Packet Transmission Time Research Articles

Opportunistic Channel-Aware Spectrum Access for Cognitive Radio Networks with Interleaved Transmission and Sensing

Opportunistic spectrum access in a cognitive radio network has been a challenge due to the dynamic nature of spectrum availability and possible collisions between the primary user (PU) and the secondary user (SU). To maximize the spectrum utilization, we propose a spectrum access strategy where SU's packets are interleaved with periodic sensing to detect PU's return. Similar to earlier works on distributed opportunistic scheduling (DOS), we formulate the sensing/probing/access process as a maximum rate-of-return problem in the optimal stopping theory framework and show that the optimal channel access strategy is a pure threshold policy. We consider a realistic channel and system model by taking into account channel fading and sensing errors. We jointly optimize the rate threshold and the packet transmission time to maximize the average throughput of SU, while limiting interference to PU. Our numerical results show that significant throughput gains can be achieved with the proposed scheme compared to other well-known schemes. Our work sheds light on designing DOS protocols for cognitive radio with optimal transmission time that takes into account the dynamic nature of PUs.

On the Performance of Underlay Cognitive Radio Networks Using M/G/1/K Queueing Model

Motivated by a realistic scenario for cognitive radio systems, we model the underlay cognitive radio network (CRN) under interference power constraint imposed by the primary network as an M/G/1/K queueing system. The respective embedded Markov chain is provided to analyze several key queueing performance measures. In particular, the equilibrium probabilities of all states are derived and utilized to evaluate throughput, blocking probability, mean packet transmission time, mean number of packets in the system, and mean waiting time of an underlay CRN with Nakagami-m fading channels.

A channel reuse strategy with adaptive channel allocation for all-optical WDM networks

The fundamental problems of WDM networks are: (1) high rate of control packet loss and (2) high propagation delay for each (re)transmission. In this paper, we minimize the station randomness to access the control architecture introducing a collisions-free access scheme. We propose a synchronous protocol according which at the end of the propagation delay each station applies a distributed algorithm for packet transmission following the data channel collisions and the receiver collisions avoidance algorithms. We introduce two data transmission stages. The time difference between them is one packet transmission time. At the end of the first stage all data channels are free and can be reused by the remaining data packets during the second stage. The proposed protocol ensures a totally collisions-free performance. The main advantage is that the data channels reuse strategy applied during the second stage provides enhanced transmission probability to the rejected packets during the first stage. This allows the data packets to try retransmission in the same cycle without requiring control packets re-coordination that increases propagation delay. Thus, we achieve large number of data packets transmission, even more than the data channels number, providing throughput improvement and delay reduction, comparing with other studies.

A hybrid reservation-based MAC protocol for underwater acoustic sensor networks

Due to the characteristics of underwater acoustic channel, such as long propagation delay and low available bandwidth, media access control (MAC) protocol designed for the underwater acoustic sensor network (UWASN) is quite different from that for the terrestrial wireless sensor network. However, for the contention-based MAC protocols, the packet transmission time is long because of the long preamble in real acoustic modems, which increase the packet collisions. And the competition phase lasts for long time when many nodes are competing for the channel to access. For the schedule-based MAC protocols, the delay is too long, especially in a UWASN with low traffic load. In order to resolve these problems, a hybrid reservation-based MAC (HRMAC) protocol is proposed for UWASNs in this paper. In the proposed HRMAC protocol, the nodes reserve the channel by declaring and spectrum spreading technology is used to reduce the collision of the control packets. Many nodes with data packets to be transmitted can reserve the channel simultaneously, and nodes with reserved channel transmit their data in a given order. The performance analysis shows that the proposed HRMAC protocol can improve the channel efficiency greatly. Simulation results also show that the proposed HRMAC protocol achieves better performance, namely higher network throughput, lower packet drop ratio, smaller end-to-end delay, less overhead of control packets and lower energy overhead, compared to existing typical MAC protocols for the UWASNs.

SCTP Tunneling: Flow Aggregation and Burst Transmission to Save Energy for Multiple TCP Flows over a WLAN

SUMMARY To raise the energy efficiency of wireless clients, it is important to sleep in idle periods. When multiple network applications are running concurrently on a single wireless client, packets of each application are sent and received independently, but multiplexed at MAC-level. This uncoordinated behavior makes it difficult to control of sleep timing. In addition, frequent state transitions between active and sleep modes consume non-negligible energy. In this paper, we propose a transport-layer approach that resolves this problem and so reduces energy consumed by multiple TCP flows on a wireless LAN (WLAN) client. The proposed method, called SCTP tunneling, has two key features: flow aggregation and burst transmission. It aggregates multiple TCP flows into a single SCTP association between a wireless client and an access point to control packet transmission and reception timing. Furthermore, to improve the sleep efficiency, SCTP tunneling reduces the number of state transitions by handling multiple packets in a bursty fashion. In this study, we construct a mathematical model of the energy consumed by SCTP tunneling to assess its energy efficiency. Through numerical examples, we show that the proposed method can reduce energy consumption by up to 69%.

