Abstract In this paper, we discuss scalable content‐oriented routing that enables storing, sharing, and searching data totally within the urban VANET. We introduce a scalable proactive content discovery scheme, hierarchical bloom‐filter routing (HBFR), to tackle mobility, large population, and rich content challenges of VANETs. Our simulation results show that HBFR achieves low latency and high content availability with relatively low overhead in practical VANET scenarios. In particular, HBFR improves the response time by up to 45% compared with the conventional Content Centric Networking (CCN) and reduces the traffic by up to 85% compared with timer‐based intelligent content search. HBFR suits the popular private data services the best and also achieves low response time comparable with that of flooding‐based content discovery when applying to popular public data services.Copyright © 2014 John Wiley & Sons, Ltd.

Recently, Information Centric Networking (ICN) has attracted much attention also for mobiles. Unlike host-based communication models, ICN promotes data names as the first-class citizen in the network. However, the current ICN name-based routing requires Interests be routed by name to the nearest replica, implying the Interests are flooded in VANET. This introduces large overhead and consequently degrades wireless network performance. In order to maintain the efficiency of ICN implementation in VANET, we propose an opportunistic geo-inspired content based routing method. Our method utilizes the last encounter information of each node to infer the locations of content holders. With this information, the Interests can be geo-routed instead of being flooded to reduce the congestion level of the entire network. The simulation results show that our proposed method reduces the scope of flooding to less than two hops and improves retrieval rate by 1.42 times over flooding-based methods.

In this paper, we discuss scalable content-oriented routing that enables storing, sharing and searching data totally within the VANET. We introduce a proactive content discovery scheme, Hierarchical Bloom-Filter Routing (HBFR), to tackle mobility, large population and rich content challenges of VANETs. HBFR is compared to the popular ICN reactive content discovery scheme in practical VANET scenarios. The results show that HBFR suits non-sharable data services, while reactive ICN inspired content discovery works well with popular sharable data. We suggest a hybrid approach that adaptively utilizes proactive and reactive schemes for time-sensitive data in ICN VANET.

TCP over Mobile Ad-hoc Networks (MANETs) is challenging due to frequent route breaks, high random errors, and DATA-ACK interference. Network coded multipath approaches have been shown in several previous studies to be an effective transmission paradigms in disruptive networks. However, most of the previous studies either have no adaptive redundancy control or rely on theoretical models that require knowledge at all relays of the entire network state. In this paper, we propose a network coded multipath scheme for conventional TCPCodeMP that adapts to frequent link changes in MANET and requires no explicit control messages. The scheme exploits multiple-path redundancy and maintains total transparency to transport layer protocols. The proposed coding scheme is based on three components: (1) random linear coding scheme with adjustable redundancy, (2) multipath routing, (3) ACK Piggy coding. Simulation results show that in a 3-hop static scenario, the proposed multipath scheme improves TCP flows goodput by 70% compared to our previous single-path scheme. In an extreme MANET scenario where two TCP sessions co-exists and nodes are moving as fast as 25 m/s with up to 40% packet error rate (an environment in which regular TCP collapses completely), CodeMP achieves at least 700Kbps aggregate TCP goodput, with a Jain's fairness index of 0.99.

In this paper, we propose a novel TCP congestion control algorithm, named TCP SPC, which improves upon the performance of TCP Reno in wireless networks. TCP SPC exploits statistic process control (SPC) methods that have been used effectively in a variety of monitoring and control applications other than TCP. A TCP SPC sender uses RTT statistics to judge the network status, whereby the congestion window can be adjusted more intelligently. Comparing with conventional TCP, TCP SPC is more robust to sporadic losses due to wireless channel errors. Such errors often cause conventional TCP to over react, leading to unnecessary congestion window reduction. TCP SPC controls the congestion window in a way that is completely transparent to intermediate nodes and the destination. Therefore, it is compatible with any TCP implementation at the destinations. In this paper, we introduce TCP SPC and its implementation in a simulation environment. The simulation results show that TCP SPC can significantly improve throughput and fairness, especially in wireless networks with high-error links.

