903407
On integrating fluid models with packet simulation
Fluid models have been shown to he efficient and accurate in modelling large IP networks. However, unlike packet models, it is difficult to extract packet-level information from them. In this paper, we present a hybrid simulation method that maintains the performance advantage of fluid models while providing detailed packet level information for selected packet traffic flows. We propose two models to account for the interaction between background TCP traffic in a fluid network and foreground packet traffic of interest. The first assumes that the packet traffic poses a negligible load on the fluid network whereas the second accounts for the added load by transforming the packet traffic into fluid flows and solving the resulting enhanced fluid model. The first of these yields an efficient one pass solution algorithm whereas the second requires an additional pass to account for the packet traffic load. We establish the correctness of both approaches and present their implementation within ns-2. Comparisons between the hybrid models and a classical packet simulation show the two pass approach to be quite accurate and computationally efficient.
15563828
Self-similarity and long range dependence on the internet: a second look at the evidence, origins and implications
In this paper we critically reexamine some of the long standing beliefs regarding self-similarity and long range dependence (LRD) on the Internet. Power law tails have been conjectured to be a cause of LRD. In this paper, we reexamine the claims regarding heavy tails. We first examine the generative models for the heavy tail phenomena, both in terms of the fragility of some proposed mechanisms to modeling perturbations as well as the weak statistical evidence for the mechanisms. Next, we take a look at some of the implications of LRD in key performance aspects of Internet algorithms. Finally, we present an alternative model explaining the LRD phenomena of Internet traffic. We argue that the multiple time-scale nature of the generation of traffic and transport protocols make the observation of LRD inevitable.
6965590
An information-theoretic approach to network monitoring and measurement
Network engineers and operators are faced with a number of challenges that arise in the context of network monitoring and measurement. These include: i) how much information is included in measurement traces and by how much can we compress those traces?, ii) how much information is captured by different monitoring paradigms and tools ranging from full packet header captures to flow-level captures (such as with NetFlow) to packet and byte counts (such as with SNMP)? and iii) how much joint information is included in traces collected at different points and can we take advantage of this joint information? In this paper we develop a network model and an information theoretic framework within which to address these questions. We use the model and the framework to first determine the benefits of compressing traces captured at a single monitoring point, and we outline approaches to achieve those benefits. We next consider the benefits of joint coding, or equivalently of joint compression of traces captured a different monitoring points. Finally, we examine the difference in information content when measurements are made at either the flow level or the packet/byte count level. In all of these cases, the effect of temporal and spatial correlation on the answers to the above questions is examined. Both our model and its predictions are validated against measurements taken from a large operational network.
1409797
On the TCP-Friendliness of VoIP Traffic
Recently, some concerns have been raised regarding whether the rapid growth of the UDP traffic due to the Skype-like applications will throttle down regular TCP users because UDP flows are unresponsive to network congestion, i.e., UDP senders do not reduce their sending rates when congestion occurs in the network. However, most UDP based real time applications, such as Voiceover-IP (VoIP), drop out completely if the user perceived quality becomes unacceptable as the network congestion increases. This user back-off mechanism effectively reduces UDP traffic rate at the aggregated level when the network is congested. In this paper, we investigate the fairness issue between VoIP flows and TCP flows under different network environment. Our study explicitly takes into account both transport layer congestion control mechanism built-into TCP protocol stack and the self-adaptiveness of VoIP users. Various models are developed to characterize VoIP user back-off behaviors in response to call quality degradation resulted from packet loss and delay inside the network. The comparison between VoIP user back-off and TCP rate adaption shows that not only VoIP flows consume much less bandwidth than TCP flows, but also VoIP traffic is indeed very responsive to congestion when the network is overloaded.
12544972
Fluid models and solutions for large-scale IP networks
In this paper we present a scalable model of a network of Active Queue Management (AQM) routers serving a large population of TCP flows. We present efficient solution techniques that allow one to obtain the transient behavior of the average queue lengths, packet loss probabilities, and average end-to-end latencies. We model different versions of TCP as well as different versions of RED, the most popular AQM scheme currently in use. Comparisons between our models and <tt>ns</tt> simulation show our models to be quite accurate while at the same time requiring substantially less time to solve, especially when workloads and bandwidths are high.
