Technical Reports

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Plug and play optical (PPO) nodes: network functionalities and built-in fiber characterization techniques
(The University of Texas at Dallas, 2007-05-07) Cerutti, Isabella, 1973-; Fumagalli, Andrea; Hui, Rongqing; Monti, Paolo, 1973-; Paradisi, Alberto; Tacca, Marco, 1973-; Eric Jonsson School of Engineering and Computer Science.
Plug and play optical (PPO) nodes may be used to facilitate the deployment of optical networks. PPO nodes must be able to learn about the signal propagation properties of the surrounding optical fibers and make their wavelength routing decisions based on the collected data. This paper discusses what are the open challenges that must be overcome to provide cost effective and performing ad hoc networking solutions based on PPO nodes. Three possible PPO node hardware architectures trading off complexity, cost and functionalities are presented along with their built-in fiber characterization techniques.
Numerical methods for the accurate calculation of spherical bessel functions and the location of MIE resonances
(The University of Texas at Dallas, 2013-04-16) Cantrell, C. D., (Cyrus D.), 1940-; Center for Applied Optics
This report reviews numerical methods for the accurate calculation of spherical Bessel functions and for the location of Mie resonances in a dielectric sphere. Detailed numerical results are presented for a real index of refraction n = 1.47. FORTRAN source listings are provided for computer programs that implement the algorithms described in the text.
End-to-end QoS guarantee in heterogeneous wired-cum-wireless networks
(The University of Texas at Dallas, 2013-04-16) Li, Ming, 1974-; Zhu, Hua, 1975-; Sathyamurthy, Sathish, 1979-; Prabhakaran, B.; Chlamtac, Imrich
With information access becoming more and more ubiquitous, there is a need for providing QoS support for communication that spans wired and wireless networks. For the wired side, RSVP/SBM has been widely accepted as a flow reservation scheme in IEEE 802 style LANs. In this paper, we investigate the integration of RSVP and a RSVP-like flow reservation scheme in wireless LANs, as an end-to-end solution for QoS guarantee in wired-cum-wireless networks. We propose WRESV, an RSVP-like flow reservation and admission control scheme for IEEE 802.11 wireless LAN. Using WRESV, wired/wireless integration can be easily implemented by cross-layer interaction at the Access· Point. Main components of the integration are RSVP-WRESV parameter mapping, and the initiation of new reservation messages, depending on where senders/receivers are located. In addition, we also propose various optimizations for supporting multicast session, mobility management, and admission control.
Distributed Admission Control for IEEE 802.11 Ad Hoc Networks
(The University of Texas at Dallas, 2013-04-16) Zhu, Hua, 1975-; Li, Ming, 1974-; Chlamtac, Imrich; Prabhakaran, B.
IEEE 802.11 has very poor performance in terms of throughput and transmission delay when the traffic load reaches the saturation condition. Admission control must be provided in order to guarantee the service of existing traffic. Unfortunately, the normalized saturation throughput is variable corresponding to different traffic statistics (i.e. bit-rate and average packet length) . Therefore it does not perform well if the station admits traffic simply based on certain threshold of the normalized throughput. Most existing analytical models for IEEE 802.11 MAC adopt quite strict assumptions of saturation conditions and simplified traffic scenarios. Nevertheless, it is more realistic to analyze the non-saturation condition under heterogeneous traffic scenarios. Moreover, an accurate analytical model under non-saturation condition is critical for the correctness of admission control decisions. In this paper, (1) we propose a unified analytical model which is the first model capable of analyzing performance under both non-saturation and saturation conditions; (2) we then introduce a new performance criterion, saturation coefficient Cn,sat, which reflects the degree of saturation experienced by any specific station; (3) finally we propose a distributed admission control scheme for IEEE 802.11 based on this criterion. With this scheme, any station can make local decision on whether admitting/rejecting a new traffic. The accuracy of the proposed analytical model and performance of the proposed admission control scheme are validated by simulations.
On the complexity of clustering multi-hop wireless networks
(The University of Texas at Dallas, 2013-04-18) Basagni, Stefano, 1965-; Eric Jonsson School of Engineering and Computer Science
A Distributed Clustering Algorithm (DCA) is presented that partitions the nodes of a fully mobile network (multi-hop network) into clusters, thus giving the network a hierarchical organization. Nodes are grouped by following a new weight-based criterium that allows the choice of the nodes that coordinate the clustering process based on node mobility-related parameters. The DCA time complexity is proven to be bounded by a network parameter Db that depends on the possibly changing topology of the network rather than on its size, i.e., the invariant number of the network nodes. Simulation results are given which demonstrate that in a mobile scenario Db-and thus the DCA time complexity-is logarithmic in the size of the network. This result improves exponentially a previously known upper bound on the time complexity of distributed clustering for multi-hop wireless networks.
