@article{yoon_lee_yun_rhee_2016, title={ACMI: FM-Based Indoor Localization via Autonomous Fingerprinting}, volume={15}, ISSN={["1558-0660"]}, DOI={10.1109/tmc.2015.2465372}, abstractNote={We present ACMI, an FM-based indoor localization system that does not require proactive site profiling. ACMI constructs the fingerprint database based on pure estimation of indoor received signal strength (RSS) distribution, where only the signals transmitted from commercial FM radio stations are used. Based on extensive field measurement study, we established our own signal propagation model that harnesses FM radio characteristics and open information of FM transmission towers in combination with the floor-plan of a building. Output of the model is an RSS fingerprint database. Using the fingerprint database as a knowledge base, ACMI refines a positioning result via the two-step process; parameter calibration and path matching, during its runtime. Without site profiling, our evaluation indicates that ACMI in seven campus locations and three downtown buildings using eight distinguished FM stations finds positions with only about 6 and 10 meters of errors on average, respectively.}, number={6}, journal={IEEE TRANSACTIONS ON MOBILE COMPUTING}, author={Yoon, Sungro and Lee, Kyunghan and Yun, YeoCheon and Rhee, Injong}, year={2016}, month={Jun}, pages={1318–1332} }
 @article{jiang_wang_lee_rhee_2016, title={DRWA: A receiver-centric solution to bufferbloat in cellular networks}, volume={15}, DOI={10.1109/tmc.2015.2510641}, abstractNote={The problem of overbuffering in the current Internet (termed as bufferbloat) has drawn the attention of the research community in recent years. Cellular networks keep large buffers at base stations to smooth out the bursty data traffic over the time-varying channels and are hence apt to bufferbloat. However, despite their growing importance due to the boom of smart phones, we still lack a comprehensive study of bufferbloat in cellular networks and its impact on TCP performance. In this paper, we conducted extensive measurement of the 3G/4G networks of the four major U.S. carriers and the largest carrier in Korea. We revealed the severity of bufferbloat in current cellular networks and discovered some ad-hoc tricks adopted by smart phone vendors, which mitigate the impact of bufferbloat but result in performance degradation under various practical scenarios. To address the problem, we propose dynamic receiver window adjustment (DRWA) that requires slight TCP modification only in smart phones, thus guarantees quick deployment via over-the-air updates. Our extensive real-world tests confirm that DRWA reduces the latency of TCP flows by 25-49 percent and increase TCP throughput by up to 51 percent in certain scenarios. It is further verified that DRWA has significant effect on the latency of Voice-over-IP traffic and on the traffic going through TCP split scenarios with performance enhancing proxy.}, number={11}, journal={IEEE Transactions on Mobile Computing}, author={Jiang, H. Q. and Wang, Y. G. and Lee, K. and Rhee, I.}, year={2016}, pages={2719–2734} }
 @inproceedings{chung_rhee_2015, title={An unobtrusive interaction interface for multiple co-located mobile devices}, DOI={10.1109/wimob.2015.7348028}, abstractNote={In this paper, we propose a practical interaction interface for a local set of devices to connect to each other without requiring a lot of effort from their users. We find that highly time-correlated Wi-Fi signal measures experience less variation in their received signal strength (RSS), which alleviates the impediment of the RSS-based solution. We also notice that each room observes significantly discrete signal signature even when they are adjacent to each other. We leverage these observations and rely on the RSS measure to detect and unobtrusively pair devices in the same space. To achieve our goal, we devise a new similarity metric for RSS comparison and propose a means of selecting the cluster threshold. We implement a prototype named Flock for Android devices. By relying on our client-server system architecture, mobile users can interface with others in a few seconds without having to search-and-select nearby devices.}, booktitle={Ieee international conference on wireless and mobile computing}, author={Chung, S. and Rhee, I.}, year={2015}, pages={683–690} }
 @article{lee_jeong_yi_won_rhee_chong_2015, title={Max Contribution: An Online Approximation of Optimal Resource Allocation in Delay Tolerant Networks}, volume={14}, ISSN={["1558-0660"]}, DOI={10.1109/tmc.2014.2329001}, abstractNote={In this paper, a joint optimization of link scheduling, routing and replication for delay-tolerant networks (DTNs) has been studied. The optimization problems for resource allocation in DTNs are typically solved using dynamic programming which requires knowledge of future events such as meeting schedules and durations. This paper defines a new notion of approximation to the optimality for DTNs, called snapshot approximation where nodes are not clairvoyant, i.e., not looking ahead into future events, and thus decisions are made using only contemporarily available knowledges. Unfortunately, the snapshot approximation still requires solving an NP-hard problem of maximum weighted independent set (MWIS) and a global knowledge of who currently owns a copy and what their delivery probabilities are. This paper proposes an algorithm, Max-Contribution (MC) that approximates MWIS problem with a greedy method and its distributed online approximation algorithm, Distributed Max-Contribution (DMC) that performs scheduling, routing and replication based only on locally and contemporarily available information. Through extensive simulations based on real GPS traces tracking over 4,000 taxies and 500 taxies for about 30 days and 25 days in two different large cities, DMC is verified to perform closely to MC and outperform existing heuristically engineered resource allocation algorithms for DTNs.}, number={3}, journal={IEEE TRANSACTIONS ON MOBILE COMPUTING}, author={Lee, Kyunghan and Jeong, Jaeseong and Yi, Yung and Won, Hyungsuk and Rhee, Injong and Chong, Song}, year={2015}, month={Mar}, pages={592–605} }
 @article{zhao_sichitiu_rhee_2015, title={N-body: A social mobility model with support for larger populations}, volume={25}, ISSN={["1570-8713"]}, DOI={10.1016/j.adhoc.2014.10.005}, abstractNote={An accurate reproduction of real human movement is essential in simulations of MANETs in order to obtain meaningful performance results. Existing models capturing real world mobility features often require knowledge of the underlying dynamics of the target scenario, therefore limiting the application scope. In this paper we tackle this problem from a different perspective. Rather than considering the details of the target scenario, we extract features from a sample trace, and synthesize traces that have similar features. In particular, as human activities are often socially organized, resulting in a tendency of forming groups, we propose an N-body mobility model that captures the group forming tendency from traces of a small number of nodes, and reproduces them in mobility traces of a larger population. Through simulation we show that the N-body model is capable of synthesizing the group forming behavior similar to that observed from sample traces.}, journal={AD HOC NETWORKS}, author={Zhao, Chen and Sichitiu, Mihail L. and Rhee, Injong}, year={2015}, month={Feb}, pages={185–196} }
