15937667
A dynamic programming methodology for managing prerecorded VBR sources in packet-switched networks
Broadband networks will increasingly carry prerecorded traffic, such as high-fidelity audio, short multimedia clips, and full-length movies. We study how to manage the transmission and transport of traffic from prerecorded VBR sources so that network resources are efficiently utilized and end users receive satisfactory service. Specifically, we study Piecewise Constant-Rate Transmission and Transport (PCRTT), whereby the server transmits and the network transports each connection's packets at different constant rates over a small number of intervals. We show how Dynamic Programming (DP) can be applied to find optimal PCRTT rates and intervals for a wide variety of optimization criteria, including criteria which explicitly account for delays to user interaction (pause, fast forward, and rewind). We also introduce two admission policies for PCRTT: peak-rate admission and packing admission. For peak-rate admission, for each video the network allocates an end-to-end CBR connection; the rate of the CBR connection is equal to the maximum PCRTT rate. For packing admission, for each video the network reserves a series of CBR connections of different rates over specific time intervals. Using public domain MPEG traces, we present several numerical examples which illustrate the traffic management schemes and the DP methodology.
18166886
On Routing in ATM Networks
Alternative routing of calls has long been acknowledged as a means of increasing call throughput and robustness in the telephone network. Given these performance gains, it is natural to consider dynamic routing of Virtual Circuits (VCs) in Asynchronous Transfer Mode (ATM) networks. Unlike telephone networks, VCs have heterogeneous bandwidth characteristics and Quality of Service requirements that the routing algorithm must take into account in order to optimize performance. In this paper we attempt to classify ATM networks according to the network characteristics that have the greatest bearing on the performance of dynamic routing algorithms; we also discuss appropriate routing algorithms for diierent classes of ATM network. The classiication is based on the degree of heterogeneity of the sources and the degree of statistical multiplexing.
22940589
Asynchronous voice: a personal account
Asynchronous voice is the interactive communication process of people leaving voice messages for other people and the other people responding with their voice messages. A primitive form of asynchronous voice is a kind of telephone tag in which people use voice mail to have an interactive conversation. The author gives a personal account of his work with asynchronous voice and asynchronous learning.
1908016
Optimal peer selection for P2P downloading and streaming
In a P2P system, a client peer may select one or more server peers to download a specific file. In a P2P resource economy, the server peers charge the client for the downloading. A server peer's price would naturally depend on the specific object being downloaded, the duration of the download, and the rate at which the download is to occur. The optimal peer selection problem is to select, from the set of peers that have the desired object, the subset of peers and download rates that minimizes cost. In this paper we examine a number of natural peer selection problems for both P2P downloading and P2P streaming. For downloading, we obtain the optimal solution for minimizing the download delay subject to a budget constraint, as well as the corresponding Nash equilibrium. For the streaming problem, we obtain a solution that minimizes cost subject to continuous playback while allowing for one or more server peers to fail during the streaming process. The methodologies developed in this paper are applicable to a variety of P2P resource economy problems.
27961905
Performance evaluation of redirection schemes in content distribution networks
Content distribution on the Web is moving from an architecture where objects are placed on a single, designated server to an architecture where objects are replicated on geographically distributed servers and clients transparently access a nearby copy of an object. In this paper we study how the different redirection schemes used in modern content distribution networks affect the user-perceived performance in normal Web page viewing. Using both simulations and experiments with real Web servers we show that redirection schemes that require clients to retrieve different parts of a Web page from different servers yield sub-optional performance compared to schemes where a client accesses only one server for all the parts of a Web page. This implies that when replicating Web pages, we should treat the whole page (HTML and images) as a single entity.
6975415
Distributing Layered Encoded Video through Caches
The efficient distribution of stored information has become a major concern in the Internet which has increasingly become a vehicle for the transport of stored video. Because of the highly heterogeneous access to the Internet, researchers and engineers have argued for layered encoded video. We investigate delivering layered encoded video using caches. Based on the stochastic knapsack theory, we develop a model for the layered video caching problem. We propose heuristics to determine which videos and which layers in the videos should be cached in order to maximize the revenue from the streaming service. We evaluate the performance of our heuristics through extensive numerical experiments. We find that, for typical scenarios, the revenue increases nearly logarithmically with the cache size and linearly with the link bandwidth that connects the cache to the origin servers. We also consider service models with request queuing and negotiations about the delivered stream quality and find that both extensions provide only small revenue increases.
14305268
Relations with relation names as arguments: algebra and calculus
We consider a version of the relational model in which relation names may appear as arguments of other relations. Allowing relation names as arguments provides enhanced modelling capabilities, allowing some object-oriented features to be expressed within the relational model. We extend relational algebra with operators for accessing relations, and also define a relational calculus based on the logic HiLog. We prove two equivalence results between extensions of relational algebra provide higher expressive power than relational algebra on any given database. Finally, we argue that the extensions proposed here are relatively easy to provide in practice, and should be expressible within modern query languages.
