6688024
Error-resilient real-time video communications over IP-based LANs
Video communication over IP networks involves more issues than that over ATM networks in terms of error control. First, IP networks provide neither prioritized transmission nor guaranteed QOS for data packets. Second, video streams need to be packetized well before transmission over IP networks in order to have good error resilience characteristics. Finally, the mitigation of spatial and temporal error propagation in IP networks is very different from that in ATM networks upon the loss of IP packets. In this paper, we develop an error-resilient video communication system based on the H.323 family of ITU-T recommendations. With a low-delay backward channel for packet receipt reports, bidirectional error resilience mechanisms are employed to avoid error spreading in the temporal domain. Two operation modes, i.e., ACK and NACK, are devised for two communicating parties to eliminate error propagation after either one frame lag or one round trip delay without consuming much additional bandwidth as compared to simple INTRA updates. Our system can also adaptively choose an operation mode to maintain a satisfactory video quality at the decoder under variable channel error conditions. It is shown by experimental results that our error control scheme is suitable for video transmission over IP-based LANs at packet loss rates up to 20%.
37840776
Design and implementation of a network application architecture for thin clients
This paper explores the issues and the techniques of enabling multimedia applications for the thin client computing. Our study on the network applications over thin clients is devoted to the universal plug-in architecture which supports multimedia applications over thin clients. With the proposed architecture, the universal plug-in technique is devised to shift jobs from thin clients to a supporting server, thus reducing the computing overhead required by the thin clients. In addition, this plug-in architecture is implemented and empirically evaluated It is shown by our experiments that the proposed architecture not only significantly enhances the multimedia capability of thin clients but also reduces the memory consumed by the clients for various applications, showing the very advantage of the universal plug-in architecture for thin clients of limited resources.
29466407
An adaptive transmission scheme for audio and video synchronization based on real-time transport protocol
Multimedia streams impose tight temporal constraints since different kinds of continuous multimedia streams have to be played synchronously. We devise in this paper an adaptive transmission scheme to ensure the continuous and synchronous playback of audio and video streams based on Real-time Transport Protocol. Realization of our adaptive scheme is composed of a series of operations in three stages, namely, (1) dynamic reordering mechanism, (2) decoding-recovery mechanism, and (3) adaptive synchronization mechanism. An empirical study is conducted to provide insights into our adaptive transmission scheme. As validated by our simulation results, the adaptive transmission mechanism is able to strike a good balance of both stable playback and the end-to-end delay reduction. Furthermore, we analyze the jitter resistance, the end-to-end delay, and the buffer size required in order to enhance the applicability of this scheme to more applications that require the transmission of multimedia data.
14887651
Adaptive recovery techniques for real-time audio streams
There are a number of packet-loss recovery techniques proposed for streaming audio applications. However, there are few works that are able to exploit the tradeoff between the recovery quality and the computational complexity. We develop a recovery method, called DSPWR (Double Sided Pitch Waveform Replication) which is able to tolerate a much higher packet loss rate. In essence, DSPWR is composed of several procedures devised to improve the quality of the reconstructed speech. It is noted that a more sophisticated recovery scheme that can tolerate a higher degree of packet loss in general requires a larger computational cost. In view of this, we evaluate the quality of the reconstructed speech under different packet loss rates for various receiver-based recovery methods, and compare the computational complexity among these methods. Under the acceptable speech quality whose MOS (Mean Opinion Score) is above 3.5, we develop an adaptive mechanism that can select the recovery method with the minimal complexity in accordance with different packet loss rates encountered. To conduct real experiments in the networks, we implement these recovery methods and evaluate the performance of DSPWR devised and the adaptive recovery techniques empirically. As validated by our experimental results, the adaptive mechanism is able to strike a compromise between the computational overhead and the quality of the speech desired.
18278456
On General Results for All-to-All Broadcast
All-to-all broadcast refers to the process by which every node broadcasts its certain piece of information to all other nodes in the system. In this paper, we develop all-to-all broadcast schemes by dealing with two classes of schemes. A prior scheme based on generation of minimal complete sets is first described, and then a new scheme based on propagation of experts is developed. The former always completes the broadcasting in the minimal number of steps and the latter is designed to minimize the number of messages. Performance of these two classes of schemes is comparatively analyzed. The all-to-all broadcast scheme desired can be derived by combining the advantages of these two classes of schemes.
