Accelerometer is the predominant sensor used for low-power context detection on smartphones. Although low-power, accelerometer is orientation and position-dependent, requires a high sampling rate, and subsequently complex processing and training to achieve good accuracy. We present an alternative approach for context detection using only the smartphone's barometer, a relatively new sensor now present in an increasing number of devices. The barometer is independent of phone position and orientation. Using a low sampling rate of 1 Hz, and simple processing based on intuitive logic, we demonstrate that it is possible to use the barometer for detecting the basic user activities of IDLE, WALKING, and VEHICLE at extremely low-power. We evaluate our approach using 47 hours of real-world transportation traces from 3 countries and 13 individuals, as well as more than 900 km of elevation data pulled from Google Maps from 5 cities, comparing power and accuracy to Google's accelerometer-based Activity Recognition algorithm, and to Future Urban Mobility Survey's (FMS) GPS-accelerometer server-based application. Our barometer-based approach uses 32 mW lower power compared to Google, and has comparable accuracy to both Google and FMS. This is the first paper that uses only the barometer for context detection.

As the current generation of mobile smartphones become more powerful, they are being used to perform more resource intensive tasks making battery lifetime a major bottle-neck. In this paper, we present a technique called dynamic AoV lookahead for reducing wireless interface power consumption upto 50% while playing a popular, yet resource intensive, mobile multiplayer games.

Due to their thin size, vivid colors, high contrast and power efficiency, OLED (Organic Light-Emitting Diode) display and its variants such as AMOLED (Active Matrix OLED) displays are increasingly replacing traditional LCD (Liquid Crystal Display) screens in smart phones. However, the power efficiency of OLED screens greatly depends on the luminance and colors of the displayed contents on the screen. Web browsing is one of the most widely used applications in mobile devices. In this paper, we present our cloud service, which intelligently re-paints the web pages in real-time with power efficient colors and HVS (Human Visual System) based tone mapping techniques, without adversely affecting the identity (brand color) of the web pages as well as the user's browsing experience. El-pincel helps to save up to 60% of OLED energy with color combinations that ensure good legibility and pleasing affective response to human eyes.

With mobile devices becoming ubiquitous, collaborative applications have become increasingly pervasive. In these applications, there is a strong need to obtain a count of the number of mobile devices present in an area, as it closely approximates the size of the crowd. Ideally, a crowd counting solution should be easy to deploy, scalable, energy efficient, be minimally intrusive to the user and reasonably accurate. Existing solutions using data communication or RFID do not meet these criteria. In this paper, we propose a crowd counting solution based on audio tones, leveraging the microphones and speaker phones that are commonly available on most phones, tackling all the above criteria. We have implemented our solution on 25 Android phones and run several experiments at a bus stop, aboard a bus, within a cafeteria and a classroom. Experimental evaluations show that we are able to achieve up to 90% accuracy and consume 81% less energy than the WiFi interface in idle mode.

In this paper, we present a dual-radio framework for implementing MAC protocols in wireless sensor networks. The framework is based on the observation that MAC operations can be categorized into time-dependent and bandwidth-dependent. Unlike existing dual-radio systems, we do not propose a new MAC protocol. Instead, we show how a given MAC protocol can be re-implemented using a dual-radio framework resulting in substantial energy savings. Our approach is generic. Different categories of MAC protocols can be re-implemented using dual radios, including synchronous (e.g., SMAC), asynchronous (e.g., BMAC) and hybrid (e.g., SCP-MAC). The proposed framework is easy-to-implement. We have been able to re-implement SMAC, BMAC and SCP-MAC in TinyOS to dual-radio implementations using a combination of mica2 and micaZ motes. Extensive evaluation shows that a reduction of up to 5 times in energy consumption can be attained.

Due to their thin size, vivid colors, high contrast and power efficiency, OLED and its variants such as AMOLED screens are increasingly replacing traditional LCD screens in mobile phones (eg. Google Nexus One, Samsung Galaxy S phones). However, the power efficiency of OLED screens greatly depends on the luminance and colors of the displayed contents on the screen. Web browsing is one of the most widely used applications in mobile devices. We demonstrate our cloud service, which intelligently re-paints the web pages in real-time with power efficient colors and tone mapping techniques without adversely affecting the user experience in reading the page and the identity of the page. Transformation of images, flash contents and videos in client itself will incur significant computational and energy overhead. El-pincel is designed as a cloud service to avoid any additional overhead to the mobile device.

