An increasing number of high performance internetworking protocol routers, LAN and asynchronous transfer mode (ATM) switches use a switched backplane based on a crossbar switch. Most often, these systems use input queues to hold packets waiting to traverse the switching fabric. It is well known that if simple first in first out (FIFO) input queues are used to hold packets then, even under benign conditions, head-of-line (HOL) blocking limits the achievable bandwidth to approximately 58.6% of the maximum. HOL blocking can be overcome by the use of virtual output queueing, which is described in this paper. A scheduling algorithm is used to configure the crossbar switch, deciding the order in which packets will be served. Previous results have shown that with a suitable scheduling algorithm, 100% throughput can be achieved. In this paper, we present a scheduling algorithm called iSLIP. An iterative, round-robin algorithm, iSLIP can achieve 100% throughput for uniform traffic, yet is simple to implement in hardware. Iterative and noniterative versions of the algorithms are presented, along with modified versions for prioritized traffic. Simulation results are presented to indicate the performance of iSLIP under benign and bursty traffic conditions. Prototype and commercial implementations of iSLIP exist in systems with aggregate bandwidths ranging from 50 to 500 Gb/s. When the traffic is nonuniform, iSLIP quickly adapts to a fair scheduling policy that is guaranteed never to starve an input queue. Finally, we describe the implementation complexity of iSLIP. Based on a two-dimensional (2-D) array of priority encoders, single-chip schedulers have been built supporting up to 32 ports, and making approximately 100 million scheduling decisions per second.

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The iSLIP scheduling algorithm for input-queued switches

Sensor networks, a new class of devices has the potential to revolutionize the capture, processing, and communication of critical data for use by first responders. CodeBlue integrates sensor nodes and other wireless devices into a disaster response setting and provides facilities for ad hoc network formation, resource naming and discovery, security, and in-network aggregation of sensor-produced data. We designed CodeBlue for rapidly changing, critical care environments. To test it, we developed two wireless vital sign monitors and a PDA-based triage application for first responders. Additionally, we developed MoteTrack, a robust radio frequency (RF)-based localization system, which lets rescuers determine their location within a building and track patients. Although much of our work on CodeBlue is preliminary, our initial experience with medical care sensor networks raised many exciting opportunities and challenges.

/pdf/sensor-networks-for-emergency-response-challenges-and-25gfdlp1ho.pdf

Sensor networks for emergency response: challenges and opportunities

With an increasing emphasis on security, automated personal identification based on biometrics has been receiving extensive attention over the past decade. Iris recognition, as an emerging biometric recognition approach, is becoming a very active topic in both research and practical applications. In general, a typical iris recognition system includes iris imaging, iris liveness detection, and recognition. This paper focuses on the last issue and describes a new scheme for iris recognition from an image sequence. We first assess the quality of each image in the input sequence and select a clear iris image from such a sequence for subsequent recognition. A bank of spatial filters, whose kernels are suitable for iris recognition, is then used to capture local characteristics of the iris so as to produce discriminating texture features. Experimental results show that the proposed method has an encouraging performance. In particular, a comparative study of existing methods for iris recognition is conducted on an iris image database including 2,255 sequences from 213 subjects. Conclusions based on such a comparison using a nonparametric statistical method (the bootstrap) provide useful information for further research.

Personal identification based on iris texture analysis

It is well known that head-of-line blocking limits the throughput of an input-queued switch with first-in-first-out (FIFO) queues. Under certain conditions, the throughput can be shown to be limited to approximately 58.6%. It is also known that if non-FIFO queueing policies are used, the throughput can be increased. However, it has not been previously shown that if a suitable queueing policy and scheduling algorithm are used, then it is possible to achieve 100% throughput for all independent arrival processes. In this paper we prove this to be the case using a simple linear programming argument and quadratic Lyapunov function. In particular, we assume that each input maintains a separate FIFO queue for each output and that the switch is scheduled using a maximum weight bipartite matching algorithm. We introduce two maximum weight matching algorithms: longest queue first (LQF) and oldest cell first (OCF). Both algorithms achieve 100% throughput for all independent arrival processes. LQF favors queues with larger occupancy, ensuring that larger queues will eventually be served. However, we find that LQF can lead to the permanent starvation of short queues. OCF overcomes this limitation by favoring cells with large waiting times.