In this paper, we present the design, implementation and evaluation of a new TCP protocol, TCP-AW (TCP adaptive Westwood). This study was motivated by the intent to address simultaneously several challenging network scenarios, including high bandwidth efficiency in long and fat pipes, RTT fairness, and friendliness to legacy protocol, in a single protocol. TCP-AW leverages the key features of TCP Westwood and TCP adaptive Reno, namely, eligible rate estimation and delay- based adaptive AIMD parameter tuning, respectively. Extensive simulation and measurement results show that TCP AW yields good utilization of available bandwidth and achieves better RTT fairness. As for coexistence with TCP-NewReno, our major safety objective, was that new protocol compares more favorably than other promising protocols such as Hamilton-TCP, CUBIC and Compound-TCP. In contrast to other proposals, TCP-AW has no notions of small and large bandwidth delay product, instead, it scale seamlessly from current Internet paths to faster long distance paths.

As network topologies have grown in size and complexity, it is becoming a daunting task for network administrators to keep track the capacity dimensioning of newly installed web-servers within a single or multiple providers. In fact, monitor capacity dimensioning is not a trivial activity since network state changes rather frequently, in particular, in academic environments. In this paper, we describe estimation algorithms and the software architecture of an efficient network management suite to automatically mine path capacity and minimum delays from a venture point to a set of observed web servers. The principle of the suite is based on packet dispersion techniques and repetitive non-intrusive measurements. We provide analytical insights, simulation results and some real case studies where we argument about the correctness, accuracy and usefulness of the suite in the context of management and operation of complex IP based networks.

The paper describes a measurement campaign recently carried out by University of Bologna (UoB), National Inter-University Consortium for Telecommunications-(CNIT) and University of California Los Angeles (UCLA), on the CNIT GEO Skyplex platform. The aim of the experiments is the performance assessment of a wide range of TCP enhancements on network environments that include a real GEO satellite link. Measurements were carried out by means of the integrated UoB-CNIT testbed, fully controlled by remote through a Web interface. Analysis of live experiments data confirm the challenges posed by GEO sat channels, and show a negative influence of the Skyplex BoD technique on TCP start-up performance. Among the TCP enhancements compared in the paper, best results are provided by TCP Hybla and TCP Westwood, with an advantage of the former in heterogeneous environments characterized by a high level of RTT unfairness.

This paper studies the TCP performance with delayed ack in wireless networks (including ad hoc and WLANs) which use IEEE 802.11 MAC protocol as the underlying medium access control. Our analysis and simulations show that TCP throughput does not always benefit from an unrestricted delay policy. In fact, for a given topology and flow pattern, there exists an optimal delay window size at the receiver that produces best TCP throughput. If the window is set too small, the receiver generates too many acks and causes channel contention; on the other hand, if set the window too high, the bursty transmission at the sender triggered by large cumulative acks will induce interference and packet losses, thus degrading the throughout. In wireless networks, packet losses are also related to the length of TCP path; when traveling through a longer path, a packet is more likely to suffer interference. Therefore, path length is an important factor to consider when choosing appropriate delay window sizes. In this paper, we first propose an adaptive delayed ack mechanism which is suitable for ad hoc networks, then we propose a more general adaptive delayed ack scheme for ad hoc and hybrid networks. The simulated results show that our schemes can effectively improve TCP throughput by up to 30% in static networks, and provide more significant gain in mobile networks. The proposed schemes are simple and easy to deploy.

In this article we study a smooth and efficient transport protocol for real-time video over wireless networks. The proposed scheme, named the video transport protocol (VTP), has a new and unique end-to-end rate control mechanism that aims to avoid drastic rate fluctuations while maintaining friendliness to legacy protocols. VTP is also equipped with an achieved rate estimation scheme and a loss discrimination algorithm, both end-to-end, to cope with random errors in wireless networks efficiently. We show by analysis that VTP preserves most of the convergence properties of AIMD and converges to its fair share fast. VTP is compared to two recent TCP friendly rate control (TFRC) extensions, namely TFRC Wireless and MULTFRC, in wired-cum-wireless scenarios in Ns-2. Results show that VTP excels in all tested scenarios in terms of smoothness, fairness, and opportunistic friendliness. VTP is also implemented to work with a video camera and an H.263 video codec as part of our hybrid testbed, where its good performance as a transport layer protocol is confirmed by measurement results.

