Loss-pair measurement was proposed a decade ago for discovering network path properties, such as ... more Loss-pair measurement was proposed a decade ago for discovering network path properties, such as a router's buffer size. A packet pair is regarded as a loss pair if exactly one packet is lost. Therefore, the residual packet's delay can be used to infer the lost packet's delay. Despite this unique advantage shared by no other methods, no loss-pair measurement in actual networks has ever been reported. In this paper, we further develop the loss-pair measurement and make the following contributions. First, we characterize the residual packet's delay by including other important factors (such as the impact of the first packet in the pair) which were ignored before. Second, we employ a novel TCP-based probing method to measure from a single endpoint all four possible loss pairs for a round-trip network path. Third, we conducted loss-pair measurement for 88 round-trip paths continuously for almost three weeks. Being the first set of loss-pair measurement, we obtained a number of original results, such as prevalence of loss pairs, distribution of different types of loss pairs, and effect of route change on the paths' congestion state.
In this paper, we propose Cloak—a new class of reliable timing channels—which is fundamentally di... more In this paper, we propose Cloak—a new class of reliable timing channels—which is fundamentally different from other timing channels in several aspects. First, Cloak encodes a message by a unique distribution of N packets over X TCP flows. The combinatorial nature of the encoding methods increases the channel capacity largely with (N,X). Second, Cloak offers ten different encoding and decoding methods, each of which has a unique tradeoff among several important considerations, such as channel capacity and the need for packet marking. Third, the packet transmissions modulated by Cloak could be carefully crafted to mimic the normal TCP flows in a typical TCP-based application session. Although Cloak’s basic idea is simple, we show in this paper how we tackle a number of challenging issues systematically. Our experiment results collected from PlanetLab nodes and a test bed suggest that Cloak is feasible under various network conditions and different round-trip delays.
International Journal of Radiation Oncology Biology Physics, 1998
To evaluate the efficacy of intraarterial 90yttrium (90Y) microspheres in nonresectable hepatocel... more To evaluate the efficacy of intraarterial 90yttrium (90Y) microspheres in nonresectable hepatocellular carcinoma (HCC). Patients with nonresectable HCC, but without extrahepatic disease, who also had lung shunting < 15% and tumor-to-normal ratio > or =2, as determined by simulation using (99m)technetium macroaggregated albumin, were entered into the study. The radiation dose delivered to the lungs, tumor, and normal liver was estimated by a partition model. 90Y microspheres were infused into the hepatic artery at the time of hepatic angiography or through an implanted arterial portacatheter under fluoroscopy. Repeated treatments were given for residual or recurrent tumor. Response to treatment was monitored by serum alpha-fetoprotein or ferritin levels, together with serial computed tomography. Seventy-one patients, including 20 patients with postoperative recurrence, were initially treated with an activity of 0.8 to 5.0 Giga-Becquerel (GBq) (21.6-135.1 mCi) (median 3.0 GBq or 81.1 mCi) of 90Y microspheres. There was a 50% reduction in tumor volume in 19 (26.7%) patients after the first treatment. However, the overall objective response in terms of changes in alpha-fetoprotein levels was 89% [partial response (PR) 67%, complete response (CR) 22%] among the 46 patients with raised pretreatment levels. The serum ferritin level in the other 25 patients dropped by 34 to 99% after treatment. Treatment was repeated in 15 patients. The maximum number of treatments was 5 and the maximum total activity was 13.0 GBq (351.4 mCi), given in 3 treatments. The estimated radiation doses to the nontumorous liver ranged from 25 to 136 Gy (median 52 Gy) in the first treatment and the highest total radiation dose was estimated to be 324 Gy. For the tumors, the estimated radiation doses ranged from 83 to 748 Gy (median 225 Gy) in the initial treatment and the highest cumulative dose reached was 1580 Gy. The residual tumors were resected in 4 patients. Two of these had complete histological remission, but only occasional viable tumor cells were found in the necrotic centers of the tumors resected from the other 2 patients. The median survival of the 71 patients was 9.4 months (range 1.8 to 46.4 months). Treatment was well tolerated and there was no bone-marrow toxicity, or clinical evidence of radiation hepatitis or pneumonitis. Selective internal radiation therapy using 90Y microspheres is effective for selected cases of nonresectable HCC and is well tolerated. The objective response rate in terms of drop in tumor marker levels is higher than that based on reduction in tumor volume shown by computed tomography. The nontumorous liver appears more tolerant to internal radiation than external beam radiation. Selective internal radiation treatment may convert nonresectable tumors to resectable ones.
