Showing papers on "Network topology published in 1995"

Characterization and generation of a general class of resource-constrained project scheduling problems

Abstract: This paper addresses the issue of how to generate problem instances of controlled difficulty. It focuses on precedence- and resource-constrained (project) scheduling problems, but similar ideas may be applied to other network optimization problems. It describes a network construction procedure that takes into account a) constraints on the network topology, b) a resource factor that reflects the density of the coefficient matrix, and c) a resource strength, which measures the availability of resources. The strong impact of the chosen parametric characterization of the problems is shown via an in depth computational study. Instances for the single- and multi-mode resource-constrained project scheduling problem are benchmarked by using the state of the art (branch and bound) procedures. The results provided, demonstrate that the classical benchmark instances used by several researchers over decades belong to the subset of the very easy ones. In addition, it is shown that hard instances, being far more smalle...

A distributed routing algorithm for mobile wireless networks

Abstract: We present a loop-free, distributed routing protocol for mobile packet radio networks. The protocol is intended for use in networks where the rate of topological change is not so fast as to make “flooding” the only possible routing method, but not so slow as to make one of the existing protocols for a nearly-static topology applicable. The routing algorithm adapts asynchronously in a distributed fashion to arbitrary changes in topology in the absence of global topological knowledge. The protocol's uniqueness stems from its ability to maintain source-initiated, loop-free multipath routing only to desired destinations with minimal overhead in a randomly varying topology. The protocol's performance, measured in terms of end-to-end packet delay and throughput, is compared with that of pure flooding and an alternative algorithm which is well-suited to the high-rate topological change environment envisioned here. For each protocol, emphasis is placed on examining how these performance measures vary as a function of the rate of topological changes, network topology, and message traffic level. The results indicate the new protocol generally outperforms the alternative protocol at all rates of change for heavy traffic conditions, whereas the opposite is true for light traffic. Both protocols significantly outperform flooding for all rates of change except at ultra-high rates where all algorithms collapse. The network topology, whether dense or sparsely connected, is not seen to be a major factor in the relative performance of the algorithms.

A measurement-based admission control algorithm for integrated services packet networks

Abstract: Many designs for integrated service networks offer a bounded delay packet delivery service to support real-time applications. To provide bounded delay service, networks must use admission control to regulate their load. Previous work on admission control mainly focused on algorithms that compute the worst case theoretical queueing delay to guarantee an absolute delay bound for all packets. In this paper we describe a measurement-based admission control algorithm for predictive service, which allows occasional delay violations. We have tested our algorithm through simulations on a wide variety of network topologies and driven with various source models, including some that exhibit long-range dependence, both in themselves and in their aggregation. Our simulation results suggest that, at least for the scenarios studied here, the measurement-based approach combined with the relaxed service commitment of predictive service enables us to achieve a high level of network utilization while still reliably meeting the delay bound.

Atomic Broadcast

Abstract: In distributed systems subject to random communication delays and component failures, atomic broadcast can be used to implement the abstraction of synchronous replicated storage, a distributed storage that displays the same contents at every correct processor as of any clock time. This paper presents a systematic derivation of a family of atomic broadcast protocols that are tolerant of increasingly general failure classes: omission failures, timing failures, and authentication-detectable Byzantine failures. The protocols work for arbitrary point-to-point network topologies, and can tolerate any number of link and process failures up to network partitioning. After proving their correctness, we also prove two lower bounds that show that the protocols provide in many cases the best possible termination times.

Locating nearby copies of replicated Internet servers

Abstract: In this paper we consider the problem of choosing among a collection of replicated servers, focusing on the question of how to make choices that segregate client/server traffic according to network topology. We explore the cost and effectiveness of a variety of approaches, ranging from those requiring routing layer support (e.g., anycast) to those that build location databases using application-level probe tools like traceroute. We uncover a number of tradeoffs between effectiveness, network cost, ease of deployment, and portability across different types of networks. We performed our experiments using a simulation parameterized by a topology collected from 7 survey sites across the United States, exploring a global collection of Network Time Protocol servers.