TCP suffers from known problems in constrained environments such as satellite and wireless networks. And the problems grow more severe as networks grow increasingly integrated and diverse, where local optimization fail to suffice. One established method for dealing with these problems involves subdividing, or splitting the end-to-end TCP connection into a number of sub-connections. In this paper, we take an indepth look at the buffer requirements for "split connections". After briefly introducing the mechanics of a split connection, we proceed to identify a simple analytic model describing the behavior of the split connection and develop a number of design "rules of thumb" based on our analysis. We compare the results of simulations with the model and measure the efficacy of our design constraints, finding them to improve both the stability and performance of splitting. Finally, we discover that when used properly, oversubscribing, i.e., advertising non-existent space, may greatly reduce the required per-connection buffer-space in some situations.

In this paper, we propose a new version of TCP to improve (1) efficiency in wired-wireless combined networks with nonnegligible random packet losses, and also (2) friendliness to existing protocols, such as TCP-Reno. TCP-Westwood (TCPW) was proposed to improve efficiency in such networks; however, it is shown to be unfriendly to existing protocols under certain RTT and/or router buffer capacities. Since friendliness to existing protocols is one of the most important issues in a real network environment where different protocols coexist, we propose TCPW-BBE (TCPW with buffer and bandwidth estimation) to ensure the friendliness even under varying effective buffer capacities. Based on buffer capacity estimation mechanism, TCPW-BBE reacts more appropriately to a packet loss event, whether the loss is due to congestion or link errors. Simulation results show that TCPW-BBE maintains friendliness to TCP-Reno in networks for a broad range of buffer capacities, RTT, with/without RED routers, yet retaining the efficiency of the original TCPW.

Traditional IP multicast faces a serious state scalability problem when there are a large number of groups in the network. Recently, a novel approach called aggregated multicast was proposed [6], in which multiple groups share one delivery tree. A key problem in aggregated multicast is group-tree matching (i.e., assigning groups to trees). In this paper, we formally study the dynamic version of the group-tree matching problem. We propose a generic dynamic on-line algorithm (GDOA) and provide an approach to determine the upper bound on its performance. We quantitatively compare the performance of GDOA and other existing on-line heuristics. Extensive simulations demonstrate that GDOA is a very practical solution with promising performance and reasonable computation requirement.

Introducing node mobility into the network also introduces new anonymity threats. Nevertheless, this important change of the concept of anonymity has not been studied in state-of-art network security research. This paper presents the needed study. Then we show that anonymous routing in mobile networks has great impact on routing performance. We calls for the attention to devise new and efficient anonymous routing schemes for mobile ad hoc networks.

Real-time streaming over wireless links is challenging. The streaming protocol must be efficient and robust to random wireless loss, fair to itself, and friendly to legacy TCP. Various solutions have been proposed in the literature, among which the video transport protocol (VTP), TFRC wireless, and MULTFRC are end-to-end representatives. In this paper we provide an in-depth comparison on the performance of VTP, TFRC wireless, and MULTFRC in various wireless scenarios. The results show that VTP and TFRC wireless both perform well and deliver similar performance, with VTP exhibiting greater efficiency and smoothness in presence of heavy errors. In contrast, MULTFRC performs less satisfactorily, as it experiences large rate fluctuation and slow convergence caused by the frequent changes in the number of simultaneous connections.

Vertical handoffs between different wireless technologies usually lead to dramatic changes in the link capacity. A successful QoS solution for vertical handoffs must be able to fast track the capacity changes and agilely adapt the delivery rates and qualities of the ongoing applications. Though traditional AIMD-based source adaptation schemes (as found in TCP, TFRC, etc.) have been well designed for mild, gradual rate adjustments required by load fluctuations and network congestion, their response time is inadequate when the rate must be adjusted to the drastic network capacity changes that are typical in vertical handoff scenarios. To expedite the response to such changes, we propose in this paper two adaptive algorithms, named the fast rate adaptation (FRA) and early rate reduction (ERR), that are launched when the handoff is from low to high capacity (LOW-to-HIGH) or from high to low capacity (HIGH-to-LOW), respectively. We also propose two vertical handoff notification mechanisms to work with FRA and/or ERR, i.e. the implicit handoff notification (IHN) and explicit handoff notification (EHN). We show by simulation that our proposed schemes are able to provide better QoS support than the traditional AIMD based schemes during vertical handoffs.

