously delivering wired and wireless services in the integrated optical-wireless and wavelength-division-multiplexing passive-optical-network access networks. The actual applications consisting of 270-Mb/s uncompressed standard-definition TV signal and 2.5-Gb/s data channels for downstream are successfully transmitted over a 25-km fiber and a 10.2-m indoor wireless link with less than a 1.5-dB power penalty. The results show that this integrated system is a practical solution to deliver superbroadband information services to both stationary and mobile users.

We propose a bidirectional wavelength-division-multiplexed passive optical network by employing gain-saturated reflective semiconductor optical amplifiers (RSOAs) for wavelength-independent optical network terminals. The fabricated RSOA module has the input saturation power less than 13 dBm and its saturated gain higher than 13 dB within the -band for arbitrary polarization states. The upstream signals are generated by remodulating the downstream signals whose modulation amplitude is squeezed through gain-saturated RSOAs. We present experimental results on bidirectional transmission with 1.25 Gb/s for upstream and 2.5 Gb/s for downstream data rates over 20-km transmission distance.

Location-Based Services (LBS) use positioning technology to provide individual users the capability of being constantly reachable and accessing network services while ‘on the move’. However, privacy concerns associated with the use of LBS may ultimately prevent consumers from gaining the convenience of ‘anytime anywhere’ personalized services. We examine the adoption of this emerging technology through a privacy lens. Drawing on the privacy literature and theories of technology adoption, we use a survey approach to develop and test a conceptual model to explore the effects of privacy concerns and personal innovativeness on customers’ adoption of LBS. In addition, as a number of IS researchers have shown that customers differ in their decision making for continued adoption as compared to initial decision making, we test the research model separately for potential and experienced customers. The results indicate that privacy concerns significantly influence continued adoption as compared to initial adoption. The implications for theory and practice are discussed.

In this paper, the authors propose a next-generation hybrid WDM/TDM optical access network architecture called Stanford University aCCESS or SUCCESS. This architecture provides practical migration steps from current-generation time-division multiplexing (TDM)-passive optical network (PONs) to future WDM optical access networks. The architecture is backward compatible for users on existing TDM-PONs, while simultaneously capable of providing upgraded high-bandwidth services to new users on DWDM-PONs through advanced WDM techniques. The SUCCESS architecture is based on a collector ring and several distribution stars connecting the CO and the users.

In this paper, we studied SC generation in fiber lasers and in optical fibers pumped by different light sources which include fs and ps pulse sources, and continuous-wave (CW) amplified spontaneous emission (ASE) light sources. First, we demonstrated SC generation with a 10dB spectral bandwidth of 430nm in a fiber ring laser with conventional nonlinear fiber. Second, we proposed and demonstrated a new and efficient approach to generation of a CW SC in optical fibers pumped by a CW ASE light. A bandwidth of 268nm (at -15dB level) with an average spectral density of 2.7mW/nm was demonstrated. Various approaches to flattening the spectrum and increasing the spectral width were also studied. The application of this SC source in WDM passive optical access networks (WDM-PONs) was investigated. Third, the approach of SC generation in a fiber combination of standard SMF and nonlinear DSF pumped by an all-fiber fs pulse Master Oscillator Power Amplifier (MOPA) system was developed. A spectral bandwidth of over 1000nm was demonstrated. Finally, the generation of broad comb-like-spectral light based on the pulse compression of 40GHz optical pulses in a new nonlinear dispersion-decreasing fiber with high SBS threshold was studied. A continuum light source with over 125 channels and a channel spacing of 40 GHz was achieved. The use of this continuum light source as WDM source in WDM-PONs was investigated.

Internet routers require buffers to hold packets during times of congestion. The buffers need to be fast, and so ideally they should be small enough to use fast memory technologies such as SRAM or all-optical buffering. Unfortunately, a widely used rule-of-thumb says we need a bandwidth-delay product of buffering at each router so as not to lose link utilization. This can be prohibitively large. In a recent paper, Appenzeller et al. challenged this rule-of-thumb and showed that for a backbone network, the buffer size can be divided by √ N without sacrificing throughput, where N is the number of flows sharing the bottleneck. In this paper, we explore how buffers in the backbone can be significantly reduced even more, to as little as a few dozen packets, if we are willing to sacrifice a small amount of link capacity. We argue that if the TCP sources are not overly bursty, then fewer than twenty packet buffers are sufficient for high throughput. Specifically, we argue that O(log W ) buffers are sufficient, where W is the window size of each flow. We support our claim with analysis and a variety of simulations. The change we need to make to TCP is minimal-each sender just needs to pace packet injections from its window. Moreover, there is some evidence that such small buffers are sufficient even if we don't modify the TCP sources so long as the access network is much slower than the backbone, which is true today and likely to remain true in the future.

