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Network on-Chips (NoC) have emerged as an attractive communication architecture to address the increasing demand for communication in performance-sensitive applications. Employing differentiated services is a widely used approach to support QoS (Quality of Service) by relatively prioritizing traffic in the networks employing connection-less communication mechanisms. In this paper we present an analytical evaluation of the average message latency for wormhole-routed interconnect architectures exploiting a traffic prioritization mechanism to achieve differentiated services-based QoS. To verify the validity of the model we apply the method to the Spidergon NoC and compare the model against the results obtained from a discrete-event simulator developed using OMNET++.

Broadcasting in Mobile Ad Hoc Networks is a fundamental process for nodes to maintain network connectivity and stability, providing support to management procedures in order to exchange control information and aiding routing protocols to keep up to date records of routes to all possible destinations. The most commonly used broadcast scheme in MANETs is Simple Flooding (SF) due to its simplicity. SF is found to be neither resource efficient nor reliable, especially in dense and highly populated networks. Various adaptive schemes have been proposed to alleviate the effects caused by SF that take into account network conditions and other limitations. Adaptivity is most commonly implemented with the support of hello protocols. It is critical to decide upon the best frequency value to be used by the hello protocol in order to avoid introducing unnecessary control overhead. In this paper, we demonstrate the need for a hello protocol with frequency adaptivity compared to either fixed or plain dynamic frequency implementations as part of an adaptive probabilistic broadcast scheme. Furthermore, we introduce the use of Fuzzy Logic to control the frequency of a hello protocol and thus to achieve optimum results for a novel broadcast algorithm that bases its rebroadcast decision on a probability model. Our simulation results clearly demonstrate the superiority of our proposed scheme when Fuzzy Logic is incorporated by the hello protocol used to implement adaptivity against fixed and dynamic frequency alteration approaches.

Mobile and static nodes in battlefields or within the vicinity of disaster areas may not depend on fixed infrastructure for communication. To rapidly provide the required communication between the nodes in such environments, a Mobile Ad hoc Network (MANET) is the only available platform. With no fixed infrastructure, the efficient use of MANETs resources is highly crucial for the successful communication between mobile nodes. In situations where both the transmitting and the receiving nodes are placed within the transmission range of each other, communication is possible through a single-hop connection. In all other scenarios where the nodes are distanced, the exchange of packets is possible as long as a multi-hop path is available between them. Despite the unique characteristics of MANETs, they share many attributes and operations with other traditional networks. DNS lookups, exchange of control packets for management purposes and routing discovery requests are some examples of common operations, which all require broadcasting pieces of information across the network. However, due to lack of a centralised administrative and hardware, some modification is required to adopt broadcast operation for MANET environment. The most straightforward broadcast mechanism used in MANETs is Simple Flooding (SF). The algorithmic procedure followed in SF is very simple, thus making its implementation and integration inside more complex operations fairly undiscomforting. In SF, upon reception of a broadcast packet the receiver will check whether or not this is a duplicate packet. If it is a new packet it will immediately retransmit it to all of its neighbouring nodes. Simply flooding the entire network may be the fastest and easiest way for a node to broadcast information over the network but it has been found to be a very unreliable and resource inefficient mechanism leading to the Broadcast Storm Problem (Ni et al., 1999) especially in highly populated and dense networks. Over the past few years many studies (Leng et al., 2004), (Zhu et al., 2004), (Qayyum et al., 2002), (Hsu et al., 2005), (Purtoosi et al., 2006), (Barrit et al., 2006), (Bauer et al., 2005) have proposed novel broadcast mechanisms to alleviate the effects of SF. Early works were focused on developing schemes where the rebroadcast decision is made based on fixed and pre-determined threshold values. Probability-Based (PB), Counter-Based (CB) and DistanceBased (DB) are three schemes which have been proposed based on the concept of introducing a threshold value. PB bases it rebroadcasting decision on a fixed probability value, CB decides it by counting the number of received duplicate packets and finally the

Broadcasting is a vital communication mechanism in Mobile Ad Hoc Networks, as it is the key element for exchanging control packets to support some services such as management and routing protocols. Simple Flooding, which is mostly used as the broadcasting mechanism, is neither resource efficient nor reliable especially in high populated and dense networks. The Distance-Based(DB) scheme is one of the schemes proposed to alleviate the Flooding effects. However, DB uses constant pre-determined distance threshold value regardless of network dynamics. In this paper, we propose an adaptive Distance-Based (DibA)scheme, which locally determines the density of the network and adjusts the distance threshold of everyr ebroadcasting operation without relying on HELLO packets or GPS systems. Our simulation study shows that our proposed scheme achieves considerable performance improvement over DB while the average value of transmission packets is not a function of network size.

