This paper introduces two new algorithms for fault-tolerant design of multi-layered networks, both of which extend the previously published multi-layered market algorithm (MMA), by including provision of additional resources to be used during network failure events. The new algorithms are called resilient MMA (RMMA) and failure-traffic MMA (FTMMA). RMMA runs MMA iteratively and independently for each failure scenario. FTMMA treats each failure event as a type of traffic, which enables more efficient sharing of network resources. Both RMMA and FTMMA consider a range of single physical link failures and aim to maximize earnings before interest and tax (EBIT). The costs considered in the EBIT evaluation include amortized capital and operational expenditures and penalties (compensation to the customers when the service is degraded). They both focus on optimizing resource provisioning, in particular, capacity assignment, for fault-tolerant and cost-effective design of multi-layered networks. The novel aspects of RMMA and FTMMA include the incorporation of variable bit rate traffic streams in fault-tolerant multilayered network design, together with the aim to maximize EBIT. RMMA and FTMMA are validated by comparing designs with those produced by an integer linear programming benchmark for small-size networks. Numerical results show that FTMMA can more efficiently allocate capacity for failures by sharing these resources across different failure events.

In this paper, we describe and test a new approach to better service based on recently obtained understanding of social network behaviour. This method is complementary to DiffServ. We call this new method Defensive Services (DefServ) because rather than focussing on differentiation based on previously nominated preferences, it focuses on protection of normal traffic, based on observation and detection of unusual traffic. It is uses a new queue discipline called mice and elephants (MAE).

Net ML is a system which runs in a browser - with help from "the cloud'" which can be used to analyse and design networks. Versions of Net ML have existed for 10 years however the version now available is the first to include full graphical editing as well as a rich collection of network design and analysis tools. Net ML provides a way to navigate through views of one network, and through a network of networks. The software itself is networked and provides the means for network researchers to jointly develop networks and algorithms for research and educational purposes. The tools provided in Net ML include layered and single-layer network design, robust network design, availability analysis, and loss analysis. Networks can also be transformed by means of XSLT scripts.

This paper provides a new formula for dimensioning of a link fed by fractional Brownian input. This formula is obtained based on another new approximate result for the stationary workload distribution of a queue loaded by fractional Brownian input. An efficient approach to simulate such a queue is also presented. Agreement between the analytical and the simulation results has been demonstrated numerically.

Five properties of an architecture for secure access to web services are defined and two existing architectures are evaluated according to these criteria. References to these criteria in the literature and evaluation of the security architectures are tabulated in the conclusion. Policy-sufficiency is defined as the requirement that any meaningful statements can be expressed in policy definitions of the architecture. Protocol neutrality is the requirement that a protocol exchange which is logically equivalent to a valid protocol sequence is also valid. Predicate-boundedness is the constraint that a fixed, finite set of predicates (or language constructs) will be sufficient for security policy definitions, i.e. the language does not need to be incrementally extended indefinitely. Protocol-closure requires that security protocols can be combined together arbitrarily to make new protocols. Finally, processing complexity constrains algorithms for evaluating security rules to be of satisfactory (low) complexity. No existing security architectures receive a tick for all five of these criteria. The RW architecture is more successful in this regard than the simpler XACML architecture.

The use of passive optical networks (PONs) enables access rates of multi-Gbit/sec bandwidth and provision of quality of service for high definition multimedia services. In this paper, we consider and analyse a generic multi-priority dynamic bandwidth allocation (DBA) algorithm for TDM PONs serving multimedia traffic in an upstream link. PON traffic is served strictly according to its priority. We consider this DBA algorithm using two approaches: (i) the algorithm assigns a fixed service quantum to each priority service and (ii) different service quanta are assigned to different priority services. The mean message delay is evaluated using a multiqueue processor sharing (MPS) model and an MPS with Heterogeneous Traffic (MPS-HT)model for the two approaches respectively. The MPS model is a classical processor sharing model limited by the critical assumption that there is egalitarian service sharing among all users, which is inefficient for multimedia applications in PONs. We extend the MPS model to a general MPS-HT model that enables the analysis of message delay performance in the case where the service quanta may be different for different services.

This paper presents the Poisson Pareto burst process (PPBP) as a simple but accurate model for Internet traffic. It presents formulae relating the parameters of the PPBP to measurable traffic statistics, and describes a technique for fitting the PPBP to a given traffic stream. The PPBP is shown to accurately predict the queueing performance of a sample trace of aggregated Internet traffic. We predict that in few years, natural growth and statistical multiplexing will lead to an efficient optical Internet.

We present a new perspective on effective bandwidths which allows us to squeeze the most from a network while still meeting QoS constraints. We show that if buffer space requirements are also considered, the effective bandwidth of a given stream can be considerably reduced. This reduction in capacity is shown to have little or no impact on the ability of the network to meet the QoS constraints of the stream. We also show that even with a fixed buffer threshold, Gaussian traffic streams can provide a multiplexing gain not predicted by traditional effective bandwidths.

We introduce a new framework for various measurement-based connection admission control (MBCAC) schemes for a multiservice network. Then, using heterogeneous bursty multimedia traffic traces, efficiency and simplicity tradeoffs are obtained by simulations. For all our MBCAC schemes, we use a procedure of 'available bandwidth' evaluation based on online measurements and an adaptive feedback mechanism. The online measurement concept is based on the use of different 'traffic histograms' that maintain records of the aggregated traffic in a link over a range of time-scales. The most complex MBCAC scheme involves measuring and then storing of all traffic information for every connection, the use of a 'warming up period' technique, and updating the histograms when a connection departs. However, for the other simpler MBCAC schemes, various aspects of the most complex scheme are eliminated or simplified. We also consider two model-based CAC schemes, i.e., Gaussian and effective bandwidth, where a priori statistical knowledge of the connections are known in advance. Given that the traffic is known beforehand, the performance of such schemes will be better than if the statistics are not exactly known. A comparison between such model-based CAC schemes with our MBCAC schemes provides a benchmark that gives the best efficiency and QoS a model-based CAC may achieve. Simulation results demonstrate that while the best efficiency achievable by the model-based gives efficiency of 80%, the most complex MBCAC schemes achieved 81% efficiency, and the simplest MBCAC schemes obtained 76% value.

