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.

Current means of providing loop-back recovery, which is widely used in SONET, relies on fiber-based recovery, where a fiber is used to back up another fiber. We present WDM-based loop-back recovery for optical networks where wavelengths are used to back up other wavelengths. We present two new algorithms for performing WDM-based loop-back over optical mesh networks. The first algorithm performs recovery for link failures. We compare its operation with known ways of providing loop-back recovery and show that the known methods are not applicable to WDM-based recovery. The second algorithm performs WDM loop-back recovery for node failures. We illustrate the operation of both algorithms and prove their validity. We discuss the advantages of WDM-based loop-back for flexibility in WDM service provisioning.

We describe an architecture and medium access control (MAC) protocol for WDM networks. The system is based on a broadcast star architecture and uses an unslotted access protocol and a centralized scheduler to efficiently provide bandwidth-on-demand in WDM networks. To overcome the effects of propagation delays the scheduler measures the delays between the terminals and the hub and takes that delay into account when scheduling transmissions. Simple scheduling algorithms, based on a look-ahead capability, are used to overcome the effects of head-of-line blocking. An important application area for this system is in optical access networks, where this novel MAC protocol can be used to access wavelengths in a WDM passive optical network (PON).

We present a new algorithm which creates redundant trees on arbitrary node-redundant or link-redundant networks. These trees are such that any node is connected to the common root of the trees by at least one of the trees in case of node or link failure. Our scheme provides rapid preplanned recovery of communications with great flexibility in the topology design. Unlike previous algorithms, our algorithm can establish two redundant trees in the case of a node failing in the network. In the case of failure of a communications link, our algorithm provides a superset of the previously known trees.

We present a new algorithm for automatic protection switching (APS) which creates node (edge) redundant trees on any node (edge)-redundant network. These trees are desirable for performing multicasting with APS. Our algorithm is based on constructing trees with appropriate associated directions. The algorithm gives great flexibility in the choice of trees.

Most existing wavelength-division multiplexed (WDM) networks employ circuit switching, typically with one session having exclusive use of one entire wavelength. Consequently, they are not suitable for data applications involving bursty traffic patterns. The All-Optical Network (AON) Consortium has developed an all-optical LAN/MAN test bed which provides time-slotted WDM service. We explore extensions of this service to achieve fine-grained statistical multiplexing with different virtual circuits time sharing the wavelengths in a fair manner. We develop a very fast, best effort time-slotted WDM network protocol with very good fairness and throughput characteristics. As an additional design feature, our protocol supports the assignment of guaranteed bandwidths (GBW) to selected sessions. This feature acts as a first step toward supporting integrated services at the optical layer in WDM networks.

We propose a new algorithm for constructing redundant trees over any edge or node-redundant network in order to perform automatic protection switching in the presence of edge or node failures. Existing redundancy schemes and their topological requirements are reviewed. We describe our algorithm and give an overview of its essential properties. The algorithm is polynomial in the number of nodes. We present an example of the construction of a lowest cost redundant topology for a given configuration and of the operation of our algorithm on that topology. The algorithm is particularly well suited to multicast networks and optical networks, where trees may be created by signal splitting.

We propose a new algorithm for the dynamic centralized wavelength assignment problem in fixed-routing WDM networks without wavelength conversion. The blocking performance of our algorithm is better in many cases (and no worse in tire cases we studied) than other previously proposed algorithms. The performance improvement of our algorithm over other algorithms is high for multi-fiber ring networks with a moderate number of fibers per link. In a multi-fiber mesh-torus network, the difference in performance is not as significant, but the blocking probabilities for all algorithms approach those achievable by wavelength conversion as the number of fibers per link increases. We also extend an earlier analytical model for predicting the blocking probability with and without wavelength conversion to dense multi-fiber networks. Finally, our simulation results on multi-fiber rings and mesh-tori reveal surprising results about the benefits of wavelength conversion as the number of fibers per link increases.

This paper makes the first known attempt to study wavelength-routing networks and the effects of wavelength conversion under dynamic non-Poisson traffic. An approximation that characterizes any non-Poisson traffic by its first two moments is utilized. The arrival occupancy distribution of busy wavelengths for this approximate process is derived and is used to analyze the effects of wavelength conversion. The model predicts that traffic peakedness plays an important role in determining the blocking performance, and also that wavelength conversion gain is insensitive to traffic peakedness over a large range.

