This investigation addresses an important and difficult combinatorial optimization problem in the design and management of telecommunication systems known as the path assignment problem. The path assignment problem is specified by a set of demands on a network with given link capacities. Each demand must be assigned to exactly one routing path in such a way that the total amount of traffic routed over any link does not exceed that link’s capacity. Given a network and a path assignment, the problem of interest is to maximize the available bandwidth (throughput) for a new demand. Network managers are concerned with the quality of service provided by their networks, and so they are reluctant to make major changes to an operating network that may inadvertently result in service disruptions for numerous clients simultaneously. Therefore, the objective of this investigation is to develop and test optimization models and algorithms that produce a series of throughput-improving modifications to the original path assignment. This allows network managers to implement the improved routing in stages with minimal changes to the overall routing plan between any two consecutive stages. Although the procedure may only reroute a few demands at each stage, the routing after the last stage should be as close as possible to an optimal routing. That is, it must maximize the throughput for the new demand. We present integer programming models and associated solution algorithms to maximize the throughput with a sequence of incremental path modifications. The algorithms were implemented with the AMPL modeling language and the CPLEX ILP solver, and tested on a family of five different data sets based on a European network widely studied in the literature. Empirical results show that the incremental approach finds near-optimal results within reasonable limits on CPU time.

Handovers in mobile packet networks commonly produce packet loss, delay and jitter, thereby significantly degrading network performance. Mobile IPv6 handover performance is strongly topology dependent and results in inferior service quality in wide area scenarios. To approach seamless mobility in IPv6 networks predictive, reactive and proxy schemes have been proposed for improvement. In this article we analyse and compare handover performance and frequencies for the corresponding protocols, as they are an immediate measure on service quality. Using analytical methods as well as stochastic simulations, we calculate the performance decreases originating from different handover schemes, the expected number of handovers as functions of mobility and proxy ratios, as well as the mean correctness of predictions. In detail we treat the more delicate case of these rates in mobile multicast communication. It is obtained that performance benefits, expected from simple analysis of predictive schemes, do not hold in practice. Reactive and predictive handovers rather admit comparable performance. Hierarchical proxy environments—foremost in regions of high mobility—can significantly reduce the processing of inter–network changes. Reliability of handover predictions is found on average at about 50%.

The IETF developed two main approaches to provide QoS aware services in the Internet: Integrated Services (IntServ) and Differentiated Services (DiffServ). Both have well known pros and cons (e.g., [Huston, 24; Bernet et al., 2]). The stateful IntServ has a greater level of accuracy and a finer level of granularity. The stateless DiffServ possesses excellent scaling properties, but lacks a standardized admission control scheme and, upon overload in a given service class, degradation of service can occur. To provide QoS in DiffServ, three possible strategies are: (i) plain and heavy over-dimensioning; (ii) admission control at the borders of the DiffServ region, coupled with suitable assumptions on the distribution of the traffic within the region, which can lead to over-dimensioning, even if less severe than the previous one; (iii) per-node admission control within the region. Following RFC2990, we recently proposed an “admission control function which can determine whether to admit a service differentiated flow along the nominated network path” [Huston, 24], i.e., the third of the above strategies. This function, named GRIP (Gauge and Gate Reservation with Independent Probing), can provide strict QoS guarantees by means of stateless DiffServ-compliant procedures. This feature is paid with a potential loss of efficiency, with respect to an ideal, stateful admission control. The goal of this paper is to evaluate analytically such loss of efficiency, in a specific heterogeneous scenario. In other words, we want to estimate how much resources we can waste if we go stateless and avoid state maintenance functions. The comparison between stateless and stateful approaches is performed under the constraint of strictly offering the same performance levels, in terms of, e.g., loss probability and delay.

We propose a new multicast communication paradigm called “spatiotemporal multicast” for supporting applications which require spatiotemporal coordination in wireless sensor networks. In this paper we focus on a special class of spatiotemporal multicast called “mobicast” featuring a message delivery zone that moves at a constant velocity $$\vec v$$ . The key contributions of this work are: (1) the specification of mobicast and its performance metrics, (2) the introduction of four different mobicast protocols along with the analysis of their performance, (3) the introduction of two topological network compactness metrics for facilitating the design and analysis of spatiotemporal protocols, and (4) an experimental evaluation of compactness properties for random sensor networks and their effect on routing protocols.