Wavelength continuity constraint in differentiated reliability (DiR) WDM rings
(The University of Texas at Dallas, 2013-04-18) Fumagalli, Andrea; Tacca, Marco, 1973-; Eric Jonsson School of Engineering and Computer Science. Center for Advanced Telecommunications Systems and Services (CATSS); Texas Higher Education Coordinating Board; Texas Telecommunications Engineering Consortium (TxTEC); National Science Foundation (U.S.)
The concept of Differentiated Reliability (DiR) was recently introduced by the authors to provide multiple reliability degrees (or classes) at the same network layer using a common protection mechanism, e.g., path switching. According to the DiR concept, each connection at the layer under consideration is guaranteed a minimum reliability degree, defined as the Maximum Failure Probability allowed for that connection. The reliability degree chosen for a given connection is thus determined by the application requirements, and not by the actual network topology, design constraints, robustness of the network components, and span of the connection. In the paper the DiR concept is applied to designing the Wavelength Division Multiplexing (WDM) layer of a ring network in which wavelength conversion is not available. To solve the routing and wavelength assignment problem at the WDM layer an efficient algorithm is proposed that resorts to reusable protection wavelengths while guaranteeing the required reliability degree of each connection. Lower bounds on the network bandwidth required by two approaches - respectively based on non-reusable and reusable protection wavelengths - reveal interesting properties of the DiR concept and the proposed algorithm.
Distributed and mobility-adaptive clustering for ad hoc networks
(The University of Texas at Dallas, 2013-04-18) Basagni, Stefano, 1965-; Eric Jonsson School of Engineering and Computer Science
A distributed algorithm is presented that partitions the nodes of a fully mobile network (ad hoc network) into clusters, thus giving the network a hierarchical organization. The algorithm is proven to be adaptive to changes in the network topology due to nodes' mobility and to nodes addition/removal. A new weight-based mechanism is introduced for the efficient cluster formation/maintenance that allows the cluster organization to be configured for specific applications and adaptive to changes in the network status, not available in previous solutions. Simulation results are provided that demonstrate up to an 85% reduction on the communication overhead associated with the cluster maintenance with respect to clustering algorithms previously proposed.
A scalable and adaptive fair access protocol for slotted WDM bus network
(The University of Texas at Dallas, 2013-04-18) Fumagalli, Andrea; Grasso, Robert, 1972-; Eric Jonsson School of Engineering and Computer Science; National Science Foundation (U.S.); Centro Studi e Laboratori Telecomunicazioni (Turin, Italy) (CSELT)
The recent progress of optical technologies has made it possible to increase the number of wavelengths (channels) practically available in the fiber by almost one order of magnitude. With this rapid growth, access protocols originally designed for systems with a few wavelengths may not be adequate to fully utilize the optical bandwidth that is becoming available through this technological breakthrough. This is the case with access protocols designed for unidirectional fiber bus network. The paper proposes a novel access protocol for multi-channel all-optical folded bus network whose performance scales well with the number of wavelengths. This result is achieved using a load balancing algorithm that runs independently at each node and evenly distributes the traffic among the wavelengths. With the proposed protocol, the packet average access delay at a given bandwidth utilization increases only marginally as the number of wavelengths (and proportionally the offered load) is grown in the system. In addition, at all source nodes fair access delay is guaranteed by the protocol under any stable load condition, including non uniform and bursty traffic.
Multi-rate and multi-hop optical carriers in WDM ring
(The University of Texas at Dallas, 2013-04-18) Cerutti, Isabella, 1973-; Fumagalli, Andrea; Tacca, Marco, 1973-; Lardies, Ana; Jagannathan, Rajesh Shanmugavel, 1971-; Eric Jonsson School of Engineering and Computer Science. Center for Advanced Telecommunications Systems and Services (CATSS); Texas Higher Education Coordinating Board
Transparency of the optical layer offers the possibility to design a network that operates at varying transmission bit rates. While variable bit rate interfaces are being tested and will soon provide the possibility to optimally select the transmission rate for each lightpath, the potential advantages of relying upon multiple transmission rates in the optical network are ready yet to be fully explored. In this paper we define the concept of Multi-hop and Multi-rate (M&M) network in which the tributary signal is transmitted over a sequence of lightpaths, with each lightpath operating at its own transmission rate, which is determined by a number of factors including the end node's interface, amount of multiplexed traffic and cost of the network components. The potential advantages provided by the M&M network when compared to first generation optical networks (i.e., SONET/SDH), single- and multi-hop (constant bit rate) optical networks, are discussed in general and demonstrated numerically in a WDM ring. Presented results show that the network cost reduction achieved by the M&M design is a function of the cost ratio between the optical bandwidth (wavelengths) and the optical terminals.
