Nischal M. Piratla

Reordering of Packets due to Multipath Forwarding - An Analysis

Increased parallelism in routers necessary to handle high link speeds and large routing tables, wireless ad hoc routing, QoS provisioning, and overlay routing, are some of the factors that lead to an increase in reordering on the Internet. Packet reordering due to packet forwarding over multiple paths is investigated. An analytical model is derived for load splitting scenarios and verified using emulated topologies. The resulting reordering is profiled using reorder density, and analyzed with respect to path delays, path probabilities and number of paths. The variation of packet displacement with delay variation and forwarding probabilities is quantified. The special case corresponding to two paths is evaluated in detail. For any load splitting, the increase in the difference in the delay between paths leads to increased reordering, making the paths with closer delay values more preferable. The model can also be applied to a single-path case where reordering is caused by wide delay variation among packets, by deriving an equivalent set of probabilities corresponding to path splitting scenario.

Overcoming the effects of correlation in packet delay measurements using inter-packet gaps

The end-to-end delay of packets in data streams is characterized with emphasis on effects due to cross traffic, sending rate and packet size. Measurements indicate that modeling delay of a packet stream with high sending rates, as a fraction of bandwidth, is difficult due to the correlations among the delay values. The correlations among inter-packet gaps (IPG) at these rates, however, are negligible. At lower sending rates, the delay correlations are negligible and the distribution of delay can be used as a delay model. We exploit the relation between delay and IPG to show that end-to-end delay can be approximated by a Markov process. Thus, a complete solution is presented for modeling delay for all sending rates. Further, a correlation estimation model is provided for delay and IPG values.

Reorder density (RD): a formal, comprehensive metric for packet reordering

The increase in link speeds, increased parallelism within routers and switches, QoS support and load balancing among links, all point to future networks with increased packet reordering. Unchecked, packet reordering will have a significant detrimental effect on the end-to-end performance, while resources required for dealing with packet reordering at routers and end-nodes will grow considerably. A formal analysis of packet reordering is carried out and Reorder Density (RD) metric is defined for measurement and characterization of packet reordering. RD captures the amount and degree of reordering, and can be used to define the reorder response of networks under stationary conditions. Properties of RD are derived, and it is shown that the reorder response of the network formed by cascading two subnets is equal to the convolution of the reorder responses of individual subnets. Packet reordering over the Internet is measured and used to validate the derivations.

A neural network based real-time gaze tracker

A real-time gaze-tracking system that estimates the users eye gaze and computes the window of focused view on a computer monitor has been developed. This artificial neural network based system can be trained and customized for an individual. Unlike existing systems in which skin color features and/or other mountable equipment are needed, this system is based on a simple non-intrusive camera mounted on the monitor. Gaze point is accurately estimated within a 1 in. on a 19-in. monitor with a CCD camera having a 640 × 480 image resolution. The system performance is independent of users forward and backward as well as upward and downward movements. The gaze-tracking system implementation and the factors affecting its performance are discussed and analyzed in detail. The features and implementation methods that make this system real-time are also explained.

On Monitoring of End-to-End Packet Reordering over the Internet

End-to-end reordering of packets on Internet is investigated. Packet streams transferred over the Internet are used to analyze the long-term and short-term trends in reordering. Reorder density (RD) is used to capture comprehensively and concisely the nature of reordering present in a stream. Simpler metrics are derived from RD for monitoring of long-term reordering trends. Reorder entropy characterizes the reordering in a stream using a single value, reflecting the fraction of packets displaced as well as the magnitude displacements. The mean displacement of packets, defined with respect to late packets, early packets or all the packets, together with the percentage of packets that are displaced can also be used for this purpose. The pros and cons of each of these for monitoring long-term trends in reordering are addressed. The measurements presented indicate that for some end-to-end links the packet reordering shows clear daily and weekly trends

Jiminy: a scalable incentive-based architecture for improving rating quality

In this paper we present the design, implementation, and evaluation of Jiminy: a framework for explicitly rewarding users who participate in reputation management systems by submitting ratings. To defend against participants who submit random or malicious ratings in order to accumulate rewards, Jiminy facilitates a probabilistic mechanism to detect dishonesty and halt rewards accordingly. Jiminys reward model and honesty detection algorithm are presented and its cluster-based implementation is described. The proposed framework is evaluated using a large sample of real-world user ratings in order to demonstrate its effectiveness. Jiminys performance and scalability are analysed through experimental evaluation. The system is shown to scale linearly with the on-demand addition of slave machines to the Jiminy cluster, allowing it to successfully process large problem spaces.

Establishing User Profiles in the MediaScout Recommender System

The MediaScout system is envisioned to function as personalized media (audio, video, print) service within mobile phones, online media portals, sling boxes, etc. The MediaScout recommender engine uses a novel stereotype-based recommendation engine. Upon the registration of new users the system must decide how to classify the new users to existing stereotypes. In this paper we present a method to achieve this classification through an anytime, interactive questionnaire, created automatically upon the generation of new stereotypes. A comparative study performed on the IMDB database illustrates the advantages of the new system

On reorder density and its application to characterization of packet reordering

A formal approach for characterizing, evaluating and modeling packet reordering is presented. Reordering is, a phenomenon that is likely to become increasingly common on the Internet, and it can have an adverse impact on end-to-end performance and network resource utilization. Reorder density (RD) is a comprehensive metric for reordering. Several properties of RD are presented that provide insight into the nature of reordering present in a sequence. Based on measurements of packet reordering, certain basic patterns of reordering that are prevalent on the Internet are identified. By focusing on these basic patterns, a model is developed for reordering in networks involving two parallel paths, using a simple load-balancing scenario as an example. The model is verified using an emulation testbed

On Growth of Parallelism within Routers and Its Impact on Packet Reordering

The network link speeds increase at a higher rate compared to processing speeds. This coupled with the increase in size of router tables demand higher levels of parallelism within router hardware. However, such parallelism introduces unintended consequences that potentially may negate some of the performance gains provided by the improved technology. The growth trends of computing speeds, link speeds, and routing table sizes are used to evaluate one such consequence, packet reordering within routers. Results presented show the trends related to the degree of hardware parallelism and packet reordering.

Reducing the effects of cross traffic in packet-pair based bottleneck capacity measurements

The accuracy of the currently available bottleneck capacity measurement tools that use the packet pair technique is significantly affected by cross traffic and queuing delays. The impact of these factors is investigated, and a new technique is presented to overcome these effects by estimating the jitter based on packets sent around the same time as the packet pair. A tool based on this principle, Captool, measures the end-to-end bottleneck capacity by reducing these adverse effects, thereby increasing the accuracy of the end-to-end measurements.