Differentiated Reliability (DiR) in Multi-layer Optical Networks

当前的光网络通常提供两种程度的业务可靠性：完全（100%）保护（例如，在网络中存在单个故障时）和无（0%）保护。这反映了历史上的二元性，这种二元性源于曾经划分的电话和数据环境，其中面向电路的服务需要保护，即在故障时提供随时可用的备用资源来取代工作资源，而面向数据报的服务依赖于恢复，即通过路由表更新等动作动态搜索和重新分配受影响的资源。然而，目前的趋势是逐渐推动网络设计向一个统一的解决方案发展，除了传统的语音和数据业务外，还将支持各种新颖的多媒体应用。在过去十年中，这种趋势的证据是服务质量（QoS）和差异化服务（在同一网络中提供不同水平的服务性能）等概念日益重要。根据今天竞争激烈的网络不能再提供纯粹的语音和数据报服务这一事实，完全保护和不受保护之间的历史二元性（在单个故障情况下100%和0%的可靠性）正在迅速过时。现代网络不能再把可靠性的选择限制在这两个极端的程度上。另一方面，虽然在QoS和差异化服务方面做了很多工作，但令人惊讶的是，关于开发差异化网络可靠性以适应网络设计方式的这种变化的讨论和建议却很少。在该提案中，研究人员提出要解决设计具有成本效益的多层网络架构的问题，该网络架构能够根据应用程序的要求提供各种可靠性程度（而不是仅0%和100%）。在该方案中，首次正式引入了差异化可靠性（DiR）的概念，并利用线路交换或路径交换等共同的保护机制，在同一层提供多个可靠性等级（等级）。根据DiR概念，所考虑的层中的每个连接都被分配了一个最小可靠度，定义为连接在任何给定时间可用的概率。为给定连接选择的总体可靠性程度由应用程序需求决定。因此，在多层网络中，下层可以从实际的网络拓扑、约束、设备技术等方面透明地为上层提供所需的可靠性程度。连接的成本取决于所选择的可靠性程度，DiR提供了多种选项。本研究探讨了基于dir的多层光网络设计的多个方面，特别强调了IP/WDM架构。DiR网络的最佳设计通常是极其复杂的，并且需要专门的技术，以便在可接受的计算时间内处理它。因此，随着对基于dir的网络体系结构和建模的研究，研究人员提出了一种强大的新型离散优化范式来有效地处理困难的任务。该优化方法基于对二值域的傅里叶变换技术的采用和调整。这种独特的技术使得对复杂的设计/优化问题实现有效的“过滤”成为可能，使得解决方案在计算上可行的同时仍然保持足够的精度。

Current optical networks typically offer two degrees of service reliability: full (100%) protection (e.g., in presence of a single fault in the network) and no (0%) protection. This reflects the historical duality that has its roots in the once divided telephone and data environments, in which the circuit oriented service required protection, i.e., provisioning readily available spare resources to replace working resources in case of fault, while the datagram oriented service relied upon restoration, i.e., on dynamic search for and reallocation of affected resources via such actions as routing table updates. The current trend, however, is gradually driving the design of networks towards a unified solution that will support, together with the traditional voice and data services, a variety of novel multimedia applications. Evidence of this trend over the last decade is the growing importance of concepts, such Quality of Service (QoS) and Differentiated Services to provide varying levels of service performance in the same network. According to the fact that today's competitive networks can no longer provide only pure voice and datagram services, the historical duality between fully protected and unprotected (100% and 0% reliability in case of a single fault) is rapidly becoming obsolete. Modern networks can no longer limit the options of reliability only to these two extreme degrees. On the other hand, while much work is being done on QoS and Differentiated Services, surprisingly little has been discussed about and proposed for developing differentiated network reliability to accommodate this change in the way networks are designed. In this proposal, the researchers proposed to address the problem of designing cost effective multi-layer network architectures that are capable of providing various reliability degrees (as opposed to 0% and 100% only) as required by the applications. In the proposal, the concept of Differentiated Reliability (DiR) is for the first time formally introduced and applied to provide multiple reliability degrees (classes) in the same layer using a common protection mechanism, e.g., line switching or path switching. According to the DiR concept, each connection in the layer under consideration is assigned a minimum reliability degree, defined as the probability that the connection is available at any given time. The overall reliability degree chosen for a given connection is determined by the application requirements. In a multi-layer network, the lower layer can thus provide the above layers with the desired reliability degree, transparently from the actual network topology, constraints, device technology, etc. The cost of the connection depends on the chosen reliability degree, with a variety of options offered by DiR. The proposed research explores the multifaceted aspects of DiR-based design of multi-layer optical networks, with specific emphasis on the IP/WDM architecture. Optimally designing a DiR network is in general extremely complex and will require special techniques tailored to handle it with acceptable computational time. Therefore, along with research on the architecture and modeling of DiR-based networks the researchers propose a powerful novel discrete optimization paradigm to efficiently handle the difficult tasks. The optimization approach is based on adopting and adjusting the Fourier Transform technique for binary domains. This unique technique makes it possible to realize an efficient "filtering" of the complex design/optimization problem, such that the solution becomes computationally feasible, while still preserving sufficient accuracy.