Sid Chaudhuri

Capacity performance of dynamic provisioning in optical networks

This paper describes an architecture and analyzes the performance of dynamic provisioning of lightpaths in an optical network. In dynamic provisioning, a lightpath is set up in real-time without rearranging the working and protection routes of existing lightpaths, and without the knowledge of future lightpath provisioning events. This paper develops a general model of the physical topology of the optical network, and outlines routing approaches for dynamic provisioning of lightpaths. It analyzes via simulations the performance of dynamically provisioned unprotected, 1+1 protected and mesh-restored lightpaths. The analysis of the efficiency of network utilization of dynamic provisioning focuses on the spare capacity needed for protection, and in particular focuses on the impact of sharing of wavelength channels for mesh-restored lightpaths. The main conclusion from the performance studies is that significant capacity gains are achieved with sharing of wavelength-channels for mesh-restored lightpaths with dynamic provisioning even for sparse topologies, and even at moderate loads.

Lightpath re-optimization in mesh optical networks

Intelligent mesh optical networks deployed today offer unparalleled capacity, flexibility, availability, and, inevitably, new challenges to master all these qualities in the most efficient and practical manner. More specifically, demands are routed according to the state of the network available at the moment. As the network and the traffic evolve, the lightpaths of the existing demands becomes sub-optimal. In this paper we study two algorithms to re-optimize lightpaths in resilient mesh optical networks. One is a complete re-optimization algorithm that re-routes both primary and backup paths, and the second is a partial re-optimization algorithm that re-routes the backup paths only. We show that on average, these algorithms allow bandwidth savings of 3% to 5% of the total capacity in scenarios where the backup path only is re-routed, and substantially larger bandwidth savings when both the working and backup paths are re-routed. We also prove that trying all possible demand permutations with an online algorithm does not guarantee optimality, and in certain cases does not achieve it, while for the same scenario optimality is achieved through re-optimization. This observation motivates the needs for a re-optimization approach that does not just simply look at different sequences, and we propose and experiment with such an approach. Re-optimization has actually been performed in a nationwide live optical mesh network and the resulting savings are reported in this paper, validating reality and the usefulness of re-optimization in real networks.

Stochastic approaches to compute shared mesh restored lightpaths in optical network architectures

We assess the benefits of using statistical techniques to ascertain the shareability of protection channels when computing shared mesh restored lightpaths. Current deterministic approaches require a detailed level of information proportional to the number of active lightpaths, and do not scale well as traffic demands and network grow. With the proposed approach, we show that less information, independent of the amount of traffic demand, is sufficient to determine the shareability of protection channels with remarkable accuracy. Experiments also demonstrate that our approach yields faster computation times with no significant penalty in terms of capacity usage.

Enhanced algorithm cost model to control tradeoffs in provisioning shared mesh restored lightpaths

In this write-up we propose an algorithm-centered metric to vary the weight put on the solutions cost and on the average backup lengths while selecting a primary-backup pair from a set of candidate routes. We assess the effect of our metric on these two contradicting objectives and show that it offers the leverage to achieve the desired compromise. We first present the cost model, we then describe the algorithm used in our experiments to illustrate the effect of this cost model, and we finally conclude with the results of our experiments.

Analysis of enhanced OSPF for routing lightpaths in optical mesh networks

We discuss enhancements to the OSPF (open shortest path first) protocol for routing and topology discovery in optical mesh networks. OSPFs opaque LSA (link state advertisement) mechanism is used to extend OSPF to disseminate optical resource related information through optical LSAs. Standard link-state database flooding mechanisms are used for distribution of optical LSAs. Each optical LSA carries optical resource information pertaining to a single optical link bundle between two adjacent OXCs (optical cross connects), allowing for fine granularity changes in topology to be incorporated in path computation algorithms. OSPF packets are carried over a single IP control channel between adjacent OXCs. We analyze the performance of OSPF with optical extensions. Specifically, we compute control channel bandwidth used due to LSA updates. We also estimate the amount of memory required to store the LSA database. Finally, we study CPU usage for computing primary and backup lightpaths. Our analysis shows that the control channel bandwidth usage, memory requirement, and CPU usage are small enough to not be limiting factors for designing optical networks with single OSPF areas consisting of a large number (more than 500) of OXCs.

Comparison of centralized and distributed provisioning of lightpaths in optical networks

This paper compares centralized and distributed online provisioning approaches in optical networks. In the centralized approach, complete network state is available for path computation. In the distributed approach, summarized information is available for path computation.

Invited: Routing Strategies for Capacity-Efficient and Fast-Restorable Mesh Optical Networks

Wavelength division multiplexed (WDM)-based mesh network infrastructures that route optical connections using intelligent optical cross-connects (OXCs) are emerging as the technology of choice to implement the next generation core optical networks. In these architectures a single OXC is capable of switching tens of terabits of traffic per second. With such data transfer rates at stake, it becomes increasingly challenging for carriers to (1) efficiently and cost-effectively operate and manage their infrastructure, and (2) cope with network failures while guaranteeing prescribed service level agreements (SLAs) to their customers. Proper routing of primary and backup paths is a critical component of the routing and restoration architecture required to meeting these challenges. In this paper we review some of the various strategies and approaches proposed so far to intelligently route connections while at the same time providing guaranteed protection against various types of network failures. We explore the tradeoffs associated with these approaches, and investigate in particular different, sometimes competing aspects, such as cost/capacity required, level of protection (link vs. node failure), restoration time, and complexity of route computation.

Role of optical network and spare router strategy in resilient IP backbone architecture

At the heart of IP backbone networks are the core IP routers with throughput of hundreds of Gb/s. These routers with interfaces operating at the per-wavelength bit rates are directly connected via point-to-point WDM optical-transport systems. For acceptable service reliability even for best effort services typically two interconnected routers are used for redundancy in each backbone node. It has been established that the majority of the traffic in a node is transit traffic and a significant cost reduction can be achieved by siphoning off the transit traffic from the IP layer into the optical layer. In this paper we discuss the current trend in the IP backbone network which is poised to take over other premium services, in addition to best effort IP services, as an integrated transport platform. We discuss several network architecture options with the critical attribute being that it must be as resilient as the current SONET transport network. We propose an innovative architecture option in which a resilient network is built with current router technology. In another option we assume that the router layer can be as resilient as the current SONET layer with the emerging resilient router technology. We perform an economic evaluation and discuss the reliability of these network architectures.

Pre-emptive reprovisioning in mesh optical networks

Pre-emptive reprovisioning is a method to perform reprovisioning of a backup path in advance of a second failure, to reduce the time to recover service from seconds (reprovisioning) to milliseconds (restoration). We evaluate the tradeoff between benefits and operational complexity.

Addressing transparency in DWDM mesh survivable networks

We identify the penalties incurred in all-optical networks on routing and restoration operations. We show that these penalties can be avoided with opaque switches interfaced by transponders. we demonstrate that transparent OXCs may be short of important functionality, and usability necessary to build robust and cost-effective networks. We arrive at our conclusion mainly by quantifying the amount of resources required to accommodate predefined OC48 traffic forecasts in the proposed architectures. We show that carriers opting for all-optical solutions will have to over build their infrastructures and surmount tremendous management obstacles in order to be competitive.