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As one of the main data transport protocols of delay/disruption-tolerant networking (DTN), Licklider transmission protocol (LTP) is designed to provide reliable data delivery in an interplanetary Internet environment characterized by frequent and lengthy link disruptions and extremely long signal propagation delays. Some studies have been done on the performance of LTP in cislunar and Mars communications. However, to date the effect of link disruption on LTP for Mars communications has received little attention. In this paper, an analytical framework is presented for the effect of link disruption on reliable data delivery and performance of LTP in Mars communications. The analysis focuses on how various link disruptions affect the number of transmission attempts, the consequent round-trip time (RTT) of data exchange, and the resulting goodput performance of LTP for reliable data block delivery in Mars communications. The analytical framework is validated by means of realistic data block transmission experiments using a PC-based experimental infrastructure, and it can be used to predict the performance of LTP over a deep-space vehicle communication channel in presence of link disruption. [ABSTRACT FROM AUTHOR]

Load balancing in datacenter networks (DCNs) is an important and challenging task for datacenter managers. A number of sophisticated technologies have been proposed to improve load balancing performance in a complicated circumstance, i.e., with various traffic characteristics. Many approaches need a high cost to implement, such as changing switch hardware. The efficiency problem has not been well addressed. MPTCP was proposed as a low-cost approach to improve data transmission in DCNs, which uses subflows to balance workloads across multiple paths. However, current MPTCP is not satisfying, especially when there are rack-local flows or many-to-one short flows. In this article, we propose DCMPTCP to improve the efficacy of MPTCP. We gradually develop three mechanisms. First, DCMPTCP identifies rack-local traffic and eliminates unnecessary subflows to reduce the overhead. Second, DCMPTCP estimates flow length and establishes subflows in a smarter way. Third, DCMPTCP strengthens explicit congestion notification to improve the congestion control performance on inter-rack many-to-one short flows. We have implemented DCMPTCP in both the Linux kernel and ns-3 simulator. Our comprehensive testbed experiments and simulations show that DCMPTCP outperforms MPTCP in both 1 Gbps testbed, and 10 Gbps large-scale simulation network. [ABSTRACT FROM AUTHOR]

With the development of vehicle networks, the information transmission between vehicles is becoming increasingly important. Many applications, particularly regarding security, are based on communication between vehicles. These applications have strict requirements for factors such as the quality of communication between vehicles and the time delay. Many theoretical communication protocols ignore the presence of buildings or other obstacles that are present during practical use, especially in urban areas. These obstacles can cause a signal to fade or even block direct communication. Many vehicles are often parked at the roadside. Because of their location, these parked vehicles can be used as relays to effectively reduce the shadowing effect caused by obstacles and even solve communication problems. In this paper, we study the problem of parked-vehicle-assistant relay routing communication in vehicle ad hoc networks. We propose an efficient parked vehicle assistant relay routing algorithm that is composed of four parts: a periodic Hello packet exchange mechanism, candidate relay list update, communication link quality evaluation, and candidate relay list selection. Simulation results reveal obvious advantages for indexes such as the quality of communication, success rate, and time delay. [ABSTRACT FROM AUTHOR]

We propose a vehicle-to-roadside communication protocol based on distributed clustering where a coalitional game approach is used to stimulate the vehicles to join a cluster, and a fuzzy logic algorithm is employed to generate stable clusters by considering multiple metrics of vehicle velocity, moving pattern, and signal qualities between vehicles. A reinforcement learning algorithm with game theory based reward allocation is employed to guide each vehicle to select the route that can maximize the whole network performance. The protocol is integrated with a multi-hop data delivery virtualization scheme that works on the top of the transport layer and provides high performance for multi-hop end-to-end data transmissions. We conduct realistic computer simulations to show the performance advantage of the protocol over other approaches. [ABSTRACT FROM AUTHOR]

In a distributed computing environment, real-time tasks communicate via a network infrastructure whose stability significantly impacts timing predictability. Network stability includes two aspects. First, the network has to guarantee the deadline requirements of real-time message transmissions in the absence of network failures. Second, the network needs to support dynamic recovery when network failures occur. This paper generalizes previous static routing approaches, which address the first aspect of the network stability, by developing a dynamic failure recovery policy and a protocol to address the second aspect of the network stability. We derive new real-time forwarding paths without compromising the capability of network devices to guarantee deadlines of concurrent real-time transmissions. We implement this mechanism on a network simulation platform and evaluate it on real hardware in a local cluster to demonstrate its feasibility and effectiveness. Experiments confirm the ability to bound recovery delays based on the network parameters. [ABSTRACT FROM AUTHOR]

In this paper, we consider multichannel ALOHA for a wireless sensor network (WSN), where sensors’ signals are correlated. The impact of the number of channels on the length of information that an access point (AP) can collect is investigated. Under a certain distributed signal source model, in order for the AP to have a sufficiently long length of information, we show that the number of channels is to be larger than the square of the average number of active nodes. Thus, when the number of channels is limited, we need to use re-transmissions. To this end, we propose an adaptive transmission approach that can effectively exploit the correlation between the collected signals at the AP and nodes’ signals using Slepian–Wolf coding to shorten the total transmission time, which results in a more energy efficient WSN. [ABSTRACT FROM AUTHOR]

A cooperative wireless-powered communication network protocol is proposed, in which user far away from a hybrid access point (H-AP) is capable of harvesting wireless powers by overhearing the uplink signals of users that are relatively nearer to the H-AP, in addition to downlink signal broadcast by the H-AP. In this setting, time allocations for the downlink transmission of the H-AP and the uplink transmission for the users are jointly optimized for two different purposes. First, the weighted sum-rate maximization problem is solved for a given total transmission time. Then, the total transmission time is minimized under a minimum rate constraint, and an efficient algorithm is also presented to solve the optimal solution by a line search strategy. Numerical results demonstrate that the proposed schemes significantly increase the far user's rate, which in turn improves user fairness and transmission delay. [ABSTRACT FROM PUBLISHER]