On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave cl... more On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave clouds downstream of the Rocky mountains. Wave morphology was deduced by applying linear perturbation theory to in-situ measurements of the Meteorological Measurement System (MMS) and remotely sensed isentrope profiles of the Micro-wave Temperature Profiler (MTP). Vertical winds from the MMS were consistent with updraft velocities derived from air parcel displacements estimated from the MTP. Derived wave characteristics and co61ing rates are useful inputs to cloud microphysics models.
Successional patterns are dependent on the nature of the substratum, water flow, concentrations o... more Successional patterns are dependent on the nature of the substratum, water flow, concentrations of organics as well as the availability of bacteria, algal spores and invertebrate larvae in the coastal environment. Bacteria play an especially important role in biofilm formation as they are generally the earliest colonizers. In the present study, both winter and summer biofilm succession patterns were examined on glass coverslips inverted on experimental racks attached at two tidal levels on a sheltered shore in Hong Kong. In the succession, bacteria were followed by diatoms and cyanobacteria. Encrusting algae appeared in the late stages of the experiment (day 80 in summer and day 60 in winter). Colonization by bacteria was much slower in summer and their density remained low throughout the experimental period. The first appearance of diatoms and cyanobacteria, however, was more rapid in the summer. Bacteria and diatoms on the low-shore surfaces also had a faster succession rate than on the high-shore surfaces, suggesting that desiccation/aerial temperature are the causal factors for such differences.
This article presents a summary overview of a recently completed, 12-month duration programme to ... more This article presents a summary overview of a recently completed, 12-month duration programme to deploy TRIZ-based tools in a number of companies in Hong Kong and China.
Exploiting packets' timing information for covert communication in the Internet has been explored... more Exploiting packets' timing information for covert communication in the Internet has been explored by several network timing channels and watermarking schemes. Several of them embed covert information in the inter-packet delay. These channels, however, can be detected based on the perturbed traffic pattern, and their decoding accuracy could be degraded by jitter, packet loss and packet reordering events. In this paper, we propose a novel TCP-based timing channel, named TCP-Script to address these shortcomings. TCPScript embeds messages in "normal" TCP data bursts and exploits TCP's feedback and reliability service to increase the decoding accuracy. Our theoretical capacity analysis and extensive experiments have shown that TCPScript offers much higher channel capacity and decoding accuracy than an IP timing channel and Jit-terBug. On the countermeasure, we have proposed three new metrics to detect aggressive TCPScript channels.
In the current Internet landscape, a stub autonomous system (AS) could choose from a number of pr... more In the current Internet landscape, a stub autonomous system (AS) could choose from a number of providers and peers to advertise its routes. However, the route selection may not always result in a best choice in terms of end-to-end path performance. Instead of having an AS to monitor all possible paths, we argue that it is much more effective and beneficial for a number of neighboring ASes to cooperate in the path measurement. In this paper, we present a neighbor-cooperative measurement system in which each participating AS conducts measurement using their current routes for the same set of remote endpoints. A collation of the measurement results can help identify and correct poor routes, compare different providers' network services, and diagnose network performance problems. We report measurement results from an actual deployment involving eight neighboring universities for over a year.
