Consistency management in Deno

We describe a new replicatedobject protocol designed for use in mobile and weaklyconnected environments. The protocol differs from previous protocols in combining epidemic information propagation with voting, and in using fixed perobject currencies for voting. The advantage of epidemic protocols is that data movement only requires pairwise communication. Hence, there is no need for a majority quorum to be available and simultaneously connected at any single time. The protocols increase availability by using voting, rather than primarycopy or primarycommit schemes. Finally, the use of perobject currencies allows voting to take place in an entirely decentralized fashion, without any server having complete knowledge of group membership. We show that currency allocation can be used to implement diverse policies. For example, uniform currency distributions emulate traditional voting schemes, while allocating all currency to a single server emulates a primarycopy scheme. We present simulation results showing both schemes, as well as the performance advantages of using currency proxies to temporarily reallocate currency during planned disconnections. Furthermore, we discuss an initial design of the underlying replicatedobject system and present a basic API.     

Mobility Management for Hierarchical Wireless Networks

In this paper, we consider the mobility management in large, hierarchically organized multihop wireless networks. The examples of such networks range from battlefield networks, emergency disaster relief and law enforcement etc. We present a novel network addressing architecture to accommodate mobility using a Home Agent concept akin to mobile IP. We distinguish between the physical routing hierarchy (dictated by geographical relationships between nodes) and logical hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). The performance of the mobility management scheme is investigated through simulation.     

Simulation‐based performance evaluation of routing protocols for mobile ad hoc networks

In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packetlevel simulations. The ad hoc networks are multihop wireless networks with dynamically changing network connectivity owing to mobility. The protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, endtoend delay, and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of ondemand routing protocols use much lower routing load, especially with small number of peertopeer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and endtoend delay performance.     

Optical-LSP Establishment and a QoS Maintenance Scheme Based on Differentiated Optical QoS Classes in OVPNs

A virtual private network (VPN) over Internet has the benefit of being cost-effective and flexible. However, it has difficulties providing sufficient QoS and adequate transmission capacity for high bandwidth services. Given the increasing demand for high bandwidth Internet and the demand for QoS assurances in a VPN over Internet, IP/generalized multi-protocol label switching (GMPLS) based on a control plane combined with a high-bandwidth, dense-wavelength division multiplexing (DWDM) optical network is seen as a very favorable approach for realizing the future optical VPN (OVPN) over IP/GMPLS over DWDM. Within this architecture, providing QoS guaranteed multimedia services with a differentiated QoS guaranteed protocol framework with QoS recovery is one of the key issues to implement. Therefore, we suggest in this paper optical-label switched path (O-LSP) establishment and its QoS maintenance scheme based on differentiated optical QoS-service (DOQoS) classes. They are the key components for this DOQoS framework in assuring end-to-end QoS in an OVPN over IP/GMPLS over DWDM architecture.     

Artificial synesthesia via sonification: A wearable augmented sensory system

A design for an implemented, prototype wearable artificial sensory system is presented, which uses data sonification to compensate for normal limitations in the human visual system. The system gives insight into the complete visiblelight spectra from objects being seen by the user. Longterm wear and consequent training might lead to identification of various visuallyindistinguishable materials based on the sounds of their spectra. A detailed system design and results of user testing are presented, and many possible extensions to both the sonification and the sensor package are discussed.     

Floor acquisition multiple access (FAMA) in single‐channel wireless networks

The FAMANCS protocol is introduced for wireless LANs and adhoc networks that are based on a single channel and asynchronous transmissions (i.e., no time slotting). FAMANCS (for floor acquisition multiple access with nonpersistent carrier sensing) guarantees that a single sender is able to send data packets free of collisions to a given receiver at any given time. FAMANCS is based on a threeway handshake between sender and receiver in which the sender uses nonpersistent carrier sensing to transmit a requesttosend (RTS) and the receiver sends a cleartosend (CTS) that lasts much longer than the RTS to serve as a busy tone that forces all hidden nodes to back off long enough to allow a collisionfree data packet to arrive at the receiver. It is shown that carrier sensing is needed to support collisionfree transmissions in the presence of hidden terminals when nodes transmit RTSs asynchronously. The throughput of FAMANCS is analyzed for singlechannel networks with and without hidden terminals; the analysis shows that FAMANCS performs better than ALOHA, CSMA, and all prior proposals based on collision avoidance dialogues (e.g., MACA, MACAW, and IEEE 802.11 DFWMAC) in the presence of hidden terminals. Simulation experiments are used to confirm the analytical results.     