Wireless multimedia networks: cross-layer access protocols based on sequential opportunistic decoding (SOD)
(The University of Texas at Dallas, 2013-05-23) Jegbefume, Onyemelem, 1977-; Saquib, M.; Tacca, Marco, 1973-; Fumagalli, Andrea; Monti, Paolo, 1973-; Eric Jonsson School of Engineering and Computer Science.
Spread spectrum (SS) solutions offer well understood advantages to wireless networking, e.g., robustness to noise and interference, concurrent asynchronous transmissions, effective power and transmission rate control mechanisms. One of the authors' recent advances in this field makes it possible to take SS solutions to the next performance level, i.e., sequential opportunistic decoding, or SOD for short. SOD is based on transmitting data symbols multiple times within the frame using non-orthogonal partial signature waveforms or mini-frames. Depending on the received instantaneous signal-to-interference-plus-noise ratio (SINR), a given subset of such mini-frames may suffice to reliably decode the data symbols. The best performing subset contains mini-frames that are received under better-than-average SINR channel conditions - i.e., these are referred to as the opportunistic mini-frames. By instantaneously controlling the number of mini-frames transmitted, SOD also offers distributed adaptable processing gain. The objective of this report is to propose cross-layer medium access control (MAC) protocols based on SOD. These protocols are especially suited to operate in a crowded radio spectrum, e.g., when multiple WLANs and/or wireless sensor networks coexist in the same radio space, possibly supporting multimedia applications. This unique advantage originates from the integration of two sub-layers. The lower sub-layer (SOD-MAC) applies the SOD adaptable processing gain to contain both the level of interference in the radio channel and network latency. It also minimizes the power consumption at the node and supports multiple c1asses of service. The upper sub-layer (ARQ-MAC) enables statistical multiplexing of an unbounded number of attempts of frame transmission generated by uncoordinated active nodes and it provides the automatic retransmission request (ARQ) capabilities. In essence, the uniqueness of these cross-layer access protocols is their ability to achieve efficient statistical multiplexing of traffic generated by uncoordinated nodes while containing the level of interference in the radio channel. The challenge is to combine frame retransmission schemes and SOD adaptable processing gain strategies in the most effective way, while keeping the access protocols in the stable region. The payoff is the ability to: increase the radio channel utilization, contain network latency, reduce energy consumption at the wireless node, and provide a QoS platform for both real-time and datagram traffic.
The PlaNet-PTN module: a single layer design tool for packet transport networks
(The University of Texas at Dallas, 2013-05-23) Razo, Miguel; Litovsky, Arie; Huang, Wanjun, 1978-; Sivasankaran, Arularasi; Tang, Limin, 1977-; Vardhan, Hars; Tacca, Marco, 1973-; Fumagalli, Andrea; Monti, Paolo, 1973-; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.
PlaNet is a multilayer network planning tool developed at the University of Texas at Dallas. This paper illustrates some of the features of PlaNet-PTN, one of the modules available in the PlaNet tool. PlaNet-PTN can be used to design and plan a single layer packet transport network (PTN). Quality of protection, routing constraints, minimization of the network equipment cost, and user's desired run time of the tool are just some examples of the features available in PlaNet. As shown in the paper, the PlaNet-PTN planning module is able to provide, among others, optimization of Label Switched Path (LSP) routes, link capacity placement, node and link equipment configuration.
Building alternate multitasking trees in MPLS networks
(The University of Texas at Dallas, 2013-05-23) Tang, Limin, 1977-; Billenhalli, Shreejith; Vardhan, Hars; Tacca, Marco, 1973-; Fumagalli, Andrea; Monti, Paolo, 1973-; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.; Next Generation Optical Network (NeGONet) Group; Kungl. Tekniska högskolan (KTH). Photonics and Microwave Engineering (FMI). School of Information and Communication Technology; Royal Institute of Technology (Kista, Sweden)
An algorithm for computing alternate multicast trees in packet transport networks is proposed in this paper. The algorithm efficiently computes multiple sub-optimal tree candidates for a given multicast service request. The algorithm builds on the widely used computation of K ordered loopless shortest paths and can be applied to any connected network topology. Simulation experiments obtained for a multiprotocol label switching (MPLS) network are presented to evaluate the effectiveness and performance of the algorithm.