This paper investigates collaborative spectrum sharing (CSS) for which a cognitive secondary transmitter acts as a decode-and-forward (DF) relay for two primary users (PUs) occupying an interfering multiple-access channel. PUs are assumed to send their signals simultaneously; hence, interference between the primary signals exists due to the multiple-access nature. The secondary user (SU) selects and forwards one of the PU's signals to a desired destination, and at the same time, the SU also transmits its own signal only if it is not harmful to PUs. The selection of a primary signal to relay is investigated, depending on SU's knowledge of two primary source–destination channels, for which closed-form outage probabilities for PUs and SU are provided accordingly. With the help of the closed-form PU's outage probability, an optimal selection strategy between the primary signals and an optimal power allocation between the primary and secondary signals are also obtained in closed form, which minimizes SU's outage probability while keeping the PU's outage performance at an SU-free level. Numerical investigation is used to verify and illustrate the analysis given in this paper. Numerical results also show that the SU's performance can vary significantly according to the amount of channel knowledge that the SU can have. [ABSTRACT FROM PUBLISHER]

Buffer sizing is an important network configuration parameter that impacts the quality of service characteristics of data traffic. With falling memory costs and the fallacy that "more is better," network devices are being overprovisioned with large buffers. This may increase queueing delays experienced by a packet and subsequently impact stability of core protocols such as TCP. The problem has been studied extensively for wired networks. However, there is little work addressing the unique challenges of wireless environments such as time-varying channel capacity, variable packet inter-service time, and packet aggregation, among others. In this article we discuss these challenges, classify the current state-of-the-art solutions, discuss their limitations, and provide directions for future research in the area. [ABSTRACT FROM PUBLISHER]

The performance of delay/disruption tolerant networking (DTN) protocols in cislunar and deep-space communication systems has previously been studied by simulation. However, little work has been seen in characterizing in an analytical manner the performance of DTN protocols for space with respect to asymmetric channel rates. We present a performance characterization of the recently developed DTN Licklider transmission protocol (LTP) convergence layer adapter (CLA) (or simply LTPCL) over cislunar space channels with data-rate asymmetry. Analytical models are built to characterize LTPCL with respect to the minimum number of bundle protocol (BP) bundles that should be aggregated to avoid delay in acknowledgment (ACK) transmission and the optimal number of bundles to be aggregated for the best transmission efficiency of BP/LTPCL, with the effect of full overhead at all layers taken into consideration. The models are validated by file transfer experiments running BP/LTPCL protocols using a PC-based testbed. [ABSTRACT FROM AUTHOR]

Wireless sensor networks with mobile sinks, mWSNs, have attracted a lot of attention recently. This is because sink mobility can greatly alleviate the hotspot issue in WSNs and further prolong the network lifetime. However, sink mobility also causes unexpected changes in network topology and data routing paths, which can largely affect the routing performance in such networks. Design of efficient routing protocols for mWSNs has been a critical issue, and much work has been carried out in this aspect. In this article, we first classify existing protocols based on different design criteria and then present a survey of the state-of-the-art routing protocols in this area. We illustrate how each of the protocols works, and discuss their advantages and disadvantages. Finally, we point out some future directions for efficient routing in mWSNs. [ABSTRACT FROM AUTHOR]

We consider an erasure multi-way relay channel (EMWRC) in which several users share their data through a relay over erasure links. Assuming no feedback channel between the users and the relay, we first identify the challenges for designing a data sharing scheme over an EMWRC. Then, to overcome these challenges, we propose practical low-latency and low-complexity data sharing schemes based on fountain coding. Later, we introduce the notion of end-to-end erasure rate (EEER) and analytically derive it for the proposed schemes. EEER is then used to calculate the achievable rate and transmission overhead of the proposed schemes. Using EEER and computer simulations, the achievable rates and transmission overhead of our proposed schemes are compared with the ones of one-way relaying. This comparison implies that when the number of users and the channel erasure rates are not large, our proposed schemes outperform one-way relaying. We also find an upper bound on the achievable rates of EMWRC and observe that depending on the number of users and channel erasure rates, our proposed solutions can perform very close to this bound. [ABSTRACT FROM AUTHOR]

Voice over Internet Protocol (VoIP) applications based on peer-to-peer (P2P) communications have been experiencing considerable growth in terms of number of users. To overcome filtering policies or protect the privacy of their users, most of these applications implement mechanisms such as protocol obfuscation or payload encryption that avoid the inspection of their traffic, making it difficult to identify its nature. The incapacity to determine the application that is responsible for a certain flow raises challenges for the effective management of the network. In this paper, a new method for the identification of VoIP sessions is presented. The proposed mechanism classifies the flows, in real-time, based on the speech codec used in the session. To make the classification lightweight, the behavioral signatures for each analyzed codec were created using only the lengths of the packets. Unlike most previous approaches, the classifier does not use the lengths of the packets individually. Instead, it explores their level of heterogeneity in real time, using entropy to emphasize such feature. The results of the performance evaluation show that the proposed method is able to identify VoIP sessions accurately and simultaneously recognize the used speech codec. [ABSTRACT FROM AUTHOR]

