Ahsan Habib - Academia.edu (original) (raw)
Papers by Ahsan Habib
![Research paper thumbnail of Oxidative DNA damage induced by HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) buffer in the presence of Au(III](https://attachments.academia-assets.com/49302638/thumbnails/1.jpg)
](Journal of Inorganic Biochemistry, 2004
Oxidative DNA damage was investigated by free radicals generated from HEPES (2-[4-(2-hydroxyethyl... more Oxidative DNA damage was investigated by free radicals generated from HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) buffer, which is widely used in biochemical or biological studies, in the presence of Au(III). The effect of free radicals on the DNA damage was ascertained by gel electrophoresis, electron spin resonance (ESR) spectroscopy and circular dichroism (CD) spectroscopy. ESR results indicated the generation of nitrogen-centered cationic free radicals from the HEPES in the presence of Au(III) which cause the DNA damage. No ESR spectra were observed for phosphate, tris(hydroxymethyl)aminomethane (Tris-HCl) and acetate buffers in the presence of Au(III) or for HEPES buffer in the presence of other metal ions such as Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) or [Au(III)(TMPyP)] 5+ and [Pd(II)(TMPyP)] 4+ , where [H 2 (TMPyP)] 4+ denotes tetrakis(1methylpyridium-4-yl)porphyrin. Consequently, no DNA damage was observed for these buffer agents (e.g., phosphate, Tris-HCl or acetate) in the presence of Au(III) or for HEPES in the presence of other metal ions or the metalloporphyrins mentioned above. No detectable inhibitory effect on the DNA damage was observed by using the typical scavengers of reactive oxygen species (ROS) Å OH, O 2 ÀÅ and H 2 O 2 . This non-inhibitory effect indicated that no reactive oxygen species were generated during the incubation of DNA with HEPES and Au(III). The drastic change in CD spectra from positive ellipticity to negative ellipticity $ at 270 nm with increasing concentration of Au(III) also indicated the significant damage of DNA. Only HEPES or Au(III) itself did not damage DNA. A mechanism for the damaging of DNA is proposed.
Inorganica Chimica Acta, 2004
The fluorescence and phosphorescence studies on the interactions of Au(III), Pt(II) and Pd(II) de... more The fluorescence and phosphorescence studies on the interactions of Au(III), Pt(II) and Pd(II) derivatives of tetrakis(1-methylpyridinium-4yl)porphyrin (H 2 (TMPyP) 4þ ) with pBluescript II plasmid DNA have been conducted at 0.1 M NaCl, pH 7.5 and 25°C
Bulletin of The Chemical Society of Japan, 2005
Gold nanoparticle formation was found from tetrachloroaurate(III) in the presence of Good's Buffe... more Gold nanoparticle formation was found from tetrachloroaurate(III) in the presence of Good's Buffers, such as 2morpholinoethanesulfonic acid (MES) and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES), which are used widely in laboratories for studies of analytical, inorganic, physical, and bio-chemistry as well as biology. The obtained gold nanoparticles were examined by Ultraviolet-Visible Spectroscopy (UV-vis), Dynamic Light Scattering (DLS) and Electrophoretic Light Scattering (ELS) in an aqueous system and by transmission electron microscopy (TEM) for particle morphologies. UV-vis spectra showed absorption maxima at 530and530 and 530and750 nm, depending on the buffer reagents and their concentration, pH, and ionic strength. The size and the surface zeta potential of the formed nanoparticles were 23 to 73 nm and À30 to À12 mV, respectively. The TEM pictures clearly indicated the formation of finely dispersed, chained, or aggregated gold nanoparticles, depending on the experimental conditions. The mechanism of gold nanoparticle formation was studied by the measurements of cyclic voltammetry (CV) and electron spin resonance (ESR). MES and HEPES showed a positive anodic peak at approximately þ800 mV vs Ag/AgCl electrode, which indicated that these buffering agents have mild reducing ability. ESR results indicated the generation of nitrogen-centered cationic free radicals from these Good's Buffers in the presence of Au(III), resulting in the formation of gold nanoparticles. A reaction mechanism is proposed.
