18311613
Fair scheduling in an optical interconnection network
Existing fair scheduling schemes have focused primarily on scheduling multiple flows to a single output. The limited work that has focused on scheduling multiple flows to multiple outputs has assumed a non-blocking, slotted-time, cell-based network with a centralized controller. This paper presents a fair scheduler suitable for use in bufferless circuit-switched blocking networks operating with distributed, asynchronous controllers and variable length messages. We begin by describing the potential for starvation in the Gemini interconnect network, an optical, circuit-switched network. A proposed distributed fair scheduler is presented and shown to solve this problem. The tradeoffs and limitations of performing many-to-many fair scheduling in general, and that of our fair scheduler in particular, are discussed.
206622431
Pin Limitations and Partitioning of VLSI Interconnection Networks
Multiple processor interconnection networks can be characterized as having N' inputs and N' outputs, each being B' bits wide. A major implementation constraint of large networks in the VLSI environment is the number of pins available on a chip, Np. Construction of large networks requires partitioning of the N' * N' * B' network into a collection of N * N switch modules with each input and output port being B (B ≤ B') bits wide. If each module corresponds to a single chip, then a large network can be implemented by interconnecting the chips in a particular manner. This correspondence presents a methodology for selecting the optimum values of N and B given values of N', B', Np, and the number of control lines per port. Models for both banyan and crossbar networks are developed and arrangements yielding minimum: 1) number of chips, 2) average delay through the network, and 3) product of number of chips and delay, are presented.
5272318
On Designing Interconnection Networks for Multiprocessors
This paper considers various physical constraints which influence the design of interconnection networks used in multiprocessor systems. Design expressions are presented for implementing an N log N packet passing interconnection network composed for circuit switched crossbar chip modules. Expressions reflecting chip level and board level pin and area constraints are derived and used to determine the network delay expected at a given clock frequency. Logic and memory delay, signal path delay, clock skew and clock tree delay parameters are defined and used to determine the maximum frequency which can be obtained with a given design. An example 2048x2048 network... Read complete abstract on page 2.
18137632
Collecting Data About Logic Simulation
Design of high-performance hardware and software-based gate-switch-level logic simulators requires knowledge about the logic simulation process itself. Unfortunately, little data is publicly available concerning key aspects of this process. An example of this is the lack of published empirical measurements relating to the time distribution of events generated by such simulators. This paper presents a gate-switch-level logic simulator lsim which is oriented towards the collection of data about the simulation process. The basic components of lsim are reviewed, and its relevant data gathering facilities are discussed. An example is presented which illustrates the use of lsim in gathering data on event distributions and on communications requirements under alternative logic circuit partitionings.
27473158
Interconnection Networks: Physical Design and Performance Analysis
This paper considers various physical constraints which influence the design of interconnection networks used in multiprocessor systems. Design expressions are presented for implementing an N log N packet passing interconnection network composed of circuit switched crossbar chip modules. Expressions reflecting chip level and board level pin and area constraints are derived and used to determine the network delay expected at a given clock frequency. Logic and memory delay, signal path delay, clock skew, and clock distribution delay parameters are defined and used to determine the maximum frequency which can be obtained with a given design. An example 2048 × 2048 network design is considered. This example indicates that using aggressive packaging and MOS technology, a clock frequency of about 40 Mhz is achievable. However, even at this frequency, this network would result in a one-way delay (ignoring blocking and hot spot delays) of about 1 μsec. A read operation from memory requiring a round trip would thus require about 2 μsec. This represents considerable slowdown when compared with accessing strictly local memory and appears to be a major problem in the design of network centered multiprocessor architectures.
34325813
Timing Control of VLSI Based NlogN and Crossbar Networks
Two basic data flow control methods for circuit switched, pipelined networks of the general nlogn and crossbar (cb) topologies are modelled and their effects on overall data rates achievable are determined. The synchronous method uses a global clock and as network modules grow, clock skew and clock tree charge/discharge times grow resulting in lower data rates. The asynchronous method relies on local request/acknowledge signals to control data movement and hence its performance is less affected by system growth. 12 references.
2567437
Dynamic Query Operator Scheduling for Wide-Area Remote Access
Distributed databases operating over wide-area networks such as the Internet, must deal with the unpredictable nature of the performance of communication. The response times of accessing remote sources can vary widely due to network congestion, link failure, and other problems. In such an unpredictable environment, the traditional iterator-based query execution model performs poorly. We have developed a class of methods, called query scrambling, for dealing explicitly with the problem of unpredictable response times. Query scrambling dynamically modifies query execution plans on-the-fly in reaction to unexpected delays in data access. In this paper we focus on the dynamic scheduling of query operators in the context of query scrambling. We explore various choices for dynamic scheduling and examine, through a detailed simulation, the effects of these choices. Our experimental environment considers pipelined and non-pipelined join processing in a client with multiple remote data sources and delayed or possibly bursty arrivals of data. Our performance results show that scrambling rescheduling is effective in hiding the impact of delays on query response time for a number of different delay scenarios.
