Search

A new problem of spectrum scarcity has emerged due to the incredible technological advances in wireless communication. The spectrum scarcity issue is a bottleneck for the next generation of wireless communications. Therefore, efficient spectrum utilization has attracted considerable attention. This paper proposes a novel method of utilizing the white spaces in the licensed spectrum while ensuring the incumbent licensees' rights. The protocol predicts the incumbents' arrival using a historical prediction method and protects the incumbent users from the interference of opportunistic spectrum users. Distributed sensing is used to determine the network wide spectrum opportunity. The channel access delay in the proposed protocol is evaluated by simulation and mathematical analysis. The protocol has the advantages of a decentralized system, flexibility and low computing complexity. The simulations show that the protocol outperforms the existing opportunistic spectrum-sharing, media-access-control protocols in terms of the goodput and delay.

Available bandwidth is usually sensitive to network anomalies such as physical link failure, congestion, and DDoS attack. Thus, real-time available bandwidth information can be used to detect network anomalies. Many schemes have been proposed to estimate the end-to-end available bandwidth or end-to-end capacity. However, the problem of estimating the available bandwidth for a specific remote link has not been investigated in detail yet. We propose a new scheme to estimate the available bandwidth ratio of a remote link or remote path segments, a group of consecutive links, without deploying our tool at the remote nodes. The scheme would be helpful in accurately pinpointing anomalous links. Two streams of ICMP timestamp packets are sent to both end nodes of a target link according to a Poisson process, and the available bandwidth ratio for the target link is estimated based on the measured packet delay. Since the proposed scheme needs not incur a short-term congestion, unlike conventional end-to-end available bandwidth estimation mechanisms, the intrusiveness is low and the proposed scheme overcomes the limitation of conventional approaches, inability to probe the links beyond the tight link with the minimum available bandwidth. The performance of the proposed scheme is evaluated by ns-2 simulation.

Many existing medium access control protocols for cognitive radio wireless sensor networks waste bandwidth and suffer from delay because of the fixed channel negotiation period in the common control channel. In this paper, we propose a medium access control protocol for cognitive radio wireless sensor networks that adjusts the channel negotiation period based on network density. We simulate the proposed approach and compare it to the performance of the fixed channel negotiation period based approaches. The results show that the proposed approach efficiently utilizes white spaces and increases the aggregated goodput.

This paper analyzes the minimal backlogging-based available bandwidth estimation mechanism to strengthen the theory behind the mechanism. The minimal backlogging method estimates the available bandwidth using the statistic of the probing traffic service rate. We show that the statistic of the probing traffic service rate is a consistent estimator of the available bandwidth for a G/G/1 queueing system under minimal backlogging condition to support the minimal backlogging method theoretically. In order to emulate the minimal backlogging method in a real multi-hop network, we detect the minimal backlogging condition or closeness of the probing rate to the available bandwidth based on the busy period length, and change the probing rate adaptively to maintain the minimal backlogging condition. We explain that the minimal backlogging condition or available bandwidth might be detected more accurately by the busy period of probing packets than by the gap response curve or rate response curve, and enhance the minimal backlogging method further by introducing a new initial probing rate estimation mechanism. A reasonable range of available bandwidth for a short time interval can be obtained using the mean and variance of the estimated available bandwidth, since the proposed mechanism can estimate the available bandwidth quickly and track it adaptively. The proposed mechanism is implemented in a Linux environment. The performance of our scheme is compared to those of conventional available bandwidth estimation mechanisms through experiments on a test-bed with single-hop or multiple-hop topologies.

Cooperative communications aim to gain spatial diversity from stations cooperating during data transmission without requiring multiple transceiver antennas on the same station. However, performance from cooperative communications highly depends on the relay-selection method. This paper proposes and evaluates a distributed relay-selection method based on the signal-to-noise ratio of the communication links of candidate relay nodes. A node is selected as a relay node based on the signal-to-noise ratio of its communication link. Moreover, data might be delivered through a relay node that can support high transmission rate rather than through a direct link with a low transmission rate. This paper provides a detailed analysis of the collision probability in the proposed method as compared to a conventional random backoff method. Results demonstrate that the proposed relay-selection method reduces collision probability, and hence, enhances system throughput.