Online Adaptive Compression in Delay Sensitive Wireless Sensor Networks

Compression, as a popular technique to reduce data size by exploiting data redundancy, can be used in delay sensitive wireless sensor networks (WSNs) to reduce end-to-end packet delay as it can reduce packet transmission time and contention on the wireless channel. However, the limited computing resources at sensor nodes make the processing time of compression a nontrivial factor in the total delay a packet experiences and must be carefully examined when adopting compression. In this paper, we first study the effect of compression on data gathering in WSNs under a practical compression algorithm. We observe that compression does not always reduce packet delay in a WSN as commonly perceived, whereas its effect is jointly determined by the network configuration and hardware configuration. Based on this observation, we then design an adaptive algorithm to make online decisions such that compression is only performed when it can benefit the overall performance. We implement the algorithm in a completely distributed manner that utilizes only local information of individual sensor nodes. Our extensive experimental results show that the algorithm demonstrates good adaptiveness to network dynamics and maximizes compression benefit.

Applications of Belief Propagation in CSMA Wireless Networks

Belief propagation (BP) is an efficient way to solve inference problems in graphical models, such as Bayesian networks and Markov random fields. It has found great success in many application areas due to its simplicity, high accuracy, and distributed nature. This paper is a first attempt to apply BP algorithms in CSMA wireless networks. Compared to prior CSMA optimization algorithms such as ACSMA, which are measurement-based, BP-based algorithms are proactive and computational, without the need for network probing and traffic measurement. Consequently, BP-based algorithms are not affected by the temporal throughput fluctuations and can converge faster. Specifically, this paper explores three applications of BP. 1) We show how BP can be used to compute the throughputs of different links in the network given their access intensities, defined as the mean packet transmission time divided by the mean backoff countdown time. 2) We propose an inverse-BP algorithm to solve the reverse problem of how to set the access intensities of different links to meet their target throughputs. 3) We introduce a BP-adaptive CSMA algorithm to find the link access intensities that can achieve optimal system utility. The first two applications are NP-hard problems, and BP provides good approximations to them. The advantage of BP is that it can converge faster compared to prior algorithms like ACSMA, especially in CSMA networks with temporal throughput fluctuations. Furthermore, this paper goes beyond BP and considers a generalized version of it, GBP, to improve accuracy in networks with a loopy contention graph. The distributed implementation of GBP is nontrivial to construct. A contribution of this paper is to show that a maximal clique method of forming regions in GBP: 1) yields accurate results; and 2) is amenable to distributed implementation in CSMA networks, with messages passed between one-hop neighbors only. We show that both BP and GBP algorithms for all three applications can yield solutions within seconds in real operation.

끊김 없는 핸드오프를 위한 다중 인터페이스 이동형 게이트웨이 설계 및 구현

이동형 게이트웨이(MG: Mobile Gateway)는 버스와 같은 차량에 탑승한 사용자들에게 인터넷 서비스를 제공하기 위한 무선랜 장치이다. 논문에서 다루는 MG는 인터넷 연결을 위해 도로변에 설치된 무선랜 기반 소형기지국(RSU AP : Road Side Unit AP)에 접속한다. 차량 이동 중에도 안정적인 통신 서비스를 제공하려면 MG의 접속 RSU가 바뀌는 핸드오프 과정이 빠르고 안정적으로 처리되어야 한다. 그런데 무선랜 기술 특성 상 핸드오프 과정의 통신 단절을 줄이는 데는 물리적 한계가 있다. 본 논문에서는 RSU 접속을 위한 무선랜 인터페이스를 복수 개로 사용하여 끊김 없는 핸드오프를 실현하는 다중 인터페이스 MG (MIMG : Multi-Interface MG)를 제안한다. 안정적인 핸드오프를 위한 구체적 방법으로 MIMG로부터 RSU로의 패킷 전송 단절을 제거하기 위한 Link Sharing 기법, RSU로부터 MIMG로의 패킷 전송 단절을 제거하기 위한 Path Sharing 기법을 제안한다. 우리는 임베디드 보드를 이용하여 제안한 핸드오프 기법을 실현한 MIMG를 구현하였고 이를 이용하여 성능 평가실험을 수행하였다. 실험 결과 단일 인터페이스를 가진 MG와 달리 MIMG는 핸드오프 시의 통신 단절을 제거할 수 있었고 대역폭도 50% 이상 향상됨을 확인하였다. Mobile Gateway(MG) is a wireless LAN device to provide internet services to a passenger on vehicles like a bus. For using internet services, MG connects the Road Side Unit AP(RSU AP) based on WLAN .To provide a stable communication service on the moving vehicle, handoff changing MG's RSU must be handled fast and stably. However, it has a physical limits to remove a disconnection time of handoff process by reason of its technological features. In this paper, we suggest a MIMG(Multi-Interface Mobile Gateway) executing seamless handoff by using multiple wireless LAN interfaces for connecting RSU. In the detailed way to do stable handoff, we suggest the "Link Sharing Technique" to disconnection time of packet transmission for RSU to MIMG and the "Path Sharing Technique" to remove disconnection time of packet transmission for MIMG to RSU. we implemented the MIMG which performs the suggested handoff technique. We confirmed the superiority of our system by remove of the disconnection time(0 ms), and improved over 50 % of the communication bandwidth.