Monitoring network services and diagnosing their problems often require active probing methods. C... more Monitoring network services and diagnosing their problems often require active probing methods. Current probing methods, however, are becoming unreliable, because of interferences from various middleboxes, and inadequate due to their limited path metrics support. In this paper, we present the design and implementation of OneProbe, a new TCP probing method for reliable and metric-rich path monitoring. We have implemented HTTP/OneProbe (i.e., OneProbe for HTTP) which sends TCP data probes containing legitimate HTTP requests to induce HTTP responses for path measurement. Since the probing method is based on TCP's basic data transmission mechanisms, OneProbe works correctly on all major operating systems and web server software, and on 93% of the 37,874 websites randomly selected from the Internet. We also successfully deployed HTTP/OneProbe to monitor a number of network paths for over a month and obtained interesting and useful measurement results.
lyzed for the last few years. However, the analysis usually assumed that routers and TCP flows ar... more lyzed for the last few years. However, the analysis usually assumed that routers and TCP flows are not under any network attacks. In this paper, we investigate how the performance of TCP flows is affected by denial-of-service (DoS) attacks under the Drop Tail and various AQM schemes. In particular, we consider two types of DoS attacks-the traditional flooding-based DoS (FDDoS) attacks and the recently proposed Pulsing DoS (PDoS) attacks. Both analytical and simulation results support that the PDoS attacks are more effective than the FDDoS attacks under the same average attack rate. Moreover, the Drop Tail surprisingly outperforms the RED-like AQMs when the router is under a PDoS attack, whereas the RED-like AQMs perform better under a severe FDDoS attack. On the other hand, the Adaptive Virtual Queue algorithm can retain a higher TCP throughput during PDoS attacks as compared with the RED-like AQMs.
The central Rocky Mountain region of North America lies at the biogeographic crossroads of the Ro... more The central Rocky Mountain region of North America lies at the biogeographic crossroads of the Rocky Mountains, Great Plains, and Great Basin. Here, we examine genetic patterns in an abundant, widely distributed, and ecologically important rodent species, the long-tailed vole (Microtus longicaudus), across this climatically and tectonically dynamic landscape. We examine patterns of genetic diversity in relation to the species' overall phylogeographic distribution using mitochondrial cytochrome-b sequences from modern, historic, ancient, and published samples. Our analyses reveal extensive genetic diversity in the central Rockies, a lack of population structure, and a lack of concordance between genetic and morphological subspecies distributions. Patterns of genetic variation in late-Holocene and modern populations are similar. We conclude that geographical features such as the Continental Divide, previously isolated glacial cover, and major rivers do not result in persistent genetic structure within the long-tailed vole. We also conclude that the central Rocky Mountain region is a zone of secondary contact for divergent mitochondrial lineages of the long-tailed vole.
International Journal on Interactive Design and Manufacturing (ijidem), 2007
Port container terminal operation requires a skill workforce who participates in performing a num... more Port container terminal operation requires a skill workforce who participates in performing a number major operation including container loading/unloading, task planning, scheduling of terminal resources, operating of crane systems, etc. in a highly coordinated manner. To facilitate the optimal design of terminal operation for both management and operators, and to provide a flexible environment for operator training and skill evaluation, a real-time distributed virtual environment that simulates container terminal operation is developed. The system includes an imseCAVE, which is a low cost fully immersive virtual reality system developed at the University of Hong Kong, together with several network computers that are linked to the imseCAVE for remote control and monitoring of terminal operations, and providing user interfaces that simulate the planning systems for terminal operations. The simulator recreates a vivid terminal operating environment that is found useful for both teaching and research in logistics and other related fields.
The accuracy and speed of path capacity measurement could be seriously affected by the presence o... more The accuracy and speed of path capacity measurement could be seriously affected by the presence of cross traffic on the path. In this paper, we propose a new cross-traffic filtering method called minimum delay difference (MDDIF). Unlike the classic packet-pair dispersion techniques, the MDDIF method can obtain accurate capacity estimate from the minimal possible delay of packets from different packet pairs. We have proved that the MDDIF method is correct and that it takes less time to obtain accurate samples than the minimum delay sum (MDSUM) method. We also present analytical and measurement results to evaluate the MDDIF method and to compare its performance with the MDSUM method.