This paper presents steps towards creating a general model for aggregated traffic streams. We show that fitting the mean, variance and Hurst parameter is insufficient to consistently model a long range dependent traffic stream. A fourth parameter, the "level of aggregation", is required. We also show that with increased aggregation, the behaviour of a traffic stream tends towards that of a fractal Gaussian process.

The paper provides insight into the performance of a candidate IEEE 802.14 MAC protocol for hybrid fibre/coax (HFC) networks, by simulation. The simulations make use of two types of input traffic: measured traffic traces, and randomly generated memoryless traffic. It is confirmed that the protocol does not reach congestion collapse under any traffic load, and this is found to hold regardless of traffic type. The paper demonstrates that memoryless traffic streams cannot be used for dimensioning guidelines as they underestimate delay as compared to real traffic traces. The paper also compares between the performance of the protocol loaded by traffic traces with that of a benchmark based on an ideal multiplexer under the same traffic conditions. It is demonstrated that both the throughput and delay performance of the protocol converge to that of an ideal multiplexer, with an increasing number of active stations.

We consider the P/sub i/-persistent protocol and we derive approximate analytical results for the unfinished work distribution at each node on the bus under the assumption that the arrival process at each node follows a discrete time Gaussian process. A deterministic version of the protocol, which reduces the variance of the service process and therefore improves queueing performance, is also considered. The solution is simple and fast to compute and is not overly sensitive to the number of nodes. Simulation results indicate that the results are accurate so long as the performance can be accurately approximated based on the dominant effect of an exponential tail in the distribution of queued load. The results are also applicable to a single server Gaussian queue with priorities.

It has been observed by many authors that under reasonable regularity conditions, the stationary distribution of queued work in a queueing system has an exponential tail. This has been observed in practise in a great variety of communications systems. The main result of this paper is a general equation for the decay coefficient of this tail. A procedure for estimating the weight of the tail is also described. The proof relies on the assumption that future values of the net input process are independent of values in the past after a sufficiently long delay but the equation does not reflect this assumption and it is conjectured that the formula holds good even when the input process retains some degree of correlation over time intervals of arbitrary length. Several examples are considered including some which do not assume that the distribution of the inputs is Gaussian. The method for determining the decay coefficient for the tail in these examples relies on finding the zero of a sample nonlinear equation.>

A queueing network structured as a directed tree, where only transmissions towards its head are allowed, is considered. Input to each queue is assumed to follow a discrete-time Gaussian process. To compute loss probabilities, each queue is considered independently and its input statistics are derived by approximating output statistics of its immediate sources. Performance statistics of a single Gaussian queue can be accurately approximated as a function of three parameters: the mean and variance of the arrival process, and a parameter related to the asymptotic rate of the long term variance. Of these three parameters only the variance changes when the traffic is filtered through an infinite buffer queue. The authors derive an approximation of the variance of the output process. Comparisons with simulations show that the approximation is accurate. Having the parameters of the output process, the single queue analysis is extended to a tree type network of queues. A small example of a network of three queues is simulated and the performance results are found to be close to results obtained analytically.>

This paper provides a method for approximating the probability distributions of stationary statistics in FIFO single server queues. The method is based on the Wiener-Hopf factorization technique, and is applied to semi-Markov queues where the underlying state space is of unlimited size. It has been established that the tail of the distribution of the waiting time or unfinished work in such queues is negative exponential, and in this paper we estimate the parameters of that exponential term. A particularly important case, which is treated here, is a model for a statistical multiplexer where the net input process forms a stationary ergodic Gaussian discrete-time stochastic process. In this case, it is possible to derive analytically a simple formula in a closed form for the approximation. The formula is in terms of three parameters of the net input process: the mean, the variance, and the autocovariance sum. This provides a solid theoretical basis for traffic characterization by these parameters. Comparison with simulation results show that the method is accurate. Also presented is a result for a special case where the arrival process is autoregressive.>

A method for approximating the probability distributions of stationary statistics in first-in, first-out (FIFO) single server queues is provided. The method is based on the Wiener-Hopf factorization technique and is applied to semi-Markov queues with the underlying state space of unlimited size. A particularly important case is a model for a statistical multiplexer where the net input process forms a stationary ergodic Gaussian discrete-time stochastic process.>

The near end crosstalk (NEXT) model proposed by Cravis and Crater [1] is analyzed to give the covariance of NEXT, with good agreement between theory and measurements on multipair cable. The covariance of NEXT is then used to estimate the variance of the meansquare NEXT interference between PCM systems operating under the same cable sheath. These results are used to derive the required minimum mean NEXT loss\mu_{0}'as a function of the number of PCM systemsN, the NEXT loss standard deviation σ, and pertinent PCM system parameters. Comparisons with the minimum mean NEXT loss proposed in [4] and [5],\mu_{0}'', and that proposed in [1],\mu_{0}''', show that:-0.4 < \mu_{0}'' - \mu_{0}' < 2dB, for1 \leq N \leq 500and6 \leq \sigma \leq 14, while-16 < \mu_{0}''' - \mu_{0}' < 6dB, for25 \leq N \leq 500and6 \leq \sigma \leq 14, for all pertinent PCM system parameters.