Showing papers in "Computer Networks in 2002"
TL;DR: The concept of sensor networks which has been made viable by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics is described.
Abstract: This paper describes the concept of sensor networks which has been made viable by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed.
17,936 citations
TL;DR: The paper presents the overall design of Annotea and describes some of the issues the project has faced and how it has solved them, including combining RDF with XPointer, XLink, and HTTP.
Abstract: Annotea is a Web-based shared annotation system based on a general-purpose open resource description framework (RDF) infrastructure, where annotations are modeled as a class of metadata . Annotations are viewed as statements made by an author about a Web document. Annotations are external to the documents and can be stored in one or more annotation servers . One of the goals of this project has been to re-use as much existing W3C technology as possible. We have reached it mostly by combining RDF with XPointer, XLink, and HTTP. We have also implemented an instance of our system using the Amaya editor/browser and a generic RDF database, accessible through an Apache HTTP server. In this implementation, the merging of annotations with documents takes place within the client. The paper presents the overall design of Annotea and describes some of the issues we have faced and how we have solved them.
565 citations
TL;DR: It is revealed that the applicability of traffic prediction is limited by the deteriorating prediction accuracy with increasing prediction interval, and quantized reference to the optimal online traffic predictability for network control purposes is provided.
Abstract: This paper assesses the predictability of network traffic by considering two metrics: (1) how far into the future a traffic rate process can be predicted with bounded error; (2) what the minimum prediction error is over a specified prediction time interval. The assessment is based on two stationary traffic models: the auto-regressive moving average and the Markov-modulated poisson process. In this paper, we do not aim to propose the best traffic (prediction) model, which is obviously a hard and arguable issue. Instead, we focus on the constrained predictability estimation with assumption and discussion about the modeling accuracy. The specific time scale or bandwidth utilization target of a predictive network control actually forms the constraint. We argue that the two models, though both short-range dependent, can capture statistics of (self-similar) traffic quite accurately for the limited time scales of interests in measurement-based traffic management. This argument, in mathematical terms, simply reflects the fact that the summarized exponential (correlation) functions may approximate a hyperbolical one very well. Our study reveals that the applicability of traffic prediction is limited by the deteriorating prediction accuracy with increasing prediction interval. From both analytical and numerical studies, we explore the different roles of traffic statistics, either at the 1st-order or the 2nd-order, in traffic predictability. Particularly, the statistical multiplexing and proper measurement (e.g. sampling/filtering) of traffic show positive effects. Experimental results suggest promising backbone traffic prediction, and generally enhanced predictability if small time-scale traffic variations, which are usually of less importance to bandwidth allocation and call admission control, have been filtered out. The numerical results in the paper provide quantized reference to the optimal online traffic predictability for network control purposes.
252 citations
TL;DR: This paper presents call admission control and bandwidth reservation schemes in wireless cellular networks that have been developed based on assumptions more realistic than existing proposals, and adaptively control the admission threshold to achieve a better balance between guaranteeing handoff dropping probability and maximizing resource utilization.
Abstract: This paper presents call admission control and bandwidth reservation schemes in wireless cellular networks that have been developed based on assumptions more realistic than existing proposals. In order to guarantee the handoff dropping probability, we propose to statistically predict user mobility based on the mobility history of users. Our mobility prediction scheme is motivated by computational learning theory, which has shown that prediction is synonymous with data compression. We derive our mobility prediction scheme from data compression techniques that are both theoretically optimal and good in practice. In order to utilize resource more efficiently, we predict not only the cell to which the mobile will handoff but also when the handoff will occur. Based on the mobility prediction, bandwidth is reserved to guarantee some target handoff dropping probability. We also adaptively control the admission threshold to achieve a better balance between guaranteeing handoff dropping probability and maximizing resource utilization. Simulation results show that the proposed schemes meet our design goals and outperform the static-reservation and cell-reservation schemes.
209 citations
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TL;DR: The definition of keys for XML documents is discussed, paying particular attention to the concept of a relative key , which is commonly used in hierarchically structured documents and scientific databases.
Abstract: We discuss the definition of keys for XML documents, paying particular attention to the concept of a relative key , which is commonly used in hierarchically structured documents and scientific databases.