On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave cl... more On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave clouds downstream of the Rocky mountains. Wave morphology was deduced by applying linear perturbation theory to in-situ measurements of the Meteorological Measurement System (MMS) and remotely sensed isentrope profiles of the Micro-wave Temperature Profiler (MTP). Vertical winds from the MMS were consistent with updraft velocities derived from air parcel displacements estimated from the MTP. Derived wave characteristics and cooling rates are useful inputs to cloud microphysics models.
Strifeshadow Fantasy (SSF) is a massive, multiplayer online, role-playing game. Players of this g... more Strifeshadow Fantasy (SSF) is a massive, multiplayer online, role-playing game. Players of this game, acting as avatars, search for the ancient signs, and their goals are to defeat the God of Destruction. Players can adventure in the game alone or co-operate with the others through the chat box. SSF is available for free and there are currently more than 10,000 registered users. In this article, we highlight the overall software architecture of SSF, which is based on a simple server-client model and HTTP. We will also describe in details two problems encountered in the course of designing SSF and the solutions to them. The first one is a local state consistency problem which is to ensure that each client participating in the game will eventually receive all the state updates once and only once. The second one is a connection jamming problem that is a result of using nonpersistent HTTP connections for the communication between the game server and clients.
In this paper, we present preliminary results of measuring TCP data-path quality using a new meas... more In this paper, we present preliminary results of measuring TCP data-path quality using a new measurement tool called OneProbe. Unlike the existing tools, OneProbe uses legitimate TCP data probes to profile TCP data-path quality by sampling round-trip delay, one-way loss rate, and one-way reordering rate at the same time. This paper presents a set of recent measurement studies on a set of web servers hosting the Beijing Olympic Games in China and Hong Kong.
Loss-pair measurement was proposed a decade ago for discovering network path properties, such as ... more Loss-pair measurement was proposed a decade ago for discovering network path properties, such as a router's buffer size. A packet pair is regarded as a loss pair if exactly one packet is lost. Therefore, the residual packet's delay can be used to infer the lost packet's delay. Despite this unique advantage shared by no other methods, no loss-pair measurement in actual networks has ever been reported. In this paper, we further develop the loss-pair measurement and make the following contributions. First, we characterize the residual packet's delay by including other important factors (such as the impact of the first packet in the pair) which were ignored before. Second, we employ a novel TCP-based probing method to measure from a single endpoint all four possible loss pairs for a round-trip network path. Third, we conducted loss-pair measurement for 88 round-trip paths continuously for almost three weeks. Being the first set of loss-pair measurement, we obtained a number of original results, such as prevalence of loss pairs, distribution of different types of loss pairs, and effect of route change on the paths' congestion state.
In this paper, we propose Cloak—a new class of reliable timing channels—which is fundamentally di... more In this paper, we propose Cloak—a new class of reliable timing channels—which is fundamentally different from other timing channels in several aspects. First, Cloak encodes a message by a unique distribution of N packets over X TCP flows. The combinatorial nature of the encoding methods increases the channel capacity largely with (N,X). Second, Cloak offers ten different encoding and decoding methods, each of which has a unique tradeoff among several important considerations, such as channel capacity and the need for packet marking. Third, the packet transmissions modulated by Cloak could be carefully crafted to mimic the normal TCP flows in a typical TCP-based application session. Although Cloak’s basic idea is simple, we show in this paper how we tackle a number of challenging issues systematically. Our experiment results collected from PlanetLab nodes and a test bed suggest that Cloak is feasible under various network conditions and different round-trip delays.