In this paper, we show how tone mapping techniques can be used to dynamically increase the image brightness, thus allowing the LCD backlight levels to be reduced. This saves significant power as the majority of the LCD's display power is consumed by its backlight. The Gamma function (or equivalent) can be efficiently implemented in smartphones with minimal resource cost. We describe how we overcame the Gamma function's non-linear nature by using adaptive thresholds to apply different Gamma values to images with differing brightness levels. These adaptive thresholds allow us to save significant amounts of power while preserving the image quality. We implemented our solution on a laptop and two Android smartphones. Finally, we present measured analytical results for two different games (Quake III and Planeshift), and user study results (using Quake III and 60 participants) that shows that we can save up to 68% of the display power without significantly affecting the perceived gameplay quality.

The current generation of mobile smartphones are not just devices for voice communication. Instead, they are frequently used as mobile PC replacements that are used to edit documents, browse the web, check email, and play games. However, this functionality comes at the cost of battery lifetimes. Indeed, to maintain the slim form factor required for these phones (which impacts the amount of battery that can be put into the phone), it is quite common for the battery lifetimes of smartphones to be significantly shorter compared to previous generation of "dumber" phones.

As bandwidth in the Internet continues to grow, there will be more and more long fat network pipes with abundant residual bandwidth. At the same time, there is also a gradual and steady increase in the deployment of Internet endpoints equipped with different variants of high speed TCP. In this work, we first illustrate drawbacks associated with two widely deployed high speed TCP variants, namely: cubic TCP and compound TCP. We show that even with common and reasonable settings, problems can arise. Next, we present synchronized TCP (Sync-TCP), a new delay-based high speed congestion control (HSCC) algorithm. The approach taken by Sync-TCP is novel in the following ways. First, Sync-TCP exploits synchronization. The key insight of Sync-TCP is that if competing flows could detect the same congestion signal through queue delay, these flows can coordinate their congestion control behaviors. Second, using only the basic mechanism, Sync-TCP will yield to legacy TCP when congestion is detected. Hence, Sync-TCP is designed to not hurt applications using legacy TCP or interactive applications. We performed extensive simulation and some testbed evaluations to show that Sync-TCP achieves its design goals and it performs better than existing HSCC approaches including Fast TCP, Compound TCP and Cubic TCP, especially in the trade-off between throughput and friendliness.

Asymmetric links commonly exist in low power wireless sensor networks. However, it is difficult to discover and exploit them efficiently. In this work, we propose DEAL, a link management scheme to Discover and Exploit Asymmetric Links efficiently in dense wireless sensor networks. Equipped with a novel feedback mechanism, DEAL dynamically adapts its link maintenance mechanism based on the estimated link quality, and manages the (small) neighbor table so as to retain the most useful information. We implement DEAL in TinyOS and evaluate its performance using both TOSSIM and testbed. The simulation results show that more than 80% of asymmetric links can be discovered and maintained with minimum overhead. Using a collection tree application and ETX as the routing metric, the average path ETX can be reduced by up to 20%. Testbed evaluation also shows that DEAL improves the network routing performance by identifying useful asymmetric links.

Connectivity-based routing protocols provide an attractive option for point to point communication in wireless networks due to its potential for low routing overhead. However, when the entire hop-count vector is used to address each node, the communication and storage overhead in the packets are often so high that it is not feasible to implement existing connectivity- based routing protocols infeasible on resource-constrained sensor networks. In this paper, we apply the technique of dimension reduction, in particular principle component analysis (PCA), to the hop-count vectors. Compared to the original hop-count vector, the embedding coordinates preserve the network geometry with much lower overhead, making their use much more practical on current sensor platform. Simulation results show that the coordinates computed by PCA can achieve higher packet delivery ratio, lower path stretch and shorter flooding range in local minimum cases. We have also implemented the PCA algorithm on MICAz motes and conducted experiments in a testbed containing 48 nodes deployed on two floors of an office building. With the use of 9 landmark nodes and only 3 dominant components, the PCA coordinates can achieve 95% of the delivery ratio obtained using full hop-count vector and maintain an low path stretch of 1.12.