Next generation wireless network standards are currently being defined. The access network architectures have several specialized components tailored for their respective wireless link technologies even though the services provided by these different wireless networks are fairly similar. In this paper, we propose a homogeneous IPbased network as a common access network for the different wireless technologies. The IP-based access network uses the internet standard, Mobile IP, for supporting macro-mobility of mobile hosts and HAWAII for supporting micro-mobility and paging functionality of current wireless networks. We also illustrate how the proposed IPbased solution can interwork with existing infrastructure so that deployment can be incremental.

We investigate the use of optical differential phase-shift keying (DPSK) as the downstream modulation format in a low-cost upstream data remodulation scheme for a wavelength-division multiplexing (WDM)-based passive optical network. A 2.5-Gb/s upstream data transmitter is realized by directly modulating a Fabry-Pérot (FP) laser, injection-locked with a 10-Gb/s downstream optical DPSK signal. A simple polarization-offset technique is proposed to largely minimize the induced power penalty. Index Terms-differential phase-shift keying (DPSK), modulation, passive optical networks (PONs), wavelength-division multiplexing (WDM).

Development in wireless access technologies and multihomed personal user devices is driving the way towards a heterogeneous wireless access network environment. Success in this arena will be reliant on the ability to offer an enhanced user experience. Users will plan to take advantage of the competition and always connect to the network which can best service their preferences for the current application. They will rely on intelligent network selection decision strategies to aid them in their choice. The contribution of this paper is to propose an intelligent utility-based strategy for network selection in this multi-access network scenario. A number of utility functions are examined which explore different user attitudes to risk for money and delay preferences related to their current application. For example we show that risk takers who are willing to pay more money get a better service.

Collaborative beamforming has been recently introduced in the context of wireless sensor networks (WSNs) to increase the transmission range of individual sensor nodes. In this paper, it is proposed to model the spatial distribution of sensor nodes in a cluster using Gaussian probability density function (pdf). Gaussian pdf is more appropriate for many WSN applications than the previously considered uniform pdf which is more suitable when sensor nodes are deployed one at a time. The average beampattern and its characteristics, the distribution function of the beampattern level in the sidelobe region, and the upper bound on the outage probability of sidelobes are derived using the theory of random arrays.

In the ICEBERG project at U. C. Berkeley, we are developing an Internet-based integration of telephony and data services spanning diverse access networks. Our primary goals are extensibility, scalability, robustness and personalized communication. We leverage the Internet's low cost of entry for service creation, provision, deployment, and integration. In this article, we present our solutions to signaling, easy service creation, resource reservation, admission control, billing and security in the ICEBERG network architecture.

Abstract-While the backbone networks have experienced substantial changes in the last decade; the access networks have not changed much. Recently, passive optical networks (PONs) seem to be ready for commercial deployment in access networks due to the ...

The ever growing bandwidth in access networks, in combination with IPTV and Video on Demand (VoD) offerings, opens up unlimited possibilities to the users. The operators can no longer compete solely on the number of channels or content and increasingly make High Definition channels and Quality of Experience (QoE) a service differentiator. Currently the most reliable way of assessing and measuring QoE is conducting subjective experiments, where human observers evaluate a series of short video sequences, using one of the international standardized subjective quality assessment methodologies. Unfortunately, since these subjective experiments need to be conducted in controlled environments and pose limitations on the sequences and overall experiment duration they cannot be used for reallife QoE assessment of IPTV and VoD services. In this article, we propose a novel subjective quality assessment methodology based on full length movies. Our methodology enables audiovisual quality assessment in the same environments and under the same conditions users typically watch television. Using our new methodology we conducted subjective experiments and compared the outcome with the results from a subjective test conducted using a standardized method. Our findings indicate significant differences in terms of impairment visibility and tolerance and highlight the importance of real-life QoE assessment.