International Journal of Radiation Oncology Biology Physics, 1998
To evaluate the efficacy of intraarterial 90yttrium (90Y) microspheres in nonresectable hepatocel... more To evaluate the efficacy of intraarterial 90yttrium (90Y) microspheres in nonresectable hepatocellular carcinoma (HCC). Patients with nonresectable HCC, but without extrahepatic disease, who also had lung shunting < 15% and tumor-to-normal ratio > or =2, as determined by simulation using (99m)technetium macroaggregated albumin, were entered into the study. The radiation dose delivered to the lungs, tumor, and normal liver was estimated by a partition model. 90Y microspheres were infused into the hepatic artery at the time of hepatic angiography or through an implanted arterial portacatheter under fluoroscopy. Repeated treatments were given for residual or recurrent tumor. Response to treatment was monitored by serum alpha-fetoprotein or ferritin levels, together with serial computed tomography. Seventy-one patients, including 20 patients with postoperative recurrence, were initially treated with an activity of 0.8 to 5.0 Giga-Becquerel (GBq) (21.6-135.1 mCi) (median 3.0 GBq or 81.1 mCi) of 90Y microspheres. There was a 50% reduction in tumor volume in 19 (26.7%) patients after the first treatment. However, the overall objective response in terms of changes in alpha-fetoprotein levels was 89% [partial response (PR) 67%, complete response (CR) 22%] among the 46 patients with raised pretreatment levels. The serum ferritin level in the other 25 patients dropped by 34 to 99% after treatment. Treatment was repeated in 15 patients. The maximum number of treatments was 5 and the maximum total activity was 13.0 GBq (351.4 mCi), given in 3 treatments. The estimated radiation doses to the nontumorous liver ranged from 25 to 136 Gy (median 52 Gy) in the first treatment and the highest total radiation dose was estimated to be 324 Gy. For the tumors, the estimated radiation doses ranged from 83 to 748 Gy (median 225 Gy) in the initial treatment and the highest cumulative dose reached was 1580 Gy. The residual tumors were resected in 4 patients. Two of these had complete histological remission, but only occasional viable tumor cells were found in the necrotic centers of the tumors resected from the other 2 patients. The median survival of the 71 patients was 9.4 months (range 1.8 to 46.4 months). Treatment was well tolerated and there was no bone-marrow toxicity, or clinical evidence of radiation hepatitis or pneumonitis. Selective internal radiation therapy using 90Y microspheres is effective for selected cases of nonresectable HCC and is well tolerated. The objective response rate in terms of drop in tumor marker levels is higher than that based on reduction in tumor volume shown by computed tomography. The nontumorous liver appears more tolerant to internal radiation than external beam radiation. Selective internal radiation treatment may convert nonresectable tumors to resectable ones.
On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave cl... more On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave clouds downstream of the Rocky mountains. Wave morphology was deduced by applying linear perturbation theory to in-situ measurements of the Meteorological Measurement System (MMS) and remotely sensed isentrope profiles of the Micro-wave Temperature Profiler (MTP). Vertical winds from the MMS were consistent with updraft velocities derived from air parcel displacements estimated from the MTP. Derived wave characteristics and co61ing rates are useful inputs to cloud microphysics models.
Successional patterns are dependent on the nature of the substratum, water flow, concentrations o... more Successional patterns are dependent on the nature of the substratum, water flow, concentrations of organics as well as the availability of bacteria, algal spores and invertebrate larvae in the coastal environment. Bacteria play an especially important role in biofilm formation as they are generally the earliest colonizers. In the present study, both winter and summer biofilm succession patterns were examined on glass coverslips inverted on experimental racks attached at two tidal levels on a sheltered shore in Hong Kong. In the succession, bacteria were followed by diatoms and cyanobacteria. Encrusting algae appeared in the late stages of the experiment (day 80 in summer and day 60 in winter). Colonization by bacteria was much slower in summer and their density remained low throughout the experimental period. The first appearance of diatoms and cyanobacteria, however, was more rapid in the summer. Bacteria and diatoms on the low-shore surfaces also had a faster succession rate than on the high-shore surfaces, suggesting that desiccation/aerial temperature are the causal factors for such differences.
