Vladimir Shurbanov

Coordinated flocking of UAVs for improved connectivity of mobile ground nodes

Unmanned aerial vehicles (UAV) have been used by the military for surveillance and reconnaissance operations for the past few decades. The recent proliferation of wireless networking technologies enables the equipment of UAVs with wireless transceivers, and that can in turn allow them to communicate with the friendly ground nodes as well as other UAVs. Since rugged ground terrain can result in significant signal attenuation, the ground network can be severely partitioned. However the lower propagation loss between ground and airborne nodes can be effectively utilized to connect the islands of connectivity on the ground to farm a unified ad hoc network. In this paper, we investigate the UAV placement and navigation strategies with the end goal of improving network connectivity. Since the ground nodes can be mobile, a fixed placement strategy is either inadequate or wasteful; hence, we propose to use local flocking rules that aerial living beings like birds and insects follow, to meet our goals. We show by simulation that a flocking based navigation strategy is adaptive to the motion of ground nodes and can indeed maintain high connectivity in a mobile ground network.

Dynamic reconfiguration in high-speed computer clusters

High-speed local and system area networks may change their topology due to switching on/off of routers and hosts or due to component failures. In such cases, a reconfiguration algorithm must be executed to restore the network connectivity and thus achieve high system reliability. However, most of the solutions are based either on redundant network paths or on regular network topologies.The purpose of this paper is to specify NetRec, a novel algorithm for dynamically reconfiguring an arbitrary network topology when a permanent node fault occurs. Unlike other reconfiguration algorithms, NetRec is applicable for all high-speed computer networks and is compatible with all modern routing techniques, including wormhole-based system area networks. It restores the network connectivity by building a tree that spans all immediate neighbors of the faulty node that are still connected to the network. The algorithm is distributed and does not require any global knowledge.

Performance evaluation of the ServerNet(R) SAN under self-similar traffic

Self-similar traffic distributions have been observed in a wide range of networking applications and models such as LANs, WANs, telnet, FTP, WWW, ISDN, SS7 and VBR traffic over ATM. Therefore, it has been suggested that many other theoretical protocols and systems need to be reevaluated under this different type of traffic before practical implementations potentially show their faults. The ServerNet SAN is a new core technology for server architectures that focuses on moving data. It is a wormhole-routed, packet-switched, point-to-point network with special attention paid to reducing latency and assuring reliability. In this paper we investigate the implications of self-similar traffic distributions in the ServerNet SAN, and compare the results with those obtained on the basis of the Poisson assumption.

The effect of the router arbitration policy on the scalability of ServerNet™ topologies

Abstract Multistage networks are finding increasing use in building clusters of workstations and PCs. The networks that support such connectivity must provide high bandwidth, low latency, scalability, low cost, high level of usability, and reliability [1]. A key parameter that influences the network performance characteristics such as maximum latency, throughput, scalability and tree saturation, is the arbitration policy implemented in routers.

Energy-conserving reception protocols for mobile ad hoc networks

The importance of conserving the limited battery energy available in mobile tactical communication systems is well appreciated in their design. Radio transceivers are major energy consumers in such systems, however fundamental advancements to increase battery capacity and/or reduce transceiver power requirements are not expected in the near future; therefore, energy-conserving techniques are the main avenue for extending system life. In this paper, we propose a suite of reception protocols that support episodic powering down of the radio receiver during periods of low communication activity. The suite covers a range of varying implementation complexion, control-traffic overhead, and energy-saving capability, thus an appropriate solution can be selected according to the particular tactical application. The protocols are considered in the framework of asynchronous (e.g. CSMA) channel access but can be easily adapted to synchronous channel access methods as well. We evaluate the performance of two protocols from the suite in the context of a proactive link-state routing protocol and show that they are capable of significantly reducing energy consumption with little additional complexity and acceptable performance penalties.

Maximum delivery time and hot spots in ServerNet/sup TM/ topologies

This paper centers on analysis of the performance characteristics of ServerNet topologies, concentrating on the prediction through simulation and statistical analysis of the maximum two-way delivery time, the identification of congested links (hot spots) and tree saturation. ServerNet/sup TM/, developed by Tandem Computers Inc., is a wormhole-routed, packet-switched, point-to-point network, with special attention paid to reducing latency and to assuring reliability. ServerNet uses multiple high-speed, low-cost routers to rapidly switch data directly between data sources and destinations. Our study is based on data generated by a simulation tool. Statistical analysis and inference methods were used to process the samples generated by the simulator and to obtain estimates for the maximum two-way packet delivery time. Link usage statistics were recorded by the simulator for the purpose of performing a detailed investigation of congestion effects and hot spots. Hot spots may cause the occurrence of tree saturation in the network i.e., where an individual tree will become congested (tree saturation) while all other trees are mostly idle, which leads to significant performance degradation.

