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Onboard mobile networking is a new communica- tion paradigm where in-vehicle mobile router (MR) connects a large number of passengers to the Internet via cellular (or satellite) networks. All communication to and from the public transport is transparently handled by the MR. In this commu- nication model, a call blocking of the MR would immediately disrupt on-going sessions of potentially large number of on- board passengers. This observation motivates us to investigate techniques that can reduce, and possibly regulate, call blocking probability of MRs. In this paper, we investigate two different techniques to achieve this objective. The first technique, called ca- pacity reservation (CR), reserves a portion of the total base station capacity for exclusive use by the MRs, thus giving them priority over other calls. In the second technique, called probabilistic admission control (PAC), no capacity is reserved, but other on- going calls in the base station can be interrupted to accommodate arrival of MR calls. PAC regulates the interruptions in the system by probabilistically admitting other calls. Performance of our control algorithms are evaluated and compared by discrete event simulation.

One of the critical issues in Web-based e-commerce has been how to efficiently and effectively integrate and query heterogeneous, diverse e-catalogs. We propose an integration framework for building and querying catalogs. Our approach is based on a hybrid of peer-to-peer data sharing paradigm and Web-services architecture. Peers in our system serve as domain-specific data integration mediators. Links between peers are established based on the similarity of the domain they represent. The relationships are used for routing queries among peers. As the number of catalogs involved grow larger, the need for filtering irrelevant data sources will become increasingly high. We apply a summarisation technique to summarise the content of catalogs. The summaries are used to pre-selecting data sources that are relevant to a user query.

Increasing demand on the scarce radio spectrum indicates that availability of required radio resources (e.g. wireless bandwidth) at a given time and location will be less certain in the future. Resource uncertainty inhibits many future applications that require large amount of resources to be guaranteed at specific times and locations. In order to address the problem of resource uncertainty, these applications may need to reserve network resources in advance. However, in order to support percall advance reservation, the network must store, process, and access large volume of reservation data efficiently. In particular, the admission control functions must have fast and scalable access to these reservation data for making effective decisions regarding the acceptance and rejection of both immediate and future calls. In this paper, we propose a distributed reservation database architecture that features proactive processing and delivery of reservation data to admission control functions located in each radio base-station. To demonstrate the effectiveness of our architecture, we present results from a prototype experiment that compared the proposed proactive approach with the traditional query-based data delivery approach. With proactive approach, the response time of admission control was 20 times or more faster than traditional query-based approach in our experiments.

In geographic routing, nodes need to maintain up-to-date positions of their immediate neighbours for making effective forwarding decisions. Periodic broadcasting of beacon packets that contain the geographic location coordinates of the nodes is a popular method used by most geographic routing protocols to maintain neighbour positions. We contend that periodic beaconing regardless of network mobility and traffic pattern does not make optimal ulilisation of the wireless medium and node energy. For example, if the beacon interval is too small compared to the rate at which a node changes its current position, periodic beaconing will create many redundant position updates. Similarly, when only a few nodes in a large network are involved in data forwarding, resources spent by all other nodes in maintaining their neighbour positions are greatly wasted. To address these problems, we propose the Adaptive Position Update (APU) strategy for geographic routing. Based on mobility prediction, APU enables nodes to update their position adaptively to the node mobility and traffic pattern. We embed APU into the well known Greedy Perimeter Stateless Routing Protocol (GPSR), and compare it with original GPSR in the ns-2 simulation platform. We conducted several experiments with randomly generated network topologies and mobility patterns. The results confirm that APU significantly reduces beacon overhead without having any noticeable impact on the data throughput of the network. This result is further validated through a trace driven simulation of a practical vehicular ad-hoc network topology that exhibits realistic movement patterns of public transport buses in a metropolitan city.

