Catálogo de publicaciones - libros

In telecommunications networks, usually an aggregation of information units (a batch) is transmitted instead of individual information units. In order to obtain performance measures for such networks, we analyze a discrete-time queueing model with a batch server operating under the minimum batch size (MBS) service policy. Specifically, we calculate the steady-state probability generating function (PGF) of the system contents at the beginning of an arbitrary slot. This PGF enables us to derive some important performance measures.

Furthermore, we investigate, through some numerical examples, the influence of some parameters on the optimal choice of the MBS. In this paper, we focus on the influence of the load and the distribution of the service times.

Derivatives of blocking probabilities of multi-service loss networks are important for traffic engineering. An explicit formula for the derivatives of blocking probabilities with respect to offered traffics is obtained expressed by stationary probabilities of global state probabilities. The approach is based on the convolution algorithm. It allows us to find expressions for the derivatives in a much more easy way than known so far. It is briefly shown how derivatives can be applied for approximate evaluation of performance measures and for studying the error of performance measures estimation caused by small changes of offered traffic. The results can also be applied for network optimization.

A goal of modern broadband networks is their ability to provide stringent QoS guarantees to different classes of users. This feature is often related to events with a small probability of occurring, but with severe consequences when they occur.

In this paper we focus on the overflow probability estimation and analyze the performance of Bridge Monte-Carlo (BMC), an alternative to Importance Sampling (IS), for the Monte-Carlo estimation of rare events with Gaussian processes.

After a short description of BMC estimator, we prove that the proposed approach has clear advantages over the widespread IS in terms of variance reduction. Finally, to better highlight the theoretical results, we present some simulation outcomes for a single server queue fed by fraction Brownian motion, the model in the framework of long range dependent traffic.

The functioning of an ad hoc network is based on the supportive contributions of all of its members. Nodes behave as routers and take part in route discovery and maintenance. In this paper, a forwarding protocol is presented that stimulates node cooperation to improve the throughput of the network. The incentive mechanism is provided through a micropayment protocol that deals with the cooperation range of the users. Most cooperative nodes intrinsically benefit of the best routes and availability and they take preference in front of selfish ones.

A potential solution for building ad-hoc networks is described. It is based on the Technoconcepts’ TSR chipset. This chipset provides direct conversion of RF signals to baseband. Such RF/D chips convert the received signals into digital form immediately after the antenna, making it possible to provide all required signal processing in digital form, thus allowing adaptive frequency bands free of interference. This flexibility provides the most favorable conditions for quality communications. The offered solution has its own set of challenges. The paper describes the major challenges, and the potential ways of addressing them. An example of possible ad-hoc network architectures is presented that is based on the RF/D chips.

In location tracking, there is a trade-off between data accuracy of mobile targets and energy efficiency of sensor nodes. If the number of nodes is increased to track a mobile target, the level of data accuracy increases, but the energy consumption of nodes increases. In this paper, we propose a new location tracking scheme that considers these two factors. The proposed scheme is designed to track mobile targets in a cluster-based sensor network. In order to increase the energy efficiency of sensor nodes, a portion of nodes that detect the mobile target is selected to track the target using the backoff procedure. In addition, we consider data accuracy as controlling the number of nodes by varying the transmission range of the nodes. We perform a simulation to evaluate the performance of the proposed scheme over sensor networks. We provide simulation results comparing the proposed scheme with the general approach. The simulation results show that the proposed scheme has the excellent performance over a broad range of parameters.

A mobile ad hoc network (MANET) station acts both as a source packet generator and transit packet forwarder. With selfish stations and the absence of administrative cooperation enforcement, the lack of forwarding incentives has long been recognized as a serious design problem in MANETs. Reputation systems discourage selfishness by having past cooperation increase the present source packet throughput. We describe a simple watchdog-controlled first-hand reputation system and point to a form of selfishness not addressed by existing research, arising from . If the watchdog at a station cannot tell a nearby station’s source packets from transit packets, that station is tempted to admit more source packet traffic than a fair local admittance control (LAC) scheme permits. We analyze a related noncooperative and characterize three types of its Nash equilibria. Next we propose a simple packet forwarding protocol by the name (D&F) and using an approximate performance model show that, when properly configured, D&F leads to a fair and efficient game outcome.

Existing wireless networks have little in common, as they are designed around vendor-specific devices that use specific radio access technologies to provide particular functionality. Next generation networks seek to integrate wired and wireless networks in order to provide seamless services to the end user. Seamless Mobility is an experiential architecture, predicated on providing mechanisms that enable a user to accomplish his or her tasks without regard to technology, type of media, or device. This paper examines how autonomic mechanisms can satisfy some of the challenges in realizing seamless mobility solutions.

Multirate wireless networks in general share a common problem for the transmission of VoIP traffic, since the rate changes of some of the flows affect the transmission of all others, which causes an unacceptable voice quality degradation. In this work, an admission control algorithm is combined with a codec selection block to mitigate this negative effect. This centralized admission control is able to block or drop calls in order to maintain the system stability despite rate changes. Moreover, the integrated codec selection block is able to select the most adequate VoIP codec for each incoming or already active call based on the channel rate used and according to a number of optimization policies. Several such policies are designed and evaluated in this paper. Results show that this combined adaptive solution provides a beneficial trade-off among the performances of the different codecs in terms of MOS, blocking and dropping probability and cell resource usage. Furthermore, a number of interesting singularities deriving from the multirate nature of the network are identified.

Network-based Localized Mobility Management (NetLMM) is an outstanding candidate solution for the mobility management controlled by the network. In NetLMM, mobile nodes (MNs) can be provided mobility services without any installation of mobility-support stack. However, there is a restriction that the MN is able to have the mobility only within a single localized mobility domain (LMD). In this paper, we propose a novel Inter-LMD handoff mechanism in order to eliminate the shortcoming of the current NetLMM protocol. The proposed Inter-LMD handoff mechanism enables that the MN hands off across LMDs, even if the MN does not have a functionality of Mobile IPv6 (MIPv6). According to the performance evaluation, the proposed Inter-LMD handoff mechanism has approximately 5.8% more overhead than the current Inter-LMD handoff of MIPv6-capable devices, while the current NetLMM protocol does not support the handoff of MIPv6-incapable devices.