Architecting noncooperative networks

Abstract: In noncooperative networks users make control decisions that optimize their individual performance measure. Focusing on routing, two methodologies for architecting noncooperative networks are devised, that improve the overall network performance. These methodologies are motivated by problem settings arising in the provisioning and the run time phases of the network. For either phase, Nash equilibria characterize the operating point of the network. The goal in the provisioning phase is to allocate link capacities that lead to systemwide efficient Nash equilibria. The solution of such design problems is, in general, counterintuitive, since adding link capacity might lead to degradation of user performance. For systems of parallel links, it is shown that such paradoxes cannot occur and that the optimal solution coincides with the solution in the single-user case. Extensions to general network topologies are derived. During the run time phase, a manager controls the routing of part of the network flow. The manager is aware of the noncooperative behavior of the users and makes its routing decisions based on this information while aiming at improving the overall system performance. We obtain necessary and sufficient conditions for enforcing an equilibrium that coincides with the global network optimum, and indicate that these conditions are met in many cases of interest. >

System for managing topology of a network in spanning tree data structure by maintaining link table and parent table in each network node

Abstract: A topology manager within a data communication network including a number of nodes interconnected by bi-directional links, wherein each said node is provided with means for dynamically setting and storing within the node a full topology database including full parent-node-relationship references. The system is is capable of fast path determination and fast spanning tree recovery based on the topology database contents.

Code assignment for hidden terminal interference avoidance in multihop packet radio networks

Abstract: Hidden terminal interference is caused by the (quasi-) simultaneous transmission of two stations that cannot hear each other, but are both received by the same destination station. This interference lowers the system throughput and increases the average packet delay. Some random access protocols that reduce this interference have been proposed, e.g., BTMA protocol. However, the hidden terminal interference can be totally avoided only by means of code division multiple access (CDMA) schemes. In the paper, the authors investigate the problem of assigning orthogonal codes to stations so as to eliminate the hidden terminal interference. Since the codes share the fixed channel capacity allocated to the network in the design stage, their number must not exceed a given bound. The authors seek assignments that minimize the number of codes used. They show that this problem is NP-complete, and thus computationally intractable, even for very restricted but very realistic network topologies. Then, they present optimal algorithms for further restricted topologies, as well as fast suboptimal centralized and distributed heuristic algorithms. The results of extensive simulation set up to derive the average performance of the proposed heuristics on realistic network topologies are presented. >

Competitive algorithms for distributed data management

Abstract: We deal with the competitive analysis of algorithms for managing data in a distributed environment. We deal with the file allocation problem, where copies of a file may be be stored in the local storage of some subsets of processors. Copies may be replicated and discarded over time so as to optimize communication costs, but multiple copies must be kept consistent and at least one copy must be stored somewhere in the network at all times. We deal with competitive algorithms for minimizing communication costs, over arbitrary sequences of reads and writes, and arbitrary network topologies. We define the constrained file allocation problem to be the solution of many individual file allocation problems simultaneously, subject to the constraints of local memory size. We give competitive algorithms for this problem on the uniform network topology. We then introduce distributed competitive algorithms for on-line data tracking (a generalization of mobile user tracking) to transform our competitive data management algorithms into distributed algorithms themselves.

Performance and status monitoring in a computer network

Abstract: Provided is a method and a system for computer network monitoring, implemented in a network in which processes communicate using message queuing. Each node of the network has a network management program installed thereon which includes two independent components: a Point Of Control (POC) program for initiating network tests by injecting a test message into the network and for receiving responses from all the nodes of the network; and a Network Test Program (NTP) for sending a reply message to the single POC for a particular test when the NTP receives test messages within that test, and for propagating the test by forwarding a message to all of the current node's adjacent nodes. Test results are analyzed at the POC for display to the network administrator. Injected test messages propagate throughout the network in a self-exploring manner, exploiting the parallelism of the network. The individual nodes are not required to know the network topology other than to know their nearest neighbor nodes.