This article presents a summary overview of a recently completed, 12-month duration programme to ... more This article presents a summary overview of a recently completed, 12-month duration programme to deploy TRIZ-based tools in a number of companies in Hong Kong and China.
Exploiting packets' timing information for covert communication in the Internet has been explored... more Exploiting packets' timing information for covert communication in the Internet has been explored by several network timing channels and watermarking schemes. Several of them embed covert information in the inter-packet delay. These channels, however, can be detected based on the perturbed traffic pattern, and their decoding accuracy could be degraded by jitter, packet loss and packet reordering events. In this paper, we propose a novel TCP-based timing channel, named TCP-Script to address these shortcomings. TCPScript embeds messages in "normal" TCP data bursts and exploits TCP's feedback and reliability service to increase the decoding accuracy. Our theoretical capacity analysis and extensive experiments have shown that TCPScript offers much higher channel capacity and decoding accuracy than an IP timing channel and Jit-terBug. On the countermeasure, we have proposed three new metrics to detect aggressive TCPScript channels.
In the current Internet landscape, a stub autonomous system (AS) could choose from a number of pr... more In the current Internet landscape, a stub autonomous system (AS) could choose from a number of providers and peers to advertise its routes. However, the route selection may not always result in a best choice in terms of end-to-end path performance. Instead of having an AS to monitor all possible paths, we argue that it is much more effective and beneficial for a number of neighboring ASes to cooperate in the path measurement. In this paper, we present a neighbor-cooperative measurement system in which each participating AS conducts measurement using their current routes for the same set of remote endpoints. A collation of the measurement results can help identify and correct poor routes, compare different providers' network services, and diagnose network performance problems. We report measurement results from an actual deployment involving eight neighboring universities for over a year.
Monitoring network services and diagnosing their problems often require active probing methods. C... more Monitoring network services and diagnosing their problems often require active probing methods. Current probing methods, however, are becoming unreliable, because of interferences from various middleboxes, and inadequate due to their limited path metrics support. In this paper, we present the design and implementation of OneProbe, a new TCP probing method for reliable and metric-rich path monitoring. We have implemented HTTP/OneProbe (i.e., OneProbe for HTTP) which sends TCP data probes containing legitimate HTTP requests to induce HTTP responses for path measurement. Since the probing method is based on TCP's basic data transmission mechanisms, OneProbe works correctly on all major operating systems and web server software, and on 93% of the 37,874 websites randomly selected from the Internet. We also successfully deployed HTTP/OneProbe to monitor a number of network paths for over a month and obtained interesting and useful measurement results.
lyzed for the last few years. However, the analysis usually assumed that routers and TCP flows ar... more lyzed for the last few years. However, the analysis usually assumed that routers and TCP flows are not under any network attacks. In this paper, we investigate how the performance of TCP flows is affected by denial-of-service (DoS) attacks under the Drop Tail and various AQM schemes. In particular, we consider two types of DoS attacks-the traditional flooding-based DoS (FDDoS) attacks and the recently proposed Pulsing DoS (PDoS) attacks. Both analytical and simulation results support that the PDoS attacks are more effective than the FDDoS attacks under the same average attack rate. Moreover, the Drop Tail surprisingly outperforms the RED-like AQMs when the router is under a PDoS attack, whereas the RED-like AQMs perform better under a severe FDDoS attack. On the other hand, the Adaptive Virtual Queue algorithm can retain a higher TCP throughput during PDoS attacks as compared with the RED-like AQMs.