209 citations
TL;DR: The in-depth cause of several serious problems encountered in transmission control protocol (TCP) connections in an IEEE 802.11 based multi-hop network are revealed and it is concluded that the current version of this wireless LAN protocol does not function well inMulti-hop ad hoc networks.
Abstract: The IEEE 802.11 medium access control (MAC) protocol is a standard for wireless LANs, it is also widely used in almost all test beds and simulations for the research in wireless mobile multi-hop ad hoc networks. However, this protocol was not designed for multi-hop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multi-hop connectivity is one of the most prominent features. In this paper, we focus on the following question: can IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in transmission control protocol (TCP) connections in an IEEE 802.11 based multi-hop network, we show that the current TCP protocol does not work well above the current 802.11 MAC layer. The relevant problems include the TCP instability problem found in this kind of network, the severe unfairness problem, and the incompatibility problem. We illustrate that all these problems are rooted in the MAC layer. Furthermore, by revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multi-hop ad hoc networks. We thus doubt whether the current WaveLAN based system is workable as a mobile multi-hop ad hoc test bed. All the results shown in this paper are based on NS2 simulations, and are compatible with the results from the OPNET simulations.
178 citations
TL;DR: Future evolution of the Web is discussed, and some important issues for search engines will be scheduling and query execution as well as increasingly heterogeneous architectures to handle the dynamic Web.
Abstract: In this paper we study several dimensions of Web dynamics in the context of large-scale Internet search engines. Both growth and update dynamics clearly represent big challenges for search engines. We show how the problems arise in all components of a reference search engine model. Furthermore, we use the FAST Search Engine architecture as a case study for showing some possible solutions for Web dynamics and search engines. The focus is to demonstrate solutions that work in practice for real systems. The service is running live at www.alltheweb.com and major portals worldwide with more than 30 million queries a day, about 700 million full-text documents, a crawl base of 1.8 billion documents, updated every 11 days, at a rate of 400 documents/second. We discuss future evolution of the Web, and some important issues for search engines will be scheduling and query execution as well as increasingly heterogeneous architectures to handle the dynamic Web.
135 citations
TL;DR: The proposed two level model for TCP connection arrivals in local area networks, which has a small number of parameters which are inferred from real traffic collected at a firewall, shows that traffic synthesized with the model closely matches the original data.
Abstract: We propose a two level model for TCP connection arrivals in local area networks. The first level are user sessions whose arrival is time-varying Poisson. The second level are connections within a user session. Their number and mean interarrival times are independent and biPareto across user sessions. The interarrivals within a user session are Weibull, and across all users are correlated Weibull. Our model has a small number of parameters which are inferred from real traffic collected at a firewall. We show that traffic synthesized with our model closely matches the original data. We extend this approach to a general model involving shot noise and show it is asymptotically consistent with more common fractal models used in data networks. Finally, we show that this model extends to the wide area network applications without alteration and it predicts smoothing of wide area network traffic profiles due to spatial aggregation, which we observe experimentally by synthetically creating a large aggregate TCP load.
134 citations
TL;DR: Redland is a flexible and efficient RDF system that complements this power and provides high-level interfaces allowing instances of the model to be stored, queried and manipulated in C, Perl, Python, Tcl, Java and other languages.
Abstract: Resource description framework (RDF) is a general description technology that can be applied to many application domains. Redland is a flexible and efficient RDF system that complements this power and provides high-level interfaces allowing instances of the model to be stored, queried and manipulated in C, Perl, Python, Tcl, Java and other languages. It is implemented using an object-based API, providing several of the implementation classes as modules which can be added, removed or replaced to allow different functionality or application-specific optimisations. The framework provides the core technology for developing new RDF applications, experimenting with implementation techniques, APIs and representations.
132 citations
TL;DR: This paper introduces and analyzes an architecture called Transport Layer Mobility that allows mobile nodes to not only change their point of attachment to the Internet within a corporate domain, but also to control which network interfaces are used for the different kinds of data leaving from and arriving at the mobile node.
