The paper relates to multi-resource sharing between flows with heterogeneous requirements as arises in networks with wireless links or software routers implementing network function virtualization. Bottleneck max fairness (BMF) is a sharing objective in this context with good performance. The paper shows that BMF results when local fairness is imposed at each resource while flow rates are controlled by an end-to-end window. We analytically prove convergence to BMF under a fluid model when flows share a network limited to 2 resources while numerical results confirm BMF convergence for larger networks. Simulation results illustrate the impact of packetized transmission.

Designing efficient and fair algorithms for sharing multiple resources between heterogeneous demands is becoming increasingly important. Applications include compute clusters shared by multi-task jobs and routers equipped with middleboxes shared by flows of different types. We show that the currently preferred objective of Dominant Resource Fairness (DRF) has a significantly less favorable efficiency-fairness tradeoff than alternatives like Proportional Fairness and our proposal, Bottleneck Max Fairness. We propose practical algorithms to realize these sharing objectives and evaluate their performance under a stochastic demand model. It is shown, in particular, that the strategyproofness property that motivated the choice of DRF for an assumed fixed set of jobs or flows, is largely irrelevant when demand is dynamic.

When IEEE 802.11 access points (APs) share the same channel in a multi-cell WLAN, their downlink transmissions can interfere. Typically, an AP whose scheduled transmission to some user is blocked by another cell will apply the CSMA/CA back-off algorithm and continue to make reattempts to the same user. Through analytical models and simulations, we demonstrate that significant capacity gains can be attained by choosing an alternative destination for the reattempt. Results demonstrate that a simple random choice of alternative destination brings almost the same gain as a more sophisticated algorithm that seeks to maximize spatial reuse.

This paper contributes to the definition of an association policy for a multi-channel, multiple AP WLAN that depends on both physical rate and realised throughput. We show that existing proposals are inefficient when several APs share the same channel and define a new policy that is demonstrated to be close to optimal. Policies are compared through their traffic capacity defined as the network stability limit. We determine this capacity analytically using the fluid limit method for some simple network configurations deriving insight into the structure of the optimal policy. The quasi-optimality of our proposal is verified by simulation of a more complex network configuration.

Performance of WLANs has been extensively studied during the past few years. While the focus has mostly been on isolated cells, the coverage of WLANs is in practice most often realised through several cells. Cells using the same frequency channel typically interact through the exclusion region enforced by the RTS/CTS mechanism prior to the transmission of any packet.

An enhanced flow-aware Internet is arguably a more effective means of ensuring adequate performance than implementing the complex standardized QoS architectures. This flow-aware network would provide flow-level performance guarantees for real time and data applications by implementing per-flow fair queueing and by limiting the impact of overload through flow level admission control. The paper discusses the feasibility of the implied router mechanisms and proposes original solutions that minimize the necessary overhead with respect to the current best effort network. Preferred solutions significantly reduce requirements for flow state by employing directly addressed bitmaps to record flow status, as necessary for scheduling and admission control, respectively.

Though initially designed for data transport, there is increasing interest in using the 802.11 WLAN protocol for voice and other real time services. This paper presents a performance model for voice over WLAN under distributed control. The model is based on classical decoupling arguments and allows an analytical evaluation of network capacity in terms of tuneable protocol parameters. We determine parameter settings that maximize the number of simultaneous conversations and demonstrate the significant impact on capacity of the voice packet size. Models are developed for both dedicated and integrated networks using the priority features of 802.11e

Despite its well-known advantages, per-flow fair queueing has not been deployed in the Internet mainly because of the common belief that such scheduling is not scalable. The objective of the present paper is to demonstrate using trace simulations and analytical evaluations that this belief is misguided. We show that although the number of flows in progress increases with link speed, the number that needs scheduling at any moment is largely independent of this rate. The number of such active flows is a random process typically measured in hundreds even though there may be tens of thousands of flows in progress. The simulations are performed using traces from commercial and research networks with quite different traffic characteristics. Analysis is based on models for balanced fair statistical bandwidth sharing and applies properties of queue busy periods to explain the observed behaviour.

