Formulation, implementation considerations, and first performance evaluation of algorithmic solutions - D4.1

Deliverable D4.1 del projecte Europeu OneFIT (ICT-2009-257385)This deliverable contains a first version of the algorithmic solutions for enabling opportunistic networks. The presented algorithms cover the full range of identified management tasks: suitability, creation, QoS control, reconfiguration and forced terminations. Preliminary evaluations complement the proposed algorithms. Implementation considerations towards the practicality of the considered algorithms are also included.Preprin

Performance Improvement Of Mac Layer In Terms Of Reverse Direction Transmission Based On IEEE 802.11n

Medium access control (MAC) layer is one of the most prominent topics in the area of wireless networks. MAC protocols play a big role in improving the performance of wireless networks, and there are many challenges that have been addressed by the researchers to improve the performance of MAC layer in the family of IEEE 802.11. The physical data rate in IEEE 802.11n may reach 600 Mbps, this high data rate does not necessary transform into good performance efficiency, since the overhead at the MAC layer signifies that by augmenting PHY rates the effectiveness is automatically reduced. Therefore, the main objective of next generation wireless local area networks (WLANs) IEEE 802.11n is to achieve high throughput and able to support some applications such as TCP 100 Mbps and HDTV 20 Mbps and less delay. To mitigate the overhead and increase the MAC efficiency for IEEE 802.11n, one of the key enhancements at MAC layer in IEEE 802.11n is a reverse direction transmission. Reverse direction transmission mainly aims to accurately exchange the data between two devices, and does not support error recovery and correction; it drops the entire erroneous frame even though only a single bit error exists in the frame and then causes a retransmission overhead. Thus, two new schemes called (RD-SFF) Reverse Direction Single Frame Fragmentation and (RD-MFF) Reverse Direction Multi Frame Fragmentation are proposed in this study. The RD-SFF role is to aggregate the packets only into large frame, while RD-MFF aggregate both packets and frames into larger frame, then divided each data frame in both directions into subframes, Then it sends each subframe over reverse direction transmission. During the transmission, only the corrupted subframes need to be retransmited if an error occured, instead of the whole frame. Fragmentation method is also examined whereby the packets which are longer when compared to a threshold are split into fragments prior to being combined. The system is examined by simulation using NS-2. The simulation results show that the RD-SFF scheme significantly improves the performance over reverse direction transmission with single data frame up to 100%. In addition, the RD-MFF scheme improvers the performance over reverse direction transmission with multi data frames up to 44% based on network condition. These results show the benefits of fragmentation method in retransmission overhead and erroneous transmission. The results obtained by ON/OFF scheme takes into account the channel condition to show the benefits of our adaptive scheme in both ideal as well as erroneous networks. In conclusion, this research has achieved its stated objective of mitigation the overhead and increase the MAC efficiency for IEEE 802.11n. Additionally, the proposed schemes show a significant improvement over the reverse direction in changing network conditions to the current network state

QoS-aware flow monitoring and event creation in heterogeneous MPLS-based Wireless Mesh Networks supporting unidirectional links

Proceedings of: IEEE 9th Malaysia International Conference on Communications (MICC 2009), 15-17 December 2009, Kuala Lumpur, MalaysiaMonitoring is a crucial task in QoS-aware networks since it provides statistics to verify that the network performs within the committed QoS parameters. It is especially important in a resource-constrained Carriergrade Wireless Mesh Access Network (CG-WMAN) in order to monitor a node’s neighborhood, established links as well as MPLS QoS-traffic flows, so-called Label-Switched Paths (LSPs). In this paper, we present a monitoring architecture for LSPs in a heterogeneous CG-WMAN, where configurable Rating Agents perform adaptive per-LSP event creation based on monitoring statistics, QoS-requirements and overall network state. Keeping the footprint of the monitoring mechanism at a minimum, our approach is based on quasipassive monitoring minimizing the transmission of extra frames. To support unidirectional links as well as 1-to-N multicast trees, a receiving side feedback-free mechanism is proposed which can be extended with transmitting side functionality. Initial results obtained in our testbed show that we can reliably detect under-performing links according to the QoS requirements of the payload.European Community's Seventh Framework ProgramPublicad

Improving Performance for CSMA/CA Based Wireless Networks

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based wireless networks are becoming increasingly ubiquitous. With the aim of supporting rich multimedia applications such as high-definition television (HDTV, 20Mbps) and DVD (9.8Mbps), one of the technology trends is towards increasingly higher bandwidth. Some recent IEEE 802.11n proposals seek to provide PHY rates of up to 600 Mbps. In addition to increasing bandwidth, there is also strong interest in extending the coverage of CSMA/CA based wireless networks. One solution is to relay traffic via multiple intermediate stations if the sender and the receiver are far apart. The so called “mesh” networks based on this relay-based approach, if properly designed, may feature both “high speed” and “large coverage” at the same time. This thesis focusses on MAC layer performance enhancements in CSMA/CA based networks in this context. Firstly, we observe that higher PHY rates do not necessarily translate into corresponding increases in MAC layer throughput due to the overhead of the CSMA/CA based MAC/PHY layers. To mitigate the overhead, we propose a novel MAC scheme whereby transported information is partially acknowledged and retransmitted. Theoretical analysis and extensive simulations show that the proposed MAC approach can achieve high efficiency (low MAC overhead) for a wide range of channel variations and realistic traffic types. Secondly, we investigate the close interaction between the MAC layer and the buffer above it to improve performance for real world traffic such as TCP. Surprisingly, the issue of buffer sizing in 802.11 wireless networks has received little attention in the literature yet it poses fundamentally new challenges compared to buffer sizing in wired networks. We propose a new adaptive buffer sizing approach for 802.11e WLANs that maintains a high level of link utilisation, while minimising queueing delay. Thirdly, we highlight that gross unfairness can exist between competing flows in multihop mesh networks even if we assume that orthogonal channels are used in neighbouring hops. That is, even without inter-channel interference and hidden terminals, multi-hop mesh networks which aim to offer a both “high speed” and “large coverage” are not achieved. We propose the use of 802.11e’s TXOP mechanism to restore/enfore fairness. The proposed approach is implementable using off-the-shelf devices and fully decentralised (requires no message passing)