Abstract: Mobile nodes of the future will be equipped with multiple network interfaces to take advantage of overlay networks, yet no current mobility systems provide full support for the simultaneous use of multiple interfaces. The need for such support arises when multiple connectivity options are available with different cost, coverage, latency and bandwidth characteristics, and applications want their data to flow over the interface that best matches the characteristics of the data. In this paper we introduce and analyze an architecture called Transport Layer Mobility that allows mobile nodes to not only change their point of attachment to the Internet within a corporate domain, but also to control which network interfaces are used for the different kinds of data leaving from and arriving at the mobile node. We implement our transport layer mobility scheme using a split–connection proxy architecture and a new technique called TCP Splice that gives split–connection proxy systems the same end-to-end semantics as normal TCP connections. We introduce the architecture, present its system aspects, investigate its performance and present its reliability properties. The analytical aspects of the protocol, in particular its pseudo-code, its properties and its validation are given in a related Technical Report.
127 citations
IBM1
TL;DR: Key aspects of ANDES are that it uses XML technologies for data extraction, including Extensible HTML and Extensible Stylesheet Language Transformations, and provides access to the “deep Web”.
Abstract: We describe an Extensible Markup Language (XML)-based methodology for Web data extraction that extends beyond simple “screen scraping”. An ideal data extraction process can digest target Web databases that are visible only as Hypertext Markup Language (HTML) pages, and create a local replica of those databases as a result. What is needed is more than a Web crawler and set of Web site wrappers. A comprehensive data extraction process must deal with such obstacles as session identifiers, HTML forms, client-side JavaScript, incompatible datasets and vocabularies, and missing and conflicting data. Proper data extraction also requires solid data validation and error recovery to handle data extraction failures. Our ANDES software framework helps solve these problems and provides a platform for building a production–quality Web data extraction process. Key aspects of ANDES are that it uses XML technologies for data extraction, including Extensible HTML and Extensible Stylesheet Language Transformations, and provides access to the “deep Web”.
TL;DR: By analysis and simulations, this paper shows how TCP performance varies as a function of the amount of FEC, and studies in detail this bandwidth tradeoff between TCP and FEC.
Abstract: Forward error correction (FEC) is widely used for the improvement of the quality of noisy transmission media as wireless links. This improvement is of importance for a transport protocol as TCP which uses the loss of packets as an indication of network congestion. FEC shields TCP from losses not caused by congestion and helps it to improve its throughput but on the other hand it consumes a part of the available bandwidth that could be used by TCP. In this paper we study in detail this bandwidth tradeoff between TCP and FEC. By analysis and simulations we show how TCP performance varies as a function of the amount of FEC.
TL;DR: A distributed optimal location algorithm that requires small nodal memory capacity and computational power is developed that simplifies the combination operation used in the design of a dynamic program.
Abstract: The delivery of large files to individual users, such as video on demand or application programs to the envisioned network computers is expected by many to be one of the main tasks of broadband communication networks. This requires high bandwidth capacity as well as fast and dense storage servers. This motivates multimedia service providers to optimize the delivery network, as well as the electronic content allocation.A hierarchical architecture for the distribution of multimedia content was introduced by Nussbaumer, Patel, Schaffa, and Sterbenz (INFOCOM 94). They addressed the trade-off between bandwidth and storage requirements that results from the placement of the content servers in the hierarchy tree. They presented a centralized algorithm to compute the best level of the hierarchy for the server location to minimize the combined cost of communication and storage.In this work we solve a general case where servers can be placed at different levels of the hierarchy. We develop a distributed optimal location algorithm that requires small nodal memory capacity and computational power. Previous results for related problems for caching system design are of higher complexity. Previous results for related classic operations research problems are limited to centralized algorithms, based on linear programming, that are not easy to convert into distributed algorithms. Instead, to obtain our results, we observed that the use of dynamic programming naturally lends itself to a distributed implementation.For the specific problem at hand, we also managed to find a natural function (a generalization of the problem) that simplifies the combination operation used in the design of a dynamic program.
TL;DR: The design and use of a synthetic web proxy workload generator called ProWGen is described to investigate the sensitivity of web proxy cache replacement policies to five selected web workload characteristics, finding three replacement policies are relatively insensitive to the percentage of one-timers in the workload.