Back-propagation network and its configuration for blood vessel detection in angiograms

Abstract: A neural-network classifier for detecting vascular structures in angiograms was developed. The classifier consisted of a multilayer feedforward network window in which the center pixel was classified using gray-scale information within the window. The network was trained by using the backpropagation algorithm with the momentum term. Based on this image segmentation problem, the effect of changing network configuration on the classification performance was also characterized. Factors including topology, rate parameters, training sample set, and initial weights were systematically analyzed. The training set consisted of 75 selected points from a 256/spl times/256 digitized cineangiogram. While different network topologies showed no significant effect on performance, both the learning process and the classification performance were sensitive to the rate parameters. In a comparative study, the network demonstrated its superiority in classification performance. It was also shown that the trained neural-network classifier was equivalent to a generalized matched filter with a nonlinear decision tree. >

Predictive Q-Routing: A Memory-based Reinforcement Learning Approach to Adaptive Traffic Control

Abstract: In this paper, we propose a memory-based Q-Iearning algorithm called predictive Q-routing (PQ-routing) for adaptive traffic control. We attempt to address two problems encountered in Q-routing (Boyan & Littman, 1994), namely, the inability to fine-tune routing policies under low network load and the inability to learn new optimal policies under decreasing load conditions. Unlike other memory-based reinforcement learning algorithms in which memory is used to keep past experiences to increase learning speed, PQ-routing keeps the best experiences learned and reuses them by predicting the traffic trend. The effectiveness of PQ-routing has been verified under various network topologies and traffic conditions. Simulation results show that PQ-routing is superior to Q-routing in terms of both learning speed and adaptability.

On generalized fat trees

Abstract: We introduce and analyze a new family of multiprocesser interconnection networks, called generalized fat trees, which include as special cases the fat trees used for the connection machine architecture CM-5, pruned butterflies, and various other fat trees proposed in the literature. The generalized fat trees provide a formal unifying concept to design and analyse a fat tree based architecture. The extended generalized fat tree network XGFT(h; m/sub 1/, ..., m/sub h/; w/sub 1/, ..., w/sub h/) of height h has /spl Pi//sub i=1//sup h/ m/sub i/ leaf processors and the inner nodes serve only as switches or routers. Each non-leaf node in level i has m/sub i/ children and each non-root has w/sub i+1/ parent nodes. The generalized fat trees provide regularity, symmetry, recursive scalability, maximal fault-tolerance, logarithmic diameter bisection scalability, and permit simple algorithms for fault tolerant self-routing and broadcasting. These networks are also versatile, since they can efficiently embed rings, meshes and tori, trees, pyramids and hypercubes. >

Routing method for setting up a service between an origination node and a destination node in a connection-communications network

Abstract: A setup procedure employing distributed hop-by-hop routing reduces the number of signaling messages needed to establish a service (i.e., connection), thus enhancing network performance. A service is setup between an origination node and a destination node which are a part of a network of communication nodes interconnected by links. Each node maintains a topological database representing the network topology. Initially, a setup message for initiating the service is transmitted from the origination node to a neighboring node that serves as a local node. The topological database is then updated after the local node receives the setup message by eliminating links connected to a particular set of nodes. This set of nodes includes those nodes other than the local node that have previously transmitted a setup or failure message for the service. A shortest path is next determined from the local node to the destination node over the updated topology and another setup message is transmitted from the local node to a first neighboring node in the shortest path. The previously-mentioned steps are repeated, beginning with the step of updating the topological database, where the neighboring node now serves as a subsequent local node. The steps are repeated until either a setup message reaches the destination node so that the service enters a connected state or no shortest path is found at the origination node, which indicates that the service has failed to enter a connected state.

Emerging technologies for fiber network survivability

Abstract: Reducing network protection costs, while maintaining an acceptable level of survivability, has become an important challenge for network planners and engineers. This article will review technology and architectures that may be used to implement cost effective survivable fiber networks for each transport layer, and discuss the interworking system between survivability mechanisms across different layers and associated open issues. Standards development, product availability and the current status of deployment will also be reviewed. The first section reviews a class of survivable fiber network architectures that has been deployed or is scheduled to be deployed. Next is a review of emerging technologies for these survivable architecture implementations. These emerging technologies include SONET, ATM, and passive optical technology. Finally the issue of multiple layer interworking on SONET/ATM networks is discussed. >

