2477251
PCR-assist CBR for delivering pre-recorded MPEG-2 transport streams
Transmitting compressed variable bit-rate (VBR) video with a traditional constant bit-rate (CBR) service for continuous playback requires a large buffer on the viewer's side. In this paper, we study a new CBR transmission scheme which employs the program clock references (PCR) that are embedded in the MPEG-2 transport streams to reduce the buffer requirement. The scheme is called "PCR-assist CBR" (PCBR). The PCBR scheme uses PCRs to examine its transmission regularly. It holds up the transmission if it is ahead of schedule. Based on experimental results with video traces, the PCBR scheme reduces the buffer requirement at the cost of a higher transmission rate.
12802794
A systematic approach to design the network-based learning environment for home and office
An effective network-based learning environment provides synchronous and asynchronous education to learners who are physically, remote from or opt to telecommute to the base location of instruction. The environment provides content creation, user registration, course material storage, multiple delivery means, and end-user viewing tools. An intriguing aspect of the environment is how to model a lecture in terms of pre-, in-, and post-class information. We regard a lecture model collectively as an activity consisting of three elements: lecture materials, lecture presentation, and lecture interaction. We derive the synchronization specification for the media objects and define strong-weak networked hyperlink (SWNH) to represent the lecture structure and inter/intra media object reference in the distributed network environment. The specification and representation exhibit an object-oriented modular design. The presentation of the lecture embody both the event-driven and timeline-based presentation synchronization where the browsing and authoring tools developed earlier fit right into the learning environment, e.g. FLIPS and HQT by the authors, or are immediately available through other providers, e.g. Web browsers.
11088545
Supporting Random Access on Real-Time Retrieval of Digital Continuous Media
In addition to the large data size requirement and real-time constraint in continuous media, future video applications such as video editing demand a random access capability at the video-frame level. This paper introduces our study on effective buffering control for the real-time retrieval of jitter-free digital video medium. We adopt a video-frame level approach to maintaining the flexibility on placement and analysing the efficiency of the buffering schemes. An integrated solution which offers efficient buffering schemes and flexible storage placement to support random access is our goal. We present two buffering schemes: the two-buffer scheme and the k-buffer compensation scheme. The two-buffer scheme requires that all the frames in a block are stored consecutively, while providing random access between blocks. However, this intuitive buffering scheme potentially requires a large block size and buffer space. The k-buffer compensation scheme is proposed to resolve this large buffer space requirement, by using more than two buffers and requiring a minimal number of blocks randomly placed in each cylinder. This scheme differs from the contiguous placement scheme because individual blocks can be stored anywhere in each cylinder. Compared to the two-buffer scheme, the k-buffer compensation scheme requires less buffer space, has higher disk utilization and finer granularity on disk data transfer. The placement requirements are more flexible and implementable than the contiguous and storage pattern placement schemes. Experimental measurement results reveal the significant improvements on the buffer-size reduction and placement flexibility by using the k-buffer compensation scheme. Extensions of the k-buffer compensation scheme to support multiple streams are also addressed.
7236819
Creating a virtual network laboratory
Networking courses are traditionally conceptual in nature, with little opportunity for students to apply what they have learned in order to strengthen their knowledge. To support these courses, the University of Minnesota established a hands-on network laboratory. Educational and operational concerns have surfaced throughout the years due to the physical laboratory constraints and difficulty of satisfying the high demand. To address these issues, and to overcome the shortcomings of current approaches, we are developing a virtual network laboratory environment to eliminate most of the constraints, though it is not necessarily replacing all of the physical settings at once. The kernel consists of a collection of online multimedia learning modules which integrate the key laboratory devices with instructional material. The modules are designed to allow students to carry out hands-on networking in a virtual environment or through remote access. This virtual laboratory is easily accessible over the Internet.
9780632
An integrated admission control scheme for the delivery of streaming media
Quality of service (QoS) assurance is a major concern in media-on-demand (MoD) systems. Admission control is one of the most important issues that need to be addressed for QoS assurance. Also, smoothing is a basic technique for the media server to improve its bandwidth and buffer utilization. However, existing approaches cannot achieve the best resource utilization because (1) they cannot fully utilize the time-varying buffer spaces available at both server and client sides due to the separation of admission control and smoothing processes, and (2) the computing time is unacceptable for media of long duration. In this paper, we formulate the admission control as an integer programming problem and propose several heuristic methods for solving the problem. Specially, we introduce an efficient scheme, called batched admission (BA) scheme, which integrates admission control, transmission rate smoothing, and batching, to achieve best resource utilization with guaranteed QoS. Experimental studies show that the BA scheme outperforms existing approaches.
2453836
On connectivity of consecutive-d digraphs
The concept of a consecutive-d digraph was proposed by Du, Hsu and Hwang as a generalization of de Bruijn digraphs, Kautz digraphs, and their generalizations given by Imase and Itoh and Reddy, Pradhan and Kuhl. In this paper, we determine the connectivity of consecutive-d digraphs and study how to modify consecutive-d digraphs to reach maximum connectivity. Our results will generalize and improve several existing results on the connectivity of de Bruijn digraphs, Kautz digraphs and Imase-Itoh digraphs.
39689433
On 1-rate Wide-sense Nonblocking for 3-stage Clos Networks
Abstract This paper considers the multirate environment in which each network link has a unity capacity and each call is associated with a rate w, 1 ⩾ w>0. The multirate environment is reduced to the 1 -rate environment if all rates are identical. Circuit switching is a special case of 1 -rate in which the constant rate is w = 1. We establish some general relations between wide-sense nonblocking in circuit switching and 1-rate wide-sense nonblocking for the 3-stage Clos network. We also give necessary and sufficient conditions for a 3-stage Clos network with two input switches and two output switches to be wide-sense nonblocking, and give a necessary condition when there are three input switches and three output switches. We conjecture that 1-rate wide-sense nonblocking implies circuit switching wide-sense nonblocking and give some partial evidence.
17041567
On-line scheduling of small open shops
We investigate the problem of on-line scheduling open shops of two and three machines with an objective of minimizing the schedule makespan. We first propose a 1.848-competitive permutation algorithm for the non-preemptive scheduling problem of two machines and show that no permutation algorithm can be better than 1.754-competitive. Secondly, we develop a (27/19)-competitive algorithm for the preemptive scheduling problem of three machines, which is most competitive.
24107558
Lower Bounds on the Minus Domination and k-Subdomination Numbers
A three-valued function f defined on the vertex set of a graph G = (V,E), f : V → {-1, 0, 1} is a minus dominating function if the sum of its function values over any closed neighborhood is at least one. That is, for every v ∈ V, f(N[v]) ≥ 1, where N[v] consists of v and all vertices adjacent to v. The weight of a minus function is f(V) = Σv∈V f(v). The minus domination number of a graph G, denoted by γ-(G), equals the minimum weight of a minus dominating function of G. In this paper, sharp lower bounds on minus domination of a bipartite graph are given. Thus, we prove a conjecture proposed by J. Dunbar etc. (Discrete Math. 199(1999) 35-47), and we give a lower bound on γks(G) of a graph G.