An accurate analytical model on blocking performance of multicast three-stage networks

The fast deployment of broadband networks and the evolution of communication services has revealed the importance of a network-wide availability of multicast communications, that is from one source to multiple destinations. This paper considers three-stage switching networks able to support multicast traffic, i.e. connections in which one inlet of a node is connected to more than one outlet of the node at the same time. An analytical model is developed here that evaluates the blocking probability of multicast connections taking into account statistically the correlation between occupancy events in links belonging to different interstage patterns. Such new model proves to be more accurate than any previous model addressing the same issue. Interestingly enough, unlike other models the new formulation is consistent with the theoretical conditions of a non-blocking three-stage switching network.     

Models of blocking probability in all-optical networks with andwithout wavelength changers

We introduce a traffic model for circuit-switched all optical networks which we then use to calculate the blocking probability along a path for networks with and without wavelength changers. We investigate the effects of path length, switch size, and interference length (the expected number of hops shared by two sessions which share at least one hop) on blocking probability and the ability of wavelength changers to improve performance. Our model correctly predicts unobvious qualitative behaviour demonstrated in simulations by other authors     

Admission policies for integrated voice and data traffic in CDMApacket radio networks

The authors derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code division multiple access (CDMA) with direct-sequence spread spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. The admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized. In addition, new data arrivals are rejected if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then, a value iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies find application in emerging commercial CDMA packet radio networks including cellular networks, personal communication networks, and networks of LEO satellites for global communications     

Performance analysis of k-fold multicast networks

Multicast involves transmitting information from a single source to multiple destinations, and is an important operation in high-performance networks. A k-fold multicast network was recently proposed as a cost-effective solution to providing better quality-of-service functions in supporting real-world multicast applications. To give a quantitative basis for network designers to determine the suitable value of system parameter k under different traffic loads, in this paper, we propose an analytical model for the performance of k-fold multicast networks under Poisson traffic. We first give the stationary distribution of network states, and then derive the throughput and blocking probability of the network. We also conduct extensive simulations to validate the analytical model, and the results show that the analytical model is very accurate under the assumptions made. The analytical and simulation results reveal that by increasing the fold of the network, network throughput increases very fast when the fanouts of multicast connections are relatively small, compared with the network size.     

A computational model for estimating blocking probabilities of multifiber WDM optical networks

In this letter, we propose a computational model for calculating blocking probabilities of multifiber wavelength division multiplexing (WDM) optical networks. We first derive the blocking probability of a fiber based on a Markov chain, from which the blocking probability of a link is derived by means of conditional probabilities. The blocking probability of a lightpath can be computed by a recursive formula. Finally, the network-wide blocking probability can be expressed as the ratio of the total blocked load versus the total offered load. Simulation results for different fiber-wavelength configurations conform closely to the numerical results based on our proposed model, thus demonstrating the feasibility of our proposed model for estimating the blocking performance of multifiber WDM optical networks.     

Computing approximate blocking probabilities for transparent waveband switching based WDM networks using hierarchical cross-connects

An analytical model is presented to study the dynamics of wavelength division multiplexing (WDM) networks with waveband switching (WBS). The reduced load approximation method is considered to compute approximated network blocking probabilities in WBS-based WDM networks. The analytical model considers the link blocking probability due to insufficient link capacity and an impact of the waveband granularity (G). The analytical model also considers the node blocking probability due to unavailability of a switch port at the wavelength cross connect (WXC) layer of an Hierarchical cross connect (HXC) switch node. The set of nonlinear equations is obtained with the link independence assumption and solved using repeated substitutions. The accuracy of the analytical model is examined by comparing with simulation results considering the random-fit algorithm for waveband and wavelength assignments in different network scenarios. Lightpaths are routed between source and destination (s-d) HXC switch nodes using shortest path first (SPF) routing. An impact of the switch parameter to limit the input and the output WXC switch ports of an HXC switching node is also being investigated using the analytical model as well as through simulation results.     