In this paper, we propose a novel downlink resource management framework for multiservice WiMAX (Worldwide Interoperability for Microwave Access) networks. Our framework consists of two major components: adaptive power allocation (APA) and call admission control (CAC). We formulate each of them as an optimization problem, where the demands of both WiMAX service providers and subscribers are taken into account. To solve the optimization problems, we develop a fairness-constrained greedy revenue algorithm for downlink APA optimization and a utility-constrained greedy approximation algorithm for downlink CAC optimization. Our simulation results show that, when combining the APA and CAC optimization methods together, the proposed resource management framework can meet the expectations of both service providers and subscribers.

The sensitiveness toward energy consumption problems is driving Telecommunications operators to optimize network equipment utilization. Since cellular systems are often dimensioned for peak hour traffic, during low traffic periods, such as night, many devices are underutilized but still, by being active, consume power. In this paper, we show that dynamic planning, consisting in reducing the number of active access devices when traffic is low, can achieve significant power saving. In our study, we consider three different UMTS scenarios with a simplified traffic model describing three classes of services, quality of service guarantees, link-budget, propagation and electromagnetic exposure constraints.

Cognitive radio (CR) has been considered as a promising technology to improve the spectrum utilization. In this paper we analyze the capacity of a CR network with average received interference power constraints. Under the assumptions of uniform node placements and a simple power control scheme, the maximum transmit power of a target CR transmitter is characterized by its cumulative distribution function (CDF). We study two CR scenarios for future applications. The first scenario is called the CR based central access network, which aims at providing broadband access to CR devices. In the second scenario, the so-called CR assisted virtual multiple-input multiple-output (MIMO) network, CR is used to improve the access capability of a cellular system. The uplink ergodic channel capacities of both scenarios are derived and analyzed with an emphasis on understanding the impact of numbers of primary users and CR users on the capacity. Numerical and simulation results suggest that the CR based central access network is more suitable for less-populated rural areas where a relatively low density of primary receivers is expected; while the CR assisted virtual MIMO network performs better in urban environments with a dense population of mobile CR users.

Access networks consume a significant portion of overall Internet energy consumption. With the increase of bit-rate requirements in access networks, future-proof access technologies should be energy efficient. In this paper, we show how we can build a very high-throughput "green" hybrid wireless-optical broadband access network (WOBAN). We devise novel energy-saving techniques for WOBAN to improve its energy efficiency and network utilization. We present a mixed integer linear program (MILP) model, which acts as a benchmark for evaluating our techniques. We analyze the impact of energy-aware design and protocols on the performance of WOBAN over dynamic traffic profiles. Illustrative numerical examples show that, with suitable design parameters, we can efficiently reduce energy consumption in WOBAN without significantly impacting the network performance.

This article provides an overview of a network-based model of power consumption in Internet infrastructure. This model provides insight into how different parts of the Internet will contribute to network power as Internet access increase over time. The model shows that today the access network dominates the Internet's power consumption and, as access speeds grow, the core network routers will dominate power consumption. The power consumption of data centers and content distribution networks is dominated by the power consumption of data storage for material that is infrequently downloaded and by the transport of the data for material that is frequently downloaded. Based on the model several strategies to improve the energy efficiency of the Internet are presented.

1] As the number of ground-based and space-based receivers tracking the Global Positioning System (GPS) satellites steadily increases, it is becoming possible to monitor changes in the ionosphere continuously and on a global scale with unprecedented accuracy and reliability. As of August 2005, there are more than 1000 globally distributed dual-frequency GPS receivers available using publicly accessible networks including, for example, the International GPS Service and the continuously operating reference stations. To take advantage of the vast amount of GPS data, researchers use a number of techniques to estimate satellite and receiver interfrequency biases and the total electron content (TEC) of the ionosphere. Most techniques estimate vertical ionospheric structure and, simultaneously, hardware-related biases treated as nuisance parameters. These methods often are limited to 200 GPS receivers and use a sequential least squares or Kalman filter approach. The biases are later removed from the measurements to obtain unbiased TEC. In our approach to calibrating GPS receiver and transmitter interfrequency biases we take advantage of all available GPS receivers using a new processing algorithm based on the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This new capability is designed to estimate receiver biases for all stations. We solve for the instrumental biases by modeling the ionospheric delay and removing it from the observation equation using precomputed GIM maps. The precomputed GIM maps rely on 200 globally distributed GPS receivers to establish the ''background'' used to model the ionosphere at the remaining 800 GPS sites.