Secure routing in MANETs using local times

We present a new approach to secure routing in mobile ad-hoc networks based solely on the relative transmission times of overhead packets. Unlike most previous works aimed at securing route computation, we eliminate a key vulnerability (explicitly stated routing metrics) altogether. We introduce the Secure Time-Ordered routing Protocol (STOP), which uses time-based orderings to ensure the establishment of multiple loop-free paths between a source and a destination. STOP is the first routing protocol to use performance-based path selection without source routing, path vectors, or complete topology information, making it far more efficient that similar approaches. We prove that adversaries cannot take any action to manipulate the time-based ordering so as to unfairly gain control of the forwarding topology and, by design, nodes which drop data packets will be avoided. Furthermore, at convergence, traffic load is evenly distributed over the well-performing paths, so adversaries cannot gain complete control over the data flow through temporary good behavior. Simulation results show that the countermeasures in STOP are effective against a variety of attacks from independent and colluding adversaries, and that this improved security does not come at the expense of routing performance.

LAAP: A Learning Automata-based Adaptive Polling Scheme for Clustered Wireless Ad-Hoc Networks

In multi-hop ad hoc networks, besides collision-free transmissions, channel utilization should be also enhanced due to the scarce bandwidth. In this paper, we propose a learning automat-based adaptive polling scheme for medium access scheduling in clustered wireless ad-hoc networks to enhance the channel utilization. In this scheme, each cluster-head takes the responsibility of coordinating intra-cluster transmissions so that no collisions occur. Taking advantage of learning automaton, each cluster-head learns the traffic parameters of its own cluster members. Cluster members are prioritized based on these traffic parameters. Each cluster-head then takes the traffic parameters into consideration for finding an optimal channel access scheduling within its cluster. By the proposed polling scheme, each cluster member is assigned a portion of bandwidth proportional to its need (i.e., traffic load). The results show that the proposed channel assignment policy considerably improves the channel utilization. Simulation experiments also show the superiority of the proposed polling-based medium access scheme over the existing methods in terms of channel utilization, waiting time for packet transmission, and control overhead.

The Usefulness of Overheard Information for Collision Avoidance in a Single-hop Underwater Acoustic Networks

A MAC protocol that depends on overheard information for its collision avoidance, such as Carrier Sense Multiple Access (CSMA) [1], may not work well in underwater, due to the long propagation delay characteristic of an underwater acoustic (UWA) channel. In such channel, the overheard information may already become obsolete by the time it reaches the node and, thus, should not be taken into account in the collision avoidance mechanism.Intuitively, the degree of usefulness of overheard information plays an important role in determining the network performance for channel listening-based MAC protocols. In this paper, we analytically study the usefulness of overheard information for collision avoidance in two different channel listening-based MAC protocols: (1) CSMA [1] and (2) Aloha-CA [2]. From our study, it is shown that the overheard information is beneficial for collision avoidance only if certain conditions can be satisfied. More specifically, in order for a node that overhears an ongoing transmission to be able to utilize the extracted information for collision avoidance, the node must be within a bounded region that is determined by the relative positions of the sender and the receiver, the packet's transmission time, as well as the length of the packet's header. Based on this analysis, we also present the “usefulness index (U)” which is defined as the degree of usefulness of information overheard.