Performance Analysis of an Improved Common Radio Resource Management Algorithm Based on Load Balance and Service Characteristics

In order to provide users with satisfactory quality of service and reduce service cost as much as possible, a key issue is how to manage radio resources reasonably and effectively in heterogeneous wireless networks (HWNs). Based on load balance and service characteristics, a common radio resource management (CRRM) algorithm for HWNs consisting of CDMA2000 and IEEE802.11 is proposed. The proposed algorithm selects appropriate access and handoff networks for new and handoff calls respectively, according to users’ mobility characteristic, location information, service type and network load. The performance of the proposed algorithm is analyzed based on a three-dimensional Markov chain model. Based on the HWNs model and handoff rate analysis, the model’s parameters are determined. In order to resolve the steady-state distribution of the three-dimensional Markov model, successive over-relaxation iteration method is adopted to work out steady state equations. According to the steady state probabilities of the Markov model, the closed formulas of HWNs performance metrics are given to evaluate the proposed CRRM algorithm, e.g. call blocking probability, handoff blocking probability, throughput, and service cost. For the purpose of illustrating advantages of the proposed algorithm, two other CRRM algorithms are employed for comparison. The simulation results show that the proposed algorithm can effectively reduce call blocking probability, and improve HWNs throughput.     

Performance of demand assignment TDMA and multicarrier TDMAsatellite networks

The authors develop an analytical model of satellite communication networks using time-division multiple-access (TDMA) and multiple-carrier TDMA (MC-TDMA) systems to support circuit-switched traffic. The model defines the functions required to implement fixed assignments (FAs), variable destinations (VDs), and demand assignments (DAs). The authors describe a general system model for the various allocation schemes and traffic activity. They define analytical expressions for the blocking and freeze-out probabilities. This is followed by the derivation of the satellite capacity requirements at a specified performance level for FA, VD, and DA systems with and without digital speech interpolation. The analysis of disjoint pools and combined pools in DA systems is presented and attention is given to MC-TDMA with limited connectivity demand assignment. Expressions for the required satellite capacity for specified traffic and performance are derived along with numerical results. The degree of complexity and implementation alternatives for the various allocation schemes are considered     

An adaptive channel preemption model for small‐cell embedded large‐cellular networks

In this paper, we present an analytical model of adaptive channel preemption (ACP) for small‐cell embedded large‐cellular (SCELC) networks. An SCELC network consists of a fixed base station (FBS) with large coverage and many embedded base stations (EBS) with relatively small coverage. Channel capacity in an FBS cell may become insufficient when traffic is unexpectedly increased particularly in some special occasion. This paper considers two aspects of dynamically allocating channels for an SCELC network. First, by increasing one or more EBS cells within an FBS cell, the proposed ACP can reduce blocking probability of new calls. Second, to reduce dropping probability of handoff calls, the proposed ACP allows a handoff call to preempt an on‐going call, when the latter is located in an EBS cell or in the overlapping area of two adjacent FBS cells. For the purpose of performance evaluation, we build an analytical model with 4‐tuple Markov chains. Numerical results reveal that embedding one or more EBS cells inside an FBS cell needs to be done carefully since it results in a tradeoff between the reduction of new‐call blocking probability and the increase of handoff‐call dropping probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Call blocking probability and bandwidth utilization of OFDM subcarrier allocation in next-generation wireless networks

Various studies have devised OFDM subcarrier-allocation schemes in next-generation wireless networks. However, the subcarrier-allocation system performance has seldom been assessed, especially in terms of the call blocking probability (CBP) and bandwidth utilization.(BU). This study proposes a batch-arrival bath-loss queueing model to evaluate the performance or the subcarrier-allocation system,and derives expressions for calculating two important system performance measurements, CBP and BU. Simulation results. indicate that the measures appear to work. The model should be helpful for constructing OFDM based wireless networks.     