Finding a simple path with multiple must-include nodes
(The University of Texas at Dallas, 2013-05-23) Vardhan, Hars; Billenahalli, Shreejith, 1982-; Huang, Wanjun, 1978-; Razo, Miguel; Sivasankaran, Arularasi; Tang, Limin, 1977-; Monti, Paolo, 1973-; Tacca, Marco, 1973-; Fumagalli, Andrea; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.
This document presents an algorithm to find a simple path in the given network with multiple must-include nodes. The problem of finding a simple path with only one must-include node can be solved in polynomial time using lower bound max-flow approach. However, including multiple nodes in the path has been shown to be a NP-Complete. This problem may arise in network areas such as forcing the route to go through particular nodes, which have wavelength converter (optical), have monitoring provision (telecom), have gateway functions (in OSPF) or are base stations (in MANET). Also, network standards allow loose definition of routing by requiring one or more nodes to be in the routing of Link State Packet. In this document, a heuristic algorithm is described to find a simple path between a pair of terminals, which has constraint to pass through a certain set of other nodes. The algorithm is comprised into two main steps: (1) considering a pair of nodes in sequence from source to destination as a segment and then computing candidate paths between each segment, and (2) combining paths, one from each segment, in order to make simple path from source to destination. The max-flow approach is used to find candidate paths, a which provides maximum number of edge disjoint paths for individual segments. The second step of the algorithm uses backtracking algorithm for combining paths. The time complexity of the first step of the algorithm is O(kiVIIEI 2 ), where k is the number of must-include nodes. The time complexity of step (2) depends upon total number of candidate paths which are not touching any one of the candidates of other segments. So, the worse case time complexity of step (2) is O(.Ak), where .A is the maximum nodal degree of the network. However, we show that step (2) has minimal effect on the algorithm and it does not grow exponentially with k in this application. Later, we also show that initial re-ordering of the given sequence of must-include nodes can improve the result. The experimental results show that the algorithm is successful in computing near optimal path in reasonable time. keywords: constrained path computation, graph theory, heuristic algorithm, max flow, network route.
An analytical model with improved accuracy of IEEE 802.11 protocol under unsaturated conditions
(The University of Texas at Dallas, 2013-05-23) Vijayasankar, Kumaran, 1984-; Taufique, Azar; Kannan, Lakshmi Narasimhan, 1984-; Tacca, Marco, 1973-; Fumagalli, Andrea; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.
In this work the authors present an analytical model that - compared to previously published work- more accurately captures the delay of IEEE 802.11 protocol under low, medium, and near-saturation load conditions. A Markov chain is used to keep track of the instantaneous number of (active) nodes that have a frame to transmit. The number of active nodes varies over time and is a function of various parameters, including the frame individual maximum retransmission count. One advantage of the proposed analytical model is its ability to estimate the IEEE 802.11 protocol latency and delivery ratio in the presence of quality of service (QoS) classes, each class being defined by a specific maximum retransmission count. Such QoS classes can be adopted to support real time applications for which both latency and delivery ratio must be closely monitored for satisfactory operation. The analytical estimation of these performance parameters may offer useful feedback to admission control schemes.
Cooperative communications in multihop networking: a case study based on the IEEE 802.11 protocol
(The University of Texas at Dallas, 2013-05-24) Kannan, Lakshmi Narasimhan, 1984-; Vijayasankar, Kumaran, 1984-; ChanneGowda, Divya, 1981-; Agarwal, Niraj, 1977-; Fumagalli, Andrea; Tacca, Marco, 1973-; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.
This paper combines multi-hop networking with single-hop cooperative communications. The solution is built upon the standard IEEE 802.11 protocol operating in the ad hoc mode. A simulation based comparison is carried out in order to evaluate the performance gains and benefit of cooperative communications applied to multi-hop networking. Preliminary results indicate that network performance in terms of both throughput and end-to-end delay improves. Additionally, cooperative communications increases robustness against uncertainties in the wireless channel.
Optimization of interference alignment beamforming vectors
(The University of Texas at Dallas, 2013-05-24) Kim, Douglas E.; Torlak, Murat; Eric Jonsson School of Engineering and Computer Science.
Interference alignment, while optimum in its achievement of the maximum degrees of freedom for the K user interference channel, does so only at high SNR and for large numbers of dimensions over which to align the interference, n. A sizable SNR penalty is paid in order to approach the theoretical outerbound and only grows increasingly higher for larger n. For the single antenna, K = 3 interference channel, an efficient means of drastically reducing the required power to approach the outerbound of 3/2 is presented. By no longer using a vector of all ones in the creation of the transmit beamforming vectors as originally proposed, a new weighted vector w is designed in order to distribute the power across the precoding vectors more evenly. Furthermore, we introduce a new structure of beamforming vectors that also provides significant savings in SNR independently of vector w. By doing so, our proposed designs achieve the same degrees of freedom of the original scheme at only a fraction of the SNR.