Connectivity-based routing protocols use the hop count vector to a group of anchors for packet forwarding. Due to the discrete nature of hop count based coordinates, without an effective recovery mechanism, these protocols will frequently encounter failures at network local minimum sites. In this paper, we propose a new connectivity-based routing protocol named Hop Distance Routing(HDR) with an efficient distance metric called hop distance. To ensure packet delivery, HDR complements greedy forwarding with a tree based recovery method, which allows the packet to traverse the branches and escape from local minimum locations. By labeling each tree node with an angle range, HDR can identify the subtree where the destination resides and forward the packet towards it until greedy forwarding can be resumed. Compared to other connectivity-based routing protocols such as NoGeo, BVR, LCR and VPCR, performance results show that the HDR protocol provides the highest packet delivery ratio and the lowest path stretch with the minimal communication overhead for each packet delivery on the node density range from 1.76 to 17.67.

In recent years, many high-speed congestion control (HSCC) algorithms have been proposed for utilizing network pipes with huge bandwidth-delay product (BDP), and some of them have also been implemented in popular operating systems. Considering the extremely long round trip propagation delay (RTPD) of satellite network, it is very likely that these algorithms are triggered when TCP flows pass through satellite network. But the existing algorithms are normally evaluated on network pipes with high bandwidth and moderate RTPD (< 400 ms). This paper is an attempt to study these algorithms on a simulated satellite network with moderate bandwidth and extremely long RTPD. Their effects on the existing applications, especially World Wide Web (WWW) and the emerging streaming applications, are emphasized. Different queue sizes are also used in simulation with the aim of investigating how to provision satellite link's queue for well accommodating flows driven by HSCC algorithms. Through this study, we find that Compound-TCP, Cubic-TCP, and H-TCP can not work well on satellite network. Currently, satellite link should use moderate queue size for accommodating flows driven by HSCC algorithms. As for end hosts, when they find that round trip time (RTT) is very long, HS-TCP should be adopted for high throughput while avoiding to hurt the existing applications as little as possible.

Topology discovery in sensor network is useful in any practical deployment of the network. Topology information helps the administrators monitor, debug and perform proactive control and management obtaining topology for dense wireless sensor network is expensive due to limited bandwidth and contention for the wireless channel. In this paper, we consider the problem of efficiently obtaining network topology where the locations and associated node identifiers are known by the central controller (sink). Although the locations of the nodes are known, the connectivity between any two nodes cannot be determined by distance information alone due to irregular radio coverage and obstacles. We propose a location-aided topology discovery algorithm (LAD) that requires O(log(|M|)) data units per node in common cases, and O(|M|) data units per node in the worst case, where M is the set of directly communicable neighbors of a particular node. Simulation results show that the overhead reduction ranges from 70% to over 95%.

While wireless networks are generally deployed in three dimensional environments, most geometric routing protocols are designed and evaluated with a focus on two dimensional space. In this paper, we present a connectivity based routing protocol in 3D space named Spherical Coordinate Routing(SCR), which exploits connectivity-based greedy forwarding for efficient routing paths and a spherical coordinate tree based recovery method to guarantee packet delivery. SCR can deploy multiple recovery trees simultaneously to enhance the routing efficiency and resilience against network dynamics. Simulation results show that the packet delivery ratio of SCR is 22% ~ 63% higher than that of BVR, LCR and NoGeo, at the critical node density range of 4 to 8. The amount of forwarding traffic required per packet delivery is considerably lower than protocols relying on scoped flooding based recovery. The SCR protocol can efficiently recover from topology changes due to clustered node failures, while maintaining excellent path stretch and traffic load performance in a 3D network topology.

Connectivity monitoring is useful in practical deployment of wireless sensor network. In order to understand the behavior and performance bottleneck, knowledge of the network connectivity is crucial. In this paper, we propose a flexible and efficient connectivity monitoring algorithm (H2CM) that has three components and operates in a divide and conquer manner. The components include hop vector distance based filtering, Bloom filters and signature hashing and are designed to work with different combinations of network and neighbor set sizes. In simulation, communication cost reduction of H2CM compare to maximal compression of neighborhood information varies from 65% to 85% for large networks (> 1000 nodes) and from 40% to 70% for a medium size network (a few hundred nodes). We have also implemented the algorithm in TinyOS and evaluated its performance on a testbed with 34 motes.