Shareholder agreements govern the relations among shareholders in privately-held companies, such ... more Shareholder agreements govern the relations among shareholders in privately-held companies, such as joint ventures or venture capital-backed firms. We provide an economic explanation for the use of put and call options, pre-emption rights, catch-up clauses, drag-along rights, demand rights, and tag-along rights in shareholder agreements. We view these clauses as a response to a problem of dynamic, double moral hazard, whereby the value of the venture depends on ex ante investments and ex post transfers. Contract clauses i) preserve the incentives to make ex ante investments and ii) minimize ex post transfers. We extend our framework to discuss the use of other clauses, such as the option to extend the life of a business alliance. (JEL: G34).
We study the economic aspects of P2P systems. We present a cost-profit analysis of a media stream... more We study the economic aspects of P2P systems. We present a cost-profit analysis of a media streaming service deployed over a peer-to-peer (P2P) infrastructure. We consider the limited capacity as well as the heterogeneity of peers in the analysis. The analysis shows that with the appropriate incentives for participating peers, the service provider achieves more profit. In addition, the analysis shows how the service provider can maximize its revenue by controlling the amount of incentives offered to peers.
Computer Networks, 2004
Continuous monitoring of a network domain poses several challenges. First, routers of a network d... more Continuous monitoring of a network domain poses several challenges. First, routers of a network domain need to be polled periodically to collect statistics about delay, loss, and bandwidth. Second, this huge amount of data has to be mined to obtain useful monitoring information. This increases the overhead for high speed core routers, and restricts the monitoring process from scaling to a large number of flows. To achieve scalability, polling and measurements that involve core routers should be avoided. We design and evaluate a distributed monitoring scheme that uses only edge-toedge measurements, and scales well to large network domains. In our scheme, all edge routers form an overlay network with their neighboring edge routers. The network is probed intelligently from nodes in the overlay to detect congestion in both directions of a link. The proposed scheme involves only edge routers, and requires significantly fewer number of probes than existing monitoring schemes. Through analytic study and a series of experiments, we show that the proposed scheme can effectively identify the congested links. The congested links are used to capture the misbehaving flows that are violating their service level agreements, or attacking the domain by injecting excessive traffic.
Multimedia Systems, 2005
We present CollectCast, a peer-to-peer (P2P) service for media streaming where a receiver peer is... more We present CollectCast, a peer-to-peer (P2P) service for media streaming where a receiver peer is served by multiple sender peers. CollectCast operates at the application level but infers underlying network properties to correlate end-to-end connections between peers. The salient features of CollectCast include: (1) a novel multisender selection method that exploits the performance correlation and dependency among connections between different candidate senders and the receiver, (2) a customization of network tomography techniques and demonstration of improved practicality and efficiency, and (3) an aggregation-based P2P streaming mechanism that sustains receiver-side quality in the presence of sender/network dynamics and degradation. We have performed both real-world (on PlanetLab) and simulation evaluation of CollectCast. Our simulation results show that for a receiver, CollectCast makes better selection of multiple senders than other methods that do not infer underlying network properties. Our PlanetLab experiments are performed using a P2P media streaming application (called PROMISE) which we developed on top of CollectCast. Both packet-level and frame-level performance of MPEG-4 video streaming demonstrates the practicality and effectiveness of CollectCast.
We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The me... more We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The mechanism provides incentives for cooperation through service differentiation. Contributors to the system are rewarded with flexibility and choice in peer selection, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. Through simulation and wide-area measurement studies, we verify that the mechanism can provide near optimal streaming quality to the cooperative users until the bottleneck shifts from the sources to the network.
Incentive mechanisms for peer-to-peer media streaming
Abstract— We propose a rank-based peer-selection mechanism for peer-to-peer media streaming syste... more Abstract— We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The mechanism provides incentives for cooperation through service differentiation. Contributors to the system are rewarded with flexibility and choice in peer selection, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. Through simulation and wide-area
Computer Networks, 2007
An appealing solution for a networked end host to circumvent last mile congestion is to connect t... more An appealing solution for a networked end host to circumvent last mile congestion is to connect to multiple service providers simultaneously, which is known as multihoming. The differences in peering relationships among different service providers make it possible for multihomed hosts to use significantly different routes to the same destination. Therefore, multihoming can dynamically avoid points of congestion in the network by taking advantage of the choice among different routes available at any given time.