The broadcast process is a vital mechanism in Mobile Ad Hoc Networks (MANETs), as it is the key element for maintaining network connectivity and stability by aiding management tools to distribute control packets and routing protocols to keep their routing tables up to date. Simple Flooding (SF) is the simplest broadcast scheme to use in MANETs. It is neither resource efficient nor reliable, especially in high populated and dense networks. The Probability-Based (PB) scheme is one of the schemes proposed to alleviate the SF effects, also known as Broadcast Storm Problem. The algorithm for PB dictates the use of a fixed and pre-determined probability threshold value regardless of network dynamics. In this paper, we propose an Adaptive Probability-Based (ProbA) scheme, which locally makes a decision upon the density volume of the network and adjusts the probability threshold accordingly. ProbA does not rely on exchanging of HELLO packets or using GPS systems. Our extensive simulation study shows that our proposed broadcast scheme considerably outperforms the PB scheme while achieving minimal volumes of energy consumption.

TCP, the facto standard used in today's Internet, has been found to perform poorly in Mobile Ad Hoc Networks (MANETs). This is exacerbated by contention with increasing UDP-based high priority multimedia traffic and the class differentiation introduced in current QoS protocols, which results into TCP starvation and increased spurious timeouts. In this paper, we propose a cross-layer TCP enhancement (E-TCP) that makes use of TCP bidirectionality to avoid TCP traffic starvation and spurious retransmissions in presence of high priority traffic. E-TCP is based on prioritizing TCP acknowledgement packets and on adjusting TCP retransmission timer based on the medium contention. Our simulation results reveal considerable improvements in TCP performance in terms of gooput, delay and retransmission efficiency, while the better channel utilization results into even better high priority traffic performance.

In Mobile Ad-hoc Networks (MANETs), the majority of protocols developed to date provide QoS mechanisms by assigning high priority to delay-sensitive applications. While today's Internet traffic is still dominated by TCP based applications, the negative effects of the IEEE 802.11e service differentiation scheme on TCP performance in the presence of high priority traffic have not been widely reported in the literature. This paper presents the results of simulation based experiments designed to investigate these issues and how they can be addressed. In this paper we first evaluate the performance of TCP in 802.11e MANETs when competing with high priority VoIP traffic. We then propose a novel TCP-friendly scheme, called IEDCA, to improve IEEE 802.11e EDCA mechanism by assigning the highest priority to TCP acknowledgement packets. Our results show that the proposed scheme improves TCP performance significantly while having very negligible effects on voice traffic.

With the increase of multimedia traffic over the past few years and traffic differentiation introduced by IEEE 802.11e, nodes with delay-sensitive multimedia traffic tend to be busy for long periods, thus exacerbating the congestion problem in mobile ad hoc networks (MANETs). Although most of the existing routing protocols are based on the shortest path algorithm, some other metrics like load and delay have also been considered in some other research. In this paper, we first expose that the performance of MANETs routing protocols is highly dependent on the type of traffic generated or routed by intermediate nodes. This paper proposes a Type of service aware routing protocol (TSA), an enhancement to AODV, which uses both the ToS and traditional hop count as route selection metrics. TSA avoids congestion by distributing the load over a potentially greater area and therefore improving spatial reuse. Our simulation study reveals that TSA considerably improves the throughput and packet delay of both low and high priority traffic under different network operational conditions.

TCP, the transport protocol used to carry the major portion of the internet traffic, performs poorly in Mobile Ad Hoc Networks (MANETs) as broadly reported in the literature. This is mainly due to the interactions between TCP and lower layers protocols. Among these, routing protocols have perhaps the greatest impact on the performance of TCP. In this paper, by extensive simulation, we evaluate how TCP interacts with some of the IETF standardised reactive (AODV, DSR) and proactive (OLSR) routing protocols under varying network conditions such as load, size and mobility. In contrast to most of previously reported studies, which have relied solely on TCP traffic, we consider a more realistic traffic carrying a mixture of Constant Bit Rate (CBR) and TCP. We also show how appropriate tuning of route expiry parameters in reactive protocols can improves TCP performance considerably while still generating less routing overhead.