/pdf/achieving-100-throughput-in-an-input-queued-switch-1twzpb7d3w.pdf

Achieving 100% throughput in an input-queued switch

It is well known that head-of-line (HOL) blocking limits the throughput of an input-queued switch with FIFO queues. Under certain conditions, the throughput can be shown to be limited to approximately 58%. It is also known that if non-FIFO queueing policies are used, the throughput can be increased. However it has not been previously shown that if a suitable queueing policy and scheduling algorithm are used then it is possible to achieve 100% throughput for all independent arrival processes. In this paper we prove this to be the case using a simple linear programming argument and quadratic Lyapunov function. In particular we assume that each input maintains a separate FIFO queue for each output and that the switch is scheduled using a maximum weight bipartite matching algorithm.

/pdf/achieving-100-throughput-in-an-input-queued-switch-30gnma36nn.pdf

The application of neural networks to the optimum routing problem in packet-switched computer networks, where the goal is to minimize the network-wide average time delay, is addressed. Under appropriate assumptions, the optimum routing algorithm relies heavily on shortest path computations that have to be carried out in real time. For this purpose an efficient neural network shortest path algorithm that is an improved version of previously suggested Hopfield models is proposed. The general principles involved in the design of the proposed neural network are discussed in detail. Its computational power is demonstrated through computer simulations. One of the main features of the proposed model is that it will enable the routing algorithm to be implemented in real time and also to be adaptive to changes in link costs and network topology. >

Neural networks for shortest path computation and routing in computer networks

A neural network implementation of an input access scheme in a high-speed packet switch for broadband ISDN (integrated services digital network) is presented. In this switch, each input maintains a separate queue for each output; thus, in an (n*n) switch there will be n/sup 2/ input queues. Using synchronous operation, at most one packet per input and output will be transferred at every slot. A neural network maximizing the throughput of this switch is determined, and the form of the energy function, its optimized parameters, and the connection matrix are given. Simulations with random inputs have yielded results close to optimal throughput. This neural network can be implemented with the existing technology for medium switching sizes. >

A neural network implementation of an input access scheme in a high-speed packet switch

A study of the performance of a cyclic-priority input access mechanism for a multicast switch is carried out. The method is a derivative of the ring token reservation method which eliminates the unfairness of the ordinary ring token reservation. It has the further advantage of being simple and easy to implement. The primary performance measurements are the switch throughput and the packet delay. A key assumption is that all copies of the same packet must be switched in the same slot. >

Performance analysis of cyclic-priority input access method for a multicast switch

In this paper, we study the statistical properties of the connectivity of vehicular ad hoc networks (VANETs) with user mobility at the steady state. It is assumed that the nodes travel along a single dimensional strip with finite length. The nodes arrive at the service strip through one of the traffic entry points following a Poisson process and move along the strip in the same direction according to a user mobility model until they reach their exit point. The service strip allows the users with different speeds to pass each other. The nodes, which are within the service strip, are able to participate in communications. We derive the probability distribution of the user population size within the service strip and node's location distribution. Then, we determine the mean cluster size, fraction of nodes within the cluster and probability that nodes will form a single cluster. This work shows significance of mobility on the connectivity of ad hoc networks. The results of the paper may be used to avoid traffic congestion in the highways.

A Performance Modeling of Vehicular Ad Hoc Networks (VANETs)

In this paper, we study the statistical properties of the connectivity of VANETs with user mobility at the steady state. We assume a network of highways with arbitrary topology. The nodes arrive at the network through one of the traffic entry points following a Poisson process and move within the network according to a mobility model. The path of a node within the network is determined through a routing matrix. The system is modeled as a BCMP network of queues. We derive the probability distribution of the node population size within the network. Then, we determine the probability distribution of the cluster size seen by a new node arriving along a path. The presented numericals results illustrate the effect of mobility on connectivity. The results of the paper may be used to study the routing algorithms, throughput or delay in VANETs.

M. Mehmet Ali

Papers

Neural networks for shortest path computation and routing in computer networks

A neural network implementation of an input access scheme in a high-speed packet switch

Performance analysis of cyclic-priority input access method for a multicast switch

A Performance Modeling of Vehicular Ad Hoc Networks (VANETs)

Generalized Performance Modeling of Vehicular Ad Hoc Networks (VANETs)