Conventional Ethernet protocols struggle to meet the scalability and performance requirements of data centers. Viable replacements have been proposed for data center ethernet (DCE): link-layer Multipathing (MP) is deployed to replace spanning tree protocol (STP) and thus improve network throughput; end-to-end link-layer congestion control (CC) is proposed to better guarantee loss-free frame delivery for Ethernet. However, little work has been done to incorporate MP and CC to offer a more comprehensive solution for DCE. In this paper, we propose a two-tier solution by integrating our dynamic load balancing Multipath (DLBMP) scheme with CC. Instead of using two separate parameters, i.e., path load and buffer level, to trigger MP and CC, our solution only needs to monitor path load metric to manage MP and CC in an integrated way. Different from a single CC mechanism, which generates congestion notifications from network core, our integrated CC can make use of link load information in access switches which directly inform sources to control their traffic admission. To minimize overhead and accelerate update, SDN techniques are employed in our implementation, which decouples routing intelligence from data transmission. Hence, data sources can react more rapidly to congestion and network can be guaranteed with loss-free delivery. In addition, our MP scheme is further improved by introducing application-layer flow differentiation. With such a fine flow differentiation (FFD) mechanism, traffic can be more evenly distributed along multipaths, resulting in better bandwidth utilization. Simulation results show that our combined solution can further improve network throughput with FFD mechanism and guarantee loss-free delivery with integrated CC. [ABSTRACT FROM PUBLISHER]

We study the capacity scaling laws for the cognitive network that consists of the primary hybrid network (PhN) and secondary ad hoc network (SaN). PhN is further comprised of an ad hoc network and a base station-based (BS-based) network. SaN and PhN are overlapping in the same deployment region, operate on the same spectrum, but are independent with each other in terms of communication requirements. The primary users (PUs), i.e., the ad hoc nodes in PhN, have the priority to access the spectrum. The secondary users (SUs), i.e., the ad hoc nodes in SaN, are equipped with cognitive radios, and have the functionalities to sense the idle spectrum and obtain the necessary information of primary nodes in PhN. We assume that PhN adopts one out of three classical types of strategies, i.e., pure ad hoc strategy, BS-based strategy, and hybrid strategy. We aim to directly derive multicast capacity for SaN to unify the unicast and broadcast capacities under two basic principles: 1) The throughput for PhN cannot be undermined in order sense due to the presence of SaN. 2) The protocol adopted by PhN does not alter in the interest of SaN, anyway. Depending on which type of strategy is adopted in PhN, we design the optimal-throughput strategy for SaN. We show that there exists a threshold of the density of SUs according to the density of PUs beyond which it can be proven that: 1) when PhN adopts the pure ad hoc strategy or hybrid strategy, SaN can achieve the multicast capacity of the same order as it is stand-alone; 2) when PhN adopts the BS-based strategy, SaN can asymptotically achieve the multicast capacity of the same order as if PhN were absent, if some specific conditions in terms of relations among the numbers of SUs, PUs, the destinations of each multicast session in SaN, and BSs in PhN hold. [ABSTRACT FROM AUTHOR]

The resources especially energy in wireless sensor networks (WSNs) are quite limited. Since sensor nodes are usually much dense, data sampled by sensor nodes have much redundancy, data aggregation becomes an effective method to eliminate redundancy, minimize the number of transmission, and then to save energy. Many applications can be deployed in WSNs and various sensors are embedded in nodes, the packets generated by heterogenous sensors or different applications have different attributes. The packets from different applications cannot be aggregated. Otherwise, most data aggregation schemes employ static routing protocols, which cannot dynamically or intentionally forward packets according to network state or packet types. The spatial isolation caused by static routing protocol is unfavorable to data aggregation. To make data aggregation more efficient, in this paper, we introduce the concept of packet attribute, defined as the identifier of the data sampled by different kinds of sensors or applications, and then propose an attribute-aware data aggregation (ADA) scheme consisting of a packet-driven timing algorithm and a special dynamic routing protocol. Inspired by the concept of potential in physics and pheromone in ant colony, a potential-based dynamic routing is elaborated to support an ADA strategy. The performance evaluation results in series of scenarios verify that the ADA scheme can make the packets with the same attribute spatially convergent as much as possible and therefore improve the efficiency of data aggregation. Furthermore, the ADA scheme also offers other properties, such as scalable with respect to network size and adaptable for tracking mobile events. [ABSTRACT FROM AUTHOR]

We present the Secure SOurce-BAsed Loose Synchronization (SOBAS) protocol to securely synchronize the events in the network, without the transmission of explicit synchronization control messages. In SOBAS, nodes use their local time values as a one-time dynamic key to encrypt each message. In this way, SOBAS provides an effective dynamic en-route filtering mechanism, where the malicious data is filtered from the network. With SOBAS, we are able to achieve our main goal of synchronizing events at the sink as quickly, as accurately, and as surreptitiously as possible. With loose synchronization, SOBAS reduces the number of control messages needed for a WSN to operate providing the key benefits of reduced energy consumption as well as reducing the opportunity for malicious nodes to eavesdrop, intercept, or be made aware of the presence of the network. Albeit a loose synchronization per se, SOBAS is also able to provide $(7.24 \mu)$s clock precision given today's sensor technology, which is much better than other comparable schemes (schemes that do not employ GPS devices). Also, we show that by recognizing the need for and employing loose time synchronization, necessary synchronization can be provided to the WSN application using half of the energy needed for traditional schemes. Both analytical and simulation results are presented to verify the feasibility of SOBAS as well as the energy consumption of the scheme under normal operation and attack from malicious nodes. [ABSTRACT FROM PUBLISHER]