 @article{zavala_murukannaiah_poosamani_finin_joshi_rhee_singh_2015, title={Platys: From Position to Place-Oriented Mobile Computing}, volume={36}, ISSN={["0738-4602"]}, url={https://publons.com/publon/21294393/}, DOI={10.1609/aimag.v36i2.2584}, abstractNote={The Platys project focuses on developing a high‐level, semantic notion of location called place. A place, unlike a geospatial position, derives its meaning from a user's actions and interactions in addition to the physical location where it occurs. Our aim is to enable the construction of a large variety of applications that take advantage of place to render relevant content and functionality and, thus, improve user experience. We consider elements of context that are particularly related to mobile computing. The main problems we have addressed to realize our place‐oriented mobile computing vision are representing places, recognizing places, and engineering place‐aware applications. We describe the approaches we have developed for addressing these problems and related subproblems. A key element of our work is the use of collaborative information sharing where users' devices share and integrate knowledge about places. Our place ontology facilitates such collaboration. Declarative privacy policies allow users to specify contextual features under which they prefer to share or not share their information.}, number={2}, journal={AI MAGAZINE}, author={Zavala, Laura and Murukannaiah, Pradeep K. and Poosamani, Nithyananthan and Finin, Tim and Joshi, Anupam and Rhee, Injong and Singh, Munindar P.}, year={2015}, pages={50–62} }
 @inproceedings{poosamani_rhee_2015, title={Towards a practical indoor location matching system using 4G LTE PHY layer information}, DOI={10.1109/percomw.2015.7134048}, abstractNote={Predicting the location of a user in indoor settings in a practical and energy-efficient manner is (still) a very non-trivial task. The latest challenge in indoor localization is not to design specialized sensors but to design and implement practical data fusion methods using the already available technologies. Current state-of-the-art indoor localization techniques utilize Wi-Fi and a variety of sensors inside smart phones to predict user location. Some also require site-specific input such as indoor floor plans or the location of Wi-Fi access points. In this paper, we propose to use physical (PHY) layer information from 4G cellular network signals such as Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) to logically predict user location. Since the cellular signals are received by the smart phones at no additional cost, our methodology is very energy-efficient. We implement a prototype system in Android and evaluated it over 60 indoor locations. The prediction accuracy ranged up to 91% with an average localization error of less than 2.3m for any combination of 4G PHY layer information. The results show promise for improvements in current indoor localization systems using cellular signals.}, booktitle={2015 IEEE International Conference on Pervasive Computing and Communication Workshops (PERCOM workshops)}, author={Poosamani, N. and Rhee, I.}, year={2015}, pages={284–287} }
 @article{jeong_lee_yi_rhee_chong_2014, title={ExMin: A routing metric for novel opportunity gain in Delay Tolerant Networks}, volume={59}, ISSN={["1872-7069"]}, DOI={10.1016/j.bjp.2013.11.006}, abstractNote={Delay Tolerant Networks (DTNs) are characterized by intermittently connected links formed by mobile nodes' probabilistic encounters. Most DTN routing techniques use the first encountered node who has smaller routing metric as a relay node. Prior work on DTN routing can be broadly classified into one which takes the minimum out of expected delays for all possible individual routing paths, referred to as MinEx, as a routing metric to decide the next hop relay node. Fundamentally, MinEx has no difference from the shortest path computation in conventional multi-hop networks, where a link weight is the expected inter-meeting time. However in DTNs, nodes meet intermittently by their mobility, hence the links formed from the meetings are probabilistic. In this environment, MinEx often fails to accurately estimate the actual delay since opportunism in nodes' intermittent meeting is not properly taken into account. In this paper, to exploit the true opportunism, we first propose a metric called ExMin which stochastically calculates the metric by taking the expectation of the minimum delays over all possible routes. We further show that ExMin can be computed online by relying only on local information sharing. Our extensive experiments involving three realistic network scenarios created by two vehicle traces (about 1500 Shanghai taxies and 500 San Francisco taxies) and one human mobility trace (93 KAIST students) show that ExMin outperforms MinEx by up to 30% under either of DTN environments allowing single-copy or multi-copies of a packet.}, journal={COMPUTER NETWORKS}, author={Jeong, Jaeseong and Lee, Kyunghan and Yi, Yung and Rhee, Injong and Chong, Song}, year={2014}, month={Feb}, pages={184–196} }
 @article{wang_rozhnova_narayanan_oran_rhee_2013, title={An improved hop-by-hop interest shaper for congestion control in named data networking}, volume={43}, DOI={10.1145/2491224.2491233}, abstractNote={Hop-by-hop interest shaping has been proposed as a viable congestion control mechanism in Named Data Networking (NDN). Interest shaping exploits the strict receiver-driven traffic pattern and the symmetric bidirectional forwarding in NDN to control the returning data rate. In this paper, we point out that both interests and contents contribute to congestion and their interdependence must be considered in any interest shaping algorithm. We first analyze this issue mathematically by formulating it as an optimization problem to obtain the optimal shaping rate. Then a practical interest shaping algorithm is proposed to achieve high link utilization without congestive data loss. We further note that flow differentiation in NDN is complicated and design our scheme independently of traffic flows. We demonstrate our hop-by-hop interest shaper in conjunction with simple Additive-Increase-Multiplicative-Decrease (AIMD) clients using the ns3-based NDN simulator (ndnSIM). Our results show that the proposed shaping algorithm can effectively control congestion and achieve near-optimal throughput.}, number={4}, journal={Computer Communication Review}, author={Wang, Y. G. and Rozhnova, N. and Narayanan, A. and Oran, D. and Rhee, I.}, year={2013} }
 @article{lee_lee_yi_rhee_chong_2013, title={Mobile Data Offloading: How Much Can WiFi Deliver?}, volume={21}, ISSN={["1558-2566"]}, DOI={10.1109/tnet.2012.2218122}, abstractNote={This paper presents a quantitative study on the performance of 3G mobile data offloading through WiFi networks. We recruited 97 iPhone users from metropolitan areas and collected statistics on their WiFi connectivity during a two-and-a-half-week period in February 2010. Our trace-driven simulation using the acquired whole-day traces indicates that WiFi already offloads about 65% of the total mobile data traffic and saves 55% of battery power without using any delayed transmission. If data transfers can be delayed with some deadline until users enter a WiFi zone, substantial gains can be achieved only when the deadline is fairly larger than tens of minutes. With 100-s delays, the achievable gain is less than only 2%-3%, whereas with 1 h or longer deadlines, traffic and energy saving gains increase beyond 29% and 20%, respectively. These results are in contrast to the substantial gain (20%-33%) reported by the existing work even for 100-s delayed transmission using traces taken from transit buses or war-driving. In addition, a distribution model-based simulator and a theoretical framework that enable analytical studies of the average performance of offloading are proposed. These tools are useful for network providers to obtain a rough estimate on the average performance of offloading for a given WiFi deployment condition.}, number={2}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Lee, Kyunghan and Lee, Joohyun and Yi, Yung and Rhee, Injong and Chong, Song}, year={2013}, month={Apr}, pages={536–550} }