Predictive Caching Strategy for On-Demand Routing Protocols in Wireless Ad Hoc Networks

Route caching strategy is important in on-demand routing protocols in wireless ad hoc networks. While high routing overhead usually has a significant performance impact in low bandwidth wireless networks, a good route caching strategy can reduce routing overheads by making use of the available route information more efficiently. In this paper, we first study the effects of two cache schemes, link cache and path cache, on the performance of on-demand routing protocols through simulations based on the Dynamic Source Routing (DSR) protocol. Since the path cache DSR has been extensively studied, we focus in this paper on the link cache DSR in combination with timer-based stale link expiry mechanisms. The effects of different link lifetime values on the performance of routing protocol in terms of routing overhead, packet delivery ratio and packet latency are investigated. A caching strategy incorporating adaptive link timeout is then proposed, which aims at tracking the optimal link lifetime under various node mobility levels by adaptively adjusting the link lifetime based on the real link lifetime statistics. The performance of the proposed strategy is then compared with the conventional path cache DSR. The results show that without a timeout mechanism, a link cache scheme may suffer severe performance degradation due to the use of broken routes, while the proposed adaptive link cache strategy achieves significantly improved performance by reducing the routing overhead when the network traffic load is high.     

MA‐WATM: A new approach towards an adaptive wireless ATM network

In a cellular multimedia network like wireless ATM (WATM), self control seems primordial. Our new approach is based on the application of DAI (distributed artificial intelligence) techniques in order to build a selfadaptive network within random nonuniform traffic conditions. Attempting to achieve a high network capacity in terms of resource allocation and air interface BER (bit error rate), we propose to apply intelligent agent features to enhance the architecture of WATM systems. In fact, the intelligent platform MAWATM (multiagent wireless ATM) is used to provide a flexible integration of the multiagent technique in wireless entities, BSs (base stations), MSs (mobile stations) and MSCs (mobile switching centers). Two applications are investigated and explored by simulations in order to bear out the feasibility of the multiagent approach.     

On the design of feedback controllers to achieve prescribed initial value constraints

The problem of designing a stabilizing compensator for a control system to achieve prescribed initial value constraints ⁽ⁱ⁾(0⁺)=y_i is considered. Indeed, modulo certain technical conditions, such a compensator exists if and only if y_i=0;i= 0,1,...,rp +rt –2; whererp is the relative degree of the plant andrt is the relative degree of the system input. This theorem is derived and a complete parameterization of the set of compensators that achieve the prescribed design constraints is formulated.This research was supported in part by NSF Grant No. 921106.     

Construction of Time-Relaxed c-Broadcast Networks

C-broadcasting is an information dissemination task where a message, originated at any node in a network, is transmitted to all other nodes with the restriction that each node having the message can transmit it to almost c neighbors simultaneously. If the transmission time of the message is set to be one time unit, a minimal c-broadcast network (c-MBN) is a communication network in which c-broadcasting from any node can be accomplished in log _c+1 n time units, where n is the number of nodes and log _c+1 n is the fastest possible broadcast time. If networks are sparse, additional time units may be required to perform c-broadcasting. A time-relaxed c-broadcast network, denoted as (t,c)-RBN, is a network where c-broadcasting from any node can be completed in log _c+1 n+t time units. In this paper, a network compounding algorithm is proposed to construct large sparse (t,c)-RBNs by linking multiple copies of a time-relaxed network of small size using the structure of another time-relaxed network. Computational results are presented to show the effectiveness of the proposed algorithm.     