In many communication standards, several variable length frames generated by some source coder may be aggregated at a given layer of the protocol stack in the same burst to be transmitted. This decreases the signalization overhead and increases the throughput. However, after a transmission over a noisy channel, Frame Synchronization (FS), i.e., recovery of the aggregated frames, may become difficult due to errors affecting the bursts. This paper proposes several robust FS methods making use of the redundancy present in the protocol stack combined with channel soft information. A trellis-based FS algorithm is proposed first. Its efficiency is obtained at the cost of a large delay, since the whole burst must be available before beginning the processing, which might not be possible in some applications. Thus, a low-delay and reduced-complexity Sliding Window-based variant is introduced. Second, an improved version of an on-the-fly three-state automaton for FS is proposed. Bayesian hypothesis testing is performed to retrieve the correct FS. These methods are compared in the context of the WiMAX MAC layer when bursts are transmitted over Rayleigh fading channels. [ABSTRACT FROM AUTHOR]

Diversity Combining (DC) and Multipacket Detection (MPD) are efficient techniques that cope with packet errors due to severe propagation conditions and/or collisions. To evaluate their network performance on a network simulator, an accurate characterization of the Bit Error Rate (BER) and Packet Error Rate (PER) can successfully replace the behavior of the PHY layer. This choice is better in terms of computational time than implementing a full PHY layer to be jointly simulated with the upper layers. In this paper, an analytical model is proposed to compute the BER and PER of DC, MPD and hybrid techniques, considering a Single-Carrier with Frequency-Domain Equalization (SC-FDE) scenario. The paper also considers two frequency-domain detection methods: a simple linear receiver and a powerful iterative receiver. The proposed model is simple and versatile, since it can support nonhomogeneous transmitting powers, and different channel conditions concerning retransmissions and channel randomization techniques. Several simulations show that the proposed model provides accurate BER and PER results for a wide range of scenarios. [ABSTRACT FROM AUTHOR]

This paper considers a random access system where each sender is in one of two possible states, active or not active, and the states are only known to the common receiver. Active senders encode data into independent information streams, a subset of which is decoded depending on the collective interference. An information-theoretic formulation of the problem is presented and the set of achievable rates is characterized with a guaranteed gap to optimality. Inner and outer bounds on the capacity region of a two-sender system are tight in the case of a binary-expansion deterministic channel and differ by less than one bit in the case of a Gaussian channel. In systems with an arbitrary number of senders, the symmetric scenario of equal access probabilities and received power constraints is studied and the system throughput, i.e., the maximum achievable expected sum rate, is characterized. It is shown that a simple coding scheme where active senders transmit a single message is optimum for a binary-expansion deterministic channel and achieves within one bit of the optimum in the case of a Gaussian channel. Finally, a comparison with the slotted ALOHA protocol is provided, showing that encoding rate adaptation at the transmitters achieves constant (rather than zero) throughput as the number of users tends to infinity. [ABSTRACT FROM AUTHOR]

This paper studies the throughput performance of hybrid automatic repeat request (HARQ) protocols over block fading Gaussian channels. It proposes new protocols that use the available feedback bit(s) not only to request a retransmission, but also to inform the transmitter about the instantaneous channel quality. An explicit protocol construction is given for any number of retransmissions and any number of feedback bits. The novel protocol is shown to simultaneously realize the gains of HARQ and of power control with partial channel state information. Remarkable throughput improvements are shown, especially at low and moderate signal-to-noise ratio (SNR), with respect to protocols that use the feedback bits for retransmission request only. In particular, for the case of a single retransmission and a single feedback bit, it is shown that the repetition is not needed at low SNR where the throughput improvement is due to power control only. On the other hand, at high SNR, the repetition is useful and the performance gain comes from a combination of power control and ability to make up for deep fades. [ABSTRACT FROM PUBLISHER]

Information-theoretically secure string oblivious transfer (OT) can be constructed based on discrete memoryless channel (DMC). The oblivious transfer capacity of a channel characterizes—similarly to the (standard) information capacity—how efficiently it can be exploited for secure oblivious transfer of strings. The OT capacity of a generalized erasure channel (GEC)—which is a combination of a (general) DMC with the erasure channel—has been established by Ahlswede and Csizar at ISIT'07 in the case of passive adversaries. In this paper, we present the protocol that achieves this capacity against malicious adversaries for GEC with erasure probability at least 1/2. Our construction is based on the protocol of Crépeau and Savvides from Eurocrypt'06 which uses interactive hashing (IH). We solve an open question posed by the above paper, by basing it upon a constant round IH scheme (previously proposed by Ding at TCC'04). As a side result, we show that the Ding IH protocol can deal with transmission errors. [ABSTRACT FROM PUBLISHER]

Two dual questions in quantum information theory are to determine the communication cost of simulating a bipartite unitary gate, and to determine their communication capacities. We present a bipartite unitary gate with two surprising properties: 1) simulating it with the assistance of unlimited EPR pairs requires far more communication than with a better choice of entangled state, and 2) its communication capacity is far lower than its capacity to create entanglement. This suggests that 1) unlimited EPR pairs are not the most general model of entanglement assistance for two-party communication tasks, and 2) the entangling and communicating abilities of a unitary interaction can vary nearly independently. The technical contribution behind these results is a communication-efficient protocol for measuring whether an unknown shared state lies in a specified rank-one subspace or its orthogonal complement. [ABSTRACT FROM PUBLISHER]