Striping is a resource aggregation technique that can improve application performance for a multi... more Striping is a resource aggregation technique that can improve application performance for a multihomed host by utilizing multiple interfaces. In this position paper, we argue in favor of decoupling striping primitives from all of the traditional layers of the networking protocol stack, and instead resurrecting the session layer for striping. Session layer striping indeed allows applications to take advantage of multihoming, while avoiding most of the deployability issues traditionally linked with modifiying application layer code. We illustrate our argument with a strawman architecture for a session layer striping protocol, and sketch how such a protocol could be implemented.
Denial of Service (DoS) attacks are a serious threat for the Internet. DoS attacks can consume me... more Denial of Service (DoS) attacks are a serious threat for the Internet. DoS attacks can consume memory, CPU, and network resources and damage or shut down the operation of the resource under attack (victim). The quality of service (QoS) enabled networks, which offer different levels of service, are vulnerable to QoS attacks as well as DoS attacks. The aim of a QoS attack is to steal network resources, e.g., bandwidth, or to degrade the service perceived by users. We present a classification and a brief explanation of the approaches used to deal with the DoS and QoS attacks. Furthermore, we propose network monitoring techniques to detect service violations and to infer DoS attacks. Finally, a quantitative comparison among all schemes is conducted, in which, we highlight the merits of each scheme and estimate the overhead (both processing and communication) introduced by it. The comparison provides guidelines for selecting the appropriate scheme, or a combination of schemes, based on the requirements and how much overhead can be tolerated.
We study the verification of data integrity during peerto-peer media streaming sessions. Challeng... more We study the verification of data integrity during peerto-peer media streaming sessions. Challenges include the timing constraint of streaming as well as the untrustworthiness of peers. We show the inadequacy of existing authentication protocols, and propose, Block-Oriented Probabilistic Verification (BOPV), an efficient protocol that utilizes message digest and probabilistic verification. We then propose One Time Digest Protocol (OTDP) and Tree-based Forward Digest Protocol (TFDP) to further reduce the communication overhead. A comprehensive comparison is presented comparing the performance of existing protocols and our protocols, with respect to overhead, security assurance level, and packet loss tolerance. Finally, simulation and wide-area experiments are conducted to evaluate the performance of our protocols.
Multihoming media streaming
Abstract Residential multihoming provides path redundancy as well as path diversiv that can be us... more Abstract Residential multihoming provides path redundancy as well as path diversiv that can be used to improve not just network availability, but also application-layer quality of service. The path diversity can be effeciively utilized by a streaming application to achieve high quality ...
We design and evaluate an adaptive traffic conditioner to improve application performance over th... more We design and evaluate an adaptive traffic conditioner to improve application performance over the differentiated services assured forwarding behavior. The conditioner is adaptive because the marking algorithm changes based upon the current number of flows traversing through an edge router. If there are a small number of flows, the conditioner maintains and uses state information to intelligently protect critical TCP packets. On the other hand, if there are many flows going through the edge router, the conditioner only uses flow characteristics as indicated in the TCP packet headers to mark without requiring per flow state. Simulation results indicate that this adaptive conditioner improves throughput of data extensive applications like large FTP transfers, and achieves low packet delays and response times for Telnet and WWW traffic.
MMS: A Multihome-aware Media Streaming System
Multihoming provides highly diverse redundant paths in terms of average hop count, latency, loss ... more Multihoming provides highly diverse redundant paths in terms of average hop count, latency, loss ratio, and jitter. In this paper, we first explore topological path diversity and show that multihoming can significantly reduce the path overlap when a multihomed receiver conducts media ...
IEEE Transactions on Multimedia, 2006
We propose a service differentiated peer selection mechanism for peer-to-peer media streaming sys... more We propose a service differentiated peer selection mechanism for peer-to-peer media streaming systems. The mechanism provides flexibility and choice in peer selection to the contributors of the system, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. The proposed incentive mechanism follows the characteristics of rank-order tournaments theory that considers only the relative performance of the players, and the top prizes are awarded to the winners of the tournament. Using rank-order tournaments, we analyze the behavior of utility maximizing users. Through simulation and wide-area measurement studies, we verify that the proposed incentive mechanism can provide near optimal streaming quality to the cooperative users until the bottleneck shifts from the streaming sources to the network.