16499822
Publish/Subscribe on the Web at Extreme Speed
This demonstration presents Le Subscribe an event notification system for the Web. It is widely accepted that the majority of human information will be on the Web in ten years. As pointed out in [6], besides systems for searching, querying and retrieving information from the Web, there is a need for systems being able to capture the dynamic aspect of the web information by notifying users of interesting events. This functionality is crucial for web users (or applications) who want to exploit highly dynamic web information such as stock markets updates or auctions. A tool that implements this functionality must be scalable and efficient. Indeed, it should manage millions of user demands for notifications (i.e. subscriptions); It should handle high rates of events (several millions per day) and notify the interested users in a short delay. In addition, it should provide a simple and expressive subscription interface and efficiently cope with high volatility of web user demands (new subscriptions, new users and cancellations). Finally, it should facilitate integration of similar kinds of information issued by different publishers (e.g. new auctions coming from distinct auction sites). The classical approach for query subscription is a mediator system where queries are periodically evaluated against static data. This static approach does not scale for high rate of events and a large number of volatile subscriptions, since it requires the storage of large event histories between two successive computations and requires repeated complex multi-query optimization. In Le Subscribe we adopt a different approach where events are processed on-the-fly to discover matching subscriptions. Our main contributions in Le Subscribe are: A semi-structured event model which is well suited for the information published on the Web, and flexible enough to support easy integration of publishers. Founded by “Instituto Superior Técnico” Technical University of Lisbon and by a JNICT fellowship of Program PRAXIS XXI (Portugal) A subscription language which is designed to be simple while supporting the most usual queries on event notifications. An efficient matching algorithm for processing events in real time which can handle a large number of volatile subscriptions and supporting high event rates. Simple interfaces for publishing and subscribing which enable an easy integration of the system in the Web. The system supports both HTTP protocol and Java RMI. The demonstration consists of an application whose goal is to notify interested users of items put up for auction. These items are captured by Le Subscribe from a set of auction Web sites, e.g. ebay [5], amazon [2] or yahoo [15], or can be transmitted to our system using a web interface. Every day, the system has to handle a large number of items. For example, ebay publishes about 560000 new auction items per day.
7365552
Tail recursion elimination in deductive databases
We consider an optimization technique for deductive and relational databases. The optimization technique is an extension of the magic templates rewriting, and it can improve the performance of query evaluation by not materializing the extension of intermediate views. Standard relational techniques, such as unfolding embedded view definitions, do not apply to recursively defined views, and so alternative techniques are necessary. We demonstrate the correctness of our rewriting. We define a class of “nonrepeating” view definitions, and show that for certain queries our rewriting performs at least as well as magic templates on nonrepeating views, and often much better. A syntactically recognizable property, called “weak right-linearity”, is proposed. Weak right-linearity is a sufficient condition for nonrepetition and is more general than right-linearity. Our technique gives the same benefits as right-linear evaluation of right-linear views, while applying to a significantly more general class of views.
1995310
Cache Conscious Indexing for Decision-Support in Main Memory
We study indexing techniques for main memory, including hash indexes, binary search trees, T-trees, B+-trees, interpolation search, and binary search on arrays. In a decision-support context, our primary concerns are the lookup time, and the space occupied by the index structure. Our goal is to provide faster lookup times than binary search by paying attention to reference locality and cache behavior, without using substantial extra space. We propose a new indexing technique called \Cache-Sensitive Search Trees" (CSS-trees). Our technique stores a directory structure on top of a sorted array. Nodes in this directory have size matching the cache-line size of the machine. We store the directory in an array and do not store internal-node pointers; child nodes can be found by performing arithmetic on array osets. We compare the algorithms based on their time and space requirements. We have implemented all of the techniques, and present a performance study on two popular modern machines. We demonstrate that with This research was supported by a David and Lucile Packard Foundation Fellowship in Science and Engineering, by an NSF Young Investigator Award, by NSF grant number IIS-98-12014, and by NSF CISE award CDA-9625374.
970550
Realizing parallelism in database operations: insights from a massively multithreaded architecture
A new trend in processor design is increased on-chip support for multithreading in the form of both chip multiprocessors and simultaneous multithreading. Recent research in database systems has begun to explore increased thread-level parallelism made possible by these new multicore and multithreaded processors. The question of how best to use this new technology remains open, particularly as the number of cores per chip and threads per core increase. In this paper we use an existing massively multithreaded architecture, the Cray MTA-2, to explore the implications that a larger degree of on-chip multithreading may have for parallelism in database operations. We find that parallelism in database operations is easy to achieve on the MTA-2 and that, with little effort, parallelism can be made to scale linearly with the number of available processor cores.