This paper analyzes the impact and benefits of infrastructure support in improving the throughput scaling in networks of n randomly located wireless nodes. The infrastructure uses multiantenna base stations (BSs), in which the number of BSs and the number of antennas at each BS can scale at arbitrary rates relative to n. Under the model, capacity scaling laws are analyzed for both dense and extended networks. Two BS-based routing schemes are first introduced in this study: an infrastructure-supported single-hop (ISH) routing protocol with multiple-access uplink and broadcast downlink and an infrastructure-supported multihop (IMH) routing protocol. Then, their achievable throughput scalings are analyzed. These schemes are compared against two conventional schemes without BSs: the multihop (MH) transmission and hierarchical cooperation (HC) schemes. It is shown that a linear throughput scaling is achieved in dense networks, as in the case without help of BSs. In contrast, the proposed BS-based routing schemes can, under realistic network conditions, improve the throughput scaling significantly in extended networks. The gain comes from the following advantages of these BS-based protocols. First, more nodes can transmit simultaneously in the proposed scheme than in the MH scheme if the number of BSs and the number of antennas are large enough. Second, by improving the long-distance signal-to-noise ratio (SNR), the received signal power can be larger than that of the HC, enabling a better throughput scaling under extended networks. Furthermore, by deriving the corresponding information-theoretic cut-set upper bounds, it is shown under extended networks that a combination of four schemes IMH, ISH, MH, and HC is order-optimal in all operating regimes. [ABSTRACT FROM PUBLISHER]

Two distinct, but overlapping, networks that operate at the same time, space, and frequency is considered. The first network consists of n randomly distributed primary users, which form an ad hoc network. The second network again consists of m randomly distributed ad hoc secondary users or cognitive users. The primary users have priority access to the spectrum and do not need to change their communication protocol in the presence of the secondary users. The secondary users, however, need to adjust their protocol based on knowledge about the locations of the primary users to bring little loss to the primary network's throughput. By introducing preservation regions around primary receivers, a modified multihop routing protocol is proposed for the cognitive users. Assuming m=n^\beta with \beta>1, it is shown that the secondary network achieves almost the same throughput scaling law as a stand-alone network while the primary network throughput is subject to only a vanishingly small fractional loss. Specifically, the primary network achieves the sum throughput of order n^1/2 and, for any \delta>0, the secondary network achieves the sum throughput of order m^1/2-\delta with an arbitrarily small fraction of outage. Thus, almost all secondary source-destination pairs can communicate at a rate of order m^-1/2-\delta. [ABSTRACT FROM PUBLISHER]

Overheads incurred by network protocols diminish the capacity available for relaying useful data in a dynamic communications network. Discovering lower bounds on the amount of protocol overhead incurred is important for the development of efficient network protocols and for characterizing the effective capacity available for network users. This paper presents an information-theoretic framework for characterizing the minimum protocol overheads incurred for maintaining location information in a network with mobile nodes. Specifically, the minimum overhead problem is formulated as a rate-distortion problem. The formulation may be applied to networks with arbitrary traffic arrival and location service schemes. Lower bounds are derived for the minimum overheads incurred for maintaining the location of the nodes and consistent neighborhood information in terms of node mobility and packet arrival processes. This leads to a characterization of the deficit caused by the protocol overheads on the overall transport capacity. [ABSTRACT FROM PUBLISHER]

Future experiments at the new accelerator facility FAIR (Facility for Antiproton and Ion Research) for research with ion and anti-proton beams require new developments in front-end electronics to tolerate high data rates. We have developed a PCI Express (PCIe) card and front-end cards equipped with the small form-factor pluggable (SFP) transceivers for data transfer via optical fiber. A new protocol has been designed and implemented in FPGAs in order to provide communication between the PCIe card and the front-end cards. The standard data acquisition (DAQ) system at GSI, Multi-Branch System (MBS), has been upgraded to support the PCIe cards and is stable with data transfer rates of 200 Mbytes per second. [ABSTRACT FROM PUBLISHER]

Amongst link technologies, InfiniBand has gained wide acceptance in the framework of High Performance Computing (HPC), due to its high bandwidth and in particular to its low latency. Since InfiniBand is very flexible, supporting several kinds of messages, it is suitable, in principle, not only for HPC, but also for the data acquisition systems of High Energy Physics (HEP) Experiments. [ABSTRACT FROM PUBLISHER]

Central cryptographic functionalities such as encryption, authentication, or secure two-party computation cannot be realized in an information-theoretically secure way from scratch. This serves as a motivation to study what (possibly weak) primitives they can be based on. We consider as such starting points general two-party input-output systems that do not allow for message transmission and show that they can be used for realizing unconditionally secure bit commitment as soon as they are nontrivial, i.e., cannot be securely realized from distributed randomness only. [ABSTRACT FROM PUBLISHER]

A bidirectional channel network-on-chip (BiNoC) architecture is proposed to enhance the performance of on-chip communication. In a BiNoC, each communication channel allows to be dynamically self-reconfigured to transmit flits in either direction. This added flexibility promises better bandwidth utilization, lower packet delivery latency, and higher packet consumption rate. Novel on-chip router architecture is developed to support dynamic self-reconfiguration of the bidirectional traffic flow. This area-efficient BiNoC router delivers better performance and requires smaller buffer size than that of a conventional network-on-chip (NoC). The flow direction at each channel is controlled by a channel direction control (CDC) algorithm. Implemented with a pair of finite state machines, this CDC algorithm is shown to be high performance, free of deadlock, and free of starvation. Extensive cycle-accurate simulations using synthetic and real-world traffic patterns have been conducted to evaluate the performance of the BiNoC. These results exhibit consistent and significant performance advantage over conventional NoC equipped with hard-wired unidirectional channels. [ABSTRACT FROM PUBLISHER]