In recent years, many different kinds of wireless access networks have been deployed for the Internet and have become inseparable parts of the Internet. But TCP, the most widely used transport protocol of the Internet, was designed for stationery hosts. In particular, TCP faces severe challenges when user moves around in these networks and handoff occurs frequently. In this paper, TCP handoff (TCP-HO), a practical end-to-end mechanism, is proposed for improving TCP performance in heterogeneous mobile environments. TCP-HO assumes that a mobile host is able to detect the completion of handoff immediately and has a coarse estimation of new wireless link's bandwidth. When a mobile host detects handoff completion, it will immediately notify the server through two duplicate ACKs, whose TCP option also carries the bandwidth of new wireless link. After receiving this notification, the server begins to transmit immediately and keeps updating ssthresh according to the bandwidth from mobile host and its new RTT samples. This updating will be stopped after four RTT samples or after congestion is detected. TCP-HO has been implemented in FreeBSD 5.4. Experimental results show that TCP-HO does improve TCP performance without adversely affecting cross traffic in a heterogeneous mobile environment.

Geographic face routing provides an attractive way for packet delivery in wireless networks due to its high reliability and low overhead. A good face routing protocol should provide guaranteed packet delivery and efficient routing paths. In this paper, we present a new face routing method named GFRIS that has both features by actively probing each face for the face size and the unique face identification sequence -face ID. Face switch occurs only if the outgoing edge intersects with the local minimum-destination line at a progressing location and the edge is shared between two different faces. To avoid the huge performance penalty when selecting an inefficient face traversal direction on a large face, GFRIS uses the face size to trigger the bounded face traversal procedure as proposed earlier in GOAFR+. Simulation results show that, by using face ID to assist face switch and adaptively applying the normal and bounded face traversal rules according to the face size, GFRIS achieves lower path stretch factor compared to GFG, GPSR, GFG2 and GOAFR+. The worst case performance of GFRIS is even better than that of GOAFR+ in critical node densities from 4 to 7.

In MANETs, majority of performance studies are carried out via simulations, where node mobility and radio propagation models play a crucial role. However, popular simulation tools, like NS-2 and GloMoSim, use simplistic random mobility patterns and free space radio propagation models. Such simplification ignores many crucial details in environment where movements are not random and obstacles are common. To have a better understanding of MANET protocols, there is a need for a tool that can generate more realistic mobility scenarios and provide better radio propagation model. This paper presents EGRESS, which is built on top of NS-2 and consists of two major components: SGT and ORPM. SGT is a tool that generates node movements in an urban environment with buildings and pathways. ORPM is an obstructive radio propagation model, which enhances the existing radio models in NS-2 by taking into account obstacles in a 3D environment. We believe EGRESS is the first open source tool that provides such integrated and more realistic features for simulating urban environment. Our simulation results show that using more realistic scenarios can have a significant impact on network topology and performance of routing protocols

A wireless sensor network is normally a multi-hop wireless ad hoc network whose purpose is to transmit events sensed by sensors to the sink. Since sensor nodes are normally powered by non-rechargeable and non-replaceable battery, an energy efficient event transport service is crucial for extending the life time of a wireless sensor network. Due to the possibility of crossing multiple lossy links between the source and the sink, many events may be lost before they arrive at the sink. In addition, the overhead of low layer protocols is very large due to the short event data. These two factors can result in significant event loss and waste of energy. Many mechanisms have been proposed on other networks to improve reliability and reduce overhead. Due to scarce memory and poor computing ability of sensor nodes in a sensor network, these mechanisms may not be feasible to implement and they may not work efficiently with respect to energy. In this paper, PMC (Pipelined Multiple Copies) is proposed for transmitting events in a wireless sensor network, with the goals of achieving low event loss rate and high energy efficiency. In PMC, multiple copies of an event are pipelined and transmitted in several consecutive frames according to Silent CSMA, a variant of CSMA/CA. Multiple copies of an event reduce end-to-end event loss rate and Silent CSMA reduces packet energy consumption significantly.

Environmental monitoring and surveillance is a popular application of wireless sensor network. In such an application, the data transmitted are tagged with geographic information. A network with better coverage provides better quality-of-service since it will be able to monitor its area of responsibility more effectively. In this work, we study the impact of congestion on coverage of the sensor network. Congestion can negatively impact the performance since it can result in reduced coverage and power wastage. In this paper, we present a buffer management scheme called most redundant drop (MRD) and a scheduling algorithm called coverage transmit (CT) that make use of spatial information in sensor data to improve network coverage. Compared to drop-tail and FIFO, MRD and CT improve coverage by up to 75% when exact sensor location is available. Furthermore, as exact locations may not be available in practice, MRD and CT are evaluated using a modified DV-hop scheme that provides approximate localization. Simulation results show that substantial improvement can also be obtained using only approximated locations