Abstract: This paper describes the design and use of a synthetic web proxy workload generator called ProWGen to investigate the sensitivity of web proxy cache replacement policies to five selected web workload characteristics. Three representative cache replacement policies are considered in the simulation study: a recency-based policy called least-recently-used, a frequency-based policy called least-frequently-used-with-aging, and a size-based policy called greedy-dual-size.Trace-driven simulations with synthetic workloads from ProWGen show the relative sensitivity of these cache replacement policies to three web workload characteristics: the slope of the Zipf-like document popularity distribution, the degree of temporal locality in the document referencing behaviour, and the correlation (if any) between document size and document popularity. The three replacement policies are relatively insensitive to the percentage of one-timers in the workload, and to the Pareto tail index of the heavy-tailed document size distribution. Performance differences between the three cache replacement policies are also highlighted.
TL;DR: It is shown how RDFS can be extended to include a more expressive knowledge representation language, Ontology Inference Layer (OIL), which would enrich it with the required additional expressivity and the semantics of that language.
Abstract: Recently, a widespread interest has emerged in using ontologies on the Web. Resource Description Framework Schema (RDFS) is a basic tool that enables users to define vocabulary, structure and constraints for expressing meta data about Web resources. However, it includes no provisions for formal semantics, and its expressivity is not sufficient for full-fledged ontological modeling and reasoning. In this paper, we will show how RDFS can be extended to include a more expressive knowledge representation language. That, in turn, would enrich it with the required additional expressivity and the semantics of that language. We do this by describing the ontology language Ontology Inference Layer (OIL) as an extension of RDFS. An important advantage to our approach is that it ensures maximal sharing of meta data on the Web: even partial interpretation of an OIL ontology by less semantically aware processors will yield a correct partial interpretation of the meta data.
TL;DR: This work presents MTCP, a congestion control scheme for large-scale reliable multicast that incorporates several novel features, and proposes new techniques that can effectively handle instances of congestion occurring simultaneously at various parts of a multicast tree.
Abstract: We present MTCP, a congestion control scheme for large-scale reliable multicast. Congestion control for reliable multicast is important, because of its wide applications in multimedia and collaborative computing, yet non-trivial, because of the potentially large number of receivers involved. Many schemes have been proposed to handle the recovery of lost packets in a scalable manner, but there is little work on the design and implementation of congestion control schemes for reliable multicast. We propose new techniques that can effectively handle instances of congestion occurring simultaneously at various parts of a multicast tree.Our protocol incorporates several novel features: (1) hierarchical congestion status reports that distribute the load of processing feedback from all receivers across the multicast group, (2) the relative time delay concept which overcomes the difficulty of estimating round-trip times in tree-based multicast environments, (3) window-based control that prevents the sender from transmitting faster than packets leave the bottleneck link on the multicast path through which the sender's traffic flows, (4) a retransmission window that regulates the flow of repair packets to prevent local recovery from causing congestion, and (5) a selective acknowledgment scheme that prevents independent (i.e., non-congestion-related) packet loss from reducing the sender's transmission rate. We have implemented MTCP both on UDP in SunOS 5.6 and on the simulator ns, and we have conducted extensive Internet experiments and simulation to test the scalability and inter-fairness properties of the protocol. The encouraging results we have obtained support our confidence that TCP-like congestion control for large-scale reliable multicast is within our grasp.
TL;DR: In this article, the authors identify and analyze separately the two mechanisms within TCP that are responsible for this scaling behavior: timeouts and congestion avoidance, and provide analytical models for both mechanisms that, under the proper loss probabilities, accurately predict the range in time-scales and the strength of the sustained correlation structure of the traffic sending rate of a single TCP source.
Abstract: The statistical characteristics of network traffic--in particular the observation that it can exhibit long range dependence--have received considerable attention from the research community over the past few years. In addition, the recent claims that the TCP protocol can generate traffic with long range dependent behavior has also received much attention. Contrary to the latter claims, in this paper we show that the TCP protocol can generate traffic with correlation structures that spans only an analytically predictable finite range of time-scales. We identify and analyze separately the two mechanisms within TCP that are responsible for this scaling behavior: timeouts and congestion avoidance. We provide analytical models for both mechanisms that, under the proper loss probabilities, accurately predict the range in time-scales and the strength of the sustained correlation structure of the traffic sending rate of a single TCP source. We also analyze an existing comprehensive model of TCP that accounts for both mechanisms and show that TCP itself exhibits a predictable finite range of time-scales under which traffic presents sustained correlations. Our claims and results are derived from Markovian models that are supported by simulations. We note that traffic generated by TCP can be misinterpreted to have long range dependence, but that long range dependence is not possible due to inherent finite time-scales of the mechanisms of TCP.