In this paper, we study the application of physical layer network coding to the joint design of uplink and downlink transmissions, where the base station and the relay have multiple antennas, and all M mobile stations only have a single antenna. A new network coding transmission protocol is proposed, where 2M uplink and downlink transmissions can be accomplished within two time slots. Since each single antenna user has poor receive capability, precoding at the base station and relay has been carefully designed to ensure that co-channel interference can be removed completely. Explicit analytic results have been developed to demonstrate that the multiplexing gain achieved by the proposed transmission protocol is M, much better than existing time sharing schemes. To further increase the achievable diversity gain, two variations of the proposed transmission protocols have also been proposed when there are multiple relays and the number of the antennas at the base station and relay is increased. Monte-Carlo simulation results have also been provided to demonstrate the performance of the proposed network coded transmission protocol. [ABSTRACT FROM AUTHOR]

In a secure message transmission (SMT) scenario, a sender wants to send a message in a private and reliable way to a receiver. Sender and receiver are connected by n wires, t of which can be controlled by an adaptive adversary with unlimited computational resources. In Eurocrypt 2008, Garay and Ostrovsky considered an SMT scenario where sender and receiver have access to a public discussion channel and showed that secure and reliable communication is possible when n \geq t+1. In this paper, we will show that a secure protocol requires at least three rounds of communication and two rounds invocation of the public channel and hence give a complete answer to the open question raised by Garay and Ostrovsky. We also describe a round optimal protocol that has constant transmission rate over the public channel. [ABSTRACT FROM AUTHOR]

Policy-based management allows the deployment of networks offering quality services in environments beyond the reach of real-time human control. A policy-based protocol stack middleware, the context-aware broker, has been developed by the authors to autonomically manage the remote deep space network. In this article example policy rules demonstrate the concept, and prototype results from ns-2.30 show the overall positive costbenefit impact in an example scenario. [ABSTRACT FROM AUTHOR]

The recent advances in wireless client devices and the crucial role of multimedia communications in our society have motivated relevant standardization efforts, such as the IP multimedia subsystem, to support session control, mobility, and interoperability in all-IP next-generation networks. IMS has already driven the design of commercial mobile multimedia, but exhibits limited support for service continuity during handoffs. In particular, it omits advanced techniques to reduce/eliminate handoff delays, especially during vertical handoffs (i.e., change of the wireless technology employed by a client to access the wired Internet, e.g., from UMTS to WiFi). We propose an original solution for session continuity based on the primary design guideline of cleanly and effectively separating the signaling plane (for session reconfiguration via SIP) from the media delivery plane (data transmission and related handoff management operations). Our optimized handoff management techniques exploit terminal-based decentralized predictions to minimize service-level handoff delays. Different from other recent related work, our proposal fully complies with the standard IMS infrastructure and works at the application level. The reported experimental results point out that our solution, available as an open source tool for the IMS community, reduces playout interruption times relevantly by introducing a limited and scalable signaling overhead. [ABSTRACT FROM AUTHOR]

Phase ambiguities affect any joint decoding and channel estimation algorithm over fading channels, making codes that mitigate this problem of considerable interest. This work presents a design that transforms a Space-Time Trellis Code (STTC), prone to carrier phase ambiguities, into a Phase Ambiguity Diminishing STTC (PAD-STTC) that is robust to such impairment. A PAD-STTC can be considered as a Multiple STTC (MSTTC) with special constellation mappings. The design criteria for these mappings are developed in this work by trading among the PAD property, diversity, and coding gain. Two PAD-STTC structures termed PAD1-STTC and PAD2-STTC are proposed, where PAD2-STTC increases the number of states over the constituent STTC. Computer simulation results indicate that PAD-STTCs can solve the phase ambiguity problem and provide a larger diversity gain than the constituent STTC over high Doppler fading channels. Moreover, with the same constituent STTC, the PAD2-STTC outperforms the PAD1-STTC at the expense of increased complexity. [ABSTRACT FROM AUTHOR]

In this paper, we propose a general phase rotated conjugate cancellation (PRCC) scheme for intercarrier interference (ICI) cancellation in orthogonal frequency division multiplexing (OFDM) systems. We also derive the optimal phase rotation for this general scheme such that the carrier-to-interference ratio would be maximized. It is shown that the previous conjugate cancellation (CC) scheme is equivalent to a special case of our proposed scheme. The general PRCC scheme not only inherits advantages of the conventional CC scheme, such as backward compatibility with the existing OFDM systems, low receiver complexity, and two-path diversity, but also provides better performance, especially at high frequency offset situations. [ABSTRACT FROM AUTHOR]

This paper presents a strategy for the design of bandwidth-efficient LDPC codes with unequal error protection. Bandwidth efficiency is obtained by appropriately designing the codes for higher order constellations, assuming an AWGN channel. The irregularities of the LDPC code are designed, using the Gaussian approximation of the density evolution, to enhance the unequal error protection property of the code as well as account for the different bit error probabilities given by the higher order constellation. The proposed code design algorithm is flexible in terms of the number and proportions of protection classes. It also allows arbitrary modulation schemes. Our method combines the design of unequal error protection LDPC codes for the binary input AWGN channel with the code design for higher order constellations by dividing the variable node degree distribution into sub-degree distributions for each protection class and each level of protection from the modulation. The results show that appropriate code design for higher order constellations reduces the overall bit-error rate significantly. Furthermore, the unequal error protection capability of the code is increased, especially for high SNR. [ABSTRACT FROM AUTHOR]