Providing broadband Internet access in mobile hotspots (e.g. public transport vehicles) through high-speed on-board local area networks and mobile routers is becoming an increasingly popular area of research and development. Mobile hotspot operators can provide faster, cheaper, and more stable communication services to on-board passengers using the multihoming technique, whereby the mobile router is connected to a diverse array of wireless access technologies (e.g., GPRS, UMTS, CDMA, and 802.11) through a multiplicity of wireless service providers. For mobile hotspot operators, how to "best" distribute the user traffic among the set of available access networks; which may change frequently during the trip; becomes a challenging task. In this paper, we propose and compare two traffic distribution schemes: in-transit and pre-transit, which are designed to take the benefit of multi-homing. The intransit scheme computes optimum traffic distribution on-the-fly, while the pre-transit scheme exploits the repetitive route of a public transport vehicle and computes the whole set of traffic (re)distributions before the trip starts. The objective of the traffic distribution computations is to optimize the profit and performance for the mobile hotspot operator. Using a generic public transport mobility model, we provide results from a detailed simulation study of these two schemes under different user demands.

Billing and charging is a hard issue, but an extremely important one given the increasingly commercial nature of the Internet. Economic analysis and emerging Internet technologies have stimulated charging research to new levels, and many, approaches have been produced by the Internet community in response to such stimulus, but little standardisation has resulted. This paper is a sampling of the diverse area of Internet charging, highlighting some of the key directions in previous research and giving examples of specific work.

The active programmable network (APN) has begun a new phenomenon in the logical view towards network in the Internet domain. Traditional technologies based on IP have viewed the network as a black box where the network is hidden from the upper layers. The advantage of this model is the simplicity and the robustness it can offer. However, this model may not be appropriate for the future applications of the Internet where the integration of services are expected. The APN can be considered as an alternative model where components within the network are open for programmability.

This paper reports implementation and experimentation of a new IP rate control protocol proposed to alleviate congestion in the gateway of a LAN connected to external networks. Congestion is avoided by using explicit rate notification to LAN hosts via new ICMP control messages. In addition to avoiding congestion, the protocol also allows for greater fairness and priority in network traffic, while having no impact on traffic outside the local network. The implementation of the IP rate control protocol in a Linux platform is described followed by experiments conducted at the network laboratory of Monash University. Experimental results show that IP rate control can be very effective in controlling congestion at the LAN gateway by controlling host transmission rates. IP rate control reduces queueing delay and packet loss rate at the LAN gateway.

The paper proposes feedback control theory based adaptive resource management techniques for multi-service wireless cellular networks to keep the handoff failure rate (HFR) below a target value regardless of the traffic dynamics and the bandwidth requirements of the service types. We propose two types of feedback control functions: integral (I) and proportional integral (PI). For each control function, two different types of algorithms are proposed. In the shared reservation (SR) algorithm, the reserved resources are shared by all types of services. In contrast, each service type has its own reserved resources in the reservation per service (RPS) algorithm. Performance of the controllers is evaluated through discrete event simulation. Simulation results indicate that both I and PI can maintain target HFR for any service type, even when the traffic load rapidly fluctuates and system parameters vary over a wide range. The performance of the I control function is better than PI. Between SR and RPS, SR has lower complexity and superior performance in terms of total carried traffic.

We investigate the effects of using a dual transmission power scheme for quality-of-service (QoS) differentiation in IEEE 802.11 wireless LANs. By setting hosts to transmit at different power levels, we enhance the likelihood that a high-power frame gets received correctly when a collision involving frames from both power levels occurs due to the capture effect. We develop a Markov model for the IEEE 802.11 DCF in a dual transmission power system over a Rayleigh-fading channel, and use it to evaluate the resulting performance, in terms of the key metrics of throughput and delay. Specifically, we study how the performance of the service classes depends on the proportion of hosts from each service class and the transmission power ratio, and demonstrate that, counter-intuitively, this dependence may be non-monotonic

As wireless networking products and ad-hoc networks become more popular, the resource usage in routing packets for other network users will become an issue for users and developers of ad-hoc wireless products. In this paper, we propose a novel monitoring tool called WANMon (wireless ad-hoc network monitoring tool). WANMon can be installed on a wireless node to monitor resource usage (such as network usage, power usage, memory usage, and CPU usage) at the node, in the context of how much of resource is used for supporting the node's own applications versus the usage for routing data of other network users in an ad-hoc wireless network. We discuss design of WANMon, and present our prototype implementation of WANMon in Linux, which provides a starting point for further research and a basis for developing a fully featured ad-hoc wireless network monitoring tool.