This paper is concerned with estimating the available bandwidth, the residual processing capacity, of a single-server queueing system whose service rate and the input traffic load are not known in advance. We analyze the minimal-backlogging method which has been proposed to estimate the available bandwidth by sending probing packets. We show that an M / G / 1 queueing system probed by the minimal-backlogging method is stable. A consistent estimator of the inverse of available bandwidth is proposed based on the sojourn times of the probing packets. We also estimate the available bandwidth of a local server which is connected to the probing node with non-zero delay as an application of the theory developed for a single-server queue. We evaluate the accuracy of the proposed available bandwidth estimation scheme by simulation.

Computer worms and bots are significant threats to large networks because they can spread very rapidly and are used for DDoS. The first phase of worms and bots begins by scanning vulnerable hosts. Missing on-going scanning activity can significantly deteriorate network performance. We propose a new scanning detection scheme, SherLOCK, based on the connection attempt success ratio. The proposed scheme can detect scanners with guaranteed false positive and false negative probabilities and with a limited memory size. Detection of scanners at high-speed links requires a high-speed memory and such memory devices are expensive and limited in size. We reduce the memory requirement by applying the Bloom filter. We show how slow scanners can be detected with a guaranteed performance for a given offered traffic load and memory size. This study can help to design the system that satisfies the target performance requirement. The detection performance is guaranteed under the assumption that malicious scanners and benign hosts have distinct behaviors in terms of the connection success ratio. We extend the proposed detector with a sampling mechanism to detect more intelligent scanners with guaranteed performance. These include scanners that use a list of pre-acquired IP addresses. We evaluate the performance of the proposed scheme through experiment using well-known traffic traces.

It is very important to allocate and manage resources for multimedia traffic flows with real-time performance requirements in order to guarantee quality of service (QoS). In this paper, we develop a scalable architecture and an algorithm for admission control of real-time flows. Since individual management of each traffic flow on each transit router can cause a fundamental scalability problem in both data and control planes, we consider that each flow is classified at the ingress router and data traffic is aggregated according to the class inside the core network as in a DiffServ framework. In our approach, admission decision is made for each flow at the edge (ingress) routers, but it is scalable because per-flow states are not maintained and the admission algorithm is simple. In the proposed admission control scheme, an admissible bandwidth, which is defined as the maximum rate of a flow that can be accommodated additionally while satisfying the delay performance requirements for both existing and new flows, is calculated based on the available bandwidth measured by edge routers. The admissible bandwidth is a threshold for admission control, and thus, it is very important to accurately estimate the admissible bandwidth. The performance of the proposed algorithm is evaluated by taking a set of simulation experiments using bursty traffic flows.

Security techniques like cryptography and authentication can fail to protect a network once a node is compromised. Hence, trust establishment continuously monitors and evaluates node behavior to detect malicious and compromised nodes. However, just like other security schemes, trust establishment is also vulnerable to attack. Moreover, malicious nodes might misbehave intelligently to trick trust establishment schemes. Unfortunately, attack-resistance and robustness issues with trust establishment schemes have not received much attention from the research community. Considering the vulnerability of trust establishment to different attacks and the unique features of sensor nodes in wireless sensor networks, we propose a lightweight and robust trust establishment scheme. The proposed trust scheme is lightweight thanks to a simple trust estimation method. The comprehensiveness and flexibility of the proposed trust estimation scheme make it robust against different types of attack and misbehavior. Performance evaluation under different types of misbehavior and on-off attacks shows that the detection rate of the proposed trust mechanism is higher and more stable compared to other trust mechanisms.

The traffic patterns of today's IP networks exhibit two important properties: self-similarity and long-range dependence. The fractional Brownian motion is widely used for representing the traffic model with the properties. We consider a single server fluid queueing system with input process of a fractional Brownian motion type. Packet-loss probability and mean delay are considered as QoS. We show that there is a scaling property among the stationary queue-length distributions of different input parameters and service rates. We also evaluate the scaling factor. From the scaling property, we drive formulas for the effective bandwidth to guarantee the QoS in a single source and multiple sources cases. The formulas indicate that it is essential to evaluate the distribution functions of a type of random variables. For multiple sources the shape of an admissible region and multiplexing gain are analyzed. Finally, numerical examples are shown to validate the proposed scheme.