Transmission control protocol Westwood (TCPW) has been shown to provide significant performance improvement over high-speed heterogeneous networks. The key idea of TCPW is to use eligible rate estimation (ERE) methods to intelligently set the congestion window (cwnd) and slow-start threshold (ssthresh) after a packet loss. ERE is defined as the efficient transmission rate eligible for a sender to achieve high utilization and be friendly to other TCP variants. This work presents TCP Westwood with agile probing (TCPW-A), a sender-side only enhancement of TCPW, that deals well with highly dynamic bandwidth, large propagation time/bandwidth, and random loss in the current and future heterogeneous Internet. TCPW-A achieves this goal by adding the following two mechanisms to TCPW. 1) When a connection initially begins or restarts after a timeout, instead of exponentially expanding cwnd to an arbitrary preset sthresh and then going into linear increase, TCPW-A uses agile probing, a mechanism that repeatedly resets ssthresh based on ERE and forces cwnd into an exponential climb each time. The result is fast convergence to a more appropriate ssthresh value. 2) In congestion avoidance, TCPW-A invokes agile probing upon detection of persistent extra bandwidth via a scheme we call persistent noncongestion detection (PNCD). While in congestion avoidance, agile probing is actually invoked under the following conditions: a) a large amount of bandwidth that suddenly becomes available due to change in network conditions; b) random loss during slow-start that causes the connection to prematurely exit the slow-start phase. Experimental results, both in ns-2 simulation and lab measurements using actual protocols implementation, show that TCPW-A can significantly improve link utilization over a wide range of bandwidth, propagation delay, and dynamic network loading.

TCP throughput limitations over wireless links have received considerable attention in the last few years. One of the problems is that TCP congestion control interprets packet losses as an indication of congestion, whereas in wireless links, losses could be due to transient link quality degradations. In this paper, we propose and study a link layer solution and evaluate its effects on TCP in the context of Bluetooth. We enhance the Bluetooth link layer to make use of channel state information and accordingly adapt the Bluetooth packet type to enhance TCP throughput We propose a simple analytical method to determine the optimal packet type for a given channel state by adding FEC support or changing packet size. Since wireless interfaces, such as 802.11 or Bluetooth, can provide information regarding the channel state using relevant APIs, this simple enhancement can easily be added to the link layer. We implemented this functionality in the Bluetooth link layer. Our simulation experiments show that the proposed adaptive packet type solution significantly improves TCP throughput. The throughput enhancement increases with the error rate. For high error rates close to 0.1%, the link layer enhanced with the adaptive scheme is able to maintain good TCP throughput, whereas throughput is almost zero when the adaptive scheme is not used.

TCP westwood (TCPW) has been shown to provide significant performance improvement over high-speed heterogeneous networks. The key idea of TCPW is to use eligible rate estimation (ERE) methods, to set the congestion window (cwnd) and slow start threshold (ssthresh) after a packet loss. ERE is defined as the transmission rate a sender ought to use to achieve high utilization and remain friendly to other TCP variants. This paper presents TCP westwood with agile probing (TCPW-A), a sender-side only enhancement of TCPW. TCPW-A perform well when faced with highly dynamic bandwidth, large propagation time/bandwidth, and random loss in the current and future heterogeneous Internet. TCPW-A achieves its goal by incorporating the following, two mechanisms: 1) when a connection initially begins or re-starts after a timeout, instead of exponentially expanding cwnd to an arbitrary preset ssthresh and then going into linear increase. TCPW-A uses agile probing, a mechanism that repeatedly resets ssthresh based on ERE and forces cwnd into an exponential climb each time. The result is fast convergence to a more appropriate ssthresh value. 2) In congestion avoidance, TCPW-A invokes agile probing upon indication of unused extra bandwidth via a scheme we call load gauge (LG). Experimental results, both in Ns-2, and in measurements using FreeBSD implementation, show that TCPW-A can significantly improve link utilization over a wide range of bandwidth, propagation delay and dynamic network loading.