33317527
Learning Large-Alphabet and Analog Circuits with Value Injection Queries
We consider the problem of learning an acyclic discrete circuit with n wires, fan-in bounded by k and alphabet size s using value injection queries. For the class of transitively reduced circuits, we develop the Distinguishing Paths Algorithm, that learns such a circuit using (ns)O(k) value injection queries and time polynomial in the number of queries. We describe a generalization of the algorithm to the class of circuits with shortcut width bounded by b that uses (ns)O(k+b) value injection queries. Both algorithms use value injection queries that fix only O(kd) wires, where d is the depth of the target circuit. We give a reduction showing that without such restrictions on the topology of the circuit, the learning problem may be computationally intractable when s = nΘ(1), even for circuits of depth O(log n). We then apply our large-alphabet learning algorithms to the problem of approximate learning of analog circuits whose gate functions satisfy a Lipschitz condition. Finally, we consider models in which behavioral equivalence queries are also available, and extend and improve the learning algorithms of [5] to handle general classes of gates functions that are polynomial time learnable from counterexamples.
18640612
On approximating minimum vertex cover for graphs with perfect matching
It has been a challenging open problem whether there is a polynomial time approximation algorithm for the VERTEX COVER problem whose approximation ratio is bounded by a constant less than 2. In this paper, we study the VERTEX COVER problem on graphs with perfect matching (shortly, VC-PM). We show that if the VC-PM problem has a polynomial time approximation algorithm with approximation ratio bounded by a constant less than 2, then so does the VERTEX COVER problem on general graphs. Approximation algorithms for VC-PM are developed, which induce improvements over previously known algorithms on sparse graphs. For example, for graphs of average degree 5, the approximation ratio of our algorithm is 1.414, compared with the previously best ratio 1.615 by Halldorsson and Radhakrishnan.
15870210
SAS: A Scalar Anonymous Communication System
Anonymity technologies have gained more and more attention for communication privacy. In general, users obtain anonymity at a certain cost in an anonymous communication system, which uses rerouting to increase the system's robustness. However, a long rerouting path incurs large overhead and decreases the quality of service (QoS). In this paper, we propose the Scalar Anonymity System (SAS) in order to provide a tradeoff between anonymity and cost for different users with different requirements. In SAS, by selecting the level of anonymity, a user obtains the corresponding anonymity and QoS and also sustains the corresponding load of traffic rerouting for other users. Our theoretical analysis and simulation experiments verify the effectiveness of SAS.
36997041
The Logic of Only Knowing as a Unified Framework for Non-Monotonic Reasoning
We propose to use the logic of only knowing (OL) by Levesque [10] as a unified framework that encompasses various non-monotonic formalisms and logic programming. OL is a modal logic which can be used to formalize an agent's introspective reasoning and to answer epistemic queries to databases. The OL logic allows one to formally express the statement “α is all I know” (in symbols, Oα) and to perform inferencing based on only-knowing, which is very useful for commonsense reasoning. Another nice thing about the OL logic is that it has a clear model-theoretic semantics and a simple proof theory, which is sound for the quantificational case, and both sound and complete for the prepositional case. We establish the relations between OL and various non-monotonic logics (such as default logic, circumscription) and logic programming, thus extending the existing works relating the OL logic with other non-monotonic reasoning formalisms (e.g., Levesque showed that autoepistemic logic can be embeded in OL). This is accomplished by finding the connection between OL and MBNF, the logic of Minimal Belief and Negation as Failure proposed by Lifschitz [12, 13], which is known to have close relationship with logic programming and other non-monotonic logics. Our results show that OL can be used as a unified framework to compare different non-monotonic formalisms based on the same domain.
40634947
Experiments Study on a Dynamic Priority Scheduling for Wireless Sensor Networks
Wireless Sensors Networks (WSNs) represent a new generation of embedded systems, which deploy wireless ad hoc communication mechanisms to route a sensory data from the originator sensor node to the base station. One of the most important issues in wireless sensor networks is to support real-time QoS, which is fundamentally a challenging problem. In this paper, we introduce EDBP scheduling algorithm for sensor network along with a MAC protocol based on the dynamic priority assignment EDBP. Two different platforms based experiment projects are designed to test our proposal.