IEEE Transactions on Knowledge and Data Engineering, 2005
We design a Tree-based Forward Digest Protocol (TFDP) to verify data integrity in distributed med... more We design a Tree-based Forward Digest Protocol (TFDP) to verify data integrity in distributed media streaming for content distribution. Several challenges arise, including the timing constraint of streaming sessions, the involvement of multiple senders, and the untrustworthiness of these senders. A comprehensive comparison is presented on the performance of existing protocols and TFDP, with respect to communication and computation overhead. Both simulation and Internet-based experimental results are presented to demonstrate the effectiveness of TFDP.
We present the design, implementation, and evaluation of PROMISE, a novel peer-to-peer media stre... more We present the design, implementation, and evaluation of PROMISE, a novel peer-to-peer media streaming system encompassing the key functions of peer lookup, peer-based aggregated streaming, and dynamic adaptations to network and peer conditions. Particularly, PROMISE is based on a new application level P2P service called CollectCast. CollectCast performs three main functions: (1) inferring and leveraging the underlying network topology and performance information for the selection of senders; (2) monitoring the status of peers and connections and reacting to peer/connection failure or degradation with low overhead; (3) dynamically switching active senders and standby senders, so that the collective network performance out of the active senders remains satisfactory. Based on both real-world measurement and simulation, we evaluate the performance of PROMISE, and discuss lessons learned from our experience with respect to the practicality and further optimization of PROMISE.
TCP connection throughput is inversely proportional to the connection Round Trip Time (RTT). To m... more TCP connection throughput is inversely proportional to the connection Round Trip Time (RTT). To mitigate TCP bias to short RTT connections, a differentiated services traffic conditioner can ensure connections with long RTTs do not starve when connections with short RTTs get all extra resources after achieving the target rates. Current proposals for RTT-aware conditioners work well for a small number of connections when most TCP connections are in the congestion avoidance phase. If there is a large number of TCP connections, however, connections time-out and go to slow start. We show that current RTT-aware conditioners over-protect long RTT flows and starve short RTT flows in this case. We design and evaluate a conditioner based on RTT as well as the Retransmission Time-out (RTO). The proposed RTT-RTO aware traffic conditioner works well for realistic situations with a large number of connections. Simulation results in a variety of situations confirm that the conditioner mitigates RTT bias.
Journal of Inorganic Biochemistry, 2004
Oxidative DNA damage was investigated by free radicals generated from HEPES (2-[4-(2-hydroxyethyl... more Oxidative DNA damage was investigated by free radicals generated from HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) buffer, which is widely used in biochemical or biological studies, in the presence of Au(III). The effect of free radicals on the DNA damage was ascertained by gel electrophoresis, electron spin resonance (ESR) spectroscopy and circular dichroism (CD) spectroscopy. ESR results indicated the generation of nitrogen-centered cationic free radicals from the HEPES in the presence of Au(III) which cause the DNA damage. No ESR spectra were observed for phosphate, tris(hydroxymethyl)aminomethane (Tris-HCl) and acetate buffers in the presence of Au(III) or for HEPES buffer in the presence of other metal ions such as Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) or [Au(III)(TMPyP)] 5+ and [Pd(II)(TMPyP)] 4+ , where [H 2 (TMPyP)] 4+ denotes tetrakis(1methylpyridium-4-yl)porphyrin. Consequently, no DNA damage was observed for these buffer agents (e.g., phosphate, Tris-HCl or acetate) in the presence of Au(III) or for HEPES in the presence of other metal ions or the metalloporphyrins mentioned above. No detectable inhibitory effect on the DNA damage was observed by using the typical scavengers of reactive oxygen species (ROS) Å OH, O 2 ÀÅ and H 2 O 2 . This non-inhibitory effect indicated that no reactive oxygen species were generated during the incubation of DNA with HEPES and Au(III). The drastic change in CD spectra from positive ellipticity to negative ellipticity $ at 270 nm with increasing concentration of Au(III) also indicated the significant damage of DNA. Only HEPES or Au(III) itself did not damage DNA. A mechanism for the damaging of DNA is proposed.