Spare bandwidth is required for recovering the network service from network faults. However, it degrades the efficiency of network utilization. Spare bandwidth demand can be reduced significantly by letting spare bandwidth be shared among several network services. Spare bandwidth reserved on a network element can be shared by a set of network services for a network fault if they are not simultaneously affected by the network fault. A new, and more practical spare bandwidth sharing scheme, which is based on the network reliability, is proposed in this paper. In the proposed scheme, multiple link failures are allowed with a given link failure rate, and a reasonable restoration level of near 100%; while in the conventional scheme, only a single link failure, and 100% restoration level are considered. To develop the spare bandwidth sharing scheme, we first investigate the framework for evaluating the reliability of path-based network services, and then we explain the proposed spare bandwidth sharing scheme with decision parameters such as lifetime of the path, restoration level, and the maximum number of working paths which can be protected by a backup link. Simulation results show that the proposed spare bandwidth sharing scheme requires a smaller amount of spare bandwidth than the conventional scheme.

Mobile hosts (MHs) in all IP-based mobile networks must update their current location to receive incoming packets. The MHs are idle for most of time. Both registration of approximate location information and paging can facilitate efficient power management for the idle MHs. Furthermore, the MHs can be in switch-off state for battery power conservation. Mobile IP, the current standard for IP-based mobility management, needs to be enhanced for use in all IP-based mobile networks. Mobility management in all IP-based mobile networks should consider idle and detached MH states as well as active MH state. A mobility management scheme for all IP-based mobile networks is introduced in this paper. This scheme includes management of communicating, attentive, idle, and detached states. We model MH behavior in the networks when the binding-lifetime-based registrations are utilized as a means of identifying that an MH is switched off. The steady-state probabilities for MH state transitions are derived, and an optimal rate of binding-lifetime-based registrations that results in minimum network cost is derived.

The original distributed-queueing request update multiple-access (DQRUMA)/multicode code-division multiple-access (MC-CDMA) protocol was developed as a channel access protocol for wireless packet CDMA networks. This protocol has recently attracted considerable attention. We modify the original protocol, which was designed for data traffic only, to additionally accommodate voice traffic and call it the A-Protocol. We propose a new packet CDMA protocol that enhances the A-Protocol by improving the utilization of receivers in a base station and call it the E-Protocol. In the E-Protocol, an access request is attempted with a randomly chosen code at a request minislot. We analytically evaluate the performance of both protocols and compare analytical results with computer simulation. Analytical results agree well with simulation results.

Rendezvous is a process of two or more cognitive radio nodes gathering on the same channel at the same time for a negotiation to establish data communications. This paper discusses rendezvous issues in cognitive radio networks. It details why rendezvous is an issue in cognitive radio networks and how rendezvous works. It classifies channel access methods, and details sequence-based channel-hopping methods. It surveys existing works on blind rendezvous and compares the proposed algorithms in terms of the maximum time to rendezvous. This paper discusses the properties that an efficient channel-hopping rendezvous algorithm should have and illustrates common issues in the existing rendezvous methods. It also explains open research issues in the rendezvous area.

In this letter, an enhanced version of Address Resolution Protocol (ARP) is proposed to prevent ARP poisoning-based Man-in-the-Middle (MITM) attacks. The proposed mechanism is based on the following concept. When a node knows the correct Media Access Control (MAC) address for a given IP address, if it retains the IP/MAC address mapping while that machine is alive, then MITM attack is impossible for that IP address. In order to prevent MITM attacks even for a new IP address, a voting-based resolution mechanism is proposed. The proposed scheme is backward compatible with existing ARP and incrementally deployable.

A new mechanism to estimate available bandwidth for multiple hop routes is proposed based on a minimally backlogging concept. Since the proposed mechanism can estimate the available bandwidth quickly and track it adaptively, a reasonable range of available bandwidth for a short time interval can be obtained using the mean and variance of the estimated available bandwidth. The performance of the proposed mechanism is verified by simulation in a multiple hop network topology.

In this article, an enhanced version of address resolution protocol (ARP) is proposed to prevent ARP poisoning-based man-in-the-middle (MITM) attacks in wired or wireless LAN environments. The proposed mechanism is based on the idea that when a node knows the correct MAC address for a given IP address, if it does not delete the mapping while the machine is alive, then MITM attack is not possible for that IP address. In order to prevent MITM attack even for a new IP address, we propose a new IP/MAC mapping conflict resolution mechanism based on computational puzzle and voting. Our proposed scheme can efficiently mitigate ARP poisoning-based MITM attacks, even in Wi-Fi hot-spots where wireless machines can easily come and leave, since the proposed mechanism does not require manual configuration if the proposed ARP is deployed through operating system (OS) upgrade. The proposed scheme is backward compatible with the existing ARP protocol and incrementally deployable with benefits to the upgraded machines.

