S. Ramasubramanian

Bio: S. Ramasubramanian is an academic researcher from University of Arizona. The author has contributed to research in topics: Routing protocol & Shared Risk Resource Group. The author has an hindex of 1, co-authored 1 publications receiving 21 citations.

On failure dependent protection in optical grooming networks

Abstract: Resiliency to link failures in optical networks is becoming increasingly important due to the increasing data rate in the fiber. Path protection schemes attempt to guarantee a backup path for a connection upon a failure in the network, thereby reducing the recovery time for a connection. In this paper, we develop a failure dependent path protection scheme that dynamically assigns a primary path and backup paths, one for each failure that would affect the primary path. A connection established on the primary path will be re-established on its backup path only if a failure in the network affects the connection. We evaluate the performance of our developed protocol and compare with an alternative approach based on sub-graph routing that achieves high network utilization and low blocking probability at the cost of re-establishing connections even if the failure in the network does not affect the primary path of the connection. We observe that up to a factor of eight reduction in the number of reconfiguration scenarios is achieved with less than 10% reduction in effective network utilization and less than 3% reduction in fairness metrics for tolerating any single link failure in NSFNET and ARPA-2 networks. The failure dependent protection approach developed in this paper is also applicable to any general failure scenarios that are modeled as shared risk link group failures.

Dual-link failure resiliency through backup link mutual exclusion

Abstract: Networks employ link protection to achieve fast recovery from link failures. While the first link failure can be protected using link protection, there are several alternatives for protecting against the second failure. This paper formally classifies the approaches to dual-link failure resiliency. One of the strategies to recover from dual-link failures is to employ link protection for the two failed links independently, which requires that two links may not use each other in their backup paths if they may fail simultaneously. Such a requirement is referred to as backup link mutual exclusion (BLME) constraint and the problem of identifying a backup path for every link that satisfies the above requirement is referred to as the BLME problem. This paper develops the necessary theory to establish the sufficient conditions for existence of a solution to the BLME problem. Solution methodologies for the BLME problem is developed using two approaches by: 1) formulating the backup path selection as an integer linear program; 2) developing a polynomial time heuristic based on minimum cost path routing. The ILP formulation and heuristic are applied to six networks and their performance is compared with approaches that assume precise knowledge of dual-link failure. It is observed that a solution exists for all of the six networks considered. The heuristic approach is shown to obtain feasible solutions that are resilient to most dual-link failures, although the backup path lengths may be significantly higher than optimal. In addition, the paper illustrates the significance of the knowledge of failure location by illustrating that network with higher connectivity may require lesser capacity than one with a lower connectivity to recover from dual-link failures.

Supporting multiple protection strategies in optical networks

Abstract: This paper develops a framework to support multiple protection strategies in optical networks, which is in general applicable to any connection-oriented network. The capacity available on a link for routing primary and backup connections are computed depending on the protection strategy. The paper also develops a model for computing service outage and failure recovery times for a connection where notifications of failure location are broadcast in the network. The effectiveness of employing multiple protection strategies is established by studying the performance of three networks for traffic with four types of protection requirement.

On the partial path protection scheme for wdm optical networks and polynomial time computability of primary and secondary paths

Abstract: As a generalization of the traditional path protection (PP) scheme in WDM networks where a backup path is needed for each active path, the partial path protection (PPP) scheme uses a collection of backup paths to protect an active path, where each backup path in the collection protects one or more links on the active path such that every link on the active path is protected by one of the backup paths. While there is no known polynomial time algorithm for computing an active path and a corresponding backup path using the PP scheme for a given source destination node pair, we show that an active path and a corresponding collection of backup paths using the PPP scheme can be computed in polynomial time, whenever they exist, under each of the following four network models: (a) dedicated protection in WDM networks without wavelength converters; (b) shared protection in WDM networks without wavelength converters; (c) dedicated protection in WDM networks with wavelength converters; and (d) shared protection in WDM networks with wavelength converters. This is achieved by proving that that for any given source $s$ and destination $d$ in the network, if one candidate active path connecting $s$ and $d$ is protectable using PPP, then any candidate active path connecting $s$ and $d$ is also protectable using PPP. It is known that the existence of PP implies the existence of PPP while the reverse is not true. We demonstrate a similar result in the case of segmented path protection. This fundamental property of the PPP scheme is of great importance in the context of achieving further research advances in the area of protection and restoration of WDM networks.

Traffic grooming in WDM mesh networks with guaranteed survivability

Abstract: Traffic grooming techniques in optical networks are attracting increasing research attention in order to handle the huge bandwidth mismatch between high capacity lightpaths and low-rate individual traffic requests. It is important to have guaranteed survivability of all user connections in such networks. Path protection has emerged as a widely accepted technique for survivable WDM network design. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new design strategy for survivable traffic grooming in WDM networks, under specified resource constraints. Our approach addresses the complete design problem including logical topology design, RWA, and routing of (subwavelength) requests over the logical topology. We further ensure that the resultant logical topology is able to handle the entire traffic request after any single link failure. We first present two ILP formulations for optimally designing a survivable logical topology, and then propose a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection.