Wu-chi Feng

GPS-based message broadcast for adaptive inter-vehicle communications

The intelligent transportation systems (ITS) use advanced communications and control technologies to improve current transportation systems. To achieve many ITS applications, the ability to exchange messages between vehicles is necessary. This is generally required as inter vehicle communication (IVC). IVC can be considered as a special case of ad hoc networks, where nodes only move along predefined road paths. We propose new broadcast protocols that make use of global positioning system (GPS) information to enhance the performance of broadcast service in IVC. The ability to efficiently broadcast messages is necessary for any communications in IVC (e.g, updating routing tables, etc). We propose two algorithms that effectively reduce the number of re-broadcast messages without affecting the number of hosts (vehicles) that receive the broadcast. The simulation results show up to several hundred percentage of bandwidth utilization improvement can be achieved by our proposed broadcast protocols.

A comparison of bandwidth smoothing techniques for the transmission of prerecorded compressed video

The transfer of prerecorded, compressed video requires multimedia services to support large fluctuations in bandwidth requirements on multiple time scales. Bandwidth smoothing techniques can reduce the burstiness of a variable-bit-rate stream by prefetching data at a series of fixed rates, simplifying the allocation of resources in video servers and the communication network. Given a fixed client-side prefetch buffer several bandwidth smoothing algorithms have been introduced that are provably optimal under certain constraints. This paper presents a collection of metrics for comparing these smoothing algorithms and evaluating their cost-performance trade-offs. Due to the scarcity of available trace data, we have constructed a video capture testbed and generated a collection of twenty full-length, motion-JPEG encoded video clips. Using these video traces and a range of client buffer sizes, we investigate the interplay between the performance metrics through simulation experiments. The results highlight the unique strengths and weaknesses of each algorithm.

GPS-based message broadcasting for inter-vehicle communication

Intelligent Transportation Systems (ITS) have become a focus for many countries. To achieve ITS, Inter Vehicle Communication (IVC) is required for the exchange and distribution of data such as congestion or emergency information. If this communication can be done without fixed infrastructure, the systems can be deployed quickly and on a larger scale. Ad hoc networking technologies are one such technology to achieve IVC. However, if generic ad hoc network solutions are applied directly to IVC, performance can degrade quickly as the system scales particularly for broadcast type messages. In this paper we propose two new broadcast protocols that reduce bandwidth required for broadcast communication by taking advantage of a vehicles highly directional movement and Global Positioning Information. To show the performance of our new protocols, we compare our approach with generic ad hoc broadcasting techniques. Our results show that it is possible to achieve several hundred percent improvement of bandwidth utilization with very slight sacrifice of reachability.

Provisioning on-line games: a traffic analysis of a busy counter-strike server

This poster describes the results of a 500 million packet trace of a popular on-line, multiplayer, game server. The results show that the traffic behavior of this heavily loaded game server is highly predictable and can be attributed to the fact that current game designs target the saturation of the narrowest, last-mile link (i.e. 56k modems). Specifically, in order to maximize the interactivity of the game itself and to provide relatively uniform experiences between players playing over different network speeds, on-line games typically fix their usage requirements in such a way as to saturate the network link of their lowest speed players. While the traffic observed is highly predictable, the trace also indicates that these on-line games provide significant challenges to current network infrastructure. As a result of synchronous game logic requiring an extreme amount of interactivity, a close look at the trace reveals the presence of large, highly periodic, bursts of small packets. With such stringent demands on interactivity, routers must be designed with enough capacity to quickly route such bursts without delay. As current routers are designed for bulk data transfers with larger packets, a significant, concentrated deployment of on-line game servers will have the potential for overwhelming current networking equipment.

Quality-adaptive media streaming by priority drop

This paper presents a general design strategy for streaming media applications in best effort computing and networking environments. Our target application is video on demand using personal computers and the Internet. In this scenario, where resource reservations and admission control mechanisms are not generally available, effective streaming must be able to adapt in a responsive and graceful manner. The design strategy we propose is based on a single simple idea, priority data dropping, or priority drop for short. We evaluate the efficacy of priority drop as an adaptation tool in the video and networking domains. Our technical contribution with respect to video is to show how to express adaptation policies and how to do priority-mapping, an automatic translation from adaptation policies to priority assignments on the basic units of video. For the networking domain, we present priority-progress streaming, a real-time best-effort streaming protocol. We have implemented and released a prototype video streaming system that incorporates priority-drop video, priority mapping, and priority-progress streaming. Our system demonstrates a simple encode once, stream anywhere model where a single video source can be streamed across a wide range of network bandwidths, on networks saturated with competing traffic, all the while maintaining real-time performance and gracefully adapting quality.