Inorganica Chimica Acta, 2004
The fluorescence and phosphorescence studies on the interactions of Au(III), Pt(II) and Pd(II) de... more The fluorescence and phosphorescence studies on the interactions of Au(III), Pt(II) and Pd(II) derivatives of tetrakis(1-methylpyridinium-4yl)porphyrin (H 2 (TMPyP) 4þ ) with pBluescript II plasmid DNA have been conducted at 0.1 M NaCl, pH 7.5 and 25°C
Bulletin of The Chemical Society of Japan, 2005
Gold nanoparticle formation was found from tetrachloroaurate(III) in the presence of Good's Buffe... more Gold nanoparticle formation was found from tetrachloroaurate(III) in the presence of Good's Buffers, such as 2morpholinoethanesulfonic acid (MES) and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES), which are used widely in laboratories for studies of analytical, inorganic, physical, and bio-chemistry as well as biology. The obtained gold nanoparticles were examined by Ultraviolet-Visible Spectroscopy (UV-vis), Dynamic Light Scattering (DLS) and Electrophoretic Light Scattering (ELS) in an aqueous system and by transmission electron microscopy (TEM) for particle morphologies. UV-vis spectra showed absorption maxima at 530and530 and 530and750 nm, depending on the buffer reagents and their concentration, pH, and ionic strength. The size and the surface zeta potential of the formed nanoparticles were 23 to 73 nm and À30 to À12 mV, respectively. The TEM pictures clearly indicated the formation of finely dispersed, chained, or aggregated gold nanoparticles, depending on the experimental conditions. The mechanism of gold nanoparticle formation was studied by the measurements of cyclic voltammetry (CV) and electron spin resonance (ESR). MES and HEPES showed a positive anodic peak at approximately þ800 mV vs Ag/AgCl electrode, which indicated that these buffering agents have mild reducing ability. ESR results indicated the generation of nitrogen-centered cationic free radicals from these Good's Buffers in the presence of Au(III), resulting in the formation of gold nanoparticles. A reaction mechanism is proposed.
Shareholder agreements govern the relations among shareholders in privately-held companies, such ... more Shareholder agreements govern the relations among shareholders in privately-held companies, such as joint ventures or venture capital-backed firms. We provide an economic explanation for the use of put and call options, pre-emption rights, catch-up clauses, drag-along rights, demand rights, and tag-along rights in shareholder agreements. We view these clauses as a response to a problem of dynamic, double moral hazard, whereby the value of the venture depends on ex ante investments and ex post transfers. Contract clauses i) preserve the incentives to make ex ante investments and ii) minimize ex post transfers. We extend our framework to discuss the use of other clauses, such as the option to extend the life of a business alliance. (JEL: G34).
We study the economic aspects of P2P systems. We present a cost-profit analysis of a media stream... more We study the economic aspects of P2P systems. We present a cost-profit analysis of a media streaming service deployed over a peer-to-peer (P2P) infrastructure. We consider the limited capacity as well as the heterogeneity of peers in the analysis. The analysis shows that with the appropriate incentives for participating peers, the service provider achieves more profit. In addition, the analysis shows how the service provider can maximize its revenue by controlling the amount of incentives offered to peers.
Computer Networks, 2004
Continuous monitoring of a network domain poses several challenges. First, routers of a network d... more Continuous monitoring of a network domain poses several challenges. First, routers of a network domain need to be polled periodically to collect statistics about delay, loss, and bandwidth. Second, this huge amount of data has to be mined to obtain useful monitoring information. This increases the overhead for high speed core routers, and restricts the monitoring process from scaling to a large number of flows. To achieve scalability, polling and measurements that involve core routers should be avoided. We design and evaluate a distributed monitoring scheme that uses only edge-toedge measurements, and scales well to large network domains. In our scheme, all edge routers form an overlay network with their neighboring edge routers. The network is probed intelligently from nodes in the overlay to detect congestion in both directions of a link. The proposed scheme involves only edge routers, and requires significantly fewer number of probes than existing monitoring schemes. Through analytic study and a series of experiments, we show that the proposed scheme can effectively identify the congested links. The congested links are used to capture the misbehaving flows that are violating their service level agreements, or attacking the domain by injecting excessive traffic.