 @article{lee_kim_chong_rhee_yi_shroff_2013, title={On the Critical Delays of Mobile Networks Under Levy Walks and Levy Flights}, volume={21}, ISSN={["1558-2566"]}, DOI={10.1109/tnet.2012.2229717}, abstractNote={Delay-capacity tradeoffs for mobile networks have been analyzed through a number of research works. However, Lévy mobility known to closely capture human movement patterns has not been adopted in such work. Understanding the delay-capacity tradeoff for a network with Lévy mobility can provide important insights into understanding the performance of real mobile networks governed by human mobility. This paper analytically derives an important point in the delay-capacity tradeoff for Lévy mobility, known as the critical delay. The critical delay is the minimum delay required to achieve greater throughput than what conventional static networks can possibly achieve (i.e., O(1/√n) per node in a network with n nodes). The Lévy mobility includes Lévy flight and Lévy walk whose step-size distributions parametrized by α ∈ (0,2] are both heavy-tailed while their times taken for the same step size are different. Our proposed technique involves: 1) analyzing the joint spatio-temporal probability density function of a time-varying location of a node for Lévy flight, and 2) characterizing an embedded Markov process in Lévy walk, which is a semi-Markov process. The results indicate that in Lévy walk, there is a phase transition such that for α ∈ (0,1), the critical delay is always Θ(n<sup>[1/2]</sup>), and for α ∈ [1,2] it is Θ(n<sup>[(α)/2]</sup>). In contrast, Lévy flight has the critical delay Θ(n<sup>[(α)/2]</sup>) for α ∈ (0,2].}, number={5}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Lee, Kyunghan and Kim, Yoora and Chong, Song and Rhee, Injong and Yi, Yung and Shroff, Ness B.}, year={2013}, month={Oct}, pages={1621–1635} }
 @inproceedings{yoon_li_liew_choudhury_rhee_tan_2013, title={QuickSense: Fast and energy-efficient channel sensing for dynamic spectrum access networks}, DOI={10.1109/infcom.2013.6567028}, abstractNote={Spectrum sensing, the task of discovering spectrum usage at a given location, is a fundamental problem in dynamic spectrum access networks. While sensing in narrow spectrum bands is well studied in previous work, wideband spectrum sensing is challenging since a wideband radio is generally too expensive and power consuming for mobile devices. Sequential scan, on the other hand, can be very slow if the wide spectrum band contains many narrow channels. In this paper, we propose an analog-filter based spectrum sensing technique, which is much faster than sequential scan and much cheaper than using a wideband radio. The key insight is that, if the sum of energy on a contiguous band is low, we can conclude that all channels in this band are clear with just one measurement. Based on this insight, we design an intelligent search algorithm to minimize the number of total measurements. We prove that the algorithm has the same asymptotic complexity as compressed sensing while our design is much simpler and easily implementable in the real hardware. We show the availability of our technique using hardware devices that include analog filters and analog energy detectors. Our extensive evaluation using real TV “white space” signals shows the effectiveness of our technique.}, booktitle={2013 proceedings ieee infocom}, author={Yoon, S. and Li, L. E. and Liew, S. C. and Choudhury, R. R. and Rhee, I. and Tan, K.}, year={2013}, pages={2247–2255} }
 @inproceedings{selvanayagam_wang_jiang_lee_rhee_2012, title={Reducing redundant cross-ISP traffic in peer-to-peer systems via explicit coordination}, DOI={10.1109/ccnc.2012.6181137}, abstractNote={Locality-aware P2P file sharing systems have drawn the attention of the research community as a promising technique to alleviate the tussle between P2P traffic and ISPs. However, existing locality-based schemes mainly focus on how to distinguish whether a peer is local or not and pay less attention to how to utilize the locality information. Typically, they simply bias the peer selection towards local peers in the hope that it will reduce cross-ISP traffic. In this paper, we argue that such coarse-grained control is inadequate and propose a fine-grained mechanism called Swarm-over-Swarm (SOS). Through explicit coordination on piece selection among local peers, SOS is much more effective in reducing redundant cross-ISP traffic than existing schemes. We implement SOS in both NS-2 and a real BitTorrent client and demonstrate the effectiveness of our solution via both simulations and Internet experiments.}, booktitle={2012 ieee consumer communications and networking conference (ccnc)}, author={Selvanayagam, A. H. A. and Wang, Y. G. and Jiang, H. Q. and Lee, K. and Rhee, I.}, year={2012}, pages={603–607} }
 @article{lee_hong_kim_rhee_chong_2012, title={SLAW: Self-Similar Least-Action Human Walk}, volume={20}, ISSN={["1558-2566"]}, DOI={10.1109/tnet.2011.2172984}, abstractNote={Many empirical studies of human walks have reported that there exist fundamental statistical features commonly appearing in mobility traces taken in various mobility settings. These include: 1) heavy-tail flight and pause-time distributions; 2) heterogeneously bounded mobility areas of individuals; and 3) truncated power-law intercontact times. This paper reports two additional such features: a) The destinations of people (or we say waypoints) are dispersed in a self-similar manner; and b) people are more likely to choose a destination closer to its current waypoint. These features are known to be influential to the performance of human-assisted mobility networks. The main contribution of this paper is to present a mobility model called Self-similar Least-Action Walk (SLAW) that can produce synthetic mobility traces containing all the five statistical features in various mobility settings including user-created virtual ones for which no empirical information is available. Creating synthetic traces for virtual environments is important for the performance evaluation of mobile networks as network designers test their networks in many diverse network settings. A performance study of mobile routing protocols on top of synthetic traces created by SLAW shows that SLAW brings out the unique performance features of various routing protocols.}, number={2}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Lee, Kyunghan and Hong, Seongik and Kim, Seong Joon and Rhee, Injong and Chong, Song}, year={2012}, month={Apr}, pages={515–529} }
 @inproceedings{yoon_rhee_jung_daneshrad_kim_2011, title={Contrabass: Concurrent transmissions without coordination for ad hoc networks}, DOI={10.1109/infcom.2011.5934890}, abstractNote={A practical protocol jointly considering PHY and MAC for MIMO based concurrent transmissions in wireless ad hoc networks, called Contrabass, is presented. Concurrent transmissions refer to simultaneous transmissions by multiple nodes over the same carrier frequency within the same interference range. Contrabass is the first-to-date open-loop based concurrent transmission protocol which implements simultaneous channel training for concurrently transmitting links without any control message exchange. Its MAC protocol is designed for each active transmitter to independently decide to transmit with near optimal transmission probability. Contrabass maximizes the number of successful concurrent transmissions, thus achieving very high aggregate throughput, low delays and scalability even under dynamic environments. The design choices of Contrabass are deliberately made to enable practical implementation which is demonstrated through GNURadio implementation and experimentation.}, booktitle={2011 proceedings ieee infocom}, author={Yoon, S. and Rhee, I. and Jung, B. C. and Daneshrad, B. and Kim, J. H.}, year={2011}, pages={1134–1142} }