Purpose: This paper examines the challenges female entrepreneurs face in the development of their business in the context of Nigeria. In so doing, it addresses a gap in the literature on the experiences of female entrepreneurs in a non-Western context and acknowledges the contribution that women make in this area of work.

There have been several studies in the past years that investigate the impact of network delay on multi-user applications. Primary examples of these applications are real-time multiplayer games. These studies have shown that high network delays and jitter may indeed influence the player's perception of the quality of the game. However, the proposed test values, which are often high, are not always representative for a large percentile of on-line game players. We have therefore investigated the influence of delay and jitter with numbers that are more representative for typical access networks. This in effect allows us to simulate a setup with multiplayer game servers that are located at ISP level and players connected through that ISP's access network. To obtain further true-to-life results, we opted to carry out the test using a recent first person shooter (FPS) game, Unreal Tournament 2003. It can, after all, be expected that this new generation of games has built-in features to diminish the effect of small delay values, given the popularity of playing these games over the Internet. In this paper, we have investigated both subjective perceived quality and objective measurements and will show that both are indeed influenced by even these small delay and jitter values.

Welcome to this special issue of the EURASIP Journal on Wireless Communications and Networking (JWCN). This special issue is devoted to the topic of the latest research and development on Broadband Wireless Access (BWA) from physical and network layers to practical applications. BWA is the combined consequence of recent advances in wireless communications, high demands on multimedia services, and also increasing requirements on the ubiquitous computing capability. Various BWAs are being standardized by international organizations, for example, IEEE 802.16 WiMAX and the 3rd Generation Partnership Project's High Speed Packaet Access (HSPA) and its Long-Term Evolution (LTE). These technologies provide the reliable means for delivering telecommunication services over the Internet, supporting transmission rates up to several megabits per second at distances as far as tens of kilometers.

The advantages of employing passive optical architectures in the access network have been largely recognized. Particularly, recent developments in optical technologies have made the realization of wavelength division multiplexing passive optical networks (WDM PONs) feasible and cost-effective. These networks are more future-proof than conventional PONs, thanks to their intrinsic optical transparency and their extremely high transmission capacity. A very useful optical routing device, called waveguide grating router, is the basic building-block of new PON architectures capable of connecting a large number of users or to improve the use of the optical bandwidth. In this paper, we analyze the connectivity of WDM PONs composed of multiple stages of WGR devices. A design tool is also presented which is able to easily evaluate the connectivity functions of complex WDM PONs. The feasibility of these architectures is discussed by considering the costs and the technological limitations on the optical components.

The assumption that all nodes cooperate to relay packets for each other may not be realistic for commercial wireless ad hoc networks. An autonomous (selfish) node in a wireless network has two disincentives for forwarding for others: energy expenditure (real cost) and possible delays for its own data (opportunity cost). We introduce a mechanism that "fosters cooperation through bribery" in the context of forwarding in ad hoc networks. Using a microeconomic framework based on game theory, we design and analyze a pricing algorithm that encourages forwarding among autonomous nodes by reimbursing forwarding. Taking a joint network-centric and user-centric approach, the revenue maximizing network and utility (measured in bits-per-Joule) maximizing nodes interact through prices for channel use, reimbursements for forwarding, transmitter power control, as well as forwarding and destination preferences. In a three-node (two-sources, one-access-point) network, the network converges to an architecture that induces forwarding only when the network geometries are such that forwarding is likely to increase individual benefits (network revenue and node utilities). For other geometries, the network converges to architectures that do not favor forwarding. We then generalize to a multinode network, where it is seen that the nodes' willingness to forward decrease for large ratios of the average internodal distance to the smallest distance between the access point and any source node. Pricing with reimbursement generally improves the network aggregate utility (or aggregate bits-per-Joule), as well as utilities and revenue compared with the corresponding pricing algorithm without reimbursement.

