Timeout Expires Research Articles

Minimum connected dominating set based RSU allocation for smartCloud vehicles in VANET

Nodes (smartCloud vehicles) of minimum connected dominating set form a virtual backbone in a wireless vehicular ad hoc network. A minimum connected dominating set is a minimum set of connected nodes such that every other node in the network is one hop connected with a node in this set. A smartCloud vehicle sends periodic beacon messages (Coordinates) to nearest roadside unit. Every time check smartCloud vehicle or Star whether it belongs to a connected dominating set (CDS). SmartCloud Vehicles in the CDS use a shorter waiting period and retransmit coordinates to same RSU. At time-out expiration, a smartCloud vehicle to address next RSU connectivity and appearance of new neighbors transmits the coordinates. In general, the problem is proved to be NP-hard. In this paper we find a minimum connected dominating set for certain vehicular ad hoc networks. Simulation-based performance evaluation for improving speed, transmission range, processing power, delay using graphs.

Gateway-Assisted Retransmission for Lightweight and Reliable IoT Communications.

Message Queuing Telemetry Transport for Sensor Networks (MQTT-SN) and Constrained Application Protocol (CoAP) are two protocols supporting publish/subscribe models for IoT devices to publish messages to interested subscribers. Retransmission mechanisms are introduced to compensate for the lack of data reliability. If the device does not receive the acknowledgement (ACK) before retransmission timeout (RTO) expires, the device will retransmit data. Setting an appropriate RTO is important because the delay may be large or retransmission may be too frequent when the RTO is inappropriate. We propose a Gateway-assisted CoAP (GaCoAP) to dynamically compute RTO for devices. Simulation models are proposed to investigate the performance of GaCoAP compared with four other methods. The experiment results show that GaCoAP is more suitable for IoT devices.

Решение автоматных уравнений для временных автоматов относительно параллельной композиции

The problem of designing an unknown component that combined with the known part of a discrete event system satisfies the given overall specification arises in a number of applications. In this paper, we extend the known results for classical Finite State Machines (FSM) to Finite State Machines with Timeouts (TFSM). A TFSM is an FSM augmented with an input and an output timeout functions, prescribing the change of current state if no input is applied until a specified timeout expires and system delays needed to response to applied input, respectively. We represent the behavior of a TFSM by the corresponding regular language. The parallel composition of two TFSMs S and P is defined via composition of languages L(S) and L(P) intersected with L(MC), where MC is a maximal TFSM over input and output alphabets of the composition. The unknown component X is then designed as a solution to the equation where A and X are compared by ≤ with C. Here A is a context, C is a specification, and ≤ is the reduction relation which specifies that the behavior of a system to be designed is contained in that of the specification. Similar to classical FSMs, the equation is transformed to a language equation, the largest solution for which provides the largest solution to the solvable TFSM equation. After the largest solution is derived, a corresponding reduction can be extracted in order to provide the component with required properties. The application areas vary from testing in context to quality optimization of service compositions. Future work includes studying equation solvability criteria and properties of nondeterministic and partial specifications and solutions.

QoS aware transmission control scheme for multihop WiMAX network

SUMMARYThe IEEE 802.16j Mobile Multihop Relay (MMR) WiMAX network allows the number of hops between the end user and the base station to be more than two hops. It supports non‐real‐time Polling Service, which considers the minimum reserved rate and the maximum sustained rate as a QoS requirements. The reliability of sending the data over MMR WiMAX is achieved by using Transmission Control Protocol (TCP) in transport layer and automatic repeat request in the link layer. However, the use of automatic repeat request in the link layer makes the round trip time fluctuate rapidly, which increases the possibility of retransmission timeout (RTO) expiration. TCP performance degrades because of frequent timeout, and hence the QoS transmission rates cannot be satisfied. Therefore, this paper presents an RTO smoothing scheme and QoS aware transmission control to enhance the performance of data transmission over MMR WiMAX networks. The RTO smoothing scheme aims to reduce the frequent timeout occurrences. The slow start threshold and maximum congestion window are adjusted to satisfy the required QoS and it provides transmission rate fairness for the users at different hops. The results showed that, the proposed schemes reduce the timeout, and improve the utilization of the allocated resources and TCP throughput. Copyright © 2012 John Wiley & Sons, Ltd.