The central Rocky Mountain region of North America lies at the biogeographic crossroads of the Ro... more The central Rocky Mountain region of North America lies at the biogeographic crossroads of the Rocky Mountains, Great Plains, and Great Basin. Here, we examine genetic patterns in an abundant, widely distributed, and ecologically important rodent species, the long-tailed vole (Microtus longicaudus), across this climatically and tectonically dynamic landscape. We examine patterns of genetic diversity in relation to the species' overall phylogeographic distribution using mitochondrial cytochrome-b sequences from modern, historic, ancient, and published samples. Our analyses reveal extensive genetic diversity in the central Rockies, a lack of population structure, and a lack of concordance between genetic and morphological subspecies distributions. Patterns of genetic variation in late-Holocene and modern populations are similar. We conclude that geographical features such as the Continental Divide, previously isolated glacial cover, and major rivers do not result in persistent genetic structure within the long-tailed vole. We also conclude that the central Rocky Mountain region is a zone of secondary contact for divergent mitochondrial lineages of the long-tailed vole.
International Journal on Interactive Design and Manufacturing (ijidem), 2007
Port container terminal operation requires a skill workforce who participates in performing a num... more Port container terminal operation requires a skill workforce who participates in performing a number major operation including container loading/unloading, task planning, scheduling of terminal resources, operating of crane systems, etc. in a highly coordinated manner. To facilitate the optimal design of terminal operation for both management and operators, and to provide a flexible environment for operator training and skill evaluation, a real-time distributed virtual environment that simulates container terminal operation is developed. The system includes an imseCAVE, which is a low cost fully immersive virtual reality system developed at the University of Hong Kong, together with several network computers that are linked to the imseCAVE for remote control and monitoring of terminal operations, and providing user interfaces that simulate the planning systems for terminal operations. The simulator recreates a vivid terminal operating environment that is found useful for both teaching and research in logistics and other related fields.
The accuracy and speed of path capacity measurement could be seriously affected by the presence o... more The accuracy and speed of path capacity measurement could be seriously affected by the presence of cross traffic on the path. In this paper, we propose a new cross-traffic filtering method called minimum delay difference (MDDIF). Unlike the classic packet-pair dispersion techniques, the MDDIF method can obtain accurate capacity estimate from the minimal possible delay of packets from different packet pairs. We have proved that the MDDIF method is correct and that it takes less time to obtain accurate samples than the minimum delay sum (MDSUM) method. We also present analytical and measurement results to evaluate the MDDIF method and to compare its performance with the MDSUM method.
On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave cl... more On two days during SUCCESS, the NASA DC-8 flew carefully designed flight tracks to sample wave clouds downstream of the Rocky mountains. Wave morphology was deduced by applying linear perturbation theory to in-situ measurements of the Meteorological Measurement System (MMS) and remotely sensed isentrope profiles of the Micro-wave Temperature Profiler (MTP). Vertical winds from the MMS were consistent with updraft velocities derived from air parcel displacements estimated from the MTP. Derived wave characteristics and cooling rates are useful inputs to cloud microphysics models.
Strifeshadow Fantasy (SSF) is a massive, multiplayer online, role-playing game. Players of this g... more Strifeshadow Fantasy (SSF) is a massive, multiplayer online, role-playing game. Players of this game, acting as avatars, search for the ancient signs, and their goals are to defeat the God of Destruction. Players can adventure in the game alone or co-operate with the others through the chat box. SSF is available for free and there are currently more than 10,000 registered users. In this article, we highlight the overall software architecture of SSF, which is based on a simple server-client model and HTTP. We will also describe in details two problems encountered in the course of designing SSF and the solutions to them. The first one is a local state consistency problem which is to ensure that each client participating in the game will eventually receive all the state updates once and only once. The second one is a connection jamming problem that is a result of using nonpersistent HTTP connections for the communication between the game server and clients.
In this paper, we present preliminary results of measuring TCP data-path quality using a new meas... more In this paper, we present preliminary results of measuring TCP data-path quality using a new measurement tool called OneProbe. Unlike the existing tools, OneProbe uses legitimate TCP data probes to profile TCP data-path quality by sampling round-trip delay, one-way loss rate, and one-way reordering rate at the same time. This paper presents a set of recent measurement studies on a set of web servers hosting the Beijing Olympic Games in China and Hong Kong.
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