13098192
On the impact of concurrent downloads
Concurrent downloads accelerate information access speed for individual Web users. The speed-up comes from multiple connections launched for one subject download, which leads to unfairness at user level. We study the impact of concurrent downloads on the network. Particularly, we investigate the fairness between users who employ different downloading concurrency. We also discuss how concurrent downloads affect the transient behavior of the network.
753155
Spare Capacity Planning for Survivable Mesh Networks
The design of survivable mesh based STM networks has received considerable attention in recent years and is a complex multiconstraint optimization problem. In this paper, a new spare capacity planning methodology is proposed utilizing genetic algorithms. The method is based on forcing flows/traffic which are on paths that are disjoint to share backup spare capacity. The major advantages of the new approach are a polynomial time complexity and the capability of incorporating nonlinear variables such as nonlinear cost functions into the solution algorithm. Numerical results illustrating the form of the genetic algorithm solution and comparing the proposed methodology to existing techniques from the literature are presented.
24959035
A Novel Constraint-Based Approach to Online Graphics Recognition
Online graphics recognition has become the key problem for pen-based user interface on small screen devices, such as PDA and Tablet PC. In this paper, a novel constraint-based approach to online graphics recognition is proposed. The key idea of our approach is that when the user is drawing a graphic object, the system can extract the constraints between primitives and basic shapes from the object and use these constraints to retrieve similar graphic objects from the database at run time. The user can then choose the standard object from the ranked list of results to replace his sketches before he finishes drawing all strokes of the object. For this purpose, we summarize three types of primitives and several types of basic shapes as the basic components of a graphic object. We also define a set of constraints between primitives and basic shapes to represent their structural relations. The algorithms for online constraint extraction and graphics recognition are also presented. Experimental results show that our approach is efficient for online graphics recognition and effective for improving the user’s productivity.
132343
Approaching optimal peer-to-peer overlays
In unstructured peer-to-peer (P2P) systems, there exists a serious topology mismatch problem between physical and logical network. We first analyze the relationship between the property of the overlay and the corresponding message duplications incurred by queries in a given overlay, and prove that computing an optimal overlay with global knowledge is an NP-hard problem. Motivated by the analysis results, we design a distributed overlay optimization algorithm, THANCS, to attack topology mismatch. We demonstrate its performance by comprehensive simulations in dynamic environments. The proposed THANCS has three major strengths. First, it does not need any global knowledge. Second, its optimization convergent speed is fast. Third, it is orthogonal with other types of advanced search approaches.
14532857
Projecting registration error for accurate registration of overlapping range images
Abstract In this paper, we propose a novel algorithm for the automatic registration of two overlapping range images. Since it is relatively difficult to compare the registration errors of different point matches, we project them onto a virtual image plane for more accurate comparison using the classical pin-hole perspective projection camera model. While the traditional ICP algorithm is more interested in the points in the second image close to the sphere centred at the transformed point, the novel algorithm is more interested in the points in the second image as collinear as possible to the transformed point. The novel algorithm then extracts useful information from both the registration error and projected error histograms for the elimination of false matches without any feature extraction, image segmentation or the requirement of motion estimation from outliers corrupted data and, thus, has an advantage of easy implementation. A comparative study based on real images captured under typical imaging conditions has shown that the novel algorithm produces good registration results.
29553031
S-Club: an overlay based efficient service discovery mechanism in CROWN grid
Information service plays a key role in grid system, handles resource discovery and management process. Employing existing information service architectures suffers from poor scalability, long search response time, and large traffic overhead. In this paper, we propose a service club mechanism, called S-Club, for efficient service discovery. In S-Club, an overlay based on existing GIS mesh network of CROWN is built, so that GISs are organized as service clubs. Each club serves for a certain type of service while each GIS may join one or more clubs. S-Club is adopted in RLDS as the information service in CROWN grid and the performance of S-Club is evaluated by comprehensive simulations. The results show that S-Club scheme significantly improves search performance and outperforms existing approaches