.4brtroct- Nest generation nehvorlis with large bandwidth and long drlay pose a major challenge to TCP performance, especially during the startup period. In this paper we evaluate the performance of TCP RenaiNcwrcno. Vegns and Hoe's modification in large bandwidth delay nrhvork. We propose n modified Slow-start mechanism, rnllcd Adaptive Start (Astart), to improve the startup performance in such networks. When a connection initially begins or re-starts after a coarse timrout,- Astart ndaptivcly and repentedly resets the Slow-start Threshold (suthreslr) based on an cligihlr sending I'iitr estimation mrchanisrn proposrd in TCP Westwond. By iidapting to network conditions during the startup phase. it wndw is able to grow the congestion window (ocnh fast without incurring risk of huNw owrflow and multiple Iossrs. Simulation rxpcrirncnts show that Astart can significantly improve the link utiliiation under various bandwidth, buNrr sur;~nd round-trip propagation timrs. The mrthud avoids both under-utiliriition dur to prrmature Slowstart termination, as wcll ils multiple I~XII~S due to initinlly setting srrlire.sli too high, or. increaing nmd tin) fiat. Experiments also show that Astart uchiews good fttirnrss rind fricndlincss toward TCP NewReno. Lab measuremrnts using a FrreBSD Astart implementation are also reported in this paper, providing futrhcr evidence of the gains nchirvahlr via Astart. Kqw-orr%r-congesrionn control;.sIow-.start; rate estimution. large bundwidth ddq nehvorks I.

Wireless communication is inherently vulnerable to errors from the dynamic wireless environment. Link layer packets discarded due to these errors impose a serious limitation on the maximum achievable throughput in the wireless channel. To enhance the overall throughput of wireless communication, it is necessary to have a link layer transmission scheme that is robust to the errors intrinsic to the wireless channel. To this end, we present interleaved-forward error correction (I-FEC), a clever link layer coding scheme that protects link layer data against random and busty errors. We examine the level of data protection provided by I-FEC against other popular schemes. We also simulate I-FEC in Bluetooth, and compare the TCP throughput result with Bluetooth's integrated FEC coding feature. We show that I-FEC consistently and significantly outperforms other link layer coding schemes by providing an impressive amount of protection against heavy channel burst errors.

CapProbe is an inexpensive and accurate means to estimate capacity. CapProbe combines both dispersion and end-to-end delay to estimate the capacity of the narrowest link on a path. We evaluate in this paper the accuracy of CapProbe estimation, and its dependence on end systems speed, packet sizes, narrow link speeds, and other system parameters. We test kernel and user level implementations of CapProbe and find the kernel implementation to be much more accurate. We also evaluate through experiments the effect of probing packet size on the accuracy of CapProbe estimation. Finally, we explore the idea of a "passive CapProbe" within the context of a TCP flow. Passive here means that the dispersion and delay observed for the TCP flow data and ACK packets, without introducing any additional probing packets. We test active and passive versions of CapProbe with TCP. The active version is found to produce more accurate capacity estimates than the passive version.

An end-to-end "foreground/background" priority scheme is useful for end hosts to utilize the residual capacity left unused by high-priority foreground applications. Several end-to-end prioritization schemes, such as TCP-LP (Low Priority) and TCP-Nice, have been proposed, however, the residual capacity cannot be fully utilized by these schemes. We propose TCP Westwood Low Priority (TCPW-LP), a scheme that maximizes the utilization of residual capacity without intrusion on coexisting foreground flows. TCPW-LP employs an "Early Window Reduction" mechanism to reduce its congestion window as a reaction to incipient congestion. To achieve high efficiency, the reaction is based on the estimation whether the congestion is caused by the foreground traffic or not. Simulation results show that TCPW-LP appropriately defers to foreground flows. Further, under a wide range of buffer capacity and link error losses, TCPW-LP better utilizes the residual capacity than other proposed priority schemes or even TCP Reno.

