Polly Huang

Advances in network simulation

Network researchers must test Internet protocols under varied conditions to determine whether they are robust and reliable. The paper discusses the Virtual Inter Network Testbed (VINT) project which has enhanced its network simulator and related software to provide several practical innovations that broaden the conditions under which researchers can evaluate network protocols.

Dynamics of IP traffic: a study of the role of variability and the impact of control

Using the ns-2-simulator to experiment with different aspects of user- or session-behaviors and network configurations and focusing on the qualitative aspects of a wavelet-based scaling analysis, we present a systematic investigation into how and why variability and feedback-control contribute to the intriguing scaling properties observed in actual Internet traces (as our benchmark data, we use measured Internet traffic from an ISP). We illustrate how variability of both user aspects and network environments (i) causes self-similar scaling behavior over large time scales, (ii) determines a more or less pronounced change in scaling behavior around a specific time scale, and (iii) sets the stage for the emergence of surprisingly rich scaling dynamics over small time scales; i.e., multifractal scaling. Moreover, our scaling analyses indicate whether or not open-loop controls such as UDP or closed-loop controls such as TCP impact the local or small-scale behavior of the traffic and how they contribute to the observed multifractal nature of measured Internet traffic. In fact, our findings suggest an initial physical explanation for why measured Internet traffic over small time scales is highly complex and suggest novel ways for detecting and identifying, for example, performance bottlenecks.This paper focuses on the qualitative aspects of a wavelet-based scaling analysis rather than on the quantitative use for which it was originally designed. We demonstrate how the presented techniques can be used for analyzing a wide range of different kinds of network-related measurements in ways that were not previously feasible. We show that scaling analysis has the ability to extract relevant information about the time-scale dynamics of Internet traffic, thereby, we hope, making these techniques available to a larger segment of the networking research community.

Quantifying Skype user satisfaction

The success of Skype has inspired a generation of peer-to-peer-based solutions for satisfactory real-time multimedia services over the Internet. However, fundamental questions, such as whether VoIP services like Skype are good enough in terms of user satisfaction,have not been formally addressed. One of the major challenges lies in the lack of an easily accessible and objective index to quantify the degree of user satisfaction.In this work, we propose a model, geared to Skype, but generalizable to other VoIP services, to quantify VoIP user satisfaction based on a rigorous analysis of the call duration from actual Skype traces. The User Satisfaction Index (USI) derived from the model is unique in that 1) it is composed by objective source-and network-level metrics, such as the bit rate, bit rate jitter, and round-trip time, 2) unlike speech quality measures based on voice signals, such as the PESQ model standardized by ITU-T, the metrics are easily accessible and computable for real-time adaptation, and 3) the model development only requires network measurements, i.e., no user surveys or voice signals are necessary. Our model is validated by an independent set of metrics that quantifies the degree of user interaction from the actual traces.

Sensor-assisted wi-fi indoor location system for adapting to environmental dynamics

Wi-Fi based indoor location systems have been shown to be both cost-effective and accurate, since they can attain meter-level positioning accuracy by using existing Wi-Fi infrastructure in the environment. However, two major technical challenges persist for current Wi-Fi based location systems, instability in positioning accuracy due to changing environmental dynamics, and the need for manual offline calibration during site survey. To address these two challenges, three environmental factors (people, doors, and humidity) that can interfere with radio signals and cause positioning inaccuracy are identified. Then, we have proposed a sensor-assisted adaptation method that employs RFID sensors and environment sensors to adapt the location systems automatically to the changing environmental dynamics. The proposed adaptation method performs online calibration to build multiple context-aware radio maps under various environmental conditions. Experiments were performed on the sensor-assisted adaptation method. The experimental results show that the proposed adaptive method can avoid adverse reduction in positioning accuracy under changing environmental dynamics.

A non-instrusive, wavelet-based approach to detecting network performance problems

The main objective of this paper is to explore how much information about the characteristics of end-to-end network paths can be inferred from relying solely on passive packet-level traces of existing traffic collected from a single tap point in the network. To this end, we show that a number of structural properties of aggregate TCP/IP packet traces reveal themselves and can be compared across different time periods and across paths of the traffic destined to different subnets by exploiting the built-in scale-localization ability of wavelets. In turn, these structural properties and the resulting comparisons suggest the feasibility of new approaches for inferring and detecting qualitative aspects of network performance in a fashion that is similar to relying on active measurements, but without disturbing or biasing the metrics of interest. To showcase the feasibility, we developed WIND, a prototype tool for Wavelet-based INference for Detecting network performance problems and illustrate its capabilities to detect anomalies in underlying network path conditions with two examples of passively measured packet traces from two different networking environments. We address and experiment with ways of validating the output of WIND and end with a discussion of the potential of full-fledged wavelet-based analysis (i.e., the ability to localize a signal in scale and time) for future measurement studies.