In this paper, we propose a highly efficient key agreement scheme based on a novel key tree construction for ad hoc networks. The key tree is constructed taking into consideration of the multicast tree which represents the underlying network topology. Our scheme greatly reduces the communications and computation cost for group key agreement and has high flexibility in having dynamic group memberships. We implement our scheme in ns-2 and evaluate its performance in terms of overhead and communication cost. The simulation results show that our scheme enjoys great advantages over other schemes in the literature

The conference key distribution scheme (CKDS) enables three or more parties to derive a common conference key to protect the conversation content in their conference. Designing a conference key distribution scheme for mobile communications is a difficult task because wireless networks are more susceptible to attacks and mobile devices usually obtain low power and limited computing capability. In this paper we study a conference scheme for mobile communications and find that the scheme is insecure against the replay attack. With our replay attack, an attacker with a compromised conference key can cause the conferees to reuse the compromised conference key, which in turn completely reveals subsequent conversation content.

The middleware in distributed computing coordinates a group of servers to accomplish a resource intensive task; however, without resource monitoring, the server selection algorithms will not be sophisticated enough to provide satisfying results at all time. This paper presents a smart TCP socket library using server workload feedback to improve selection techniques. Users are able to specify server requirements by using a predefined meta language. Monitoring components such as the server probes and monitors are in charge of monitoring the server resource usage, network metrics and performing security measurements. Based on the user's request and available server resources, the user request handler called wizard will recommend the most suitable servers to user applications. The centralized and the distributed modes are both provided so that the socket library can be adapted to both small distributed systems and a large scale grid.

TCP, perhaps the most widely used transport protocol, was designed for wired links and stationary hosts. But more and more links with different characteristics are used to access the Internet. The variations in link characteristics present different problems to TCP and enhancement of TCP performance over these links remains an active area of research. Since the current core network of the Internet is composed mainly of optical fiber links and high speed routers, the characteristics of the access link (or the last link) usually dominate the characteristics of the end-to-end network path. As a result, if the client can acquire the characteristics of the access link (e.g. through measurement), the TCP server can utilize heuristics that exploit the access link's characteristics in order to improve the performance of TCP. In this paper, we propose and evaluate the performance of several heuristics that exploit knowledge of access link characteristics such as bandwidth and packet error rate. Simulation results show that these heuristics can indeed improve TCP performance significantly and demonstrate the potential benefits of using heuristics that adjust TCP congestion control behaviors to match the access link characteristics.

Wireless networks have gained overwhelming popularity over their wired counterpart due to their great flexibility and convenience, but access control of wireless networks has been a serious problem because of the open medium. Passwords remain the most popular way for access control as well as authentication and key exchange. But existing password-based access control protocols are not satisfactory in that they do not provide DoS-resistance or anonymity. In this paper we analyze the weaknesses of an access control protocol using passwords for wireless networks in IEEE LCN 2001, and propose a different access control protocol using passwords for wireless networks. Our new protocol avoids the weaknesses of the previous protocol, and the client can anonymously authenticate himself to the server with a human-memorable password, while the server is free of DoS attacks. We also present detailed security and performance analysis for our protocols, and show that our protocol is both secure and efficient for access control in wireless networks

In this paper, we review a PKC (public key cryptosystem) based protocol, referred to as the Stanford protocol, aimed at overcoming several security deficiencies in IEEE 802.1X and to provide access control in both wireless and wired networks. One main objective of the Stanford protocol is to provide DoS resistance for the wireless network. Meanwhile, in the wireless environment, identity confidentiality of the mobile user is especially important since the disclosed identity could be used to locate the user and track his movement. But our analysis shows that the Stanford protocol fails to fulfill these requirements. So we propose a new PKC-based protocol that not only provides DoS resistance and perfect forward secrecy, but also provides identity anonymity for the clients. We also present detailed security and performance analysis for our protocol, and show that our protocol is secure and efficient for access control in wireless networks.

Fast and seamless localized mobility management is one of the key challenges for future "all IP" based communication networks. Although several proposals for micromobility management have been made in the recent past, almost all of them propose a proxy based solution for location management. In this work, we present a novel approach for providing micromobility in IPv6 networks called auto-update micromobility (AUM). AUM exploits the IPv6 addressing structure to simplify location management and also provides full support for seamless, fast handoff.