The rapid progress of communications technology has created new opportunities for modeling and optimizing the design of local telecommunication systems. The complexity, diversity, and continuous evolution of these networks pose several modeling challenges. In this paper, we present an overview of the local telephone network environment, and discuss possible modeling approaches. In particular, we (i) discuss the engineering characteristics of the network, and introduce terminology that is commonly used in the communications industry and literature; (ii) describe a general local access network planning model and framework, and motivate different possible modeling assumptions; (iii) summarize various existing planning models in the context of this framework; and, (iv) describe some new modeling approaches. The discussion in this paper is directed both to researchers interested in modeling local telecommunications systems and to planners interested in using such models. Our goal is to present relevant aspects of the engineering environment for the local access telecommunication network, and to discuss the relationship of the engineering issues to the formulation of economic decision models. We indicate how changes in the underlying switching and transmission technology affect the modeling of the local telephone network. We also review various planning issues and discuss possible optimization approaches for treating them. will have access to a broad range of new services combirung voice, data, graphics, and video. New applications include telemetry, database access, videophone facilities, improved networking services, access to packet networks, and customer controlled network management. Telephone companies are already planning for an even more ambitious expansion of services and capabilities (the so-called broadband ISDN network) when fiber optics will permeate the entire communication system, all the way to the individual customers' homes (Kostas (1984), Dettmer (1985), Toth, Colombini, McClaren, and Yates (1985), The Economist (1987), Fortune (1988)). Thus, ISDN combined with the new switching and transmission technologies is expected to greatly stimulate network usage. To accomodate the anticipated demand increase, telephone companies have initiated extensive modeling and planning efforts to expand and upgrade their switching and transmission facilities.-1 Network modernization and expansion is particularly critical in the local access component of the communication system, both for strategic and economic reasons. In the last few years, the long-distance carriers have almost completed the transition to digital switching technologies and fiber optic transmission. In contrast, the technological changes in the local telephone network, which accounts for approximately 60% of the total investment in communication facilities, have been much more modest. For instance, in 1987, only 20% of all the local access networks in the U. S. employed digital switching (The Economist, 1987). Thus, the ability to offer the proposed advanced ISDN telecommunication services is limited by the current capabilities of local networks, and local telephone companies face competitive pressures to upgrade their networks rapidly. Because modernizing and expanding switching and transmission facilities requires enormous investments, telephone compianies typically priortize expansion projects based on demand growth potential and emphasize cost effectiveness in implementing the selected projects. For each project, network planners face complex choices concerning where and when to expand capacity or replace current technology in order to meet the increasing demand for different types of services. The emergence of new communication technologies has created additional decision alternatives and tradeoffs and, hence, new modeling challenges that did not arise in the traditional analog and copper environment. For instance, deploying concentrators and multiplexers in the local access network now provides an alternative method (instead of cable expansion) for increasing network capacity. As a consequence, network planners require new decision support models to identify cost effective expansion and modernization strategies. This paper focuses on contemporary expansion planning models for the local access component (from the customer premises to the serving sv^tching center) of public telephone networks. We do not address design issues, such as the blocking of potential transmissions or network vulnerability, that are more relevant for long-distance networks. Similarly, our models might not apply directly to data networks or rural networks since these latter network types employ different technologies (for example, rural networks use radio transmission, and data networks employ packet switching) and different design criteria (e.g., reducing packet delay in data networks). Our purpose in this papjer is to discuss alternative modeling approaches rather than a specific methodology for local access network planning. The various models that we consider differ in their another based on tree covering concepts. Section 5 offers concluding remarks. 2. The Local Telecommunication Network This section describes the Icxral access network, traces its evolution over the last few decades, and introduces some communications terminology. CXir intent is to describe some important technological features so that we can represent them adequately in economic planning models. 2.1 The Communication Network Hierarchy Most rudonal telecommunications networks can be broadly divided into the three main levels shown in Figure 1, namely, (i) the long-distance, toll or inter-city network that typically connects city pairs through gateway nodes (also called point-of-presence nodes, Lavin (1987)); (ii) the inter-office or switching center network within each city that interconnects switching centers (also called local exchanges, or central offices) in different subdivisions (clusters of customers), and provides access to the gateway node(s); and, (iii) the local access network that connects individual subscribers belonging to a cluster to the corresponding switching center. These three levels of the communication system hierarchy differ in several respects: the processing capabilities and amount of intelligence they contain, the technologies they employ, the services they perform, and their design criteria. For instance, the local access network typically has a tree configuration and contains a dedicated communication channel connecting each customer to the switching center. Currently, most (approximately 80% in the U.S.) local access networks use analog transmission on copp>er cables, and do not contain electronic devices. In contrast, thelong-distance network has a relatively dense topology providing multiple communication paths between each origindestination pair. The gateway nodes on this network contain intelligent hardware to perform switching, traffic compression (concentration), and some service functions (such as directory assistance). The long-distance networks in the U.S. are almost completely digitized, and employ high frequency transmission using fiber optics, microwave (radio), and satellite communications. The inter-office