Broadcasting with seamless transition from static to highly mobile wireless ad hoc, sensor and vehicular networks

In a broadcasting task, source node wants to send the same message to all the other nodes in the network. Existing solutions range from connected dominating set (CDS) based on static networks to blind flooding for moderate mobility and hyper-flooding for highly mobile and frequently partitioned networks. Existing protocols for all scenarios are based on some threshold parameters (e.g. speed, which may be expensive to gather) to locally select between these three solution approaches. Here, we describe a new seamless broadcasting from static to mobile protocol, which adjusts itself to any mobility scenario without using any mobility or density-related parameter. Unlike existing methods for highly mobile scenarios, in the proposed method, two nodes do not transmit every time they discover each other as new neighbours. Each node maintains a list of two hop neighbours by periodically exchanging ‘hello’ messages, and decides whether or not it is in CDS. Upon receiving the first copy of message intended for broadcasting, it selects a waiting timeout and constructs two lists of neighbours: neighbours that received the same message and neighbours that did not receive it. Nodes not in CDS select longer timeouts than nodes in CDS. These lists are updated upon receiving further copies of the same packet. When timeout expires, node retransmits if the list of neighbours in need of message is non-empty. ‘Hello’ messages received while waiting, or after timeout expiration may revise all lists (and CDS status) and consequently the need to retransmit. This provides a seamless transition of protocol behaviour from static to highly mobile scenarios, which is applicable to a variety of multi-hop wireless networks.

Acknowledgment-Based Broadcast Protocol for Reliable and Efficient Data Dissemination in Vehicular Ad Hoc Networks

We propose a broadcast algorithm suitable for a wide range of vehicular scenarios, which only employs local information acquired via periodic beacon messages, containing acknowledgments of the circulated broadcast messages. Each vehicle decides whether it belongs to a connected dominating set (CDS). Vehicles in the CDS use a shorter waiting period before possible retransmission. At time-out expiration, a vehicle retransmits if it is aware of at least one neighbor in need of the message. To address intermittent connectivity and appearance of new neighbors, the evaluation timer can be restarted. Our algorithm resolves propagation at road intersections without any need to even recognize intersections. It is inherently adaptable to different mobility regimes, without the need to classify network or vehicle speeds. In a thorough simulation-based performance evaluation, our algorithm is shown to provide higher reliability and message efficiency than existing approaches for nonsafety applications.

Improving Performance of Remote TCP in Cognitive Radio Networks

Recent advances in cognitive radio technology have drawn immense attention to higher layer protocols above medium access control, such as transmission control protocol (TCP). Most proposals to improve the TCP performance in cognitive radio (CR) networks have assumed that either all nodes are in CR networks or the TCP sender side is in CR links. In those proposals, lower layer information such as the CR link status could be easily exploited to adjust the congestion window and improve throughput. In this paper, we consider a TCP network in which the TCP sender is located remotely over the Internet while the TCP receiver is connected by a CR link. This topology is more realistic than the earlier proposals, but the lower layer information cannot be exploited. Under this assumption, we propose an enhanced TCP protocol for CR networks called TCP for cognitive radio (TCP-CR) to improve the existing TCP by (1) detection of primary user (PU) interference by a remote sender without support from lower layers, (2) delayed congestion control (DCC) based on PU detection when the retransmission timeout (RTO) expires, and (3) exploitation of two separate scales of the congestion window adapted for PU activity. Performance evaluation demonstrated that the proposed TCP-CR achieves up to 255% improvement of the end-to-end throughput. Furthermore, we verified that the proposed TCP does not deteriorate the fairness of existing TCP flows and does not cause congestions.