BAHAMA: a broadband ad-hoc wireless ATM local-area network

Abstract: We describe the theory, design and ongoing prototyping of a wireless ATM LAN/PBX capable of supporting mobile users with multi-Mb/s access rates and multi-Gb/s aggregate capacities. Our proposed LAN consists of network nodes called portable base stations (PBS) providing microcell coverage. The PBSs are designed to be low-cost, compact and high-speed and can be relocated conveniently. We employ a concept of ad-hoc networking in the layout of the PBS-to-PBS interconnection. That is, the PBSs can be distributed in an arbitrary topology to form a backbone network and can be reconfigured with relative ease. The PBS-to-PBS backbone links are high-speed (Gb/s) for supporting high system capacity. Although they can either be wired or wireless, our emphasis is on wireless implementations. The user-to-PBS links, on the other hand, are primarily for mobile access (e.g., 2-20 Mb/s) and therefore are wireless. Wired connections from stationary users to PBSs are also possible. Typical mobile users are assumed to be laptops or notebook computers. Services supported include conventional data applications (e.g., over TCP/IP or SPX/IPX) as well as multimedia (video, voice and data) applications with QoS (quality-of-service) guarantees. A "aireless ATM" concept is proposed so as to provide seamless internetworking with other wired ATM local and wide-area networks. Algorithms and control in our network are highly distributed for simple implementations and ease of mobility management. A new wireless VP/VC concept and a homing algorithm are described to provide ATM cell routing and connections in the network. PBS hardware and software architectures are discussed. Call management, network management and signaling are designed for simplicity, high performance and modular implementations. A fast network restoration scheme is proposed to cope with the potential link or node failures in the ad-hoc network. Error control is addressed taking the unreliable wireless links into consideration. Finally, a prototyping project called BAHAMA (broadband ad hoc ATM anywhere) for demonstrating this network concept is briefly outlined.

Routing and wavelength assignment methods in single-hop all-optical networks with blocking

Abstract: We consider single-hop all-optical networks in which wavelength-routed connections (lightpaths) between source-destination pairs are dynamically established and torn down in response to a random pattern of arriving connection requests and connection holding times. A connection request may be blocked if no wavelength is available on a suitable path from source to destination. For these networks we consider several methods for routing and wavelength assignment which combine in various ways three main principles: wavelength reservation, protecting threshold and alternate routes. The methods are evaluated and compared in two case studies. In this type of network the traffic over lightpaths consisting of multiple links is susceptible to high blocking probabilities, which can interfere with the quality of service requirements. It is shown that some of the routing and wavelength assignment methods studied have the potential to overcome this difficulty.

IEEE 1394 High Performance Serial Bus: The Digital Interface for ATV

Abstract: The advent of the digital video revolution has created the need for a high-speed digital interface between consumer electronic devices in the home. Examples of this include the interface between a set-top box, a television, and a DVCR or camcorder using MPEG-2 transport streams, and the control and data between interactive games, computers and other devices. Clearly, an interface that supports the general transfer of data is required. The IEEE 1394 standard provides an optimum solution. This paper discusses our proposed implementation of a 1394 based solution and discusses its capabilities and operation in the interactive consumer ATV environment. >

ATM network topology auto discovery method

Abstract: A network topology discovery method automatically recognizes the physical connection relationships of each ATM switch and each ATM terminal within an ATM network. Each ATM switch and ATM terminal mutually exchanges, by ILMI protocol, port identifiers that identify every ATM port of the ATM switch or ATM terminal as well as network addresses of network management agents that manage the ATM switch and the ATM terminal, to neighboring ATM switches and ATM terminals that are directly connected to its ports. Each ATM switch and ATM terminal stores tables for each of its ATM ports that include port identifiers which indicate the identities of connected ports as well as the network addresses of the network management agents that manage the neighboring ATM switches and ATM terminals. The ATM switches or ATM terminals automatically recognize the local connection relationships with its neighboring ATM switches or ATM terminals, using a network management system, by accessing connection information and then automatically recognizing the physical connection relationships of each ATM switch and each ATM terminal. The network management system recognizes the configuration within an ATM network, whether the network management system is inside or outside the ATM network, including when a router or existing LAN coexists with the ATM network. The identities of ports connected to each port are recognized, when a plurality of links exist between ATM switches, without requiring the assignment of a respective one of its ATM network management agents to each ATM switch. Interfaces between ATM switches as well as between an ATM switch and an ATM terminal are also automatically identified.