Based on an analysis of the statistical nature of IP traffic and the way this impacts the performance of voice, video, and data services, we question the appropriateness of commonly proposed quality-of-service mechanisms. This paper presents the main points of this analysis. We also discuss pricing issues and argue that many proposed schemes are overly concerned with congestion control to the detriment of the primary pricing function of return on investment. Finally, we propose an alternative flow-aware networking architecture based on a novel router design called cross-protect. In this architecture, performance requirements are satisfied without explicit service differentiation, creating a particularly simple platform for the converged network.

We suggest that satisfactory statistical performance guarantees for streaming flows can be fulfilled when their packets receive expedited forwarding in non-preemptive priority queues. This relies on the conjecture that jitter remains negligible in the network such that performance measures can be bounded by assuming flows constitute Poisson arrival processes of maximum transfer unit (MTU) sized packets. We provide analytical and simulation evidence in support of this conjecture and show how it leads to simple engineering rules for both constant and variable rate streaming traffic.

In this paper we study the statistics of the realized throughput of elastic document transfers, accounting for the way network bandwidth is shared dynamically between the randomly varying number of concurrent flows. We first discuss the way TCP realizes statistical bandwidth sharing, illustrating essential properties by means of packet level simulations. Mathematical flow level models based on the theory of stochastic networks are then proposed to explain the observed behavior. A notable result is that first order performance (e.g., mean throughput) is insensitive with respect both to the flow size distribution and the flow arrival process, as long as "sessions" arrive according to a Poisson process. Perceived performance is shown to depend most significantly on whether demand at flow level is less than or greater than available capacity. The models provide a key to understanding the effectiveness of techniques for congestion management and service differentiation.

This paper describes a novel approach for real-time defect detection targeted to web inspection systems using real-time processing of raster scanned images. Our new method utilizes a fuzzy fusion of texture features to detect image rows that contain defects, without requiring access to the two dimensional frame data. The method is suitable for in-camera processing where an FPGA is directly connected to the digitized video stream. This method is successfully implemented in the limited resources of one FPGA without the use of a frame-grabber.

We present a rate control algorithm adapted to MPEG video coders ensuring that output conforms to the parameters of a leaky-bucket network access controller. The algorithm avoids unpredictable rate variations without the rigidity and systematic coding delay of constant bit-rate (CBR) coders, and makes possible resource provision for guaranteed quality of service. A relatively large burst tolerance parameter allows considerable scope for variation at GoP scale, and only restricts the natural rate when necessary to avoid long-term overloads. Possible multiplexing schemes are discussed distinguishing buffer provision for cell-scale and burst-scale congestion.

When variable-bit-rate sources are multiplexed in an asynchronous transfer mode (ATM) network, there arise queues with a particular form of correlated arrival process. Such queues are analyzed by exploiting a result expressing the distribution of work in system of the G/G/1 queue originally derived by V.E. Benes (1963). A simple alternative demonstration of this result is analyzed and extended to the case of fluid input systems. The result is applied first to a queue where the arrival process is a superposition of periodic sources (the Sigma D/sub i//D/1 queue), and then to a variable-input-rate constant-output-rate fluid system. The latter is shown to model the so-called burst component of the considered superposition queuing process. The difference between this and the real queue, the cell component, can be evaluated by means of the results obtained for the Sigma D/sub i//D/1 queue. The relative importance of these two components is explored with reference to the particular case of a superposition of on/off sources.>

The authors consider the queue arising in a multiservice network using ATM (asynchronous transfer mode) when a superposition of periodic streams of constant-length cells is multiplexed on a high-speed link. An exact closed formula is derived for the queue length distribution in the case where all streams have the same period, and tight upper and lower bounds are obtained on this distribution when the periods are different. Numerical results confirm that the use of a Poisson approximation (i.e. the M/D/1 queue) can lead to a significant overestimation of buffer requirements, particularly in the case of heavy loads. Buffer requirements for a mixture of different period streams can be accurately estimated from the upper bound on the queue length distribution. For given load, requirements increase with the number of long-period (i.e. low-bit rate) sources. The results are deduced from a novel characterization of the single-server constant service time queue, which should be useful in other applications.>