Reconfigurable optical networks: a cross layer approach
(The University of Texas at Dallas, 2013-05-24) Roshani-Tabrizi, Reza, 1976-; Monti, Paolo, 1973-; Tacca, Marco, 1973-; Fumagalli, Andrea; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.
This paper presents the Pruning with Memory (PWM) algorithm, which computes a cross layer optimal reconfiguration sequence in reconfigurable IP/MPLS over optical networks.
Trading network management complexity for blocking probability when placing optical regenerators
(The University of Texas at Dallas, 2013-05-24) Savasini, Marcio S.; Monti, Paolo, 1973-; Fumagalli, Andrea; Tacca, Marco, 1973-; Waldman, Helio; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.; State University of Campinas. Faculdade de Engenharia Eletrica e de Computacao.
Optical signal regenerators (3R) are required to overcome the adverse effect of fiber and other transmission impairments. 3R units may be placed either at every node (full placement) or at some selected nodes (sparse placement) of the optical network. It has been argued [1] that while the latter placement strategy may not be optimal in terms of the total number of 3R units required to support a given set of static traffic demands, it offers a number of practical advantages over the former, e.g., a contained complexity of network management in terms of signaling overhead. In this paper the full and sparse placement strategies are compared in a dynamic optical network, whereby lightpaths are set up and torn down to best fit the offered changing demands. The study shows that the blocking probability due to the lack of available 3R units achieved by the sparse placement strategy may be comparable to the one achieved by the full placement strategy. Surprisingly, it may even be lower in some cases, thus providing an additional motivation in favor of the sparse placement strategy. The study also shows that the algorithm used to choose the nodes where to place the 3R units must be designed carefully. Two placement algorithms are compared, reporting differences in signaling overhead level as high as 6 times (when achieving a desired level of lightpath connectivity) and differences in blocking probabilities as high as two orders of magnitude (when using the same level of signaling overhead).
Ad Hoc 802.11b cooperative protocols: performance in a slow fading channel
(The University of Texas at Dallas, 2013-05-24) Agarwal, Niraj, 1977-; ChanneGowda, Divya, 1981-; Kannan, Lakshmi Narasimhan, 1984-; Tacca, Marco, 1973-; Fumagalli, Andrea; Eric Jonsson School of Engineering and Computer Science. Open Networking Advanced Research (OpNeAR) Laboratory.
This paper investigates the use of cooperative communications in the context of ad hoc IEEE 802.11b to combat radio signal degradations due to slow fading. The performance gain of both an existing cooperative protocol and the one proposed in the paper is discussed. It is quantitatively shown how much the two cooperative protocols increase throughput, lower delivery latency, and extend transmission span, when compared to the conventional IEEE 802.11b protocol. These features may help improve connectivity and network performance in ad hoc applications, where nodes’ relative locations are difﬁcult to control and predict.
Surface profile determination of phase shift masks by inverse scatterometry
(The University of Texas at Dallas, 2013-06-03) Byrne, Dale M.; Reed, Jeffrey Alan, 1961-; AI Assaad, Rayan M., 1977-; Eric Jonsson School of Engineering and Computer Science.
This report describes research conducted by Research Associate Jeffrey A. Reed and graduate student Rayan AI Assaad under the direction of Dr. Dale M. Byrne, at the University of Texas at Dallas. The period of investigation extended from September 1, 2002 to January 15,2003. The research and results reported here were directed toward the problem of determining the surface relief profile of phase-shift masks using the analysis technique that was developed by Byrne et al.1 The goal was to determine the accuracy that resulted when scatterometric data were processed using the above stated technique. Further investigations were made into the effect of "second surface interactions"; specifically how the second surface interactions affected the data collected by a scatterometer. These investigations were quite enlightening in that they produced rather negative results; hence further investigations were undertaken to develop methods to circumvent the problems created by the second surface interactions. In Section II we describe the general scatterometric configuration and provide an overview of the analysis technique of Byrne et a1. 1 We illustrate the technique using simulated scatterometric data derived from a structure that represents a phase-shift mask. At the conclusion of Section II we simulate the effect of a "second surface interaction." In Section III we discuss one method to eliminate the effects of "second surface interactions" so that their effect on scatterometric data is removed. We then consider the consequences of this method as they relate to some basic design parameters of scatterometric instrumentation.

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