Multimedia Systems, 2005
We present CollectCast, a peer-to-peer (P2P) service for media streaming where a receiver peer is... more We present CollectCast, a peer-to-peer (P2P) service for media streaming where a receiver peer is served by multiple sender peers. CollectCast operates at the application level but infers underlying network properties to correlate end-to-end connections between peers. The salient features of CollectCast include: (1) a novel multisender selection method that exploits the performance correlation and dependency among connections between different candidate senders and the receiver, (2) a customization of network tomography techniques and demonstration of improved practicality and efficiency, and (3) an aggregation-based P2P streaming mechanism that sustains receiver-side quality in the presence of sender/network dynamics and degradation. We have performed both real-world (on PlanetLab) and simulation evaluation of CollectCast. Our simulation results show that for a receiver, CollectCast makes better selection of multiple senders than other methods that do not infer underlying network properties. Our PlanetLab experiments are performed using a P2P media streaming application (called PROMISE) which we developed on top of CollectCast. Both packet-level and frame-level performance of MPEG-4 video streaming demonstrates the practicality and effectiveness of CollectCast.
We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The me... more We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The mechanism provides incentives for cooperation through service differentiation. Contributors to the system are rewarded with flexibility and choice in peer selection, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. Through simulation and wide-area measurement studies, we verify that the mechanism can provide near optimal streaming quality to the cooperative users until the bottleneck shifts from the sources to the network.
Incentive mechanisms for peer-to-peer media streaming
Abstract— We propose a rank-based peer-selection mechanism for peer-to-peer media streaming syste... more Abstract— We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The mechanism provides incentives for cooperation through service differentiation. Contributors to the system are rewarded with flexibility and choice in peer selection, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. Through simulation and wide-area
Computer Networks, 2007
An appealing solution for a networked end host to circumvent last mile congestion is to connect t... more An appealing solution for a networked end host to circumvent last mile congestion is to connect to multiple service providers simultaneously, which is known as multihoming. The differences in peering relationships among different service providers make it possible for multihomed hosts to use significantly different routes to the same destination. Therefore, multihoming can dynamically avoid points of congestion in the network by taking advantage of the choice among different routes available at any given time.
Striping is a resource aggregation technique that can improve application performance for a multi... more Striping is a resource aggregation technique that can improve application performance for a multihomed host by utilizing multiple interfaces. In this position paper, we argue in favor of decoupling striping primitives from all of the traditional layers of the networking protocol stack, and instead resurrecting the session layer for striping. Session layer striping indeed allows applications to take advantage of multihoming, while avoiding most of the deployability issues traditionally linked with modifiying application layer code. We illustrate our argument with a strawman architecture for a session layer striping protocol, and sketch how such a protocol could be implemented.
Denial of Service (DoS) attacks are a serious threat for the Internet. DoS attacks can consume me... more Denial of Service (DoS) attacks are a serious threat for the Internet. DoS attacks can consume memory, CPU, and network resources and damage or shut down the operation of the resource under attack (victim). The quality of service (QoS) enabled networks, which offer different levels of service, are vulnerable to QoS attacks as well as DoS attacks. The aim of a QoS attack is to steal network resources, e.g., bandwidth, or to degrade the service perceived by users. We present a classification and a brief explanation of the approaches used to deal with the DoS and QoS attacks. Furthermore, we propose network monitoring techniques to detect service violations and to infer DoS attacks. Finally, a quantitative comparison among all schemes is conducted, in which, we highlight the merits of each scheme and estimate the overhead (both processing and communication) introduced by it. The comparison provides guidelines for selecting the appropriate scheme, or a combination of schemes, based on the requirements and how much overhead can be tolerated.
We study the verification of data integrity during peerto-peer media streaming sessions. Challeng... more We study the verification of data integrity during peerto-peer media streaming sessions. Challenges include the timing constraint of streaming as well as the untrustworthiness of peers. We show the inadequacy of existing authentication protocols, and propose, Block-Oriented Probabilistic Verification (BOPV), an efficient protocol that utilizes message digest and probabilistic verification. We then propose One Time Digest Protocol (OTDP) and Tree-based Forward Digest Protocol (TFDP) to further reduce the communication overhead. A comprehensive comparison is presented comparing the performance of existing protocols and our protocols, with respect to overhead, security assurance level, and packet loss tolerance. Finally, simulation and wide-area experiments are conducted to evaluate the performance of our protocols.
