Launching a denial of service (DoS) attack is trivial, but detection and response is a painfully slow and often a manual process. Automatic classification of attacks as single- or multi-source can help focus a response, but current packet-header-based approaches are susceptible to spoofing. This paper introduces a framework for classifying DoS attacks based on header content, transient ramp-up behavior and novel techniques such as spectral analysis. Although headers are easily forged, we show that characteristics of attack ramp-up and attack spectrum are more difficult to spoof. To evaluate our framework we monitored access links of a regional ISP detecting 80 live attacks. Header analysis identified the number of attackers in 67 attacks, while the remaining 13 attacks were classified based on ramp-up and spectral analysis. We validate our results through monitoring at a second site, controlled experiments, and simulation. We use experiments and simulation to understand the underlying reasons for the characteristics observed. In addition to helping understand attack dynamics, classification mechanisms such as ours are important for the development of realistic models of DoS traffic, can be packaged as an automated tool to aid in rapid response to attacks, and can also be used to estimate the level of DoS activity on the Internet.

MMCC, the multimedia conference control program, is a window-based tool for connection management. It serves as an application interface to a wide-area network packet teleconferencing system, in which it is used not only to orchestrate multisite conferences, but also to provide local and remote audio and video control, and to interact with other conference-oriented tools that support shared workspaces. In this paper we document the design, operation and continued evolution of MMCC. We present MMCC's general architecture model, its connection control protocol and its relationship to other system components. This discussion raises issues about configuration management and the impact of conferencing over the Internet. Finally, we discuss MMCC's influence on current directions for research in multimedia connection management, and on our efforts to design a scalable Internet teleconferencing architecture.

This memorandum is a companion document to the current version of the RTP protocol specification draft-ietf-avt-rtp-*.ftxt,psg. It discusses protocol aspects of transporting real-time services (for example, voice or video) over packet-switched networks such as the Internet. It compares and evaluates design alternatives for a real-time transport protocol, providing rationales for the design decisions made for RTP. Also covered are issues of port assignment and multicast address allocation. An appendix provides a comprehensive glossary of terms related to multimedia conferencing. This document is a product of the Audio-Video Transport working group within the Internet Engineering Task Force. Comments are solicited and should be addressed to the working group's mailing list at rem-conf@es.net and/or the author(s). INTERNET-DRAFT draft-ietf-avt-issues-02.ps May 9, 1994 Contents 1 Introduction 4 2 Goals 7 3 Services 9 3.1 Control and Data : : : : : : : : : : : : : : : : : : : : : : : : ...

In compute-intensive multimedia applications, the computer not only manipulates media, but also digests it and performs independent actions based on media content. We present a design approach that applies the programming techniques of visualization systems to the development of compute-intensive multimedia applications. We describe an implementation based on this approach, and report performance measurements that demonstrate it is practical. We conclude with a description of some applications that have been implemented and a discussion of the implications for the design and engineering of operating systems. 1 Introduction The term multimedia generally refers to the capture, storage, retrieval, and presentation of audio and video data using computers. Today's multimedia applications include online encyclopedias and video-conferencing systems. In these applications, the computer acts as a mediator between the application author and user, in the case of the online encyclopedia, or betw...

ion for Grouping and Controlling Media Streams Kurt Rothermel, Tobias Helbig University of Stuttgart, Institute of Parallel and Distributed High-Performance Systems (IPVR) Breitwiesenstraße 20-22, D-70565 Stuttgart, Germany {rothermel,helbig}@informatik.uni-stuttgart.de Abstract Synchronization plays an important role in multimedia systems at various levels of abstraction. In this paper, we propose a set of powerful abstractions for controlling and synchronizing continuous media streams in distributed environments. The proposed abstractions are based on a very general computation model, which allows media streams to be processed (i.e. produced, consumed or transformed) by arbitrarily structured networks of linked components. Further, compound components can be composed of existing ones to provide higher levels of abstractions. The clock abstraction is provided to control individual media streams, i.e. streams can be started, paused or scaled by issuing the appropriate clock operations...

Abstract–The synchronization problem for audio/visual reproduction has consumed engi-neers since the advent of recorded audio and images and the first multimedia productions. As computers have evolved to support programmed reproduction of multimedia information, the complexity but not the character or interest have changed. In the digital domain, synchro-nization problems exist due to data distribution and communications, random events caused by human-computer interaction, and general computer and communications performance limitations. This rich research domain has led to numerous approaches to the modeling and execution of multimedia synchronization scenarios. Unfortunately, these approaches are difficult to compare and evaluate due to their varied theoretical bases and modeling techniques. In this paper we develop a uniform, theoretical foundation for discussing multimedia syn-chronization and temporal specification. We propose a temporal reference framework and use it to compare existing temporal specification schemes and their relationships to multime-dia synchronization. The ensuing comparison of existing specification and synchronization techniques demonstrates the utility of the framework.

. Protocols for synchronizing data streams should be highly adaptive with regard to both changing network conditions as well as to individual user needs. The Adaptive Synchronization Protocol we are going to describe in this paper supports any type of distribution of the stream group to be synchronized. It incorporates buffer level control mechanisms allowing an immediate reaction on overflow or underflow situations. Moreover, the proposed mechanism is flexible enough to support a variety of synchronization policies and allows to switch them dynamically during presentation. Since control messages are only exchanged when the network conditions actually change, the message overhead of the protocol is very low. 1 Introduction In multimedia systems, synchronization plays an important role at several levels of abstraction. At the data stream level, synchronization relationships are defined among temporally related streams, such as a lip-sync relationship between an audio and a vi...

: Stream synchronization is widely regarded as a fundamental problem in the field of multimedia systems. Solutions to this problem can be divided into adaptive and rigid mechanisms. While rigid mechanisms are based on worst-case assumptions, adaptive ones monitor the underlying network and are able to adapt themselves to changing network conditions. In this paper, we will present an adaptive stream synchronization protocol. This protocol supports any kind of distribution of the sources and sinks of the streams to be synchronized. It is based on a buffer level control mechanism, allowing immediate corrections when the danger of a buffer overflow or underflow is recognized. Moreover, the proposed protocol is flexible enough to support a wide variety of synchronization policies, which can be dynamically changed while synchronization is in progress. Finally, the message overhead of this protocol is low because control messages are only exchanged when network conditions change. Keywords: d...

We present the architecture, technology and experimental applications of a real-time, multi-site, interactive and collaborative environment called Distributed Immersive Performance (DIP). The objective of DIP is to develop the technology for live, interactive musical performances in which the participants - subsets of musicians, the conductor and the audience - are in different physical locations and are interconnected by very high fidelity multichannel audio and video links. DIP is a specific realization of broader immersive technology - the creation of the complete aural and visual ambience that places a person or a group of people in a virtual space where they can experience events occurring at a remote site or communicate naturally regardless of their location. The DIP experimental system has interaction sites and servers in different locations on the USC campus and at several partners, including the New World Symphony of Miami Beach, FL. The sites have different types of equipment to test the effects of video and audio fidelity on the ease of use and functionality for different applications. Many sites have high-definition (HD) video or digital video (DV) quality images projected onto wide screen wall displays completely integrated with an immersive audio reproduction system for a seamless, fully three-dimensional aural environment with the correct spatial sound localization for participants. The system is capable of storage and playback of the many streams of synchronized audio and video data (immersidata), and utilizes novel protocols for the low-latency, seamless, synchronized realtime delivery of immersidata over local area networks and widearea networks such as Internet2. We discuss several recent interactive experiments using the system and many technical cha...

this paper takes both a look back and a look forward to describe research directions for this important multimedia application area.