Low-rate TCP-targeted denial-of-service (DoS) attacks aim at the fact that most operating systems in use today have a common base TCP retransmission timeout (RTO) of 1 sec. An attacker injects periodic bursts of packets to fill the bottleneck queue and forces TCP connections to timeout with near-zero throughput. This work proposes randomization on TCP RTO as defense against such attacks. With RTO randomization, an attacker cannot predict the next TCP timeout and consequently cannot inject the burst at the exact instant. An analytic performance model on the throughput of randomized TCP is developed and validated. Simulation results show that randomization can effectively mitigate the impact of such DoS attacks while maintaining fairness and friendliness to other connections.

Video streaming has become a popular form of transferring video over the Internet. With the emergence of mobile computing needs, a successful video streaming solution demands 1) uninterrupted services even with the presence of mobility and 2) adaptive video delivery according to current link properties. We study the need and evaluate the performance of adaptive video streaming in vertical handoff scenarios. We use universal seamless handoff architecture (USHA) to create a seamless handoff environment, and use the video transfer protocol (VTP) to adapt video streaming rates according to "eligible rate estimates". Using testbed measurements experiments, we verify the importance of service adaptation, as well as show the improvement of user-perceived video quality, via adapting video streaming in the vertical handoffs.

We present a new capacity estimation technique, called CapProbe. CapProbe combines delay as well as dispersion measurements of packet pairs to filter out samples distorted by cross-traffic. CapProbe algorithms include convergence tests and convergence speed-up techniques by varying probing parameters. Our study of CapProbe includes a probability analysis to determine the time it takes CapProbe to converge on the average. Through simulations and measurements, we found CapProbe to be quick and accurate across a wide range of traffic scenarios. We also compared CapProbe with two previous well-known techniques, pathchar and pathrate. We found CapProbe to be much more accurate than pathchar and similar in accuracy to pathrate, while providing faster estimation than both. Another advantage of CapProbe is its lower computation cost, since no statistical post processing of probing data is required.

The problem of estimating the capacity of an Internet path is one of fundamental importance. Due to the multitude of potential applications, a large number of solutions have been proposed and evaluated. The proposed solutions so far have been successful in partially addressing the problem, but have suffered from being slow, obtrusive or inaccurate. In this work, we evaluate CapProbe, a low-cost and accurate end-to-end capacity estimation scheme that relies on packet dispersion techniques as well as end-to-end delays. The key observation that enabled the development of CapProbe is that both compression and expansion of packet pair dispersion are the result of queuing due to cross-traffic. By filtering out queuing effects from packet pair samples, CapProbe is able to estimate capacity accurately in most environments, with minimal processing and probing traffic overhead. In fact, the storage and processing requirements of CapProbe are orders of magnitude smaller than most of the previously proposed schemes. We tested CapProbe through simulation, Internet, Internet2 and wireless experiments. We found that CapProbe error percentage in capacity estimation was within 10% in almost all cases, and within 5% in most cases.

Several satellite systems currently in operation or under development claim to support broadband Internet applications. In these scenarios, transmission control protocol (TCP) plays a critical role. Unfortunately, when used with satellite links, TCP suffers from a number of well-known performance problems, especially for higher data rates and high altitude satellites with longer delays. In response to these difficulties, the satellite and Internet research communities have developed a large gamut of solutions ranging from architectural modifications to changes in the TCP protocol. Among these, one approach requiring minimal modifications involves splitting the TCP connection in two or more segments with one segment connecting terrestrial nodes across the satellite network. In this paper, we consider an evolution of this idea: placing a TCP proxy on board the satellite that further subdivides the end-to-end connection into separate TCP connections between ground and space. We focus upon the efficient use of buffer resources on board the satellite, while at the same time enhancing TCP performance. We evaluate two TCP protocol versions, TCP NewReno and TCP Westwood. We consider various geosynchronous earth orbit satellite scenarios, with and without the split proxy, and with different channel error conditions (random errors, shadowing, etc.). Using simulation, we show that an on-board proxy provides a number of distinct advantages and can enhance throughput up to threefold for both TCP New Reno and TCP Westwood, in some scenarios, with relatively modest on-board buffering requirements. The main contributions of this paper are: the on-board split proxy concept, the buffer management strategy, the use of a realistic "urban shadowing" model in the evaluation, and the extensive comparison of the recently announced TCP Westwood with the traditional TCP New Reno.