How sensitive are online gamers to network quality

Game-playing time is strongly related to network QoS, helping determine user satisfaction and deliver better service quality to online gamers.

Game traffic analysis: an MMORPG perspective

Online gaming is one of the most profitable businesses on the Internet. Of all the genres of online games, MMORPGs (Massive Multiplayer Online Role Playing Games) have become the most popular among network gamers, and now attract millions of users who play in an evolving virtual world simultaneously over the Internet. To gain a better understanding of game traffic and contribute to the economic well-being of the Internet, we analyze a 1356-million-packet trace from a sizeable MMORPG called ShenZhou Online. This work is, as far as we know, the first formal analysis of MMORPG server traces.We find that MMORPG and FPS (First-Person Shooting) games are similar in that they both generate small packets and require low bandwidths. In practice, the bandwidth requirement of MMORPGs is the lower of the two due to less real-time game playing. More distinctive features are the strong periodicity, temporal locality, irregularity, and self-similarity observed in MMORPG traffic. The periodicity is due to a common practice in game implementation, where game state updates are accumulated within a fixed time window before transmission. The temporal locality in game traffic is largely due to the games nature, whereby one action leads to another. The irregularity, which is unique to MMORPG traffic, is due to the diversity of the games design so that the behavior of users can vary drastically, depending on the quest at hand. The self-similarity of the aggregate traffic is due to the heavy-tailed active/idle activities of individual players. Moreover, we show that the arrival of game sessions within 1 h can be modelled by a Poisson model, while the duration of game sessions is heavy-tailed.

The diet-aware dining table: observing dietary behaviors over a tabletop surface

We are what we eat. Our everyday food choices affect our long-term and short-term health. In the traditional health care, professionals assess and weigh each individuals dietary intake using intensive labor at high cost. In this paper, we design and implement a diet-aware dining table that can track what and how much we eat. To enable automated food tracking, the dining table is augmented with two layers of weighing and RFID sensor surfaces. We devise a weight-RFID matching algorithm to detect and distinguish how people eat. To validate our diet-aware dining table, we have performed experiments, including live dining scenarios (afternoon tea and Chinese-style dinner), multiple dining participants, and concurrent activities chosen randomly. Our experimental results have shown encouraging recognition accuracy, around 80%. We believe monitoring the dietary behaviors of individuals potentially contribute to diet-aware healthcare.

Enabling large-scale simulations: selective abstraction approach to the study of multicast protocols

Due to the complexity and scale of the current Internet, large scale simulation is an increasingly important tool to evaluate network protocol design. Parallel and distributed simulation is one appropriate approach to the simulation scalability problem, but it can require expensive hardware and have high overhead. We investigate a complementary solution-simulation abstraction. Just as a custom simulator includes only details necessary for the task at hand, a general simulator can support configurable levels of detail for different simulations. We demonstrate two abstraction techniques in multicast simulations and show that they each help to gain one order of magnitude in performance. Although abstraction simulations are not identical to more detailed simulations, in many cases these differences are small and result in minimal changes in the conclusions drawn from simulations.

TUIC: enabling tangible interaction on capacitive multi-touch displays

We present TUIC, a technology that enables tangible interaction on capacitive multi-touch devices, such as iPad, iPhone, and 3Ms multi-touch displays, without requiring any hardware modifications. TUIC simulates finger touches on capacitive displays using passive materials and active modulation circuits embedded inside tangible objects, and can be used with multi-touch gestures simultaneously. TUIC consists of three approaches to sense and track objects: spatial, frequency, and hybrid (spatial plus frequency). The spatial approach, also known as 2D markers, uses geometric, multi-point touch patterns to encode object IDs. Spatial tags are straightforward to construct and are easily tracked when moved, but require sufficient spacing between the multiple touch points. The frequency approach uses modulation circuits to generate high-frequency touches to encode object IDs in the time domain. It requires fewer touch points and allows smaller tags to be built. The hybrid approach combines both spatial and frequency tags to construct small tags that can be reliably tracked when moved and rotated. We show three applications demonstrating the above approaches on iPads and 3Ms multi-touch displays.