The paper is concerned with optimizing end-to-end window controls that achieve proportional fairness in the long run, and then investigating their transient or short-term fairness. An abstracted stochastic model of a bottlenecked connection is employed and the window control is designed to minimize the buffer queue variance while keeping the mean queue level at a target value, taking the round-trip delay into account. A generalized window control aimed at reducing window size fluctuations is also derived. The effects of both the target queue length and a weighting parameter on the short-term fairness, as measured by short-term fairness indices calculated over short time intervals, are investigated using ns-2 simulations.

Useless packet transmission (UPT) arises when a multimedia stream becomes unintelligible because too many packets, in aggregate, are dropped by fair queuing algorithms at routers, even with low drop rates at individual routers. We propose two UPT avoidance (UPTA) schemes for networks with multiple congested links: partial UPTA (P-UPTA), which is core-stateless, and centralized UPTA (C-UPTA), which employs a bottleneck fairshare discovery (BFD) protocol to determine a flow's global fairshare. Our simulation study shows that P-UPTA eventually detects UPT, but bandwidth may be wasted on upstream links before UPT is detected, whereas C-UPTA avoids UPT in all situations as it always drops useless packets at the network edge. We quantitatively analyse the performance of C-UPTA in conjunction with WFQ, in terms of TCP throughput, file download time, MPEG-2 video intelligibility, and fairness. The results reveal that, for the scenarios simulated, the TCP throughput is improved by up to 50% without any significant impact on the intelligibility of the MPEG-2 video and the fairness of the scheduling algorithm.

The extension of Internet services to public transport passengers is slowly becoming inevitable. To this end, it is envisaged that high-speed local area networks will be deployed on-board public transport vehicles (e.g., buses, trains, ships and planes). The on-board LAN will be connected to the Internet via an on-board mobile router (MR). The passengers simply connect their devices to the on-board LAN and start enjoying Internet services. The mobility of the entire on-board network including the passenger devices is managed transparently by the MR. However, the mobility of the router (and the entire IP subnet) gives rise to several unique challenges for achieving end-to-end resource reservation. In this paper we propose a novel extension for RSVP, which addresses these issues. The proposed On-Board RSVP protocol can effectively, transparently, and scalably support end-to-end resource reservation in on-board IP networks. A key feature of On-Board RSVP is that it retains the basic building blocks of the original RSVP, minimising the changes required to existing RSVP infrastructure. The high level of dynamism associated with the QoS resource demand in an on-board communication system results in excessive signaling and processing overhead at the MR and the intermediate routers along the end-to-end paths. To address this issue, we propose and discuss two new aggregation schemes for handling the large number of RSVP setup messages: Cardinal Operating Policy (COP) and Temporal Operating Policy (TOP).

Emerging mobile wireless networks are characterized by significant uncertainties in mobile user population and system resource state. Such networks require adaptive resource management that continuously monitor the system and dynamically adjust resource allocations, such as the number of guard channels reserved for handoff calls, for efficient system performance. The main objective of this research is to manage resource such a way so that it can maintain the target call dropping probability as well as utilize the scarce wireless resource efficiently. We propose a simple adaptive resource management scheme which is event based to adjust the number of guard channels for maintaining target call dropping probability. We try to evaluate the performance of the proposed scheme using extensive discrete event simulation. The results indicate that the scheme can guarantee the target call dropping probability under a variety of traffic conditions, and so can utilize the scarce wireless resource efficiently.