System design choices in personal communications

Abstract: The authors outline techniques for dealing with variable propagation conditions for single user channels. They perform comparisons of interference averaging and avoidance multiple access strategies for cellular systems, with capacity as a function of minimum acceptable signal to interference ratio. They discuss some interference suppression methods. Multiple base stations are presented as a means of further increasing capacity. Throughout all of the above, the discussion is centered on connection-oriented traffic such as voice and video, with communication mediated by a network of base stations. The authors then discuss three different personal communication systems being developed at UCLA, illustrating some of the design trade-offs available in achieving low power consumption, high spectral efficiency, and flexible network topology. They conclude with a summary of their perception of the system design choices available at the physical layer. >

Integer programming based topology selection of cell-level analog circuits

Abstract: A new approach to cell-level analog circuit synthesis is presented. This approach formulates analog synthesis as a Mixed-Integer Nonlinear Programming (MINLP) problem in order to allow simultaneous topology and parameter selection. Topology choices are represented as binary integer variables and design parameters (e.g., device sizes and bias voltages) as continuous variables. Examples using a Branch and Bound method to efficiently solve the MINLP problem for CMOS two-stage op amps are given. >

Spanning tree method for link state aggregation in large communication networks

Abstract: We consider a communication network in which dynamic routing is used for establishing connections that support information transfer between end-users. Link state information is exchanged and maintained up-to-date among network nodes for path computation and network resource allocation. When the population of users is large, the amount of link state information can be overwhelming. A common solution is to use a hierarchical structure. In this paper, we present a method for aggregating link state information in a hierarchical network. We assume that each link state parameter associated with a link is symmetrical in both directions of the link. The key idea for the method is to first reduce the original subnetwork topology to a full-mesh representation that consists of a logical link for each pair of border nodes in the subnetwork, and then encode the link state information associated with the full-mesh representation with an appropriate spanning tree.

Batch transfer system and method for high performance graphic display of network topology

Abstract: Discovery/layout software (101) configures a general purpose computer system to act as a management station (100') using the industry standard SNMP protocol. The discovery/layout software (101) has a discovery mechanism (302) and a layout mechanism (304) which, in combination, permit the discovery/layout software (101) to provide various submaps (202-210) on demand to a display (108). The submaps (202-210) are directed to various hierarchical views of the network (118). The discovery mechanism (302) monitors and discovers the device configuration on the network (118) and maintains a topology data base (314) indicative thereof. A layout mechanism (304) has a translator (318) which converts the topology data from the topology data base (314) to map data, which is maintained in a map data base (326). Significantly, topology data is received by the translator (318) in a batch and, in addition, map data is transferred from the translator (318) in a batch so that context switching involving the change of control over the processor (102) and operating system (122) is minimized and the performance of the management station (100') is significantly enhanced.

Traffic routing for satellite communication system

Abstract: Methods and apparatus which route, control and manage traffic throughout a Satellite Communication System operating in low Earth orbit are disclosed. Voice, video and data traffic from terrestrial gateways (G) and from portable (P), mobile (M) or fixed (F) terminals are directed up through the constellation of satellites (S) and back down to destinations on Earth. The satellites provide continuous worldwide communication services while insuring uniform end-to-end transmission delays. The satellite network is highly adaptive to the constantly changing network topology, and will offer a synchronous circuit switched communication service that provides sequential delivery of user data, regardless of the type of the data transmitted. The network employs datagram switching, as opposed to conventional virtual circuit switching techniques. Packets associated with a single phone call do not necessarily travel along the same route, and consequently arrive at their common destinations at different times with a variable transmission delay. Packets (26) received from a portable (P), mobile (M) or fixed (F) terminal, from a satellite (S), or from a stationary gateway (G) are dispatched from an origin node (OUR -- NODE) to a destination node (DEST -- NODE) according to address instructions carried in the packet header (28). At each node, propagation delay vectors OUR -- DELAY -- EST DEST -- NODE, ! are calculated using local computers. These delay vectors estimate a time delay which the packet (26) encounters in traveling from the origin node (OUR -- NODE) to the destination node (DEST -- NODE). An optimal route (opt -- link) is then selected from the set of calculated delay vectors, and the packet (26) is routed to the destination node (DEST -- NODE) via the pathway (opt -- link) that insures both the lowest end-to-end delay and the best overall traffic management of the network.