Estimation of Fading Statistics of Nakagami Channel with Weibull Distributed Tolerable Outage Time

Characterization of a mobile radio channel plays an important role in designing a reliable wireless communication system. Such channels are analyzed by two state model, namely satisfactory and outage state. This paper presents the analysis to estimate fading parameters of wireless channel with omission of certain outage durations which are considered as “Tolerance time”. Minimum outage duration which can be tolerated by a wireless fading channel to achieve desired packet error rate is defined as tolerance time. Normally a system with tolerable minimum outage time is analyzed based on Fade Duration Distribution (FDD) function over Rayleigh channel. In this paper Weibull function is used as FDD for varying tolerance time. The approach is simple and in general applicable from Rayleigh to Nakagami channels. The analysis is extended to study the effect of Tolerance time on channel fading statistics such as Average Fade Duration (AFD) and frequency of outage. Further the effects of various fade margin and Doppler spread on fading parameters are also investigated. The analysis can also be used in case of timeout expiration, connection resetting and congestion window control.

Two schemes to reduce latency in short lived TCP flows

Motivated by the amount of short-lived TCP traffic due to interactive applications like Web browsing, we propose two schemes to reduce the download time of TCP flows. Both schemes explicitly try to overcome the long delay suffered when TCP has to recover from the loss of the last data segment in a flow, loss for which fast retransmit cannot be triggered. The first scheme consists in transmitting twice the last segment, while the second one exploits the reception of the duplicate ACK caused by the delivery of the FIN segment. Both schemes allow the transmitter to recover the loss without waiting for a retransmission timeout expiration, thus providing quicker recovery with up to 50% gain.

Localized Sensor Area Coverage with Low Communication Overhead

We propose several localized sensor area coverage protocols for heterogeneous sensors, each with arbitrary sensing and transmission radii. Sensors are assumed to be time synchronized, and active sensors are determined at the beginning of each round. The approach has a very small communication overhead since prior knowledge about neighbor existence is not required. Each node selects a random timeout and listens to messages sent by other nodes before the timeout expires. Sensor nodes whose sensing area is not fully covered (or fully covered but with a disconnected set of active sensors) when the deadline expires decide to remain active for the considered round, and transmit an activity message announcing it. There are four variants in our approach, depending on whether or not withdrawal and retreat messages are transmitted. Covered nodes decide to sleep, with or without transmitting withdrawal message to inform neighbors about the status. After hearing from more neighbors, active sensors may observe that they became covered, and may decide to alter their original decision and transmit a retreat message. Our simulation shows reduced message overhead while preserving coverage quality compared to existing method based on hello messages followed by retreat ones.

An Extended Service Filtering Technique for Mass Calling-Type Services Using Intelligent Peripheral in an SCP-Bound Network

This paper proposes an extended service filtering technique to prevent overload in service control point (SCP) due to televoting (VOT) or mass calling (MAS) services with the heavy traffic characteristics. Also, this paper compares this extended technique with the existing overload control techniques, and calculates steady state call blocking probabilities in intelligent network (IN) under overload conditions. The proposed technique considers SCP overload and IN Capability Set (CS)-1 services (such as VOT or MAS service) that have to use the specialized resources of intelligent peripheral (IP). This technique uses first an activating step in which SCP requests service filtering to service switching point (SSP). Then, in the filtering step, SSP sends filtering results to SCP periodically or each N-calls. Also, when filtering time-out expires, SSP stops service filtering, and sends service filtering response to SCP in the deactivating step. This paper applies this technique to VOT/MAS service, and calculates SCP and SSP-IP (circuit) call blocking probabilities by using an analytical VOT/MAS service model. With the modeling and analyzing of this new technique, it shows that this technique reduces the traffic flow into SCP from SSP and IP prominently.