We present the design of a rate feedback architecture for TCP/IP networks. The architecture allows the traffic sources to receive periodic feedback of available rates from the network using ICMP. The sources shape their traffic according to the feedback rate. The performance of the proposed architecture is evaluated using computer simulations. Our results demonstrate that the proposed rate feedback architecture can significantly improve TCP throughput and fairness when buffering capacity in the network is extremely limited. The architecture also improves packet loss rate, delay and delay jitter in the network.

Because of the growing investment in both IP and ATM networks, designing efficient IP-ATM gateways for interconnecting these two networks has become very important. One of the main design issues is buffer dimensioning at the gateway for optimum performance. Modeling IP-ATM gateways helps obtaining the optimum design. However, due to very complex nature of an IP-ATM gateway, only models for gateways with infinite buffers have been studied previously. In this paper, an M/G/1/N model for studying the performance of IP-ATM gateway with finite buffers is presented. The performance of the IP-ATM gateway as a function of the buffer size is studied through analysis of the proposed model. The accuracy of the proposed model is verified through simulation.

Two types of errors are common in packet data transmission systems, namely the random single bit error and the burst error. We define the burst error as a consequence of the error in bits in a packet. The burst error can be independent or correlated with the single bit error within a packet, depending on the source of errors. Although the conventional models assume either independent or correlated errors, in many practical transmission systems, both types of errors are present. We propose and develop statistical models to compute the average bit error rate by simultaneously considering both the independent and the correlated errors. The results obtained from our models suggest that the conventional models may underestimate the actual bit error rate in certain systems. The proposed models are fairly general and may be applied to any transmission systems, including cellular systems, where the errors are affected by both the independent and correlated phenomena.

This paper models an acknowledgement and retransmission based transport protocol with window flow control over cell based switch using closed loop concepts; acknowledgements are based on packets (multiple cells). Calculation of cell loss probability at the switch is shown for such a model.

An analytic model for an end-to-end acknowledgement and retransmission-based transport protocol with window flow control over a cell-based switch has been developed; acknowledgements are based on packets of multiple cells. Using this model the effect of packet size, window size, and buffer size on the effective throughput or goodput of on overloaded system, where N such end-to-end sources are multiplexed onto a cell-switch, is investigated. It is shown that, for fixed window size either very small or very large packets will have better goodput. For large window and large packets, increasing the buffer size at the cell-switch will actually decrease the goodput in the overloaded case.

The design of rate allocation and queue length control in computer networks is treated as a stochastic optimal control problem. The performance index is chosen to achieve the twin objectives of minimising queue length fluctuations and fully utilising the available bandwidth. Simple, practically realisable optimal control schemes are obtained for both LANs and WANs. An adaptive scheme is proposed where the auto-regressive parameters of the traffic, needed for gain calculations, are estimated by an LMS algorithm. Discrete event simulations are carried out to verify the fluid-flow models used in developing the controllers, to compare their performance against PI controllers proposed previously, and to study the effect of self-similar traffic. Two key results are obtained. First, queue-length fluctuations, and hence potentially packet losses, are much smaller for the optimal feedforward controller than for the PI controller. Second, in contrast to uncontrolled queues, the queue length variance decreases with increasing Hurst parameter for self-similar traffic.

The recent auctioning of wireless bandwidth in various countries indicates that the service provided by Telcos over these networks will be very expensive. A new type of architecture is currently evolving as a low cost alternative cellular wireless service by allowing the users to play the role of a wireless network operator. Some users of the current Internet may install a low cost base station based on their needs and interconnection between these base stations will form a grid of wireless Internet. This paper provides a survey on related work that either uses ad-hoc mobile networking or a combination of fixed and wireless networking. Finally we present an alternate architecture and describe new issues that arise from this new type of architecture.