Design and implementation of network puzzles

Client puzzles have been proposed in a number of protocols as a mechanism for mitigating the effects of distributed denial of service (DDoS) attacks. In order to provide protection against simultaneous attacks across a wide range of applications and protocols, however, such puzzles must be placed at a layer common to all of them; the network layer. Placing puzzles at the IP layer fundamentally changes the service paradigm of the Internet, allowing any device within the network to push load back onto those it is servicing. An advantage of network layer puzzles over previous puzzle mechanisms is that they can be applied to all traffic from malicious clients, making it possible to defend against arbitrary attacks as well as making previously voluntary mechanisms mandatory. In this paper, we outline goals which must be met for puzzles to be deployed effectively at the network layer. We then describe the design, implementation, and evaluation of a system that meets these goals by supporting efficient, fine-grained control of puzzles at the network layer. In particular, we describe modifications to existing puzzle protocols that allow them to work at the network layer, a hint-based hash-reversal puzzle that allows for the generation and verification of fine-grained puzzles at line speed in the fast path of high-speed routers, and an iptables implementation that supports transparent deployment at arbitrary locations in the network.

Achieving faster failure detection in OSPF networks

A network running OSPF takes several tens of seconds to recover from a failure, using the current default parameter settings. The main component of this delay is the time required to detect a failure using the hello protocol. Reducing the value of the hellointerval can speed up the failure detection time. However, too small a value of the hellointerval can result in an increase in network congestion, potentially causing multiple consecutive hellos to be lost. This can lead to a false breakdown of adjacencies between routers. Such false alarms not only disrupt network traffic by causing unnecessary routing changes, but also increase the processing load on the routers, which may potentially lead to routing instability. In this paper, we investigate the following question - what is the optimal value for the hellointerval that will lead to fast failure detection in the network, while keeping occurrences of false alarms within acceptable limits? We examine the impact of both network congestion and the network topology on the optimal value for the hellointerval. Additionally, we investigate the effectiveness of faster failure detection in achieving fast failure recovery in OSPF networks.

An optimal bandwidth allocation strategy for the delivery of compressed prerecorded video

Abstract. The transportation of prerecorded, compressed video data without loss of picture quality requires the network and video servers to support large fluctuations in bandwidth requirements. Fully utilizing a client-side buffer for smoothing bandwidth requirements can limit the fluctuations in bandwidth required from the underlying network and the video-on-demand servers. This paper shows that, for a fixed-size buffer constraint, the critical bandwidth allocation technique results in plans for continuous playback of stored video that have (1) the minimum number of bandwidth increases, (2) the smallest peak bandwidth requirements, and (3) the largest minimum bandwidth requirements. In addition, this paper introduces an optimal bandwidth allocation algorithm which, in addition to the three critical bandwidth allocation properties, minimizes the total number of bandwidth changes necessary for continuous playback. A comparison between the optimal bandwidth allocation algorithm and other critical bandwidth-based algorithms using 17 full-length movie videos and 3 seminar videos is also presented.

A Survey of Application Layer Techniques for Adaptive Streaming of Multimedia

Though the integrated services model and resource reservation protocol (RSVP) provide support for quality of service, in the current Internet only best-effort traffic is widely supported. New high-speed technologies such as ATM (asynchronous transfer mode), gigabit Ethernet, fast Ethernet, and frame relay, have spurred higher user expectations. These technologies are expected to support real-time applications such as video-on-demand, Internet telephony, distance education and video-broadcasting. Towards this end, networking methods such as service classes and quality of service models are being developed. Todays Internet is a heterogeneous networking environment. In such an environment, resources available to multimedia applications vary. To adapt to the changes in network conditions, both networking techniques and application layer techniques have been proposed. In this paper, we focus on the application level techniques, including methods based on compression algorithm features, layered encoding, rate shaping, adaptive error control, and bandwidth smoothing. We also discuss operating system methods to support adaptive multimedia. Throughout the paper, we discuss how feedback from lower networking layers can be used by these application-level adaptation schemes to deliver the highest quality content.

Efficient multi-layer coding and encryption of MPEG video streams

This paper introduces a novel, light-weight video encryption algorithm that supports light-weight, multi-layered encryption. The objectives of this encryption algorithm are to reduce the total amount of data encrypted (while providing reasonable privacy and security) and to allow for the playback of the encrypted stream in the presence of network packet loss and bit-errors. The latter property allows for the easy adaptation of encrypted video over best-effort networks, such as the Internet. This algorithm partitions the stream into three layers and provides encryption on the lower two layers. An adaptive algorithm is provided that shows how to adaptively partition the video data so that the user can ensure a maximum peak signal to noise ratio in the base layer. Our results show that we can provide security by encrypting only a fraction of the data depending on the level of security the user requires.