This paper presents an enhanced permeable layer mechanism useful for highly robust packetized multimedia transmission. Packet header recovery at various protocol layers using MAP estimation is the cornerstone of the proposed solution. The inherently available intra-layer and inter-layer header correlation proves to be very effective in selecting a reduced set of possible header configurations for further processing. The best candidate is then obtained through soft decoding of CRC protected data and CRC redundancy information itself. Simulation results for WiFi transmission using DBPSK modulated signals over AWGN channels show a substantial (4 to 12 dB) link budget improvement over classical hard decision procedures. We also introduce a sub-optimal and hardware realizable version of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Wireless sensor networks are mainly designed for environment surveillance, wherein wireless sensor nodes cooperate to get their job done. Generally, wireless sensors are battery powered; therefore, it is crucial for them to efficiently use their battery resources. Most of the existing power-saving protocols achieve power savings by periodically putting sensor nodes to sleep. Such a regular sleep/awake mechanism fails to adjust a sensor node's sleep duration based on its traffic load, thus causing either lower power efficiency or higher latency. Furthermore, sensors may be deployed in hostile environments and may thus unexpectedly fail. Most power-saving protocols do not promptly react to such link breakage, resulting in long transmission delays. In this paper, we propose a quorum-basedmedium access control (QMAC) protocol that enables sensor nodes to sleep longer under light loads. Since traffic flows toward the sink node in wireless sensor networks, a new concept, i.e., the next-hop group, is also proposed to reduce transmission latency. Simulation results verify that the proposed QMAC saves more energy and keeps the transmission latency low. [ABSTRACT FROM AUTHOR]

Existing work has shown that random coding across multicast sessions can significantly reduce system delay. However, such a scheme requires the strong assumption that each source has priori information of other sources' messages. The broadcasting nature of radio propagation can provide an opportunity to realize collaboration across sessions without causing much system overhead. In this paper, we propose the application of network coding to multisource-multidestination (MSMD) scenarios and provide formal analysis for the improvement of system delay. In particular, two types of analytical results have been developed, with one based on the outage probability and the other based on the use of practical convolutional codes. Monte Carlo simulation results have also been provided to demonstrate the delay performance of the proposed network-coded protocol. [ABSTRACT FROM AUTHOR]

In this paper, three clock-synchronization algorithms for wireless sensor networks (WSNs) under unknown delay are derived. They include the maximum-likelihood estimator (MLE), a generalization of the estimator of Noh et al., and a novel low-complexity estimator. Their corresponding performance bounds are derived and compared, and complexities are also analyzed. It is found that the MLE achieves the best performance with the price of high complexity. For the generalized version of the estimator of Noh et al., although it has low complexity, its performance is degraded with respect to the MLE. On the other hand, the newly proposed estimator achieves the same performance as the MLE, and the complexity is at the same level as that of the generalized version of the estimator of Noh et al. [ABSTRACT FROM AUTHOR]

WiMAX network services cannot generally be provided for special purpose devices such as credit card systems and surveillance systems since they are designed to operate only with WCM which should be installed on personal computer/smart card (PC/SC) with Windows platform. In this paper, we propose a design and implementation technique called tiny- WiMAX Connection Manager (t- WCM) for non-PC/SC WCM to provide WiMAX services to special purpose devices. The t- WCM is composed mainly of three units; WiMAX module Control Unit (WCU), Data Surveillance Unit (DSU), and External device Program Unit (EPU). It also has TCP/IP protocol stack and RTOS kernel, and performs data transmission between external end user `s device and remote server system over WiMAX networks. For the performance evaluation of the proposed t- WCM, we have implemented the t- WCM and tested it under a commercial mobile WiMAX network environment. From the experimental results, the t- WCM is verified to show almost equal stability and delay performances with the legacy WCM and xDSL, and especially better than 1xEV-DO. As a result, it has a strong possibility to apply the t- WCM to many types of special purpose embedded systems, and consequently to provide various WiMAX network services to them. [ABSTRACT FROM AUTHOR]

The IEEE 802.1X is utilized in mobile Worldwide Interoperability for Microwave Access (WiMAX) authentication. This procedure incurs a long delay in WiMAX handoff. To resolve this issue, this paper proposes a key caching mechanism to eliminate the nonnecessary IEEE 802.1X authentication cost in WiMAX handoff. This mechanism is investigated through analytic and simulation modeling. Our study indicates that the key caching scheme can effectively speed up the handoff process. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the effects of the probabilities of detection, false alarm, and frame collision survival (in the presence of simultaneous transmissions) on medium access control (MAC) protocols using impulse-radio-ultrawideband (IR-UWB) energy-collection noncoherent receivers. The MAC protocols that were considered are all IEEE 802.15.4 compatible, i.e., the IEEE 802.15.4a optional UWB clear-channel-assessment mode, the IEEE 802.15.4a ALOHA mode, and a protocol termed preamble sense multiple access (PSMA). The impact on the network throughput, energy consumption, and delay are analytically derived and verified by simulation. The results show that these effects have a considerable impact on the performance of IR-UWB MAC protocols, and a classical analysis does not properly evaluate the protocols' performances. The results compare the performances of the MAC protocols and highlight a number of issues with regard to adapting narrowband protocols to UWB systems. The probability of frame collision survival on simultaneous transmissions is shown to have a significant impact on the performance of a MAC protocol. The comparison shows superior performance of the PSMA protocol under typical wireless-sensor-network operation ranges. [ABSTRACT FROM AUTHOR]

This paper proposes a novel framework for the cross-layer analysis and design of wireless networks combining adaptive modulation and coding (AMC) at the physical layer with an automatic repeat request (ARQ) protocol at the data-link layer. Most previous works rely on first-order amplitude-based finite-state Markov chains (AFSMCs) to model the physical layer. It is shown that these models present several deficiencies that could compromise the design of higher layer protocols. Thus, a physical-layer first-order 2-D Markov model using both the amplitude and the rate of change of the fading envelope is presented. Based on this multidimensional physical-layer Markov model, the quality-of-service (QoS) performance at the data-link layer is investigated through the use of two different approaches. The first one relies on an analytical framework based on a discrete-time Markov chain (DTMC) that jointly describes the statistical behavior of the arrival process, the queueing system, and the physical layer. The second one is based on the effective-bandwidth and effective-capacity theories. Both the DTMC-based and the effective-bandwidth/capacity-based approaches are analyzed and compared in combination with our proposed physical-layer first-order 2-D Markov model in a cross-layer design aiming to satisfy the required average packet loss `probability constraint by maximizing the average throughput of the system. Numerical results show that our proposed framework represents a significant improvement over previous models. [ABSTRACT FROM AUTHOR]