Proceedings - Conference on Local Computer Networks, LCN

Protocols such as TCP and congestion control mechanisms like TFRC (TCP-friendly rate control) suffer in a hybrid wired-cum-wireless scenario where losses can occur for reasons other than congestion, viz., due to bit errors in the wireless link. The existing solutions to address the problem either misclassify the losses, violate end-to-end semantics, do not coexist with IPSec or are TCP-specific. We have previously proposed an innovative mechanism, secure performance enhancing proxy (SPEP), which preserves end-to-end semantics, ensures end-to-end security and enhances performance. We show that the decoupling of loss differentiation from the loss recovery mechanism enables SPEP to serve as a generic loss differentiation mechanism at the network layer. We show by means of test bed experiments that SPEP works in conjunction with any transport layer and protocols such as UDP with TFRC.

A number of micromobility protocols have been proposed in the recent past for IPv4 based networks. We present auto-update micromobility (AUM) - a novel approach for providing micromobility in IPv6 environments. The proposed scheme exploits the basic IPv6 feature of a hierarchical addressing structure for efficient location management and provides specialized mechanisms for seamless mobility support. AUM takes an end-to-end approach to micromobility rather than the proxy approach taken by current proposals. This results in much simplified routing and a scalable architecture.

Knowledge of network path characteristics enables upper layers to improve performance through adaptation protocols which adjust behaviors according to current network path characteristics. For a mobile node of a wireless network, this knowledge is especially valuable because the characteristics of the wireless link, which often dominate network path characteristics, change frequently and abruptly due to mobility, fading, and contention among nodes. Due to the dynamics and precious bandwidth of the wireless link, the commonly used probing packet methods are not appropriate for estimating the characteristics of a network path with a wireless link. We propose a new mechanism to estimate link characteristics of IEEE 802.11 DCF (distributed coordination function) based wireless LAN (WLAN), one of the most popular wireless access networks. Instead of sending probing-packets, a mobile node estimates its link characteristics based on wireless link quality and the contention status of the whole WLAN. We implement this mechanism and test its accuracy in NS2.

Achieving improved TCP performance together with ensuring end-to-end security necessitates the co-existence of security mechanisms like IPSEC and performance enhancing solutions. However, IP security and TCP performance have been traditionally dealt with in a mutually exclusive manner. We propose an innovative mechanism, secure performance enhancing proxy (SPEP) to address the seemingly arduous problem of enhancing TCP performance over wireless networks, preserving end-to-end TCP semantics as well as ensuring end-to-end security. The proposed SPEP scheme decouples loss detection and loss distinction mechanism from loss recovery mechanism which not only facilitates in performance improvement but also offers multifarious advantages discussed in the paper. We have implemented the proposed scheme in FreeBSD 4.5 and conducted experiments in a controlled test bed setup. Our results show improved TCP performance in a secured environment with introduction of minimal overhead.

Depending on the bandwidth and round trip time of a network path, certain network connections may need different socket buffers than others. However, most TCP implementations use default socket buffer size for all the connections. This leads to a wastage of kernel memory for low bandwidth, long round trip time network paths and inefficiency for long fat W. Rechard Stevens (1994) network paths. To tackle this problem, we implement a TCP socket buffer auto-tuning daemon. It will periodically tune the socket buffer size of each connection to an optimal value according to the network status of each connection, without the intervention of user or change of network application. The tuning daemon can run on different machines and communicate with each other, send tuning request to the remote daemon and exchange the tuning information. Experiment results are presented to show that this daemon can improve the throughput for network application.

In spite of the larger performance gain such as higher throughput and almost zero packet retransmissions compared to TCP Reno, TCP Vegas still has a few obstacles for it to be deployed in the Internet. Studies have shown unfair treatment to Vegas connections when they compete with Reno connections. Other issues identified with TCP Vegas are problems of rerouting, persistent congestion, and discrepancy in flow rate tied with starting times and link bandwidth. We reinvestigate these issues rind propose modifications to the congestion avoidance mechanism of the TCP Vegas, with the slow-start and congestion recovery algorithms of Vegas remaining untouched. Unlike the solutions proposed in the recent past to deal with some of these issues, our solution it neither dependent on any critical parameter values nor on the buffer management scheme at the routers (e.g., RED). Our experiments show that the modified TCP Vegas (Vegas-A) it able to obtain a fairer share of the network bandwidth when competing with other TCP flows. We also show that Vegas-A can tackle rerouting issues and rectify Vegas's bias against higher bandwidth flows. At the same time, our experiments prove that Vegas-A preserves the properties of Vegas that have made it a noteworthy protocol.