Computing blocking probabilities in survivable WDM optical networks

One of the most important performance measurements in wavelength-division multiplexing (WDM) networks is the call blocking probability. In this paper, we present an approximate analytical method to evaluate the blocking probabilities in survivable WDM networks with dynamically arriving connection requests. Our approach utilizes the wavelength independence whereby WDM network can be regarded as an aggregation of disjoint single wavelength sub-networks with a common physical topology. In each single wavelength sub-network, we derive the calculation of the blocking probability from an exact analysis. We assume dedicated protection with fixed routing and either first-fit or random wavelength assignment. Simulation results demonstrate the accuracy of the proposed method.     

Blocking performance analysis on adaptive routing over WDM networks with finite wavelength conversion capability

Analytical blocking probability analysis is important for network design. In this paper, we present an analytical model for the blocking probability analysis on adaptive routing over the WDM networks with finite wavelength conversion capability. Modeling the finite nature of wavelength conversion has been a difficult task. We make use of the idea of segmented route to handle the finite wavelength conversion property. In this approach, a route is divided into a number of segments separated by wavelength converting nodes. We then combine the single-link model and the overflow model to derive the network-wide blocking probability. There are two distinct features in our technique. First, a concept of segmented route is used. Second, link state is considered when calculating the traffic flow. The latter ensures that the analytical results match closely to practical network status. Extensive simulations show that the analytical technique is effective in modeling the blocking probability performance for sparse networks.     

Development and Comparison Between Resource Allocation Strategies Based on Intelligent Scheme and Traditional Distributed Dynamic Resource Allocation Strategies in Mobile Communication Networks

The third generation of mobile communication aims to transmit not only voice and text but also videos and multimedia data. Furthermore, in the future it is expected to involve web browsing, file transfer, and database access. This requires wireless cellular networks to efficiently support packet data traffic. Therefore, challenge in the design of wireless networks is to support both voice and packet data service of traffic with different QoS-parameters. On the other hand one aspect of this challenge is to develop an efficient scheme for assigning resources to new arriving calls or handoff of different traffic types. Since the blocking probability is one of the most important QoS- parameters, the QoS of wireless cellular networks are often measured in terms of two probabilities, the first is the new call blocking probability that a new call cannot be satisfied because of the unavailability of a proper free channel, and the second is the handoff blocking probability that a proper free channel is not available when a mobile station (MS) wants to move into a neighboring cell. To meet this aspect of the challenge, this proposal proposes a new assignment scheme based on intelligent methodologies to utilize frequency spectrum efficiently and to reduce call blocking probabilities. Jamal Raiyn received the first MS degree (Diplom) in applied mathematics from Siegen University in Germany, in 1998, and the second MS degree in mathematics and computer science from Hannover University in Germany, in 2000. From January 2001 to April 2002, he worked in institute for Data Communications System at the University of Siegen in Germany. Since September 2002 till now, he is a lecturer in computer science department at the Al-Kasemi Academy in Israel, and he is working toward PhD degree at BIU in Tel-Aviv/Israel. In addition a fellow researcher in school for electrical engineering Tel-Aviv University in Israel.     

IMPACT OF BUSY LINES AND MOBILITY ON CALL BLOCKING IN A PCS NETWORK

Several analytical models have been proposed to study the blocking probability for personal communications service networks or mobile phone networks. These models cannot accurately predict the blocking probability because they do not capture two important features. First, they do not capture the busy-line effect. Even if a cell has free channels, incoming and outgoing calls must be dropped when the destination portable is already in a conversation. Second, they do not capture the mobility of individual portables. In these models, mobility is addressed by net hand-off traffic to a cell, which results in traffic with a smaller variance to a cell compared with the true situation. We propose a new analytic model which addresses both the busy-line effect and individual portable mobility. Furthermore, our model can be used to derive the portable population distribution in a cell. The model is validated against the simulation experiments. We indicate that the previously proposed models approximate a special case of our model where the number of portables in a cell is 40 times larger than the number of channels.     