In cognitive radio sensor networks, the routing methods including multiple relays have been extensively studied to achieve higher throughput and lower end-to-end delay. As one of innovative approaches, the opportunistic routing scheme was proposed. In this paper, the effectiveness of the opportunistic transmission in terms of reliability and delay of transmission is verified with an analytical way. For the analysis, we establish the probabilistic model with respect to distance and the number of relay nodes under the Rayleigh fading channels including path loss effects. Under this model, we develop a generic Markov chain model to obtain the analytical results and verify the effectiveness of the statistical analysis. The results show that an opportunistic transmission approach is better than traditional multihop transmissions in terms of successful data delivery with fewer transmissions. Consequently, it can provide an energy efficient transmission mechanism for cognitive radio sensor networks.

We propose a two-stage Distributed Denial of Service (DDoS) defense system, which can protect a given subnet by serving existing flows and new flows with a different priority based on IP history information. Denial of Service (DoS) usually occurs when the resource of a network node or link is limited and the demand of the users for that resource exceeds the capacity. The objective of the proposed defense system is to provide continued service to existing flows even in the presence of DDoS attacks, and we attempt to achieve this goal by discriminating existing flows from new flows. The proposed scheme can protect existing connections effectively with a reduced memory size by reducing the monitored IP address set through sampling in the first stage and using Bloom filters. We evaluate the performance of the proposed scheme through simulation.

Rapid growth of Internet traffic causes a new challenge in the design of high-speed switches. One of main design issues for high-speed switches is a scalability problem. This paper proposes a scalable crossbar matrix (SCM) switch architecture, which consists of multiple crossbar switch units (XSU) with virtual output queues (VOQs) at the inputs and single-cell scheduling decomposition buffers (SDBs) at the outputs. We propose a distributed scheduling algorithm for the proposed scalable crossbar switch architecture, which consists of a credit based SLIP (C-SLIP) scheduling for crossbar switch units and backlog weighted round robin (BWRR) scheduling for switching fabric output ports. In this paper, we show that large-scale switch fabric can be built up by small-size crossbar switch units with improved delay performance and enough arbitration time margins. The simulation results show that the proposed switch architecture and distributed scheduling algorithm can provide 100% throughput under i.i.d. uniform traffic with a single iteration arbitration in a time slot.

Conventional input switches usually employ a single crossbar switch fabric to transfer cells from input buffers to output ports. This type of switch suffers from input and output cell contention problems which cause lower performance than for output buffer switches. However, dividing one crossbar fabric into several smaller crossbar fabrics, we can decrease the input and output contention probabilities. Based on this principle, we propose a new decomposed crossbar switch architecture. Since a decrease in input and output contention probabilities causes an increase in the grant probability for the cells at input buffers, the proposed decomposed crossbar switches yield better performance than conventional input switches. We derive the grant probability for a simple arbitration algorithm and evaluate the performance of the proposed switch architecture in terms of the average cell latency through simulation.

Real-time traffic requires strict delay constraints in terms of maximum cell transfer delay (CTD) and cell delay variation (CDV). In order to support the required quality of service (QoS) of each connection in ATM networks, it is important to estimate the current status of networks by using local information such as cell delay and delay variation in switches. We develop a framework for obtaining delay distribution in a single switch module by monitoring the internal buffer. We also propose a new delay estimation mechanism utilizing a fast convolution approximation scheme in order to reduce the number of operations and the required amount of the data for estimating end-to-end delay. The feasibility of the proposed delay estimation mechanism is verified by simulation for various types of CBR and VBR traffic loads.

A simple convolution approximation scheme is proposed to reduce the number of operations and the required amount of data in ATM networks. This approximation method can be used to estimate the end-to-end cell delay variation (CDV) using local information about cell delays in asynchronous transfer mode (ATM) networks.

Although a jamming attack is an important problem in Wi-Fi networks, there is no effective solution to this problem yet. In this paper, we propose a new approach to resolve jamming attacks in Wi-Fi networks based on the concept of channel hopping. If we assume that the attacker does not jam all the channels simultaneously, then it might be possible to circumvent a jamming attack by changing the channel. A channel hopping mechanism is designed so that the access point (AP) and a normal user can agree on the next channel with a high probability without pre-sharing of any secret information between the AP and a user node. The proposed scheme is evaluated through experiment in a test bed.