In this paper, we consider a radio-based communication network in which a single, high speed radio channel is shared by some plurality of small portable “notebooks”. Such a system has the potential to provide LAN-like service within buildings, allowing the portable "notebooks" to access the CPU and data resources of a wired network. In this harsh indoor fading environment, a base-station approach is used. We propose a modified polling scheme for the indoor radio LAN channel. The base station regularly polls each remote, in response to which the remote either generates a "keep alive" packet or a request packet, allowing the base to fetch the requested information from the wired network and scheduling a reply to that remote. The efficiency of such a scheme is studied and the expected turn-around delay as a function of network loading is approximately obtained. A system stability under such a scheme is derived. For a polling cycle of 20 milliseconds and a network containing 10 or 50 users, for example, the maximum link efficiency is 97% and 87%, respectively, assuming that the link speed is 5 Mbps.

MapReduce is a new parallel programming model initially developed for large-scale web content processing. Multidimensional data analysis applications meet the issues of large scale dataset. The arrival of MapReduce provides a chance to utilize the commodity hardware for massively parallelizing multidimensional data analysis applications. The translation and optimization from relational algebra operators to MapReduce programs is still an open and dynamic research field. In this paper, we focus on a special type of data analysis query, namely, Multiple Group-by query. We firstly discuss the communication cost of MapReduce model, then we give an initial implementation of Multiple Group-by query. After that, we propose an optimized version which addresses and reduce the communication cost. According to the experimental measurements, our optimized version shows a better accelerating ability and a better scalability than the other version. We also formally evaluate our results, and give a set of execution time estimations for both the initial implementation and the optimized one.

In this paper, the “Wireless Integrated Multiple Access (WIMA) with Speech Activity Detector (SAD)” protocol for Time Division Duplex (TDD) and Frequency Division Duplex (FDD) hierarchies is proposed and analyzed. This scheme is based on a mixture of movable-boundary WIMA protocol and speech activity process. Both voice and data traffic are handled on a packet reservation basis. The access slot of every uplink frame is allocated on the last slot to save the waiting time of queuing data. The expected data-packet delay for fixed-boundary WIMA, movable-boundary WIMA, and WIMA/SAD protocols are evaluated. Numerical results illustrate the dependence of performance on the system parameters, and demonstrate that the WIMA/SAD protocol provides a lower expected data-packet delay than the movable-boundary WIMA protocol for the values of voice-call completion probability ( μ _v) less than 0.1. As μ _v increases, the expected data-packet delay of the WIMA/SAD protocol approaches to movable-boundary WIMA protocol. The maximum data throughput of WIMA/SAD protocol has smaller variation than that of the movable-boundary WIMA protocol when voice-call completion ratio is changed.

In this paper we propose high throughput collision free, mobility adaptive and energy efficient medium access protocol (MAC) called Collision Free Mobility Adaptive (CFMA) for wireless sensor networks. CFMA ensures that transmissions incur no collisions, and allows nodes to undergo sleep mode whenever they are not transmitting or receiving. It uses delay allocation scheme based on traffic priority at each node and avoids allocating same backoff delay for more than one node unless they are in separate clusters. It also allows nodes to determine when they can switch to sleep mode during operation. CFMA for mobile nodes provides fast association between the mobile node and the cluster coordinator. The proposed MAC performs well in both static and mobile scenarios, which shows its significance over existing MAC protocols proposed for mobile applications. The performance of CFMA is evaluated through extensive simulation, analysis and comparison with other mobility aware MAC protocols. The results show that CFMA outperforms significantly the existing CSMA/CA, Sensor Mac (S-MAC), Mobile MAC (MOB-MAC), Adaptive Mobility MAC (AM-MAC), Mobility Sensor MAC (MS-MAC), Mobility aware Delay sensitive MAC (MD-MAC) and Dynamic Sensor MAC (DS-MAC) protocols including throughput, latency and energy consumption.