“Energy Efficient Ethernet” enhanced with a QoS-aware sleep mode controller

Operating costs and scalability of nowadays telecommunication networks are largely impacted by energy consumption of network equipments. In packet switching devices it is especially due to packet processing, queuing, and input/output interface functionalities. Different approaches to reduce energy consumption in packet switches are emerging, some exploit under-laid optical bypass of transit traffic to reduce their capacity and interfaces, others simplify their operations or turn off some of their functionalities when unnecessary. The IEEE standardization body developed a standard on Energy Efficient Ethernet IEEE P802.3az that defined a mechanism allowing to de-activate the Physical layer elements during periods of low link utilization. It is based on a protocol that coordinates transitions to and from a lower power consumption mode without changing the link status and dropping frames. Time needed by such transitions is, however, comparable with packet transmission time; that makes energy efficiency of the method far from being proportional to interfaces unused capacity. Solutions proposed in the literature to improve EEE performance are mainly based on the buffer and burst approach, which, making the transmission non continuous, creates more opportunities for long sleeping period. Such solutions, however, if applied across the network, strongly impact packet delay requirements. In this paper, a traffic management mechanism that controls sleeping period to reduce EEE transitions overhead while meeting delay constraints of data flows is proposed. Starting from the consideration that in Ethernet network provisioning is static, i.e. service level agreement parameters of each flow are configured on switches output ports of its path via management plane at the set-up phase, the proposed method off-line determines, for each output port, if the activation of a dummy flow, associated to the quiet period, can provide power consumption reduction without impacting data flows delay requirements. On ports where the dummy flow is activated the sleeping period is triggered by the scheduler mechanism each time a dummy packet is served. A comparative analysis between the standard EEE, with and without the support of buffer and burst functionality, and the proposed method has been carried out in order to quantify the improvements in terms of energy efficiency and to assess its effectiveness in terms of Quality of Service QoS.

Deadlock Free Routing Algorithm for Minimizing Data Packet Transmission in Network on Chip

Network on chip (NoC) has been proposed as a solution for addressing the design challenges of future high performance nanoscale architectures. In NoCs, the traditional routing schemes are routing packets through a single path or multiple paths from one source node to a destination node, minimizing the congestion in the routing architecture. Although these routing algorithms are moderately efficient, they are time dependent. To reduce overall data packet transmission time in the network, the authors consider a network with multiple sources and multiple destinations. Multi-dimensional routing problems appear naturally in several resource allocation problems, communication networks and wireless sensor networks. In this paper, the authors have constructed a deadlock-free multi-dimensional path routing algorithm for minimizing the congestion in NoC.

Cross-Layer Design of Rateless Random Network Codes for Delay Optimization

We study joint network and channel code design to optimize delay performance. Here the delay is the transmission time of information packets from a source to sinks without considering queuing effects. In our systems, network codes (network layer) are on top of channel codes (physical layer) which are disturbed by noise. Network codes run in a rateless random method, and thus have erasure-correction capability. For the constraint of finite transmission time, transmission errors are inevitable in the physical layer. A detection error in the physical layer means an erasure of network codewords. For the analysis, we model the delay of each information generation in the network layer as independent, identically distributed random variables. The calculation approaches for delay measures are investigated for coded erasure networks. We show how to evaluate the rate and erasure probability of a set of channels belonging to one cut. We also show that the min-cut determines the decoding error probability in the sinks if the number of information packets is large. We observe that for a given amount of source information, larger packet length leads to fewer packets to be transmitted but higher physical-layer detection error probabilities. Further, longer transmission time (delay) in the physical-layer causes smaller detection error probability at the physical layer. Thus, both parameters have opposite impacts on the physical and network layer, considering delay. We should find the optimal values of them in a cross-layer approach. We then formulate the problems of optimizing delay performance, and discuss solutions for them.

Delay performance of cognitive radio networks for point-to-point and point-to-multipoint communications

In this article, we analyze the packet transmission time in spectrum sharing systems where a secondary user (SU) simultaneously accesses the spectrum licensed to primary users (PUs). In particular, under the assumption of an independent identical distributed Rayleigh block fading channel, we investigate the effect of the peak interference power constraint imposed by multiple PUs on the packet transmission time of the SU. Utilizing the concept of timeout, exact closed-form expressions of outage probability and average packet transmission time of the SU are derived. In addition, employing the characteristics of the M/G/1 queuing model, the impact of the number of PUs and their peak interference power constraint on the stable transmission condition and the average waiting time of packets at the SU are examined. Moreover, we then extend the analysis for point-to-point to point-to-multipoint communications allowing for multiple SUs and derive the related closed-form expressions for outage probability and successful transmission probability for the best channel condition. Numerical results are provided to corroborate our theoretical results and to illustrate applications of the derived closed-form expressions for performance evaluation of cognitive radio networks.