 @inproceedings{lee_kim_chong_rhee_yi_2011, title={Delay-capacity tradeoffs for mobile networks with levy walks and levy flights}, DOI={10.1109/infcom.2011.5935159}, abstractNote={This paper analytically derives the delay-capacity tradeoffs for Lévy mobility: Lévy walks and Lévy flights. Lévy mobility is a random walk with a power-law flight distribution. α is the power-law slope of the distribution and 0 &#60; α ≤ 2. While in Lévy flight, each flight takes a constant flight time, in Lévy walk, it has a constant velocity which incurs strong spatio-temporal correlation as flight time depends on traveling distance. Lévy mobility is of special interest because it is known that Lévy mobility and human mobility share several common features including heavy-tail flight distributions. Humans highly influence the mobility of nodes (smartphones and cars) in real mobile networks as they carry or drive mobile nodes. Understanding the fundamental delay-capacity tradeoffs of Lévy mobility provides important insight into understanding the performance of real mobile networks. However, its power-law nature and strong spatio-temporal correlation make the scaling analysis non-trivial. This is in contrast to other random mobility models including Brownian motion, random waypoint and i.i.d. mobility which are amenable for a Markovian analysis. By exploiting the asymptotic characterization of the joint spatio-temporal probability density functions of Lévy models, the order of critical delay, the minimum delay required to achieve more throughput than Θ(1/√n) where n is the number of nodes in the network, is obtained. The results indicate that in Lévy walk, there is a phase transition that for 0 &#60; α &#60; 1, the critical delay is constantly Θ(n<sup>1/2</sup>) and for 1 ≤ α ≤ 2, is Θ(n<sup>α/2</sup>). In contrast, Lévy flight has critical delay Θ(n<sup>α/</sup>2) for 0 &#60; a ≤ 2.}, booktitle={2011 proceedings ieee infocom}, author={Lee, K. and Kim, Y. and Chong, S. and Rhee, I. and Yi, Y.}, year={2011}, pages={3128–3136} }
 @article{rhee_shin_hong_lee_kim_chong_2011, title={On the Levy-Walk Nature of Human Mobility}, volume={19}, ISSN={["1558-2566"]}, DOI={10.1109/tnet.2011.2120618}, abstractNote={We report that human walks performed in outdoor settings of tens of kilometers resemble a truncated form of Levy walks commonly observed in animals such as monkeys, birds and jackals. Our study is based on about one thousand hours of GPS traces involving 44 volunteers in various outdoor settings including two different college campuses, a metropolitan area, a theme park and a state fair. This paper shows that many statistical features of human walks follow truncated power-law, showing evidence of scale-freedom and do not conform to the central limit theorem. These traits are similar to those of Levy walks. It is conjectured that the truncation, which makes the mobility deviate from pure Levy walks, comes from geographical constraints including walk boundary, physical obstructions and traffic. None of commonly used mobility models for mobile networks captures these properties. Based on these findings, we construct a simple Levy walk mobility model which is versatile enough in emulating diverse statistical patterns of human walks observed in our traces. The model is also used to recreate similar power-law inter-contact time distributions observed in previous human mobility studies. Our network simulation indicates that the Levy walk features are important in characterizing the performance of mobile network routing performance.}, number={3}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Rhee, Injong and Shin, Minsu and Hong, Seongik and Lee, Kyunghan and Kim, Seong Joon and Chong, Song}, year={2011}, month={Jun}, pages={630–643} }
 @article{ha_rhee_2011, title={Taming the elephants: New TCP slow start}, volume={55}, ISSN={["1872-7069"]}, DOI={10.1016/j.comnet.2011.01.014}, abstractNote={Standard slow start does not work well under large bandwidth-delay product (BDP) networks. We find two reasons for this problem in three popular existing operating systems: Linux, FreeBSD and Windows XP. The first reason is that heavy packet losses occur because of the exponential increase of the congestion window during standard slow start. Recovering from heavy packet losses puts extremely high loads on end systems, rendering the end systems completely unresponsive for a long period of time, and results in a long blackout period without transmission. This problem commonly occurs with all three operating systems. The second reason is that some proprietary protocol optimizations applied to slow start happen to slow down the loss recovery followed by slow start. Although improving the system bottleneck by optimizing data structures is valuable especially for addressing the processing overload with heavy packet losses, it is not effective for the prolonged loss recovery caused by proprietary optimizations. In addition, a large number of packet losses are not desirable since they waste network bandwidth and lead TCP into frequent timeouts and loss synchronization which results in under-utilization of the network. We propose a new slow start algorithm, called Hybrid Start (HyStart), that finds a “safe” exit point for slow start at which it can terminate and safely advance to the congestion avoidance phase without causing heavy packet loss. HyStart uses ACK trains and RTT delay samples to detect whether (1) the forward path is congested or (2) the current size of the congestion window has reached the available capacity of the forward path. HyStart is a plugin to TCP senders and requires no change on TCP receivers. We implement HyStart for TCP-NewReno and TCP-SACK in Linux and compare its performance with five different slow start schemes on the TCP receivers of the three different operating systems on the Internet and also in lab testbeds. Our results indicate that HyStart works consistently well under diverse network environments, including asymmetric links, wireless networks, and high and low BDP networks. Especially with different operating system receivers (Windows XP and FreeBSD), HyStart improves the start-up throughput of TCP significantly by more than 2 to 3 times and is the default slow start algorithm of CUBIC since Linux 2.6.29.}, number={9}, journal={COMPUTER NETWORKS}, author={Ha, Sangtae and Rhee, Injong}, year={2011}, month={Jun}, pages={2092–2110} }
 @article{le_rhee_2010, title={Implementation and experimental evaluation of multi-channel MAC protocols for 802.11 networks}, volume={8}, ISSN={["1570-8713"]}, DOI={10.1016/j.adhoc.2009.12.004}, abstractNote={Multi-channel MAC protocols have recently obtained considerable attention in wireless networking research because they promise to increase capacity of wireless networks significantly by exploiting multiple frequency bands. However, most of these protocols remain as pure academic interest since they only exist on paper and in simulation code but have no practical implementation. In this paper, we report lessons learned from our endeavor in which we implement three representative multi-channel MAC protocols: Asynchronous Multi-channel Coordination Protocol (AMCP), Multi-channel MAC (MMAC), and Slotted Seeded Channel Hopping (SSCH) on off-the-shelf IEEE 802.11 hardware. We explore practical impacts of these multi-channel MAC protocols and present results of our experimental performance evaluation. The major findings of our performance evaluation are: (1) all multi-channel MAC protocols underperform the original 802.11 MAC at low load, (2) all multi-channel MAC protocols give better performance than the original 802.11 MAC at medium and high load, (3) AMCP performs worst among all multi-channel MACs in one-hop and multi-hop 802.11b scenario but delivers the best performance in multi-hop 802.11a scenario, and (4) SSCH attains the best results in one-hop scenarios or at low loads but loses its effectiveness at high loads in multi-hop scenarios.}, number={6}, journal={AD HOC NETWORKS}, author={Le, Long and Rhee, Injong}, year={2010}, month={Aug}, pages={626–639} }