The paper concerns TCP Westwood, a recently-developed modification of TCP, in combination with RED queue management. We develop a fluid-flow model of the protocol, and use it to study both equilibrium and dynamic features. On the equilibrium side, we identify the scaling of the congestion window with loss-probability, and compare it to TCP NewReno. We also use the model to find the boundary of stability, beyond which we see large oscillations; we find that the stable region of TCP Westwood is enhanced with respect to TCP NewReno. Furthermore we show preliminary evidence that oscillations, when they occur, have a limited impact on network throughput.

Wireless links are error-prone. In next generation wireless networks, link capacities will still grow. It is known that in such configurations the performance of current TCP variants degrades severely. In this paper we propose a new transmission strategy for TCP in high error situations- bulk repeat (BR). We apply BR to TCP westwood (TCPW). BR has only three sender-side modifications to TCP, i.e. bulk retransmission, fixed retransmission timeout and intelligent window adjustment. BR permits efficient recovery from multiple losses in the same congestion window. To discriminate error from congestion loss, a loss discrimination algorithm (LDA), based on spike and rate gap threshold, is used. Simulation results in wireless network scenarios show that TCPW BR improves throughput performance up to an order of magnitude over TCPW and newreno when the error rate is high (>5%). The results also show that TCPW BR has satisfactory fairness and friendliness to TCP newreno.

Bluetooth "scatternets" are targeting wider geographical area applications in factories, warehouses, shopping malls and various sensor network applications. Though some earlier work has looked at scatternet formation and scheduling issues, less attention has been given to optimizing scatternet topologies. We consider in this paper topological design of scatternets, taking into consideration application traffic requirements. We study appropriate topologies, and size the network in terms of piconets. We develop a scatternet queuing model and use it to compare the delay-throughput characteristics of various topologies. We find that the best topology is application independent. The analytical model is also used to determine the optimal point to operate a scatternet, i.e., the traffic load that saturates the network. We validate all out analytical results by simulations.

TCP Westwood (TCPW) is a recently proposed sender side modification of TCP congestion control. TCPW relies an bandwidth share estimation techniques to enhance congestion control over high speed and/or wireless networks. The bandwidth share estimation methods turn out to be critical to guarantee both throughput improvement and friendliness towards widely used TCP protocols such as NewReno. In this paper we propose a new bandwidth share estimation technique, called "adaptive bandwidth share estimation", or ABSE. ABSE adapts to changing network congestion level, round trip times, and other relevant network conditions, as well as to the rate at which such changes occur. We compare the throughput gain and friendliness of ABSE with that of NewReno and previous estimation methods used for TCPW. We test the new technique using different simulation scenarios, including RED, to show the benefit of our proposed ABSE estimation method.

TCP performance can be significantly affected when the buffer capacity at routers is small. This is possible when either many flows share the network or the bandwidth-delay product is large (e.g. satellite links). The behavior of various versions of TCP with respect to buffer capacity issues has not been studied in much detail. We investigate the behavior and performance of different TCP variants under small buffer capacity conditions. We recognize TCP pacing as a potential solution. However, instead of using TCP's sending rate as the dictating metric, we make use of the bandwidth-share estimate (BSE), maintained by TCP Westwood, to set the pacing interval. We call this newly proposed protocol paced-Westwood. We also show the need to scale BSE further to mitigate the effects of positive feedback in BSE. For this, we propose a further enhancement that we call /spl alpha/-paced Westwood that uses a scaling parameter /spl alpha/ to enforce convergence of BSE and the pacing interval. The proposed /spl alpha/-paced Westwood uses its BSE to space the packet bursts during the slow-start phase, resulting in a superior throughput in the troublesome low buffer capacity cases. With the help of simulations, we show that our enhanced TCP Westwood outperforms both unpaced as well as paced TCP NewReno under low buffer capacity networks.