An approximate model for the computation of blocking probabilities in cellular networks with repeated calls

A novel approximate model is proposed for the evaluation of call blocking probabilities in mobile cellular networks with just one service class. The accuracy of the approximate model is assessed by comparison against results of detailed simulation experiments, a previously proposed model, and upper and lower bounds to the call blocking probability. Numerical results show that the proposed model is accurate, in spite of its remarkably small state space. This revised version was published online in June 2006 with corrections to the Cover Date.     

On spatially disjoint lightpaths in optical networks

Within the communication networks, a delayed constrained data packet is the one that will be dropped if not being served before a certain deadline time, which causes data packet loss affecting the quality of service (QoS). In this paper, we study the blocking probability and the mean delay of such delay constrained packets in an asynchronous single-wavelength optical buffer in optical packet switching networks, where the packet arrival process follows the Poisson process and the packet-length distribution is assumed to be general. We obtain the integral equations of the modeled system and the exact expressions of blocking probabilities and the mean delays. Numerical examples are provided to validate the results with interesting observations being highlighted.     

Optimal cost/performance design of ATM switches

This paper proposes a methodology for performing an evaluation and optimization of the cost of an ATM switching architecture under performance constraints given in terms of virtual connection blocking probability. An analysis of blocking networks is developed, and combined with known results concerning nonblocking networks, provides a theoretical model which relates traffic characteristics, network topology and blocking probability in a multirate/multiservice broadband environment. An analysis of the characteristics determining the cost of a generic ATM switch implementation follows. The model is oriented to optimize both the topological parameters and the speed advantage, with respect to the main cost factors of VLSI-based switching networks i.e., components count and complexity, interconnection costs     

Delay-on-Demand: A Signaling Protocol to Reduce Blocking Probability in Optical Burst-Switching Networks

Optical burst switching (OBS) is emerging as one promising switching paradigm for the next generation optical networks. To support multiple services in burst-switching networks, the OBS paradigm should support some quality-of-service (QoS) provisioning. A major design issue in such networks is to reduce the blocking probability of the bursts arising due to resource contention at the intermediate core router. In this paper, we propose a signaling protocol which we call ‘Delay-on-Demand’ (OBS-DoD), to reduce blocking probability and support QoS in optical burst-switching networks. The proposed scheme guarantees that at least one of the bursts succeeds depending on its priority, propagation delay from the ingress router, and the burst-size when contention occurs at the core router. For this, we use a control packet to delay, in case of a contention, the transmission of bursts at the ingress router. We compare the performance of our proposal, by simulation, with an earlier proposed scheme, and show that the proposed OBS-DoD outperforms the earlier scheme in reducing the blocking probability. For simulation, we generated bursty traffic using an M/Pareto distribution.     

An electromagnetic model for multiconductor connectors

An electromagnetic model for the response of multiconductor connectors is presented. The model is based on the canonical problem of the electromagnetic response of a thin circumferential slot in the shield of a cylindrical multiconductor transmission line (MTL). The problem is formulated for a shielded MTL of arbitrary cross section with impressed sources driving the interior of the MTL. The problem of interior-to-exterior coupling is solved by treating the slot as a thick aperture in the shield. The equivalence principle is used to divide the original problem into three separate parts. Two coupled integral equations are obtained for the equivalent surface magnetic currents, which are solved by the method of moments, and equivalent networks are presented. The equivalent networks consist of three generalized admittances, one of which is interpreted in terms of a connector admittance     

The performance of a timer-controlled token passing mechanism withfinite buffers in an industrial communication network

The timer-controlled token-passing mechanism widely used in industrial communication networks is analyzed. Several real network parameters, such as finite buffers and finite token-holding time (THT), which generally determine the overall performance of a network, are considered. The approximate matrix equation between the queue length distribution and the token rotation time is derived. Based on this matrix equation, the equations for the mean waiting time and the blocking probability are also derived. These equations can be easily solved using personal computers, due to its simple matrix structure and small computation time. Using these equations, the performance of field bus or other timer-controlled token-passing networks can be more accurately evaluated, since finite size buffers and finite THT are considered. The approximation error is shown to be small by computer simulation