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.

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Advances in network simulation

"Access is the killer app" is the vision of the Daedalus project at UC Berkeley. Being able to be connected seamlessly anytime anywhere to the best network still remains an unfulfilled goal. Often, even determining the "best" network is a challenging task because of the widespread deployment of overlapping wireless networks. We describe a policy-enabled handoff system that allows users to express policies on what is the "best" wireless system at any moment, and make tradeoffs among network characteristics and dynamics such as cost, performance and power consumption. We designed a performance reporting scheme estimating current network conditions, which serves as input to the policy specification. A primary goal of this work is to make it possible to balance the bandwidth load across networks with comparable performance. To avoid the problem of handoff instability, i.e., many mobile hosts making the same handoff decision at essentially the same time, we designed randomization into our mechanism. Given the current "best" network, our system determines whether the handoff is worthwhile based on the handoff overhead and potential network usage duration.

Policy-enabled handoffs across heterogeneous wireless networks

The development of context-aware applications will require tools that are based on clearly defined models of context and system software architecture. This essay introduces models for each of these, examines the tradeoffs among the different alternatives, and describes a blackboard-based context architecture that is being used in the construction of interactive workspaces.

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Architectures for context

Several recent proposals for an "active networks" architecture advocate the placement of user-defined computation within the network as a key mechanism to enable a wide range of new applications and protocols, including reliable multicast transports, mechanisms to foil denial of service attacks, intra-network real-time signal transcoding, and so forth. This laudable goal, however, creates a number of very difficult research problems, and although a number of pioneering research efforts in active networks have solved some of the preliminary small-scale problems, a large number of wide open problems remain. In this paper, we propose an alternative to active networks that addresses a restricted and more tractable subset of the active-networks design space. Our approach, which we (and others) call "active services", advocates the placement of user-defined computation within the network as with active networks, but unlike active networks preserves all of the routing and forwarding semantics of current Internet architecture by restricting the computation environment to the application layer. Because active services do not require changes to the Internet architecture, they can be deployed incrementally in today's Internet.We believe that many of the applications and protocols targeted by the active networks initiative can be solved with active services and, toward this end, we propose herein a specific architecture for an active service and develop one such service in detail --- the Media Gateway (MeGa) service --- that exploits this architecture. In defining our active service, we encountered six key problems --- service location, service control, service management, service attachment, service composition, and the definition of the service environment --- and have crafted solutions for these problems in the context of the MeGa service. To verify our design, we implemented and fielded MeGa on the UC Berkeley campus, where it has been used regularly for several months by real users who connect via ISDN to an "on-line classroom". Our initial experience indicates that our active services prototype provides a very flexible and programmable platform for intra-network computation that strikes a good balance between the flexibility of the active networks architecture and the practical constraints of incremental deployment in the current Internet.

/pdf/an-active-service-framework-and-its-application-to-real-time-33dnedd98v.pdf

An active service framework and its application to real-time multimedia transcoding

Hashes are short summaries or signatures of data files which can be used to identify the file. The disclosed method generates robust hashes for multimedia content, for example, audio clips. The audio clip is divided into successive (preferably overlapping) frames. For each frame, the frequency spectrum is divided into bands. A robust property of each band (e.g. energy) is computed and represented by a respective hash bit. An audio clip is thus represented by a concatenation of binary hash words, one for each frame. To identify a possibly compressed audio signal, a block of hash words derived therefrom is matched by a computer with a large database. Such matching strategies are also disclosed. In an advantageous embodiment, the extraction process also provides information as to which of the hash bits are the least reliable. Flipping these bits considerably improves the speed and performance of the matching process.

Generating and matching hashes of multimedia content

Real-time multimedia streams like audio and video are now integral data types in modern programming environments. Although a great deal of research has investigated effective and efficient programming support for manipulating such streams and although the design of digital media "middleware" is fairly well understood, no widely available or commonly accepted programming model exists within the research community. The authors believe this lack of common practice impedes our collective progress because it prevents disparate research groups from easily leveraging each other's work. They propose a solution to this problem that combines the best features of a number of existing multimedia toolkits-Berkeley's Continuous Media Toolkit, MIT's VuSystem, and the LBL/UCB MBone tools-into a fine-grained, extensible, and high performance toolkit. They describe the convergence of these three toolkits into a common programming infrastructure and argue that the availability and acceptance of the middleware could potentially facilitate and accelerate breakthroughs in multimedia networking.

/pdf/toward-a-common-infrastructure-for-multimedia-networking-4p4x3pvn44.pdf

Toward a common infrastructure for multimedia-networking middleware

We have developed and demonstrated a remote continuous media playback application called cmplayer, using the Berkeley Continuous Media Toolkit (CMT). Cmp layer can be used in conjunction with aWorld W]de Web browserto access remotely stored continuous media data (i.e., video and audio) and provide synchronized playback of multiple media streams. The cmplayer communicates witha server process also written with CMT to stream media data across the network using adaptive control to compensate forlimitednetwork bandwidth, server utilization, and client CPU resources. Asimple script format isusedto indicate thelocation of each piece of media data (i.e., hostname, port number and the filename) and specify source synchronization between media streams. Multiple video and audio streams can be specified. In addition, scrolling text streams and streams of Tcl commands can be integrated as stream types. A stream can be stored in multiple media data files distributed on different servers. Cmplayer script files are ASCII text and are typically less than 10 lines long. Cmplayer provides full VCR-like controls and random access into any point of the video.

Synchronized continuous media playback through the World Wide Web

In this paper, we describe the design and implementation of a prototype software video production switcher, vps, that improves the quality of the content of MBone broadcasts. vps is modeled after the broadcast television industry's studio production switcher. It provides special effects processing to incorporate audience discussions, add titles and other information, and integrate stored videos into the presentation. vps is structured to work with other MBone conferencing tools. The ultimate goal is to automate the production of MBone broadcasts.

Software-only video production switcher for the internet MBone

American English to 1865

We have developed an application for use in the production of digital video broadcasts. This application, the Software Video Production Switcher, is an extensible application that is used to manage a set of continuous video inputs in realtime. The switcher takes these video inputs and performs user-directed actions to produce a single output video stream. These actions include simple cuts between video streams, more complex video transitions, and special video effects. The output stream can then be broadcast onto a network and received by remote viewer applications for playback.

David Simpson

Papers

Toward a common infrastructure for multimedia-networking middleware

Synchronized continuous media playback through the World Wide Web

Software-only video production switcher for the internet MBone

American English to 1865

Software video production switcher