A fault recovery system that is fast and reliable is essential to today's networks, as it can be used to minimize the impact of the fault on the operation of the network and the services it provides. This paper proposes a methodology for performing automatic protection switching (APS) in optical networks with arbitrary mesh topologies in order to protect the network from fiber link failures. All fiber links interconnecting the optical switches are assumed to be bidirectional. In the scenario considered, the layout of the protection fibers and the setup of the protection switches is implemented in nonreal time, during the setup of the network. When a fiber link fails, the connections that use that link are automatically restored and their signals are routed to their original destination using the protection fibers and protection switches. The protection process proposed is fast, distributed, and autonomous. It restores the network in real time, without relying on a central manager or a centralized database. It is also independent of the topology and the connection state of the network at the time of the failure.

Abstract—Current means of providing loop-back recovery, which is widely used in SONET, rely on ring topologies, or on overlaying logical ring topologies upon physical meshes. Loop-back is desirable to provide rapid preplanned recovery of link or node failures in a bandwidth-efficient distributed manner. We introduce generalized loop-back, a novel scheme for performing loop-back in optical mesh networks. We present an algorithm to perform recovery for link failure and one to perform generalized loop-back recovery for node failure. We illustrate the operation of both algorithms, prove their validity, and present a network management protocol algorithm, which enables distributed operation for link or node failure. We present three different applications of generalized loop-back. First, we present heuristic algorithms for selecting recovery graphs, which maintain short maximum and average lengths of recovery paths. Second, we present WDM-based loop-back recovery for optical networks where wavelengths are used to back up other wavelengths. We compare, for WDM-based loop-back, the operation of generalized loop-back operation with known ring-based ways of providing loop-back recovery over mesh networks. Finally, we introduce the use of generalized loop-back to provide recovery in a way that allows dynamic choice of routes over preplanned directions. Index Terms—WDM, loop-back, network restoration, mesh networks. I.

Current optical networks are migrating to wavelength division multiplexing (WDM)-based fiber transport between traditional electronic multiplexers/demultiplexers, routers, and switches. Passive optical add--drop WDM networks have emerged but an optical data network that makes full use of the technologies of dynamic optical routing and switching exists only in experimental test-beds. This paper will discuss architecture and technology issues for the design of high performance optical data networks with two classes of technologies, WDM and time division multiplexing (TDM). The WDM network architecture presented will stress WDM aware internet protocol (IP), taking full advantage of optical reconfiguration, optical protection and restoration, traffic grooming to minimize electronics costs, and optical flow-switching for large transactions. Special attention is paid to the access network where innovative approaches to architecture may have a significant cost benefit. In the more distant future, ultrahigh-speed optical TDM networks, operating at single stream data rates of 100 Gb/s, may offer unique advantages over WDM networks. These advantages may include the ability to provide integrated services to high-end users, multiple qualityof -service (QoS) levels, and truly flexible bandwidth-on-demand. We will give an overview of an ultrahigh-speed TDM network architecture and describe recent key technology developments such as high-speed sources, switches, buffers, and rate converters. Index Terms---Optical data processing, optical fiber communication, optical fiber LAN, optical signal processing, time division multiaccess, time division multiplexing, wavelength division multiplexing. I.

We study the relationship between failure localization and the properties of link restoration algorithms, employing a quantitative measure of a network's ability to recover from two-link failures. This model allows us to consider issues of failure localization that cannot be addressed through models that assume only single failures. Based on the relationship between algorithmic properties and restoration failures, we construct a failure classification hierarchy that provides insight as to the relative value of advances in algorithm design. Finally, we apply this classification scheme to three networks from the literature and discuss the results in terms of their importance for link restoration algorithms. We find that the topological constraints on restoration paths required by algorithms that embed rings within mesh networks result in significant degradation of failure localization. The preselection of restoration paths (as opposed to selection at the time of failure) also has a nega...

In this paper, we propose a new protection scheme, which we term partial path protection (PPP), to select endto -end backup paths using local information about network failures. PPP designates a different restoration path for every link failure on each primary path. PPP also allows reuse of operational segments of the original primary path in the protection path. A novel approach used in this paper is that of a dynamic call-by-call model with blocking probability as the performance metric, this model is in contrast with traditional capacity-efficiency measurement for batch call arrivals. Additionally, we show that a simple method based on shortest path routing for which primary paths are selected first is more effective than a greedy approach that minimizes, for each call arrival, the number of wavelengths used by the primary and backup path jointly.