Static weighted routing strategy on two-layer complex networks

The routing strategy is important to information dissemination and exchange in complex communication networks. The traditional routing strategies are often insufficient to alleviate congestion and enhance the utilization efficiency of two-layer complex networks. In this paper, a novel efficient static weighted routing strategy is proposed. The weight of the logical edges mapped on the hub nodes at the physical layer is assigned a higher weight according to the degree of nodes. Then packets choose the routing path with the minimum sum weight of logical edges. It is found that the average packet transmission time and average throughput have been improved greatly compared to the shortest path routing strategy in two-layer complex networks.

Attacks in Wireless Networks

Communications in wireless networks has been facilitating numerous emerging applications that require packet delivery from one or more senders to multiple receivers. Communications are susceptible to various kinds of attacks due to insecure wireless channels. Communications in wireless networks remains a challenging and critical issue. This paper presents recent advances in security requirements and services in communications in wireless networks. Wireless networks are being used in many commercial and military applications to collect event driven and real time data. Deployment nature of networks makes them vulnerable to security threats. Due to the resource limitations traditional security measures are not more enough to keep safe the nodes. Research in network security domains has produced several security solutions. In this paper we have observed security mechanisms. We have studied these security mechanisms with respect to packet overheads and compared the packet transmission time, average latency and energy consumption. The comparison shows that the packet overheads are lesser as compared to other schemes. It have been observed that packet delivery ratio decreases when we increase number of nodes while energy and latency increases.

Analytic approximations of queues with lightly- and heavily-correlated autoregressive service times

We consider a single-server queueing system. The arrival process is modelled as a Poisson process while the service times of the consecutive customers constitute a sequence of autoregressive random variables. Our interest into autoregressive service times comes from the need to capture temporal correlation of the channel conditions on wireless network links. If these fluctuations are slow in comparison with the transmission times of the packets, transmission times of consecutive packets are correlated. Such correlation needs to be taken into account for an accurate performance assessment. By means of a transform approach, we obtain a functional equation for the joint transform of the queue content and the current service time at departure epochs in steady state. To the best of our knowledge, this functional equation cannot be solved by exact mathematical techniques, despite its simplicity. However, by means of a Taylor series expansion in the parameter of the autoregressive process, a “light-correlation” approximation is obtained for performance measures such as moments of the queue content and packet delay. We illustrate our approach by some numerical examples, thereby assessing the accuracy of our approximations by simulation. For the heavy correlation case, we give differential equation approximations based on the time-scale separation technique, and present numerical examples in support of this approximation.

BEWARE: Background Traffic-Aware Rate Adaptation for IEEE 802.11

IEEE 802.11-based devices employ rate adaptation algorithms to dynamically switch data rates to accommodate the fluctuating wireless channel conditions. Many studies observed that when there are other stations transmitting in the network, existing rate adaptation performance degrades significantly due to its inability to differentiate losses between wireless noise and contention collisions. In this paper, we first conduct a systematic evaluation on the effectiveness of various rate adaptation protocols, which try to address this issue by exploiting optional RTS frames to isolate the wireless losses from collision losses. We observe that these existing schemes do not perform well in many background traffic scenarios and can mislead the rate adaptation algorithms to persist on using similar data rate combinations regardless of background traffic level, thus resulting in performance penalty in certain scenarios. The fundamental challenge is to dynamically adjust the rate selection decision objectives with respect to different background traffic levels, as well as fluctuating wireless conditions. In light of such observations, we design a new Background traffic-aWAre RatE adaptation algorithm (BEWARE) that addresses the above challenge. BEWARE uses a mathematical model to calculate on the fly the expected packet transmission time based on current wireless channel and background traffic conditions. We implement BEWARE design in a Linux-based driver, and the test-bed experiment results show that BEWARE outperforms other rate adaptation algorithms by up to 250% in various indoor and outdoor scenarios.

An analytical model for input-buffered optical packet switches with reconfiguration overhead

The overhead associated with reconfiguring a switch fabric in optical packet switches is an important issue in relation to the packet transmission time and can adversely affect switch performance. The reconfiguration overhead increases the mean waiting time of packets and reduces throughput. The scheduling of packets must take into account the reconfiguration frequency. This work proposes an analytical model for input-buffered optical packet switches with the reconfiguration overhead and analytically finds the optimal reconfiguration frequency that minimizes the mean waiting time of packets. The analytical model is suitable for several round-robin (RR) scheduling schemes in which only non-empty virtual output queues (VOQs) are served or all VOQs are served and is used to examine the effects of the RR scheduling schemes and various network parameters on the mean waiting time of packets. Quantitative examples demonstrate that properly balancing the reconfiguration frequency can effectively reduce the mean waiting time of packets.