This paper studies the effects of tuning delay of transmitters in packet-based optical broadcast networks. We consider scheduling of random traffic with tunable transmitters and fixed-tuned receivers and obtain the degradation imposed by tuning delay using several performance criteria, such as schedule completion time, average packet delay, and session blocking rates. We show that for off-line scheduling the effects of tuning delay are small even if the tuning time is as large as the packet duration. We provide a lower bound to the expected completion time of any off-line schedule with an arbitrary number of wavelengths. We then describe a near-optimal schedule which is based on the principle of having idle transmitters tune to wavelengths just-in-time to start their transmissions. Stability and capacity issues in the transmission of real-time traffic are considered and a queueing-theoretic analysis of average packet delay is given. The packet delay is found to be insensitive to tuning delay under near-optimal transmission scheduling. Finally we extend the model to connection-oriented networks and evaluate the session blocking performance for scheduled circuit connections.

We describe recent results of the Advanced Research Projects Agency (ARPA) sponsored Consortium on Wideband All-Optical Networks which is developing architectures, technology components, and applications for ultrafast 100 Gb/s time-division multiplexing (TDM) optical networks. The shared-media ultrafast networks we envision are appropriate for providing low-access-delay bandwidth on demand to both future high-burst rate (100 Gb/s) users as well aggregates of lower-rate users (i.e., a heterogeneous user population). To realize these goals we are developing ultrafast network architectures such as HLAN, described here, that operate well in high-latency environments and require only limited processing capability at the ultrafast bit rates. We also describe results on 80-Gb/s, 90-km soliton transmission, 100-Gb/s soliton compression laser source technology, picosecond short-pulse fiber ring lasers, picosecond-accuracy optical bit-phase sensing and clock recovery, all-optical injection-locked fiber figure-eight laser clock recovery, short-pulse fiber loop storage, and all-optical pulse width and wavelength conversion.

We introduce a traffic model for circuit-switched all optical networks which we then use to calculate the blocking probability along a path for networks with and without wavelength changers. We investigate the effects of path length, switch size, and interference length (the expected number of hops shared by two sessions which share at least one hop) on blocking probability and the ability of wavelength changers to improve performance. Our model correctly predicts unobvious qualitative behaviour demonstrated in simulations by other authors.

We describe some of the results of the Advanced Research Projects Agency (ARPA) sponsored Consortium on Wideband All-Optical Networks in developing architectures, technology components, and applications for the realization of scaleable, wideband, and transparent optical wavelength-division multiplexing (WDM) networks. Our architecture addresses all-optical transport over the wide, metropolitan, and local areas. It utilizes wavelength partitioning, routing, and active multiwavelength cross-connect switches to achieve a network that is scaleable in the number of users, data rates, and geographic span. The network supports two services which can be point-to-multipoint or multipoint-to-multipoint simplex or duplex connections. The A service is a transparent physically circuit-switched service and the B-service is a scheduled time-slotted circuit which is transparent within its time slots. We have developed a 20-channel local and metropolitan area WDM testbed deployed in the Boston area, now undergoing characterization and experimental applications.

We consider the effects of tuning delay in optical broadcast networks. We show that for off-line scheduling these effects are small even if the tuning time is as large as the packet duration. In particular, we consider scheduling of random traffic with tunable transmitters and fixed-tuned receivers. We provide a lower bound to the completion time of any off-line schedule with an arbitrary number of wavelengths. We then describe a near-optimal schedule which is based on the principle of having idle transmitters tune to wavelengths just-in-time to start their transmissions. Stability and capacity issues in the transmission of real-time traffic are considered. We show that the scheduling problem admits a single stable equilibrium point, and point out how the traffic capacity of a broadcast network can be reached. We also consider the implications in connection-oriented networks.

The authors consider optical networks using wavelength division multiplexing, where the path a signal takes is determined by the network switches, the wavelength of the signal, and the location the signal originated. Therefore, a signal is routed through a combination of circuit switching and wavelength routing (assigning it a wavelength). They present a bound on the minimum number of wavelengths needed based on the connectivity requirements of the users and the number of switching states. In addition, they present a lower bound on the number of switching states in a network using a combination of circuit switching, wavelength routing, and frequency changing. The bounds hold for all networks with switches, wavelength routing, and wavelength changing devices. Several examples are presented including a network with near optimal wavelength re-use.>