KEYWORDS: Sensors, Sensor networks, Network architectures, Bismuth, Chromium, Wireless communications, Data communications, Fusion energy, Personal digital assistants, Data fusion
Rapid technological advances in wireless communication have made it
possible for networking sensor devices. Given the low computation and battery power capacities of these sensor nodes, the key design factors of network protocols are self-configuring, energy-efficient, adaptive, and scalable. We presented the multi-hop infrastructure network architecture (MINA) for a wireless sensor network consisting of a few hundred sensors that communicate data to a base station (BS). We designed a Unified Network Protocol Framework for MINA that encompasses network organization, medium access control (MAC) and routing protocols. In this paper, we improve it by adaptively varying transmission range to maintain network connectivity. It is a derivative-free optimization algorithm. The BS periodically evaluates the objective function, chooses the appropriate transmission range and broadcasts it to the sensor nodes that then update the transmission range. The advantages are: (i) Avoids the disconnectivity; (ii) Maximizes the number of nodes that can be connected to the BS, (iii) Minimizes the energyxdelay metric and (iv) Avoids the "hot-spot" nodes in the network. The performance in terms of delay, throughput, energy consumption and network lifetimes, is studied in detail using discrete-event simulation compared with other protocol. The results show that it is energy efficient in a large scale network.
In this paper, we investigate the problem of enhancing dual-failure restorability in path-protected mesh-restorable optical wavelength division multiplexed (WDM) networks. A key finding of recent studies that have demonstrated the need to survive simultaneous dual-link failures is that designs providing complete (i.e. 100%) protection from all dual-failures may need almost thrice the spare capacity compared to a system that protects against all single-link failures. However, it has also been shown that systems designed for 100% single-link failure protection can provide reasonable protection from dual-link failures. Thus, the motivation of this work is to develop a hybrid mechanism that provides maximum (close to 100%) dual-failure restorability with minimum additional spare capacity. The system architecture considered is a circuit-switched WDM network with dynamic arrival of sessions requests. We also consider sparse wavelength conversion, where only some nodes have converters. We propose an adaptive mechanism, which we term active protection, that builds upon a pro-active path protection to provide complete single-failure restorability and adds dynamic segment-based restoration. The objective is to optimize network survivability (and minimize spare capacity needs) with ragard to dual-link failures while maintaining complete single-failure restorability. The basic premise of the algorithm is to identify scenarios in the dual-link failure model that necessitate additional spare capacity and provide protection for those scenarios only. Our findings indicate that the proposed scheme achieves close to complete (100%) dual-failure restorability with only maximum of 3% wavelength-links needing two backups even at high loads. Moreover, at moderate to high loads, our scheme attains close to 16% improvement over the base model that provides complete single-failure restorability.
The upcoming Ultra-wide-band (UWB) radio technology holds great promise for revolutionizing wireless communications. UWB radios transmit using precise, very short (e.g. picosecond) impulses spread over a very large bandwidth (up to a few Ghz). The significant advantages of this technology are low-power operation, mitigated multi-path fading effects, high bit-rates and unique precise position/timing location ability. However, one of the drawbacks of this technology, in its current state, is the high channel acquisition time, i.e. the time for a transmitter and receiver to achieve bit synchronization. This tends to be quite high, of the order of a few milli-seconds. Hence, it is important for current medium access control (MAC) protocol design to consider the impact of acquisition time. In this paper, we study the performance of two standard MAC protocols - the distributed CSMA/CA protocol and the centralized TDM protocol in the context of UWB wireless local area networks. We study effects of varying packet frame sizes and packet arrival rates and present a quantification of the impact of acquisition time on overall performance.
In this paper, we study restoration mechanisms to handle channel and
link failures in an optical WDM wavelength-routed wide-area backbone
network based on a mesh topology. The solution uses a small number of
tunable lasers per link to provide restoration capability. In
addition to link failures, we consider individual channel failures link-level mechanisms are presented: redirection algorithm (RDA) and
disjoint path algorithm (DPA). These mechanisms use WDM-specific link
information to compute the link restoration routes. We present
results based on discrete-event simulations to understand the
performance of the proposed mechanisms, in terms of restoration
efficiency and restoration times. The results show that for networks
of varying size and node degree with 32 wavelengths on each link,
using as few as 8 tunable lasers per link provides good
restoration efficiency under moderate traffic load.
which might occur when one or more transceivers fail at the source of the
lightpath or due to a failure in the switch fabric.
Restoration is first attempted using the tunable lasers to
transmit on the failed wavelengths. If all the failed lightpaths
cannot be restored using the tunable lasers, unused wavelengths on the
same link are used (this requires optical wavelength conversion at the
nodes). For the remaining lightpaths requiring restoration,
link-level restoration mechanisms are attempted. Two different
In this paper, we study the problem of employing virtual private network (VPN) over wavelength division multiplexing networks to facilitate the guarantee of diverse quality of service requirements of different VPNs. A wavelength routed backbone network is considered. A VPN is specified by the desired logical topology and an a priori traffic matrix.
KEYWORDS: Receivers, Transmitters, Wavelength division multiplexing, Stars, Local area networks, Control systems, Process control, Data transmission, Channel projecting optics, Optical components
Extensive research and considerable progress in the dense optical wavelength division multiplexing (WDM) technology has made it the most likely candidate for implementation in next-generation high performance switches, LANs and MANs. The first key challenge is the continuous development of cost-effective optical components in order to realize practical networks. The next main challenge is to design an effective channel access protocol that will: (a) take full advantage of the existing and emerging optical technologies, (b) fairly and successfully coordinate transmissions between the networks nodes, and (c) efficiently manage the enormous fiber bandwidth. There have been many access protocols proposed for WDM networks including quite a few proposals that require many more channels than the number of nodes. The practical device characteristics impose an upper limit on the number of available WDM channels. Our focus in this paper is on systems with many nodes and small number of channels. We study the use of in-band signaling mechanism compared to the separate control channel (out-band signaling) approach. Signaling is used to achieve coordination between source and destination with respect the communication channel. The objective of this paper is to understand the key trade-offs in the protocol design for such networks through close examinations of the two approaches. Our intent is not to claim the superiority of either approach, rather to stimulate further studies on such systems.
Wavelength Division Multiplexing (WDM) enables partitioning the enormous bandwidth of photonic networks into multiple smaller, more manageable, multiple access channels. These channels operate at a data rate which matches the electronic interface speed, viz. Gbps. Media access protocols for an optically interconnected star-coupled WDM network with no control channel are introduced and compared. The channels are preallocated to nodes where each node has a home channel that it uses for all data reception. If the number of nodes exceeds the number of channels, home channels are shared among nodes. This approach does not require both tunable transmitters and tunable receivers reducing system complexity and is not limited by the number of channels available. A generalized random access protocol and an interleaved time division multiplexed protocol are compared. Both protocols require a fast tunable transmitter and a slow (or fixed) tunable receiver per node. Each node has a set of queues of variable capacity -- one per data channel. The switching time of tunable transmitters has a significant impact on system performance and techniques are developed to reduce the impact. Detailed discrete-event simulation results are used to evaluate system performance in terms of network throughput and average packet delay with variation in the number of nodes and channels and transmitter switching latency.
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