Consolee Mbarushimana

Comparative Study of Reactive and Proactive Routing Protocols Performance in Mobile Ad Hoc Networks

The mobility of nodes in mobile ad hoc networks (MANETs) results in frequent changes of network topology making routing in MANETs a challenging task. Some studies have been reported in the literature to evaluate the performance of the proposed routing algorithms. However, since the publication of experimental standards for some routing protocols by IETF, little activity has been done to contrast the performance of reactive against proactive protocols. This paper evaluates the performance of reactive (AODV, DSR) and proactive (OLSR) routing protocols in MANETs under CBR traffic with different network conditions. Our results, contrarily to previously reported studies conducted on the same routing protocols, show the superiority of proactive over reactive protocols in routing such traffic at the cost of a higher routing load.

Congestion Avoidance Routing Protocol for QoS-Aware MANETs

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.

TSLA: A QoS-Aware On-Demand Routing Protocol for Mobile Ad Hoc Networks

The complexity of Mobile Ad Hoc Networks (MANETs) has led to the extensive research in the development of their routing protocols as reported in literature. Although most of the proposed routing protocols are based on the shortest path algorithm, some other metrics like load and network congestion have also been considered in some other research. However, with the introduction of traffic differentiation in IEEE 802.11e, congestion effect becomes more distinct as the nodes with delay-sensitive multimedia applications tend to be busy for prolonged periods. This has received little attention in the literature to date. 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. We then propose Type of Service and Load Aware routing protocol (TSLA), an enhancement to AODV that uses both the traffic load and the type of service as additional metrics. To our knowledge, TSLA is the first to avoid congestion by distributing the load over a potentially greater area and conducting the traffic through less busy nodes and, therefore, less congested routes. Our simulation study reveals a persistent improvement in throughput and packet delay of both low and high priority traffic.

A cross-layer TCP enhancement in QoS-aware mobile ad hoc networks

With the increase of multimedia traffic over the Internet, current network protocols are largely concerned with the QoS requirements of delay-sensitive applications. 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 todays 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 adequately addressed in the literature. 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. Our simulation-based performance study demonstrates that our proposed scheme IEDCA not only improves the performance of TCP significantly, it also facilitates the voice traffic transmission.

A cross-layer support for TCP enhancement in QoS-aware mobile ad hoc networks

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 todays 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.

E-TCP: Enhanced TCP for IEEE802.11e Mobile Ad Hoc Networks

TCP, the facto standard used in todays 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.

TCP Enhancement in IEEE 802.11e Wireless Networks

Wireless networks and multimedia applications are two rapidly emerging technological trends. The IEEE 802.11e protocol has been developed to support QoS for such delay-sensitive applications in wireless networks. This protocol has also been extensively studied in the literature over the past few years, and several mechanisms to improve its performance have been proposed concentrating on ways to reinforce QoS guarantees for delay-sensitive applications. While the Internet traffic is still dominated by TCP-based applications, the negative effects of IEEE 802.11e service differentiation scheme on the performance of TCP have not received enough attention. In this paper, we first, as an attempt to highlight these effects, evaluate the performance of TCP in 802.11e WLANs when competing with high priority VoIP traffic. We then evaluate the enhancement achievable by our proposed cross-layer schemes, IEDCA and RE-TCP, which exploit the TCP bidirectional nature to alleviate TCP starvation and consequently improving its performance. Our simulation results show significant improvements in terms of TCP goodput, retransmissions and segment delay (without any negative effect on the performance of delay-sensitive applications).

Resource Efficient TCP: Reducing Contention-Induced Spurious Timeouts in QoS -Aware MANETs

The bandwidth is one of the most precious resources in mobile ad hoc networks (MANETs); their network protocols should therefore be able to achieve an increase in efficiency of bandwidth utilization. TCP, which implements flow control to regulate the network traffic, plays a significant role in determining the workload of the network. However, spurious TCP retransmissions can increase the link utilization and consequently limiting the amount of spare bandwidth available as extensively reported in the literature. This problem is exacerbated by the presence of high priority traffic and traffic differentiation introduced in IEEE 802.11e. In this paper, we focus on the optimization of TCP for resource efficiency, by limiting the number of contention-induced retransmissions. Using feedback from the MAC layer, the TCP layer can be notified of the medium contention state and adjusts its retransmission timer accordingly. Our simulation results demonstrate the effectiveness of our proposal in various scenarios. Our proposal achieves a gain of 15% in resource utilization and reduces power consumption by retransmitting fewer segments; it also improves TCP performance in terms of goodput and end-to-end delay.

The effect of routing protocol dynamics on TCP performance in mobile ad hoc networks

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.

Alleviating contention-induced spurious timeouts in QoS-aware MANETs

The bandwidth is one of the most precious resources in Mobile Ad Hoc Networks (MANETs); their network protocols should therefore be able to achieve an increase in efficiency of bandwidth utilisation. TCP, which implements flow control to regulate the network traffic, plays a significant role in shaping the workload of the network. However, spurious TCP retransmissions can increase the link utilisation, consequently limiting the amount of spare bandwidth available as extensively reported in the literature. This problem is exacerbated by the presence of high priority traffic and traffic differentiation introduced in IEEE 802.11e. In this paper, we focus on the optimisation of TCP for resource efficiency, by limiting the number of contention-induced retransmissions. Using a cross-layer technique, TCP can be notified of the medium contention state and adjusts its retransmission timer accordingly. Our simulation results demonstrate the effectiveness of our proposal in various scenarios. A 15% gain in resource utilisation is obtained, fewer packets are retransmitted thus reducing the overall power consumption and TCP goodput is improved.