Multihoming media streaming
Abstract Residential multihoming provides path redundancy as well as path diversiv that can be us... more Abstract Residential multihoming provides path redundancy as well as path diversiv that can be used to improve not just network availability, but also application-layer quality of service. The path diversity can be effeciively utilized by a streaming application to achieve high quality ...
We design and evaluate an adaptive traffic conditioner to improve application performance over th... more We design and evaluate an adaptive traffic conditioner to improve application performance over the differentiated services assured forwarding behavior. The conditioner is adaptive because the marking algorithm changes based upon the current number of flows traversing through an edge router. If there are a small number of flows, the conditioner maintains and uses state information to intelligently protect critical TCP packets. On the other hand, if there are many flows going through the edge router, the conditioner only uses flow characteristics as indicated in the TCP packet headers to mark without requiring per flow state. Simulation results indicate that this adaptive conditioner improves throughput of data extensive applications like large FTP transfers, and achieves low packet delays and response times for Telnet and WWW traffic.
MMS: A Multihome-aware Media Streaming System
Multihoming provides highly diverse redundant paths in terms of average hop count, latency, loss ... more Multihoming provides highly diverse redundant paths in terms of average hop count, latency, loss ratio, and jitter. In this paper, we first explore topological path diversity and show that multihoming can significantly reduce the path overlap when a multihomed receiver conducts media ...
IEEE Transactions on Multimedia, 2006
We propose a service differentiated peer selection mechanism for peer-to-peer media streaming sys... more We propose a service differentiated peer selection mechanism for peer-to-peer media streaming systems. The mechanism provides flexibility and choice in peer selection to the contributors of the system, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. The proposed incentive mechanism follows the characteristics of rank-order tournaments theory that considers only the relative performance of the players, and the top prizes are awarded to the winners of the tournament. Using rank-order tournaments, we analyze the behavior of utility maximizing users. Through simulation and wide-area measurement studies, we verify that the proposed incentive mechanism can provide near optimal streaming quality to the cooperative users until the bottleneck shifts from the streaming sources to the network.
IEEE Transactions on Knowledge and Data Engineering, 2005
We design a Tree-based Forward Digest Protocol (TFDP) to verify data integrity in distributed med... more We design a Tree-based Forward Digest Protocol (TFDP) to verify data integrity in distributed media streaming for content distribution. Several challenges arise, including the timing constraint of streaming sessions, the involvement of multiple senders, and the untrustworthiness of these senders. A comprehensive comparison is presented on the performance of existing protocols and TFDP, with respect to communication and computation overhead. Both simulation and Internet-based experimental results are presented to demonstrate the effectiveness of TFDP.
We present the design, implementation, and evaluation of PROMISE, a novel peer-to-peer media stre... more We present the design, implementation, and evaluation of PROMISE, a novel peer-to-peer media streaming system encompassing the key functions of peer lookup, peer-based aggregated streaming, and dynamic adaptations to network and peer conditions. Particularly, PROMISE is based on a new application level P2P service called CollectCast. CollectCast performs three main functions: (1) inferring and leveraging the underlying network topology and performance information for the selection of senders; (2) monitoring the status of peers and connections and reacting to peer/connection failure or degradation with low overhead; (3) dynamically switching active senders and standby senders, so that the collective network performance out of the active senders remains satisfactory. Based on both real-world measurement and simulation, we evaluate the performance of PROMISE, and discuss lessons learned from our experience with respect to the practicality and further optimization of PROMISE.
TCP connection throughput is inversely proportional to the connection Round Trip Time (RTT). To m... more TCP connection throughput is inversely proportional to the connection Round Trip Time (RTT). To mitigate TCP bias to short RTT connections, a differentiated services traffic conditioner can ensure connections with long RTTs do not starve when connections with short RTTs get all extra resources after achieving the target rates. Current proposals for RTT-aware conditioners work well for a small number of connections when most TCP connections are in the congestion avoidance phase. If there is a large number of TCP connections, however, connections time-out and go to slow start. We show that current RTT-aware conditioners over-protect long RTT flows and starve short RTT flows in this case. We design and evaluate a conditioner based on RTT as well as the Retransmission Time-out (RTO). The proposed RTT-RTO aware traffic conditioner works well for realistic situations with a large number of connections. Simulation results in a variety of situations confirm that the conditioner mitigates RTT bias.