A medium access control (MAC) technique for multi-hop wireless networks with quality of service (QoS) assurance is introduced The proposed protocol deals with most of the hidden node problems in a multi-hop environment and also provides service differentiation for various types of traffic: real-time constant bit rate (CBR) traffic, real-time variable bit rate (VBR) traffic, and non-real-time datagram traffic, by guaranteeing bounded delay for real-time traffic, at the same time avoiding lockout of datagram traffic. It uses a distributed mechanism of scheduling and reserving the channel access for real-time sessions. Transmission of datagram or starting packet of a new realtime session is granted only after checking the reservation such that they do not affect the scheduled ongoing real-time sessions. The protocol has been implemented and tested using the VINT Network Simulator 2 (NS2). The performance evaluation and comparison confirm the improved QoS features and multimedia support compared to various existing QoS enabled MAC protocols.

Wireless sensor networks are widely used in data acquisition frameworks. Unlike conventional networked devices, wireless sensors run on low power energy sources, and have limited memory buffers, minimal computational complexity, and low processing speeds. As such, the complexities involved with conventional network protocols cannot be realized in wireless sensors. A data dissemination protocol for wireless sensor network should be well aware of sensor limitations. In addition, it should also take into consideration, the unique aspects of applications running over wireless sensor networks. In this paper, we propose a new network protocol, Simple Wireless Sensor Protocol (SWSP) for wireless sensors which provides a reliable data communication between wireless sensors with minimum resource overhead.

This paper reports a study on the performance enhancements of two extensions to the standard TCP implementation - Selective Acknowledgement (SACK) and Header Checksum (HACK) - over satellite links that are characterized by high latency and high bit error rate. We also examine the effectiveness of TCP Trunk, an edge-to-edge aggregation and congestion control mechanism, over the satellite link. Our study on the effect of varying the TCP window size over a long latency link for New Reno, SACK, HACK and TCP Trunk implementations show that increasing window size does improve the performance, but only up to a certain value of the window size, and a further increase actually reduces the performance. Other interesting observations from our experimental study are: SACK enabled TCP Trunk across the satellite link edge routers can improve the throughput regardless of the end host TCP implementation; disabling the link layer CRC and instead implementing the HACK extension to the TCP (and of course HACK+ SACK) can improve the throughput further.

The bias of TCP's congestion avoidance mechanism against connections with long round trip times (RTT) is a known fact. Many alternative congestion avoidance policies have been proposed to improve the fairness. Though the proposed policies attempt to address and resolve the fairness issue, we show that they tend to be harmful to connections that traverse either slow links, like 56 Kbps modem links, or long thin networks (LTN), like cellular links. We specifically consider a very common scenario where the last-hop link connecting the end user (i.e., client) may be a slow link or LTN. In this case, the TCP sender (i.e., server) is usually unaware of the network path, and when it is equipped with such policies, it increases probing into the network in a quest for the non-existent bandwidth. We conduct simulation studies to evaluate the impact of the proposed policies on connections that traverse either slow links or LTNs. We notice that the proposed policies cause increased buffer overflows at the last-hop router, thereby degrading the performance of the connection. We study the impact of increased buffer sizes at the last-hop router and also the effect of advertising a limited receive window. We show that the impact of the policies, on connections traversing slow links or LTNs, can be reduced by selectively disabling the policies.

This paper presents a residential gateway (RG) architecture that addresses the problems of bandwidth allocation for multiple home appliances and services in home area network (HAN). Our architecture approaches the problems by focusing on two important factors: automatic device discovery and dynamic bandwidth allocation. The architecture optimizes the utilization of the limited bandwidth to achieve quality of service (QoS). A prototype is built based on this architecture to demonstrate the QoS feature that we have implemented in a residential gateway.

IPv4 to IPv6 transition is an inevitable process when deploying IPv6 networks within the present IPv4 Internet. The transition process is complex as it has to deal with issues related to IPv4-IPv6 interoperability including routing, DNS, error handling etc. A new solution named DTTS (dynamic tunneling transition solution) for IPv4 to IPv6 transition based on a dynamic tunneling technique and a dual stack approach is presented. The dynamic tunneling technique is used to encapsulate an IPv4 packet in an IPv6 packet to achieve transparent and scalable transition. This technique, coupled with the dual stack approach, enables IPv4 applications to run and interact with other IPv4 applications in both IPv4 and IPv6 network environments without any modification and recompilation, and without NAT (network address translator), nor any application proxy or gateway.