Improved Approaches for Cost-Effective Traffic Grooming in WDM Ring Networks: Uniform-Traffic Case*

To fully utilize the capabilities of a SONET/ADM network, traffic grooming is needed to multiplex a number of lower-rate traffic streams into a higher-rate stream, and vice versa. Although the capacity of a SONET ring network can be upgraded by operating it over multiple wavelengths, the corresponding network design may be costly if it employs a large number of ADMs. A cost-effective design attempts to minimize the total number of ADMs used in the network while carrying the offered traffic. We introduce and evaluate the performance characteristics of two new traffic-grooming approaches for WDM ring networks, called single-hop and multihop. Our single-hop implementation uses the simulated-annealing heuristic. After placing all the traffic on virtual circles, we group the circles in order to reduce the number of ADMs in the network. Our multihop implementation places an ADM at each node based on the requested traffic in the traffic-demand matrix; then, it tries to groom the wavelengths which can be groomed. We select one of the nodes to be the hub node which has an ADM for each wavelength. The hub node, therefore, can bridge traffic between all of the wavelengths. Each algorithm is specified and illustrated by a simple example. Our results demonstrate that it is beneficial to use a single-hop approach based on simulated annealing for a small grooming ratio, but for a large grooming ratio and node number, we advocate the use of the multihop approach.     

Mobile ATM buffer capacity analysis

This paper extends a stochastic theory for buffer fill distribution for multiple on and off sources to a mobile environment. Queue fill distribution is described by a set of differential equations assuming sources alternate asynchronously between exponentially distributed periods in on and off states. This paper includes the probabilities that mobile sources have links to a given queue. The sources represent mobile user nodes, and the queue represents the capacity of a switch. This paper presents a method of analysis which uses mobile parameters such as speed, call rates per unit area, cell area, and call duration and determines queue fill distribution at the ATM cell level. The analytic results are compared with simulation results.This paper is partially funded by ARPA contract number J-FBI-94-223.The Mathematica code for this paper can be found on http://www.tisl.ukans.edu/sbush.     

On the structure of the privacy hierarchy

An N argument function f(x ₁,...,x _N ) is called t-private if a protocol for computing f exists so that no coalition of at most t parties can infer any additional information from the execution, other than the value of the function. The motivation of this work is to understand what levels of privacy are attainable. So far, only two levels of privacy are known for N argument functions which are defined over finite domains: functions that are N-private and functions that are (N – 1)/2-private but not N/2-private.In this work we show that the privacy hierarchy for N-argument functions which are defined over finite domains, has exactly (N + 1)/2 levels. We prove this by constructing, for any N/2 t N – 2, an N-argument function which is t-private but not (t + 1)-private.This research was supported by US-Israel Binational Science Foundation Grant 88-00282.     

Pure mode versus mixed mode interfacing between analog circuits

The concepts of transmission error and mismatch factor ^–1 are introduced to evaluate the effect of impedance mismatch on the accuracy of broadband signal transmission between two feedback amplifiers. It is shown that, in comparison with the error introduced by the feedback amplifiers, becomes negligible for pure V.M. (voltage mode) or C.M. (current mode) signal transmission; in the mixed mode, in which a V.M. output circuit feeds a C.M. input circuit, or vice versa, may become significant. Computer simulations show that the pure mode also yields reduced T.H.D., improved bandwidth and improved transient response. It is also shown that a particular combination between the kind of feedback and the active circuit to which it is applied, termed enhancing combination, further increases the accuracy of signal transmission.1. The notation (OL) relates to the open-loop value of the parameter involved.2. It can be shown that rule 2 does not apply to a low-noise preamplifier.     

Time‐varying modeling of a nonstationary signal

In this paper, a method for modeling a nonstationary signal using timevarying parameters by considering that the signal is generated by a linear, timevarying (LTV) system with a stationary white noise input is presented. This method is based on the Wold–Cramer (WC) representation of a nonstationary signal. Because the relationship between the generalized transfer function of an LTV system and the timevarying coefficients of the difference equation of a discretetime system is not addressed so far in the literature, therefore, in this paper a solution to this problem is proposed. A simple relationship between the system generalized transfer function and the timevarying parameters of the system is derived, then an MLS algorithm is developed to solve for the system timevarying parameters. Computer simulation illustrating the effectiveness of our algorithm is presented.     