In absence of any link layer traffic controls or priority-queuing mechanism in LAN infrastructure (such as shared media LAN), the subnet bandwidth management based approach of managing bandwidth is limited to only the total amount of traffic load imposed by RSVP associated flows. In such cases no mechanism is available to separate RSVP flows from best effort traffic. This brings the usefulness of the subnet bandwidth manager into question. This uses a combination of integrated services of a specific link layer model based on RSVP and an IP rate-control approach for best effort traffic to manage intra-domain traffic in a differentiated services network.

As the name suggests, voice over Internet Protocol (VoIP) refers to the technology that allows transmission of voice over IP networks. Using VoIP, we can make telephone calls over the Internet or any IP-based corporate networks. With VoIP in place, the Internet does not remain a data-only network; it becomes a telephone network as well. So, what is the motivation for VoIP? There are several appealing reasons why we want this technology. The most compelling reason behind the emergence of this technology is the enormous cost savings through integration of both voice and data, two large revenue-making media for telecommunication companies, over the same communication infrastructure. The other major motivation for VoIP is the widespread adoption of IP platform. Today IP is a well-entrenched technology which is deployed in servers, routers, desktop PCs, laptops, and in many hand-held mobile devices, such as palmtops and PDAs. If voice signals could be transported over IP, then voice could be delivered to all these devices, making these devices much more useful than they already are. This chapter discusses several aspects of VoIP: (1) Advanced applications powered by VoIP, (2) the technical challenges and solutions for making VoIP a reality, (3) various VoIP configurations, and (4) the protocols and standards for VoIP. We conclude the chapter by discussing the future of VoIP.

The thrust of this study is to construct an MPLS test-bed using open hardware and software and later use this test-bed for experimenting various traffic engineering options available with MPLS. We have constructed a test-bed using Pentium PCs and Linux and used this test-bed to try a well-known MPLS traffic engineering feature of separating flows into multiple trunks. The purpose of this separation is to experimentally assess the quality of service benefits we can expect from MPLS networks. We experiment with a hierarchical separation structure where the first level of separation is based on the transport layer used (TCP or UDP). This high level separation prevents UDP from unfairly grabbing the available bandwidth from TCP applications. Since different applications using TCP have different needs, e.g., some might want high bandwidth while others are more sensitive to packet delay, the second level of separation is based on application type. The results from our open experimental test-bed confirms the intuitive results by demonstrating better QoS with the flow separation in the MPLS core.

ATM is a connection oriented network while IP is based on a connectionless protocol. Connecting the two networks requires protocol conversion. When IP packets arrive at the interconnection between the two networks, signalling is used to open a switched virtual circuit on the ATM side. In this paper, we look at the management of the ATM connection with a view to reducing the cost of the connection. We develop and compare the cost functions of three connections management policies: the delayed vacation policy, the control operating policy and the permanent virtual circuit. Furthermore, we have developed the conditions under which the control operating policy (COP) will be more cost effective than the other two policies. We conclude that there always exists some condition under which the COP will be better than the other two policies.

TiO2 nanofibers (30–50 nm diameter), fabricated by the electro-spinning process, were modified with organo-silane agents via a coupling reaction and were grafted with carbohydrate molecules. The mixture was carbonized to produce a uniform coating of amorphous carbon on the surface of the TiO2 nanofibers. The TiO2@C nanofibers were characterized by high resolution electron microscopy (HRTEM), x-ray diffraction (XRD), x-ray photoelectron (XPS), Fourier transform infrared (FTIR) and UV-vis spectroscopy. The photocatalytic property of the functional TiO2 and carbon nanocomposite was tested via the decomposition of an organic pollutant. The catalytic activity of the covalently functionalized nanocomposite was found to be significantly enhanced in comparison to unfunctionalized composite and pristine TiO2 due to the synergistic effect of nanostructured TiO2 and amorphous carbon bound via covalent bonds. The improvement in performance is due to bandgap modification in the 1D co-axial nanostructure where the anatase phase is bound by nano-carbon, providing a large surface to volume ratio within a confined space. The superior photocatalytic performance and recyclability of 1D TiO2@C nanofiber composites for water purification were established through dye degradation experiments.