Optimizing router arbitration in point-to-point networks

In this article we introduce and evaluate a method for optimizing the router arbitration policy in point-to-point networks. These networks use multiple high-speed, low-cost routers to rapidly switch data directly between data sources and destinations. We assume that routers use an arbitration algorithm that has the ability to assign different priorities to different links thus controlling the distribution of available bandwidth among channels. We propose an analytical method that allows us to determine the correct priorities for channels so as to achieve fair arbitration thus minimizing latency, increasing throughput and eliminating tree saturation. In our study we used data generated by a simulation tool to validate the proposed analytical model for determining the weights (priorities) of router ports and to evaluate the resulting performance improvements. Link usage statistics were recorded by the simulator for the purpose of performing a detailed investigation on congestion effects particularly tree saturation. The method was applied to the ServerNet(TM) System Area Network (SAN), developed by Tandem Computers Inc.

The effect of the router arbitration policy on the scalability of ServerNet/sup TM/ topologies

We extend a previously introduced method for optimizing the arbitration policy employed by ServerNet routers and we evaluate the methods effect on scalability. The ServerNet/sup TM/ system area network (SAN), developed by Tandem Computers Inc., is a wormhole-routed, packet-switched, point-to-point network, with special attention paid to reducing latency and to assuring reliability. The ServerNet SAN uses multiple high-speed, low-cost routers to rapidly switch data directly between data sources and destinations. The ServerNet router arbitration algorithm has the ability to assign different priorities to different links thus controlling the distribution of available bandwidth among channels. We propose an analytical method that allows us to determine the correct priorities for channels so as to achieve fair arbitration thus increasing throughput and scalability, minimizing latency, and eliminating tree saturation. In our study we use data generated by a simulation tool to validate the proposed analytical model for determining the weights of router ports and to evaluate the resulting performance improvements.

Flow Control in ServerNetR Clusters

This paper investigates the performance implications of several end-to-end flow-control schemes based on the ServerNetR systemarea network. The static window (SW), packet pair (PP), and the simplified packet pair (SPP) flow control schemes are studied. Additionally, the alternating static window (ASW) flow control is defined and evaluated. Previously, it has been proven that the packet-pair scheme is stable for store-and-forward networks based on Rate Allocation Servers. The applicability of a PP flow control to wormhole-routing networks is studied and evaluated through simulation. It is shown that if high throughput is desired, ASW is the best method for controlling the average latency. On the other hand, if low throughput is acceptable, SPP can be applied to maintain low latencies.

Maximum delivery time and hot spots in ServerNet TM topologies

Abstract This paper will center on analysis of the performance characteristics of ServerNet topologies, concentrating on the prediction, through simulation and statistical analysis, of the maximum two-way delivery time, the identification of congested links (hot spots) and tree saturation. ServerNet TM , developed by Tandem Computers Inc., is a wormhole-routed, packet-switched, point-to-point network, with special attention paid to reducing latency and to assuring reliability. ServerNet uses multiple high-speed, low-cost routers to rapidly switch data directly between data sources and destinations. The maximum two-way delivery time is necessary for determining the values of timeout counters, which are relevant to the fault-tolerant aspect of the system, and the QoS guarantees. Hot spots may cause the occurrence of tree saturation in the network i.e., where an individual tree will become congested (tree saturation) while all other trees are mostly idle, which leads to significant performance degradation. Our study is based on data generated by a simulation tool. Statistical analysis and inference methods were used to process the samples generated by the simulator and to obtain estimates for the maximum two-way packet delivery time. These methods were also used to determine the number of the samples that were required to produce estimates of the desired accuracy. Both the degree of confidence and the percentage of packets are determined by the number of samples generated by the simulator. This allows us to control the quality and accuracy of the estimate to suit our needs. Link usage statistics were recorded by the simulator for the purpose of performing a detailed investigation of congestion effects and hot spots. The study of the static and dynamic link usage statistics revealed that the extreme values of the two-way maximum delivery time were caused by links operating under heavy traffic loads and that under certain traffic patterns a tree saturation effect occurs.