The message flow model for routing in wormhole-routed networks

Abstract: In this paper, we introduce a new approach to deadlock-free routing in wormhole-routed networks called the message flow model. This method may be used to develop deterministic, partially-adaptive, and fully-adaptive routing algorithms for wormhole-routed networks with arbitrary topologies. We first establish the necessary and sufficient condition for deadlock free routing, based on the analysis of the message flow on each channel. We then use the model to develop new adaptive routing algorithms for 2D meshes. >

Topological design and routing for low-Earth orbit satellite networks

Abstract: We investigate a topological design and routing problem for low Earth orbit (LEO) satellite communication networks where each satellite can have a limited number of direct inter-satellite links (ISLs) to a subset of satellites within its line-of-sight. First, we model LEO satellite network as a FSA (finite state automaton) using satellite constellation information. Second, we solve a combined topological design and routing problem for each configuration corresponding to a state in the FSA. The topological design (or link assignment) problem deals with the selection of ISLs, and the routing problem handles the traffic distribution over the selected links to maximize the number of carried calls. This NP-complete mixed integer optimization problem is solved by a two-step heuristic algorithm that first solves the topological design problem, and then finds the optimal routing. The algorithm is iterated using the simulated annealing technique until the near-optimal solution is found. The link assignment table and the routing table that are pre-calculated off-line for each state are loaded into the satellites and a new set of these tables are retrieved at each state transition. The simulation result shows that the proposed method is applicable to practical LEO satellite networks.

On the Bounded-Skew Clock and Steiner Routing Problems

Abstract: We study theminimum-cost bounded-skewrouting tree (BST) problem under the linear delay model. This problem captures several engineering tradeoffs in the design of routing topologies with controlled skew. We propose three tradeoff heuristics. (1) For a fixed topology Extended-DME (Ex-DME) extends the DME algorithm for exact zero-skew trees via the concept of a merging region. (2) For arbitrary topology and arbitrary embedding, Extended Greedy-DME (ExG-DME) very closely matches the best known heuristics for the zero-skewcase,and for the infinite-skewcase (i.e., the Steiner minimal tree problem). (3) For arbitrary topology and single-layer (planar) embedding, the Extended Planar-DME (ExP-DME) algorithm exactly matches the best known heuristic for zero-skewplanar routing, and closely approaches the best known performance for the infinite-skewcase. Ourwork provides unifications of the clock routing and Steiner tree heuristic literatures and gives smooth cost-skew tradeoff that enable good engineering solutions.

Scalable distributed computing environment

Abstract: The present invention relates to disbributed computing systems and is more particularly directed to an architecture and implementation of a scalable distributed computing environment which facilitates communication between independently operating nodes on a single network or on interconnected networks, which may be either homogeneous or heterogeneous. The present invention is a dynamic, symmetrical, distributed, real-time, peer-to-peer system comprised of an arbitrary number of identical (semantically equivalent) instances, i.e., kernels, that together form a logical tree. The kernels exhibit unified and consistent behavior at run time through a self-configuring and self-maintaining logical view of the network. Each kernel resides at a network node that has one or more resources associated with it. The kernels dynamically locate one another in real-time to form and maintain a hierarchical structure that supports a virtually unlimited number of independently running kernels. The system maintains its logical view of the network and user-developed programmatic resources regardless of the number and combinations of transport protocols and underlying mix of physical topologies. The system's communications services utilize a dynamic context bridge to communicate between end nodes that may not share a common transport protocol stack, thereby allowing applications residing on different stacks to communicate with one another automatically and transparently.