Debasish Datta

Impact of transmission impairments on the teletraffic performance of wavelength-routed optical networks

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks.

Transparent vs. opaque vs. translucent wavelength-routed optical networks

This study evaluates the relative merits of three approaches (transparency, opacity, and translucency) for establishing calls in a wavelength-routed optical network. Call-admission algorithms employ online bit-error-rate computation and include the effects of transmission impairments.

An Energy-Efficient Communication Scheme for Wireless Networks: A Redundant Radix-Based Approach

We propose a redundant radix based number (RBN) representation for encoding and transmitting data for applications which typically utilize low cost devices and demand low power operations with simple modulation techniques like ASK, OOK and FSK. Coupled with silent periods for communicating the digit zero, this encoded communication scheme, called as RBNSiZeComm, provides a highly energy-efficient technique for data transmission. Considering an n-bit data representation and assuming that each of the 2n binary strings is equally likely to occur, theoretically obtainable fraction of energy savings by using our proposed RBNSiZeComm transmission protocol is, on an average, 1 - n+2/4n. A hybrid modulation scheme using FSK and ASK with non-coherent detection based receiver for the RBNSiZeComm protocol has been presented. Assuming equal likelihood of all possible binary strings of a given length, there is nearly 53% savings in energy on an average at the transmitter relative to binary FSK, over additive white gaussian noise (AWGN) channels. Simulation results demonstrate that compared to binary FSK, our proposed implementation can extend the battery life of devices from about 33% to 62% on an average in applications like remote healthcare and wireless sensor networks for agriculture.

Pre-planned global rerouting for fault management in labeled optical burst-switched WDM networks

Optical burst switching (OBS) is a promising technique for supporting high-capacity bursty data traffic over optical wavelength-division-multiplexed (WDM) networks. A label-switched path can be established to forward a burst control packet (BCP) if each OBS node is augmented with an IP/MPLS controller. Such a network is called a labeled OBS (LOBS) network, and it can exploit the explicit routing and constraint-based routing properties supported in the MPLS framework to perform traffic and resource engineering. However, the burst-loss probability (denoted as BLP) can be large if the traffic is not properly engineered in a LOBS network, especially after a failure occurs. In this paper, we propose to use pre-planned global rerouting to balance network load and to restore bursts after a link fails. We apply optimization techniques to pre-plan explicit backup routes for failure scenarios. Our objective is to achieve optimal load balancing both before and after a failure such that the network state can still remain stable with minimum BLP when failure occurs. We apply the pre-planned global rerouting method in a LOBS network and study the performance of different rerouting schemes on some typical network topologies. Our illustrative numerical examples show that the BLP can be significantly reduced by 25%-99% (when the average link load is less than 0.5) using globally rerouted backup routes, when compared with the scheme without global rerouting. We also observe that the BLP is reduced by 20%-65% (when the average link load is less than 0.5) if the rerouting is done using optimization techniques, when compared with shortest-path routing.

Explicit Routing for Traffic Engineering in Labeled Optical Burst-Switched WDM Networks

Optical burst switching (OBS) is a promising technique for supporting high-capacity bursty data traffic over optical wavelength-division-multiplexed (WDM) networks. A label-switched path can be established to forward a burst control packet (BCP) if each OBS node is augmented with an IP/MPLS controller. Such a network is called a labeled OBS (LOBS) network, and it can exploit the explicit routing and constraint-based routing properties supported in the MPLS framework to perform traffic and resource engineering. In this paper, we consider the traffic-engineering problem in a LOBS network, using explicit routing to balance network load and to reduce the burst-loss probability. We model the traffic-engineering problem in a LOBS network as an optimization problem and propose two new objective functions to minimize network congestion. Our illustrative numerical examples show that the burst-loss probability can be significantly reduced using optimization technique, when compared with shortest-path routing.

SIMON: a simulator for optical networks

SIMON is an object-oriented event-driven simulation package implemented in C++ which incorporates optical device characteristics in the measurement of network-level blocking statistics. SIMON is suitable for studying the performance of large wavelength-routed optical networks, in which a call is set up in the network for a specific duration on a pre- determined lightpath. Currently the physical-layer models allow for modeling phenomena such as signal attenuation in fiber and other components, amplifier gain saturation, and homowavelength crosstalk in switches. Simulation experiments can be performed with a user-specified bit-error rate limit, which must be satisfied by any call set up in the network.

BER-based call admission in wavelength-routed optical networks

Summary form only given. The objective of the present work is to estimate the on-line BER on candidate routes and wavelengths before setting up a call. Note that the existence of other calls currently in progress, i.e., traffic variation, will affect the BER estimate (because they will affect the cross talk in cross connect switches (XCSs) and the wavelength dependence and saturation of gains and ASE noise generation in EDFAs).

Design methodology for WDM backbone networks using FWM-aware heuristic algorithm

For optical backbone networks using wavelength-division multiplexing (WDM), four-wave mixing appears as the dominant nonlinear phenomenon. In this paper a novel lightpath establishment scheme is proposed to improve physical-layer performance by restricting FWM generation.

A modified backoff algorithm for IEEE 802.11 DCF-based MAC protocol in a mobile ad hoc network

The medium access control (MAC) protocol in IEEE 802.11 wireless LAN employs distributed coordination function (DCF) with binary exponential backoff (BEB) algorithm for contention resolution. With BEB, waiting time of a node gets doubled after every unsuccessful transmission. This introduces fast-growing retransmission delays for the backlog traffic. In a mobile ad hoc network (MANET), it would be worthwhile to slow down the growth-rate of waiting time. This is expected because the nodes communicating in a MANET might move out of collision range while waiting for retransmission. In this paper, we explore a modification to BEB algorithm and evaluate its performance through extensive simulations. Simulation results indicate that the proposed modification to BEB enhances packet delivery rate and reduces average end-to-end packet delay.

TSS: An Energy Efficient Communication Scheme for Low Power Wireless Networks

Wireless sensor networks typically require low cost devices and low power operations. Hence, such networks usually employ radios with only simple modulation techniques such as ASK, OOK and FSK. We propose a new energy efficient communication scheme for wireless sensor networks that is based on the ternary number system encoding of data. An efficient algorithm for conversion from binary to ternary and vice versa is used that does not involve any division or multiplication but only addition. Our Ternary with Silent Symbol (TSS) communication scheme is similar in concepts to the RBNSiZeComm protocol proposed. However, in contrast to RBNSiZeComm, TSS simultaneously saves energy at both the transmitter and receiver due to shortening of the transmission duration. We also propose a transceiver design that uses a hybrid modulation scheme utilizing FSK and ASK so to keep the cost/complexity of the radio devices low. With a non-coherent detection based receiver and assuming equal likelihood of all possible binary strings of a given length, there is a savings of about 20% in energy on an average at the transmitter compared to binary FSK, for additive white gaussian noise (AWGN) channels. Simultaneously, there is a savings of 36.9% at the receiver too, due to the reduced length of ternary encoded transmitted data, compared to binary encoding. Coupled with the low cost and low complexity of the transceiver, these results establish the effectiveness of TSS as a suitable candidate for communication in low power wireless sensor networks.