Markers, one of the building blocks of a traffic conditioner, play a major role for resource allocation in a DiffServ network. Recently, there has been a considerable research interest in designing intelligent markers, tailored for TCP traffic. The TCP dynamics make the design of a marker difficult in many respects. We list the issues related to designing a TCP-friendly marker and propose an intelligent marker, namely, memory-based marker (MBM) to address those issues. We illustrate the benefits of the proposed marker over some existing markers in a DiffServ network. The marker was implemented in NS simulator and extensive simulations were done to study the behaviour of MBM. Our results show significant improvement in TCP performance, especially in achieving fairness among priority flows with distinct round trip times, windows, and target rates. The marker is capable of protecting TCP flows in cases of congestion caused by unruly UDP flows. We also investigate the impact of coexisting assured service UDP flows on the assurance to the TCP flows. The major benefits of MBM are its simplicity, least sensitivity to parameters and transparency to the end hosts.

Wireless networks have become increasingly common and an increasing number of devices are communicating with each other over lossy links. Unfortunately, TCP performs poorly over lossy links as it is unable to differentiate the loss due to packet corruption from that due to congestion. We present an extension to TCP which enables TCP to distinguish packet corruption from congestion in lossy environments resulting in improved performance. We refer to this extension as the HeAder ChecKsum option (HACK). We implemented our algorithm in the Linux kernel and performed various tests to determine its effectiveness. Our results have shown that HACK performs substantially better than both SACK and NewReno in cases where burst corruptions are frequent. We also found that HACK can co-exist very nicely with SACK and performs even better with SACK enabled.

Markers, one of the building blocks of traffic conditioners play a major role for resource allocation in a DiffServ network. Recently, there has been a considerable research interest in designing intelligent markers, tailored for TCP traffic. The transient congestion levels in the network can affect the TCP throughput adversely and have great impact on the effectiveness of the marker. To address this issue, we propose an intelligent marker, which relies on an ECN-like feedback control mechanism between ingress and egress traffic conditioners. We present the control architecture and the marker algorithm, and illustrate the benefits of the proposed marker in a DiffServ network. The marker was implemented in the NS simulator and extensive simulations were done to study its effectiveness in the assurance of throughput, especially under the case that AS flows require different target rates, and co-exist with the unruly UDP flows. The ECN-like feedback mechanism that we use for the marker is also suitable in an MPLS domain for providing signaling to the ingress router of a congested label switched path (LSP) to mitigate congestion via dynamic traffic engineering techniques.

This paper examines the attributes of TCP tunnels which are TCP circuits that carry IP packets and benefit from the congestion control mechanism of TCP/IP. The deployment of TCP tunnels reduces the many flows situation on the Internet to that of a few flows. TCP tunnels eliminate unnecessary packet loss in the core routers of the congested backbones which waste precious bandwidth leading to congestion collapse due to unresponsive UDP flows. We also highlight that the use of TCP tunnels can, in principle, help prevent certain forms of congestion collapse described by Floyd & Fall (see IEEE/ACM Transactions on Networking, vol.7, no.4, p.458-72, 1999). Using a testbed often Intel PCs running the Linux operating system and traffic generators simulating user applications, we explore: the benefits which TCP tunnels confer upon its payload of user IP traffic; the impact on the congestion within network backbones, and the protection that tunnels offer with respect to the various competing classes of traffic in terms of bandwidth allocation and reduced retransmissions. The deployment of TCP tunnels on the Internet and the issues involved are also discussed and we conclude that with the RFC2309 recommendation of using random early drop (RED) as the default packet-drop policy in Internet routers, coupled with the implementation of a pure tunnel environment on backbone networks makes the deployment of TCP tunnels a feasible endeavour worthy of further investigation.

A transport-independent asynchronous RPC (remote procedure call) mechanism (ASTRA) that combines the advantages of both RPC and message-passing IPC (interprocess communication) has been designed and implemented. ASTRA calls do not block the caller (client) and the replies can be received as and when they are needed, thus allowing the client execution to proceed locally in parallel with the server invocation. All the calls are received and executed by the server in the order called by the client. ASTRA is unique among other asynchronous RPC systems in allowing its users to explicitly specify whether low-latency or high-throughput is required for a call, and in providing highly optimized lightweight intramachine calls. ASTRA is built within the framework of the SHILPA distributed computing environment.>