18303958
Self-healing key distribution with revocation
We address the problem of establishing a group key amongst a dynamic group of users over an unreliable, or lossy, network. We term our key distribution mechanisms self-healing because users are capable of recovering lost group keys on their own, without requesting additional transmissions from the group manager thus cutting back on network traffic, decreasing the load on the group manager and reducing the risk of user exposure through traffic analysis. A user must be a member both before and after the session in which a particular key is sent in order to be able to recover the key through self-healing. Binding the ability to recover keys to membership status enables the group manager to use short broadcasts to establish group keys, independent of the group size. In addition, the self-healing approach to key distribution is stateless, meaning that a group member who has been off-line for some time is able to recover new session keys immediately after coming back on-line.
3112017
Distribution chain security
Digital content distribution systems will enable business models in the near future that cannot be predicted today. In this paper, we identify a new security problem that can be crucial to this enablement. The problem arises from the con icting privacy and integrity goals of middlemen in digital distribution chains. Our solution is a novel system design that incorporates obfuscated digital contracts, semi-trusted contract certi ers, and zero-knowledge proofs of arithmetic relations. Our implementation and timing experiments demonstrate that our solution is practical and eÆcient.
59766135
Improving Responsiveness for Wide-Area Data Access
Improving Resp onsiveness for WideArea Data AccessLaurent AmsalegPhilipp e BonnetMichael J FranklinINRIABullUniversity of MarylandAnthonyTomasicTolga UrhanINRIAUniversity of MarylandAbstractIn a widearea environment the time rquird to obtain data from remote sources can varyunpredictably due to network congestion link failure or other problems Traditional techniquesfor query optimization and query execution do not cope wel l with such unpredictabilityThestatic nature of those techniques prevents them from adapting to remote access delays that ariseat runtime In this paper we describe two separate but relatedtechniques aimed at tackling thisproblem The rst technique cal led Query Scrambling hides relatively short intermittent delaysby dynamical ly adjusting query execution plans onthey The second technique addresses thelongerterm unavailability of data sources by al lowing the return of partial query answers whensome of the data needed to ful ly answer a query are missingIntro ductionThe continued dramatic growth in global interconnectivity via the Internet has made aroundtheclo ckondemand access to widelydistribu ted data a common exp ectation for many computer users Advances in resource discoery heterogeneous data management and semistructured data managementare providingsemanticto ols to enable the access and correlation of data from diverse widelydistributedsources A limiting factor of suchwork however is the diculty of providing resp onsive data access tousers due to the highly varying resp onsetime and availabilitycharacteristics of remote data sources ina widearea environment Data access over widearea networks inolves a large numb er of data sourcesintermediate sites and communications links all of which are vulnerable to congestion and failuresSuch problems can intro duce signicant and unpredictabledelaysin the access of information fromremote sourcesCurrent distributed query pro cessing approaches p erform p o orly in the widearea environmentThey p ermit unexp ected delays to directly increase the query resp onse time allowing query executionCopyright IEEE Personal use of this material is permitted However permission to reprintrepublish this material for advertising or promotional purposes or for creating new col lective works for resale or rdistribution to serversor lists or to reuse any copyrightedcomponent of this work in other works must be obtainedfrom the IEEEBulletin of the IEEE Computer So cietyTechnical Committee on Data EngineeringThis work was partially supp orted by the NSF under Grant IRI by Bellcore and by an IBM SharedUniversity Researchaward Laurent Amsaleg did this work while he was at the Univy of Maryland and was supp ortedin part by an INRIA Fellowship Philipp e Bonnet and AnthonyTomasic p erformed this work in the context of Dyadean RD jointventure b etween Bull and INRIA
15095971
Cost-based query scrambling for initial delays
Remote data access from disparate sources across a wide-area network such as the Internet is problematic due to the unpredictable nature of the communications medium and the lack of knowledge about the load and potential delays at remote sites. Traditional, static, query processing approaches break down in this environment because they are unable to adapt in response to unexpected delays. Query scrambling has been proposed to address this problem. Scrambling modifies query execution plans on-the-fly when delays are encountered during runtime. In its original formulation, scrambling was based on simple heuristics, which although providing good performance in many cases, were also shown to be susceptible to problems resulting from bad scrambling decisions. In this paper we address these shortcomings by investigating ways to exploit query optimization technology to aid in making intelligent scrambling choices. We propose three different approaches to using query optimization for scrambling. These approaches vary, for example, in whether they optimize for total work or response-time, and whether they construct partial or complete alternative plans. Using a two-phase randomized query optimizer, a distributed query processing simulator, and a workload derived from queries of the TPCD benchmark, we evaluate these different approaches and compare their ability to cope with initial delays in accessing remote sources. The results show that cost-based scrambling can effectively hide initial delays, but that in the absence of good predictions of expected delay durations, there are fundamental tradeoffs between risk aversion and effectiveness.