 @inproceedings{lee_rhee_lee_yi_chong_2010, title={Mobile data offloading: How much can WiFi deliver?}, volume={40}, number={4}, booktitle={Computer Communication Review}, author={Lee, K. and Rhee, I. and Lee, J. and Yi, Y. and Chong, S.}, year={2010}, pages={425–426} }
 @article{rhee_warrier_min_xu_2009, title={DRAND: Distributed Randomized TDMA Scheduling for Wireless Ad Hoc Networks}, volume={8}, ISSN={["1558-0660"]}, DOI={10.1109/TMC.2009.59}, abstractNote={This paper presents a distributed implementation of RAND, a randomized time slot scheduling algorithm, called DRAND. DRAND runs in O(\delta ) time and message complexity where \delta is the maximum size of a two-hop neighborhood in a wireless network while message complexity remains O(\delta ), assuming that message delays can be bounded by an unknown constant. DRAND is the first fully distributed version of RAND. The algorithm is suitable for a wireless network where most nodes do not move, such as wireless mesh networks and wireless sensor networks. We implement the algorithm in TinyOS and demonstrate its performance in a real testbed of Mica2 nodes. The algorithm does not require any time synchronization and is shown to be effective in adapting to local topology changes without incurring global overhead in the scheduling. Because of these features, it can also be used even for other scheduling problems such as frequency or code scheduling (for FDMA or CDMA) or local identifier assignment for wireless networks where time synchronization is not enforced. We further evaluate the effect of the time-varying nature of wireless links on the conflict-free property of DRAND-assigned time slots. This experiment is conducted on a 55-node testbed consisting of the more recent MicaZ sensor nodes.}, number={10}, journal={IEEE TRANSACTIONS ON MOBILE COMPUTING}, author={Rhee, Injong and Warrier, Ajit and Min, Jeongki and Xu, Lisong}, year={2009}, month={Oct}, pages={1384–1396} }
 @article{warrier_janakiraman_ha_rhee_2009, title={DiffQ: Practical Differential Backlog Congestion Control for Wireless Networks}, ISBN={["978-1-4244-3512-8"]}, ISSN={["0743-166X"]}, DOI={10.1109/infcom.2009.5061929}, abstractNote={Congestion control in wireless multi-hop networks is challenging and complicated because of two reasons. First, interference is ubiquitous and causes loss in the shared medium. Second, wireless multihop networks are characterized by the use of diverse and dynamically changing routing paths. Traditional end point based congestion control protocols are ineffective in such a setting resulting in unfairness and starvation. This paper adapts the optimal theoretical work of Tassiulas and Ephremedes on cross-layer optimization of wireless networks involving congestion control, routing and scheduling, for practical solutions to congestion control in multi-hop wireless networks. This work is the first that implements in real off-shelf radios, a differential backlog based MAC scheduling and router-assisted backpressure congestion control for multi-hop wireless networks. Our adaptation, called DiffQ, is implemented between transport and IP and supports legacy TCP and UDP applications. In a network of 46 IEEE 802.11 wireless nodes, we demonstrate that DiffQ far outperforms many previously proposed "practical" solutions for congestion control.}, journal={IEEE INFOCOM 2009 - IEEE CONFERENCE ON COMPUTER COMMUNICATIONS, VOLS 1-5}, author={Warrier, Ajit and Janakiraman, Sankararaman and Ha, Sangtae and Rhee, Injong}, year={2009}, pages={262–270} }
 @article{won_cai_eun_guo_netravali_rhee_sabnani_2009, title={Multicast Scheduling in Cellular Data Networks}, volume={8}, ISSN={["1558-2248"]}, DOI={10.1109/twc.2009.080330}, abstractNote={Multicast is an efficient means of transmitting the same content to multiple receivers while minimizing network resource usage. Applications that can benefit from multicast such as multimedia streaming and download, are now being deployed over 3G wireless data networks. Existing multicast schemes transmit data at a fixed rate that can accommodate the farthest located users in a cell. However, users belonging to the same multicast group can have widely different channel conditions. Thus existing schemes are too conservative by limiting the throughput of users close to the base station. We propose two proportional fair multicast scheduling algorithms that can adapt to dynamic channel states in cellular data networks that use time division multiplexing: Inter-group Proportional Fairness (IPF) and multicast proportional fairness (MPF). These scheduling algorithms take into account (1) reported data rate requests from users which dynamically change to match their link states to the base station, and (2) the average received throughput of each user inside its cell. This information is used by the base station to select an appropriate data rate for each group. We prove that IPF and MPF achieve proportional fairness among groups and among all users in a group inside a cell respectively. Through extensive packet-level simulations, we demonstrate that these algorithms achieve good balance between throughput and fairness among users and groups.}, number={9}, journal={IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS}, author={Won, Hyungsuk and Cai, Han and Eun, Do Young and Guo, Katherine and Netravali, Arun and Rhee, Injong and Sabnani, Krishan}, year={2009}, month={Sep}, pages={4540–4549} }
 @article{cai_eun_ha_rhee_xu_2009, title={Stochastic convex ordering for multiplicative decrease internet congestion control}, volume={53}, ISSN={["1872-7069"]}, DOI={10.1016/j.comnet.2008.10.012}, abstractNote={Window growth function for congestion control is a strong determinant of protocol behaviors, especially its second and higher-order behaviors associated with the distribution of transmission rates, its variances, and protocol stability. This paper presents a new stochastic tool, called convex ordering, that provides an ordering of any convex function of transmission rates of two multiplicative-decrease protocols and valuable insights into high-order behaviors of protocols. As the ordering determined by this tool is consistent with any convex function of rates, it can be applied to any unknown metric for protocol performance that consists of some high-order moments of transmission rates, as well as those already known such as rate variance. Using the tool, it is analyzed that a protocol with a growth function that starts off with a concave function and then switches to a convex function (e.g., an odd order function such as x3 and x5) around the maximum window size in the previous loss epoch, gives the smallest rate variation under a variety of network conditions. Among existing protocols, BIC and CUBIC have this window growth function. Experimental and simulation results confirm the analytical findings.}, number={3}, journal={COMPUTER NETWORKS}, author={Cai, Han and Eun, Do Young and Ha, Sangtae and Rhee, Injong and Xu, Lisong}, year={2009}, month={Feb}, pages={365–381} }
