30399081
Hypercube connected rings: a fault-tolerant and scalable architecture for virtual lightwave network topology
A new, fault-tolerant, scalable, and modular virtual topology for lightwave networks employing wavelength division multiplexing is proposed. The proposed architecture is based on a hypercube connected ring structure that enjoys the rich topological properties of a hypercube, but it also overcomes one of its drawbacks. In a hypercube, the nodal degree increases with the number of nodes. Hence, the per-node cost of the network increase as the network size grows. However, in a hypercube connected ring network (HCRNet) the nodal degree is small and it remains constant, independent of the network population. The HCRNet, like the hypercube, is perfectly symmetric in the sense that average internodal distance in an N-node HCRNet is the same from any source node. Its average internodal distance is in the order of logN and it is comparable to other regular structures such as Trous and ShuffleNet. The authors present the structural properties of the HCRNet and the network routing.<<ETX>>
31501132
Optical switch configuration and lightpath assignment in wavelength routing multihop lightwave networks
A wide-area transparent optical network can be constructed by using wavelength routers and switches, each dealing with only a small number of wavelengths. In this work we consider the problem of configuring the wavelength routers based on the observed traffic. Various policies for wavelength routing, and the corresponding assignment of wavelengths along the routes have been studied before, which are based on minimizing congestion, average hop-distance, and call blocking probability or on maximizing carried traffic, and the number of clear channels. However these approaches often lead to scenarios where a significant number of available wavelengths at the input/output ports of the routers cannot be used due to potential wavelength conflict. The wavelength routing and assignment algorithms presented in this paper focus on maximizing the wavelength-utilization at the switching devices which also improve the overall network performance.
17465088
An efficient channel-feedback-based adaptive protocol for scheduling variable-length messages on slotted, high-speed fiber optic LANs/MANs
This paper is based on the continuation-bit approach in conjunction with a probabilistic scheduling strategy called the p/sub i/-persistent protocol. This combination has been proposed as an efficient multiple access protocol for transmitting variable-length messages on slotted, high-speed, fiber-optic, bus-structured local and metropolitan area networks (LANs/MANs). Specifically, the authors extend the previous static model on this approach to the dynamic case so that the protocol can be implemented. A dynamic simulation model of the protocol using the continuation-bit approach has been formulated, and channel feedback information has been used to calibrate the operating parameters in real time. Since the goal was to study the operation of the dynamic protocol with variable-length messages, variable-bit-rate coded (i.e., compressed) video was chosen as the traffic to be carried by the network in the illustrative examples. The simulation model indicates that channel feedback is a good approach for dynamically adjusting the network parameters as the network loading and the message lengths fluctuate. Even at a network utilization of 0.6, it was found that almost all video messages were transmitted from the station buffers before the next video message arrived.<<ETX>>
43624883
Algorithms for optimized node arrangements in ShuffleNet based multihop lightwave networks
The unique capabilities of lightwave technology are exploited in order to construct optimized regular multihop networks when the traffic flow among the network nodes is asymmetric. The specific problem addressed is as follows: given that the network nodes must be connected in a regular interconnection pattern and that the node positions in the regular network can be adjusted by properly tuning their (optical) transceivers, what is the best node placement in a given regular topology? In particular, the ShuffleNet-based regular topology is examined. ShuffleNet has the property of producing large connected graphs with small degree and diameter. In order words, it can interconnect a large number of nodes with a small number of transceivers per node such that information from a source can reach its destination in a small number of hops. Since finding the optimal node placement is a computationally hard problem, efficient heuristic algorithms are formulated to design optimized ShuffleNet structures for a given traffic matrix.<<ETX>>
206575726
Regular multihop logical topologies for lightwave networks
Several government- and industry-funded prototyping and development activities in WDM optical networks are being conducted at various R&D centers. Optical networks can be deployed on top of an existing physical fiber plant that can provide a transparent all-optical signal path to its upper layer, thereby providing broadband services. For instance, an all-optical layer between the physical and ATM layers in a B-ISDN network will significantly improve both efficiency and flexibility for the provision of broadband services. One attractive feature of optical networks is the ease of its logical reconfigurability, i.e., any desired logical network topology can be embedded on top of any given physical fiber plant, subject to the limitations on the number of available wavelengths and transceivers. The logical topologies can be broadly classified into two categories: arbitrary and regular. Nodal connectivity patterns in regular topologies are very systematic and well defined, which simplifies routing and management operations. However, it is difficult to add an arbitrary number of nodes to a regular topology and still maintain its well-defined structure. Over the past few years, several regular logical topologies have been proposed for optical networks. In this article we provide brief descriptions of these regular logical network topologies and a comparative study of their various performance metrics, e.g., average hop distance (viz. network utilization), routing, fault tolerance, and scalability.