Intelligent information dissemination services in hybrid satellite‐wireless networks

The need for rapid deployment and user mobility suggest the use of a hybrid satellitewireless network infrastructure for important situation awareness and emergency response applications. An Intelligent Information Dissemination Service (IIDS) has been developed to support the dissemination and maintenance of extended situation awareness throughout such a network information infrastructure in a seamless manner. One of the goals of IIDS is to transparently handle the mismatches in characteristics of satellite and terrestrial wireless networks, allow effective utilization of available bandwidth, and support timely delivery of highly relevant information. IIDS achieves the above by implementing user profile aggregation that incrementally aggregates users into communities sharing common interests to enable multicastbased information dissemination. Based on the user grouping, semantic profile matching customizes information streams based on matching user group interest profiles. By taking into account expected changes in user profiles, profileoriented data dissemination achieves predictive push and caching that anticipates future user needs and minimizes latency of data request by making data available before they are explicitly requested. Finally, bandwidthaware filtering adapts information streams to resource bandwidth availability to gracefully hide the bandwidth mismatch between the satellite and wireless links in the hybrid network infrastructure. The IIDS software has been deployed on the Digital Wireless Battlefield Network (DWBN) that integrates commercial offtheshelf satellite and wireless products into a heterogeneous satellite/wireless hybrid network for supporting wireless mobile multimedia services.     

A scalable wireless virtual LAN

This paper presents a Wireless Virtual Local Area Network (WVLAN) to support mobility in IPoverATM local area networks. Mobility is handled by a joint ATMlayer handoff for connection rerouting and MAClayer handoff for location tracking, such that the effects of mobility are localized and transparent to the higherlayer protocols. Different functions, such as Address Resolution Protocol (ARP), mobile location, and ATM connection admission are combined to reduce protocol overhead and frontend delay for connectionless packet transmission in connectionoriented ATM networks. The proposed WVLAN, through the use of ATM technology, provides a scalable wireless virtual LAN solution for IP mobile hosts.     

Biasing a differential pair in low-voltage analog circuits: a systematic approach

This paper deals with a systematic approach to the common mode and the differential mode biasing of a differential transistor pair. Four different variants will be shown, two of these variants show practical importance; a practical circuit of one of these variants turns out to be the traditional long-tailed pair. This variant is mainly suited, if the input signal operates at voltage level, whereas another variant has great advantages if operation at current level occurs. Besides, the latter variant turns out to be very favorable in circuits operating with a single low supply voltage. Two practical circuits based on this variant are given.     

On minimum cost isolated failure immune networks

A telecommunications network is isolated failure immune (IFI) if and only if communication between operative sites can be completed as long as network failures are isolated. It is known that the class of minimal IFI networks is equivalent to the class of spanning 2-trees. To the best of our knowledge, this work is the first computational study dealing with the construction of a minimum cost IFI network. The problem is known to be NP-complete. We develop a tabu search based heuristic for solving the minimum cost spanning 2-tree (MCS2T) problem. The complex structure of 2-trees makes the tabu search heuristic highly dependent on the starting solution. We develop four heuristic algorithms to obtain diversified good starting solutions. They are: completion of a 2-tree from a spanning tree, two greedy approaches, and a method based on the recursive definition of a 2-tree. We also formulate an integer programming problem (IP) whose objective function value is a lower bound to the MCS2T problem. We solve the IP by developing a constraint generation scheme. The algorithms were tested on complete random graphs with Euclidean distances and on two real data sets (Civil Aeronautics Board) with instances of 10, 15, 20 and 25 nodes. As a result of this research for small problems (10 and 15 nodes), the heuristic solutions are on average within 0.8% from the optimal solution and for large problems (20 and 25 nodes), the average error is less than 2.8%.