 @article{shin_chong_rhee_2008, title={Dual-resource TCP/AQM for processing-constrained networks}, volume={16}, ISSN={["1558-2566"]}, DOI={10.1109/TNET.2007.900415}, abstractNote={This paper examines congestion control issues for TCP flows that require in-network processing on the fly in network elements such as gateways, proxies, firewalls and even routers. Applications of these flows are increasingly abundant in the future as the Internet evolves. Since these flows require use of CPUs in network elements, both bandwidth and CPU resources can be a bottleneck and thus congestion control must deal with ldquocongestionrdquo on both of these resources. In this paper, we show that conventional TCP/AQM schemes can significantly lose throughput and suffer harmful unfairness in this environment, particularly when CPU cycles become more scarce (which is likely the trend given the recent explosive growth rate of bandwidth). As a solution to this problem, we establish a notion of dual-resource proportional fairness and propose an AQM scheme, called Dual-Resource Queue (DRQ), that can closely approximate proportional fairness for TCP Reno sources with in-network processing requirements. DRQ is scalable because it does not maintain per-flow states while minimizing communication among different resource queues, and is also incrementally deployable because of no required change in TCP stacks. The simulation study shows that DRQ approximates proportional fairness without much implementation cost and even an incremental deployment of DRQ at the edge of the Internet improves the fairness and throughput of these TCP flows. Our work is at its early stage and might lead to an interesting development in congestion control research.}, number={2}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Shin, Minsu and Chong, Song and Rhee, Injong}, year={2008}, month={Apr}, pages={435–449} }
 @inproceedings{rhee_shin_hong_lee_chong_2008, title={On the Levy-walk nature of human mobility}, booktitle={27th IEEE Conference on Computer Communications (Infocom), vols 1-5}, author={Rhee, L. and Shin, M. and Hong, S. and Lee, K. and Chong, S.}, year={2008}, pages={1597–1605} }
 @article{rhee_warrier_aia_min_sichitiu_2008, title={Z-MAC: A hybrid MAC for wireless sensor networks}, volume={16}, ISSN={["1558-2566"]}, DOI={10.1109/TNET.2007.900704}, abstractNote={This paper presents the design, implementation and performance evaluation of a hybrid MAC protocol, called Z-MAC, for wireless sensor networks that combines the strengths of TDMA and CSMA while offsetting their weaknesses. Like CSMA, Z-MAC achieves high channel utilization and low latency under low contention and like TDMA, achieves high channel utilization under high contention and reduces collision among two-hop neighbors at a low cost. A distinctive feature of Z-MAC is that its performance is robust to synchronization errors, slot assignment failures, and time-varying channel conditions; in the worst case, its performance always falls back to that of CSMA. Z-MAC is implemented in TinyOS.}, number={3}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Rhee, Injong and Warrier, Ajit and Aia, Mahesh and Min, Jeongki and Sichitiu, Mihail L.}, year={2008}, month={Jun}, pages={511–524} }
 @article{warrier_park_min_rhee_2007, title={How much energy saving does topology control offer for wireless sensor networks? - A practical study}, volume={30}, ISSN={["1873-703X"]}, DOI={10.1016/j.comcom.2007.05.019}, abstractNote={Topology control is an important feature for energy saving, and many topology control protocols have been proposed. Yet, little work has been done on quantitatively measuring practical performance gains that topology control achieves in a real sensor network. This is because many existing protocols either are too complex or make too impractical assumptions for a practical implementation and analysis. A rule of thumb or a practical upper bound on the energy saving gains achievable by topology control would assist engineers in estimating the overall energy budget of a real sensor system. This paper proposes a new topology control protocol simple enough to permit a straightforward stochastic analysis and also a real implementation in Mica2. This protocol is currently deployed in our testbed network of 42 Mica2 nodes. Our contribution is not on the novelty of this protocol but on a practical performance bound we can study using this protocol. The stochastic analysis reveals that topology control can achieve a power gain proportional to network density divided by a factor of eight to ten. Our experiment result from the real testbed tests confirms this finding. We also find a tradeoff in terms of throughput loss due to reduced density by topology control which amounts to about 50% throughput loss. These performance figures represent rough rules of thumb on energy efficiency achievable even by a very simple, unoptimized protocol.}, number={14-15}, journal={COMPUTER COMMUNICATIONS}, author={Warrier, Ajit and Park, Sangjoon and Min, Jeongki and Rhee, Injong}, year={2007}, month={Oct}, pages={2867–2879} }
 @article{ha_le_rhee_xu_2007, title={Impact of background traffic on performance of high-speed TCP variant protocols}, volume={51}, DOI={10.1016/j.comnet.2006.11.005}, abstractNote={This paper examines the effect of background traffic on the performance of existing high-speed TCP variant protocols, namely BIC-TCP, CUBIC, FAST, HSTCP, H-TCP and Scalable TCP. We demonstrate that the stability, link utilization, convergence speed and fairness of the protocols are clearly affected by the variability of flow sizes and round-trip times (RTTs), and the amount of background flows competing with high-speed flows in a bottleneck router. Our findings include: (1) the presence of background traffic with variable flow sizes and RTTs improves the fairness of most high-speed protocols, (2) all protocols except FAST and HSTCP show good intra-protocol fairness regardless of the types of background traffic, (3) HSTCP needs a larger amount of background traffic and more variable traffic than the other protocols to achieve convergence, (4) H-TCP trades stability for fairness; that is, while its fairness is good independent of background traffic types, larger variance in the flow sizes and RTTs of background flows causes the protocol to induce a higher degree of global loss synchronization among competing flows, lowering link utilization and stability, (5) FAST suffers unfairness and instability in small buffer or long delay networks regardless of background traffic types, and (6) the fairness of high-speed protocols depends more on the amount of competing background traffic rather than its rate variability. We also find that the presence of high-speed flows does not greatly reduce the bandwidth usage of background Web traffic.}, number={7}, journal={Computer Networks (Amsterdam, Netherlands : 1999)}, author={Ha, S. T. and Le, L. and Rhee, I. and Xu, L. S.}, year={2007}, pages={1748–1762} }