TL;DR: This paper considers source-initiated multicast session traffic in an ad hoc wireless network, operating under hard constraints on the available transmission energy as well as on bandwidth and transceiver resources, and demonstrates how the incorporation of residual energy into the cost metric used for tree construction can provide improved performance.
Abstract: In this paper we consider source-initiated multicast session traffic in an ad hoc wireless network, operating under hard constraints on the available transmission energy as well as on bandwidth and transceiver resources We describe the similarities and differences between energy-limited and energy-efficient communications, and we illustrate the impact of these overlapping (and sometimes conflicting) considerations on network operation In energy-limited applications, fundamental objectives include the maximization of a network's useful lifetime and the maximization of traffic that is delivered during this lifetime We demonstrate how the incorporation of residual energy into the cost metric used for tree construction can provide improved performance based on these criteria
TL;DR: This paper develops a rather general and easy-to-use methodology how to obtain good approximations for queue length distributions in priority and generalized processor sharing systems where the cumulative input traffic streams are modeled as general Gaussian processes with stationary increments.
Abstract: This paper develops a rather general and easy-to-use methodology how to obtain good approximations for queue length distributions in priority and generalized processor sharing systems where the cumulative input traffic streams are modeled as general Gaussian processes with stationary increments. The idea is to identify the most probable path in the threshold-exceeding event, or a heuristic approximation of it, and then to use probability estimates based on this path. The method is particularly useful for long-range dependent traffic and complicated traffic mixes, which are difficult to handle with traditional queueing theory.
TL;DR: Approaches from statistical physics are applied to investigate the structure of network models whose growth rules mimic aspects of the evolution of the World Wide Web and obtain distinct power-law forms for the in-degree and out-degree distributions with exponents that are in good agreement with current data for the web.
Abstract: Approaches from statistical physics are applied to investigate the structure of network models whose growth rules mimic aspects of the evolution of the World Wide Web. We first determine the degree distribution of a growing network in which nodes are introduced one at a time and attach to an earlier node of degree k with rate Ak∼kγ. Very different behaviors arise for γ 1. We also analyze the degree distribution of a heterogeneous network, the joint age-degree distribution, the correlation between degrees of neighboring nodes, as well as global network properties. An extension to directed networks is then presented. By tuning model parameters to reasonable values, we obtain distinct power-law forms for the in-degree and out-degree distributions with exponents that are in good agreement with current data for the web. Finally, a general growth process with independent introduction of nodes and links is investigated. This leads to independently growing sub-networks that may coalesce with other sub-networks. General results for both the size distribution of sub-networks and the degree distribution are obtained.
TL;DR: The techniques and practices of traffic engineering in contemporary IP networks are discussed, emphasizing the role of MPLS in performance optimization of the public Internet, and the impact of generalized MPLS (GMPLS) on traffic Engineering in IP-over-optical networks as the underlying technologies continue to mature.
Abstract: With the rising popularity of the Internet there have arisen corresponding requirements for network reliability, efficiency, and service quality. Internet service providers are responding to these developments by critically examining every aspect of their operational environment, looking for opportunities to scale their networks and optimize performance. In this context, traffic engineering has emerged as a major consideration in the design and operation of large public Internet backbone networks. However, the classical Internet interior gateway routing protocols hinder the practical realization of sophisticated traffic engineering policies in legacy IP networks. The advent of multiprotocol label switching (MPLS) offers the prospect to address some of the shortcomings associated with traffic engineering in IP networks. This paper discusses the techniques and practices of traffic engineering in contemporary IP networks, emphasizing the role of MPLS in performance optimization of the public Internet. We also examine the impact of generalized MPLS (GMPLS) on traffic engineering in IP-over-optical networks as the underlying technologies continue to mature.
TL;DR: Simple techniques that address factors contributing to user-perceived latency, including DNS lookup times, transmission control protocol connection–establishment, and start-of-session delays at hypertext transfer protocol (HTTP) servers are proposed, which have a potential to significantly reduce long waits.