An energy-efficient adaptive transmission protocol for ultrawideband (UWB) wireless sensor networks (WSNs), called ATP-UWSN, is described and evaluated over time-varying multipath fading channel conditions and multinode interference. Since wireless channels may greatly change from one transmission to the next, the use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of transmission parameters reduces energy consumption and interference. The proposed ATP-UWSN permits each of the sensor nodes to adapt its code rate and spreading code length (the number of pulses used per data bit) to match the predicted channel-state information (CSI). The transmission parameters are selected in accordance with the predicted CSI characteristics of the communication links in the network to achieve the desired quality of service given by the target bit-error probability. Subsequently, we develop a mathematical adaptation framework for the analytical evaluation of ATP-UWSN. Communication performance is evaluated in terms of average information throughput efficiency, which is a relevant progress-related measure for multihop WSNs that is associated with the energy consumption and throughput of a packet transmission. The analytical expression of this performance metric is defined and is used to assess the benefits of the proposed ATP-UWSN when compared with a nonadaptive transmission protocol (NATP) with fixed transmission parameters. Our results show that the ATP-UWSN outperforms the NATP and can improve the robustness of the link and reduce energy consumption by adapting the transmission parameters in response to changes in the predicted CSI. [ABSTRACT FROM AUTHOR]

In this paper, an analytical model for the non beacon-enabled mode of the IEEE 802.15.4 medium access control (MAC) protocol is provided. A wireless sensor network (WSN) composed of nodes, which transmit data to a sink through direct links, is considered. Upon reception of a query from the sink, the nodes transmit their packets by using the carrier-sense multiple access with collision-avoidance algorithm defined by IEEE 802.15.4. Our mathematical model allows the evaluation of the statistical distribution of the traffic generated by the nodes. In particular, the probability that a node succeeds when accessing the channel, and that the final sink receives a packet coming from whatever node, is derived. The results show how the distribution of traffic changes when different loads are offered to the network. Moreover, the model allows the evaluation of the optimum size a packet should have so that the success probability for its transmission is maximized. The results are validated through simulations. The model differs from those previously published by other authors in the literature as it precisely follows the MAC procedure defined by the standard in the context of the WSN scenario described. [ABSTRACT FROM AUTHOR]

We consider a network with an arbitrary number of nodes, where transmission of data packet is enhanced by a medium access control protocol that allows cooperation among nodes and solves transmission failures by an automatic repeat request (ARQ) protocol. Nodes operate in half-duplex mode and may interfere with each other as no coordination is assumed. In this scenario, we first derive the outage probability for a given number of interfering nodes and then relate the interference level to the single node behavior. We analyze the network behavior with a steady state analysis that matches the number of interfering nodes with the number of ARQ retransmissions. Two alternatives for cooperation are considered: decode and forward (DF) cooperation and multiple input-single output (MISO) cooperation, where for each packet transmission either one node transmits at a given time or two cooperating nodes transmit simultaneously. In our steady state analysis we also include an opportunistic version of DF, where cooperation is activated only when the quality of the cooperator-destination link is better than that of the source-destination link. Moreover, we investigate cooperator selection based on its distance to the destination. [ABSTRACT FROM AUTHOR]

Abstract--Open distributed systems are typically composed by an unknown number of processes running in heterogeneous hosts.. Their communication often requires tolerance to temporary disconnections and security against malicious actions. Tuple spaces are a well-known coordination model for this kind of systems. They can support communication that is decoupled both in time and space. There are currently several implementations of distributed fault-tolerant tuple spaces but they are not Byzantine-resilient, i.e., they do not provide a correct service if some replicas are attacked and start to misbehave. This paper presents an efficient implementation of a Linearizable Byzantine fault-tolerant Tuple Space (LBTS) that uses a novel Byzantine quorum systems replication technique in which most operations are implemented by quorum protocols while stronger operations are implemented by more expensive protocols based on consensus. LBTS is linearizable and wait-free, showing interesting performance gains when compared to a similar construction based on state machine replication. [ABSTRACT FROM AUTHOR]

The advent of IP/MPLS based networks allows providers to implement Integrated Services Packet Network (ISPN) concepts for IPTV applications. IPTV systems require a high level of Quality of Service (QoS) in order to win customers which are subscribed with cable companies. Packet loss probability is one of the primary QoS parameters whose value affects the user experience and which provides a quantitative measure for customers' perception of the QoS factor in practical networks. Therefore, the online accurate measurement and estimation of the packet loss probability is a key issue to be addressed. Furthermore, the packet loss probability provides the feedback information which can be used in the network based control system to maintain it at a prescribed and negotiated value. In this paper, a Reactive Estimator (RE) of the packet loss probability is constructed. As all parameters related to the network traffic, the packet loss is a non-linear and non-Gaussian stochastic process. The proposed RE has the capability to adapt to variable stochastic contexts by employing one dynamic item based on the feedback of the real-time loss ratio measurement. A series of experiments are devised on a live network to evaluate the performance of the estimator under multiple traffic arrival models and within various buffer sizes. The numeric results show that the practical estimator is accurate enough to approximate the packet loss probability, such that it can be further used as a feedback parameter in a closed control loop which can keep the packet loss probability close to a prescribed value. [ABSTRACT FROM AUTHOR]