 @article{rhee_xu_2007, title={Limitations of equation-based congestion control}, volume={15}, ISSN={["1558-2566"]}, DOI={10.1109/TNET.2007.893883}, abstractNote={We study limitations of an equation-based congestion control protocol, called TCP-Friendly Rate Control (TFRC). It examines how the three main factors that determine TFRC throughput, namely, the TCP-friendly equation, loss event rate estimation, and delay estimation, can influence the long-term throughput imbalance between TFRC and TCP. Especially, we show that different sending rates of competing flows cause these flows to experience different loss event rates. There are several fundamental reasons why TFRC and TCP flows have different average sending rates, from the first place. Earlier work shows that the convexity of the TCP-friendly equation used in TFRC causes the sending rate difference. We report two additional reasons in this paper: 1) the convexity of 1/x where x is a loss event period and 2) different retransmission timeout period (RTO) estimations of TCP and TFRC. These factors can be the reasons for TCP and TFRC to experience initially different sending rates. But we find that the loss event rate difference due to the differing sending rates greatly amplifies the initial throughput difference; in some extreme cases, TFRC uses around 20 times more, or sometimes 10 times less, bandwidth than TCP. Despite these factors influencing the throughput difference, we also find that simple heuristics can greatly mitigate the problem.}, number={4}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Rhee, Injong and Xu, Lisong}, year={2007}, month={Aug}, pages={852–865} }
 @misc{rhee_2007, title={Methods and systems for rate-based flow control between a sender and a receiver}, volume={7,304,951}, number={2007 Dec. 4}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Rhee, I}, year={2007} }
 @article{rhee_xu_2005, title={Limitations of equation-based congestion control}, volume={35}, ISSN={["1943-5819"]}, DOI={10.1145/1090191.1080099}, abstractNote={
            We study limitations of an equation-based congestion control protocol, called TFRC (TCP Friendly Rate Control). It examines how the three main factors that determine TFRC throughput, namely, the TCP friendly equation, loss event rate estimation and delay estimation, can influence the long-term throughput imbalance between TFRC and TCP. Especially, we show that different sending rates of competing flows cause these flows to experience different loss event rates. There are several fundamental reasons why TFRC and TCP flows have different average sending rates, from the first place. Earlier work shows that the convexity of the TCP friendly equation used in TFRC causes the sending rate difference. We report two additional reasons in this paper: (1) the convexity of 1/
            x
            where
            x
            is a loss event period and (2) different RTO (retransmission timeout period) estimations of TCP and TFRC. These factors can be the reasons for TCP and TFRC to experience initially different sending rates. But we find that the loss event rate difference due to the differing sending rates greatly amplifies the initial throughput difference; in some extreme cases, TFRC uses around 20 times more, or sometimes 10 times less, bandwidth than TCP.
          }, number={4}, journal={ACM SIGCOMM COMPUTER COMMUNICATION REVIEW}, author={Rhee, I and Xu, LS}, year={2005}, month={Oct}, pages={49–60} }
 @article{martin_nilsson_rhee_2003, title={Delay-based congestion avoidance for TCP}, volume={11}, ISSN={["1558-2566"]}, DOI={10.1109/TNET.2003.813038}, abstractNote={The set of TCP congestion control algorithms associated with TCP/Reno (e.g., slow-start and congestion avoidance) have been crucial to ensuring the stability of the Internet. Algorithms such as TCP/NewReno (which has been deployed) and TCP/Vegas (which has not been deployed) represent incrementally deployable enhancements to TCP as they have been shown to improve a TCP connection's throughput without degrading performance to competing flows. Our research focuses on delay-based congestion avoidance algorithms (DCA), like TCP/Vegas, which attempt to utilize the congestion information contained in packet round-trip time (RTT) samples. Through measurement and simulation, we show evidence suggesting that a single deployment of DCA (i.e., a TCP connection enhanced with a DCA algorithm) is not a viable enhancement to TCP over high-speed paths. We define several performance metrics that quantify the level of correlation between packet loss and RTT. Based on our measurement analysis we find that although there is useful congestion information contained within RTT samples, the level of correlation between an increase in RTT and packet loss is not strong enough to allow a TCP/Sender to reliably improve throughput. While DCA is able to reduce the packet loss rate experienced by a connection, in its attempts to avoid packet loss, the algorithm will react unnecessarily to RTT variation that is not associated with packet loss. The result is degraded throughput as compared to a similar flow that does not support DCA.}, number={3}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Martin, J and Nilsson, A and Rhee, I}, year={2003}, month={Jun}, pages={356–369} }
 @article{rhee_welch_2003, title={The impact of timing knowledge on the session problem}, volume={32}, ISSN={["0097-5397"]}, DOI={10.1137/S009753979936094X}, abstractNote={The session problem is an abstraction of fundamental synchronization problems in distributed systems. It has previously been used as a test case to demonstrate the differences in the time needed to solve problems in several timing models. The goal of this paper is to compare the computational power of a family of partially synchronous models by studying the time needed to solve the session problem. Four timing parameters are considered: the maximum and minimum process step times and message delays. Timing models are obtained by considering independently whether each parameter is known (i.e., is hard-wired into the processes' code) or unknown, giving rise to four shared memory models and 16 message passing models. The models are compared based on the time complexity, measured in real time, of the session problem.This paper presents a modular proof technique for obtaining asymptotically tight bounds on the time complexity of the session problem for the four shared memory models and the 16 message passing mo...}, number={4}, journal={SIAM JOURNAL ON COMPUTING}, author={Rhee, I and Welch, JL}, year={2003}, pages={1007–1039} }
 @article{rhee_balaguru_rouskas_2002, title={MTCP: scalable TCP-like congestion control for reliable multicast}, volume={38}, ISSN={["1872-7069"]}, DOI={10.1016/s1389-1286(01)00268-7}, abstractNote={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.}, number={5}, journal={COMPUTER NETWORKS}, author={Rhee, I and Balaguru, N and Rouskas, GN}, year={2002}, month={Apr}, pages={553–575} }
 @article{ramesh_rhee_guo_2001, title={Multicast with cache (Mcache): An adaptive zero-delay video-on-demand service}, volume={11}, ISSN={["1558-2205"]}, DOI={10.1109/76.911167}, abstractNote={A closed-loop (demand-driven) approach toward video-on-demand services, called multicast cache (Mcache), is discussed. Servers use multicast to reduce their bandwidth usage by allowing multiple requests to be served with a single data stream. However, this requires clients to delay receiving the movie until the multicast starts. Using regional cache servers deployed over many strategic locations, Mcache can remove the initial playout delays of clients in multicast-based video streaming. While requests are batched together for a multicast, clients can receive the prefix of a requested movie clip from caches located in their own regions. The multicast containing the later portion of the movie can wait until the prefix is played out. While this use of regional caches has been proposed previously, the novelty of our scheme lies in that the requests coming after the multicast starts can still be batched together to be served by multicast patches without any playout delays. The use of patches was proposed before, but they are used either with unicast or with playout delays. Mcache effectively hires the idea of a multicast patch with caches to provide a truly adaptive video-on demand service whose bandwidth usage is up to par with the best known open-loop schemes under high request rates while using only minimal bandwidth under low request rates. In addition, efficient use of multicast and caches removes the need for a priori knowledge of client disk storage requirements which some of the existing schemes assume. This makes Mcache ideal for the current heterogeneous Internet environments where those parameters are hard to predict. We further propose the Segmented Mcache (SMcache) scheme which is a generalized and improved version of Mcache where the clip is partitioned into several segments in order to preserve the advantages of the original Mcache scheme with nearly the same server bandwidth requirement as the open loop schemes under high request rates.}, number={3}, journal={IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY}, author={Ramesh, S and Rhee, I and Guo, K}, year={2001}, month={Mar}, pages={440–456} }