Abstract — Network survivability is a crucial requirement in high-speed optical networks. Typical approaches of providing survivability have considered the failure of a single component such as a link or a node. In this paper, we consider a failure model in which any two links in the network may fail in an arbitrary order. Three loopback methods of recovering from double-link failures are presented. The first two methods require the identification of the failed links, while the third one does not. However, precomputing the backup paths for the third method is more difficult than for the first two. A heuristic algorithm that pre-computes backup paths for links is presented. Numerical results comparing the performance of our algorithm with other approaches suggests that it is possible to achieve  ¢¡£¡¥¤ recovery from double-link failures with a modest increase in backup capacity. Index Terms—Wavelength division multiplexing (WDM), loopback recovery, restoration, double-link failures, 3-edge-connected graph. I.

Supporting fast restoration for general mesh topologies with minimal network over build is a technically challenging problem. Traditionally, ring based SONET networks have offered 50ms restoration at the cost of requiring 100% over-build. Recently, fast (local) reroute has gained momentum in the context of MPLS networks. Fast reroute, when combined with preprovisioning of protection capacities and bypass tunnels, comes close to providing fast restoration for mesh networks. Preprovisioning has the additional advantage of greatly simplifying network routing and signaling. Thus even for protected connections, online routing can now be oblivious to the offered protection, and may only involve single shortest path computations.

We present an information-theoretic framework for network management for recovery from nonergodic link failures. Building on recent work in the field of network coding, we describe the input–output relations of network nodes in terms of network codes. This very general concept of network behavior as a code provides a way to quantify essential management information as that needed to switch among different codes (behaviors) for different failure scenarios. We compare two types of recovery schemes, receiver-based and network-wide, and consider two formulations for quantifying network management. The first is a centralized formulation where network behavior is described by an overall code determining the behavior of every node, and the management requirement is taken as the logarithm of the number of such codes that the network may switch among. For this formulation, we give bounds, many of which are tight, on management requirements for various network connection problems in terms of basic parameters such as the number of source processes and the number of links in a minimum source–receiver cut. Our results include a lower bound for arbitrary connections and an upper bound for multitransmitter multicast connections, for linear receiver-based and network-wide recovery from all single link failures. The second is a node-based formulation where the management requirement is taken as the sum over all nodes of the logarithm of the number of different behaviors for each node. We show that the minimum node-based requirement for failures of links adjacent to a single receiver is achieved with receiver-based schemes.

We present an information theoretic framework for network management for non-ergodic link failures. Building on recent work in the field of network coding, we describe the input-output relations of network nodes as codes and quantify network management by the logarithm of the number of different codes needed for different failure scenarios. We give bounds on network management requirements for various network connection problems in terms of basic parameters such as the number of source processes and the number of links in a minimum sourcereceiver cut. This is the first paper to our knowledge that looks at network management for general connections.

Abstract—Conventional optical networks are based on SONET rings, but since rings are known to use bandwidth inefficiently, there has been much research into shared mesh protection, which promises significant bandwidth savings. Unfortunately, most shared mesh protection schemes cannot guarantee that failed traffic will be restored within the 50-ms timeframe that SONET standards specify. A notable exception is the p-cycle scheme of Grover and Stamatelakis. We argue, however, that p-cycles have certain limitations, e.g., there is no easy way to adapt p-cycles to a path-based protection scheme, and p-cycles seem more suited to static traffic than to dynamic traffic. In this paper we show that the key to fast restoration times is not a ring-like topology per se, but rather the ability to pre-cross-connect protection paths. This leads to the concept of a pre-cross-connected trail or PXT, which is a structure that is more flexible than rings and that adapts readily to both path-based and link-based schemes and to both static and dynamic traffic. The PXT protection scheme achieves fast restoration speeds, and our simulations, which have been carefully chosen using ideas from experimental design theory, show that the bandwidth efficiency of the PXT protection scheme is comparable to that of conventional shared mesh protection schemes. Index Terms—Bandwidth sharing, cage graph, Dijkstra algorithm, experimental design, mesh protection, mesh restoration, online algorithm, p-cycle, self-healing networks, SONET, survivable optical networks. I.