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On the Interaction Between Multiple Paths and Wireless Mesh Networks Scheduler Approaches

Multi-path routing allows building and use of multiple paths for routing between a source-destination pair. This paper investigates the problem of selecting multiple routing paths to provide better reliability and load balancing in wireless mesh networks with stationary nodes. Previous work has investigated the use of additional data redundancy to improve the throughput of the network. In these specific cases, node disjoint-ness property of the multiple paths is required. In this work we investigate multipath routing without packet duplication, and no disjointed paths for achieving better performance in terms of packet delivery rate and low delay. We propose a very simple reactive on-demand distance vector routing protocol. Multiple paths built through this approach are loop-free. In order to better exploit resources redundancy (with the term resources redundancy we mean the possibility to exploit more nodes to send data packets), it is our belief that a routing protocol cannot be independent of the MAC layer. For this reason, we evaluated our routing protocol on four different MAC approaches specifically designed for Wireless Mesh Networks (WMNs). Firstly, we implemented the Coordinated Distributed Scheduler scheme of the Std. IEEE 802.16. Secondly, since some parameters have been left unstandardized in this scheme, we proposed an enhanced version of the CDS, in which a simple and dynamic criterion has been designed to set one of these parameters. Furthermore, we proposed two different scheduling schemes called Randomized- MAC (R-MAC) and Distributed Scheduling Scheme (DSS). We evaluated the impact of multiple paths in respect of the single path on all the scheduler schemes cited above. Results show as the simple routing approach is effective with every MAC protocol considered.

Reliable multicast for the Grid: a case study in experimental computer science

In its simplest form, multicast communication is the process of sending data packets from a source to multiple destinations in the same logical multicast group. IP multicast allows the efficient transport of data through wide-area networks, and its potentially great value for the Grid has been highlighted recently by a number of research groups. In this paper, we focus on the use of IP multicast in Grid applications, which require high-throughput reliable multicast. These include Grid-enabled computational steering and collaborative visualization applications, and wide-area distributed computing. We describe the results of our extensive evaluation studies of state-of-the-art reliable-multicast protocols, which were performed on the UK's high-speed academic networks. Based on these studies, we examine the ability of current reliable multicast technology to meet the Grid's requirements and discuss future directions.

Statistical theory of Internet exploration

The general methodology used to construct Internet maps consists in merging all the discovered paths obtained by sending data packets from a set of active computers to a set of destination hosts, obtaining a graphlike representation of the network. This technique, sometimes referred to as Internet tomography, spurs the issue concerning the statistical reliability of such empirical maps. We tackle this problem by modeling the network sampling process on synthetic graphs and by using a mean-field approximation to obtain expressions for the probability of edge and vertex detection in the sampled graph. This allows a general understanding of the origin of possible sampling biases. In particular, we find a direct dependence of the map statistical accuracy upon the topological properties (in particular, the betweenness centrality property) of the underlying network. In this framework, it appears that statistically heterogeneous network topologies are captured better than the homogeneous ones during the mapping process. Finally, the analytical discussion is complemented with a thorough numerical investigation of simulated mapping strategies in network models with varying topological properties.

A Reservation-Based Multicast Protocol for WDM Optical Star Networks

In this paper, we present a reservation-based medium access control (MAC) protocol with multicast support for wavelength-division multiplexing networks. Our system is based on the single-hop, passive optical star architecture. Of the available wavelengths (channels), one channel is designated as a control channel, and the remaining channels are used for data transmission. Each node is equipped with a pair of fixed transceiver to access the control channel, and a fixed transmitter and a tunable receiver to access data channels. For easy implementation of the protocol in hardware and for precisely computing the protocol's processing overhead, we give a register-transfer model of the protocol. We simulate the protocol to study its throughput behavior, and present its analytic model. For a node to be able to send data packets in successive data slots with no time gap between them, in spite of the situation that the protocol's execution time may be longer than data transmission time, we propose the idea of multiple MAC units at each node. Unicast throughput of our protocol reaches the theoretically possible maximum throughput for MAC protocols with distributed control, and the multicast throughput is at least as good as, and even better than, those delivered by existing MAC protocols with distributed control.

NetLets: measurement-based routing daemons for low end-to-end delays over networks

Routing in the Internet is based on the best-effort mechanism, wherein the routers generally forward packets to minimize the number of hops to the destination. Furthermore, all packets of a type are treated the same independent of their size. We propose the framework of NetLets to enable the applications to send data packets to the destination with certain guarantees on the end-to-end delay. NetLets employ in situ instruments to measure the effective bandwidth and propagation delays on the links, and compute the paths with minimum measured end-to-end delay for data packets of various sizes. Based on experiments over local area networks, the paths selected by NetLets indeed achieve the minimum end-to-end delay, and our method outperformed the best-effort mechanism based on the hop count. We also describe an implementation of NetLets over the Internet to illustrate their viability for wide-area networks.

Floor acquisition multiple access (FAMA) in single-channel wireless networks

The FAMA-NCS protocol is introduced for wireless LANs and ad-hoc networks that are based on a single channel and asynchronous transmissions (i.e., no time slotting). FAMA-NCS (for floor acquisition multiple access with non-persistent carrier sensing) guarantees that a single sender is able to send data packets free of collisions to a given receiver at any given time. FAMA-NCS is based on a three-way handshake between sender and receiver in which the sender uses non-persistent carrier sensing to transmit a request-to-send (RTS) and the receiver sends a clear-to-send (CTS) that lasts much longer than the RTS to serve as a “busy tone” that forces all hidden nodes to back off long enough to allow a collision-free data packet to arrive at the receiver. It is shown that carrier sensing is needed to support collision-free transmissions in the presence of hidden terminals when nodes transmit RTSs asynchronously. The throughput of FAMA-NCS is analyzed for single-channel networks with and without hidden terminals; the analysis shows that FAMA-NCS performs better than ALOHA, CSMA, and all prior proposals based on collision avoidance dialogues (e.g., MACA, MACAW, and IEEE 802.11 DFWMAC) in the presence of hidden terminals. Simulation experiments are used to confirm the analytical results.

A transmit power control scheme for improving performance in a mobile packet radio system

The problem of a number of mobile users attempting to send data packets over a commonly shared slotted channel to a central base station is studied. A scheme for controlling the transmit power of the mobiles is proposed and shown to yield better throughputs than a conventional transmit power scheme (in which all mobiles transmit with constant power) for both nonfading and fading channels. In any given time slot, mobiles that are closer to the base station are allowed to transmit at a higher power level in an attempt to improve capture probability. >

Congestion Control in High Speed Networks via Alternate Path Routing

This paper presents a congestion control scheme based on alternate path routing. In the scheme, if a node encounters congestion or loses its preferred neighbor on its primary path to a destination, it sends data packets to that destination over precomputed alternate paths. The scheme ensures that data packets do not travel in loops and limits the spread of congestion to neighboring nodes. Simulations of the scheme show that alternate path routing reduces the number of dropped packets, achieves a more uniform link utilization and alleviates congestion in networks under light to moderate loading. When using alternate path routing, it is observed that the loss ratio closely follows the load ratio which is not true when using shortest path routing.