The design of a traffic management mechanism for intranets connected to the Internet via an available bit rate access- link is presented. Selection of control parameters for this mechanism for optimum performance is shown through analysis. An estimate for packet loss probability at the access- gateway is derived for random fluctuation of available bit rate of the access-link. Some implementation strategies of this mechanism in the standard intranet protocol stack are also suggested.

The flow of mixed convection nanofluid over wedge under the effects of porous medium is investigated. The HFE-7100 Engineered Fluid having Nimonic 80a metal nanoparticles of spherical and non-spherical shapes with different sizes is used. The particle shape effects on Bejan number and entropy generation are taken into account. The system of partial differential equations is first written in terms of ordinary differential equations using adequate similarity transformations and then solved analytically. Analytical solutions of the resulting equations are obtained for the velocity and temperature profiles. Simultaneous effects of porous medium, particle volume friction, mixed convection parameter, and angle of wedge in the presence of different shapes nanoparticles are demonstrated graphically. Effects of particle concentrations, sizes on wall stress, heat transfer coefficient of Skin friction, and Nusselt are discussed in the form of tables.

In on-board mobile networks, such as those proposed for (and employed in) public transport vehicles, users are connected to a local network that attaches to the Internet via a mobile router and a wireless link. Central and coordinated management of mobility in a single router, rather than by each user device individually, has numerous advantages; however, it also means that link outages, e.g. due to signal degradation or handoff failure, may have an immediate impact on a potentially large number of connections. We argue that the advance knowledge of public transport routes, and their repetitive nature, allows a certain degree of prediction of impending link outages, which can be used to offset their catastrophic impact. Focusing on the TCP protocol and its extension known as Freeze-TCP, we study how the performance of the protocol depends on the outage prediction probability. In particular, we propose a Markov model of Freeze-TCP and, using simulations, show that it accurately predicts the performance improvement gained by outage prediction.

This paper proposes an extension to the standard subnet bandwidth manager (SBM). The extension controls the best effort traffic on the subnet to minimize its impact on the QoS of the RSVP (resource reservation protocol) flows. The extension is achieved by adding extra messages to the standard RSVP that enables the SBM to signal the hosts about the available bandwidth. The hosts then control the rate of best effort traffic accordingly to avoid excessive collisions on the subnet. The implementation of the proposed extension on a shared Ethernet LAN demonstrates the benefits of this extension.

We describe a Java implementation of a policy based bandwidth management system using the standard policy protocols and an interface to the Linux DiffServ implementation and demonstrate the capability of our implementation in supporting policy based dynamic resource allocations in enterprise networks.

International audience; With the rapid development of e-services on the Web, increasing number of e-catalogs are becoming accessible to users. A large number of e-catalogs provide information about similar type of products/services. To simplify users information searching effort, data integration systems have being developed to integrate e-catalogs providing similar type of information such that users can query those e-catalogs with a mediator through an uniform query interface. The conventional approach to answer a query received by a mediator is to select e-catalogs purely based on their query capabilities, i.e., query interface specifications. However, an e-catalog having the capability to answer a query does not mean it has relevant answers to the query. To remedy the wasted resources of querying catalogs that do not generate an answer, in this paper, we propose to use catalog content summary as a filter and select the relevant e-catalogs to answer a given query based not only on their query capabilities but also on their content relevance to the query. A multi-attribute content (MAC) summary is proposed to describe an e-catalog with respect to its content. With MAC summary, an e-catalog is selected to answer a query only if the e-catalog is likely having answers to the query. MAC summary can be constructed and updated using answers returned from e-catalogs and therefore the e-catalogs need not be cooperative. We evaluated MAC summary on 50 e-catalogs, and the experimental results were promising.