Abstract: User-perceived latency is recognized as the central performance problem in the Web. We systematically measure factors contributing to this latency, across several locations. Our study reveals that domain name system (DNS) lookup times, transmission control protocol (TCP) connection–establishment, and start-of-session delays at hypertext transfer protocol (HTTP) servers are major causes of long waits. Moreover, wait due to these factors also afflicts high-bandwidth users, which enjoy relatively short transmission times. We propose simple techniques that address these factors: (i) pre-resolving host names (pre-performing DNS lookup), (ii) pre-connecting (prefetching TCP connections prior to issuance of HTTP request), and (iii) pre-warming (sending a “dummy” HTTP HEAD request to Web servers). Trace-based simulations demonstrate a potential to significantly reduce long waits. Our techniques are complementary to the more traditional document prefetching techniques. Like document prefetching, deployment of our techniques at Web browsers or proxies does not require protocol modifications or Web server cooperation, and the prefetching strategy itself can be based on analysing hyperlinks or request patterns. In contrast to document prefetching, they can be applied with non-prefetchable URLs. Furthermore, bandwidth overhead is minimal and they are considerably more effective in performance improvement per bandwidth used than document prefetching. We propose scalable deployment solutions to control the potential overhead to proxies and particularly to Web servers.
TL;DR: It is concluded that priority queuing is the most appropriate scheduling scheme for the handling of voice traffic, while preemption of nonvoice packets is strongly recommended for sub-10 Mbit/s links.
Abstract: In the future, voice communication is expected to migrate from the public switched telephone network to the Internet. Because of the particular characteristics (low volume and burstiness) and stringent delay and loss requirements of voice traffic, it is important to separate voice traffic from other traffic in the network by providing it with a separate queue. In this study, we conduct a thorough assessment of voice delay in this context. We conclude that priority queuing is the most appropriate scheduling scheme for the handling of voice traffic, while preemption of nonvoice packets is strongly recommended for sub-10 Mbit/s links. We also find that per-connection custom packetization is in most cases futile, i.e. one packet size allows a good compromise between an adequate end-to-end delay and an efficient bandwidth utilization for voice traffic.
TL;DR: It is shown that while for a specific network configuration, the derived delay bound is not restricted by the utilization level on the GR, it is so for a general network configuration.
Abstract: To support quality of service guarantees in a scalable manner, aggregate scheduling has attracted a lot of attention in the networking community. However, while there are a large number of results available for flow-based scheduling algorithms, few such results are available for aggregate-based scheduling. In this paper, we study a network implementing guaranteed rate (GR) scheduling with first-in-first-out aggregation. We derive an upper bound on the worst case end-to-end delay for the network. We show that while for a specific network configuration, the derived delay bound is not restricted by the utilization level on the GR, it is so for a general network configuration.
TL;DR: The main findings are the probability density function of thefLm process, several scaling results related to a single-server infinite buffer queue fed by fLm traffic, and an asymptotic lower bound for the probability of overflow.
Abstract: We introduce a general non-Gaussian, self-similar, stochastic process called the fractional Levy motion (fLm). We formally expand the family of traditional fractal network traffic models, by including the fLm process. The main findings are the probability density function of the fLm process, several scaling results related to a single-server infinite buffer queue fed by fLm traffic, e.g., scaling of the queue length, and its distribution, scaling of the queuing delay when independent fLm streams are multiplexed, and an asymptotic lower bound for the probability of overflow (decreases hyperbolically as a function of the buffer size).
TL;DR: TC-Real controls congestion as standard TCP does but allows for a measurement-based transmission strategy, which complements the "blind" increase/ decrease window adjustments, and displays an inherent property to produce comprehensive dynamics in heterogeneous environments with wired or wireless networks and delay-sensitive or -tolerant applications.
