Research Of Wavelength Assignment On WDM Optical Networks

Computer networks are primarily designed to transmit huge amount of information,or data, among worldwide communicating nodes, in which, electricity serves as themost common underlying physical media. As technology conforms to persistentevolution of civilization, especially the advent of Big-Data Era, those electricity-basednetworks prove incapable of meeting soaring standards of reliable communication.Electricity’s intrinsic characters, such as clock skew, high power consumption, magneticfields interference, cause the bottleneck in network performance and scalability, not tomention the ever-growing global telecommunication business.A popular troubleshooting idea is to replace electricity with light, that is, to buildoptical networks. Photons are superior to electrons in message transmitting for lowdelay, no interference, less power consumption and huge bandwidth. All opticalnetworks (no electrical components contained) are ideal models that bet to be excellent,while no all optical network is running so far as the result of photons’ ineffective storage.Thus, this paper addressed only opto-electronic networks that store data with electronsand transmit data with photons. WDM (Wavelength Division Multiplexing) technology,which concocts messages into optical waves with distinct wavelengths, is adopted inmost opto-electronic networks to improve throughput for the feature of paralleltransmission in a single fiber as no interference is triggered.Communication steps in WDM optical networks are periodically sequenced as:firstly, route selection, that is to determine an appropriate path, also called lightpath, foreach source-destination node pair under certain routing strategy; then wavelengthassignment, that is to properly affiliate each lightpath with an optical wave that meetstwo constraints, wavelength continuity constraint (the wavelength used in a lightpathshould be continuously the same) and distinct wavelength constraint(lightpaths sharinga same fiber should be assigned different wavelengths); lastly, message transmissionand lightpath revocation.At present, available wavelengths are relatively insufficient in large-scale WDMoptical networks, which means one or a few lightpath requests might not be successfullyestablished as wavelength resources fall short in this period, and hence being delayed tonext period, thus blocking happens. So we come to find that route selection, wavelengthassignment and blocking are not separately appearing but are so entwined together that demand consideration for the whole picture. This paper mainly addresses the problem ofwavelength assignment under three following categories of WDM optical networks, aswell as taking route selection and blocking problem into account.(1) On classical topologies. Classical topologies are regular so graph theory comesinto handy for formula derivation. We analyzed the least required number ofwavelengths for a family of classical topologies containing N nodes to realize all-to-allbroadcasts with and without wavelength converters.(2) On irregular topologies. Given a set of lightpath requests and a group ofavailable wavelengths, the corresponding wavelength assignment problem boils downto a graph coloring problem which is well known as NP-hard. We introduce a popularFirst-fit algorithm for such assignments and propose two refined versions, respectivelyaimed to cost down on time consumption and blocking probabilities.(3) On WDM-PON. After playing mathematical games, we find a way to connectWDM techniques with an engineering application named WDM-PON. WDM-PONs areapparently constructed on WDM basis, however, they are built with so complex opticalapparatus that a simple tree model does not work here, we introduce two ideas fordynamic wavelength assignment specifically to fit WDM-PON’s physical features.