On the synergy between electrical and photonic switching

This article focuses on the values of electrical switching vs. photonic switching in the context of telecom transport networks. In particular, we show that the requirement of providing agility at the optical layer in the face of traffic forecast uncertainties is served better through photonic switching. On the other hand, some of the network-level functions, such as fast protection, subwavelength aggregation, and flexible client connectivity, require electrical switching. We further argue that additional values are achieved with hybrid photonic and electrical switching, which do not exist when either of these options is used in isolation.     

Optical layer survivability: a post-bubble perspective

We revisit the topic of optical layer protection from a motivation and deployment perspective. We first discuss the changes that have occurred in optical networking in general and the implications for protection. We then discuss scenarios where optical protection makes sense, recognizing that other fast protection schemes at the client layer provide viable alternatives in certain cases. Our conclusion is that optical protection makes sense for metro networks, as long as they are based on simple dedicated schemes. When it gets to more complex shared ring and mesh protection, we believe that OEO-based schemes are more viable, whether crossconnect-based or packet-switch-based.     

Processing, crystallization and characterization of polymer derived nano-crystalline Si–B–C–N ceramics

Si–B–C–N ceramics were synthesized from boron modified poly(vinyl)silazanes with the chemical formula (B[C₂H₄–Si(CH₃)NH]₃) _n . The originally amorphous materials are crystallized at temperatures in the order of 1,800–1,900 °C, which results microstructures with grain sizes significantly below 100 nm. Several parameters of the heat treatment, including temperature, holding time and atmosphere, affect the resulting nanostructures. This and the chemical and phase composition were studied via X-ray diffraction (XRD), transmission electron microscopy (TEM), electron spectroscopic imaging (ESI) and spectrochemical analysis in order to gain an understanding of the mechanisms, which control the crystallization behavior. Ceramic samples were also produced using different particle sizes of the precursor polymer in order to quantify the effect of the varying specific surface on the crystallization behavior.     

The layout of virtual paths in ATM networks

We study the problem of designing a layout of virtual paths (VPs) on a given ATM network. We first define a mathematical model that captures the characteristics of virtual paths. In this model, we define the general VP layout problem, and a more restricted case; while the general case layout should cater connections between any pair of nodes in the network, the restricted case layout should only cater connections between a specific node to the other nodes. For the latter case, we present an algorithm that finds a layout by decomposing the network into subnetworks and operating on each subnetwork, recursively; we prove an upper bound on the optimality of the resulting layout and a matching lower bound for the problem, that are tight under certain realistic assumptions. Finally, we show how the solution for the restricted case is used as a building block in various solutions to more general cases (trees, meshes, K-separable networks, and general topology networks) and prove a lower bound for some of our results. The results exhibit a tradeoff between the efficiency of the call setup and both the utilization of the VP routing tables and the overhead during recovery from link disconnections     

Synthesis of Ultrahigh-Temperature Si–B–C–N Ceramic from Polymeric Waste Gas

A "green" route to ultrahigh-temperature Si–B–C–N ceramic from vacuum-degassing waste gas of polyborosilazane {B[C₂H₄Si(CH₃)NH]₃} _n (T2-1) has been developed. After gas-to-gel transformation, an amorphous ceramic Si_5.3B_1.0C₁₉N_3.7 was derived from the gel by dehydrocoupling and polymer-to-ceramic transformation. The ceramic started to form a nanostructure at 1700°C and resisted thermal degradation up to 2200°C in argon. This suggests that vacuum-degassing waste gases of polymer precursors may be perfect raw materials for various advanced ceramics.     

Worst-case analysis of dynamic wavelength allocation in opticalnetworks

This paper proposes algorithms for allocating wavelengths to connections (lightpaths) in optical wavelength division multiplexed networks, predominantly for ring topologies. A worst-case model is considered, where no blocking of lightpaths is allowed, and there are no assumptions made on the traffic arrival and holding times. The traffic is characterized only by its load L, which is the maximum number of lightpaths that can be present on any link, assuming no blocking. A dynamic traffic model is considered where requests to set up lightpaths arrive over time and, must be accommodated without rerouting existing lightpaths, and lightpaths may be terminated over time as well. For networks without wavelength conversion, we show that at least 0.5Llog ₂N wavelengths are required by any dynamic algorithm for rings of N nodes and present an algorithm that uses at most Llog₂ N+L wavelengths for rings and 2(L-1)log₂N for trees. We also study the worst-case behavior of the well-known first-fit algorithm, and show that it requires at most 2.52Llog₂N+5L wavelengths (small variants of these constants are proven as well). When limited wavelength conversion is allowed, we first show how to use expanders to insure no blocking in arbitrary topologies. Then, we present conversion patterns for rings with conversion degree d=2, which require Llog₂L+4L or 2Llog₂log₂L+4L wavelengths, thereby eliminating the dependence (that exists without wavelength conversion) between the number of wavelengths and N. We also consider different traffic models where lightpath setup requests arrive over time, but once set up, lightpaths are never taken down. For this model, the number of wavelengths needed is shown to be only max{0,L-d}+L for a conversion degree of d     

Cost-effective traffic grooming in WDM rings

We provide network designs for optical add-drop wavelength-division-multiplexed (OADM) rings that minimize overall network cost, rather than just the number of wavelengths needed. The network cost includes the cost of the transceivers required at the nodes as well as the number of wavelengths. The transceiver cost includes the cost of terminating equipment as well as higher-layer electronic processing equipment, which in practice can dominate over the cost of the number of wavelengths in the network. The networks support dynamic (i.e., time-varying) traffic streams that are at lower rates (e.g., OC-3, 155 Mb/s) than the lightpath capacities (e.g., OC-48, 2.5 Gb/s). A simple OADM ring is the point-to-point ring, where traffic is transported on WDM links optically, but switched through nodes electronically. Although the network is efficient in using link bandwidth, it has high electronic and opto-electronic processing costs. Two OADM ring networks are given that have similar performance but are less expensive. Two other OADM ring networks are considered that are nonblocking, where one has a wide-sense nonblocking property and the other has a rearrangeably nonblocking property. All the networks are compared using the cost criteria of number of wavelengths and number of transceivers     

Fault tolerant multiwavelength optical rings with limitedwavelength conversion

This paper presents methods for recovering from channel failures, link failures, and node failures in wavelength-division multiplexed (WDM) point-to-point links and ring networks with limited wavelength conversion/switching capabilities at the nodes. Different recovery schemes are presented to handle each type of failure. Each scheme is evaluated based on the network hardware configuration required to support it and the performance and management overheads associated with fault recovery. Although similar recovery techniques have been used in conventional networks such as SONET, the constraints due to limited wavelength conversion require new and more complex solutions