22414487
On the Effectiveness of Flow Aggregation in Improving Instruction Reuse in Network Processing Applications
Instruction Reuse is a microarchitectural technique that exploits dynamic instruction repetition to remove redundant computations at run-time. In this paper we examine instruction reuse of integer ALU and load instructions in network processing applications and attempt to answer the following questions: (1) How much of instruction repetition can be reused in packet processing applications?, (2) Can the temporal locality of network traffic be exploited to reduce interference in the Reuse Buffer and improve reuse? and (3) What is the effect of reuse on microarchitectural features such as resource contention and memory accesses? We use an execution driven simulation methodology to evaluate instruction reuse and find that for the benchmarks considered, 1 to 50% of the dynamic instructions are reused yielding performance improvement between 1 and 20%. To further improve reuse, a flow aggregation scheme as well as an architecture for exploiting the same is proposed. This scheme is mostly applicable to header processing applications and exploits temporal locality in packet data to uncover higher reuse. As a side effect, instruction reuse reduces memory traffic and improves performance.
2137839
Implementation of a Scalable Context-Aware Computing System
Context-aware computing involves the automatic tailoring of information and services based on the current location of the user. In this paper, we describe our experience in implementing Rover, a system that enables location-based services, as well as the traditional time-aware, user-aware and device-aware services. To achieve system scalability to very large client sets, Rover servers are implemented in an “action-based” concurrent software architecture that enables fine-grained application-specific scheduling of tasks. We have demonstrated its feasibility through implementations for both outdoor and indoor environments on multiple platforms.
14357613
Construction of an efficient overlay multicast infrastructure for real-time applications
This paper presents an overlay architecture where service providers deploy a set of service nodes (called MSNs) in the network to efficiently implement media-streaming applications. These MSNs are organized into an overlay and act as application-layer multicast forwarding entities for a set of clients. We present a decentralized scheme that organizes the MSNs into an appropriate overlay structure that is particularly beneficial for real-time applications. We formulate our optimization criterion as a "degree-constrained minimum average-latency problem" which is known to be NP-hard. A key feature of this formulation is that it gives a dynamic priority to different MSNs based on the size of its service set. Our proposed approach iteratively modifies the overlay tree using localized transformations to adapt with changing distribution of MSNs, clients, as well as network conditions. We show that a centralized greedy approach to this problem does not perform quite as well, while our distributed iterative scheme efficiently converges to near-optimal solutions.
8548869
OMNI: An efficient overlay multicast infrastructure for real-time applications
We consider an overlay architecture (called OMNI) where service providers deploy a set of service nodes (called MSNs) in the network to efficiently implement media-streaming applications. These MSNs are organized into an overlay and act as application-layer multicast forwarding entities for a set of clients. We present a decentralized scheme that organizes the MSNs into an appropriate overlay structure that is particularly beneficial for real-time applications. We formulate our optimization criterion as a ''degree-constrained minimum average-latency problem'' which is known to be NP-Hard. A key feature of this formulation is that it gives a dynamic priority to different MSNs based on the size of its service set. Our proposed approach iteratively modifies the overlay tree using localized transformations to adapt with changing distribution of MSNs and clients, as well as network conditions. We show that a centralized greedy approach to this problem does not perform quite as well, while our distributed iterative scheme efficiently converges to near-optimal solutions.
37654158
XML Schemas in Oracle XML DB
The W3C XML Scheme language is becomimg increasingly popular for expressing the data model for XML documents. It is a powerful language that incorporates both strutural and datatype modeling features. There are many benefits to storing XML Schema compliant data in a database system, including better queryability, optimied updates and stronger validation. However, the fidelity of the XML document cannot be sacrificed. Thus, the fundamental problem facing database implementers is: how can XML Schemes be mapped to relational (and object-relational) database without losing schema semantics or data-fidelity? In this paper, we present the Oracle XML DB solution for a flexible mapping of XML Schemas to object-relational database. It preserves document fidelity, including ordering, namespaces, comments, processing instructions etc., and handles all the XML Schema semantics including cyclic definitions, dervations (extension and restriction), and wildcards. We also discuss various query and update optimiations that involve rewriting XPath operations to directly operate on the underlying relational data.