Photonic cross-connects (PXC) play a key role in all-optical transparent networks. In this paper, the optical design and modeling of a three-dimensional microelectromechanical system (3-D MEMS) based optical switch are discussed. Basic design rules and considerations are reviewed and used to determine the optimum configuration for free-space optical switches with more than 300 ports. The optical performance of a 256 /spl times/ 256 PXC system, including a 347 /spl times/ 347 nonblocking core switch and auxiliary 2 /spl times/ 2 optical switches for 1:1 protection and optical taps for power monitoring, is presented. The core switch has 1.4-dB median insertion loss, 1.5-dB wavelength dependent loss across a broadband of 1260-1625 nm, and a typical polarization dependent loss of 0.1 dB. Environmental tests including temperature and vibration are described.

Three-dimensional MEMS photonic cross-connect switch design and performance

In wavelength division multiplexed networks (WDM) with 1:1 path protection, a link-disjoint protection (backup) path is also set up at the time of setting up a working (primary) path. Hence, the failure of a single fiber-link does not cause huge data losses. This paper considers on-line routing and wavelength assignment (RWA) of protection paths in such networks. In particular, we study two strategies based on the 1:1 path protection scheme. The static strategy establishes protection paths such that once a route and wavelength have been chosen, they are not allowed to change. On the other hand, the dynamic strategy allows for re-arrangement of protection paths, that is, both the route and wavelength chosen for a protection path can change so as to accommodate a new request. With either strategy, we assume that the working paths cannot be re-arranged. This is to prevent the disruption of on-going traffic. The two strategies are compared on the basis of the number of connection requests that can be satisfied for a given number of wavelengths, assuming that the requests come one at a time, and wavelengths are assigned according to the first-fit policy. One of the results of our study is that, contrary to intuition, the static strategy performs better than the dynamic strategy.

Dynamic establishment of protection paths in WDM networks. Part I

A computer network processes data packets in the event of a network link failure. The network includes a plurality of routers that deliver data packets to the network via a plurality of links. At least one router includes a protection cycle manager. The protection cycle manager has a protection cycle packet identifier and a protection cycle packet processor. The protection cycle packet identifier identifies, as protection cycle packets, data packets having a specific protection cycle format. The protection cycle packet processor processes protection cycle packets to determine whether the packet destination corresponds to the routing node, and if the packet destination corresponds to the routing node, the protection cycle packet is treated by the routing node as a data packet received from the packet source via the failed link. Otherwise, if the packet destination does not correspond to the routing node, the protection cycle packet is sent to a protection cycle node for the routing node.

Network data routing protection cycles for automatic protection switching

We present a high-level but extensive overview of the protocols, technologies, network architectures, and issues and challenges for next-generation optical transport networks and optical internetworks.

Optical data networking: protocols, technologies, and architectures for next generation optical transport networks and optical internetworks

The unprecedented growth of IP traffic is leading Internet service providers and network operators worldwide to investigate architectural alternatives for cost effective, reliable, scalable, and flexible multiterabit IP backbones. In this paper, several overlay, service, and transport layer networking architectures, which employ IP, MPLS, SONET/SDH, and DWDM technologies, are proposed and analyzed. Multiple parameters, such as network capacity, cost, restoration strategy, reconfigurability, and accommodation of preemptable traffic, are considered for the architectural comparison. Detailed network design and economic analysis are provided for the different alternatives considering a typical nationwide U.S. backbone with projected IP traffic in approximately three years. Several sensitivity analysis results are also shown, to evaluate the effect of cost changes in some of the critical technological factors in these architectures, such as 10 Gb/s optics cost or IP router cost. The results show the value of transport layer networking architectures for multiterabit IP backbones, and how, when compared to service layer architectures, they provide additional desirable features such as wavelength reconfigurability and restoration scalability.

Analysis and design of backbone architecture alternatives for IP optical networking

The architecture of today's long distance transmission networks, which we call the baseline architecture, is a complex and multilayered hierarchy of TDM circuits. One premise of the baseline architecture is that restoration from network failures is provided mostly by SONET/SDH rings. This article presents an alternative architecture that uses ATM and optical layer cross-connect technology for TDM services. Using a sophisticated set of network design tools developed at AT&T Labs-Research, we show that the alternative architecture offers dramatic capital savings and improved network efficiency over the baseline architecture. Most of this savings can be attributed to use of OLXC mesh network restoration, which makes more efficient use of capacity than SONET/SDH rings, and use of ATM switching for transport of TDM circuits, which consolidates the numerous TDM equipment layers inherent to the baseline architecture. In addition, motivated by the rapid growth of IP services, we analyze in the alternative architecture whether to provide restoration for IP services in the IP layer itself, by rerouting packets over precalculated restoration paths with MPLS, or to alternatively provide restoration of failed IP layer links in the OLXC layer. One potential advantage of IP layer restoration is that network operators may choose to only restore a fraction of the services, in particular the "priority" services, affected by a network failure. This article gives some methodology of how to determine this fraction at which IP layer restoration is cost-competitive with OLXC restoration.

S. Phillips

Papers

Future transport network architectures