1377609
Computing approximate blocking probabilities for large loss networks with state-dependent routing
A reduced load approximation (also referred to as an Erlang fixed point approximation) for estimating point-to-point blocking probabilities in loss networks (e.g., circuit switched networks) with state-dependent routing is considered. In this approximation scheme, the idle capacity distribution for each link in the network is approximated, assuming that these distributions are independent from link to link. This leads to a set of nonlinear fixed-point equations which can be solved by repeated substitutions. The accuracy and the computational requirements of the approximation procedure for a particular routing scheme, namely least loaded routing, is examined. Numerical results for six-node and 36-node asymmetric networks are given. A novel reduced load approximation for multirate networks with state-dependent routing is also presented. >
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.
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.
32291503
On Nonblocking Multirate Interconnection Networks
In a recent paper, Melen and Turner [SIAM J. Comput., 18 (1989), pp. 301–313] determined sufficient conditions for multirate interconnection networks to be strictly nonblocking and rearrangeable. They considered the continuous bandwidth case, which permits the bandwidth of a connection to take an arbitrary value in a given closed interval. In this paper, simple necessary and sufficient conditions for multirate interconnection networks to be strictly nonblocking for both discrete and continuous bandwidth cases are determined. New results for rearrangeable multirate networks with discrete bandwidth requirements are also given.
31310473
Packet multiplexers with adversarial regulated traffic
We consider a finite-buffer packet multiplexer to which traffic arrives from several independent sources. The traffic from each of the sources is regulated, i.e., the amount of traffic that can enter the multiplexer is constrained by known regulator constraints. The regulator constraints depend on, the source and are more general than those resulting from cascaded leaky buckets. We assume that the traffic is adversarial to the extent permitted by the regulators. For lossless multiplexing, we show that if the original multiplexer is lossless it is possible to allocate bandwidth and buffer to the sources so that the resulting segregated systems are lossless. For lossy multiplexing, we use our results for lossless multiplexing to estimate the loss probability of the multiplexer. Our estimate involves transforming the original system into two independent resource systems, and using adversarial sources for the two independent resources to obtain a bound on the loss probabilities for the transformed system. We show that the adversarial sources are not extremal on-off sources, even when the regulator consists of a peak rate controller in series with a leaky bucket. We explicitly characterize the form of the adversarial source for the transformed problem. We also provide numerical results for the case of the simple regulator.
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.
16342548
Modular acyclicity and tail recursion in logic programs
In this paper we consider two problems. The first is related to the question of acyclicity, i.e., the absence of positive and negative loops. In the absence of loops, some desirable semantic properties hold, and certain program optimizations become possible. The second problem is related to the question of tail-recursion elimination for logic programs. By not representing intermediate results of a bottomup computation, substantial savings over magic sets can be realized. In Section 2 we generalize the class of “acyclic” programs [Cav89, AB90] to what we call “modularly acyclic” programs. Acyclic programs P have the following desirable properties:
38852147
On Negation in HiLog
Abstract The logic HiLog of Chen, Kifer, and Warren has a second order syntax, while its semantics is first order. HiLog programs with negative literals in the body are considered. A stable-model semantics and a well-founded semantics for this class of program are defined, and it is shown that these semantics generalize the stable-model semantics and the well-founded semantics, respectively, for range-restricted normal programs. A second order property called preservation under extensions is proposed and investigated. Preservation under extensions ensures that the semantics of a program is not changed when rules having no symbols in common with the program are appended to the program. It is shown that for normal programs, domain independence and preservation under extensions are equivalent, while for HiLog programs, preservation under extensions is strictly stronger. Range restrictedness is generalized to HiLog programs in two ways, and it is shown that range restricted HiLog programs are preserved under extensions with respect to the well-founded semantics. Conditions under which the well-founded semantics is two-valued are investigated, and the class of modularly stratified programs is generalized to HiLog. An extension of magic-set techniques to modularly stratified HiLog programs is described.
986287
A probability collectives approach to weighted clustering algorithms for ad hoc networks
The Weighted Clustering Algorithm has been proposed for mobile ad hoc wireless networks to select a subset of the nodes to be local purveyors of media access control services to the rest of the nodes. The nodes selected are called clusterheads, and each clusterhead services the other nodes within its radio range. The underlying optimal assignment problem is NP-hard. We introduce a new metaheuristic known as probability collectives to the problem of assigning clusterheads. This is an agent-based approach, with each node in the network acting in a quasi-autonomous way. This new approach shows improved clustering results, particularly with regard to the distribution and balance of cluster sizes.
9087348
A procedural semantics for well founded negation in logic programs
We introduce global SLS-resolution, a procedural semantics for well-founded negation as defined by Van Gelder, Ross and Schlipf. Global SLS-resolution extends Prsymusinski's SLS-resolution, and may be applied to all programs, whether locally stratified or not.1 Global SLS-resolution is defined in terms of global trees, a new data structure representing the dependence of goals on derived negative subgoals. We prove that global SLS-resolution is sound with respect to the well-founded semantics, and complete for non-floundering queries.
15587034
Packet Scheduling Across Networks of Switches
Recent developments in computer and communication networks require scheduling decisions to be made under increasingly complex system dynamics. We model and analyze the problem of packet transmissions through an arbitrary network of buffered queues, and provide a framework for describing routing and migration. This paper introduces an intuitive geometric description of stability for these networks and describes some simple algorithms which lead to maximal throughput. We show how coordination over sequential timeslots by algorithms such as those based on a round robin can provide considerable advantages over a randomized scheme.