Catálogo de publicaciones - libros

Efficient channel allocation is important for meeting the quality of service (QoS) requirements of both GSM voice calls and GPRS packets in integrated GSM/GPRS networks. In this paper, we propose a new dynamic channel allocation scheme with guard channel, channel de-allocation/re-allocation for voice call and packet queue for GSM/GPRS networks. An analytic model with general GPRS channel requirement is developed to evaluate the performance of the proposed scheme. Numerical results demonstrate that the scheme can adapt to different QoS requirements of the system by adjusting the number of guard channels and the size of packet queue. Compared to some conventional schemes, the proposed scheme achieves better performance of QoS provisioning.

Link bandwidth is obviously critical for numerous network management tasks. Taking into account the issues of measuring costs and network-wide view for large IP network, a distributed measuring system would be an ideal monitoring architecture for active measuring link bandwidth. In this paper, we address the problem of efficiently measure assignment, which optimizing goal is to reduce the cost of measuring all links bandwidth. We show that this problem is NP-hard and propose an approximation algorithm with approximation ratio 2. The effectiveness of our measuring algorithm is validated by simulations evaluation over a wide range of network topologies.

Several fair queueing mechanisms based on stateless core (SCORE)/dynamic packet state (DPS) architecture have been proposed to address the scalability problem of stateful architectures. However, most of these mechanisms indiscriminatingly label every packet in edge routers while only a small fraction of the packets that come from fast flows will be dropped by core routers. Moreover, these mechanisms usually apply simple techniques to detect congestion, which makes them unable to control the queue length. In this paper, a new fair bandwidth allocation mechanism is proposed. In the new mechanism, edge routers only label the packets of long flows so that the bandwidth is preferentially allocated to short flows and the remaining is fairly allocated among the competing long flows. Furthermore, routers can keep the queue length at a reference value using active queue management (AQM) algorithm. The simulation results show that this mechanism performs well in many aspects.

Most Active Queue Management (AQM) algorithms based on control theory have difficulty in obtaining desirable performance once the network conditions or the traffic patterns change out of the presumed ones they are designed for. To address these problems, a new self-tuning AQM algorithm called STR is proposed in this paper. STR has the ability of keeping minimum variance between the instantaneous queue length of the router and the reference value by estimating the parameters of the model of controlled object online and adjusting the packet drop probability accordingly. The performance of STR is evaluated through extensive simulations. The results show that STR is robust against the great changes of the network parameters and the traffic load.

The communication between agents has some special requirements. One of them is asynchronous communication. Used communication sequence process (CSP) to descript a model of agents communication with shared buffer channel. The essence of this model is very suitable for the multi-agents communication, so it is a base for our next step job. Based on the communication model, explored the distributed tasks dealing method among joint intention agents and with description of relation between tasks we give a figure of agents’ organization. Agents communicate with each other in this kind of organization. The semantics of agent communication is another emphasis in this paper. With the detailed description of agents’ communication process, given a general agent automated negotiation protocol based on speech act theory in MAS, then we use CSP to verify this protocol has properties of safety and liveness, so prove it is logic right. At last a frame of this protocol’s realization was given.

In this paper an adaptive minimum variance controller is proposed to minimize the rate of stochastic inputs from uncontrollable high priority sources. This method avoids the computations needed for pole placement design of the minimum variance controller, and utilizes an online recursive least squares algorithm in direct tuning of the controller parameters.

Password authentication (PA) is a general and well-known technique to authenticate a user who is trying to establish a connection in distributed web services. The main idea of PA is to remove complex information from users so that they can log on servers only with a human-memorable password at anywhere. So far, many papers have been proposed to set up security requirements and improve the efficiency of PA. Most papers consider practical attacks such as password guessing, impersonation and server compromise which occur frequently in the real world. However, they missed an important and critical risk. A revealed password of a user from a server may affect other servers because most people tend to use a same password on different servers. This enables anyone who obtains a password to easily log onto other servers. In this paper, we first introduce a new notion, called “password pocket” which randomizes user’s password even if he/she types a same password on different servers. When our password pocket is used, an exposed password does not affect other servers any more. The cost of a password pocket is extremely low since it needs to store only one random number securely.

Dynamic Programming Matching (DPM) is a mathematical optimization technique for sequentially structured problems, which has, over the years, played a major role in providing primary algorithms in pattern recognition fields. Most practical applications of this method in signature verification have been based on the practical implementational version proposed by Sakoe and Chiba [1], and is usually applied as a case of = 0. We found, in this case, a modified version of DPM by applying a forward seeking implementation is more efficient, offering significantly reduced processing complexity as well as slightly improved verification performance.

Due to node mobility, the ad hoc network topology is dynamical so that on-demand routing protocols are more fit than other routing protocols. Most secure on-demand routing protocols are designed that the destination or source is able to detect the attacks on routing paths after accepting routing requests or routing replies. In this paper, we present a secure on-demand source routing protocol without the assumption of a specific cryptographic system provides per-hop broadcast authentication in routing discovery phase and security in communication phase and takes effect on our trust-based ad hoc environment. Our hop by hop broadcast authentication provides forwarding routing packets with their trust levels for abstaining from unreliable or malicious nodes. Through security analysis and discussion, we characterize our mechanism and show that it is effectively and efficiently.

We present a probabilistic packet filtering (PPF) mechanism to defend the Web server against Distributed Denial-of-Service (DDoS) attacks. To distinguish abnormal traffics from normal ones, we use Traffic Rate Analysis (TRA). If the TRA mechanism detects DDoS attacks, the proposed model probabilistically filters the packets related to the attacks. The simulation results demonstrate that it is useful to early detect DDoS attacks and effective to protect the Web servers from DDoS attacks.