The rapid advancement in wireless communication technology has spurred significant interest in the design and development of enhanced TCP protocols. Among them, TCP Westwood (TCPW) is a sender side only modification to improve TCP performance particularly over heterogeneous networks. The key idea of TCPW is to use rate estimation methods to set the congestion window and slow start threshold after a packet loss. When packet losses are not only due to buffer overflow, but random errors as well, TCPW estimation methods have been shown to provide significant performance improvement. The earliest estimation method, called bandwidth estimation (BE), however, may result in over-estimation under certain circumstances, and thus may be unfriendly toward non-TCPW traffic. TCPW CRB (combined rate and bandwidth estimation) and TCPW ABSE (adaptive bandwidth share estimation), have been later introduced to address this concern. The schemes provide better control of the tradeoffs among efficiency, friendliness, and implementation complexity. CRB may slightly sacrifice the efficiency gain to ensure friendliness. ABSE adaptivity mechanisms are more sophisticated and provide both better efficiency and friendliness.We summarize ABSE, which adapts to congestion level, as well as round drip time, and other network dynamics, thus providing enhanced and robust performance under various network conditions. Extensive experiments show that TCPW ABSE is able to enhance TCP performance significantly over "large leaky pipes", while maintaining friendliness toward TCP NewReno. We show that TCPW ABSE is robust to packet and ACK compression due to cross traffic on forward and backward paths. We also show that ABSE is robust to buffer size variations, which are inevitable in today's networks.

We propose a refinement of TCP Westwood which allows management of the efficiency/friendliness-to-NewReno tradeoff. We show that the refined TCP Westwood is able to achieve higher efficiency yet at the same time maintain friendliness. TCP Westwood (TCPW) implements a novel window congestion control algorithm based on available bandwidth estimation. The performance of TCPW has been promising, exceeding that of TCP NewReno in high speed and/or wired/wireless networks. However, under certain circumstances, TCP NewReno may experience some performance degradation because TCPW possesses more information and thus can take better advantage of available bandwidth. We propose combining the original TCPW sampling strategy that produces available bandwidth estimates (BE), with a new strategy that produces rate estimates (RE). Our studies show that RE works best when packet losses are mostly due to congestion. If on the other hand, the packet losses are mostly due to link errors, BE gives better performance. To achieve the "best of all worlds", we introduce a method we call combined rate and bandwidth estimation (CRB). A connection first infers the predominant cause of packet losses, and then uses the most appropriate estimation method. We also introduce the efficiency/friendliness tradeoff graph that provides better tradeoff visualization. In our experiments, we found that CRB provides a better compromise between efficiency and friendliness, and the means to manage such a tradeoff.

We study the performance of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end rate estimation in a way that is totally transparent to routers and to the destination. Thus, it is compatible with any network and TCP implementation. The key innovative idea is to continuously estimate, at the TCP sender, the packet rate of the connection by monitoring the ACK reception rate. The estimated connection rate is then used to compute congestion window and slow start threshold settings after a congestion episode. Resetting the window to match available bandwidth makes TCPW more robust to sporadic losses due to wireless channel problems. These often cause conventional TCP to overreact, leading to unnecessary window reduction. Experimental studies of TCPW show significant improvements in throughput performance over Reno and SACK, particularly in mixed wired/wireless networks over high-speed links. The contributions of this paper include a model for fair and friendly sharing of the bottleneck link and a Markov Chain performance model in presence of link errors/loss. TCPW performance is compared to that of TCP Reno, and analytic results are validated against simulation results. Internet and laboratory measurements using a Linux TCPW implementation are also reported, providing further evidence of the gains achievable via TCPW.

We present a performance model of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end connection bandwidth share estimation, obtained by monitoring the ACK reception rate. An analytic model using Markov Chain techniques is developed in this paper, and then used to assess the performance improvements obtained using TCPW. The model takes into account the estimation and filtering method used in TCPW, as well as the following system parameters, bottleneck link bandwidth, buffer space at the bottleneck router, end-to-end propagation time, and error rate. The model reveals substantial TCPW gains over Reno whenever losses due to link or other errors are taken into consideration. The analytic model accuracy is confirmed by comparing to simulation results.

TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links, since TCP Westwood relies on end-to-end bandwidth estimation to discriminate the cause of packet loss (congestion or wireless channel effect) which is a major problem in TCP Reno. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP “extensions” is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, it fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP source the rate of the connection by monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno, which “blindly” halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the O/H of a specialized link layer protocol.