Design of Translucent Optical WDM Networks

网络用户数量的空前增长和高带宽终端用户应用的出现，给下一代计算机网络体系结构的设计带来了新的挑战。采用波分复用(WDM)技术的光网络利用光纤的巨大容量，突破了电子网络的带宽限制。虽然这项技术看起来非常有前途，但未来这种光网络的大规模部署取决于通信网络需求和物理网络现实的快速融合。拟议中的光网络研究的重点是通过在承认现有设备的局限性的同时解决几个系统级挑战来促进这一过程。为了应对本地和长途数字通信量的爆炸性增长，目前正在现有的和新的光纤基础设施上部署许多多吉比特/秒信道的波分复用。WDM部署正在激增，因为可以通过激活现有光纤设备上的额外波长通道来经济地配置容量。然而，随着光纤容量的增长，网络节点和接入点上昂贵的电子交换机的容量承受着越来越大的压力。一种可重新配置的透明光网络，通过确保信号仅在源和目的地离开光域，从而避免不必要的光电转换，寻求提供低成本的替代方案。然而，在透明光网络中，物理层损伤会限制端到端连接的长度，这是有基本限制的。跨越多个节点和较长距离的连接可能会受到基本物理限制(如光纤色散和非线性、自发辐射噪声以及串扰等设备缺陷)造成的严重损害。由于点对点通信性能的物理原理在实验和理论上都得到了很好的理解，因此有人认为，国家规模的网络将通过在每个节点部署具有电子再生的点对点WDM来避免物理层损害。这样的网络被称为不透明光网络。与点对点链路和物理层光学设备不同，复杂的全光或光电混合网络的分析和仿真仍处于初级阶段，经过充分测试的工具才刚刚开发出来。本项目的目标是提出、评估和研究符合光设备物理层特性的下一代高带宽WDM光网络的设计方案。特别是，研究人员计划研究以下研究主题：稀疏再生和半透明光网络：关于(国家规模)光波长分割复用(WDM)网络中的透明度和不透明度，已经有很多讨论[11]。在[22]中，研究人员引入了半透明光网络的概念--一种支持网络内光信号的选择性再生的网络。研究人员的研究表明，对于中等规模的网络，半透明有助于提高网络的整体性能。对于更大规模的网络，光纤非线性和色散带来的损害不容忽视，研究人员预计可能需要更高程度的不透明度来对抗信号劣化，但这是一个有待进一步研究的开放问题。这位研究人员还计划在全国范围内的WDM网络中的选定位置调查几个信号再生器的效果。考虑功率因素的选路和波长分配：选路和波长分配(RWA)是波分复用(WDM)光网络中的一个重要问题。以前的研究已经在关于信号功率的完美条件的假设下解决了这个问题的许多变化。研究人员建议调查这一问题，同时允许分路器、复用器、交换元件、光纤链路等组件对路由信号进行降级。研究人员计划包括新型放大器和其他设备模型来表征网络的性能。

The unprecedented growth in the number of networked users and the emergence of high-bandwidth end-user applications impose new challenges in the design of architectures for next-generation computer networks. Optical networks, employing Wavelength Division Multiplexing (WDM), transcend the bandwidth limitations of electronic networks by utilizing the enormous capacity of the optical fiber. Though this technology looks extremely promising, large-scale deployment of such optical networks in the future depends on a rapid convergence of communication network requirements and physical network realities. The focus of the proposed research in optical networks is to facilitate this process, by tackling several system-level challenges while acknowledging the limitations of existing devices. Wavelength Division Multiplexing of numerous multi-gigabit/sec channels is being deployed right now on existing and new fiber infrastructure in respones to explosive growth in both local and long-haul digital traffic. WDM deployment is surging because capacity may be economically provisioned by activating additional wavelength channels on existing fiber plant. However, as the fiber capacity grows, increasing strain is placed on the capacity of costly electronic switches at network nodes and access points. A reconfigurable transparent optical network seeks to provide a low-cost alternative by ensuring that the signal leaves the optical domain only at the source and destination, thereby avoiding unnecessary opto-electronic conversion. There are, however, fundamental limits imposed by physical-layer impairments that limit the length of end-to-end connections in transparent optical networks. Connections that span several nodes and large distances may acumulate severe impairments imposed by fundametal physical constraints such as fiber dispersion and nonlinearties, spontaneous emission noise, and device imperfections such as crosstalk. Since the physics of point-to-point communications performance is well understood experimentally and theoretically, it has been argued that nation-scale networks will avoid physical-layer impairments by deploying point-to-point WDM with electronic regeneration at each node. Such a network is called an opaque optical network. Unlike the case of point-to-point links and physical-layer optical devices, the analysis and simulation of complex all-optical or hybrid optical-electronic networks is still in its infancy and well-tested tools are only now being developed. The goals of this project are to propose, evaluate and study designs for the next-generation high-bandwidth WDM-based optical networks, which are compatible with the physical-layer characteristics of optical devices. In particular, the researcher plans to investigate the following research topics: Sparse Regeneration and Translucent Optical Networks: There has been a great deal of discussion regarding transparency vs. opacity in (national-scale) optical wavelength devision multiplexed (WDM) networks [11]. In [22], the researcher introduced the notion of a translucent optical network - a network which supports selective regeneration of optical signals within the network. The researcher's study showed that, for medium-scale networks translucency can help to improve the overall network performance. For larger-scale networks, where impairments introduced by fiber nonlinearities and dispersion cannot be ignored, the researcher anticipates that a higher degree of opacity may be needed to combat signal degradations, but this is an open problem for further research. The researcher also plans to investigate the effect of a few signal regenerators at select locations in a nation-wide WDM network. Routing and Wavelength Assignment with Power Considerations: Routing and wavelength assignment (RWA) is an important problem that arises in wavelength division multiplexed (WDM) optical networks. Previous studies have solved many variations of this problem under the assumption of perfect conditions regarding the power of a signal. The researcher propose to investigate this problem while allowing for degradation of routed signals by components such as taps, multiplexers, switching elements, fiber links, etc. The researcher plans to include novel amplifier and other device models to characterize the performance of the networks.