This paper discusses the role of ad hoc networking in future wireless communications. Ad hoc networks are'classified as isolated ad hoc networks with large and small sizes, integrated ad hoc networks in various scenarios and cellular ad hoc networks for the future mobile access networks. The very low traffic performance of large scale ad hoc networks is shown by simulation results, indicating such a kind of networks having little commercial potential Small size ad hoc networks seem to be ubiquitous because of the availability of cheap wireless LAN technologies. Integration of small size ad hoc networks with the global Internet can be realized by ad hoc gateways, that are proposed in this paper. In contrast to large scale isolated ad hoc networks, traffic performance of a cellular ad hoc network is very promising, indicating that cellular ad hoc networking seems to be a promising solution to fulfill the requirements of future wireless communication systems. Keywords-ad hoc networking;beyond 3C; mukihop; ad hoc routing; mobile IP; gateway; traff7c performance.

Optical access networks are considered to be a definite solution to the problem of upgrading current congested access networks to ones capable of delivering future broadband integrated services. However, the high deployment and maintenance cost of traditional point-to-point architectures is a major economic barrier. Current TDM-PON architectures are economically feasible, but bandwidth-limited. In this article we first discuss the possible role of WDM in access networks and investigate the associated issues. We then present the Stanford University Access Hybrid WDM/TDM Passive Optical Network (SUCCESS-HPON), a next-generation hybrid WDM/TDM optical access architecture that focuses on providing a smooth migration path from current TDM-PONs to future WDM-PONs. The first testbed for this architecture is described, along with the experimental results obtained, including feasibility of bidirectional transmission on the same wavelength on the same fiber for access networks and ONU modulation of upstream data on continuous waves provided by the OLT, eliminating the need for tunable components at the ONUs. The development of a second testbed and the issues it will address, including the implementability of the SUCCESS-HPON MAC protocol and scheduling algorithms, are also described.

This paper presents an intelligent mobility management scheme for Mobile Wireless InterNet -MWIN. MWIN is a wireless service networks wherein its core network consisting of Internet routers and its access network can be built from any Internet-capable radio network. Two major standards are currently available for MWIN, i.e., the mobile IP and wireless LAN. Mobile IP solves address mobility problem with the Internet protocol while wireless LAN provides a wireless Internet access in the local area. However, both schemes solve problems independently at different layers, thereby some additional problems occur, e.g., delayed handoff, packet loss, and inefficient routing. This paper identifies these new problems and performs analyses and some real measurements on the handoff within MWIN. Then, a new handoff architecture that extends the features of both mobile IP and wireless LAN handoff mechanism was proposed. This new architecture consists of mobile IP extensions and a modified wireless LAN handoff algorithm. The effect of this enhancement provides a linkage between different layers for preventing packet loss and reducing handoff latency. Finally, some optimization issues regarding network planning and routing are addressed.

HTTP-based delivery for Video on Demand (VoD) has been gaining popularity within recent years. Progressive Download over HTTP, typically used in VoD, takes advantage of the widely deployed network caches to relieve video servers from sending the same content to a high number of users in the same access network. However, due to a sharp increase in the requests at peak hours or due to cross-traffic within the network, congestion may arise in the cache feeder link or access link respectively. Since the connection characteristics may vary over the time, with Dynamic Adaptive Streaming over HTTP (DASH), a technique that has been recently proposed, video clients may dynamically adapt the requested video quality for ongoing video flows, to match their current download rate as good as possible. In this work we show the benefits of using the Scalable Video Coding (SVC) for such a DASH environment.

The emerging context-aware applications relying on the wireless networking, require the availability of network services that provide even simple notions of context as position and identity. In the last few years several localization and tracking systems for indoor environment have been proposed. However, these systems are often very expensive since they require the installation of dedicated infrastructures of sensors based on radio, ultrasound or infrared technologies, to determine the user position. This paper aims to propose and analyze a novel indoor localization and tracking system based on the Bluetooth technology. This is a short-range, low complexity and low cost wireless technology that supports explicit device discovery services. The proposed localization system fully integrates these device discovery procedures into the infrastructure-based network of Bluetooth access points that provides the wireless connectivity inside a building. This design approach guarantees a cost-effective solution for the positioning service implementation. In this paper we have extensively investigated through simulative analysis the performances of the proposed localization system, showing that it has a negligible overhead, still providing a timely update of user location.