Abstract: We introduce a receiver-oriented approach to congestion control, demonstrated by an experimental protocol, TCP-Real. The protocol allows for a measurement-based transmission strategy, which complements the "blind" increase/ decrease window adjustments. Owing to its design, the protocol displays an inherent property to produce comprehensive dynamics in heterogeneous environments with wired or wireless networks and delay-sensitive or -tolerant applications. TCP-Real controls congestion as standard TCP does. However, its receiver-oriented nature and its "wave" communication pattern allow for two amending mechanisms: (i) congestion avoidance, which reduces unnecessary transmission gaps that hurt the performance of time-constrained applications, and (ii) advanced error detection and classification, which designates recovery tactics responsive to the nature of the errors, thereby enhancing the protocol performance over wireless links or asymmetric paths.We detail the protocol mechanisms and specification and we report extensively on the comparative fairness and efficiency evaluation of standard TCP, TCP-Real, and TCP-friendly protocols for both delay-tolerant and -sensitive applications and in both wired and wireless networks.
TL;DR: These policies for caches to proactively validate selected objects as they become stale, and thus allow for more client requests to be processed locally, are proposed and evaluated and compared using trace-based simulations.
Abstract: Web content caches are often placed between end users and origin servers as a mean to reduce server load, network usage, and ultimately, user-perceived latency. Cached objects typically have associated expiration times, after which they are considered stale and must be validated with a remote server (origin or another cache) before they can be sent to a client. A considerable fraction of cache "hits" involve stale copies that turned out to be current. These validations of current objects have small message size, but nonetheless, often induce latency comparable to full-fledged cache misses. Thus, the functionality of caches as a latency-reducing mechanism highly depends not only on content availability but also on its freshness. We propose policies for caches to proactively validate selected objects as they become stale, and thus allow for more client requests to be processed locally. Our policies operate within the existing protocols and exploit natural properties of request patterns such as frequency and recency. We evaluated and compared different policies using trace-based simulations.
TL;DR: WHIM is developed, a scalable system that allows multicast content to be marked with distinct information for distinct receivers securely and introduces two new concepts: generating a watermark based on the receiver's location in a tree overlaying the network and inserting the watermark in the content incrementally as it traverses an overlay network.
Abstract: Fingerprinting, watermarking content to identify the recipient, provides a good deterrence to unauthorized duplication and propagation of multimedia streams. This is straightforward in a unicast environment; however, in a multicast environment, inserting a fingerprint at the source does not provide any security since many receivers will share a common fingerprint. A simple solution would be to fingerprint the data for each user at the source and unicast the different streams. We aim to achieve a more scalable solution while maintaining and even increasing the level of security. To achieve this, we have developed WHIM, a scalable system that allows multicast content to be marked with distinct information for distinct receivers securely. This system introduces two new concepts: (1) generating a watermark based on the receiver's location in a tree overlaying the network and (2) inserting the watermark in the content incrementally as it traverses an overlay network. We propose and evaluate several forms of this architecture and show how it improves scalability while increasing security.
TL;DR: In this article, the authors extend the evolutionary model of the Web graph by including a non-preferential component, and view the stochastic process in terms of an urn transfer model.
Abstract: Recently several authors have proposed stochastic models of the growth of the Web graph that give rise to power-law distributions. These models are based on the notion of preferential attachment leading to the “rich get richer” phenomenon. However, these models fail to explain several distributions arising from empirical results, due to the fact that the predicted exponent is not consistent with the data. To address this problem, we extend the evolutionary model of the Web graph by including a non-preferential component, and we view the stochastic process in terms of an urn transfer model. By making this extension, we can now explain a wider variety of empirically discovered power-law distributions provided the exponent is greater than two. These include: the distribution of incoming links, the distribution of outgoing links, the distribution of pages in a Web site and the distribution of visitors to a Web site. A by-product of our results is a formal proof of the convergence of the standard stochastic model (first proposed by Simon).
TL;DR: An integrated admission control scheme to both streaming flows and elastic flows is proposed and detailed packet level simulations of TCP and UDP connections show that the proposed algorithms work satisfactory in the range of admission thresholds predicted by the fluid model.
Abstract: We propose to apply an integrated admission control scheme to both streaming flows and elastic flows. It is assumed that streaming flow packets are served with priority in network queues so that admission control ensures minimal delay for audio and video applications while preserving the throughput of document transfers. An implicit measurement-based implementation is proposed where admissibility is based on an estimation of the bandwidth a new elastic flow would acquire. An analytical fluid flow model provides insight and guides the choice of admission thresholds. Detailed packet level simulations of TCP and UDP connections show that the proposed algorithms work satisfactorily in the range of admission thresholds predicted by the fluid model.