 @article{rhee_joshi_2000, title={Error recovery for interactive video transmission over the Internet}, volume={18}, ISSN={["1558-0008"]}, DOI={10.1109/49.848254}, abstractNote={Real-time interactive video transmission in the current Internet has mediocre quality because of high packet loss rates. Loss of packets in a video frame manifests itself not only in the reduced quality of that frame but also in the propagation of that distortion to successive frames. This error propagation problem is inherent in any motion compensation-based video codec. In this paper, we present a new error recovery scheme, called recovery from error spread using continuous updates (RESCU), that effectively alleviates error propagation in the transmission of interactive video. The main benefit of the RESCU scheme is that it allows more time for transport-level recovery such as retransmission and forward error correction to succeed while effectively masking out delays in recovering lost packets without introducing any playout delays, thus making it suitable for interactive video communication. Through simulation and real Internet experiments, we study the effectiveness and limitations of our proposed techniques and compare their performance to that of existing video error recovery techniques including H.263+ (NEWPRED). The study indicates that RESCU is effective in alleviating the error spread problem and can sustain much better video quality with less bit overhead than existing video error recovery techniques under various network environments.}, number={6}, journal={IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS}, author={Rhee, I and Joshi, SR}, year={2000}, month={Jun}, pages={1033–1049} }
 @misc{rhee_2000, title={Method and systems for dynamic hybrid packet loss recovery for video transmission over lossy packet-based network}, volume={6,289,054}, number={2000 Apr 27}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Rhee, I.}, year={2000} }
 @misc{rhee_2000, title={Methods and systems for forward error correction based loss recovery for interactive video transmission}, volume={6,421,387}, number={2000 Aug 10}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Rhee, I.}, year={2000} }
 @article{rhee_martin_muthukrishnan_packwood_2000, title={Quadtree-structured variable-size block-matching motion estimation with minimal error}, volume={10}, ISSN={["1051-8215"]}, DOI={10.1109/76.825857}, abstractNote={This paper reports two efficient quadtree-based algorithms for variable-size block matching (VSBM) motion estimation. The schemes allow the dimensions of blocks to adapt to local activity within the image, and the total number of blocks in any frame can be varied while still accurately representing true motion. This permits adaptive bit allocation between the representation of displacement and residual data, and also the variation of the overall bit-rate on a frame-by-frame basis. The first algorithm computes the optimal selection of variable-sized blocks to provide the best-achievable prediction error under the fixed number of blocks for a quadtree-based VSBM technique. The algorithm employs an efficient dynamic programming technique utilizing the special structure of a quadtree. Although this algorithm is computationally intensive, it does provide a yardstick by which the performance of other more practical VSBM techniques can be measured. The second algorithm adopts a heuristic way to select variable-sized square blocks. It relies more on local motion information than on global error optimization. Experiments suggest that the effective use of local information contributes to minimizing the overall error. The result is a more computationally efficient VSBM technique than the optimal algorithm, but with a comparable prediction error.}, number={1}, journal={IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY}, author={Rhee, I and Martin, GR and Muthukrishnan, S and Packwood, RA}, year={2000}, month={Feb}, pages={42–50} }
 @misc{rhee_2000, title={System and method of error control for interactive low-bit rate video transmission}, volume={6,104,757}, number={2000 Aug. 15}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Rhee, I.}, year={2000} }
 @article{rhee_1999, title={Collaboration - Internet-style}, volume={3}, number={2}, journal={IEEE Internet Computing}, author={Rhee, I.}, year={1999}, pages={30–32} }
 @article{birman_friedman_hayden_rhee_1999, title={Middleware support for distributed multimedia and collaborative computing}, volume={29}, DOI={10.1002/(sici)1097-024x(19991210)29:14<1285::aid-spe281>3.3.co;2-n}, abstractNote={Maestro is a middleware support tool for distributed multimedia and collaborative computing applications. These applications share a common need for managing multiple subgroups while providing possibly different quality-of-service guarantees for each of these groups. Maestro's functionality maps well into these requirements, and can significantly shorten the development time of such applications. In this paper, we report on Maestro, and demonstrate its utility in implementing several multimedia and collaborative computing applications. In particular, we provide a detailed description of the implementation of IMUX, a pseudo X-server (proxy) for collaborative computing applications that is based on Maestro. Copyright © 1999 John Wiley & Sons, Ltd.}, number={14}, journal={Software, Practice & Experience}, author={Birman, K. P. and Friedman, R. and Hayden, M. and Rhee, I.}, year={1999}, pages={1285–1312} }
 @article{rhee_1998, title={A modular algorithm for resource allocation}, volume={11}, ISSN={["0178-2770"]}, DOI={10.1007/s004460050047}, number={3}, journal={DISTRIBUTED COMPUTING}, author={Rhee, I}, year={1998}, month={Aug}, pages={157–168} }
 @article{rhee_welch_1997, title={Time bounds on synchronization in a periodic distributed system}, volume={64}, ISSN={["1872-6119"]}, DOI={10.1016/S0020-0190(97)00155-5}, abstractNote={This paper studies the time required to solve the session problem in a new timing model, called the periodic model, for shared memory distributed systems. In the periodic model, each process runs at a constant unknown rate and different processes may run at different rates. Nearly matching upper and lower bounds are shown on the time complexity of the session problem in the model. These bounds indicate the inherent cost of synchronizing periodic processes in shared memory distributed systems, and the existence of time complexity gaps among the synchronous, periodic, and asynchronous timing models.}, number={2}, journal={INFORMATION PROCESSING LETTERS}, author={Rhee, I and Welch, JL}, year={1997}, month={Oct}, pages={87–93} }