Ramu Ramamurthy

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.

Capacity efficient distributed routing of mesh-restored lightpaths in optical networks

A mesh-restored lightpath in an optical network has a primary route and a diversely routed backup route. The wavelength channels on the primary route of a mesh-restored lightpath are dedicated for that lightpath whereas the wavelength channels on the backup route are shared among different mesh-restored lightpaths. Wavelength channels are shared in a way that ensures restoration of all lightpaths affected by any single link failure. In the centralized scenario, complete knowledge of the network state allows determination of the sharability of a backup channel during path computation. This information is not available in the distributed scenario. Use of 1+1 routing algorithms for mesh-restored lightpaths leads to inefficient capacity sharing. We propose distributed routing techniques to decrease the capacity efficiency gap between centralized routing and 1+1 routing of mesh-restored lightpaths. The algorithm uses information about the number of available and (shared) backup channels in a link, which can be disseminated through traffic engineering extensions to OSPF. A sharing database at each OXC maintains information about the lightpaths whose primary or backup paths traverse that OXC. The approach involves distributed determination of the sharability of a link on the backup path during path signaling using the sharing database at each OXC on the backup path. This, combined with a retry scheme facilitated by crankback routing extensions to CR-LDP/RSVP-TE to reduce lightpath blocking, leads to capacity efficient distributed routing of mesh-restored lightpaths.

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.

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.

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.

Limiting sharing on protection channels in mesh optical networks

We examine two approaches in shared mesh restoration to limiting the number of lightpaths protected by a shared-channel. The goal is to prevent shared-channels from protecting a large number of lightpaths without significantly increasing protection capacity.

Routing lightpaths in optical mesh networks with express links

Summary form only given. We examined the routing of protected lightpaths in an optical network with express links. To enable diverse routing, shared risk groups (SRGs) are assigned to the express link to be the union of all the SRGs on the underlying links. We examined the cost setting on the express links for routing the primary and backup paths. For routing primary paths, the express link is always preferred over the underlying links. For routing backup paths, the desirability of using express links depends strongly on the traffic demand. We find that biasing the routing of backup paths to mostly use underlying links while allowing express links to be used in some cases performs well in terms of switch ports and bandwidth miles used.